Phosphorous doped hydrogenated amorphous silicon films were deposited by microwave electron cyclotron resonance (ECR) plasma CVD at a substrate temperature of 100°C. Electrical, optical and hydrogen-incorporation properties of the films have been investigated. By optimizing the deposition condition, the dark conductivity of 3×10−4S/cm is realized without subsequent annealing. Relations between the film properties and ECR plasma properties have been studied by means of optical emission spectroscopy (OES) and quadrupole mass spectroscopy (QMS).

The plasma deposition of hydrogenated and fluorinated amorphous silicon (a-Si:H,F) and silicon-germanium alloys (a-Si,Ge:H,F) from SiF4-H2 and SiF 4-GeH 4-H2 mixtures, respectively, has been studied in continuous (CW) and modulated wave (MW) r.f. discharges. It has been found that the period and duty cycle of the modulated wave strongly affect the plasma composition, the surface homogeneity and the material properties. The plasma-phase characterization, performed by time resolved optical emission spectroscopy (TR-OES), supplies arguments on the origin of emitting species and on their formation kinetics. It has been found that H* and SiFx are formed by a direct electron impact process involving the same species in the ground state. In addition, the surface homogeneity and some material properties are strongly improved by plasma modulation.

Tcrtiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) were evaluated as n-type dopant precursors for low pressure chemical vapor deposition (LPCVD) of in situ doped amorphous and polycrystalline silicon from silanc. The deposition kinetics, film composition, and electrical properties obtained with TBA and TBP dopant precursors are compared to that obtained when using arsine and phosphine as dopant precursors. Compared to the hydride dopant sources, TBA and TBP provide increased safety due to their sub-atmospheric vapor pressure (≃ 200 Torr at 26°C) and lower toxicity. Using mixtures of TBA and TBP with silane and hydrogen, high quality films of arsenic and phosphorus in situ doped amorphous and polycrystalline silicon were obtained. Dopant incorporation levels ranged from 5×1019 to l.5×1021 cm−3 as measured by SIMS. The deposition rate of polycrystallinc films deposited from TBA and TBP was enhanced by a factor of-≃-3X compared to the hydride dopants for the same mole fraction of dopant precursor. The minimum resistivitics of 5.0 and 1.4 mΩ-cm were obtained, following a 1000°C, 30 second rapid thermal anneal, for ≃500Å thick films on SiO2 deposited with TBA and TBP respectively. A drawback of TBA and TBP is the incorporation of ≃1.0 atomic percent carbon which is > 15X higher than obtained when using the hydride dopant sources. Carbon was observed under all deposition conditions examined.

Diethylsilane (DES), Si(C2H5)2H2, is a promising candidate for the atomic layer epitaxy of silicon. The adsorption and decomposition kinetics of DES on silicon surfaces were studied using laser-induced thermal desorption (LITD), temperature programmed desorption (TPD), and Fourier transform infrared (FTIR) spectroscopy. FTIR studies on porous silicon surfaces indicated that DES dissociatively adsorbs below 600 K and produces Si-H and Si-C2H5 surface species. The desorption products following DES adsorption on Si(111) 7×7 were C2H4 and H2 for all surface coverages using both LITD and TPD techniques. Ethylene and H2 desorption occurred at 700 and 810 K, respectively, during TPD experiments with a heating rate of β = 9 K/s. Ethylene desorption was consistent with a β-hydrogen elimination mechanism from the Si-C2H2 surface species. Isothermal LITD studies monitored the desorption kinetics of C2 H4 from Sl (111) 7×7 as a function of time following DES exposures. The first-order ethylene desorption kinetics were Ed = 36 kcal/mol and vd = 2.7 × 109 s−1. Additional LITD measurements determined that le initial reactive sticking coefficient of DES on Si(111) 7×7 decreased versus surface temperature. The temperature-dependent sticking coefficients suggested a precursormediated adsorption mechanism.

The adsorption and desorption kinetics for SiCl4 and SiCl2H2 on Si(111) 7×7 were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. Both LITD and TPD experiments monitored SiCl2 as the main desorption product at 950 K at all coverages of SiCl4 and SiCl2H2 on Si(111) 7×7.HC1 desorption at 850 K and H2 desorption at 810 K were also observed following SiCl2H2 adsorption. Isothermal LITD measurements of SiCl4 and SiCl2H2) adsorption on Si(111) 7×7 revealed that the initial reactive sticking coefficient decreased with increasing surface temperature for both molecules. The temperature-dependent sticking coefficients were consistent with precursor-mediated adsorption kinetics. Isothermal LITD studies of SiC12 desorption revealed second-order SiCl2 desorption kinetics. The desorption kinetics were characterizedby a desorption activation energy of Ed = 67 kcal/mol and a preexponential of vd = 3.2 cm2/s. TPD studies observed that the HCI desorption yield decreased relative to H2 and SiCl2 desorption as a function of surface coverage following SiCl2H2 exposure. These results indicate that when more hydrogen desorbs as H2 at higher coverages, The remaining chlorine is forced to desorb as SiCl 2.

The desorption kinetics of hydrogen from the β1 H2 -TPD state on Si(111)7×7 and Si(100)2×l were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. Isothermal LITD studies of H2 desorption from Si(111)7×7 revealed second-order kinetics with a desorption activation energy of Ed = 62 ±4 kcal/mol and a preexponential factor of Vd = 92 ±10 cm2 /s. In contrast, H2 desorption from Si(100)2×l revealed first-order kinetics with an activation energy of Ed = 58 ±2 kcal/mol and a preexponential factor of Vd = 5.5 ±0.5 × 1015 s−1. The desorption kinetics yield similar upper limits for the Si-H bond energies but different desorption mechanisms on Si(lll)7×7 and Si(100)2×l.

Using thermal mass desorption and LEED we have studied interactions of H, C12, and F2 with a silicon (100) surface, and exchange reactions of the gases with adsorbates on the silicon (100) surface. Thermal desorption spectra were measured for surfaces dosed with H, C12, and F2 singly and then for surfaces dosed first with a halogen and then atomic hydrogen. Finally, the reverse sequence was studied, with atomic hydrogen dosing and then the halogen exposure. Results indicate that the molecular halogens C12 and F2 are not effective at removing H from a Si (100) surface. However, for the reverse reaction, atomic hydrogen appears quite effective at removing the halogens.

This study details low pressure and low temperature cleaning of Si(100) surfaces. The properties of Si surfaces exposed to variations in plasma generated H are described. The diagnostic techniques used to study the processing conditions are residual gas analysis (RGA) and emission spectroscopy. The surface is characterized by low energy electron diffraction (LEED) and angle resolved uv-photoemission spectroscopy (ARUPS). During the cleaning, Si complexes are formed which indicates the removal of species from the Si(100) surface. Plasma cleaning at 300°C results in a Si(100) surface with 2×1 surface diffraction patterns as detected by LEED. Measurements by ARUPS with He I radiation show the absence of Si surface states on the Hpassivated surface. The ARUPS measurements also indicate that the H begins to desorb from the Si(100) H-passivated surface at ∼500°C.

Fourier transform infrared (FTIR) transmission spectroscopy. was used to monitor the decomposition of H2O (D2O) and NH3(ND3) on silicon surfaces. Experiments were performed in-situ in an ultra-high vacuum (UHV) chamber using high surface area poroussilicon samples. The FTIR spectra revealed that H2O dissociates upon adsorption at 300K to form SiH and SiNH2 surface species. NH3 also issociates upon adsorption at 300 K to form SiH and SiOH2 species. Silicon samples with saturation exposures of H2O and NH3 were progressively annealed from 300 K to 860 K. The FTIR spectra of an H2O-saturated silicon surface revealed that the SiOH species decomposed to form a silicon oxide species and additional surface hydrogen between 460 K and 580 K. Likewise, the SiNH2 species decomposed between 540 K and 660 K to produce silicon nitride and additional surface hydrogen. In both cases, the Sill surface species decreased as H2 desorption from the silicon surface was observed above 700 K.

Solutions of hydrofluoric acid are used extensively in the processing of semiconductors, primarily in etching and in oxide stripping procedures. Such solutions are often buffered with ammonium fluoride to insure constant oxide stripping rates. Infrared spectroscopy of silicon and germanium surfaces treated with such solutions indicates that a thin film of ammonium salts will deposit on the materials unless they are immediately and very thoroughly rinsed following treatment. This thin film, comprised initially of ammonium bifluoride (NH4FHF), reacts with the semiconductor material to form ammonium fluoride (NH4F) as a reactive intermediate, and ammonium hexafluorometallate ((NH4)2 SiF6 or (NH4)2 GeF6). These reactions occur very slowly, over hours or days. They are apparently driven by favorable thermodynamics. This explanation is supported by the absence of comparable reactions using analogous chlorine-based solutions (HCI/NH4 CI). Aspects of the reaction mechanism for hexafluorometallate production is presented.

The kinetics of silicon oxidation by rapid thermal processing in the 1000-1200°C range have been studied with particular attention paid to the homogenization and optimization of the heating and to the initial conditions (i.e. sample preparation, insertion into the furnace and measurements of initial thickness ). Special emphasis has also been placed on the accuracy of thickness measurements using ellipsometry and adequate calculations. Comparison of the experimental and simulated thickhnesses using Han and Helms' model and comparative temperature evaluation, allowed the real temperature to be evaluated within ±5°C. Then, it was concluded that RTO kinetics does not reveal any special peculiarities in the 2-35 nm range.

Electrical measurements of RTO capacitors (C-V, I-V, V-t) have been performed. Typically, a breakdown electrical field strength (Eox) of 15 MV/cm, a Nss max of 3.1011 eV−l.cm−2, a Nss midgap of 4.1010 eV−1.cm−2 and a Qbd (charge injected at breakdown) of 40 C.cm−2 were obtained for oxide thicknesses ranging from 8 to 10 nm. These compare favorably with our better standard oxides grown at 900°C with 2% HCI in O2. We can thus conclude that RTO is a very promising process for submicron technologies.

Thermal passivation of Si1−x Gex using high pressure (10,000 psi) oxidation was studied. Alloys of Si1−xGex (with x=5.4, 11.6, and 17 at. %) approximately 200 nm thick were oxidized using two processes: (i) dry oxygen at 10,000 psi at a temperature of 550°C and (ii) conventional, 1 atm steam at 800°C. The wet oxidation conditions were chosen to produce an oxide thickness comparable (=100 nm for xGe=11.6 at. %) to that obtained during high pressure oxidation at 550°C. Auger sputter depth profiling (AES), X-ray photoelectron spectroscopy (XPS), and cross-sectional transmission electron microscopy (TEM) were used to characterize the as-grown oxides. XPS studies reveal that high pressure oxides formed from all three of the alloys of Si1−xGex have greatly enhanced incorporation of Ge compared to those grown to a similar thickness under wet atmospheric conditions. We report that a significant benefit of this increase in Ge incorporation is the minimization of Ge enrichment near the oxide/Si1−xGex interface. Cross-sectional TEM images reveal a 30 nm thick Ge-rich band at the wet oxide/alloy interface and a dramatically thinner band (<5 nm) present at the oxide/alloy interface produced by high pressure oxidation. For the atmospheric oxidation samples, interfacial misfit dislocations were observed at the alloy/substrate interface indicating that the film relaxed during oxidation. In contrast, the high pressure samples showed no interfacial defects after oxidation.

Although the oxidation of Si(111) 7×7, Ge(111) 2×8 surfaces are relatively well understood very little work has been performed at sub monolayer coverage. We have utillsed a custom-built high resolution Kelvin probe to follow the changes in work function, and changes in band-bending and surface state occupancy via Surface Photovoltage Spectroscopy (SPV). The Kelvin probe Is an Ideal tool for such analysis due to Its extremely high surface sensitivity, equivalent to 4×1010 molecules/cm2, or 0.01% of the available sites.

We observe a very rapid initial adsorption phase, which has not been found by other surface probes, e.g., AES, EELS, etc, corresponding to the formation of an elementary dipole layer. During this phase the Increase In the effective electron affinity with oxygen uptake achieves a maximum of 1V at 0.3 monolayer (ML), on SI(111) at 300 K. We report, for the first time, SPV spectra of SI(111), at 100 K, indicating quenching of a band of surface states centered around the fermi-level, quenching Is completed at the max-Imum of the work function change.

The second adsorption phase, involving oxygen penetration through the surface layer and incorporation Into the lattice, commences at 0.25 ML for Si(111) at 300 K. a much earlier stage than previously reported. Further. we find evidence of a metastable SiO2 precursor at coverages below 1 ML. The dipole layer formation (and breakup) is shown to be very sensitive to both temperature and amount of surface Carbon contamination. The second phase also Involves a substantial reduction In band-bending to nearly flat bands at 2 ML, accounting for 20% of the work function change In the case of SI and almost 90% for Ge.

Chemically assisted ion beam etching (CAIBE) of Si1−Gex films is reported. Ar+ ion sputtering in the presence of Cl2 background gas has been used to etch epitaxial films of Si1−xGex, with x ranging between 0 and 0.5. It is found that Si1−xGex, sputters more rapidly than Si, but less than Ge. The use of C12 gas enhances the sputter rates of SiGe as in the case of Si. Analysis of the etch rates indicates that the etch rate increase is due to an enhancement of the sputtering process, rather than a chemical effect.

The three dimensional equations which govern free molecular or ballistic transport and heterogeneous gas-solid reactions in features on patterned wafers during low pressure processing are reviewed. The governing equations specific to long rectangular trenches are extended to include nonuniform molecular velocity distributions in the source volume above the wafer as well as surface diffusion of adsorbed species or intermediates. Introduction of reaction stoichiometries and kinetic expressions for general deposition and etch reactions completes the specification of the problem. Local generalized sticking factors arise in the process of nondimensionalizing the governing equations.

Trialkylamine alanes are attractive precursors for the metal-organic chemical vapor deposition (MOCVD) of aluminum thin films in microelectronics applications. The weak Al-N interaction and the absence of Al-C bonds (which decompose by highly activated processes) make these compounds excellent alternatives to the most widely studied Al CVD precursor, triisobutyl aluminum (TIBA). Solid trimethylamine alane (TMAA) and liquid triethylamine alane (TEAA) have vapor pressures at room temperature of 1 and 0.5 torr, respectively. In addition, these compounds are stable, non-pyrophoric, and are easily prepared. We report parallel studies of Al CVD in a low pressure, cold wall reactor and in an ultrahigh vacuum chamber to understand both the surface chemistry and the growth morphology. These studies, in turn, are compared with the decomposition chemistry and MOCVD characteristics of TIBA.

In previous work, we found that the decomposition of trimethylgallium (TMGa) on a clean silicon substrate was dominated by interactions with the silicon substrate. In this paper, TPD, XPS, and molecular beam techniques were used to explore how the surface chemistry changes as gallium, trimethylgallium, and hydrocarbon overlayers are deposited onto the substrate. At low coverages, gallium and carbon have little effect on the TPD spectrum. However, at coverages in the order of a monolayer, the chemistry changes substantially. While on clean silicon the metal containing species are all strongly bound, on covered surfaces there are TPD peaks at 580 K and 700 K corresponding to di- and mono- methyl gallium. Dimethylgallium desorption is also observed in the beam system. There is also evidence for desorption of methyl radicals from the covered surfaces, while only methane desorption is seen with clean silicon. These results show that changes in the substrate composition can have a substantial, influence on TMGa decomposition. Hence some care must be taken when extrapolating data from UHV studies to actual growth conditions.

The preparation of aluminum-containing thin film materials by MOCVD and MOMBE for use in III-V semiconductor materials, such as HEMT devices, is currently under active investigation. The preparation of uniform, conformal aluminum and boron containing thin film materials from the chemical vapor deposition (CVD) of aluminum borane cluster precursor compounds has been studied. A variety of substrates, deposition conditions and aluminaborane precursors have been explored and their effect on film composition, growth rate and thin film morphology has been investigated. The thermal depositions of aluminum and boron-containing thin films from aluminum borohydride, AI(BH4)3, on copper, SiO2 and GaAs are reported. Boron incorporation in the films vary depending on substrate temperature, aluminaborane flow and the presence or absence of a H2 carrier. These films have been characterized by SEM, AES and XES.

The adsorption and reaction of dimethylzinc and diethylzinc on Si(100)-2×l surfaces was studied using temperature programmed desorption and high resolution electron energy loss spectroscopy. These zinc alkyls were found to dissociate at temperatures less than 300 K to produce adsorbed alkyl species and deposit zinc on the surface. During temperature programmed desorption zinc metal desorbed at 530 K leaving only alkyl species on the surface at higher temperatures. Surface methyl groups were found to decompose to carbon and hydrogen or desorb as methyl radicals, while surface ethyl groups underwent a series of surface reactions which resulted in three separate ethylene desorption peaks. The results of this study provide new insight into the reactions of group II metal alkyls on silicon surfaces.

The chemical vapor deposition of Au films by thermal decomposition from an organometallic precursor [dimethyl 1,1,1,5,5,5-hexaflouro-2,3-pentanedionato Au (III)] has been investigated for application as a interconnection metallization. The morphology and feature fill properties of deposits obtained using H2 and N2 carrier gases and varying pressure and temperature conditions were observed by cross-section scanning and transmission electron microscopy (SEM and TEM). Line patterns etched in SiO2 with aspect ratios up to 1.5 filled with few or no voids at a growth temperature of 250°C. For films deposited in H2 the Au grain size is large (on the order of the feature size). In unetched areas, however, large (600 nm) triangular-shaped structures protrude from the deposit. TEM observation shows that these structures are single-crystal Au dendrites which contain a central twinned region. Au films grown at 275°C had poor hole fills with large, irregular voids. These films exhibited large protrusions which occluded the lines and halted growth in these areas. The deposit morphology suggests a low reaction probability except at preferred crystal sites.