Selective and rapid heating method for polycrystallization of amorphous Si using microwave plasma irradiation

We have developed a new technique which enables the selective and rapid heating of semiconductor films with the high conductivity and/or high dielectric constant by using microwave plasma irradiation. In order to apply the technique to crystallization of amorphous Si, a metal such as Ni, Pt and PtPd is deposited selectively on amorphous layers, since amorphous Si has neither high conductivity nor high dielectric constant. It will be shown in this present that the temperature ramping rate and attainable highest temperature by plasma irradiation depend on gas species of the atmosphere, gas pressure and metal species. A 100 nm amorphous silicon film was deposited on a quartz substrate by molecular beam deposition method, and a Ni layer was selectively formed on the amorphous film. Then, the sample was put in a vacuum chamber and irradiated in some gas atmosphere by microwave plasma with the frequency of 2.45GH_z and the output electric power of 1kW. The color of the entire Si region of the sample was changed from red to yellow by plasma irradiation, which means that the amorphous film changes to crystalline one. The cross-sectional STEM observation shows that the sample is poly-crystallized by plasma irradiation. During irradiation, some region of Ni film evaporated, which implies that the temperature of Ni increased up to at least 1000℃. The temperature of the Si region, which is 1 mm apart from the edge of the nickel layer, increases immediately after the plasma irradiation in the hydrogen ambient. The temperature depends on the pressure, and the highest temperature of 900℃ is achieved at about 150P_a. The highest temperatures of the Si regions are obtained as functions of the pressures of helium, nitrogen and argon in addition to hydrogen. The highest temperatures are at most 400℃ in all pressure regions independently of gas species except hydrogen, which suggests that the unstable and excited hydrogen-related species such as radicals and atoms also participate in the heating process.