The application of supersonic nozzle beams to the study of the dynamics of gas-surface scattering is discussed. Examples are chosen to illustrate the use of such beam sources in synthesizing surface compounds otherwise unaccessible under normal ambient conditions in ultrahigh vacuum and the role of trapping and direct collisional activation in adsorption on surfaces.

This paper discusses the use of supersonic jets of gaseous source molecules in thin film growth. Molecular jets in free form with no skimmers or collimators in the nozzle-substrate path were used in the investigation of basic film growth processes and in practical film growth applications. The Ge growth rates were found to depend linearly on the digermane jet intensity. Furthermore, the film thickness distributions showed excellent agreement with the distribution of digermane molecules in the jet. High epitaxial Ge growth rates were achieved on GaAs (100) substrates by utilizing high-intensity pulsed jets. The practical advantages and limitations of this film growth technique are evaluated, based on the results of microstructural and electrical measurements of heteroepitaxial Ge films on GaAs (100) substrates.

Depending on the glow discharge conditions, silicon can be either deposited or etched in the SiH4/H2/Si(s)-system. At floating potential and close to the Partial Chemical Equilibrium (PCE), the etching<--> deposition process is controlled by the temperature of the sample which, in turn, determines the local departure of the system from the PCE. At a constant temperature and under PCE-conditions, low energy ion and electron bombardment of the surface promotes the deposition and etching, respectively. At ion energies above the threshold for displacement damage, decrease of the deposition and etch yield is observed. A possible mechanistic explanation is suggested.

The composition of SiOx films deposited by electron-beam evaporation of silicon in an oxygen atmosphere was measured as a function of silicon deposition rate and oxygen pressure. The compositions varied between X = 0.03 and 2.1 depending on the ratio of O2 molecules to Si atoms arriving at the substrate. Bombardment with 500 eV argon ions caused X to decrease at low arrival ratio and to increase at higher arrival ratio. The results are analyzed using an adsorption model in which chemisorption of O2 occurs after physisorption into one of two states: one on silicon and one on SiO2. A fit to the data for the unbombarded samples is achieved if physisorption occurs only on silicon. From this fit a sticking coefficient of 0.05 is obtained for O2 chemisorption on silicon. The effects of ion bombardment are consistent with the model if bombardment allows O2 to also physisorb on SiO2 and migrate to silicon where it chemisorbs.

Anisotropic etching of n+ poly-Si is achieved using a hot Cl2 molecular beam and a sidewall protection technique. A hot molecular beam is produced by a free jet expansion of a gas heated in a furnace. A nitrogen radical beam is used to prevent the sidewall etching. The etch rate of n+ poly-Si is 4.3 nm/min at the anisotropic etching condition.

There are two basic gas chemistries used for dry etching of III-V semiconductors. The most common discharges contain chlorine, but these generally give rise to somewhat rough surface morphologies for In-containing compounds. More recently methane/hydrogen mixtures have been demonstrated to give low rate, smooth etching of In-based materials. In this work we describe the use of gas mixtures containing both CH and CI species. The hydrochlorofluorocarbons CHCl2F and CHCIF2 with O2 or H2 addition were used to reactively ion etch GaAs, InP, AlGaAs, GaSb, InGaAs and AlInAs as a function of etch time, plasma power density, pressure and gas composition. At moderate power densities (0.56 W · cm−2) the etch rates are in the range 125 Å · min−1 (AlInAs) to 1000 A · min−1 (GaAs). All of the materials exhibit smooth surface morphologies over a wide range of RIE parameters and there is no significant lattice disorder introduced for low power RIE as evidenced by PL and diode I-V measurements. Thin (≤40 Å) surface residue layers of CI (3–9 at. %) and F(≤3 at. %) for all materials except AlInAs are present after dry etching, but these can be removed by simple solvent cleaning.

Recent work on low-energy ion-assisted deposition of epitaxial films is reviewed. Much of the interest in this area has centered on the use of very low ion energies (∼ 25 eV) and high fluxes (> 1 ion per deposited atom) obtained using novel ion-assisted deposition techniques. These methods have been applied in ultra-high vacuum, allowing the preparation of high-purity semiconductor materials. The following ion-surface interaction effects during epitaxy are discussed: improvements in crystalline perfection during low temperature epitaxy, ion damage effects, improved homogeneity and properties in III-V alloys grown within miscibility gaps, and changes in nucleation mechanism from Stranski-Krastanov to layer-by-layer.

Significant changes in strain are produced in SixGe1−x epitaxial films grown on Si and Ge (001) substrates as a result of low energy ion beam assisted molecular beam epitaxy (IAMBE). Films grown with concurrent Ar+ or Xe+ ion bombardment are coherent and uniformly strained in the growth direction by up to 1.5% in Ge films and 0.5% in Si films and contain no dislocations. The dependence of the films strain perpendicular to the growth surface on ion-atom flux ratio, and ion energy can be explained by the injection of uniformly distributed point defects. Post-growth isochronal annealing of SixGe1−x films suggests that the existing defects in the IAMBE films are defect complexes and that the strain relaxation path is determined by the overall thermodynamic driving force toward the strain-relieved state.

Metastable Cd(x)Pb(1–x)Te films with x values from 0 to 0.47, well past the range of bulk thermodynamic solubility, have been grown on single crystal (lll) BaF2 by co-deposition from CdTe and PbTe r.f. magnetron sputter targets. Cross-sectional transmission electron microscopy and transmission electron diffraction revealed epitaxial growth across the interface. However, the lattice of the deposited epilayers was observed to be typically rotated 180°C about the surface normal <111> axis of the substrate. Raman spectra of the alloys showed no evidence of segregation. Langmuir probe diagnostics were employed to estimate the energy of the ions incident on the substrate during growth which promote extended miscibility in the alloy epilayers.

Ag films deposited on Si(111) substrates by partially ionized beam (PIB) under conventional vacuum conditions were studied by MeV ion channeling techniques. In spite of their large lattice mismatch (24.8%), Ag films were still found to be epitaxial. With a deposition temperature of 350°C and without post-annealing, the Xmin value at the surface of a 2550 A° thick Ag film was found to be 10%. The azimuthal angular scan and the measured axial channeling dip showed that the Ag film was (111) oriented. The lattice quality of the films was comaparable to that deposited by MBE techniques. Dislocations were found in the PIB deposited Ag films. Lattice damage due to the bombardment of energetic ions was also observed. The thickness of the Ag film was found to have a pronounced effect on the crystalline quality at the surface. With the thickness increasing from 1240 A° to 2550 A°, the lattice quality at the Ag surface improved significantly, but not much change in the defect density in the Ag films was obseved.

High energy ion mixing occurs when an ion beam of a few hundred keV bombards an interface under the surface. Low energy ion mixing arises when an ion beam of a few keV bombards an interface near the surface during, for example, sputter depth profiling and low energy ion assisted deposition. At low temperatures, the rate of both high and low energy ion mixing can be influenced by thermodynamic parameters, such as the heat of mixing and the cohesive energy of solids. These effects are demonstrated by ion mixing experiments using metallic bilayers consisting of high atomic number elements. A model of diffusion in thermal spikes is used to explain this similarity. Low energy ion mixing can also be strongly affected by surface diffusion and the morphological stability of thin films. These effects are illustrated using results obtained from sputter depth profiling of Ag/Ni bilayers at elevated temperatures. High energy ion mixing at low temperatures can be influenced by the anisotropic momentum distribution in a collision cascade as seen from a set of marker experiments to determine the dominant moving species in high energy ion mixing. These similarities and differences between high and low energy ion mixing illustrate the diversity of ion-solid interactions.

Multiphoton resonance ionization spectroscopy has been used to determine the polar-angle and the kinetic-energy distributions of rhodium atoms desorbed from ion-bombarded Rh{100} surface in the fine-structure components of the a 4Fj (J=9/2 and 7/2) ground-state multiplet. The peak in the energy distribution of the metastable level (4F7/2 with excitation energy of 0.2 eV) is found to occur roughly at the same value as the ground-state (4F9/2) distribution but decays more gradually at higher energies. The measured spectra have been used to investigate the dependence of the excitation probability on the takeoff angle (θ) as well as the emission velocity (v). It is shown that the excitation probability depends strongly on these parameters, approaching an exponential dependence on l/[v cos(θ)] at higher velocities (> 5×l05cm/sec).

It has been the general consensus in the sputtering community that molecules are sputtered from a clean metal surface in much smaller quantities than atoms. Some of the existing models further suggest that the sputter yield of molecules should be even lower from a compound than from a pure metal when the constituents of the molecule do not reside on neighboring sites in the solid.

In our experiments, neutral species sputtered from single crystals of ZnS, CdS, and FeS2 by a 3 keV Ar+ beam have been observed by laser photo-ionization followed by time-of-flight mass spectrometry. While the atomic metal (Fe, Zn, Cd) and S2 were the predominant species observed, substantial amounts of S, FeS, Zn2, ZnS, Cd2, and CdS were also detected. The experimental results demonstrate that molecules represent a larger fraction of the sputtered yield than was previously believed from secondary ion mass spectrometry experiments. In addition, our data suggest that the sputtered molecules are not necessarily formed from adjacent atoms in the solid. The applicability of various sputtering models will be discussed in the light of these results.

A low energy ion beam assisted deposition (IBAD) technique has been developed to fabricate refractory W-Si-N films for the application to gate electrode of GaAs metal-semiconductor field effect transistors( MESFETs ). Thermal stability of the IBAD refractory metal/n-GaAs interface was investigated by examining the microstructure and Schottky diode characteristics. The Schottky barrier heights of 0.71, 0.84, and 0.76 eV were obtained after thermal annealing at 850°C for the W/, WN0.27/, and WSi0.3N0.4/GaAs diodes, respectively, and these values are comparable to those of the best results published with conventional reactive sputtering. While some crystalization of the deposit and reaction between film and substrate at the interface were observed with TEM for the W/ and WN/GaAs contacts annealed at 800°, the WSiN film remained amorphous and showed clear interface with the GaAs substrate without significant morphological change. The WS0.3N0.4/GaAs diode showed good thermal stability of Schottky barrier heights with only 20 meV variation in the temperature range between 700 and 850°C, and that is proposed to be due to the stable microstructure.

A spatially confined disk shaped hydrogen plasma is used for plasma assisted organometallic vapor phase epitaxy (PAOMVPE) of GaAs at substrate temperatures from 245–430°C. Feedstock gases, trimethylgallium (TMGa) and trimethylarsenic (TMAs), are introduced downstream from the disk shaped plasma in the near afterglow. Dissociation of the organometallics is dominated by VUV photons and metastable species energy transfer reactions rather than non-selective electron impact. At the temperatures employed no thermal CVD occurs. An Arrhenius plot of the growth rate shows a low activation of 3 Kcal/mole for surface mobility. The transitional temperature from amorphous to homoepitaxial growth (300°C) is determined via electron diffraction patterns from deposited films versus substrate temperature. Increases in the feedstock gas V-III ratio resulted in decreases in absolute carbon concentration in the deposited films.

Silicon nitride films (Si1−x,.Nx) have been deposited on silicon by simultaneous evaporation of silicon and bombardment of nitrogen ions. Films approximately 1 μm thick were deposited in an ambient nitrogen pressure of 50 μTorr. The substrate temperature (TSUB) ranged from nominally room temperature to 950° C for films with X between 0 and 0.6. Nitrogen atom fraction, X, was measured with Rutherford backscattering spectrometry (RBS). Refractive index was measured with near-IR reflection spectroscopy. Differences in film structure were measured by FT1R on the Si-N bond bending absorption mode, and by x-ray diffraction (XRD). X was found to depend upon the incident flux ratio of energetic nitrogen atoms to vapor silicon, and upon TSUB. Refractive index depends upon X and TSUB. XRD found evidence of the presence of amorphous structure, poly-crystalline silicon and (101) oriented β-Si3N4 depending on X and TSUB. The Si-N absorption signal increases with X and shows some structure at high TSUB.

Films of MoS2 have been successfully deposited on 440C stainless steel using an excimer laser. A comparison was made of films ablated with the laser operating at 193 nm and at 248 nm. The effects of substrate temperature were also studied. X-ray Photoelectron Spectroscopy (XPS) measurements indicated that the films were sulphur rich as compared to single crystal MoS2. Laser Raman measurements indicated that annealing was necessary to obtain crystalline films. All films exhibited coefficients of friction in the neighborhood of 0.03 in a dry nitrogen environment. Coefficients of friction in laboratory air were significantly higher.

Maskless dry etching of Mn-Zn ferrite in dich1orodif1uoromethane (CC12F2) by Ar+-ion laser (514.5 nm-line) irradiation has been investigated to obtain high etching rates and aspect-ratios of etched grooves. The etching reaction was found to be thermochemical and caused by Cl radicals thermally decomposed from CCl2F2 gas. High etching rates of up to 360 μm/s, which is about one order of magnitude higher than that in a CCl4 gas and even higher than that in a H3PO4 solution, have been achieved. A high aspect-ratio of up to 12 was obtained. Definite gas pressure and dwell time are necessary to fabricate a smooth groove.

Copper may become an alternative to aluminum as an interconnect material in future multilevel metallization schemes if it is possible to pattern Cu by dry etching in a manufacturable process. Here we report results on the reactive ion etching of Cu in SiCl4 /Ar, SiCl4/N2, and CCl2F2/Ar plasmas. Etch rates have been investigated as a function of various plasma parameters, such as gas composition, pressure, etc., and substrate temperature. We have obtained etch rates as high as 850 Å /min with SiCl4/N2 and a substrate temperature of ∼ 200 ° C. Also, it appears feasible to pattern Cu anisotropically using either polyimide or amorphous carbon as a high-temperature etch mask.

This study evaluates variations in SiCl4 reactive ion etching (RIE) process parameters in order to optimize the fabrication of lateral quantum well arrays (QWA) used in III–V semiconductor laser and detector designs. Since fabrication involves MBE regrowth on SiCl4 etched surfaces, material quality of both the etched surface and GaAs regrowth are evaluated. The variation of RIE parameters involved power levels, DC bias and etch times (10 Watts, -30V, 8 min.; 25 Watts, -100V, 5 min.; 95 Watts,-340V, 2 min.) while material removal was held constant (400nm). Evaluation of the etched surfaces revealed that the lattice damage depth exceeded lOOnm for all power levels. The extent of disorder beneath the etched surface was less for the low power long etch time. Etching at higher power levels for shorter time periods resulted in smoother surfaces and enhanced electrical characteristics, which in turn yielded a higher quality GaAs regrowth region. For the RIE parameters examined in this study, the variation in defect densities seemed to have a lesser effect on device performance as compared to the extreme differences in surface morphologies. Thus, for the parameters evaluated in this work, we suggest that QWA fabrication is optimized via SiClif RIE at the high power level for a short time period.