Method and assembly for ohmic contact in thinned silicon carbide devices
A silicon carbide semiconductor assembly and a method of forming a silicon carbide (SiC) semiconductor assembly are provided. The silicon carbide semiconductor assembly includes a semiconductor substrate and an electrode. The semiconductor substrate is formed of silicon carbide and includes a first surface, a second surface opposing the first surface, and a thickness extending therebetween. The method includes forming one or more electronic devices on the first surface and thinning the semiconductor substrate by removing the second surface to a predetermined depth of semiconductor substrate and leaving a third surface opposing the first surface. The method further includes forming a non-ohmic alloy layer on the third surface at a first temperature range and annealing the alloy layer at a second temperature range forming an ohmic layer, the second temperature range being greater than the first temperature range.
1. A method of forming a semiconductor assembly, said method comprising:
forming one or more electronic devices on a first surface of a semiconductor substrate formed of a silicon carbon (SiC) material and having a first thickness defined between the first surface and a second surface opposing the first surface;
thinning the semiconductor substrate using a mechanical grinding process on a second surface of the substrate to a second thickness, the second thickness defined between the first surface and a third surface of the substrate formed by the mechanical grinding process;
applying a metal film to the third surface;
converting the applied metal film to a non-ohmic alloy layer on the third surface by heating to a first temperature between 400° C. and 950° C. for a predetermined period of time; and
annealing the converted non-ohmic alloy layer at a temperature higher than the first temperature.
2. The method of claim 1 , wherein thinning the semiconductor substrate comprises thinning the semiconductor substrate after the forming of the one or more electronic devices on the first surface is complete.
3. The method of claim 1 , wherein thinning the semiconductor substrate comprising mechanically grinding the second surface to the predetermined depth of semiconductor substrate.
4. The method of claim 1 , wherein applying the metal film to the third surface comprises performing a vacuum evaporation of nickel (Ni) on the third surface.
5. The method of claim 1 , wherein converting the applied metal film to the non-ohmic alloy layer on the third surface comprises forming a nickel silicide (Ni 2 Si) layer of the third surface by heating the semiconductor substrate to a temperature between approximately 400° C. to approximately 500° C.
6. The method of claim 1 , wherein converting the applied metal film to the non-ohmic alloy layer on the third surface comprises forming a nickel silicide (NiSi) layer of the third surface by heating the semiconductor substrate to a temperature between approximately 420° C. to approximately 470° C.
7. The method of claim 1 , wherein annealing the converted non-ohmic alloy layer comprises annealing at least a portion of the converted non-ohmic alloy layer at the temperature higher than the first temperature range using laser energy.
8. The method of claim 1 , wherein annealing the converted non-ohmic alloy layer at the temperature higher than the first temperature range comprises annealing the converted non-ohmic alloy layer by using localized heating of portions of the third surface using laser energy directed to the portions of the converted non-ohmic alloy layer.
9. The method of claim 1 , wherein annealing the converted non-ohmic alloy layer at the temperature higher than the first temperature range comprises annealing the converted non-ohmic alloy layer using laser energy directed along a predetermined path on the converted non-ohmic alloy layer.
10. The method of claim 1 , wherein applying a metal film to the third surface comprises applying a nickel film to the third surface.
11. The method of claim 1 , wherein converting the metal film to a non-ohmic alloy layer comprises converting the metal film to a non-ohmic metal silicide alloy layer.
12. The method of claim 1 , wherein convening the metal film to a non-ohmic alloy layer on the third surface comprises converting a nickel film to a nickel silicide alloy.
13. The method of claim 1 , wherein annealing the converted non-ohmic alloy layer comprises using localized heating by a directed laser energy source.
14. The method of claim 1 , wherein annealing the converted non-ohmic alloy layer comprises heating of portions of the third surface by laser energy to a temperature greater than 1000° C.