Ryosuke Shimizu

Shape transformation of silicon trenches during hydrogen annealing

Shape transformation of silicon trenches during annealing at high temperatures in a hydrogen ambient was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). By SEM observation of the trench profiles, we found that the rate of shape transformation increases with decreasing hydrogen pressure. Performing the simulation based on a continuum surface model, we show that the shape transformation during annealing in a hydrogen ambient is due to surface self-diffusion. By quantitative comparison of the results between the experiment and simulation, we estimated the diffusion coefficients. The obtained activation energy for surface diffusion under a hydrogen pressure of 40 Torr was much higher than that measured under ultrahigh-vacuum conditions. Furthermore, it was found by AFM observation of the trench sidewall surfaces that, during the thermal treatment, the large roughness of the as-etched trench sidewall surface decreased significantly due to surface self-diffusion of silicon atoms, resulting structures with atomically flat terraces and steps.

Predictive Model Extraction for Polysilicon Low-Pressure Chemical Vapor Deposition in a Commercial Scale Reactor

Theoretical optimization of a polysilicon low-pressure chemical vapor deposition process in a commercial scale reactor for 6 in. wafers was achieved by extracting a predictive reaction model from wafer-radial and reactor-axial deposition rate distributions. The extraction involved the radial deposition rate profile on the wafer, axial deposition rate profile in the reactor, and wafer-spacing dependence of the deposition rate at the wafer center. The deduced reaction model contains two film precursors as well as SiH 4· Based on the radial deposition rate profile, the respective sticking probabilities of these two precursors were 5 X 10 -2 and 7 X 10 -4 at 550°C. Because the two precursors could not reach the wafer center due to their high sticking probabilities, as evidenced by the low deposition rate at the wafer center, the sticking probability of SiH 4 was 1.7 X 10 -6 at 550°C with an activation energy of 161 kJ/mol. The elementary reaction simulation done here included the mass transport and the gas-phase and surface elementary reactions in the reactor. Comparison between this simulation and the experimental analysis revealed that the two film precursors probably were SiH 2 and Si2H 6 .

Analysis and modeling of low pressure chemical vapor deposition of phosphorus-doped polysilicon in commercial scale reactor

In a commercial scale low pressure chemical vapor deposition (CVD) reactor, we analyzed the elementary reaction of silane based CVD with the doping gas of phosphine. The variation of conductivity in the radial direction over a monitor wafer became significant as the phosphine gas partial pressure decreased, and it reached up to about 30% at 6.5×10−4 Pa. The radial distribution of phosphorus fraction in a film, however, was smaller than 7%. On the basis of the diffusion model of chemical species into the wafer gaps, we found that the sticking probability of phosphine is 2–5×10−5, which is 1 order of magnitude larger than the one of silane. The reaction kinetics of both silane and phosphine seems almost linear, but slight nonlinearity at high phosphine concentration range was also indicated.