Growth And Research Of Strained-Si/SiGe/Si Heterojunction

SiGe is an important semiconductor material after Si and GaAs. SiGe has some better characterictics than Si. Its band can be adjusted and we can design heterojunction material structure with SiGe. Besides, SiGe is compatible with Si in semiconductor process. So SiGe devices have a high performance but need low cost. In recent years, based on SiGe, the technology of strained-Si is developing, which has highly improved the frequency and speed of CMOS and become an important means of channel engineering.In this paper, we use the CVD technology to grow SiGe/Si heterojunction material and then grow Strained-Si film. Research the impact of growth parameters on the quality of SiGe alloy and the strain of Si flim. The main work of this thesis is as follows:1. Silicon films are grown on Si(100) substrate at690℃,720℃,750℃. Research the influence of growth temperature on films’quality:when growth temperature is690℃, the silicon film is a mixed phase with crystalline and amorphous silicon, the crystallization rate is22.58%, while which is highly improved at77.34%when the growth temperature is720℃; then the sample grown at750℃is crystalline silicon, whose crystallization rate is up to98.78%. The temperature’s improving is good for the crystalline phase selection and increases crystallization rate.On Si(100) substrate with SiO2mask, silicon film is grown to calculate the growth rate and the relaxation time of growth. At the temperature of720℃,750℃and780℃,the growth rates are0.5nm/min,4.0nm/min,7.47nm/min and relaxation time of growth is10.629min,7.17min,4.867min, respectively. The increase of temperature makes the gas react more intensely, accelerates the growth rate and reduces the relaxation time of growth.2. SiGe/Si heteroj unction material is grown with single source GeH4at different temperatures and different flows of GeH4. Through analysis we get:temperature is too low to adsorb or resolve Ge atom and the diffuse of Si、Ge atom is not obvious, the quality of SiGe/Si heterojunction material is not good; then improving temperature leads to the concentration of Ge atom at the surface and forms Ge film. The SiGe/Si heterojunction material is best when grown at670℃. In addition, the high flow of GeH4can lead to large accumulation of Ge atoms at surface and the Si atoms in the Si substrate can’t fully diffuse to surface. So Ge film will easily form at surface,which is not conductive to the formation of SiGe/Si heterojunction material.3. Strained-Si film is grown on SiGe/Si heterojunction. Research the strain of silicon film when different growth temperatures and different film thickness. Used the Raman scattering method, the vibration peak of strained-Si is identified. The results show that the silicon film has strain on SiGe/Si heterojunction grown at640℃and670℃but no strain has found in the film on SiGe/Si heterojunction which is grown at700℃. The reason is high temperature can easily produce a Ge film on the surface and the silicon on it has a lattice mismatch and dislocation, thereby release the stress and is not suitable for producing strained silicon.Change the growth time of silicon. The stress decreases when the epitaxial Si film thickness increasese. The strain of silicon is biggest when growth time is40min but the strain disappears when the growth time is80min, the silicon film is relaxation.4. The method of capacitance-voltage(C-V) is used to characterize the SiGe/Si heterojunction material structure and energy band feature. And then obtain the carrier distribution with depth, the interface of heterojunction, discontinuity of energy band, the thickness of each material layer, component of Ge at Ge rich SiGe layer. The data is reliable and feasible by comparing to the results from SEM and EDS.C-V characteristic of Strained-Si/SiGe/Si multi-heterojuncion material shows carrier distribution with depth, the interface of heterojunction, discontinuity of energy band, the thickness of each material layer. The results:with temperature increasing, the atom diffuse intensely to strengthen the thickness of SiGe layer. In addition, we found the carrier concentration at the surface and substrate have no relation with the temperature.