Bottle-neck recess in a semiconductor device

Abstract

The present disclosure provides a method for fabricating a semiconductor device that includes providing a silicon substrate, forming a gate stack over the silicon substrate, performing a biased dry etching process to the substrate to remove a portion of the silicon substrate, thereby forming a recess region in the silicon substrate, performing a non-biased etching process to the recess region in the silicon substrate, thereby forming a bottle-neck shaped recess region in the silicon substrate, and epi-growing a semiconductor material in the bottle-neck shaped recess region in the silicon substrate. An embodiment may include a biased dry etching process including adding HeO2 gas and HBr gas. An embodiment may include performing a first biased dry etching process including N2 gas and performing a second biased dry etching process not including N2 gas. An embodiment may include performing an oxidation process to the recess region in the silicon substrate by adding oxygen gas to form silicon oxide on a portion of the recess region in the silicon substrate. As such, these processes form polymer protection to help form the bottle-neck shaped recess.