Method of stripping hot melt etch resists from semiconductors
View Patent ↗Hot melt etch resist is selectively applied to an anti-reflective coating or a selective emitter on a semiconductor wafer. The exposed portions of the anti-reflective coating or selective emitter are etched away using an inorganic acid containing etch to expose the semiconductor surface. The hot melt etch resist is then stripped from the semiconductor with an alkaline stripper which does not compromise the electrical integrity of the semiconductor. The exposed semiconductor is then metalized to form current tracks.
1. A method comprises:
a) providing a semiconductor substrate comprising a PN junction, a selective emitter on a front side and an electrode comprising aluminum on a back side of the semiconductor substrate with the PN junction, wherein the selective emitter comprises zones of low sheet resistivity;
b) selectively applying a hot melt etch resist consisting of one or more hydrogenated rosin resins, one or more fatty acids or salts thereof and one or more optical brighteners to the zones of low sheet resistivity of the selective emitter on the semiconductor substrate with the PN junction;
c) applying an etchant to exposed portions of the selective emitter with the PN junction to etch the exposed portions; and
d) applying a stripper consisting of 5 g/L to 50 g/L potassium carbonate and 0.1 g/L to 10 g/L potassium silicate, water and optionally one or more antifoaming agents to the semiconductor substrate with the PN junction to remove the hot melt etch resist from the selective emitter.
2. The method of claim 1 , wherein a pH of the stripper composition ranges from 8 to 12.
3. The method of claim 1 , wherein a temperature of stripping ranges from room temperature to 70° C.
4. The method of claim 1 , wherein the one or more antifoaming agents are chosen from vegetable oils, long chain fatty alcohols, silicone based antifoams, silicone glycols, fluorosilicones and ethylene oxide/propylene oxide copolymers.
5. The method of claim 1 , further comprising depositing an anti-reflective layer on the selective emitter layer after removing the hot melt etch resist.
6. The method of claim 5 , wherein the anti-reflective layer is chosen from silicon oxide, silicon nitride and a combination of silicon oxide and silicon nitride.
7. The method of claim 1 , further comprising forming current tracks on the zones of low sheet resistance.
8. The method of claim 1 , wherein the zones of low sheet resistivity are less than 60 ohms per square.
9. The method of claim 1 , wherein the one or more hydrogenated rosin resins are in amounts of 20 wt % to 30 wt %.
10. The method of claim 1 , wherein the one or more hydrogenated rosin resin is a partially hydrogenated rosin resin.
11. The method of claim 1 , wherein the one or more fatty acids are in amounts of 70 wt % to 80 wt %.
12. The method of claim 1 , wherein the one or more fatty acids are chosen from stearic acid, palmitic acid, myristic acid and salts thereof.