| 摘要 |
A method is disclosed for fabricating a semiconductor device structure which include a thin foot charge drain beneath the device on a silicon substrate. The structures retain high speed operation of SOI devices. In various embodiments, the invention includes forming a first diffusion-barrier layer on a semiconductor substrate, patterning the said first diffusion-barrier layer and the said silicon substrate to certain depth to form a trench, forming a second diffusion-barrier layer and patterning the said second diffusion-barrier layer to form a first spacer on the sidewall of the trench. Performing a directional etching to expose a portion of the sidewall of the trench. Introducing dopants into the said exposed sidewall to form a doped regions near the sidewall. Performing an isotropic etching using halogen gas plasma. Since the etch-rate of the doped silicon is higher than the undoped silicon, the doped silicon is easily and rapidly etched first, as the undoped silicon portion is exposed, the etching rate is substantially decreased or stopped forming a thin foot underneath the silicon island.
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