Reserch On The Growth Of Strained Si/Strained Sige Film By Reduced Pressure Chemical Vapor Deposition

With the scaledown of device dimensions and getting close to its physical limit, the development of very large scale integrated (VLSI) technology is facing acute challenge. It has found that strained silicon technology is an important guarantee of the realization of the32nm or even smaller characteristic dimention technology, as the introduction of strain in the crystal lattice can enhance carrier mobility and thus improve the MOSFET performance. At present, strained silicon technology is mainly realized by the introduction of the relaxed graded buffer, which however, increases the cost of the production and precludes state-of-art lithography due to depth-focus limitations. In this paper we focus on the growth of strained Si layer directly on strained SiGe layer to decrease the thickness of the epitaxial layers, thus avoid the inherent disadvantages of the graded buffer technology.Critical thickness of strained SiGe layer was investigated during the RPCVD process. Haze values measured by SP1were used to characterize relaxations of the strained SiGe layer. Results show that critical thickness values during RPCVD process are much higher than the experimental results of People and Bean who did their experiments with MBE and the theoretical datas of Jingyun Huang. At the same time, theoretical calculation of critical thickness of strained SiGe layer grown at different temperatures reveals that growth temperatures affect the critical thickness, however, when the Ge fraction is much higher, the effects of growth temperatures are not obvious at all that can be neglected.200nm-thick strained SiGe layers with various Ge fraction were grown at different temperatures ranging from600℃to750℃. X-ray double-crystal diffraction and AFM results show that the lower of the growth temperature, the higher quality of the strained SiGe films are of. More than that, an Si buffer deposited before the SiGe layer makes little difference in the surface quality of the sub-grown SiGe layer. A20nm-thick strained Si layer was then grown at650℃on the SiGe layer selected from the samples above, Raman spectra of strained Si/Strained SiGe films reveals that the degree of strain in strained Si and SiGe is0.66%and0.94%respectively, the dislocation densities of the strained Si layer ia about8×104cm-2, which is close to that of growing on relaxed SiGe layer.The strained Si/Strained SiGe films were annealed in N2at900℃for30s and1100℃for30s respectively. AFM results show that there is no obvious change in the surface roughness of strained Si layer when anneal at900℃. However, for the strained films annealed at1100℃, there is an obvious increase of surface roughness of the strained Si layer. Besides, cross-hatches are observed in the surface, which means that there is relaxation in the strained layers with the TDD (Thread Dislocation Densities) of7.4×107cm-2.