Development of high electron mobility Si transistors with a strained Si_<1-y>C_y structure

应变硅与IV族半导体合金技术作为一种有前途的技术，被广泛研究，因为与块体硅相比，它可以提高载流子迁移率。我们重点研究了应变Si/应变松弛Si <1-y>C_y结构，这些结构适用于具有新结构的器件，如垂直mosfet。在该结构中，在应变松弛的Si_<1-y>C_Y层上生长的应变Si层在平面方向上具有压应变，并且在垂直方向上载流子迁移率有望增强。为了实现这种结构，在Si上生长松弛的Si_<1-y>C_y层是很重要的。本研究在Si缓冲材料上生长了碳组成恒定的Si_<1-y>C_y单层薄膜，并通过改变薄膜厚度对其应变松弛机制进行了广泛的研究。实验结果表明，Si_<1-y>C_y层的弛豫比随厚度的增加而增大，其中厚度为1800 nm的Si_<99.0>C_<1.0>层的弛豫比可达40%。然而，通过透射电镜（TEM）观察发现，薄膜中存在许多层错和孪晶缺陷。Si_<1-y>C_y层进入应变Si的缺陷阻碍了应变Si层良好的晶体生长。相比之下，成分分级的Si_<1-x>Ge_x层被广泛用作应变松弛Si_<1-x>Ge_x结构的缓冲层。由于在低应变下发生位错成核，阶梯渐变的Si_<1-x>Ge_x缓冲层也得到了高质量的薄膜。因此，在本项目中，我们新沉积了具有阶梯渐变碳成分的Si_<1-y>C_y堆叠层（阶梯渐变Si_<1-y>C_y结构），以生长应变松弛的Si_<1-y>C_y薄膜，并研究了该结构的晶格动力学。采用Si_2H_6和SiH_3CH_3气源MBE系统制备了Si和Si_<1-y>C_y薄膜。用高分辨x射线衍射法测定了Si_<1-y>C_y的取代碳含量和晶格参数。x射线倒易晶格空间映射表明，Si_<1-y>C_y阶跃渐变结构中各层弛豫比从下到上依次增大，表明其弛豫机制与Si_<1-x>Ge_x阶跃渐变结构不同。通过使用阶梯渐变的Si_<1-y>C_y结构，我们成功地获得了比具有恒定碳组成的单一Si_<1-y>C_y缓冲结构更高的弛豫比。当膜总厚度为1000 nm时，Si_<99.0>C_<1.0>缓冲层的弛豫率为15%，而阶梯状Si_<1-y>C_y结构的顶部Si_<98.9>C_<1.1>缓冲层的弛豫率为60%。从这些结果可以看出，步进梯度Si_<1-y>C_y结构对于实现适用于垂直mosfet的应变Si/应变松弛Si_<1-y>C_y结构非常重要。少

Strained Si technology with group IV semiconductor alloys has been widely researched as a promising technique for the improvement of the performance of Si-based MOSFETs because of enhancement of carrier mobility compared with bulk Si. We have focused on strained Si/strain-relaxed Si_<1-y>C_y structures which are applicable to the devices with a new structure such as a vertical MOSFETs. In this structure, a strained Si layer grown on the strain-relaxed Si_<1-y>C_Y layer has compressive strain in the in-plane direction and an enhancement of carrier mobility in the vertical direction is expected. In order to realize this structure, growth of the relaxed Si_<1-y>C_y layer on Si is important.In our work, we grew a single Si_<1-y>C_y layer with a constant carbon composition on a Si buffer and widely studied the strain relaxation mechanism by varying its thickness. From the experiments, it was found that the relaxation ratio of the Si_<1-y>C_y layer increased with increasing the thickness and … More that the ratio of 40% was achieved by using a Si_<99.0>C_<1.0> layer with a thickness of 1800 nm. However, a cross sectional transmission electron microscopy (TEM) observation revealed that there were many stacking faults and twin defects in the films. The defects from the Si_<1-y>C_y layer into the strained Si hindered good crystal growth of the strained Si layer. In contrast, the compositionally graded Si_<1-x>Ge_x layers have been widely used as a buffer of the strain-relaxed Si_<1-x>Ge_x structures. The step-graded Si_<1-x>Ge_x buffer layers are also resulted in high quality films because dislocation nucleation occurs at low strain.Therefore, in this project, we have newly deposited the stacked Si_<1-y>C_y layers with step-graded carbon compositions (step-graded Si_<1-y>C_y structure) to grow strain-relaxed Si_<1-y>C_y films and investigated lattice dynamics of the structure. The Si and Si_<1-y>C_y films were deposited by a gas-source MBE system using Si_2H_6 and SiH_3CH_3 gases. The substitutional carbon contents and the lattice parameters of Si_<1-y>C_y were evaluated by high resolution X-ray diffractometry. X-ray reciprocal lattice space mappings showed that the relaxation ratio of the each layer increased from the bottom to the top layers in the step-graded Si_<1-y>C_y structures, implying different relaxation mechanisms from step-graded Si_<1-x>Ge_x structures. By using the step-graded Si_<1-y>C_y structure, we have successfully achieved higher relaxation ratios compared with a single Si_<1-y>C_y buffer structure with a constant carbon composition. When the total film thickness was 1000 nm, a Si_<99.0>C_<1.0> buffer layer showed the relaxation ratio of 15%, while the top Si_<98.9>C_<1.1> layer of the step-graded Si_<1-y>C_y structure showed the relaxation ratio of 60%. From these results, it was concluded that step-graded Si_<1-y>C_y structures were important to realize strained Si/strain-relaxed Si_<1-y>C_y structures which are applicable to the vertical MOSFETs. Less