Max Planck Institute of Microstructure Physics, Weinberg 2, Halle (Saale), 06120, Germany.
Nanotechnology. 2011 Jan 28;22(4):045701. doi: 10.1088/0957-4484/22/4/045701. Epub 2010 Dec 15.
We provide evidence of nanopatterning-induced bending of an ultrathin tensile strained silicon layer directly on oxide. This strained layer is achieved through the epitaxial growth of silicon on a Si(0.84)Ge(0.16) virtual substrate and subsequent transfer onto a SiO(2)-capped silicon substrate by combining hydrophilic wafer bonding and the ion-cut process. Using high resolution transmission electron microscopy, we found that the upper face of the strained silicon nanostructures fabricated from the obtained heterostructure using electron beam lithography and dry reactive ion etching displays a concave shape. This bending results from the free-surface-induced strain relaxation, which implies lattice out-of-plane expansion near the edges and concomitant contraction at the center. For a ∼ 110 nm × 400 nm × 20 nm nanostructure, the bending is associated with an angle of 1.5° between the [Formula: see text] vertical atomic planes at the edges of the ∼ 110 nm side. No bending is, however, observed at the strained Si/SiO(2) interface. This phenomenon cannot be explained by the classical Stoney's formula or related formulations developed for nanoscale thin films. Here we employed a continuum mechanical approach to describe these observations using three-dimensional numerical calculations of relaxation-induced lattice displacements.
我们提供了在氧化物上直接对超薄膜进行拉伸应变诱导弯曲的纳米图案化的证据。通过在 Si(0.84)Ge(0.16)虚拟衬底上外延生长硅，并通过结合亲水晶圆键合和离子切割工艺将其转移到 SiO(2)覆盖的硅衬底上，实现了这种应变层。使用高分辨率透射电子显微镜，我们发现通过电子束光刻和干法反应离子刻蚀从所得异质结构制造的应变硅纳米结构的上表面呈现出凹形。这种弯曲是由自由表面诱导的应变松弛引起的，这意味着在边缘附近的面外晶格扩展和同时在中心的收缩。对于一个 ∼ 110 nm × 400 nm × 20 nm 的纳米结构，弯曲与 ∼ 110 nm 边的边缘的[Formula: see text]垂直原子平面之间的 1.5°角相关。然而，在应变 Si/SiO(2)界面处没有观察到弯曲。这种现象不能用经典的 Stoney 公式或为纳米薄膜开发的相关公式来解释。在这里，我们使用三维数值计算松弛诱导的晶格位移来描述这些观察结果，采用了连续力学方法。
