Selectively etching for nanowires
A method for selectively etching silicon germanium with respect to silicon in a stack on a chuck in an etch chamber is provided. The chuck is maintained at a temperature below 15° C. The stack is exposed to an etch gas comprising a fluorine containing gas to selectively etch silicon germanium with respect to silicon.
1 . A method for forming silicon nanowires by selectively etching silicon germanium with respect to silicon in a stack on a chuck in an etch chamber, wherein the stack comprises a first silicon layer and a second silicon layer and a silicon germanium layer separating the first silicon layer and the second silicon layer, comprising:
maintaining the chuck at a temperature at or below 0° C.; and
exposing the stack to an etch gas comprising a fluorine containing gas to selectively etch silicon germanium with respect to silicon wherein the silicon germanium layer is completely etched away from between the first silicon layer and second silicon layer to form a gap between the first silicon layer and the second silicon layer to form the first silicon layer and second silicon layer into silicon nanowires; and
depositing a SiO 2 , SiN, or SiC containing layer on surfaces of the silicon nanowires using atomic layer deposition after exposing the stack to the etch gas in the etch chamber, wherein the SiO 2 , SiN, or SiC containing layer encircles the silicon nanowires.
2 . The method, as recited in claim 1 , wherein the etch gas has a total flow per etch gas molecule, and wherein the fluorine containing gas comprises fluorine, wherein the fluorine has a fluorine flow per fluorine atom, wherein a ratio of the total flow per etch gas molecule to the fluorine flow per fluorine atom is between 1000:1 to 3:1.
3 . The method, as recited in claim 1 , further comprising:
forming the etch gas into a plasma with ions and energetic neutrals of the etch gas in a remote plasma generator; and
flowing the energetic neutrals from the remote plasma generator into the etch chamber.
4 . The method, as recited in claim 3 , wherein the etch gas is not maintained as a plasma in the etch chamber so that the stack is exposed to the energetic neutrals.
5 . The method, as recited in claim 1 , wherein the etch gas further comprises a noble gas.
6 . The method, as recited in claim 1 , wherein the fluorine containing gas comprises CF 4 .
7 . The method, as recited in claim 1 , further comprises maintaining an etch chamber pressure of at least 300 mTorr.
8 . The method, as recited in claim 1 , further comprising:
transferring the stack from the etch chamber to an atomic layer deposition chamber in inert conditions.
9 . The method, as recited in claim 1 , wherein an encapsulating layer is formed on sides of the stack, the method further comprising removing the encapsulating layer from the stack using a break through process.
10 . The method, as recited in claim 9 , wherein the break through process comprises providing a wet etch of the encapsulating layer.
11 . The method, as recited in claim 10 , wherein the break through process further comprises a dry etch after the wet etch.
12 . The method, as recited in claim 9 , wherein the break through process comprises providing a vapor etch or dry etch of the encapsulating layer.
13 . The method, as recited in claim 1 , wherein the maintaining the chuck at a temperature at or below 0° C., maintains the chuck at a temperature of less than or equal to −15° C.
14 . The method, as recited in claim 1 , wherein the fluorine containing gas comprises a hydrofluorocarbon.