Fabrication of dislocation-free Si films under uniaxial tension on porous Si compliant substrates

This paper presents a method for fabricating uniaxially as well as biaxially strained Si films on porous Si substrates. Single crystalline Si films of ~ 150 nm thickness on top of porous Si substrate can be routinely obtained by self-limiting anodization of heavily doped p-type substrates with epitaxially grown thin Si overlayers. The typical structure of our samples has the porous Si region in square shape in the center of the sample surrounded by bulk Si analogous to a picture in a frame. The porous Si region undergoes volume expansion upon oxidation at low temperature (~ 500 °C) in steam. The rigid bulk Si frame constrains the porous Si region preventing it from expansion along the direction of the substrate surface. The expansion can be either uniaxial or biaxial along the sample surface if two opposite stripes of bulk Si or all four sides are removed. In this report, we describe uniaxial tensile strain of 0.83% observed in a 150 nm thick Si film without dislocation or crack.