Method for releasing a thin-film substrate
The present disclosure relates to methods for selectively etching a porous semiconductor layer to separate a thin-film semiconductor substrate (TFSS) having planar or three-dimensional features from a corresponding semiconductor template. The method involves forming a conformal sacrificial porous semiconductor layer on a template. Next, a conformal thin film silicon substrate is formed on top of the porous silicon layer. The middle porous silicon layer is then selectively etched to separate the TFSS and semiconductor template. The disclosed advanced etching chemistries and etching methods achieve selective etching with minimal damage to the TFSS and template.
1. A method for fabrication of a thin-film crystalline semiconductor substrate by releasing it from a semiconductor template through the use of a sacrificial porous semiconductor seed and release layer, the method comprising:
forming a porous semiconductor layer on a semiconductor template measuring at least 200 mm×200 mm, said porous semiconductor layer substantially conformal to said semiconductor template;
forming a thin-film crystalline semiconductor substrate on said porous semiconductor layer, said thin-film semiconductor substrate substantially conformal to said porous semiconductor layer; and
selectively and chemically wet etching said porous semiconductor layer with a high-etch-selectivity wet etchant, said wet etchant solution comprising dilute TMAH or KOH or NaOH;
releasing said thin-film semiconductor substrate as a free-standing, self-supporting semiconductor substrate from said semiconductor template via selective wet etching of said porous semiconductor layer.
2. The method of claim 1 , wherein said step of selectively etching said porous semiconductor layer further comprises degassing said etchant prior to said selective etching step.
3. The method of claim 1 , wherein said step of selectively etching said porous semiconductor layer further comprises degassing said etchant during said selective etching step.
4. The method of claim 1 , wherein said step of selectively etching said porous semiconductor layer occurs in a vacuum chamber.
5. The method of claim 1 , wherein said step of selectively etching said porous semiconductor layer further comprises ultrasonically streaming said etchant at said porous semiconductor layer.
6. The method of claim 1 , wherein said step of selectively etching said porous semiconductor layer further comprises megasonically streaming said etchant at said porous semiconductor layer.
7. The method of claim 1 , wherein said step of selectively etching said porous semiconductor layer further comprises directing acoustic waves at said porous semiconductor layer.
8. The method of claim 7 , wherein said acoustic waves comprise acoustic waves having a plurality of frequencies.
9. The method of claim 1 , wherein said step of forming a porous semiconductor layer further comprises the step of forming a porous semiconductor bi-layer comprising a low porosity layer with a porosity in the range of 15% to 30% and a high porosity layer with a porosity in the range of 60% to 85%.
10. The method of claim 9 , wherein said step of selectively etching said porous semiconductor layer further comprises mechanically delaminating said high porosity silicon layer using low frequency ultrasonic energy.
11. The method of claim 1 , wherein said step of forming a porous semiconductor layer further comprises the step of forming a porous silicon layer.
12. The method of claim 11 , wherein said etchant comprises a tetramethylammonium hydroxide (TMAH) solution.
13. The method of claim 11 , wherein said etchant comprises a tetramethylammonium hydroxide (TMAH) and ammonium persulfate crystalline additive solution.
14. The method of claim 11 , wherein said etchant comprises a potassium hydroxide (KOH) solution.
15. The method of claim 11 , wherein said etchant comprises a potassium hydroxide (KOH) and hydrofluoric (HF) acid solution.
16. The method of claim 11 , wherein said etchant comprises a potassium hydroxide (KOH) and isopropyl alcohol (IPA) solution.
17. The method of claim 11 , wherein said etchant comprises a potassium hydroxide (KOH) and surfactant solution.
18. The method of claim 11 , wherein said etchant comprises a potassium hydroxide (KOH), hydrofluoric (HF) acid, and surfactant solution.
19. The method of claim 1 , wherein said step of forming a thin-film semiconductor substrate further comprises the step of forming a thin-film silicon substrate having three-dimensional features.
20. The method of claim 1 , wherein said step of forming a porous semiconductor layer on a semiconductor template further comprises the step of forming a porous semiconductor layer on a silicon template having three-dimensional features.