Measurement of residual stress in a multi-layer semiconductor heterostructure by micro-Raman spectroscopy

Si-based multilayer structures are widely used in current microelectronics. During their preparation, some inhomogeneous residual stress is induced, resulting in competition between interface mismatching and surface energy and even leading to structure failure. This work presents a methodological study on the measurement of residual stress in a multi-layer semiconductor heterostructure. Scanning electron microscopy（SEM）, micro-Raman spectroscopy（MRS）, and transmission electron microscopy（TEM） were applied to measure the geometric parameters of the multilayer structure. The relationship between the Raman spectrum and the stress/strain on the [100] and [110] crystal orientations was determined to enable surface and crosssection residual stress analyses, respectively. Based on the Raman mapping results, the distribution of residual stress along the depth of the multi-layer heterostructure was successfully obtained.

Growth of strained-Si material using low-temperature Si combined with ion implantation technology

In order to fabricate strained-Si MOSFETs,we present a method to prepare strained-Si material with highquality surface and ultra-thin SiGe virtual substrate.By sandwiching a low-temperature Si（LT-Si） layer between a Si buffer and a pseudomorphic Si_（0.8）Ge_（0.2） layer,the surface roughness root mean square（RMS） is 1.02 nm and the defect density is 10~6 cm^（-2） owing to the misfit dislocations restricted to the LT-Si layer and the threading dislocations suppressed from penetrating into the Si_（0.8）Ge_（0.2） layer.By employing P~＋ implantation and rapid thermal annealing, the strain relaxation degree of the Si_（0.8）Ge_（0.2） layer increases from 85.09%to 96.41%and relaxation is more uniform. Meanwhile,the RMS（1.1nm） varies a little and the defect density varies little.According to the results,the method of combining an LT-Si layer with ion implantation can prepare high-quality strained-Si material with a high relaxation degree and ultra-thin SiGe virtual substrate to meet the requirements of device applications.

Impact of [110]/(001) uniaxial stress on valence band structure and hole effective mass of silicon

The valence band structure and hole effective mass of silicon under a uniaxial stress in （001） surface along the [110] direction were detailedly investigated in the framework of the k. p theory. The results demonstrated that the splitting energy between the top band and the second band for tmiaxial compressive stress is bigger than that of the tensile one at the same stress magnitude, and of all common used crystallographic direction, such as [110], [001], [110] and [100], the effective mass for the top band along [110] crystallographic direction is lower under uniaxial compressive stress compared with other stresses and crystallographic directions configurations. In view of suppressing the scattering and reducing the effective mass, the [110] crystallographic direction is most favorable to be used as transport direction of the charge carrier to enhancement mobility when a uniaxial compressive stress along [110] direction is applied. The obtained results can provide a theory reference for the design and the selective of optimum stress and crystallorgraphic direction configuration ofuniaxial strained silicon devices.