2018年8月3日星期五

High pressure in situ HCl etching of Si1−xGex versus Si for advanced devices

We have studied the gaseous hydrochloric acid selective etching of SiGe versus silicon in a reduced pressure-chemical vapor deposition reactor. Non-classical metal oxide semiconductor field effect transistors (MOSFETs) architectures, such as silicon on nothing (SON) and multi-bridge channels (MBC) devices require high SiGe:Si etch selectivities in order to get rid of the sacrificial SiGe layers. We have probed the in situ HCl etching of Si and SiGe blanket layers of SiGe/Si stacks grown selectively in the Si windows of patterned wafers ('SON-like' substrates) and of SiGe/Si superlattices ('MBC-like' substrates) as a function of the reverse absolute temperature. A switch from high temperature, diffusion-limited/low temperature, Cl-desorption-limited etch regimes to a unique LT regime, together with a significant etch rate increase, has been evidenced when drastically increasing the HCl partial pressure. Very good selectivities (versus Si) have been obtained when laterally etching high Ge content Si1−xGex layers (typically ≥30%). A preferential etch by HCl of the {1 0 0} crystallographic planes compared to the {1 1 0} ones has been noticed both for the lateral etch of the 'SON-like' patterns (preferential etch of the pattern corners) and for the 'MBC-like' patterns (fullsheet (0 0 1) etch rates ≈10 times the {1 1 0} lateral etch rates). A slight etch rate difference between 'bottom-located' and 'top-located' Si1−xGex layers in Si/SiGe superlattices has also been highlighted. This etching technique is thus usable for the processing of SON or MBC devices provided that the selective {1 0 0}:{1 1 0} HCl etch reported here is taken into account.


Source:IOPscience

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