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.

Chemical vapor deposited (CVD) tungsten silicide films were formed by a cold wall reactor. These films were annealed in N2 to investigate changes in resistivity, composition, thickness, and impurity. The change in resistivity after 1000~ annealing becomes larger as the film reaches the stoichiometric value. A composition change occurs in a film whose composition Si/W is more than 2.6. Excess Si in the WSi, films (x > 2.6) is segregated in the boundary between WSi~. and poly-Si. A thickness change of about 15% occurs after 1000~ annealing at WSi~.4 on SiO~; this value is smaller than the calculated value. F and H, which are impurities in WSi, films decrease gradually and diffuse into gate SiO~ after 1000~ annealing.Progress of metal oxide semiconductor (MOS) large scale integrated circuits (LSI) is remarkably fast. Since the one kilo bit dynamic random access memory (1 Kbit DRAM) was developed in 1970, integration has advanced 4 times every 3 years. Now, one mega bit (1 Mbit) DRAM has been manufactured as a trial. The design rule for 1 Mbit DRAM is 1.2-1.3 #m, and the cell area has become very small: ranging from 20 to 35 /~m ~. For this reason, new capacitor structures such as trench and stacked capacitors are used (1-4). TiSi~, TaSi~, and other refractory metal silicides with a base layer of poly-Si and refractory metals such as W are being used as interconnection materials.The reason for employing refractory metals or refractory metal silicides is that as the linewidth becomes narrower and line length longer, resulting in high densification of devices, the signal propagation delay times become larger with the usually used poly-Si interconnection. Currently, there are two methods for forming these films: the physical vapor deposition (PVD) method, and the chemical vapor deposition (CVD) method.Among these methods, the CVD method is frequently used because of good step coverage. For example, we refer to the studies on deposition of WSi2 films by plasma CVD (5, 6). The low pressure chemical vapor deposited WSi, film, developed by Brors et al., however, is beginning to be widely used because of lower contamination and resistivity (7). Detailed reports on resistivity and capacitance-voltage characteristics have already been written.Generally, electrical characteristics degrade in the reaction between poly-Si and SiO~ during high temperature annealing (8). Consequently, it is necessary to study reactions and composition changes which include changes of F and H in the WSi, film by annealing; the mechanism of change also needs to be studied. Hara, et at. reported that reaction between WSi, film and the reaction between poly-Si and SiO.2 begins at 1000~ (9).We report on the changes in resistivity, composition, and behavior of F and H as well as the decreasing film thickness after annealing. LOW PRESSURE WSi x CVD SYSTEM MASS FLOW F~CONTROLLER L WF6 He Sill 4 t EACTORIuLF He VALVEI PUMP VENT ~ RF Fig. 1. Schematic diagram of the cold wall CVD equipment ExperimentalWSi~ films were formed by cold wall CVD (see Fig. 1). WF6...

Tungsten silicide films were formed by the chemical vapor deposition method using the reaction WF6 and Si2H6 . The deposition rate, resistivity, composition, stress, crystal structure, and content of impurities were studied and compared with tungsten silicide films deposited by reaction of WF6 and SiH4 . The tungsten silicide films made using Si2H6 have a higher deposition rate and higher Si concentration than those made by using SiH4 at the same substrate temperature. For these reasons, the tungsten silicide films made by using Si2H6 were found to have a resistivity that is a little higher and, after annealing, a stress that is smaller than that made by SiH4 . Also, the resistance of tungsten silicide to peeling is larger than that of the film made by using SiH4 . The crystal structure of the WSix films made by Si2H6 is almost the same as that made by SiH4 ; however, a tetragonal W5Si3 structure easily forms even in Si‐rich films of WSi2.6 . Content of fluorine in films made by Si2H6 is smaller than that in films made by SiH4 .

It 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.

The reaction between chemical vapor deposited (CVD) tungsten silicide (WSix) film and aluminum film was investigated. As-deposited and annealed CVD-WSix films were used to react with aluminum film at 500~ 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 CVD-WSi~ film changed from the initial value of 2.4 to 4.0. This is due to diffusion of tungsten atoms from the as-deposited CVD-WSi~ film into the aluminum film, however, few silicon atoms diffuse into the aluminum film. On the other hand, in annealed CVD-WSix film, the composition ratio of Si/W remains unchanged from the reaction at 500~Recently, refractory metal silicides were used instead of doped polycrystalline silicon as a low resistivity electrical interconnect and gate electrode material in very large scale integrated circuits (VLSI) (1). The reason for employing refractory metal silicides is that, as the line width becomes narrower and line length longer resulting in high density circuits, signal propagation delay times become larger with doped polycrystalline silicon.WSix, MoSix, TiSix, and TaSix are known as refractory metal silicides. Of these metal silicides, the CVD-WSix film developed by Saraswat et al. is widely used because of higher purity, lower resistance, and better step coverage than sputtered WSix film (2-4). The resistivity, oxidation rate, contact resistance, adhesion to the silicon substrate, stress breakdown voltage of the gate SiOz, and the interaction with polycrystalline silicon have been investigated in order to characterize CVD-WSix and other silicide films (5-14). However, there are few papers investigating the interaction between CVD-WSix and aluminum films (15).We investigated the reaction between CVD-WSix film and evaporated aluminum film by RBS and SIMS. In this paper, the composition change of CVD-WSix films, and the profiles of chemical concentration of the composition and impurity atoms before and after reaction with aluminum film are presented. ExperimentalWSix films were deposited using cold-wall CVD equipment. The deposition temperature was 325~ and the deposition pressure was 40 Pa. The reacting gases were WF~ and Sill4 diluted with He. The flow rates of WF6 and Sill4 were 2 and 120 cm3/min, respectively, and the flow rate of He was 400 cm3/min. The film was deposited on oxidized 4 in. Si wafers. The thickness of the films were 2000A. The annealing was performed at 600~176 for 30 min in nitrogen in a diffusion furnace to avoid oxygen contamination. Immediately after removing the native oxide on CVDWSix film by 1.25% diluted HF, about 1 ~m of aluminum was evaporated on the film. The reaction between the CVD-WSix film and the aluminum film was performed at 500~ for 30-240 rain in nitrogen...