Fourier transform infrared (FTIR) transmission spectroscopy was used to compare the decomposition of trichlorosilane (SiHCl3) and trichlorogermane (GeHCl3) on silicon surfaces. Chlorosilanes, such as SiHCl3 are employed in silicon chemical vapor deposition (CVD). Chlorosilanes and chlorogermanes are also possible molecular precursors for the controlled atomic layer growth of silicon and germanium. GeHCl3 may be useful for the deposition of germanium on silicon surfaces and the growth of Si1−xGex heterostructures. The FTIR studies were performed in-situ in an ultra-high vacuum chamber on high surface area, porous silicon samples. The FTIR spectra revealed that SiHCl3 dissociatively adsorbs at 200 K to form SiH, SiClx, ClSiH and Cl2SiH surface species. The presence of ClxSiH species is revealed by ClxSiH stretching (2196 cm−1) and bending (775, 744 cm−1) vibrations. The presence of these modes indicates that there is incomplete decomposition of SiHCl3 upon adsorption at 200 K. GeHCl3 also dissociatively adsorbs at 200 K to form SiH and SiClx species. An infrared absorption feature in the Ge-H stretching region (1970–1995 cm−1) was not detected in the FTIR spectrum. The absence of a Ge-H absorption feature argues that there is a complete transfer of hydrogen from germanium to surface silicon atoms at 200 K. The thermal stabilities of the surface species were studied with annealing experiments. The Clx SiH formed upon initial SiHCl3 exposures at 200 K were observed to decompose between 200–590 K and form additional surface SiH and SiCl species. For both GeHCl3 and SiHCl3 dissociative adsorption on porous silicon, the SiCL. (x = 2 or 3) surface species were converted to silicon monochloride surface species between 200–600 K. In addition, SiH surface species were lost upon annealing between 680–780 K as H2 desorbed from the surface. The adsorption kinetics of SiHCl3 and GeHCl3 were also monitored on porous silicon at various isothermal temperatures. These experiments provide insight into the surface chemistry of chlorosilanes and chlorogermanes during CVD and atomic layer controlled growth.

Diethylgermane, (CH3CH2)2GeH2, and germanium tetrachloride, GeCl4 may be useful precursors for chemical vapor deposition (CVD) or atomic layer controlled deposition of germanium. To explore the surface chemistry of these alternative precursors, the adsorption and desorption kinetics of (CH3CH2)2GeH2 (DEG) and GeCl4 on Si(111) 7×7 have been examined using laser-induced thermal desorption (LITD), and temperature programmed desorption (TPD) techniques. Fourier transform infrared (FTIR) spectroscopy has also been employed to monitor the decomposition of DEG on porous silicon surfaces. The FTIR spectra revealed that DEG dissociatively adsorbs on porous silicon surfaces at 200 K to form SiH, GeH, and SiCH2CH3 surface species. No spectral features were observed for GeCH2CH3 surface species. The TPD studies following DEG exposures on Si(111) 7×7 observed CH2=CH2 and H2 desorption products at 700 and 800 K, respectively. The production of CH2=CH2 (ethylene) was consistent with a βhydride elimination mechanism from surface ethyl species, i.e. SiCH2CH3(ad) → SiH(ad) + CH2=CH2 (g). Similar TPD experiments following GeCl4 exposures monitored the desorption of only SiCl2 at approximately 920 K. Desorption of SiCl2 indicates that the chlorine on GeCl4 has transferred to the silicon surface. Atomic Ge was also observed to desorb at 1200 K following both DEG and GeCl4 adsorption. LITD experiments measured initial reactive sticking coefficients of So ∼0.05 for DEG and So ∼1.0 for GeCl4 at 200 K. As expected from a precursor-mediated adsorption model, the sticking coefficients decreased versus increasing surface temperature. The sticking coefficients for these germanium containing precursors were higher than the corresponding sticking coefficients for (CH3CH2)2SiH2 and SiCl4. Possible recipes for the CVD or atomic layer controlled deposition of germanium on silicon can be proposed based on the surface chemistry and adsorption and desorption kinetics for DEG and GeCl4.

The chemistry of coadsorbed H and X (X=C1, Br) on semiconductor surfaces is important in epitaxial growth of silicon from chlorosilanes and of SixGe1−x alloys, in hydrogenating/ halogenating cycles in atomic layer epitaxy, and also provides an interesting model system, yet has received little attention to date. We have investigated the interaction of HC1 and HBr with Ge(100) by temperature-programmed desorption, and find that H2, HCl and HBr each desorb with near-first-order kinetics near 570–590 K and that GeCl2 and GeBr2 desorb with near-second-order kinetics near 675 K and 710 K, respectively. Analysis of the desorption kinetics of H2 and HX provides evidence that adsorbed H and X atoms pair preferentially in a qualitatively similar way as H atoms adsorbed alone on Ge(100)2×1 or Si(100)2×1 and that pairing of H+X occurs in competition with pairing of H+H.

The adsorption and decomposition of several Ge-containing compounds on Si(100) have been investigated with the intent of elucidating the surface processes leading to the deposition of epitaxial Ge films from these gaseous sources. Exposure of digermane, Ge2H6/ to Si(100) at 110 K results in molecular adsorption and ab initio calculations are used to help interpret the low temperature ultraviolet photoelectron spectrum. Diethylgermane, GeH2Et2, chemisorbs dissociatively on Si(100) at 110 K. The adsorption products are GeH2 and adsorbed ethyl groups. Large exposures of GeH2Et2 result in the formation of a physisorbed layer of molecular GeH2Et2 on top of the dissociated layer. The surface ethyl groups thermally decompose near 670 K via a β-hydride elimination reaction evolving C2H4 into the gas phase. The interactions of Ge2H6 and GeH2Et2 with Si(100) are discussed and compared to similar experiments with GeH4 as the Ge-containing gas source.

The kinetics of surface-limited thin film growth of SiGe alloys was investigated by time-resolved surface differential reflectometry. The source gas, mixtures of disilane and digermane in ratios from 1:1 to 6:1 in helium carrier gas, was delivered to a heated Si(001) substrate by a fast-acting pulsed molecular jet valve. The adsorption and desorption kinetics were determined from the surface differential reflectance signal obtained using a polarized, high-stability HeNe probe laser. Thin film growth was studied in the temperature range of 400–600°C on Si(001) substrates. Preferential incorporation of digermane into the film produces an alloy composition that depends upon but does not mirror the gas composition. For all gas mixtures, there is a strong temperature dependence of the rate at which the adsorption layer decomposes into film plus by-product. The kinetic data and the alloy compositions provide a basis for deducing some of the characteristics of the reaction sequence that leads to SiGe alloy thin film growth.

This work explores the reactivity of HCI and methyltrichlorosilane (MTS) with polycrystalline β-silicon carbide (SiC) surfaces using temperature-programmed desorption (TPD) and Auger electron spectroscopy. HCl is a corrosive gas that inhibits SiC deposition. The results show that HCl is adsorbed by SiC, forming a stable surface chloride that could inhibit SiC deposition. TPD shows that chlorine desorbs as HCI or SiCl4, confirming that HCl can etch SiC surfaces. Desorption is rate-limited by the breaking of Si-Cl bonds. MTS is also adsorbed by SiC; its desorption is similar to that of HCI.

Monocrystalline, epitaxial cubic (100) SiC films have been grown on (100) Si substrates at 750°C, the lowest temperature reported to date, by low-pressure chemical vapor deposition, using methylsilane, SiCH3H3, a single precursor with a Si:C ratio of 1:1, and H2. Hexagonal SiC films were obtained with the aid of a remote H2 plasma, which also increased the deposition rate through a reduction in the activation enthalpy. The films were characterized by means of transmission electron microscopy, single- and double-crystal X-ray diffraction, infra-red absorption, ellipsometry, thickness measurements, four-point probe measurements, and other methods. Based on X-ray diffractometry, the crystalline quality of our β-SiC films is equivalent to that of commercial films of similar thickness. We describe the novel growth apparatus and the properties of the films.

The kinetics of SiC deposition has been studied over the temperature range 650–1050 ° C using the single-source reagents silacyclobutane (SCB) and methylsi-lane (MeSiH3 ) whose decomposition supplies the isomeric film-forming precursors H2Si = CH2 and HSiCH3, respectively. Thermal decomposition has been monitored by mass spectrometry and the SiC thin films characterized by scattering spec-trometry (RBS & ERD), FTIR spectroscopy and X-ray diffraction. Deposition rates from the two are comparable, with activation energies of 41 kcal/mole and 53 kcal/mole for SCB and MeSiH3 decomposition, respectively. Silacyclobutane deposits C-rich material lower temperatures, while SiC deposited from MeSiH3 is Si-rich at all temperatures. A mechanism for SiC CVD is proposed that is consistent with the observed kinetics and products.

Reactive molecular beam scattering techniques with mass spectrometric detection have been used to characterize the kinetics and mechanism of the decomposition of two 1,3-disilacyclobutane precursors to SiC on the Si(100) surface to yield SiC and gas-phase byproducts. Both compounds adsorb and desorb without dissociation at ambient temperature. Reaction probability increases with increasing surface temperature to a maximum exceeding 0.8 at 1100 K. Both compounds yield large quantities of gas-phase intermediates, while only one produces a significant yield of SiC in the initial collision. In situ and ex situ analysis of the SiC film indicate that it is stoichiometric SiC. A combination of mass spectrometric detection with time of flight analysis of surface reaction products permits formulation of a reaction scheme involving a multistep surface decomposition sequence.

A β-SiC epitaxial growth process, using 1,2-disilylethane (DES), was developed. DSE was selected because it contains an equal number of C and Si atoms and its reported decomposition characteristics suggest that C and Si could be obtained from it at approximately equal rates. Repeatable nucleation and epitaxial growth conditions, giving complete substrate coverage and controlled growth, were established by atmospheric pressure CVD, in an inverted-vertical reactor. A substrate temperature of 1290± 10°C was found to be optimum for β-SiC epilayer nucleation and growth. The maximum β-SiC epitaxial growth rate obtained was 10μms/hr. Undoped β-SiC epilayers were n-type (n≈1016 cm−3 ). DSE synthesis, CVD growth parameters, SiC deposition characteristics and β-SiC epitaxial film properties are described.

Thin films (2 Å - 1000 Å) of titanium, platinum, and hafnium were deposited via UHV electron beam evaporation at room temperature on n-type, (0001) alpha (6H)-SiC and compared in terms of interfacial chemistry, energy barriers to electrical conduction, and macroscopic electrical behavior. Current-voltage measurements have shown that these contacts are rectifying, all with ideality factors between 1.01 and 1.09. The lowest leakage currents (∼5 × 10−8 A/cm2 at -10 V) were determined for unannealed Pt contacts and for Hf contacts annealed at 700°C for 20 minutes. Current-voltage (I-V), capacitance-voltage (C-V), and x-ray photoelectron spectro-scopy (XPS) were among the techniques used to determine barrier heights, all of which were within a few tenths of an electron volt of 1.0 eV. The narrow range of calculated barrier heights along with the XPS valence spectrum of the chemically prepared SiC surface give evidence that the Fermi level is pinned at the semiconductor surface.

The effects of H2 and H atoms on electronic properties of crystalline silicon is of great interest to many scientists and technologists involved in developing and manufacturing of microelectronic devices. Hydrogen is of interest because of its ability to interact with defects and impurities in single crystal silicon, its abundance in many processing steps, and its effect on electronic structure of the interface between Si and SiO2. Here we present results of experiments examining the gas phase concentration of impurities during thermal oxidation and annealing of p(100) silicon. These experiments reveal that a significant quantity of hydrogen is contained in virgin wafers, which may have significant impact on thermal processing. A brief review of studies done on hydrogen diffusion in p-type silicon is provided with a perspective to the process investigated here.

Ab initio molecular orbital calculations coupled to RRKM reaction rate theory have been conducted on some important reactions involved in the oxidation of silane in a high-temperature/high H2O environment. The results indicate thatH2O acts as an oxygen donor to SiH2 to form H3SiOH or SiH2O. Subsequent reactions involve the formation of (HSiOOH, H2Si(OH)2,:Si(OH)2 or SiO). In turn SiO polymerizes into planar rings, without an activation energy barrier. A list of calculated thermochemical data are also presented for a number of equilibrium species.

The controlled atomic layer growth of SiO2 insulating layers on silicon surfaces might be achieved through the sequential reaction of SiCl4 and H2O:

(A) Si-Cl + H2O → Si-OH + HCl

(B) Si-OH + SiCl4 → Si-O-SiCl3 + HCl.

To explore this ABAB… binary reaction scheme, laser-induced thermal desorption, temperature-programmed desorption, and Auger electron spectroscopy techniques were utilized to measure the kinetics of H2O oxidation of a Si(111)7×7 surface that had been previously subjected to a saturation SiCl4 exposure. Reaction kinetics studies for the oxidation of the chlorinated surface revealed that the rate of oxygen gain and the rate of chlorine loss were equal at reaction temperatures between 200 K and 700 K. These results were consistent with a direct substitution reaction according to:

(A) Si-Cl + H2O → Si-OH + HCl.

Above 700 K, the amount of oxygen gain became progressively greater than the amount of chlorine loss. This behavior was associated with the thermal desorption of H2 and the resultant formation of new dangling bond sites for H2O adsorption. For all temperatures, the oxidation kinetics of the chlorinated surface were nearly equivalent to the kinetics for the oxidation of clean silicon. This surprising result indicates that chlorine sites and free dangling bond sites react with equal probability to H2O. The kinetics of SiCl4 deposition were also measured on a Si(111)7×7 surface previously exposed to a saturation H2O dose. This chlorination reaction occurred at a much slower rate and was not as amenable to UHV studies.

We have fabricated normal and inverted staggered a-Si:H thin film transistors, TFTs, using silicon oxide/nitride double layer dielectrics. Significant improvements in the electrical performance of these TFTs have been obtained by integrating additional processingsteps into the usual processing cycles. These include; i) a pre-deposition nitridation ofthe a-Si:H surface for the top-gate devices, and ii) a post-deposition passivation of thea-Si:H surface (i.e., the back of the channel region) for the bottom-gate structures. Improvements in the electrical properties of the a-Si:H TFTs resulting from these additionalprocessing steps are discussed.

We present data on the temperature dependence of the etch rate of silicon and silicon dioxide in order to elucidate optimum conditions for the selective oxygen removal from the silicon surface. Both, the etching temperature and ion bombardment have a pronounced influence on the surface morphology. The conditions yielding a minimum surface roughness will be presented. A careful control of the oxygen impurities of the hydrogen plasma in the range between about 1–3 ppm and 60 ppm allow us to control the degree of anisotropy of etching of patterned silicon wafers.

Chemical vapor cleaning (CVC) is an emerging technology which has been used to remove transition metal contamination from wafer surfaces. CVC is a gas phase/surface reaction which does not incorporate any wet steps nor condensation of reagents onto the wafer surface. In previous work, we reported the effective removal of trace iron and copper from native oxide surfaces using 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (HFAC) and other chelating or coordination compounds. In general, surface metal contaminants form volatile reaction products with these CVC reagents at relatively low temperatures (<300°C). In this paper, we report the extension of that work to include the facile removal of sodium from silicon oxide surfaces. Wafers doped with sodium from aqueous sodium hydroxide can be cleaned in a fully gas phase process at temperatures below 225°C.We will describe our preliminary process results, which have led to a surface sodium concentration reduction of roughly one order of magnitude. Current understanding related to the mechanisms controlling mobile ion removal will also be described.

We report a dual-function chamber integrating (a) remote RF plasma-enhanced etching of SiO2 layers on Si(100) surfaces with low energy, <100 eV, ion bombardment and (b) in-situ removal of polymeric C-F residues that are formed on the exposed Si surfaces. Using direct plasma excitation of He and downstream introduction of CF4, an SiO2 etch rate of ̃5 nm/min was obtained at a CF4 partial pressure as low as 0.25 mTorr. An exposure to atomic-H at a substrate temperature of 250°C was effective in removing polymeric residues from the Si surface, while an exposure to reactive O-species was less effective. We achieved a low-temperature, ̃300°C, homoepitaxial growth of Si on the Si(100) surface that was subjected to plasma etching followed by an exposure to atomic-H. The electrical damage of the processed Si surfaces was evaluated by a new technique, where a device-quality SiO2 film was deposited on this surface by remote PECVD and the C-V characteristics of the MOS structure were measured.

The appearance of striations on dry etched semiconductor laser mesas is a common feature of these structures. We describe a number of different methods of reducing the extent of this roughness, including the choice of dielectric etch chemistry, modification of the initial resist processing and deposition of a SiN sidewall to prevent additional rougheningduring the plasma etch step. SF6 is found to be preferable to CF4 for dielectric etching because of an absence of polymer formation. This produces smoother SiO2 sidewalls. Flood exposure of the initial photoresist mask and optimization of the postbake temperature also produces smoomer sidewalls on the subsequently etched SiO2. The sidewall can also be protected from roughening that occurs during the dry etch step by coating it with a low temperature SiN layer. A combination of all of these methods produces sidewalls with morphological variations of ≤500Å.

Silicon dioxide was deposited from tetraethylorthosilicate (TEOS) and remote microwave oxygen plasma on a heated silicon substrate in a cold-wall reactor. The deposition rate and film quality were examined as functions of substrate temperature, total pressure, absorbed plasma power and O2:TEOS flow ratio. The deposition reaction exhibited an activation energy of approximately 10 kJ/mol for substrate temperatures in the range of 323–623 K. The deposition rate reached a maximum with increasing total pressure. The rate was found to be a near-linear function of the absorbed microwave power. At fixedabsorbed power the rate reached a maximum with increasing O2:TEOS flow ratio. A one-dimensional mathematical model was developed to predict the oxygen radical concentration at the exit of the afterglow region of the oxygen discharge. Comparisons of the predicted oxygen radical concentrations with the deposition rates at corresponding deposition conditions supports the view that the overall SiO2 deposition reaction is largely controlled by the concentration of oxygen radicals. The average refractive index ofthe deposited films was 1.466 ± 0.011. Fourier transform infra-red (FTIR) transmission spectra showed significant concentrations of hydroxyls in the deposited films.