Silicon-on-insulator by graphoepitaxy and zone-melting recrystallization of patterned films

Journal of Crystal Growth 63 (1983) 527—546 North-Holland Publishing Company

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SILICON-ON-INSULATOR BY GRAPHOEPITAXY AND ZONE-MELTING RECRYSTALLIZATION OF PATFERNED FILMS Henry I. SMITH Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

M.W. GElS Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 021 73, USA

and C.V. THOMPSON

*

and H.A. ATWATER

Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Received 28 January 1983; manuscript received in final form 18 July 1983

Graphoepitaxy and zone-melting recrystallization of patterned films are reviewed, with emphasis on their application to silicon on insulator (SO!). In the case of Si graphoepitaxy by partial melting with a laser or stationary strip-heater, orientation is explained on the basis of preferential retention of those grains that have (100) texture and have <100> directions parallel to the grating axis. Graphoepitaxy encompasses a wide variety of film formation methods and mechanisms of orientation. Oscillatory CVD and solid-state surface-energy-driven secondary recrystallization are low-temperature approaches which may be able to provide SOl in those situations where the high temperature of melting (1412°C)cannot be tolerated, such as multivel integrated electronics and flat-panel displays. Zone-melting recrystallization of patterned Si films has yielded: large-area, single-grain Si films on SiO 2 via an hourglass technique; entrainment of subboundaries, grain boundaries and impurities along straight lines separated by —100 sm; and orientation filtering by growth-velocity competition.

Contents 1. Introduction 2. Graphoepitaxy — origins, theory, approaches 2.1. Origins and theory 2.2. Mechanisms and approaches 3. Si graphoepitaxy with laser and strip-heater recrystallization 4. Recent graphoepitaxy research 4.1. In-situ studies of evaporated metal films 4.2. Sn by electrodeposition 4.3. Ge and Si by Au and Ag solutions 4.4. Ge by zone melting 4.5. Sn on KCI by evaporation 4.6. SO! by chemical vapor deposition

*

IBM Postdoctoral Fellow. Currently: Department of Materials Science and Technology, Massachusetts Institute of Tech~ nology.

4.7. Graphoepitaxy by solid-state recrystallization 5. Zone-melting recrystallization of patterned films 5.1. Planar constrictions (the hourglass technique) 5.2. Subboundary termination in channels 5.3. Recrystallization of preformed islands 5.4. Entrainment of subboundaries 5.5. Vertical constriction 5.6. Orientation filtering by growth-velocity competition 6. Conclusions Acknowledgements References

1. Introduction At the present time there is considerable interest in developing techniques for producing Si films, appropriate for active devices, on insulating substrates such as Si02. The acronym SOI (silicon on

0022-0248/83/0000—0000/$03.OO © 1983 North-Holland

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insulator) has come to be accepted for this field of research. In this paper two approaches to creating oriented, single-crystal Si films on insulating substrates are reviewed: graphoepitaxy and zone-melt-

Si films on amorphous substrates, apparently their work was not pursued further. In 1972, in the Soviet-Union, Sheftal and Buzynin reported an experiment in which NH4I

ing recrystallization of patterned films. In graphoepitaxy, an artificial surface pattern is used to induce orientation in a film. In section 2 the origins, theory and the various approaches to graphoepitaxy are discussed. In section 3, Si graphoepitaxy by laser and strip-heater recrystallization is reviewed, and the practical value of such an approach to SOl assessed. In section 4, the review of graphoepitaxy is extended up to the present. It includes a description of current research on Si, which is aimed at developing lowtemperature processes with improved control of orientation. Low-temperature processes are important for flat-panel display applications, where the preferred substrate is low-cost glass, and for multilayer integrated electronics, where processes for creating single-crystal Si should not cause the temperature of pre-existing device layers to rise above about 900°C. Section 5 describes research on techniques that combine patterning of films with zone-melting recrystallization to achieve single-crystal SOl films with control of defect distribution. The special issue of the Journal, of which this paper is a part, surveys the SOl field with contributions from several laboratories. In keeping with the intent of this special issue, this article emphasizes work done at MIT.

crystallites, precipitated from solution onto diffraction gratings scratched into the surface of glass, showed a weak but definite tendency toward orientation [2]. They suggested “...that the discovery of this weak influence is of theoretical interest in that it confirms the existence of crystal particles in the medium prior to deposition.” For many years prior to this Sheftal had held the view that discrete microcrystals exist in crystallization media and contribute to ordinary crystal growth by attachment to the growing crystal [3,4]. The theory of crystal growth by attachment of microcrystalline blocks, and additional details of the NH4I experiment, and earlier experiments, are given in ref. [4]. In this paper Sheftal first introduced the term “artificial epitaxy”. In 1977 Sheftal and Klykov clarified that “artificial epitaxy” was based on forcing crystal particles to settle out in a directed manner on a relief micro-pattern corresponding to the symmetry and external shape of the precipitating crystals [5]. In this article they proposed forming an array of appropriate relief patterns on a substrate to seed it with oriented microcrystals which would yield either oriented crystal islands or single-crystal layers when they grow together [5]. They also stated that an onented deposit of Si was obtained on mechanicallyabraded W and that Ge had been grown on patterned quartz glass. Details of the Si and Ge work are given in refs. [6—12].The artificial epitaxy process was subsequently renamed “diataxy” [6—12].Klykov et al. [9] reported orientation of salol microcrystals floating within a salol melt (electric fields also were used to align the microcrystals). The use of mechanically-abraded surfaces was reported earlier by Zocher and Coper [13] who used this technique to orient dyes. They were unsuccessful in attempts to orient ionic crystals. In 1977 Smith [14] and Flanders and Smith [15] proposed the use of artificial surface grating and grid patterns to induce orientation in a film by influencing the phenomena of nucleation, growth, coalescence and recrystallization. This proposal did not invoke either oriented nucleation or the attachment of microcrystalline blocks. It was, in-

2. Graphoepitaxy

—

origins, theory and approaches

2.1. Origins and theory In 1967 Filby and Nielsen reviewed the topic of single-crystal Si films on crystalline and amorphous insulators [1]. Their review contained a brief proposal for achieving single-crystal Si on amorphous and polycrystalline substrates based on aligning nuclei, possibly by adjusting the topography of the substrate Some preliminary experiments were done, including experiments with Au—Si alloys, and some alignment was observed, but the results were considered inconclusive. Although Filby and Nielsen believed there was considerable potential for forming single-crystal or large grain “.

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stead, based on in-situ TEM studies of the early stages of nucleation and growth of films on amorphous and crystalline substrates, carried out by several workers during the early 1960’s [16,17]. Among other phenomena, these studies revealed “liquid-like” behavior in the coalescence of small (~100 nm) islands of solid-metal crystallites. Duning coalescence, changes in orientation (i.e., recrystallization and preferential grain growth) occurred readily. Metal islands in contact with natural cleavage steps were sometimes observed to be oriented with respect to the steps [18,19]. The observations of orientation pinning at a step and reorientation of small islands at coalescence [18] were the basis of the idea that one might be able to

ture profile, linewidths — 0.1 ~.tm,and long-range pattern coherence, as required for graphoepitaxy, a fabrication technology would have to be developed. Thus, research on the lithography and etching of submicrometer periodic structure was emphasized initially [21,22]. Graphoepitaxial orientation on precision relief gratings of 0.32 ~tm period in amorphous substrates was demonstrated in the PhD thesis work of Flanders [23—25].The materials studied included the liquid crystals MBBA and M24, KC1, and Sn. The liquid crystals showed very strong graphoepitaxial orientation for films 25—50 ~tm thick, sandwiched between facing surface-relief gratings etched into Si02. This confirmed the

produce a single-crystal film on a substrate of choice by first creating an artificial surface pattern of fine period and appropriate symmetry, and then depositing a film over the pattern, under conditions that allowed the film to orient itself relative to the pattern. This conception of graphoepitaxy (the name was not introduced until 1979) was pursued at MIT. The in-situ experiments, other TEM studies and theoretical considerations had shown that changes in orientation at coalescence take place most readily at small island dimensions (— 0.1 .tm), and hence it was assumed that the artificial surface patterns would have to have submicrometer spatial periods. Several years later it was recognized that in some cases, it is more desirable to induce orientation after the deposition stage, or to create the artificial pattern on the surface on the film rather than the substrate (see section 2.2). In 1968—69 some experiments on graphoepitaxy were carried out in which Si was sputtered onto surface-relief grids in Si02. These grids had been created by a combination of electron-beam lithography and rf sputter etching [20]. Examination of the Si films in a TEM, (plus Ge films deposited in the early 1970’s) showed RHEED (reflection high energy electron diffraction) patterns that differed from patterns on smooth surfaces, but the existence of a graphoepitaxial effect was not clearly demonstrated. These early experiments suffered from lack of a reliable technology for fabricating the artificial submicrometer-peniod patterns. It was clear that to achieve precise control of relief-struc-

fundamental validity of the in-situ reorientation approach to graphoepitaxy and served as a model for investigating graphoepitaxy of solid films. The KC1 was deposited from aqueous solutions as the solutions became supersaturated due to evaporation. This produced discrete crystallites that were clearly aligned with respect to the surface-relief grating, as shown in fig. 1. The angular spread in orientation was a few degrees. It appeared that preferential nucleation occurred at the relief steps and that reorientation took place either during initial growth or with annealing [24]. However, attachment of mobile microcrystals, as obtained earlier by Sheftal and Buzynin [2] under similar conditions, cannot be ruled out. Films of sputtered and vacuum-evaporated Sn showed weaklypreferred graphoepitaxial orientation [23]. The Flanders thesis [23] also presented thermodynamic and kinetic models for graphoepitaxial orientation on amorphous substrates. The thermodynamic model showed that if the interfacial tension between a given material and a flat amorphous substrate is minimum when a particular set of crystallographic planes is parallel to the substrate, this same material located over a surface-relief structure of appropriate geometry, would have minimum interfacial free-energy at a unique azimuthal orientation. Hence, the true equilibrium configuration would be a single-crystal film onented with respect to the artificial surface-relief structure. The appropriate surface-relief structure for a cubic material with natural (100) texture (i.e., {100} planes parallel to a flat amorphous sub-

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4

*

4 .4 •

w

4

~I.

i*Il~~

*

Fig. 1. Scanning transmission electron micrograph of KCI crystallites grown on a 320 nm period surface-relief grating of square-wave profile in SiO 2. The KC1 crystallites are oriented with (100) directions parallel and perpendicular to the grating axis. The grating grooves are 25 nm deep and have the lighter shading.

strate, indicating minimum interfacial-tension for this configuration) would be a square-wave-profile grating with planar facets intersecting at 90°.The driving force for orientation was shown to increase with (h/p), where p is the period of the surface-relief grating and h is the depth. For a given film material and deposition or annealing method, p should be smaller than the diameter of the naturally-occurring grains. This would, in general, imply submicrometer spatial periods. The kinetics of film formation (specifically the phenomena of nucleation, island growth, coalescence and reorientation) were analyzed, and guidelines were presented for approaching the equilibrium, minimum-free-energy graphoepitaxial orientation. In the case of liquid crystals (mesophases), alignment was explained on the basis of the same general considerations: the interfacial tension of liquid

crystals is anisotropic and, hence, minimum total free-energy (which includes interfacial free-energy plus elastic-strain energy in the adjacent bulk material) corresponds to a unique in-plane onientation [23,25]. The liquid crystals studied readily achieved the “single-crystal” equilibrium configuration, often without disclinations [23,25—27]. (See also refs. [28—30].) Shaver [26] studied the dependence of orientation on relief-grating period for three nematic liquid crystals and one smectic, using gratings of 12, 3.8, 1 and 0.32 ~tm period. The liquid crystals had domain sizes of the order of a few micrometer. He obtained excellent alignment with gratings of 0.32 ~m period in all cases, and a reduction of alignment as the grating period was increased. This confirmed theoretical expectations that grating period should be smaller than the naturally-oc-

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curring domain or grain size. He also demonstrated alignment of liquid crystals by means of 12 ~sm period surfactant gratings which had no significant surface relief (thickness (1 nm). The liquid crystals studies provided valuable guidance for later research on graphoepitaxy by solid-state recrystallization (see section 4.7). Our research on graphoepitaxy was extended to Si in mid-1978. This is discussed in section 3. Sheftal et al. [6—12]have studied in depth the orientation of Si and Ge microcrystals by the VLS method, using Ag and Au as solvents. Triangularshaped microcrystals were shown to float on top of the metallic solution within triangular reliefstructure cells, — 10 ~.smin diameter. Wetting of the cells by the metallic solution was ensured by first coating them with 0.2—1 ~tm of W, Mo or Ta. The floating crystallites were centered and onented within the triangular cells by capillary forces of the solution. Large-area films of Si and Ge were produced by further growth from these floating crystallites. 2.2.Mechanisms and approaches A variety of mechanisms can produce onientation, or induce reorientation, relative to an artifical pattern. These can be divided into two broad categories: (a) those that depend on orienting faceted microcrystals that are mobile within the medium of crystallization; and (b) those that operate on material in which crystalline grains cannot move as rigid bodies relative to the substrate. For category (a), orientation depends upon the development faceted morphologies in the mobile crystallites which either attach to relief structures [5] or acquire orientation through capillary forces [11,12]. Orientation in films with immobile crystalline grains, on the other hand, occurs either at nucleation (proposal of Filby and Nielsen [1]) or through some type of internal reorientation, or through preferential growth of a particular orientation, as discussed in more detail below. Generally speaking, when mobile microcrystals are oriented by relief structures the parts of the relief-structures which receive the microcrystals should be larger than the microcrystalline size [6]. In the case of orienting material with immobile

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grains, the opposite is true: the spatial period of the artificial pattern should, generally, be smaller than the size of grains which would naturally develop in the material [22—26].Improvement of orientation with reduction of pattern spatial-period below grain size (actually, domain size) was demonstrated clearly in the case of liquid crystals [26] and, more recently, for the case of Sn by Osaka et al. [31]. Ref. [8] has reviewed mechanisms and approaches that fall under category (a). In the remainder of this paper we discuss only mechanisms under category (b) and distinguish among 5 general approaches to obtaining graphoepitaxially-oriented films. These approaches are listed here, along with a brief description, to serve as a basis for subsequent discussions. Approaches to graphoepitaxy of translationally immobile material: (1) deposition of material onto a patterned surface, with orientation occurring at nucleation; (2) deposition of material onto a patterned surface with reorientation occurring during film growth; (3) oscillatory deposition and etch-back over a patterned surface; (4) orientation selection after film formation by partial melt back; (5) reorientation after film formation by solid-state recrystallization. In approaches (4) and (5) the patterning can be in either the substrate surface, the film itself or a layer on top of the film. Approach (1) is considered not promising, since critical nuclei are generally very small (<1 nm) compared to radii of curvature of relief structures (— 5 nm), or the dimensions of imperfections (— 5 nm) in the surface patterns that can be fabricated with current methods on amorphous substrates. (Higher precision may be obtainable on singlecrystal substrates.) Hence, the spread in the distribution of grain orientations would probably be large. Approach (2) subsumes a number of reorientation mechanisms: (a) reorientation as growth proceeds from nuclei; (b) reorientation at coalescence; (c) preferential growth of those grains that are oriented relative to an artificial pattern. Several other mechanisms are also possible. However, be-

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cause the growth process is unidirectional under approach (2), any defective areas that form are not likely to be eliminated during growth. Accordingly, significant orientation-spread is likely to be present. Approach (2) would be most effective for those materials that reorient readily. The spatial period of the pattern should be sufficiently small that crystallites can span several periods while undergoing such reorientation. In general, this implies periods <100 nm. Of course, some form of annealing could be incorporated in approach (2) [23]. Approach (3) is a refinement of approach (2). Material grown during one portion of a cycle is partially etched back during the next portion, then ~egrown, and so forth. Poorly aligned and defective regions of a film should be preferentially removed during etch-back [32]. In approach (4), material is deposited in an amorphous or fine-grain polycrystalline form over an artificial surface pattern (or the pattern is put in, or on top of, the deposited material) and, in a second step, the material is partially melted such that grains aligned with respect to the pattern are preferentially retained. (This is believed to be the mechanism operative in the Si graphoepitaxy via laser and strip-heater recrystallization, discussed in section 3.) In approach (5) material is again deposited in an amorphous or polycrystalline form. Then, orientation is induced by solid-state recrystallization. This is discussed in section 4.7. The liquidcrystal graphoepitaxy, discussed in section 2.1., is an example of approach (5), with mesophase recrystallization taking the place of solid-state recrystallization.

3. Si graphoepitaxy with laser and strip-heater re crystallization *

-

By early 1978 Gat et al. [33] and Fan and Zeiger [34] had shown that fine-grain polycrystal*

In this context we use the term “recrystallization to encompass both the traditional meaning (i.e., solid-state processes involving grain nucleation and/or growth) and melting followed by solidification, in accord with recent usage.

line Si over SiO2 could be “recrystallized” to large-grain (several ~sm diameter) material by scanning the film through a focused laser beam, a process initially called “laser annealing”. (Actually, the poly Si was melted and resolidified.) In mid 1978, experiments on graphoepitaxy by laser recrystallization * were begun on films of amorphous Si, 0.5 ~tm thick, deposited over surface-relief gratings of 3.8 p~mperiod that were etched 0.1 ~tm deep into Si02 substrates. The films were recrystallized by scanning them through a CW An-ion laser beam. RHEED patterns mdicated that Si <100> directions were predominantly parallel to the grating axis, and perpendicular to the substrate surface [35]. Subsequently, a stationary strip-heater oven was used for the Si recrystallization [36]. X-ray analysis indicated that the (100) texture was characterized by tip angles (i.e., the half-width at half-maximum (HWHM) of the distribution of the <100> directions about the substrate normal) of z~9— 2°and — 0.5°for the laser and strip-heater processes, respectively. The <100> azimuthal orientation was characterized by a spread angle (i.e., the

a 8 6

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2

1<~

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____ _________________

0 ____________________________________ 0

90

180 270 DEGREES Fig. 2. X-ray pole plots of (220) X-ray intensity from 0.5 ~tm thick graphoepitaxial silicon films as a function of the angle of rotation in the plane of the film. In both cases, the gratings were 100 nm deep and had a 3.8 ~smspatial period. (a) For a film recrystallized in a strip-heater oven. (b) For a film recrystallized with an argon ion laser.

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HWHM of the distribution of <100) directions about the grating axis), ~4, of — 10° for the laser process, and roughly half this value for the stationary strip-heater process, as illustrated in fig. 2. In the case of laser recrystallization, orientation occurred only if an O2-containing ambient gas was present to cause the formation of a native oxide (<0.1 ~smthick). The strip-heater recrystallization required a deposited SiO2 encapsulation layer over the Si. No orientation was observed if the Si was fully melted. The surfaces of the film were not smooth enough for conventional device processing, although MOSFET (metal—oxide—semiconductor, field-effect transistor) devices were made using a specially tailored process. The electron-surface -mobilities obtained in strip-heater prepared films were more than 2/3 the values obtained in equivalently-doped, conventional Si wafers. These results were obtained without any clear understanding of the mechanisms responsible for (100) texture and <100> orientation. Recently, such an understanding has emerged, and a model has been developed which explains essentially all the observations [37,38]. This is summarized in the following paragraphs. When a Si film on an SiO2 substrate, encapsulated with SiO2, is heated by irradiation, there is a range of incident radiant power density over which the Si is partially molten. For a fixed incident radiant power density, solid crystallites (variously called “lamellae”, “worms”, “ribbons”, or “islands”) are stable within the melt [38—42].Hawkins and Biegelsen [41,42] attribute this to the abrupt increase in reflectivity that accompanies the melting of Si (a semiconductor-to-metal transition). According to the Hawkins—Biegelsen model, the power density required to maintain a pool of fully-molten silicon P2, is higher than the power density required to reach the threshold for melting solid Si, P~.At any power density between P1 and ~2 the fraction of silicon in the solid state is fixed. (If silicon is melted nonradiatively, such as by thermal conduction [42] or an electrical discharge [43], the partially-molten state is not observed.) The solid crystallites in the melt have a predominance of (100) texture, as inferred from their shapes [38] and from X-ray measurements [43] made after solidification of partially-molten regions (so-called

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transition regions). Predominance of (100) texture indicates minimum free-energy for this particular orientation, which is probably due to minimum interfacial energy. The solid crystallites in a partially-molten region (whether created by a laser beam or a stripheater) that have (100) texture also have a preferential <100> orientation parallel to the grating axis, and these crystallites act as seeds during subsequent solidification of molten material. The profiles of relief gratings in SiO2 become rounded when molten Si makes contact with them. Thus, the Si crystallites which seed the solidification must be those which remain unmelted and in contact with the original grating. During solidification, film orientation is determined by the orientation of the seed crystals. Other than providing a template for preferential retention of oriented seed crystals, the surface-relief grating has no additional influence on orientation. This orientation mechanism corresponds to approach (4), discussed in section 2.2. The crystallites which seed solidification (see fig. 2 of ref. [38] are 2 urn in diameten, which is much larger than the original polycrystalline grains (— 50 nm). Presumably, grains enlarge rapidly by solid-state processes as the temperature approaches the threshold of melting (see section 4.7). Weissmantel and coworkers [44,45] have conducted an extensive series of experiments on Si graphoepitaxy in which films were deposited by CVD and ion-beam-sputtered methods, and recrystallization was carried out by laser and flashlamp irradiation. Their results are consistent with the above mechanism. In late 1980, experiments were carried out in which a molten zone, created by a strip heater, was scanned relative to a surface-relief grating. It was found that the in-plane <100> orientations in the resulting film tended to be parallel to the zonescanning direction, not the grating direction. (This line of experimentation has been reported recently by Sakano et al. [46].) Following this observation the grating was eliminated and a new encapsulation layer was introduced which was a composite of SiO2 and Si3N4 [47]. This composite encapsulation layer prevented agglomeration of molten Si in the absence of a grating, leading to film surfaces —

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that were sufficiently smooth to permit conventional device fabrication. The in-plane <100> directions were found to be within ±25°of the zone-scanning direction (HWHM, i.~O — 15°),and grains were elongated in the direction of zone

4.2. Sn by electrodeposition

motion and — 1 mm wide [48]. This technique of scanning a molten zone is now called zone-melting recrystallization (ZMR) [43,47—50]. (ZMR was used originally in the 1960’s to recrystallize Ge and InSb films [51].)Single-crystal films were produced by cross-seeding [48] and, subsequently, by zone-melting through planar constrictions [52,53] (see section 5). Thus, because of its process simplicity, ZMR became preferred over laser or stripheater graphoepitaxy for high temperature SOI. As a consequence, our research on Si graphoepitaxy shifted to basic studies of orientation mechanisms, and the exploration of low-temperature, non-melting processes for achieving single-crystal films of Si and other materials on substrates of choice. This research is discussed in section 4. Zone-melting recrystallization of patterned Si films is discussed in section 5.

he proved [56]that orientation does not take place at nucleation (the opposite conclusion was presented in ref. [55] but corrected in ref. [56]) but occurs during growth. Adhesion of the tin to the substrate was poor and the islands were believed to be quasi-mobile. Alignment was attributed to physical confinement.

Darken reported a strong graphoepitaxial orientation for Sn electrodeposited onto Cr-coated surface-relief gratings in SiO2 [55,56]. Moreover,

4.3. Ge and Si by Au and Ag solutions Mon [57,58] and Geis et al. [59] have reported experiments on Si and Ge orientation using Au and Ag solutions, similar to the experiments of Sheftal et al. (see section 2.1). Geis et al. worked with both square-wave and saw-tooth-profile relief gratings. Mon reported improved (111) texture when relief structures consisted of two gratings, one rotated by 60°relative to the other. Recently, using a two-dimensional array of rhomboid-shaped gold island 150 nm thick, on 1 ~tm centers, Mon demonstrated single-crystal islands, 130 ~m in diameter having (111) texture, with [110] directions perpendicular to the faces of the rhomboids [58]. The mechanism of orientation was not described. The use of metal solvents to achieve growth of Si and Ge is attractive because of the low temperatures involved. However, it is not clear that orientation spread can be made sufficiently small, or that problems of solvent contamination can be avoided. —

—

4. Recent graphoepitaxy research 4.1. In-situ studies of evaporated metal films Experiments on graphoepitaxy with evaporated metal films have been reported by Anton et al., using approach (2) [54]. Au, Ag, Pb, Sn, Bi and Sn—Bi alloys were deposited in-situ in a TEM over relief gratings in C substrates. They found some degrees of graphoepitaxial orientation in nearly all cases, and observed that orientation improved when two islands, at least one of which was in contact with a step, coalesced in the solid-state and changed orientation. Electron beam annealing promoted coalescence and further improved orientation. In some cases, the e-beam annealing probably induced melting (i.e., approach (4)). However, in all cases there was a spread in azimuthal orientation of several degrees (generally ~4> 10°).The best orientation was observed for the Sn/Bi alloy (44 = 10°). These experiments confirmed earlier speculation on the role of coalescence and solidstate reorientation in graphoepitaxy.

4~ 4. Ge by zone melting Sakano et al. [46] have studied graphoepitaxy of Ge films on SiO2 using a scanned molten zone. They obtained grains 2—10 ~.tmin size with preferred orientation of <100> directions parallel to the grating axis and perpendicular to the substrate plane. Control of heating was critical, and in some areas no orientation was obtained. The mechanism of orientation was not disussed in detail. If onientation occurs under conditions of partial melting, as in the case of Si (section 3), this technique would fall under approach (4).

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4.5. Sn on KC1 by evaporation Osaka et al. deposited Sn on vacuum-cleaved KC1 [31]. The cleaving produced steps with vertical sidewalls and a wide variety of in-plane directions. They found that Sn islands on smooth portions of the KC1 surface were epitaxial with the <100> direction of Sn parallel to <100> KC1. However, when Sn islands contacted a step, the (100> direction of Sn was found to be parallel to the step regardless of the orientation of the step relative to the KC1 crystallographic axes. They called this a graphoepitaxial orientation, although the steps were produced by a natural process, cleaving. They concluded from this that the graphoepitaxial effect was stronger than the epitaxial effect for the Sn/KC1 couple. They also observed that coalescence between an island that is epitaxial with respect to the substrate and an island that is located at a step leads to a single compound island that is graphoepitaxially oriented with respect to the step!. These experiments illustrate orientation mechanisms (a) and (b) under approach (2). Osaka et al. also observed that when Sn islands were located between two facing steps that were separated by < 200 nm, virtually complete graphoepitaxial orientation occurred. This confirmed the importance of having spatial periods less than, or comparable to, the size of reonientable islands. The best overall orientation was obtained in regions where steps ran parallel to the (100> direction of KC1 so that ordinary epitaxy and graphoepitaxy reinforced one another. The authors cautioned that the Sn/KC1 results are not necessanily extendable to other systems. Sn has a strong texture and seems to be weakly bonded to the KC1. The work of Osaka et al. is consistent with the results of Shimaoka and Komoniya [19]. 4.6. 501 by chemical vapor deposition As mentioned above, it is highly desirable to develop means of achieving single-crystal Si films on insulating substrates at temperatures well below melting (1412°C). In this section we describe briefly our current research on silicon graphoepitaxy by chemical-vapor deposition (CVD). Chemical-vapor deposition (CVD) of Si onto

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surface-relief structures etched into Si 3N4 has been carried out by Dana [60,61] using the reaction SiH4—’Si+2H2

(1)

in the presence of HC1 gas which provided a back-etching of the Si (e.g., Si + 2HC1 SiC12 + H2). Dana also used the reaction —~

H2,HCI

SiCl4 + 2 H2 ~

Si

+

4 HC1.

(2)

As shown in fig. 3, Si islands were confined to the grooves and took on elongated shapes. In areas of the same substrate that did not have surface-relief structures, Si islands has hemispherical shapes. The above processes are not considered optimum for basic studies of Si-CVD graphoepitaxy because they are carried out in conventional open tubes and it is difficult to control supersaturation, particularly at low supersaturation. Moreover, at high temperature the HC1 gas etches the corners of relief structures in Si 3N4, and etches SiO2 to an even greater extent. For these reasons, and in order to better implement approach (3), we currently use the equilibrium reactions Si(s) + 4 1(g) SiI4(g), Si(s) + Si14(g) 2 Si12(g),

(3) (4)

in a closed, fused-silica ampoule [62]. Oscillatory etching and growth of Si is accomplished by thermal cycling. The Si14-based reactions can be carned out at temperatures below 900°C. We anticipate that cnystallites which have a lower energy, by virtue of their orientation with respect to a surface-relief structure (or other appropriate pattern), will etch more slowly during an etching portion of a cycle and grow more rapidly during a growth portion, than crystallites having other orientations. Thus, repeated cycling should lead to preferential orientation relative to an artificial pattern. 4.7, Graphoepitaxy by solid-state recrystallization Solid-state recrystallization has been studied extensively in metals, and at least three phenomena that lead to grain enlargement have been identified [63]. distinguished by the driving force that is

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Fig. 3. Silicon islands grown on a surface-relief grating in Si

3N4 using a SiH4/HCI

0.3 ~sm and a depth of

—

C’s’D process. The grating has

a spatial period of

20 nm.

dominant. Unfortunately, there is no universal agreement on terminology. Primary recrystallization occurs in polycrystalline materials that contam a high energy-density due to dislocations or other defects. New, dislocation-free grains nucleate and grow, driven by the energy reduction that occurs as the new grains consume the highly defective ones. The second phenomenon is normal grain growth. Here the driving force arises from the reduction in grain-boundary energy that takes place when grains enlarge. In some cases, one or more grains grow abnormally large, in a “runaway” mode. This is sometimes called secondary recrystallization, although the driving force is the same as in ordinary grain growth: reduction of grain-boundary energy. The third distinct phenomenon is grain growth driven by surface energy. That is, a grain whose orientation minimizes surface energy grows at the expense of other grains,

It has been called secondary recrystallization, tertiary recrystallization and surface-energy-driven secondary recrystallization. The classic example of this phenomenon is the change in crystallographic texture, from (110) to (100), that occurs in thin sheets of 3% silicon—iron if the ambient is changed from H2 to 02 [63—65].This is attributed to changes in the anisotropic surface energy due to adsorbed gas. Grain enlargement in polycrystalline Si has been studied by Wada and Nishimatsu [66],and Mie et al. [67]. We have worked with Si and Ge films in the 10—75 nm thickness range in an effort to induce surface-energy-driven secondary recrystallization. The driving force and hence the grain size should increase with the reciprocal of the thickness [63, 68—70]. With heavy P doping of 75 nm thick Si films on SiO2 substrates, grain — 5 p.m in diameter (and in some cases larger) have been

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Graphoepitaxy and zone-melting recrystallization ofpatterned films

537

obtained by annealing well below the Si melting point. The texture was (111). We anticipate that surface-relief gratings in the substrate or the top surface of the thin film will not only enhance the driving force but will also lead to preferential growth of grains oriented with respect to the artificial pattern. This would be an example of approach (5) to graphoepitaxy. We have shown that

Before discussing patterned ZMR it is important to review briefly the essential aspects of Si ZMR. To date, all of our work on Si ZMR has used a heated carbon strip or tungsten wire to produce a long, narrow molten zone which is scanned across the Si films at about 1 mm/s [43]. The Si film is encapsulated with 0.1 to 2 p.m of Si02, followed by 30 nm of Si3N4. The substrate

patterning Ge into stripes leads to enhanced grain size with elongation parallel to the stripe axes [70]. An attractive feature of graphoepitaxy by surface-energy-driven secondary recrystallization is that it should be applicable to any material that can be deposited stoichiometrically in ultra-thin film form (i.e., t < 100 nm). Assuming that an oriented single-crystal can be established in such films, the films thickness could then be increased, as desired, by conventional means of epitaxial film growth, including molecular beam epitaxy (MBE) or CVD. It is noteworthy that surface-energydriven secondary recrystallization is probably responsible for the enormous grain sizes (— 100 p.m) observed in ultra-thin films (50 nm) of Cu—Al [71], although the authors appear not to have recognized this mechanism. Gangulee and D’Heurle [72] obtained grains larger than 100 p.m in 1 p.m thick Al—Cu films by solid-state processes. The grains had uniform texture and hence surface-energy anisotropy was probably responsible. Because of the high mobility of metal atoms and the large grains obtainable, it may be far easier to demonstrate graphoepitaxy by surfaceenergy-driven secondary recrystallization in metal films than in Si.

has generally been thermally-grown SiO2 on a Si wafer. Fused-silica substrates have also been used, but Si films — 0.5 p.m thick crack upon cooling to room temperature due to differences in the thermal expansions of SiO2 and Si. When the molten zone is initiated, it is bordered by a transition region of partially-molten Si, as discussed in section 3. As the zone is scanned forward, the unmelted crystallites of the transition region (“ribbons” or “islands”) seed solidification. The transition region has a predominant (100) texture (fig. 4 of ref. [43]), and (100) texture predominates in the solidified film. In addition, as solidification progresses there is a strong tendency for growth from seeds that have (100) texture and (100> directions close to the zone-motion direction to cut off, or occlude, growth from grains with other onientations. As a result, the spread angle, of films tends to decrease as the distance from the transition region increases. Ten mm beyond the transition region, 4~ — 15°, and all grains with ~> ±25°are occluded [48]. The predominance of (100) texture in the transition region and the resolidified material is characteristic of Si films less than about 4 p.m thick that are zone melted by means of visible or IR radiation sources. Films zone-melted by electron beam, or films thicker

5. Zone-melting recrystallization of patterned films

than about 4 p.m generally have a multiplicity of textures (see section 5.5). Beyond the transition region, and the region where highly misoriented grains are occluded, the Si films consists of elongated grains with (100) texture that are typically — 1 mm wide and extend to the end of the region scanned. Their orientations can be referred back to the transition-region seeds from which they originate. Within individual grains there are defects which appear, after appnopriate chemical etching, as fine lines, generally parallel to the direction of zone motion, and separated by distances of a few tens of micrometers.

In the zone-melting recrystallization (ZMR) process, a narrow molten zone is scanned across a thin film. It is discussed in detail in other articles of this Journal issue and in ref. [43]. Here we discuss the use of patterning in conjunction with Si ZMR. This combination has achieved singlecrystal films on amorphous substrates, entrainment of dislocations and other defects along welldefined lines, and orientation filtering. For the sake of brevity we will call this class of techniques “patterned ZMR”.

~,

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Graphoepitaxy and zone - melting recrystallization of patternedfilms

nier electronic devices. However, grain boundaries (i.e., where growths from two different seeds meet) present potential barriers to majority carriers, which is detrimental to many devices [49,50].There is enhanced lateral diffusion of dopants along grain boundaries [73,74] and, to a lesser extent, along subboundanies [75]. Thus, elimination of grain boundaries is highly desirable for microelectronic and photovoltaic devices.

Zone Motion

~ ~

~

~

MoaV~

~

5.1. Planar constrictions (the hourglass technique)

Fig. 4. Selection of a single orientation from two initial grains by zone-melting recrystallization through the constriction of an ~ourglass structure. The etch pits are on 50 ism centers,

Films without grain boundaries (i.e., grown from a single seed) have been obtained by “cross seeding” [48] and by zone-melting through narrow, planar constrictions [52,53]. Here we review only

These lines are subboundaries and consist of arrays of dislocations and other defects and impurities. They originate at the interior corners of the faceted solid—liquid interface. The crystallographic angular deviation associated with them is generally <1°. TEM analysis indicates that the material between subboundanies is dislocation-free. Subboundaries have minimal impact on majority-car-

the latter. The planar-constriction, or hourglass, technique is illustrated in fig. 4. A grid of etch pits [76] shows that two distinct grains approach the constriction but only one extends through it to seed solidification beyond the constriction. To achieve this result, polycrystalline Si was deposited over thermally oxidized Si wafers and patterned using photolithography and wet or dry etching. In the “moat” all Si was removed down to the then-

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WIDTH

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Fig. 5. Arrays of 7 adjacent hourglass patterns of rectangular geometry each differing in the length and width of the constriction, and the width of the hourglass body. (Due to limited microscope field-of-view, the figure is a montage of 4 micrographs.) Oblique illumination of the grid of etch pits covering the film discriminates the distinct grains. Note that beyond the constrictions only single-grain films exist. The horizontal bars at the top of the picture indicate the body widths of the 7 hourglass patterns.

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Graphoepitaxy and zone-melting recrystallization of patterned films

mally-grown SiO2 base. The films was then coated with a conformal encapsulation layer of 2 p.m Si02 and 40 nm Si 3N4 and the recrystallization carried out. The planar-constriction technique works very reliably for a wide variety of hourglass geometries. Fig. 5 shows results for an array having rectangulan forms. Oblique illumination of a grid of etch pits discriminates distinct grains. Note that a single orientation is obtained beyond the constriction in all cases. With the rectangular hourglass geometry, if the width beyond the constriction exceeded — 2 mm, molten silicon in the left and right corners of the pattern would become excessively undercooled before the crystal growing from the constriction could arrive there. As a result, spontaneous nucleation and local dendritic growth occurred, This can be avoided by proper design of the hourglass and control of the zone-scanning speed. For example, dendnitic growth was never observed when the moats beyond the constriction were inclined at 45°to the zone-motion direction. Biegelsen et al. [77] have patterned Si films, prior to laser melting, into a variety of shapes, some resembling the hourglass. Such patterning modified thermal profiles to suppress competitive nucleation, or provided for expansion of Si upon solidification. They also recognized the potential of constrictions to produce single-orientation films [77], as did Clawson [51]. 5.2. Subboundary termination in channels In some cases, elongated constrictions, or channets, were used in the hourglass structures. Subboundaries tended to terminate at the sides of the channel [53]. The subboundanies reappeared abouth 100 p.m beyond the end of the channel, where the hourglass structure widened out. The solidification front, which is naturally faceted [43,78], adjusts itself so that a single chevron propagates down the channel. The tendency of subboundaries to terminate at the sides of narrow channels implies that if a Si film is patterned into parallel channels with spacings close to the natural subboundary spacing, one could obtain films composed of single-crystal stripes, free of subboundaries. Experiments to date on this idea have

539

shown that effective termination of subboundaries occurs only for (100)-textured films with (100> direction within a few degrees of the channel axis. 5.3. Recrystallization ofpreformed islands A number of investigators have formed islands of polycrystalline Si over Si02 and melted them with lasers or strip-heaters to yield crystalline islands, typically tens of micrometers on an edge [73,74,77,79]. An encapsulation layer is generally necessary to prevent agglomeration. In some cases islands have been specifically shaped to influence heat flow. If an island is fully melted, solidification cannot occur until the melt undercools sufficiently for spontaneous nucleation to occur. In this case, the orientation is unpredictable. (Early reports [79] indicated (100) texture when islands are fully melted and solidified, but generally, random orientations are obtained.) Biegelsen et al. [77] have provided islands with sharp corners on one end to encourage nucleation at that single point, a two-dimensional analog of the Bnidgman—Stockbarger/Obreimov—Schubnikov techniques [80]. As mentioned above, Biegelsen et al. have also shaped islands with “moats” and “drawbridges” to allow for volume expansion upon solidification [77]. 5.4. Entrainment of subboundaries Subboundaries and grain boundaries in continuous films have been entrained by modulating the temperature contours using a lithographicallyproduced grating of stripes on top of the encapsulation layer to absorb or reflect the incident radiation, as illustrated in fig. 6 [78,81]. Absorber stripes (typically carbonized photoresist) cause the material underneath them to be at a higher temperature than the material located between stripes. The positions underneath the stripes are the last to freeze, causing the interior corners of the faceted solid/liquid interface to be locked-in or entrained by the imposed grating pattern. The results are shown in fig. 7. The material between entrained subboundaries appears, from TEM studies, to be dislocation free. Moreover, computer modelling of impurity rejection during solidification at a faceted solid/liquid interface indicates that impurities

540

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Graphoepitaxy and zone-melting recrystallization of patternedfilms

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ment could be of significant practical value. Devices could be fabricated in the high-purity, dislocation-free material between subboundaries, and

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would also tend to be rejected to the entrained subboundaries [82,83]. Experiments with Si that was heavily doped with As [43], and experiments with nonstoichiometnic InSb [82,83] confirm this impurity rejection. Thus, subboundary entrain-

.

LIQUID

Fig. 6. (a) Schematic illustration of the use of a grating of optical absorber stripes on top of an encapsulation layer to modulate the temperature profile and entrain subboundaries. (b) Illustration of the entrainment of subboundaries under the middle of the optical absorber stripes,

the subboundaries could serve as gettening sites for mobile impurities. Also, in certain applications such as photovoltaics, it might be possible to use somewhat lower grade starting material and partially refine it during the recrystallization process by rejecting impurities to the entrained subboundaries (so-called rejection channels). Recently, Maby et al. [75] have shown that enhanced diffusion occurs along subboundaries. Thus, subboundary entrainment is important for device applications. Subboundary entrainment is achieved by the .

method shown in fig. 6 only when the azimuthal orientation of the (100> direction is close to the

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Fig. 7. (a) Entrainment of subboundaries in a 1 ~sm thick Si film using a grating of carbonized photoresist. (b) Typical pattern of subboundaries in an identical sample recrystallized without an entrainment pattern.

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Graphoepitaxy and zone-melting recrystallization of patternedfilms

direction of zone motion. The entrainment technique has not been made fully reliable, but we believe this should be possible with further reSubboundaries have also been entrained with search two types of patterns on the SiO2 substrate, underneath the Si film: a grating of grooves about 0.1 p.m deep, and a grating of carbon stripes about 30 nm thick, both with periods of 100 p.m. Neither of these would be expected to modulate the temperature profile significantly. The grooves appeared to weakly pin the interior corners as they moved forward in the zone-scanning direction. The carbon stripes also induced pinning, apparently by modulating the Si interfacial energy. These two methods of subboundary entrainment are not well understood and have been less reliable than the temperature modulation method. Colinge et al. [84], using Ar-ion laser irradiation, have demonstrated that grain boundaries can be localized under anti-reflection stripes of Si3N4. The lithographically-produced pattern modulates the temperature profile so that solidification is not seeded from the edges of the laser scan path, as is typical. Instead, solidification proceeds parallel to the laser scan direction (which is parallel to the stripes), and grain boundaries are located under the antireflection stripes. With this technique the film texture was not predictable.

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Fig. 8. The vertical constriction technique is used to establish a (100) texture in thick silicon. A section of thick silicon is thinned to approximately 0.5 ~ and encapsulated with Si02 and Si3N4. Zone-melting recrystallization is begun in the thinned region, where (100) texture is predominant, and cxtended into the thick silicon.

to entry of the molten zone into the thick-Si region. The orientations established in the thin section extend into the thick section, as indicated in fig. 8. If an hourglass structure is used in the thin Si section, a single-crystal of (100) texture could, presumably, be grown in the thick Si. 5.6. Orientation filtering by growth-velocity competition As discussed above, ordinary ZMR produces films with a spread in the azimuthal orientation of the (100> direction (~ < ±25°)[43,48]. Occlusion, as a result of growth-velocity anisotropy is re-

5.5. Vertical constriction The predominance of (100) texture and of grains with (100> directions within ±25°of the direction of zone motion are not observed in Si films thicker than about 4 p.m. For many applications, especially photovoltaics and high-power integrated circuits, much thicker films are required. To achieve (100) texture in thick Si films we have used the “vertical constriction” technique illustrated schematically in fig. 8 [85,86]. A portion of a thick Si film is etched down to a thickness of about 0.5 p.m and then the entire film is encapsulated with 2 p.m of Si02 and 30 nm of Si3N4. Zone melting is initiated in the 0.5 p.m thick region so that (100) texture, occlusion of misoriented grains, and (100> directions close to the direction of zone motion are established prior

,-

d

Fig. 9. Orientation filtering. In the clear areas the Si is removed and replaced with Si02. Two grains, A and B, are shown growing into the filter through apertures a and b, respectively. Both grow laterally, but A arrives first at the constriction c, thereby occluding grain B. Three stages of filtering are depicted.

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Zone Motion

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Graphoepitaxy and zone-melting recrystallization of patterned films

______

Transition

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Fig. 10. Optical micrograph of region surrounding an Orientation filter. Oblique illumination of the matrix of etch pits indicates large grain size beyond the orientation filter.

sponsible for this limited orientation spread. Recently, we have developed an orientation-filtering technique which greatly accelerates the occlusion effect, leading to a narrower, and predictable, orientation spread [85,87]. Such control of in-plane orientation is important for the subboundary entrainment technique and for certain applications, In addition to controlling the in-plane orientation, the orientation filtering technique leads to enhanced grain size. Fig. 9 illustrates the principle of an orientation filter. Rows of rectangular voids are etched in the Si film and then filled with Si02. Two grains, A and B, of differing orientations enter the two apertures, a and b, in the row of voids. To pass through the aperture, c, the grains must grow laterally. The orientation with the fastest lateral growth rate toward the aperture c (depicted as A in fig. 9) will arrive at c first, pass through the aperture, and thereby occlude growth from crystal B. Several stages of filtering further reduce the orientation spread. Fig. 10 is an optical micrograph showing the grain size enhancement that

results from ZMR with the filter design of fig. 9. Fig. 11 shows the distribution of in-plane <100> orientations before and after passage through an orientation filter. The angle 4 9.5°corresponds to (100> directions parallel to the direct line-ofsight from a to c and b to c. Obviously, one can design filters to eliminate the direct line-of-sight, or to alter the distribution of orientations in other desired ways. It appears, for example, that a narrow distribution close to zero degrees is feasible [85,87]. =

6. Conclusions We have reviewed the current status of graphoepitaxy, with special emphasis on its application to Si on insulators, and have also reviewed the use of patterning in conjunction with zonemelting recrystallization. Graphoepitaxy is a very general method of forming oriented films which applies to solid materials as well as mesophases

HI. Smith et at total

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Graphoepitaxy and zone-melting recrystallization of patterned films

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Fig. 11. (a) Distribution of in-plane K100) orientations approximately 1 mm after the transition region and before an orientation filter. (b) Distribution of in-plane Orientations after orientation filtering. Inset shows shortest path between apertures. The angle ~ is 9.5°; the measured mean, ~‘ob,’ of the distribution was 8.2°.

(i.e., liquid crystals), and encompasses a wide variety of approaches and mechanisms of orientation. The essential idea of graphoepitaxy is that orientation is induced by an artificially-created pattern, The first success in orienting silicon on Si0 2 by graphoepitaxy involved partial melting with a laser or stationary strip-heater. The orientation which occurred is attributed to preferential retention of crystallites that were oriented relative to the

surface-relief grating. Because of orientation spread and the high temperatures involved in melting, there is no reason to prefer this particular method over zone-melting recrystallization, especially zone-melting in conjunction with film patterning. This latter category of techniques has yielded large-area, single-orientation Si films on Si02, entrainment of subboundaries and impurities along parallel rejection channels, and orientation filtering.

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Graphoepitaxy and zone - melting recrystallization of patterned films

Our current research on graphoepitaxy for Si on insulator focuses on two low-temperature approaches; oscillatory CVD using Si14-based processes and solid-state surface-energy-driven secondary recrystallization. If these or other lowtemperature approaches to Si graphoepitaxy could be perfected they could have a major impact on multilayer integrated electronics and flat-panel displays.

Acknowledgments The work described here which was carried out at MIT and MIT Lincoln Laboratory was sponsoned by the Defense Advanced Research Projects Agency, the National Science Foundation, and the Department of Energy. The latter sponsored the work on Si ZMR for photovoltaic applications. The authors are grateful to the many colleagues who contributed, especially R.W. Mountain and D.J. Silversmith.

strates (Artificial Epitaxy), in: Protessy Realnogo Kistalloobrazovaniya (Real Crystal Formation), Eds., N.y. Beby and N.N. Sheftal (Nauka, Moscow, 1977) pp. 144—150, (in Russian). [10] VI. Klykov and N.N. Sheftal, Vest. Mosk. Gas. Univ., 5cr. Geol. I (1978) 115. [11] E. Hartmann, Acta Phys. Acad. Sci. Hung. 47 (1979) 185. [12] V.1. Klykov and N.N. Sheftal, J. Crystal Growth 52 (1981) 687. [13] H. Zocher and K. Coper, Z. Physik. Chem. 132 (1928) 295; translation available in article by CD. West, Glass Industry (May 1949) 272. [14] H.I. Smith, US Patent 4,333,792, Enhanced Epitaxy and Preferred Orientations, June 8, 1982, continuation in part of Ser. No. 756,358, Jan. 3, 1977. [15] D.C. Flanders and HI. Smith, in: Proc. Symp. on Electron, Ion and Photon Beam Techology, Palo Alto, CA,

[16]

[17] [18]

References [1] J.D. Filby and S. Nielsen, Brit. J. AppI. Phys. 18 (1967) 1357, see p. 1380. [2] N.N. Sheftal and AN. Buzynin, Vestn. Mosk. Univ. 3 (1972) 102. Translation available from: National Translation Center, The John Crerar Library, 35 W. 33rd St., Chicago, IL 60616, USA. [3] N.N. Sheftal, NP. Kokorish and A.V. Krasilov, Bull. Acad. Sci. USSR 21 (1957) 140. [4] N.N. Sheftal, in: Rost Kristallov, 95 Vol. 10, Ed. N.N. Sheftal (Nauka, translation: English Moscow, 1974) N.N.p-i Sheftal, in: Growth of Crystals, Vol. 10, Ed. N.N. Sheftal (Consultants Bureau, New York, 1976). [5] N.N. Sheftal and VI. Klykov, in: Abstracts 5th Conf. on Crystal Growth, Thilisi, USSR, Sept. 1977, Vol. 1, p. 31. Translation available from: National Translation Center, The John Crerar Library, 35 W. 33rd St.. Chicago, IL 60616, USA. [6] N.N. Sheftal, Ada Phys. Acad. Sci. Hung. 47 (1979) 191. [7] VI. Klykov, N.N. Sheftal and E. Hartmann, Acta Phys. Acad. Sci. Hung. 47 (1979) 167. [8] El. Givargizov, N.N. Sheftal and VI. Kiykov, in: Current Topics in Material Science, Vol. 10, Ed. E. Kaldis (NorthHolland, Amsterdam, 1982) ch. 1, pp. 1—53. [9] VI. Klykov, R.N. Sheftal and N.N. Sheftal, Oriented Crystallization on Amorphous and Polycrystalline Sub-

[19] [20]

[21] [22]

[23]

[24] [25] [26]

[27]

[28] [29]

May 1977; D.C. Flanders and H.I. Smith, J. Vacuum Sci. Technol. 15 (1978) 1001. G. Honjo and K. Yagi, in: Current Topics in Material Science, Vol. 6, Ed. E. Kaldis (North-Holland, Amsterdam, 1980) ch. 6, pp. 196—307. This article provides a comprehensive review of in-situ experiments. K.L. Chopra, Thin Film Phenomena (McGraw-Hill, New York, 1969). K.L. Chopra, Boston College Physics Colloquium, 1967—68, unpublished. G. Shimaoka and G. Komoriya, J. Vacuum Sci. Technol. 7 (1970) 178. HI. Smith, in: Convention Digest 1969 IEEE Intern. Convention, New York, 1969, Session 2-C (IEEE, New York, 1969) pp. 90—91. HI. Smith, Proc. IEEE 62 (1974) 1361. HI. Smith and D.C. Flanders in: Enhanced Heteroepitaxy, Integrated Optical Circuits and Exploratory Materials Research, Semiannual Technical Summary Report to DARPA, MIT Lincoln Laboratory, 1 July — 31 December 1975, Flanders, D.C. ESD-TR-76-117, PhD Thesis, p. 9. MIT, Cambridge, MA (1978); reprinted as MIT Lincoln Laboratory Technical Report 533, 1978. HI. Smith and D.C. Flanders, AppI. Phys. Letters 32 (1978) 349. D.C. Flanders, D.C. Shaver and HI. Smith, Appl. Phys. Letters 32 (1978) 597. D.C. Shaver, MS Thesis, MIT, Cambridge, MA (1978); reprinted as MIT Lincoln Laboratory Technical Report 538, 1979. HI. Smith, D.C. Flanders and D.C. Shaver, in: Scanning Electron Microscopy/1978, Vol. 1, Ed. 0. Johari (SEM, AMF O’Hare, IL, 1978) pp. 33—40. H. von Kanel and J.D. Litster, Phys. Rev. A23 (1981) 3251. H. von Kanel, J.D. Litster, J. Melngailis and H.I. Smith, Phys. Rev. A24 (1981) 2713.

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[30] H.I. Smith, in: Microcircuit Engineering 80, Proc. Intern. Conf. on Microlithography, Amsterdam, 1980, Ed. R.P. Kramer (Delft University Press, 1981) p. 463. [31] T. Osaka, T. Kawana, T. Nojima and K. Heinemann, J. Crystal Growth 61(1983) 509. [32] K.A. Jackson and CE. Miller, J. Crystal Growth 42 (1977) 364. [33] A. Gat. L. Gerzberg, J.F. Gibbons, T.J. Magee, J. Peng and J.D. Hong, AppI. Phys. Letters 33 (1978) 775. [34] J.C.C. Fan, H.J. Zeiger, AppI. Phys. Letters 27 (1975) 224. [35] MW. Geis, D.C. Flanders and HI. Smith, Appl. Phys. Letters 35 (1979) 71: MW. Geis, D.C. Flanders, D.A. Antoniadis and H.I. Smith, J. Vacuum Sci. Technol. 16 (1979) 1640; MW. Geis, D.C. Flanders, D.A. Antoniadis and H.I. Smith, in: Technical Digest, 1980 Intern. Electron. Dcvices Meeting (IEEE, New York, 1980) p. 210. [36] M.W. Geis, D.A. Antonjadis, Di. Silversmith, R.W. Mountain and HI. Smith, Appl. Phys. Letters 37 (1980) 454; MW. Geis, D.A. Antoniadis, D.J. Silversmith, R.W. Mountain and HI. Smith, Japan. J. AppI. Phys. 20, Suppl. 20-1 (1981) 39; MW. Geis, D.A. Antoniadis, D.J. Silversmith, R.W. Mountain and H.I. Smith, J. Vacuum Sci. Techol. 18 (1981) 229. [37] HI. Smith and M.W. Geis, 161st Electrochem. Soc. Meeting, Montreal, Canada, 1982, Electrochem. Soc. Extended Abstracts 82-1 (1982) 249. [38] HI. Smith, CV. Thompson, M.W. Geis, R.A. Lemons and MA. Bosch, J. Electrochem. Soc. (Oct. 1983), to be published. [39] MA. Bosch and R.A. Lemons, Phys. Rev. Letters 47 (1981) 1151. [40] R.A. Lemons and MA. Bosch, AppI. Phys. Letters 39 (1981) 343; 40 (1982) 703. [41] D.K. Biegelsen, N.M. Johnson and M.D. Moyer, 161 st. Electrochem. Soc. Meeting, Montreal, Canada, 1982, Electrochem. Soc. Extended Abstracts 82-1 (1982) 229. [42] W.G. Hawkins and D.K. Biegelsen, AppI. Phys. Letters 42 (1983) 358. [43] M.W. Geis, HI. Smith, B.-Y. Tsaur, J.C.C. Fan, D.J. Silversmith and R.W. Mountain, J. Electrochem. Soc. 129 (1982) 2812; M.W. Geis, HI. Smith, B.-Y. Tsaur, J.C.C. Fan, D.J. Silversmith, R.W. Mountain and R.L. Chapman, in: Proc. Materials Research Society Conf., Boston, MA, 1982. [44] C. Weissmantel, J. Vacuum Sci. Technol. 18 (1981) 179; 277. C. Weissmantel, in: Proc. ISIAT-81, Tokyo, 1981, p. [45] C. Weissmantel, K. Breuer, J.W. Erben, W. Nowick and W. Scharff, in: Proc. 2nd Intern. Conf. on Molecular Beam Epitaxy, Tokyo, 1982. [46] K. Sakano, K. Moriwaki, H. Aritome and S. Namba, Japan. J. Appl. Phys. 21 (1982) L636. [47] E.W. Maby, M.W. Geis, Y.L. LeCoz, D.J. Silversmith, R.W. Mountain and D.A. Antoniadis, IEEE Electron Device Letters EDL-2 (1981) 241.

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Graphoepitaxy and zone - melting recrystallization of patternedfilms

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