32. Ion implantation of metals

Classified abstracts 6343-6352 31 6343. Depth profiles of manganese implants in InP after annealing This paper reports on depth profiles of Mn implants, after annealing, obtained by secondary ion mass spectrometry. Two types of samples implanted with manganese were studied: unintentioanlly doped n-type (5-.10×10~Secm -3) and n-type S-doped { n = 5 x l 0 ~ e c m - ~ l substrates. In unintentionally doped substrates it is found that Mn exhibits a well-defined two-species diffusion front as other acceptors: Be, Zn or Cd. On the contrary in S-doped substrates it does not move. The study of the correlations between the movement of the residual impurities and the implanted Mn atoms, or Zn in a comparative sample, has led us to propose a model based on an interstitial-substitutional reaction involving the impurity sites and taking place in the bulk of the semiconductor. R Chaplain et al, J appl Phys, 58, 1985, 1803-1808. 31 6344. Activation and redistribution of implanted P and B in polycrystalline Si by rapid thermal processing Rapid thermal processing (RTP) allows electrical activation of implanted semiconductors to be carried out at high temperature in times so short ( ~ 10 s) that minimal dopant redistribution occurs. Use of RTP to activate implanted species in single-crystal Si is well documented, but relatively little has been reported for poly-Si. In this paper, we present measurements on 0.4/~m thick poly-Si films implanted with n-type (3~ p+ I or p-type (* *B * ) dopants. R T P was carried out in t:acuo ( ~ 1 × 10- ~ torr~ by exposing samples for 5-30 s to the black body radiation of a graphite heater at I150-1300~C. Dopant activation and redistribution following RTP was measured by spreading resistance and four-point probe. In polySi, unlike similarly implanted and rapidly annealed single-crystal Si, we find considerable redistribution for both dopants. For P, significant dopant loss occurred from the uncapped poly-Si surface; however, a thin (600 A) SiO., cap prevented this outdiffusion. For B, on the other hand, uncapped poly-Si surfaces exhibited minimal dopant loss. The time evolution of carrier concentration profiles depended both on implant dose and R T P conditions. R Chow and R A Powell, J Vac Sci Technol. A3, 1985, 892 895. 31 6345. Formation of droplets on Si surfaces bombarded by In from a capillary type liquid metal ion source Droplet formation on Si surfaces bombarded by 10 keV beams from a liquid metal indium ion source has been observed. It has been verified that excess indium is transported in the ion beam, probably in the form of charged droplets. SIMS, SEM and RBS techniques have been used to study the distribution of droplets at the surface. At the specified ion source operating conditions, equilibrium droplet coverage is of the order of 25%. Individual droplets have an average diameter of 0.35/~m and an average height of 2.2 nm. At a b o m b a r d m e n t current density of 0.1 mA cm--', equilibrium coverage is reached in about 1 s. F Riidenauer et al, Vacuum, 35, 1985, 315.-320. 31 6346. Microfabrication with ion beams This paper covers recent research and development of new technologies - - s o m e t i m e s referred to as 'directed (or focused) ion beam techniques (FIBI' or "ion engineering'--where ion beams in vacuum or ions in plasma play the central role. The technologies are characterized by the action of accelerated ions which enhance surface or bulk chemical activities in the target (substrate) material. These inctudc ion-beam lithography, ionassisted etching and deposition and structure diagnosis with ion beams. The paper also covers the physical and engineering aspects of FIB technologies, including an evaltration of the fabrication techniques used to build three-dimensional microstructures and micromechanical devices. A J Muray and J J Muray, Vacuum, 35, 1985, 467 477.

32. ION I M P L A N T A T I O N O F M E T A L S 32 6347. Defects in amorphous ferromagnets: Effects of ion implantation The effect of boron implantation on the magnetic properties of Fes~B~ ~Niz a m o r p h o u s alloys has been investigated. The magnetization of thin film samples (3800 ,~) obtained by' rf sputtering has been studied before and after implantation of 1% atomic boron by using a S Q U I D magnetometer with magnetic fields up to 2 T. In this highly magnetostrictive material (,:.-~ 30 ppm) the saturation process and coercive field are presumably dominated by the stress field due to the defect structure. O u r analysis of the saturation process revesls that the vacancies introduced by boron implantation transform at room temperature into more stable

defects: linear defects. These results are compared with computer simulations and model structures of a m o r p h o u s metals. P Garoche and R J Gambino, J appl Phys, 57, 1985, 3520-3522. 32 6348. One MeV electron irradiation of pure nickel compared to lithiumimplanted nickel Pure nickel and lithium-implanted nickel were irradiated with I MeV electrons at the Argonne H V E M - T a n d e m facility. The lithium-implanted nickel was not damaged as readily as the pure nickel under 1 McV electron irradiation in the temperature range 20-600"C. The decreased damage accumulation in the lithiated nickel could arise from both the precipitated lithium and that in solution. The latter could slow down the nickel interstitials produced during irradiation by association, thus enhancing their recombination with vacancies. The interfaces of the precipitated lithium could also act as unbiased sinks for the vacancies and interstitials. Above 600'C, under electron irradiation, a melting process which created small irregular shaped regions occurred in the lithium-implanted nickel. Electron diffraction analysis showed that the compound LizNiO., v, as formed inside these regions. K Seshan et al, l~ad Effects, 90, 1985. 283-295. 32 6349. Durable metal carbide layers on steels formed by ion implantation at high temperatures High-power beams (4-. 10 W/cm 2) of Ti ions have been used to heat Fc and steel substrates to 600-800°C during high fluence 15 x 10 *~/cm 2) implantation. Auger sputter depth profiles find a stoichiometric TiC surface layer, about 100 nm deep. graded continuously into both Fe and steel substrates. Secondary ion mass spectrometry of Fe and steels implanted in • 3CO atmospheres indicate that the carbon originates from the bulk in carbon steels but from the atmosphere in Fe foils. Transmission electron microscopy reveals a continuous layer of fine-grained (50--100 nm) TiC crystallites in a preferred Baker--Nutting orientation relationship with respect to underlying Fc grains. Abrasive-wear measurements performed with diamond paste I 1-5 ,t,m) show the TiC layer on hardened M2 steel is 3--10 times more wear resistant than the substrate. Sliding-wear studies find an extremely durable layer that reduces friction by up to 60%, and increases by 50% the contact-stress threshold of M2 tool steel to boundary lubrication. The metallurgical processes responsible for the TiC layer ",,,ill be discussed, and the advantages of this high-temperature treatment will be presen ted. I L Singer et al, J appl Phys. 58, 1985, 1255--1258. 32 6350. Current effects in heavy arsenic implants in silicon Current effects in heavy arsenic implants into silicon protected by a SiO., layer were studied by Rutherford backscattcring spectrometry, differential sheet resistivity and Hall mobility measurements, Auger electron spectrometry and transmission electron microscopy. It was found that oxygen atoms recoiled into silicon by the impinging arsenic ions affect the solidphase epitaxial regrowth during the low-temperature ( = 500=C) postimplant anneal. A complete stopping in the regrowth was noticed in samples implanted at 10 *~' c m - - ' at low current and annealed at 500~C. These results show that the procedure suggested to obtain high-quality implanted layers, i.e., ( 1) formation of an a m o r p h o u s layer with implants at low temperature and (2) solid-phase epitaxy at about 500~C, is not suitable for implants through a SiO: layer. G F Cerofolini et al, J appl Phys, 58, 1985, 264 267. 32 6351. Surface stresses and the hardness of ion implanted aluminium The stresses resulting from the implantation of nitrogen into aluminium were measured using a strain gauge technique. The strains resulting from 400 keV and 200 keV N" implantation were measured at doses of between 5 x 10 t~ and 2 x 10 *~ ions c m - z and the corresponding stresses were calculated. Hardness measurements were made on a Vickers microhardness tester. The stresses were observed to increase linearly with dose up to about 4× 10 ~° ions cm -~ above which they relieved. No corresponding drop in hardness was observed. The relief of stress at high doses is considered to result from plastic yielding of the implanted material and not blistering or bubble formation as reported by other research workers. For the 400 keV N * implant there was a gradual increase in stress after the stress relief, suggesting the operation of work hardening mechanisms. P B Madakson, J Phys D: Appl Phy~, 18, 1985, 531-540. 32 6352. Creation of tailored surfaces using selective oxidation of ionimplanted materials Ion implantation can produce a subsurface layer composition very 49

Classified abstracts 6353-6360 different from that of the bulk material. The present work involves postimplant selective-oxidation treatments to produce a tailored surface composition. Formation of Al~Oj-rich layers on both pure iron and 304-L stainless steel was achieved by implanting aluminium and subsequently heating the implanted sample in a controlled oxidizing environment to allow the subsurface aluminium to diffuse to the surface and oxidize. The thickness and composition of the resulting oxide layer was found to be strongly dependent on (a) the oxide layer existing prior to the selective oxidation, (b) the parameters of the treatment li.e. composition and pressure of the furnace gases and time), and (c) the dose of aluminium implanted. Compositional analyses via ion backscattering and Auger electron sputter profiling were performed to study the processes and mechanisms. D W Brown et al, J Vac Sci Technol. A3, 1985, 583-587.

33. M O L E C U L A R BEAM EPITAXY 33 6353. Crystalline film quality in reduced pressure silicon epitaxy at low tempera lure The influence of deposition pressure on epitaxial crystalline film quality has been investigated with respect to vapour-phase silicon epitaxial growth ISiHzC1 z -H 2 system). It is shown that the crystalline film quality has been improved by reducing the deposition pressure. In addition, a prebaking process at reduced pressure has been found to be effective for obtaining single-crystalline silicon films with atmospheric pressure deposition as well as reduced pressure deposition. The deposition temperature can be lowered down to 930~'C with perfect crystalline film by reducing the deposition pressure. The crystalline quality ofepitaxial films grown at a low temperature of 930~C using the reduced pressure technique has been verified to be excellent by fabricating bipolar transistors with an oxide isolation technique. S .N'agao et al, J appl Phys, 57, 1985, 4589~593. 33 6354. An investigation on surface conditions for Si molecular beam epitaxial (MBE) growth Contamination-free Si substrate surfaces are vitally important to the subsequent molecular beam epitaxy (MBE) growth. A number of studies on the major contaminants, i.e. C and O, on Si surfaces have been done, and new cleaning procedures for reducing these contaminants have been proposed. However, to date the detailed behaviour of C and O on Si surfaces and their effects on the subsequent Si MBE growths are not well established. In the present work, the behaviour of the contaminants on heated Si surfaces were investigated using Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS). Also, the chemical bonding of C on Si surfaces was studied by analysing the AES line shapes of carbon and comparing them with those known carbon chemical states. For the chemical cleaning procedures used in this study, a silicon oxide protection layer is grown onto the cleaned Si surface prior to sample loading. The property of this silicon oxide layer is studied using ellipsometry measurements. To verify the effectiveness of the cleaning procedures, MBE films grown subsequently are analysed using Rutherford backscattering (RBS). The resulting channelling yield of 2.5% suggests the nearly perfect crystalline quality of these films. Deep-level transient spectroscopy (DLTS) is used to study the defect in the epilayer, and the defect concentration is determined to be in the 10 ~"~cm - 3 range. Y H Xie et al, J I/ac Sci Technol, A3, 1985. 1035 -1038. 33 6355. Epitaxial growth of lanthanide trifluorides by MBE The first epitaxial growth of a hexagonal structure lanthanide trifluoride on a semiconductor is reported: LaF 3 on Si(lll). LEED, R H E E D and X-ray diffraction studies show that the c-axis of LaF~ is normal to the Si(l 11 ) plane. A similar epitaxial relation is expected for other members of the lanthanide trifluoride family: CeF3, PrF~ and NdF3 which are isomorphous with LaF3 and have a closer (basal plane) lattice parameter match to Sill I1). The hard, water insoluble nature of these materials makes them more practicable than group It fluorides as exploratory films for semiconductor passivation, gate insulator, and epitaxial interlayers. S Sinharoy et al, J Vac Sci Technol, B3, 1985, 722-723. 33 6356. Growth in inP, GaAs and In~..~Gao..~As by chemical beam epitaxy A new epitaxial growth technique, chemical beam epitaxy (CBE), was demonstrated and investigated with the growth o f l n P and Ino.s~Ga0..,TAs GaAs. In this technique, all the sources were gaseous group Ill and group V alkyls. The In and Ga were derived by the pyrolysis at the heated 50

substrate surface of either trimethylindium ITMIn) or triethylindium ITEIn), and trimethylgallium (TMGa) or triethylgallium (TEGa), respectively. The As 2 and P2 were obtained by thermal decomposition of triethylphosphine (TEP) and trimethylarsine (TMAs) in contact with heated Ta or Mo at 950-1200°C, respectively. Unlike conventional vapour phase epitaxy, in which the chemicals reached the substrate surface by diffusing through a stagnant carrier gas boundary layer above the substrate, the chemicals in CBE were admitted into a high vacuum growth chamber and impinged directly light of sight onto the heated substrate surface in the form of molecular beams. The beam nature of CBE resulted in very efficient use of the impinging chemicals and allowed the utilization of mechanical shutters. A similar gas handling system to that employed in conventional metallorganic chemical vapour deposition ( M O C V D ) with precision electronic mass flow controllers was used for controlling the flow rates of the various gases admitted into the growth chamber. Growth rates as high as 3-5 ,um/h have been achieved for both lnP and GaAs. The InP and GaAs epilayers grown have smooth surfaces and comparable optical quality to bulk substrates. Since T M I , and TEG,~ emerged as a single mixed beam, spatial composition uniformity was automatically achieved without the need of substrate rotation in the In0.~3Ga0.,tvAs epilayers grown. Lattice mismatch Aa/a ~<4 x 10- ~"was obtained. W T Tsang, J I/ac Sci Technol, B3, 1985, 666-670. 33 6357. Investigation of MBE-grown (001) GaAs surfaces using low-dose SIMS A combined S I M S - M B E uhv system has been used for growth and subsequent analysis of differently reconstructed (1301)GaAs surfaces. Some small, but significant, differences are found in SIMS spectra from the different surfaces, indicating that the (2 × 4)As stabilized surface commonly used for MBE growth may be more 'bulklike' than other reconstructions. Spectra obtained after oxygen exposure indicate involvement of both Ga and As at the initial stages of oxidation, and the different surface reconstructions showed very similar response to oxygen exposure. These SIMS analyses do not indicate large differences in either the surface composition or chemistry of differently reconstructed surfaces. W F Croydon et al, J Vac Sci Technol, B3, 1985, 604-607. 33 6358. Molecular beam epitaxy of GaAs using a mass-separated, low-energy As ~ ion beam A new film growth technique of III-V compound semiconductors is under development where the sticking coefficient of group-V element can be increased to unity. In this technique, a group-Ill element is supplied to the substrate as a molecular beam, while a group-V element is supplied as a mass-separated, high-purity ion beam and implanted at low energy of about 100 cV. With this growth technique, epitaxial growth of GaAs on GaAs(100) is studied. Nondoped GaAs films are grown at the As + ion energy of 100 and 200 eV. Single-crystal films with flat and smooth surface and free from oval defects are obtained at 220°C or higher with the flux intensities o f a Ga molecular beam and As + ion beam at 2.0 × 10t ~/cm z s and 2.0-4.4 × 1013/cm ~ s, respectively. However, under Ga-rich conditions Ga droplets are observed on the grown films. The R H E E D pattern shows c(2 × 8) structure in the former case. Photoluminescence spectra at 4 K of the films grown at 450°C or higher show well-defined features due to bound exciton and donor-acceptor pairs at the As + ion energy of 100 eV. S Shimizu et al, J Vac Sci Technol, B3, 1985, 554--559. 33 6359. Ultrauniform In,Gat_,As layers on lnP grown by molecular beam epitaxy In the molecular beam epitaxial (MBE) growth of ln.~Ga~_~,As, quite uniform and lattice-matched In0. ~3Ga0.,,vAs epilayers have been obtained over large-size InP wafers. Composition variation of the epitaxial layer over an entire 2 in. ~ wafer is less than + 0 . 7 % ; that is, the difference of lattice mismatch between the centre and the edge of the wafer is less than 1 x 10-3. Around the centre, composition variation is less than + 0 . 2 5 % over lateral dimension of 2.5 cm. In this 2 in. ~bepitaxial wafer, the relation between electron mobility and lattice mismatch is also studied. Y Matsui et al, J Vac Sci Technol, B3, 1985, 528-530. 34. ION BEAM MIXING, I N T E R F A C E S A N D S O L I D PHASE REACTIONS 34 6360. Magnetization of very thin Ni films in epitaxial metal film sandwiches of Cu Single-crystal nickel films varying in thickness from 2 to 40 A. were