Selectively Grown SiGe And Metal-Induced Growth Of Poly-SiGe Based On UHVCVD

Silicon Germanium is an alloy of semiconductor material, which is formed through the covalent bonding between element Si and Ge atoms. SiGe is superior to Si because of band gap adjustment and strain engineering etc. SiGe is compatible with the state-of-art advanced CMOS technology. So SiGe plays an important role in today's IC. With the technology developing, SiGe is exposed to the continuous problems, once these problems are resolved, SiGe would be the driving force of extending Si-based applications and improving the performance of devices.In this dissertation, we discussed two issues about SiGe. Firstly, as the devices is scaling down, merely epitaxy of SiGe is not sufficient for the application, for example the raised S/D MOSFET, Selective growth is the key step, but the existing methods which realize the selective growth need relatively high temperature, so it's necessary to bring out the solution that can realize selectively growth of SiGe at low temperature. Secondly, as far as poly-SiGe is concerned, poly-SiGe has a promising future in application, but the present growth method can't prepare the films with high carrier mobility, due to possible defects in the materials and Ge segregation, so poly-SiGe has poor performance as active region of device. The priority is to develop the feasible growth method.Based on the above analysis, we adopt an advanced technology called UHVCVD to grow single crystalline or polycrystalline SiGe films; this technology is characterized with ultraclean environment and growth of SiGe thin films at low temperature and low pressure. These factors guarantee to obtain high quality films. Therefore, we use this technology to investigate the growth of SiGe thin films, and achieve the following results:(1) The effect of growth atmosphere on selective growth of SiGe thin films by UHVCVD was investigated, and it is shown that when the temperature is above 550℃, Ge content has an apparent effect on the selective growth. And the interaction between H₂ and GeH₄ became important at temperature below 550°C. In comparison with various growth parameters, the optimum growth atmosphere is determined: the substrate temperature of 580°C, the flow ratio of SiH4 to GeH4 (90%H2) is 5:5sccm. Under such environment, the incubation time can reach up to 40min.(2) Based on the above conclusion, the prototype of SBD has been fabricated. The result shows that not only the SBD with selective growth of SiGe simplify the fabrication process, but also the reverse saturation current is lowered by two or three orders compared with the regular SiGe SBD.(3) It's firstly reported that poly-SiGe thin films was prepared by a novel method called MIG that is a combination of MIC and CVD. The key point is poly-SiGe heteroepitaxial grow on metal silicide, the advantage of this method is that films grow accompanied by crystallization without annealing, and the growth temperature is below 600 °C, so glass can be used as the substrate, and compared with other CVD methods, there is no incubation time;(4) The effect of thickness of Ni on the grain size of SiGe thin films was also investigated, and pointed that it has crest at certain thickness, when the thickness of Ni is 60nm, the cluster size can reach 500⁶00nm.(5) In the heterostructure of SiGe/Ni, strain relaxation is the driving force for the morphology formation of Poly-SiGe. At lOPa, a continuous film can be formed, with uniform grain size, while at pressure from O.lPa to lOPa, densely packed SiGe whiskers were formed.(6) Using this method, it's very convenient to utilize the Ni silicide as self-aligned ohmic contact of SBD, the experiments have proven that the SBD based on this method has better rectification characteristic and the rectification ratio can reach up to 8000.