Method of preparing a silicon carbide wafer
A method of preparing a silicon carbide wafer for subsequent epitaxial growth thereon is disclosed. The method comprises (a) placing the silicon carbide wafer onto a support table in a plasma processing chamber such that the surface of the silicon carbide wafer distal to the support table is unmasked; (b) establishing a flow of an etch gas mixture into the plasma processing chamber, wherein the etch gas mixture comprises molecular hydrogen, H 2 ; and (c) generating a plasma from the etch gas mixture within the plasma processing chamber and using the plasma to etch the unmasked surface of the wafer so as to reduce the roughness of the unmasked surface.
1 . A method of preparing a silicon carbide wafer for subsequent epitaxial growth thereon, the method comprising:
in a plasma processing chamber containing a silicon carbide wafer mounted on a support table such that the surface of the silicon carbide wafer distal to the support table is unmasked:
establishing a flow of an etch gas mixture into the plasma processing chamber, wherein the etch gas mixture comprises molecular hydrogen, H 2 , and a noble gas, wherein the ratio of H 2 to the noble gas in the etch gas mixture is in the range of 5:1 to 1.5:1; and
generating a plasma from the etch gas mixture within the plasma processing chamber and using the plasma to etch the unmasked surface of the wafer so as to reduce the roughness of the unmasked surface.
2 . The method of claim 1 , wherein the noble gas has an atomic weight greater than 28.
3 . The method of claim 1 , wherein 5% to 40% of the etch gas mixture consists of the noble gas.
4 . The method of claim 1 , wherein the etch gas mixture further comprises one or more fluorine-bearing gases, each of the one or more fluorine-bearing gases configured to release fluorine radicals when in the plasma.
5 . The method of claim 4 , wherein the ratio of H 2 to the one or more fluorine-bearing gases in the etch gas mixture is in the range of 100:1 to 5:1.
6 . The method of claim 1 , wherein at least 20% of the etch gas mixture consists of H 2 .
7 . The method of claim 1 , wherein the wafer is oriented such that the unmasked surface is a silicon face.
8 . The method of claim 1 , further comprising, during the etching, delivering helium to the surface of the wafer proximal to the substrate table to cool the wafer.
9 . The method of claim 1 , further comprising, during etching:
applying a bias voltage to the substrate table with a first power, P1, for a first time period; and then
applying the bias voltage to the substrate table with a second power, P2, for a second time period,
wherein the noble gas has an atomic weight wherein P2 is less than P1.
10 . A method of preparing a silicon carbide wafer for subsequent epitaxial growth thereon, the method comprising:
in a plasma processing chamber containing a silicon carbide wafer mounted on a support table such that the surface of the silicon carbide wafer distal to the support table is unmasked:
establishing a flow of an etch gas mixture into the plasma processing chamber, wherein the etch gas mixture comprises:
(i) one or more fluorine-bearing gases configured to release fluorine radicals when in a plasma; and
(ii) one or more polymer-forming fluorocarbons and/or one or more polymer-forming hydrofluorocarbons; and
generating a plasma from the etch gas mixture within the plasma processing chamber and using the plasma to etch the unmasked surface of the wafer so as to reduce the roughness of the unmasked surface.
11 . The method of claim 10 , wherein the one or more fluorine-bearing gases comprise one or more of sulphur hexafluoride, SF 6 , carbon tetrafluoride, CF 4 , nitrogen trifluoride, NF 3 , and molecular fluorine, F 2 .
12 . The method of claim 10 , wherein the one or more polymer-forming fluorocarbons comprise octafluorocyclobutane, c-C 4 F 8 , and/or the one or more polymer-forming hydrofluorocarbons comprise trifluoromethane, CHF 3 .
13 . The method of claim 10 , wherein the ratio of the one or more fluorine-bearing gases to the polymer-forming fluorocarbons and/or polymer-forming hydrofluorocarbons in the etch gas mixture is in the range of 15:1 to 3:1.
14 . The method of claim 10 , wherein at least 90% of the etch gas mixture consists of the one or more fluorine-bearing gases and the one or more polymer-forming fluorocarbons and/or polymer-forming hydrofluorocarbons.
15 . A method of preparing a silicon carbide wafer for subsequent epitaxial growth thereon, the method comprising:
in a plasma processing chamber containing a silicon carbide wafer mounted on a support table such that the surface of the silicon carbide wafer distal to the support table is unmasked:
establishing a flow of an etch gas mixture into the plasma processing chamber, wherein the etch gas mixture comprises hydrogen bromide, HBr, and oxygen, O 2 ; and
generating a plasma from the etch gas mixture within the plasma processing chamber and using the plasma to etch the unmasked surface of the wafer so as to reduce the roughness of the unmasked surface,
wherein, during the etching, helium is delivered to the surface of the wafer proximal to the substrate table to cool the wafer.
16 . The method of claim 15 , wherein:
at least 40% of the etch gas mixture consists of HBr; and/or
the ratio of HBr:O 2 in the etch gas mixture is in the range of 3:1 to 1.5:1.
17 . The method of claim 15 , wherein the etch gas mixture further comprises one or more halogen-bearing gases that do not comprise bromine.
18 . The method of claim 17 , wherein the one or more halogen-bearing gases comprise one or more fluorine-bearing gases each configured to release fluorine radicals when in the plasma.
19 . The method of claim 18 , wherein the ratio of HBr to the one or more fluorine-bearing gases in the etch gas mixture is in the range of 100:1 to 2:1.