Hitoshi Tsunoda

Roughness of Silicon Surface Heated in Hydrogen Ambient

Surface roughness of a silicon wafer heated at 800 to 1100°C under atmospheric pressure in hydrogen ambient is studied. Haze of the surface becomes intense as the heating temperature is decreased. However, haze of the surface does not appear when the native oxide film on the silicon surface is completely removed. Atomic force microscopy images show that the surface heated at 900°C has many small pits whose shapes depend on the crystal plane, that is, squares for the (100) plane and triangles for the (111) plane. The pits are formed due to the difference in the chemical reaction rates between hydrogen-silicon and hydrogen-silicon dioxide. Small areas of bare silicon surface caused by the incomplete removal of the native oxide film are etched by hydrogen gas at a faster rate than the native oxide islands. The behavior of surface roughness with pressure and heating time agrees well with that predicted by the pit formation model in this study.

Change in Microroughness of a Silicon Surface during In Situ Cleaning Using HF and HCl Gases

The change in microroughness of a silicon substrate surface is studied at each step of an in situ cleaning method performed entirely in a hydrogen ambient at atmospheric pressure, which comprises the removal of native oxide film using hydrogen fluoride gas and the removal of an organic hydrocarbon film using hydrogen chloride gas. The root-mean-square average roughness and the power spectral density show that no surface roughening is caused by this in situ cleaning method. Additionally, it is shown in this study that heat-treatment at 1223 K in a hydrogen ambient at atmospheric pressure can smooth the silicon substrate surface when the surface is bare. The effect of the removal of an organic hydrocarbon film using hydrogen chloride gas on the morphology of the silicon substrate surface is also studied.

Effect of Transport Phenomena on Boron Concentration Profiles in Silicon Epitaxial Wafers

The boron concentration profile in silicon epitaxial wafers grown under atmospheric pressure was investigated in two types of epitaxial reactors. Transport phenomena are studied both by numerical calculations or by a gas flow visualization technique. The difference between the measured boron concentration profile and the calculated one using Ficks law was assumed to be due to autodoping. In epitaxial wafers grown at temperatures lower than 1273 K on a p-type substrate in a single-wafer horizontal reactor which has no recirculation of gas, the boron concentration profile changed abruptly at the interface between the epitaxial film and the substrate since the profile is formed only due to solid-state diffusion. In contrast, in a pancake reactor having large recirculation of gas, a gradual change in the boron concentration profile was observed due to autodoping via the gas phase. In conclusion, large amounts of recirculation of gas in an epitaxial reactor should be avoided to obtain an abrupt boron concentration profile.