Low temperature formation of backside ohmic contacts for vertical devices
View Patent ↗The invention comprises a method for forming a metal-semiconductor ohmic contact ( 18 ) for use in a semiconductor device ( 10 ) having a plurality of epitaxial layers ( 14 a-c ) wherein the ohmic contact ( 18 ) is preferably formed after deposition of the epitaxial layers ( 14 a-c ). The invention also comprises a semiconductor device comprising a plurality of epitaxial layers and an ohmic contact.
1. A method for forming an ohmic contact to silicon carbide ( 12 ) for a semiconductor device, the method comprising:
implanting at room temperature a selected dopant material into a surface of a silicon carbide substrate ( 12 ) thereby forming a layer ( 16 ) on the silicon carbide substrate having an increased concentration of dopant material;
annealing the implanted silicon carbide substrate a first time;
growing at least one epitaxial layer of a compound other than SiC that dissociates below the dissociation temperature at SiC ( 14 ) on the silicon carbide substrate opposite the implanted surface;
depositing a layer of metal ( 18 ) on the implanted surface of the silicon carbide substrate ( 12 ); and thereafter
annealing the metal ( 18 ) and the implanted silicon carbide substrate ( 12 , 16 ) a second time at a temperature below that at which significant degradation of the compound forming the epitaxial layer ( 14 ) would occur, but high enough to form an ohmic contact between the implanted silicon carbide ( 12 , 16 ) and the deposited metal.
2. A method according to claim 1 wherein the step of growing the epitaxial layer ( 14 ) on the silicon carbide substrate ( 12 ) precedes the first annealing of the implanted silicon carbide substrate ( 12 ).
3. A method according to claim 1 wherein the step of growing the epitaxial layer ( 14 ) on the silicon carbide substrate ( 12 ) follows the first annealing of the implanted silicon carbide substate ( 12 ).
4. A method according to claim 1 wherein the selected dopant material is selected from the group consisting of nitrogen, aluminum, arsenic, phosphorous, boron and gallium.
5. A method according to claim 1 wherein the first annealing the implanted silicon carbide substrate ( 12 , 16 ) occurs at a temperature above 1000° C. to 1300° C.
6. A method according to claim 1 wherein the metal ( 18 ) is selected from the group comprising nickel, palladium, platinum, aluminum and titanium.
7. A method according to claim 1 wherein the step of annealing the silicon carbide substrate ( 12 ) and the deposited metal ( 18 ) occurs at a temperature below 850° C.