23. Ion and plasma assisted film growth

Classifidd abstracts 6307-6314 respectively. However, at T,>~60fYC, stoichiometric films could be obtained at any P,,~,, including pure N~, greater than a critical N~ partial pressure that varied from 0.2 to 0.4 mtorr (27 to 53 mPa) as T, was increased from 600 to 800'C. The Vickers hardness H, the room temperature resistivity p, and the temperature coefficient of resistivity TCR of stoiometric TiN single crystals were found to be essentially independent of/~, and p,~:. H was determined to be 2300 ___200 kg m m - z, about 15% higher than for bulk sintered TiN, p was 18 #f~ cm, and the TCR measured at temperatures between 100 and 400 K was 6200 K - ~. The latter two results represent the lowest and highest values, respectively, yet reported for TiN films. The room temperature electron carrier concentration and mobility were determined from Hall mesurements to be 5 x 10~-" cm -~ and 6.7 cm ~ V-~ s ~. B O Johansson et al, J Vac Sci Technol, A3, 1985, 303-..307.

23

6309. 'Diamondlike' carbon films: optical absorption, dielectric properties and hardness dependence on deposition parameters An rf plasma deposition system was used to prepare amorphous 'diamondlike" carbon films. The source gases for the rf system include methane, ethylene, propane and propylene and the parameters varied were power, de substrate bias and postdeposition anneal temperature. Films were deposited on various substrates. The main diagnostics were optical absorption in the visible and in the infrared, admittance as a function of frequency, hardness and Auger and ESCA spectroscopy. Band gap is found to depend strongly on rf power level and band gaps up to 2.7 eV and hardness up to 7 Mobs were found. There appears to be an inverse relationship between hardness and optical band gap. V Natarajan et al, J I/ac Sci Technol, A3, 1985. 681-685. 23

6310. Ionized-claret-beam deposition of optical interference coatings 23. ION A N D PLASMA ASSISTED FILM G R O W T H 23 6307. Silicon epitaxy at 650-800~C using low-pressure chemical vapor

deposition both with and without plasma enhancement A system and a procedure using chemical vapour deposition of silane at very low pressures ( < 10 - : torr) have been developed for depositing uniform, specular silicon epitaxial films both with and without plasma enhancement at temperatures as low as 6 5 0 C . In situ cleaning of the substrate surface that overlaps into the deposition is the most critical aspect of the procedure. Undoped films deposited on substrates heavily doped with antimony or boron have abrupt doping profiles. Preliminary measurements indicate that the hole mobility of epitaxial films obtained with this process is 90% of that in bulk silicon. Films oxidized and decorated with a Secco etch show twice as many defects as a similarly treated substrate. N o n p l a s m a growth kinetics are sensitive to surface conditions such as crystallographic orientation, and surface diffusion of adsorbed species appears to be the rate-limiting step for depositing epitaxial films above 700~C. Around 650~C, the growth mechanism appears to change, possibly due to the increased presence of hydrogen on the surface. Finally, plasma enhances the growth rate, and plasma kinetics do not seem to be sensitive to surface conditions. T J Donahue and R Reif, J appl Phys, 57, 1985, 2757-2765. 23

6308. Studies on the mechanism of chemical sputtering of silicon by simultaneous exposure to CI2 and low-energy Ar" ions The sputtering yield of Si when bombarded with a flux ~ , , . of low-energy A r ' ions may be enhanced a few times when the Si surface is exposed simultaneously to CI~ fluxes 4)c~,about one order of magnitude larger than OA,'" The mechanism of this synergistic etching has been studied, using mass spectroscopy and time-of-flight techniques, for a q~,~,, of about 5 x 10 ~'* Ar" cm -~ s - ~ at Ar* ion energies (Et,) from 0.25 to 5 keV. CI 2 fluxes between 10 ~ and 5 x l 0 ~ 6 C l . , c m - ~ s - ~ and T in the range 300. 625 K. As has been shown previously [J Vac Sci Technol, A2, 487 11984)] the main products of the synergistic reaction are atomic Si and CI and molecular SiCI and SiCI.,; the kinetic energy distributions of the molecular products consist of two parts, a Maxwell-Boltzmann and a collision cascade-like distribution. The Maxwell-Boltzmann part decreases relative to the collision cascade-like part when 7 and/or E~, are increased and/or ~bc~, is decreased. At the same time the collision ca:,cade-like part shifts to higher kinetic energies. These observations and the dependence of the relative contributions of the various products on qbc~~, T, and E~, can be understood from the Ar ~ ion-induced mixing of adsorbed CI into the top atomic layers of the Si, in which the molecular products SiCI and SiCIz are formed and also trapped, without further chemical binding to the surrounding bulk network; and for higher Talso by the competition between the thermal reaction, yielding SiCI.~ (and SiCI z ), and synergistic etching. The yields of the molecular products SiCI and SiCI., show an increase relative to atomic Si and their binding energies arc reduced when ~bc~:is enhanced and/or E~, and/or Tare decreased. It is suggested that this is due to an increasing concentration of CI ion mixed into the top atomic la)ers of the Si. The experiments also suggest that the binding energy of atomic Si decreases systematically with increasing CI concentration in the Si. The results show that the etching of Si with CI_, under simultaneous Ar* ion bombardment is not due to stimulation of the thermal reaction but to chemically enhanced physical sputtering. J Dieleman et al, J Vac Sci Technol, B3, 1985, 1384--1392.

Ionized-cluster-beam (ICB) deposition has been used to form metal. dielectric and c o m p o u n d films for optical coa.tings. In ICB deposition, it is possible to control the mechanical, crystallographic and optical properties of films by varying the acceleration voltage and the ion content in the total flux. Experimental results of film deposition by ICB show that optical properties can be improved through proper selection of acceleration voltage and ionization ratio. Applications such as high-reflectance mirrors, AR coatings and other optical devices have been demonstrated. T Takagi and i Yamada, .4ppl Optics, 24, 1985, 879-882. 23 6311. Properties of TiO~ and SiO~ thin films deposited using ion assisted

deposition TiO z and SiO 2 films deposited using ion assisted depositions are investigated as a function of ion energy and current density. Optical constants, possible ion source contaminants and optical scatter are examined for samples deposited at ambient (~75~C) and elevated ( ~ 250~C) substrate temperatures. J R McNeil et al, Appl Optics, 24, 1985, 486-489. 23 6312. Effect of ion assisted deposition on optical scatter and surface

microstructure of thin films Ion b o m b a r d m e n t of a film during deposition has pronounced effects on the electrical, mechanical and optical properties of the film. One important optical property is the optical scatter characteristic of the film. This is determined by the film surface and volume microstructure and thus can be used as a convenient diagnostic technique to examine film morphology. We have examined these effects for metal (Cu and Mo) and dielectric (SiO 2 and TiOz) films. We observe, for example, a significant reduction in optical scatter due to surface structure ofperiod < 3 pm in the case of films deposited with simultaneous ion bombardment. Other experimental data and a simple model to explain this possible smoothing effect are presented. G A AI-Jumaily et al, J Vac Sci Technol, A3, 1985, 651 -655. 23

6313. Synthesis of compound thin films by dual ion beam deposition. !. Experimental approach The synthesis of compound thin films by dual ion beam deposition is described. In Part I of this two-part paper, the experimental approach is presented, together with an analysis of composition for the aluminiumnitrogen system. In the accompanying paper fPart ll), the properties of AI. N films are described. The dual beam technique supplies a deposition flux orAl from Ar" ion beam sputtering of an AI target. Simultaneously, a low-energy (100 500 eV) N~. ion beam bombards the growing film. Using a measured ion beam gradient across the substrate holder, a wide range of arrival rate ratios (0_ 1. We discuss the accuracy of this technique in establishing quantitative deposition parameters for compound and composite thin films. J M E Harper et al, J appl Phys, 58, 1985, 550-555. 23 6314. Synthesis of compound thin films by dual ion beam deposition. I1.

Properties of aluminum-nitrogen films We describe the properties of aluminium-nitrogen films prepared by dual ion beam deposition in which the metal atom flux is supplied by inert ion beam sputtering and the reactive flux is supplied by a low-energy 45

Classified abstracts 631 5-6322 (100-500eV) ion beam directed at the growing film. This deposition technique and the analysis of film compositions are described in Part ! of this two-part paper. The fundamental deposition parameters of arrival rates and ion energy are controlled and directly correlated to the crystallographic structure, microstructure and morphology of the films, over a range of composition from N/AI = 0 to N / A I = 1.0. AI sputter deposited in a mixture of Ar and N z forms an expanded A1 lattice with no indications of A1N formation. When the low-energy N~" beam is turned on, almost all the ionized nitrogen is incorporated in the film forming a mixture of large AI grains and fine grained AIN. In this two-phase cermet region, the resistivity shows a percolation threshold at N/AI=0.45, becoming fully insulating at about N/AI =0.75. Above the arrival rate ratio N/AI = I, excess N is rejected and the films have AIN structure. For stoichiometric AIN films the texture and microstructure depend strongly on the N~ flux and ion energy. For low ion energies (100 eV) and flux, films are formed with the c axis of the hexagonal AIN structure perpendicular to the film surface, whereas for high ion beam energies (500 eV) the c axis is close to the plane o f t h e film. The AIN grain size also increases with nitrogen ion energy. The relative contributions of chemical driving forces and ion b o m b a r d m e n t processes are discussed. H T G Hentzell et al, J appl Phys, 58, 1985, 556-563. 23 6315. Laser-induced plasmas for primary ion deposition of epitaxial Ge and

Si Films Epitaxia] Ge and Si films have been grown by primary ion deposition from laser-induced plasmas. The plasmas were formed by focusing 15 ns, 107--I08 W cm--', pulses of 5 eV photons from a K r F excimer laser onto Ge or Si single crystal wafer targets. Time-of-flight, current-voltage and film-thickness distribution measurements established that neutral atoms and ions were emitted from Ge targets with mean velocities of 1.0-1.6 × 106 cm s - 1 (corresponding to average kinetic energies of 40 to 100 eVI in a distribution that was strongly peaked in the direction normal to the target surface. Macroscopic ( ~ 1 /am dia) particles were also emitted. A shutter, synchronously triggered with the laser pulses through a delay circuit, was used as a velocity filter for removing from the beam particles with velocities up to 1.2 × I0 '~ cm s - 1. Epitaxial Ge films were grown on semi-insulating (100) GaAs substrates at temperatures between 300 and 450~C and epitaxial Si was grown on (100) Si at 700~C. Deposition rates were typically 0.5-1 ,am h - 1. Hall effect measurements carried out on the Ge/GeAs heterostructures showed that the Ge films, ~ 1 ,am thick, were p type with room temperature carrier concentrations of ~ 1 × 1018 cm -3 and hole mobilities of ~ 150 cm2/V s. D Lubben et al, J Vac Sci Technol, B3, 1985, 968.-974. 23

6316. Properties of CeO z thin films prepared by oxygen-ion-assisted deposition Thin films have been prepared by electron-beam evaporation of CeO~, where the growing film has been bombarded with oxygen ions. The packing density of the films has been increased from ~0.55 without ion bombardment to unity with b o m b a r d m e n t as determined by moisture adsorption measurements. The refractive index, extinction coefficient and scattering loss are reported for a range of ion energies from 50 to 1200 eV. The ratio of ion-current density to film growth rate required to produce films that did not adsorb moisture was found to be a m i n i m u m for ion energies in the 3 0 0 ~ 0 0 eV range. Absorption and scatter losses are smallest for the lower ion energies and the crystal structure of CeO2 films is relatively stable under ion b o m b a r d m e n t although ion-assisted films tend to be less crystalline than evaporated layers. R P Netterfield et al, Appl O~fics, 24, 1985, 2267 2272.

III. Particle beam t e c h n o l o g y and processing of materials 30. PARTICLE BEAMS A N D S O U R C E S 6317. Electron beam proximity printing: complementary-mask and levelto-level overlay with high accuracy Electron-beam proximity printing (EBP) is a promising candidate for submicron lithography because it meets the stringent requirements for resolution, throughput, and image fidelity (here defined as registration and overlay). Registration and level-to-level overlay capabilities of EBP are reported in this paper. Two levels of a chip were exposed and processed subsequently, these levels represented by two different patterns in the same 46

mask. Distortions of both patterns relative to each other, amounting up to several hundred nanometers, were detected. These distortions could be automatically compensated for during exposure to yield an average overlay better than 50 nm. Together with the low data scatter of 3or < 170 nm, this indicates high performance of the EBP registration and distortion compensation procedure. P Nehmiz et al0 J Vac Sci Technol, B3, 1985, 136-139. 30 6318. Measurement of neutral beam species ratio by solid-state detector Energy spectra of neutral hydrogen beams produced at the prototype JT60 neutral beam injector unit were measured by the solid-state detector which was developed for a neutral particle analyser for fusion devices. The ion beam species ratio estimated from the energy spectra agreed well with that measured by the Doppler-shift spectrometer. Y Ohara et al, Rev Sci Instrum, 56, 1985, 525-528. 30 6319. Collision frequencies between charged and neutral particles in a

magnetic field It is shown theoretically how much the magnetic field influences the collision frequencies between charged and neutral particles. The magnetic field B for the usual field strength does not affect the collision crosssection. However, the respective charged particles gyrate around the field lines and then the relative velocity between charged and neutral particles with B. Consequently, it is shown that, when the mean free path ,;. is large compared with 2nr L, the velocity component contribution to the collision is the velocity component due to the motion along the field axis and not that due to the gyration. Here, r~. is a Larmor radius. S Imazu et al, J appl Phys, 57, 1985, 1602-1608. 30 6320. Instrument for differential ion flux vector measurements on Spacelab 2 The differential ion flux probe (DIF probe) is a scientific instrument capable of deconvolving a multiplicity of ion streams, differing in flow direction and/or energy and independently determining the flow direction, current density, temperature and energy of each stream. The original instrument concept was developed for laboratory investigations in the area of plasma dynamics and was reported i N H Stone, Rev Sci Instrum, 48, 1458 (1977)]. Since then, the DIF probe has been redesigned and developed into a flight instrument to provide measurements of disturbed plasma flow conditions within the terrestrial ionosphere. It has flown on the STS-3 Space Shuttle mission, on sounding rockets and recently on the Spacelab-2 mission as part of the plasma diagnostics package (PDP) experiment. Herein, we discuss the unique design and operational characteristics required for the flight model of the DIF probe. N H Stone et al, Rec Sci lnstrum, 56, 1985, 1897-1902. 30 6321. Cylinder radioactive source for slow-positron beams The geometrical efficiency is calculated for a radioactive sourcemoderator assembly, which is often used for the production of slowpositron beams and comparisons are made between a cylinder source, touching the circumference of the moderator and a spot source, facing the centre of the moderator. It is shown that higher beam intensity and brightness can be obtained with the cylinder source in most practical situations. R S Brusa et al, Rec Sci Instrurn, 56, 1985, 1531- 1533. 30 6322. Status of the multiply charged heavy-ion source M I N I M A F I O S The principles, construction and performance of the M I N I A M A F I O S electron cyclotron resonance ion source (ECRIS) are reviewed. The source can operate either pulsed, with pulse width of > 50 ms, or cw, with 10 II fully stripped light ions per second and much higher a m o u n t s of lower charge state ions. The source has excellent reliability and reproducibility. It has acceptable emittance and energy dispersion. The manner of operation and adjustment of the source is very simple since it depends only on the two parameters: gas feed and rf power injected. In addition, metallic ions can be produced directly. ECRIS is well suited for injection into heavy ion accelerators and for atomic physics. Its high ion fluxes in a quasicontinuous regime are useful for numerous other applications and open new fields for scientific research with multiply charged ions. Thus, more and better sources are desired. New ideas have been proposed and new sources have been built or are under construction. We present the latest performance data of M I N I M A F I O S for gaseous elements as a reference for evaluating the performance of new ECRIS in various laboratories. For metallic ions we need more experimental results in order to establish basic data references. R Geller et al, Ret~ Sci lnstrum, 56, 1985, 1505 .1510.