Tungsten Silicide Films Research Articles

Atmospheric Pressure Chemical Vapor Deposition of Tungsten Silicide: The Dependence of Film Composition and Growth Rate on Gas Composition

We have studied the composition and thickness of films of tungsten silicide deposited by atmospheric pressure chemical vapor deposition from the reagent system , over a range of gas mixtures from of 3/1–1/30, at temperatures of 290°–300°C. Good film quality is obtained when oxygen‐free conditions are achieved. The composition of the as‐deposited film is found to depend on the ratio of W/Si in the gas phase; the same results are obtained from either or in this respect. The rate of incorporation of W in the film is a simple function of the flow and the ratio of W to Si atoms in the gas, for a broad range of compositions. The limiting composition at low W/Si ratios in the gas differs from that predicted thermodynamically, as noted by other workers.

Deposition Mechanism of Tungsten Silicide Films by Low Pressure CVD

ABSTRACTWSix thin films were deposited on SiO2/Si substrates by Low Pressure Chemical Vapor Deposition (LPCVD) using WF6 and SiH4 gases. The deposition mechanism has been studied by measuring the thickness, resistivity and composition of the films by varying deposition temperature and gas flow rate at a constant total reactant gas pressure. Below 300°C, the surface chemical reaction was the rate-limiting process and the deposition rate increased exponentially with temperature having a thermal activation energy of 3.2 kcal/mol. Meanwhile, above 300°C the reaction was governed by the mass transfer step in the gas. The deposition rate in this range is insensitive to the deposition temperature but shows dependence of the flow rate of reactant gases. AES and RBS analyses were performed to determine the stoichiometry of WSix thin film. The Si content in film gradually increased as the deposition temperature increased. The resistivity of as-deposited WSix film has dependence on both deposition temperature and Si/W ratio, and exponentially increased with a moderate slope. However, temperature insensitive behavior of resistivity appeared in the mass transfer controlled region. Such resistivity changes with temperature were discussed with the Si/W ratio and the microstructure of films.

The formation of thin-film tungsten silicide annealed in ultrahigh vacuum

Thin films of tungsten silicide have been formed by sputter depositing 710 Å of W metal onto (100)-oriented, 3–7 Ω cm, p-type silicon wafers. The samples were annealed in an ultrahigh vacuum ambient (pressure≤1.0×10−9 Torr) at temperatures ranging from 845 to 1100 °C for 30 s. The lack of oxygen contamination in the ambient allows the W-Si interaction to proceed, first producing both the W-rich W5 Si3 phase and the tetragonal WSi2 phase near 900 °C, followed by only the tetragonal, low-resistivity (30–40 μΩ cm) WSi2 phase above 1000 °C. This result is in contrast to previous work where films formed by rapid thermal processing in vacuum showed no significant W-Si interaction for temperatures below 1100 °C due to the formation of an interfacial oxide diffusion barrier gettered into the films from the 10−6 Torr ambient.

Reaction of CVD ‐ WSix Film and Al Film

The reaction between chemical vapor deposited (CVD) tungsten silicide film and aluminum film was investigated. As‐deposited and annealed films were used to react with aluminum film at 500°C. The changes of the composition ratio of Si/W before and after annealing were analyzed by Rutherford backscattering spectroscopy (RBS) and the profiles of chemical composition and impurity atoms before and after annealing were studied by secondary ion mass spectrometry (SIMS). The biggest difference was seen in the composition ratio of Si/W. The composition ratio of Si/W in as‐deposited film changed from the initial value of 2.4 to 4.0. This is due to diffusion of tungsten atoms from the as‐deposited film into the aluminum film, however, few silicon atoms diffuse into the aluminum film. On the other hand, in annealed film, the composition ratio of Si/W remains unchanged from the reaction at 500°C.

Tungsten Silicide Films Deposited by SiH2Cl2 ‐ WF 6 Chemical Reaction

This paper studies tungsten silicide films deposited by the chemical reaction. The deposition rate was held at around 1500 Å/min at temperatures above 500°C. However, the deposition rate decreased rapidly below 500°C because the surface reaction is dominant. The Si/W ratio (Si composition) of , film decreased from 2.38 to 2.15 at the flow rate changed from 4 to 6 sccm in deposition at 580°C. Resistivity decreased from 740 to 530 μΩ‐cm with these compositional changes. The resistivity increased with the increase of deposition temperature. Since tetragonal grains are grown in as‐deposited film, lower resistivity films can be achieved.

Properties of sputtered tungsten silicide films deposited with different argon pressures

The effect of Ar impurities on film properties in sputtered tungsten silicide (WSi x ) was studied. The WSi x films were deposited by dc magnetron sputtering at different Ar pressures ranging from 4 to 20 mTorr. The Ar concentration observed by Rutherford backscattering spectrometry was as high as 7.8 × 10 20 cm −3 in the film at 4 mTorr. The concentration decreased and reaches 5.1 × 10 20 cm −3 at 20 mTorr. The composition of WSi x (Si/W ratio) changed from 2.46 to 2.61. However, the resistivity showed a weak Ar pressure dependence. The same film properties were attained with an annealing at 1000° C, because the Ar concentration of the each film decreased to 2.0 × 10 20 cm −3 with this annealing.

Tungsten Film Formation on Silicon by Combining Ionic Decomposition of Metal Halides with Rapid Thermal Processing

ABSTRACTThin films of tungsten metal and tungsten silicide were formed by combination of spin-on of tungsten chloride dissolved in a volatile organic solvent, decomposition of the chloride by ion bombardment and finally heating in a new versatile Rapid Thermal Processing (RTP) system. The films resulting from this treatment were characterized by Rutherford Backscattering Spectrometry (RBS) prior to and after the ionic decomposition and heat treatment. The procedure and the results of the analysis are described and discussed in terms of process conditions in this paper.

ChemInform Abstract: Etching of Tungsten and Tungsten Silicide Films by Chlorine Atoms

Abstractis performed both within and downstream from a Cl2 plasma discharged at 200 mtorr below 150 °C. Without a discharge, molecular chlorine does not etch the films at the temp. studied.

Exafs study on tungsten silicide films

Extended X-ray absorption fine structure (EXAFS) has been used to analyze the short-range order of chemically vapor deposited (CVD) tungsten silicide films. The Fourier analysis of the W L III-edge EXAFS shows that only the first nearest Si atoms are dominant in as-deposited films. Some other structures further out appear after annealing at 400°C. The crystallinity of the films increases monotonically as the annealing temperature rises.

Investigations of the growth of tungsten and tungsten silicides on SiO 2 substrates by low pressure CVD method

Growth of tungsten and tungsten silicide films on SiO 2 substrate through the reaction via WF 6, SiH 4, and/or H 2 gases in a vertical type low pressure chemical vapor deposition (LPCVD) system was investigated. It was found that the metal tungsten can be selectively deposited on Si, but not on SiO 2. If a very small amount of SiH 4 is introduced into the reaction chamber, tungsten films can be deposited on the SiO 2 substrate, and its growth rate is highly dependent on the substrate temperature. For the growth of tungsten silicides, amorphous WSi x was observed in the as-deposited films on the SiO 2 substrate. After short annealing, formation of W and tetragonal W 5Si 3 crystallites was observed. After prolonged annealing, the film finally transforms into W and WSi 2 if x≲2.3, and transforms completely into WSi 2 if x>2.3. The resistivity of the film drops from 1400 to 160 μΩ cm after annealing at 700°C for 30 min, and begins to increase after further annealing. The change of the film resistivity can be explained by the improvement of the crystallinity, and the transformation to W 5Si 3, WSi 2, and W.

Effect of excess silicon on behavior of LPCVD WSi x films on silicon

This paper addresses the important effects of excess silicon in low pressure chemical vapor deposition tungsten silicide films on resistivity, adhesion, and stress as a function of annealing temperature with physical interpretation. Excess silicon can be incorporated in the films to lower stress, but a consequence of this is that the resistivity is increased. On annealing such fimls, excess silicon tends to diffuse out of the silicide increasing stress and lowering resistivity. Results are presented of both the stress in the films and their resistivity as a function of annealing conditions. The annealing ambient also plays a strong role in the rate at which excess silicon migrates to the surface. Oxygen greatly enhances the rate compared with argon or nitrogen.

Etching of Tungsten and Tungsten Silicide Films by Chlorine Atoms

Thin films of tungsten and tungsten silicide were etched both within and downstream from a plasma discharge at 200 mtorr pressure and temperatures below 150°C. When samples were positioned downstream from the discharge, etching proceeded solely by chemical reaction of the film with chlorine atoms. Without a discharge, molecular chlorine did not etch tungsten or tungsten silicide. Downstream and in‐plasma tungsten etch rates were approximately equal at 110°C, but the chlorine atom etch rate dropped more rapidly than the in‐plasma etch rate as temperature decreased. The chemical reaction between chlorine atoms and the tungsten film was proportional to the gas phase Cl atom mole fraction. A pretreatment consisting of either a dilute hydrofluoric acid dip or a short plasma etch cycle was necessary for atom etching of tungsten silicide films. The etch rates of tungsten silicide in plasmas were approximately an order of magnitude higher and less temperature sensitive than those in the downstream (atom) configuration.

Thickness Measurement of Aluminum, Titanium, Titanium Silicide, and Tungsten Silicide Films by X‐Ray Fluorescence

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Effects of rapid thermal processing on the formation of uniform tetragonal tungsten disilicide films on Si(100) substrates

Thin films of tungsten silicide with resistivities of 30–35 μΩ cm have been formed by sputter depositing 710 Å of W metal onto (100)–oriented, 3–7 Ω cm, p-type silicon wafers. The samples were fast radiatively processed in a rapid thermal processing (RTP) system under high vacuum for time anneals ranging from 15–20 s at two temperatures (∼1100 and ∼1150 °C). The inevitable oxide barrier at the interface is shown to decrease with increasing RTP time and temperature, evidenced by both Auger electron spectroscopy and secondary ion mass spectrometry experiments. The high film stress produced by thermal considerations does not seem to effect the resulting resistivity and, furthermore, appears to relax at higher temperatures when the film surface becomes ‘‘buckled.’’

ChemInform Abstract: Properties of Chemical Vapor Deposited Tungsten Silicide Films Using Reaction of WF6 and Si2H6.

AbstractIt is shown that CVD tungsten silicide films prepared by reaction of WF6 and Si2H6 have a higher deposition rate and higher Si content than those obtained from WF6 and SiH4 at the same substrate temperature.

Effect of fluorine in chemical-vapor-deposited tungsten silicide film on electrical breakdown of SiO2 film

The effect of fluorine in chemical-vapor-deposited tungsten silicide film on electrical breakdown of SiO2 film was investigated. Fluorine diffuses into the SiO2 film through the upper layer of poly Si above 800 °C. At 1000 °C, fluorine diffuses into the SiO2 film to a concentration on the order of 1020 cm−3. Electrical breakdown field of the SiO2 film degrades remarkably at 1000 °C. However, it was clear that the diffusion of fluorine was blocked by a thin chemical-vapor-deposited Si3N4 layer on the SiO2 film. In this case, the degradation of SiO2 film was not observed. From the above results, it is concluded that the diffusion of fluorine included in the chemical-vapor-deposited tungsten silicide film is one of the causes in degradation of electrical breakdown of the SiO2 film when the chemical-vapor-deposited tungsten silicide film was used as a gate electrode in metal oxide semiconductor integrated circuits.

TEM investigations of the tungsten silicide films on silicon

Tungsten silicide thin films were prepared by electron beam evaporation techniques. Tungsten films of 900°A thick were evaporated onto the silicon substrates. The as-deposited films were subsequently annealed in a quartz diffusion furnace under an N 2 atmosphere. X-ray diffraction and transmission electron microscopy were used to determine the structure of the annealed thin films. Grain coarsening and epitaxial silicides were observed on the as-deposited tungsten film on (100) silicon after furnace annealing at 800°C for 1 hour.

Properties of Chemical Vapor Deposited Tungsten Silicide Films Using Reaction of WF 6 and Si2 H 6

Tungsten silicide films were formed by the chemical vapor deposition method using the reaction and . The deposition rate, resistivity, composition, stress, crystal structure, and content of impurities were studied and compared with tungsten silicide films deposited by reaction of and . The tungsten silicide films made using have a higher deposition rate and higher Si concentration than those made by using at the same substrate temperature. For these reasons, the tungsten silicide films made by using were found to have a resistivity that is a little higher and, after annealing, a stress that is smaller than that made by . Also, the resistance of tungsten silicide to peeling is larger than that of the film made by using . The crystal structure of the films made by is almost the same as that made by ; however, a tetragonal structure easily forms even in Si‐rich films of . Content of fluorine in films made by is smaller than that in films made by .

Raman scattering from rapid thermally annealed tungsten silicide

Raman scattering as a technique for studying the formation of tungsten silicide is presented. The tungsten silicide films have been formed by rapid thermal annealing of thin tungsten films sputter deposited on silicon substrates. The Raman data are interpreted by using data from resistivity measurements, Auger and Rutherford backscattering measurements, and scanning electron microscopy.

High-temperature stress measurement on chemical-vapor-deposited tungsten silicide and tungsten films

Stresses in chemical-vapor-deposited tungsten silicide and tungsten films at high temperatures were measured. Tungsten silicide films were formed from WF6 and SiH4 or Si2H6. Tungsten films were formed from WF6 and H2. The stress in tungsten silicide films is tensile and in the order of 109–1010 dynes/cm2. For a composition ratio of Si/W≤2.6, the stress of a film of more than 1000 Å has a maximum at about 500 °C. On the other hand, for a composition Si/W>2.9, the stress has no maximum. The maximum of the stress is caused by crystallization of the film. The stress has two components. One component is related to the difference of the thermal expansion coefficients between the film and the Si substrate. Another is related to the film crystallization. It was found that the stress concentrates in the portion of the film nearest the substrate. The stress in tungsten films also reaches a maximum at 550 °C, similar to the tungsten silicide films. However, the cause of this behavior is not clear.