The chemical kinetics of Silicon Rich Oxide (SRO) growth in a N2O-SiH4 LPCVD reactor has been studied at deposition temperatures from 610 to 680°C and pressures from 0.4 to 0.5 torr. We can produce SRO films with a wide spectrum of input reactant ratios γ = [N2O]/[SiH4] = 1 to 40. The dependence of film composition on γ changes dramatically in a region around γ = 2.

Growth for γ < 2 is consistent with the chemical kinetics of SIPOS growth. Growth for γ > 20 can be explained by oxidation of silicon in the bulk of the growing SRO film. We can explain growth from γ ≈ 4 to 20 by considering the chemical kinetics of possible binary surface reactions which may produce Si-Si or Si-O bonds. This allows us to accurately model the dependence of SRO growth rate in this region as a function of γ, pressure, and deposition temperature.

The deposition mechanism of silicon suboxides (SiOx, x<2) prepared by remote plasma enhanced chemical vapor deposition (Remote PECVD) is investigated. These films were deposited in a Deposition/Analysis chamber designed to investigate the gas phase chemistry. In this technique, an O2/He mixture is plasma excited, and the silane reactant is injected into the deposition chamber down-stream from the plasma tube. We show that if the plasma after-glow is prevented from extending into the deposition region by an electrical grid placed between the plasma tube and the deposition region, silicon dioxide is then deposited for all O2/He mixtures investigated (0.1 to 1.0 %). In contrast, hydrogenated suboxides of silicon are deposited when the plasma after-glow is allowed to extend past the grid into the deposition region.

The properties of Plasma Enhanced Chemical Vapor Deposited (PECVD) silicon oxynitride thin films were determined for a variety of deposition conditions. The films were characterized with respect to stress, refractive index, deposition rate, hydrogen content, dielectric constant, and uniformity. The films were deposited in an Electrotech ND6200 parallel plate reactor using a silane - ammonia - nitrous oxide process gas chemistry. Deposition parameters which were investigated include process gas flow rate, power, and total pressure. The possible application of these films as both inter-layer and final passivation layers for use on GaAs ICs will be discussed.

The N2-SiH4 rf glow-discharge plasma has been analyzed by line-of-sight mass spectrometry of species impinging on the deposition electrode, including N atoms. Properties of SixNyHz films deposited from this plasma have been examined. At high rf power and low SiH4/N2, almost all of the SiH4 is consumed by reaction with N atoms at the film surface and becomes incorporated into the film. No Si-N precursor species are seen in the gas phase. This is in contrast to the NH3-SiH4 plasma, where the Si(NH2)3 radical is the key precursor. If power is insufficient or SiH4 flow is excessive, Si2Hm species are generated in the plasma. Under optimized conditions, films slightly N-rich with no Si-H bonding and only 7% H (as N-H) can be deposited at high rate. The film tensile stress of the NH3 process is absent in the N2 process due to the lesser amount of condensation that takes place during deposition. However, trench coverage is much better in the NH3 process.

An analytical model to account for the effects of gas phase reactions in CVD processes is presented. In this model a system with only two reactions, gas phase production of an intermediate and reaction of the intermediate on the surface of the substrate to form the film is considered. The reaction kinetics, convective and diffusive transport mechanisms are coupled to analyse the thickness distribution over the length of the reactor.

Theoretical deposition rate profiles in the direction of gas flow are shown with varying deposition temperatures and gas flow velocities for both surface and gas phase reaction controlled mechanisms. It has been shown that by analyzing the nature of the deposition rate profiles, the rate limiting step in a CVD process can be identified.

We have successfully deposited thin films of SiO2 on a cadmium telluride substrate at low temperature (Ts =100°C–300°C) by remote plasma enhanced chemical vapor deposition (Remote PECVD). The native oxide on the CdTe substrate has been removed, prior to deposition by either chemical etching in methanol and 1% bromine, or by dissolution in deionized water. After removal of the native oxide, the CdTe was inserted into a UHV-compatible deposition chamber and a He+ plasma treatment was performed prior to deposition of an SiO2 film. This treatment promotes strong adhesion between the deposited SiO2 film and the CdTe surface. We find that the initial oxide removal process does not influence SiO2 adhesion. The effect of the He+ plasma treatment on the CdTe surface has been studied by Auger electron spectroscopy(AES), and Reflection high energy electron diffraction (RHEED).

Chemical Vapor Deposition (CVD) of thin films for microelectronic devices has historically used source materials that are gases at room temperature [1]. The decision to use gases was largely a practical one based on the relative ease with which the flow of gaseous materials can be controlled. CVD of thin films plays a vital role in increased circuit density and performance of integrated circuits. Liquid sources offer alternative source composition, reaction kinetics and reaction mechanisms to optimize a given CVD process [2].

For example, CVD films of silicon dioxide (oxide) and oxide films modified to lower the glass transition temperature such a borophosphosilicate glass (BPSG) have traditionally used gaseous source materials such as silane, diborane and phosphine [3]. An all liquid system of tetraethylorthosilicate (TEOS), triethylborate (TEB) and triethylphosphine (TEPhine) has been found to offer superior conformality and overall safety [4]. However, from a practical standpoint, the all liquid system has historically suffered from reliable, reproducible mass flow control.

An important step in the chemical vapor deposition (CVD) of aluminum from triisobutylaluminum (TIBA) is the reaction between TIBA (adsorbed from the gas phase) and the growing aluminum surface. We have studied this chemistry by impinging TIBA under collisionless conditions in an ultra-high vacuum system onto single crystal Al(111) and Al(100) substrates. We find that when TIBA (340K) collides with an aluminum surface heated to between 500 and 600K, the aluminum atom is cleanly abstracted from this precursor with near unit reaction probability to deposit, epitaxially, carbon-free aluminum films. The gas phase products are isobutylene and hydrogen. From monolayer thermal desorption experiments, we have determined the kinetic parameters for the rate-determining step, a β-hydride elimination reaction by surface bound isobutyl ligands. Using these kinetic parameters and a Langmuir absorption model, we can predict the rate of aluminum deposition at pressures ranging from 10−6 to 1 Torr.

The decomposition of trimethylgallium (TMG) and trimethylaluminum (TMA) on Si(100) is studied by TPD, XPS, and EELS. It is found that the decomposition of TMG is largely an intramolecular process. First one of the methyl groups in the TMG reacts with a hydrogen in another methyl group liberating methane. This leaves a CH2 group bound to the gallium which is seen clearly in EELS. Subsequently, another hydrogen reacts with a methyl group producing additional methane. This leaves a gallium atom and a CH group on the surface. Hydrogen desorbs, while carbon is incorporated into the growing film. Careful calibration of the peak areas in the TPD data indicates that 2.1 ± 0.3 moles of methane, 0.5 ± 0.03 moles of hydrogen, 1 mole of gallium, and 0.95 ± 0.1 moles of surface carbon are produced for every mole of TMG which decomposes. Since, the decomposition ratio is independent of the state of the surface, the surface orientation, and the level of impurities on the surface, it appears that the surface is not a direct participant in the reaction.

TMA adsorbs as dimers. However, the dimers decompose upon heating to 400 K. Thereafter, the chemistry of TMA decomposition is similar to that for TMG. Nonetheless, the product ratio varies with the TMA coverage, the state of the surface, and the aluminum coverage. Also, silicon-carbon bonds are evident at 600 K in EELS. It is suggested, therefore, that the decomposition of TMA is similar to that of TMG, except that methyl groups in TMA have a tendency to migrate to the support. In both TMA and TMG, carbon incorporation is an intrinsic part of the decomposition process. This suggests that TMA and TMG would not be appropriate source gases when one needs to produce films with very low carbon levels.

The electronic structure of dimerized trimethylaluminum (TMA), Al2(CH3)6. adsorbed on Si(100) surfaces has been investigated using molecular orbital (MO) calculations based on a cluster description of TMA/Si(100). The calculated results suggest that the interactions between TMA and the Si(100) surface are described by overlap of the TMA electron-deficient bond and Si surface dangling-bond orbitals. The electron-deficient bond orbital is the highest occupied MO of TMA and acts as an electron acceptor for charge transfer from a surface Si atom to TMA consistent with observed core-level and valence photoelectron spectra.

Surface spectroscopic techniques have been used to investigate aluminium deposition form tri-methyl aluminium (TMA) on Si(100), and the etching of InP by chlorine. Thermal reactions and processes stimulated by UV lamps and ion beams are examined. The results are interpreted in the light of the adsorption states which are formed and the surface transformations of chemical states which are observed to occur.

The nucleation of chemical vapor deposition (CVD) using triisobutylaluminum (TIBA) on Si (100) surfaces is observed in situ with x-ray photoelectron spectroscopy (XPS). Oxygen from oxide on the silicon inhibits the rate of nucleation by reacting with adsorbed TIBA and forming a thin layer of oxidized organometallic. This layer blocks active adsorption sites and prevents further deposition. On a surface without oxide, the TIBA molecules decompose liberating aluminum that can migrate and nucleate into islands opening sites for further adsorption and film growth. By removing the oxide (native or thermal) in selected areas of the surface, the barrier to nucleation is removed and aluminum deposition can occur in a predetermined pattern.

Epitaxial Al(111) film was deposited on Si(lll) by low-pressure chemical vapor deposition with the use of tri-isobutyl aluminum (TIBA) at the substrate temperature of 400 °C with the deposition rate of 0.9 μm/min. It was necessary for epitaxy to preheat the TIBA gas just before the deposition on the substrate. The preheat was made by gas-temperature-controller provided in the chamber. The film surface was so smooth that reflectance was higher than 90 % of Si and 20 ppm of O, C, and H. No hillock appeared on the film after 430 °C annealing for 40 min. The interface of Al and Si was rather stable so that no alloy penetration occured. The possibility of epitaxial growth of Al(100) on Si(100) was also shown.

New mechanistic details regarding aluminum deposition by ArF excimer laser photodecomposition of trimethylaluminum (TMA) adsorbed on aluminum covered SiO 2/Si substrates have been obtained using a time-of-flight quadrupole mass spectrometer. CH3 radicals and Al-(CH3)n (n = 1,2,3) species are efficiently photoejected from the surface with up to 0.22 eV of translational energy. Experiments at various TMA dosing levels reveal differences in desorbed fragment translational energy presumably associated with variations in surface site binding energy. No direct evidence is found for desorption of A1 from the surface indicating that A1 is more tightly bound than methyl-aluminum fragments. By carefully monitoring changes in fragment translational energy as an A1 deposit forms on the clean SiO2/Si substrate, we examine how the surface influences the onset of A1 growth. No evidence of ethane or methane desorption from the sample surface is found implying that radical recombination and hydrogen abstraction are primarily secondary gas phase reactions which are not surface initiated.

A systematic study to find the role of different metal atoms and ligand combinations on the yield of the photoproducts generated upon irradiation of gas phase organometallics (i.e. metalalkyls) by uv excimer laser radiation was performed using laser ionization mass spectrometry.

It is shown that volatile molecular compounds with silicon-metal bonds can act as effective MOCVD precursors to metal silicides, which aredeposited as thin films under relatively mild conditions. Strategies for the design and synthesis of such “prevenient” precursors are explored, and possible extensions of this approach are considered.

Cobalt silicide films have been deposited by chemical vapor deposition using Co2 (CO)8 or HCo(CO)4 as the Co source and SiH4 or Si2 H6 as the Si source. The Co:Si ratio of the films increases with the deposition temperature, and CoSi2 stoichiometry is obtained at 300° C using SiH4 or at 225° C when Si2 H6 is the Si precursor. Resistivities of films deposited in the range CoSi2.0 to CoSi3.0. are typically 200 microohm-cm and drop to 30 – 40 microohm-cm upon annealing at 900° C.

A variety of transition-metal films have been grown by organometallic chemical vapor deposition (OMCVD) at low temperatures using hydrocarbon or hydrido-carbonyl metal complexes as precursors. The vapors of the metal complexes are transported with argon as the carrier gas, adding H2 to the stream shortly before contact with a heated substrate.

High-purity platinum films have been grown using (η5−C5H5)PtMe3 [1] or (η5−CH3C5H4)PtMe3 [2] at substrate temperatures of 180°C or 120°C, respectively. The incorporation of a methyl substituent on the cyclopentadienyl ligand decreases the melting point of the organoplatinum complex from 106°C [1] to 30°C [2] and increases the vapor pressure substantially. Film deposition also occurs at a lower substrate temperature. Analyses by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) indicate that the films are well crystallized and do not contain any observable impurities after sputter cleaning.

The substrate temperatures for the first appearance of other transition-metal films from organometallic precursors are as follows (°C): Rh(η3−C3H5)3 (120/Si), Ir(η3-C3H5)3 (100/Si), HRe(CO)5 (130/Si) and Ni(η5−CH3C5H4)2 (190/glass, 280/Si). These films are essentially amorphous and contain trace oxygen impurities (< 2%), except for the Re film, which was 10% oxygen and 20%carbon.

The energetics of decomposition of a variety of organometallic compounds have been determined from photoionization mass spectroscopy and electron impact mass spectroscopy. In particular, Pd(C5H5)(C3H5) and Pt(C5H5)(C3H5) have been studied in this fashion, and the information used to make patterned Pd/Ni/Si heterostructures by laser induced photolysis of the palladium compound and nickelocene in vacuum (MOCVD). Contamination in the thin films was determined by Auger electron spectroscopy, and compared with that found by other researchers for photo-deposition of Pt from the cyclopentadiene allyl [1].Thermodynamic data is used to explain differing contamination levels in the Pd and the Pt coatings.

New borane clusters and their corresponding transition and rare earth metal complexes are currently being investigated in our laboratories for their utility as unique source materials for the formation of both metallic and non-metallic thin films. These borane cluster complexes exhibit highly favorable properties for use in OMVPE processes, such as; (1) relatively high volatility, (2) anticipated high stability of the ligand itself to provide clean ligand-metal dissociations, (3) high temperature stabilities of the complexes, (4) readily preparable in significant quantities, and (5) availability of theoretical and spectroscopic probes of structure-reactivity relationships. In this work, we have prepared both non-metallic thin films, including materials such as boron nitride, and metallic thin films (both the transition and rare earth metals) through the use of these unique cluster materials.

Boron nitride has been investigated as a potential hard coating for use as an insulating electrical layer and protective coating. We have investigated plasma enhanced chemical vapor deposition and pyrolytic deposition of boron nitride from readily available and easily handled borane clusters. Auger electron spectroscopy was used to show that the film was high purity boron nitride of uniform composition.

The deposition of transition and rare earth metal thin-film materials of controlled stoichiometry has recently received considerable interest. We have discovered the borane cluster-assisted deposition (CAD) of metallic thin-films involving both transition and rare earth metal materials. Through the use of this unprecedented borane cluster chemical transport process, films ranging in thickness from 100 nm to several microns have been straightforwardly and systematically prepared for numerous metal and mixed-metal boroncontaining systems with controlled composition at relatively low temperatures. These new materials have been characterized by SEM and other techniques.