In this study,the growth kinetics of SiGe in a reduced pressure chemical vapor deposition system using dichlorosilane(SiH2Cl2) and germane(GeH4) as the Si and Ge precursors were investigated.The SiGe growth rate and Ge content were found to depend on the deposition temperature,GeH4 flow and reactor chamber pressure.The SiGe growth rate escalates with increasing deposition temperature,while the Ge content is reduced.The SiGe growth rate accelerates with increasing GeH4 flow,while the Ge content increases more slowly.According to the experimental data,a new relationship between Ge content(x) and F(GeH4)/F(SiH2Cl2) mass flow ratio is deduced:x2.5/(1x) = nF(GeH4)/F(SiH2Cl2).The SiGe growth rate and Ge content improve with increasing reactor chamber pressure.By selecting proper precursor flows and reactor pressure,SiGe films with the same Ge content can be fabricated at various temperatures.However,the quality of the SiGe crystals is clearly dependent on the deposition temperature.At lower deposition temperature,higher crystalline quality is achieved.Because the growth rate dramatically drops with lower temperatures,the optimum growth temperature must be a compromise between the crystalline quality and the growth rate.X-ray diffraction,Raman scattering spectroscopy and atomic force microscopy results indicate that 650°C is the optimum temperature for fabrication of Si0.75Ge0.25 film.
XUE ZhongYingCHEN DaLIU LinJieJIANG HaiTaoBIAN JianTaoWEI XingDI ZengFengZHANG MiaoWANG Xi
In this paper,we investigated the dose window of forming a continuous buried oxide(BOX) layer by single implantation at the implantation energy of 200 keV. Then,an improved two-step implantation process with second implantation dose of 3×1015 cm-2 was developed to fabricate high quality separation by implanted oxygen(SIMOX) silicon on insulator(SOI) wafers. Compared with traditional single implantation,the implantation dose is reduced by 18.2%. In addition,the thickness and uniformity of the BOX layers were evaluated by spectroscopic ellipsometry. Defect-free top Si as well as atomic-scale sharp top Si/buried oxide interfaces were observed by transmission electron microscopy,indicating a high crystal quality and a perfect structure of the SOI fabricated by two step implantation. The top Si/BOX interface morphology of the SOI wafers fabricated by single or two-step implantation was also investigated by atomic force microscopy.
During the irradiation of Ge surface with Ga+ions up to 1017ions·cm-2, various patterns from ordered honeycomb to nanograss structure appear to be decided by the ion beam energy. The resulting surface morphologies have been studied by scanning electron microscopy and atomic force microscopy. For high energy Ga+irradiation(16–30 ke V), by controlling the ion fluence, we have captured that the equilibrium nanograss morphology also originates from the ordered honeycomb structure. When honeycomb holes are formed by ion erosion, heterogeneous distribution of the deposited energy along the holes leads to viscous flow from the bottom to the plateau. Redistribution of target atoms results in the growth of protuberances on the plateau, and finally the pattern evolution from honeycomb to nanograss with an equilibrium condition.
