Structural characterization by transmission electron microscopy of silicon grown over submicrometer-period gratings of deposited tungsten

The Si overgrowth of deposited W gratings, which is the most critical step in the fabrication of the overgrown version of the Si permeable base transistor, has been characterized by transmission electron microscopy. At the high temperatures (>1000 °C) normally required for the growth of single-crystal Si, the W grating reacts with both the surrounding and depositing Si to form WSi2. Despite this conversion, conventional vapor phase epitaxial techniques can be used to overgrow the grating with a single-crystal Si layer. The overgrown layer contains a low density of observed crystal defects. The fabrication procedure used for successful overgrowth and the quality of the overgrown layer are discussed.