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The influence of stress on growth instabilities on Si substrates

机译：应力对硅衬底上生长不稳定性的影响

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The growth instabilities that develop during growth on Si substrates lead to a sinusoidal-like morphology In this paper we investigate the role of the two main parameters that influence the development of surface undulations: the surface atomic configuration of the substrate and the external stress applied to the growing film. We characterize the amplitude and the correlation length of the surface profiles by reflectivity measurements, high resolution electron microscopy (HREM) and atomic force microscopy (AFM). Concerning the role of the atomic configuration, we performed a series of experiments on various substrate misorientations (from Si(111) to high miscut angles). We show that a critical step density is necessary for the nucleation of the instability. Indeed, we find that both Si and Si_(1-x)Ge_x deposits present a perfect 2D surface when grown on singular Si(111). In contrast, in the same experimental conditions, instabilities develop on vicinal substrates from a misorientation of 2 deg and amplify with the miscut angle up to 10 deg off. Concerning the effect of stress, we find that the biaxial compressive stress applied to the growing film during Si_(1-x)Ge_x heteroepitaxy dramatically enhances the instability development. Indeed, if we compare the growth modes of Si and Si_(1-x)Ge_x (x=0.3) on 10 deg off Si(111) we find that a 10 nm thick Si_(0.7)Ge_(0.3) layer (approx 1.2precent misfit) displays an undulation comparable to that obtained for a 500 nm thick Si film. HREM analysis shows that the undulation consists of a series of low energy facets created by a step bunching mechanism. We suggest that the onset of the instability could be attributed to a change in the nature of the interactions between steps at a critical step density, due to local stresses at the step edges. The evolution of the phenomenon is then kinetically controlled by various kinetic factors (growth temperature, local flux variations, doping level, presence of H...). Ultimately, the undulatory morphology which is a metastable state kinetically evolves towards a faceted equilibrium shape.
机译：在Si衬底上生长过程中出现的生长不稳定性导致了类似正弦形的形态。在本文中，我们研究了影响表面起伏发展的两个主要参数的作用：衬底的表面原子构型和施加于衬底上的外部应力成长中的电影。我们通过反射率测量，高分辨率电子显微镜（HREM）和原子力显微镜（AFM）来表征表面轮廓的振幅和相关长度。关于原子构型的作用，我们对各种衬底取向错误（从Si（111）到大错切角）进行了一系列实验。我们表明，关键步密度对于不稳定性的成核是必要的。确实，我们发现当在奇异的Si（111）上生长时，Si和Si_（1-x）Ge_x沉积物都呈现出完美的二维表面。相比之下，在相同的实验条件下，相邻基材的不稳定性会因2度的错误取向而发展，并随着错误切割的角度最大偏离10度而放大。关于应力的影响，我们发现在Si_（1-x）Ge_x异质外延过程中施加到生长膜的双轴压缩应力显着增强了不稳定性。确实，如果我们比较Si和Si_（1-x）Ge_x（x = 0.3）在距Si（111）10度处的生长模式，我们会发现10 nm厚的Si_（0.7）Ge_（0.3）层（约1.2）百分比不匹配）显示出的起伏可与500 nm厚的Si膜相比。 HREM分析表明，起伏由阶梯聚束机制产生的一系列低能面组成。我们建议，由于台阶边缘处的局部应力，不稳定的起因可以归因于台阶之间在临界台阶密度下相互作用的性质的变化。然后，通过各种动力学因素（生长温度，局部通量变化，掺杂水平，H ...的存在）对现象的演化进行动力学控制。最终，作为亚稳态的波状形态在动力学上朝着刻面平衡形状发展。

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