[en] This book presents papers on tungsten and other refractory metals for VLSI applications. Topics include the following: Selectivity loss and nucleation on insulators, fundamental reaction and growth studies, chemical vapor deposition of tungsten, chemical vapor deposition of molybdenum, reactive ion etching of refractory metal films; and properties of refractory metals deposited by sputtering

[en] Tungsten deposited by CVD processes, has been very attractive for application in silicon integrated circuits where the dimensions are in the micron or submicron range. The bulk resistivity of tungsten is 5.3μ Ω cm and the coefficient of thermal expansion is 4.5 ppm⁰C/sup -1/ (similar to 3.1 ppm⁰C/sup -1/ (of silicon). Tungsten forms a stable silicide and can be made to form low resistance, of the order of 10-7 cm/sup -2/, contacts to silicon. In addition, the refractory nature of tungsten or molybdenum make them attractive because of electromigration resistance and the ability to withstand higher process temperatures. However, tungsten does oxidize readily and the adherence to dielectric surfaces is poor. The alternative to CVD is physical vapor deposition such as electron beam evaporation and sputter deposition. The use of electron beam evaporation leads to radiation damage due to the high energy electrons creating X-rays and the vapor from the source travels in straight lines resulting in poor step coverage. In sputtering, the radiation damage can be reduced by use of magnetron sputter sources (low voltage in comparison with the e-beam) but step coverage is still poor unless a bias deposition process is used. The adherence of the physically deposited films is poor and this is compounded by the high compressive stress that can result during sputter deposition

[en] Integrity of shallow junction devices is dependent on maintaining smooth films of constant thickness where metal contacts doped silicon. Localized silicon oxide residue can enhance the WF/sub 6//Si reaction used in LPCVD tungsten depositions resulting in unacceptably large amounts of silicon consumption. The authors investigated phenomena which cause excess WF/sub 6//Si interaction that can lead to incursions of tungsten into silicon structures. In layers between 1.0 nm and 2.0 nm thick, silicon oxide appears to catalyze the WF/sub 6//Si reaction and prevent or delay the self-limiting condition of LPCVD W film formation. Consequences for shallow junction devices are discussed, and methods to avoid this problem are presented

[en] The rate of initiation of tungsten nuclei on thermal oxide has been determined as a function of time, temperature and distance from areas of tungsten growth. The creation rate of infinitely small nuclei increases exponentially with time and decays exponentially with distance form large regions of tungsten growth. As time passes, the nucleation front progresses away from regions of tungsten deposition. The results suggest an autocatalytic nucleation phenomenon coupled with either gas phase or surface diffusion of the reactive intermediate. An activation energy for nucleation of 25 kcal mol/sup -1/ was determined using three independent methods. It is hypothesized that HF attacks the SiO/sub 2/ to form SiF/sub x/ in the presence of tungsten catalyst. Solution of the reactor continuity equation shows that the steady state HF pressure is most sensitive to reactive area (hot metallic surfaces) in the reactor

[en] Molybdenum films have been deposited by Low Pressure Chemical Vapor Deposition (LPCVD) on silicon substrates by the reduction of molybdenum hexafluoride in hydrogen and argon atmospheres. The deposition is extremely selective, with no Mo observed on silicon dioxide surfaces over the temperature range 200-400⁰C. Reduction by both hydrogen and silicon contribute to the deposition, with approximately equal, extremely high deposition rates; no self-limiting thickness was observed. Extensive TEM and SEM studies were conducted in order to characterize the microstructure of the deposited films. The main feature of the films is their extreme porosity - about 30%, which can explain many specific properties of the process and the films. On the basis of the authors' experiments they propose a model to explain the porosity of deposited films

[en] In this paper, the reliability of W gate process is discussed from three aspects; thermal stability of gate/SiO/sub 2//Si structure, oxidation resistance of W and high-purity film formation. In terms of thermal stability of refractory metals/SiO/sub 2//Si structure, it is shown that Si/SiO/sub 2/ reaction can be a key problem, rather than metal (W or Mo)/SiO/sub 2/ reaction in the case of (W or Mo)/SiO/sub 2//Si structure. A new oxidation method, wet hydrogen oxidation, can overcome the oxidation problem of W gate process, in which Si can be oxidized without oxidizing W. W gate technology using CVD method has been developed to reduce mobile ion contamination and is shown to be very promising for use in VLSIs

[en] Molybdenum films were deposited from the hydrogen reduction of MoF/sub 6/. The reaction was completely selective against deposition on silicon dioxide. The reaction with silicon is very high rate, and is not self-limiting, in contrast to the analogous reaction between WF/sub 6/ and silicon. Films of selective CVD tungsten, and sputtered TiW and Mo were ineffective as barrier films to the MoF/sub 6/-Si reaction. The TiW and Mo films, when deposited over SiO/sub 2/, were etched clean. MoF/sub 6/ also etched the oxide film. The films deposited over silicon were high in oxygen content and porous

[en] Chemical kinetics of low pressure chemical vapor deposition (LPCVD) of molybdenum on single crystal p-type (100) oriented silicon substrates were studied by hydrogen reduction of MoF/sub 6/. The pressure and temperature ranges covered were 0.9-10 torr and 250⁰C to 400⁰C, respectively. The rate of molybdenum deposition showed a square root dependence on the hydrogen partial pressure and no dependence on the MoF/sub 6/ partial pressure. The molybdenum film characteristics were dependent on the deposition conditions. Higher temperatures and pressures appeared to favor the formation of molybdenum silicide films near the molybdenum-silicon interface

[en] The deposition properties of selective tungsten have been investigated as a function of deposition temperature, pressure and a flow configuration, using a novel CVD equipment ERA-1000. The selective deposition is found to be a rate-limited process with an activation energy of 0.38eV, whose value is significantly lower than 0.7eV observed in previous works. It is also found that the deposition properties are affected by flow configuration. Turbulence favors the silicon consumption in filling contacts, or leads to the selectivity breakdown in filling vias after glow discharge treatment. These observations and the the discrepancy in activation energies are discussed

[en] Tungsten as a contact metal is selectively deposited at 300⁰C to a thickness of 430A onto p-n junctions formed in silicon by implanting B/sup +/, BF/sub 2//sup +/ and P/sup +/ over the dose range of 8 x 10/sup 14/ to 5 x 10/sup 15/ ions/cm/sup 2/. Electrical activation with minimum dopant diffusion is done by rapid thermal annealing for 10 sec at 950⁰C. The specific contact resistance and implanted layer sheet resistance are measured using Kelvin cross bridge, sheet end, and transmission line model structures. The effect of 30 min post-metallization annealing in N/sub 2/ over the temperature range of 450 to 550⁰C on these measurements is studied. Data shows that the specific contact resistance is not degraded up to at least 480⁰C, is lower in p/sup +/- than n/sup +/-Si at low doses, and is lower with BF/sub 2//sup +/ than B/sup +/ at the same dose. These results are not influenced by the choice of test structure and the dimensions of the contacts. Similarly, the junction leakage is not affected up to at least 480⁰C implying the effectiveness of the tungsten as a diffusion barrier