Shallow ion implantation in gallium arsenide

World Abstracts on Microelectronics and Reliability as well as in ion beam lithography and materials treatment. In this review the different ion optical components that can be used in such equipment are described and some indication of how the design of such components can be optimized is given. Various configurations of lenses and of beam transport devices are discussed, and different types of ion source and energy selecting devices are briefly mentioned. Particular attention is given to the ion optics employed in surface analytical instrumentation. Production of a dense low energy positive hydrogen ion beam. P. J. M. VAN BOMMEL,P. MASSMANN,E. H. A. GRANNEMAN, H. J. HOPMANand J. Los. Vacuum 34 (I-2), 25 (1984), We present measurements and computer calculations concerning the generation of a dense, quasi dc (I0 s) positive hydro= gen ion beam of energies between i and 5 keV. Maximum beam current densities ranging from 200 to 230 mA cm-2 have been transported through a three-electrode extractiondeceleration system with divergencies between 9.5 and 3.5°. The measurements are compared to trajectory calculations, carried out with a modified version of the SLAC code. The highest transmission for a low energy beam with a small divergence is obtained when the calcuated beam trajectories exhibit a cross-over in the region between the extraction and the decel electrode. This cross-over can be achieved when the extraction slit has a shaping angle (45°) smaller than the Fierce angle (67.5°). The effects of plasma and ion beam processing on the propertires of n-GaAs Schottky diodes. P. J. SMXTHand D. A. ALLAN. Vaccum 34 1-2, 209 (1984). Plasma and ion beam processing are being used increasingly in the fabrication of GaAs Logic circuits, for which the basic components are MESFETS and Shottky diodes. In this work GaAs surfaces have been subjected to typical dry processes and Schottky diodes subsequently fabricated to assess the extent of damage introduced. Measurements of the current-voltage and capacitance voltage characteristics, together with deep level transient spectroscopy (DLTS), indicate that ion milling and plasma etching both cause substantial damage within 10 nm of the metal-semiconductor interface in addition to less severe damage extending further into the semiconductor. The damage can be reduced by annealing at moderate temperatures. Ion beam sputter and plasma enhanced deposition produce less damage since particles with lower incident energies are involved and the surface becomes protected by the growing film. Beam-induced broadening effects in sputter depth profiling. KLAUS WITTMAACK. Vacuum 34 (1-2), 119 (1984). The broadening effects encountered in sputter depth profiling are reviewed in some detail. Discussion is restricted to cases where beam-induced microtopographical changes are of negligible importance. Qualitatively, the broadening effects are due to the fact that most of the energy of the incident beam is consumed for damage production in the bulk of the sample rather than for sputter ejection of surface atoms. Available models of collisional mixing are shown to describe some experimental results surprisingly well. However, experiment and theory are often not directly comparable. Analytical models predict only the smearing of a tracer atom distribution in the bulk of the sample. The sputter profile, on the other hand, constitutes a plot of an intensity, as seen by some surface analytical technique, vs the bombardment fluence. Accordingly, the sputter ejection characteristics of the sample constituents play a dominant role (selective sputtering). This feature appears to have been neglected in most of the previous studies. Rather detailed information about atomic mixing and selective sputtering can be derived from experiments involving very thin interracial layers. The element-specific character of the broadening effects is demonstrated.

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Microwave ion source for high current metal beams. NORIYUKI SAKUNDO, KATSUMITOKIGUCHIand HIDEMI KOIKE" Vacuum 34 (1-2), 245 (1984). A high current, metal ion source has been developed for application to materials modification in metals and insulators. In a microwave discharge type ion source, even highly reactive materials such as metal halides, as well as oxygen, can be used for source feed materials. The microwave ion source originally developed for conventional semiconductor fabrication has been modified to provide several mA of mass-separated metal ions. So far, ions of AI +, Ga ÷, Ti +, Hf + and Sc + have been obtained. Nanometre structures in semiconductors formed by low energy ion implantation. J. M. SHANNONand J. B. CLEGG. Vacuum 34 (1 2), 193 (1984). The formation of nanometre structures is discussed in the context of device structures which require precise doping control and layer thicknesses comparable with the carrier mean free path. It is shown that sohd phase epitaxy of amorphous structures in silicon implanted with impurities at low energies can form nanometre structures with undetectable redistribution of the impurities during regrowth based on SIMS measurements. An alternative approach suitable for forming multilayer structures is to implant impurities during epitaxial growth. Published measurements on MBE layers doped using low energy ions indicate that this is a promising technique but basic mechanisms which occur when implanting at low energies into hot single crystal substrates need to be explored further before one can conclude that the precise thickness control offered by MBE can be fully utilized. Shallow ion implantation in gallium arsenide. J. D. GRANGE, D. C. BARTLE,B. R. BROWN,C. DINEEN,K. S. KNIGHT,J. D. MEDLAND, D. K. WICKENDENand M. G. DOWSETT. Vacuum 34 (1-2), 199 (1984). An examination has been made of the electrical and structural properties of shallow (projected range ~ 0.05 rtm) silicon, selenium and sulphur implants into GaAs prior to, and following, post implantation annealing. For doses of 3-4 x 1012 cm-2 activations of 20-30 % with Hall mobilities of 2500-4500cm 2 V - 1s - 1 are measured following both encapsulated and capless annealing. A comparison between the free carrier distribution, the SIMS derived implant impurity profile and the predicted LSS implant distribution show fair agreement for these shallow implants. X-ray diffraction techniques indicate an increase in structural disorder following implantation which reduces to the level of the original substrate on annealing. Plasma enhanced deposition of "silicon nitride" for use as an encapsulant for silicon ion-implanted gallium arsenide. D. C. BARTLE, D. C. ANDREWS,J. D. GRANGE,P. G. HARRIS,A. D. TRIGG and D. K. WICKENDEN. Vacuum 34 (1-2), 315 (1984). Silicon nitride films have been produced by plasma enhanced chemical vapour deposition using silane and ammonia as the reactant gases in a Plasma-Therm PK1250PD machine. The compositions of the films have been investigated as a function of the silane to ammonia flow rate ratio used for deposition, using infra-red transmission and Auger electron spectroscopies. These techniques indicated that the plasma deposited films were silicon-rich and contained hydrogen. The oxygen content of the films was below the detection limit of Auger electron spectroscopy implying that it was less than 1%. Silicon ion-implanted semi-insulating gallium arsenide has been annealed using an approximately 1000A thick film of plasma deposited silicon nitride as an encapsulant. This capped annealing technique has achieved 70 % activations of 4x 1012cm -2, 200keV silicon implants with sheet Hall mobilities of 4000 cm 2 V- 1 s- 1 at room temperature. Free carrier concentration and Hall mobility profiles are presented. Unimplanted semi-insulating gallium arsenide samples have also been capped annealed in the same manner and maintained a sheet resistivity of greater than 107~/ square after annealing.