HCl Selective Etching of Si1-xGex versus Si for Silicon On Nothing and Multi Gate Devices

Abstract

We have studied the low temperature (~ 650oC), high HCl partial pressure (180 Torr) selective etch of SiGe versus Si inside a RP-CVD reactor. The surface roughness strongly increases while vertically etching fullsheet Si1-xGex layers. We have also laterally etched (Si / SiGe) multilayers patterned along the <110> directions. The best selectivities and the highest SiGe etch rates have been obtained for the highest Ge content studied, i.e. 40%. <111> facets have been revealed at the end of tunnels. A strong increase (x 18) of the <110> lateral HCl etch rates has been evidenced when increasing the Si0.6Ge0.4 layer thickness from 5 up to 20 nm. Very good SiGe versus Si selectivities have been obtained with slightly higher etch rates than on bulk Si when HCl etching (Si / SiGe) multilayers grown on Si0.8Ge0.2 virtual substrates. Finally, a strong HCl etch in-plane anisotropy has always been evidenced. <100> oriented pattern corners are indeed far more etched than <110> oriented edges.

Very Low Temperature (Cyclic) Deposition / Etch of In Situ Boron-Doped SiGe Raised Sources and Drains

“…Such a conclusion is also supported by Ref. 29 findings, where we showed that the surface roughness of strained, blanket Si 1-x Ge x layers (x = 0.3-0.5) definitely increased with the etched thickness. Flat surfaces were recovered as soon as the underlying Si substrates were reached.…”

HCl Selective Etching of SiGe versus Si in Stacks Grown on (110)

“…(21) and the 180 Torr value used in Refs. (22)(23) to proceed with etches on (100). Given that there is roughly a 50°C offset for a given Si etch rate in-between (100) and (110) (15), we should be able with P part.…”

“…This ratio, which is to some extent the selectivity, is equal to 4 only for 20% of Ge. Such a value is too low for a proper Si 0.8 Ge 0.2 versus Si selective removal (as in SiGe/Si stacks grown on (100) (21)(22)(23)). Significantly higher ratios, which increase as the temperature decreases and/or the Ge content increases, are obtained for Ge concentrations higher than 20%.…”

“…Selectivity in (100) stacks can also be achieved in wet benches or tools with mixtures of hydrofluoric acid, nitric acid or hydrogen peroxide and acetic acid diluted in deionized water (19)(20). Finally, gaseous hydrochloric acid (HCl) can also be used for such a selective etch in stacks grown on (100) (19), (21)(22)(23). Initial studies conducted at low HCl partial pressures (thus rather high etch temperatures) showed that lateral selectivity was indeed achievable for Ge contents superior to 20%, with however the presence of facets at the Si tunnel entrances (21).…”

“…Initial studies conducted at low HCl partial pressures (thus rather high etch temperatures) showed that lateral selectivity was indeed achievable for Ge contents superior to 20%, with however the presence of facets at the Si tunnel entrances (21). Switching afterwards to high HCl partial pressures (thus lower temperatures) provided better SiGe versus Si selectivities and reduced faceting (22)(23). The following features were identified in SiGe/Si stacks grown on (100): (i)…”