Substrate release methods and apparatuses
The present disclosure relates to methods and apparatuses for fracturing or breaking a buried porous semiconductor layer to separate a 3-D thin-film semiconductor semiconductor (TFSS) substrate from a 3-D crystalline semiconductor template. The method involves forming a sacrificial porous semiconductor layer on the 3-D features of the template. A variety of techniques may be used to fracture and release the mechanically weak porous semiconductor layer without damaging the TFSS substrate layer or the template layer such as pressure variations, thermal stress generation, and mechanical bending. The methods also allow for processing three dimensional features not possible with current separation processes. Optional cleaning and final lift-off steps may be performed as part of the release step or after the release step.
1. A method of forming a 3-D thin film semiconductor substrate (TFSS) by releasing it from a semiconductor template through the use of a buried porous semiconductor layer, comprising the steps of:
forming a buried porous semiconductor layer on a template, said buried porous semiconductor layer formed conformal to said template;
forming a TFSS on said buried porous semiconductor layer, said TFSS, said buried porous semiconductor layer, and said template forming a wafer, said TFSS having 3-D features in contact with said porous semiconductor layer;
performing at least one release step which fractures at least a portion of said buried porous semiconductor layer; and
separating said TFSS and said template.
2. The method of claim 1 , wherein said release step further comprises repeating said release step for a plurality of cycles.
3. The method of claim 1 , wherein said release step further comprises the step of applying a hydrostatic pressure to said wafer.
4. The method of claim 3 , wherein said hydrostatic pressure is in the range of approximately 0.1 GPa to 100 GPa.
5. The method of claim 1 , wherein said release step further comprises thermally expanding and/or contracting said buried porous semiconductor layer.
6. The method of claim 5 , wherein said step of thermally expanding and/or contracting said buried porous semiconductor layer further comprises the step of contacting at least one temperature controlled chuck to said wafer.
7. The method of claim 6 , wherein said at least one temperature controlled wafer chuck is in a temperature range bound between approximately −50° and 350° C.
8. The method of claim 5 , wherein said step of thermally expanding or contracting said buried porous semiconductor layer further comprises the step of heating said wafer through infrared (IR) laser irradiation.
9. The method of claim 8 , wherein said step of heating said wafer using IR laser irradiation further comprises the step of heating said wafer using a C0 2 laser.
10. The method of claim 8 , wherein said step of heating said wafer using IR laser irradiation source further comprises the step of heating said wafer using a YAG laser.
11. The method of claim 5 , wherein said step of thermally expanding or contracting said buried porous semiconductor layer further comprises the step of dispensing or immersing a wafer in a heating or cooling source.
12. The method of claim 11 , wherein said cooling source comprises at least one of liquid nitrogen, inert gases, cold air, or CO 2 snow (dry ice) or said heating source comprises at lease one of hot liquid, DI water, steam, temperature controlled oven, or hot air.
13. The method of claim 5 , wherein said step of thermally expanding or contracting said buried porous semiconductor layer further comprises the step of heating said wafer with a Rapid Thermal Processing (RTP) heating source.
14. The method of claim 1 , wherein said release step further comprises the step of exposing said wafer to ultrasonic energy.
15. The method of claim 1 , wherein said release step further comprises the step of mechanically bending said wafer.
16. The method of claim 1 , wherein said release step further comprises the step of introducing a liquid or gas into the pores of said buried porous semiconductor layer and then expanding and/or contracting said liquid or said gas.
17. The method of claim 16 , wherein said liquid or said gas comprises an etchant.
18. The method of claim 16 , wherein said step of expansion and/or contraction further comprises the step of heating or cooling of said liquid or gas, said heating or cooling resulting in a phase change of said liquid or gas.
19. The method of claim 16 , wherein said expansion step further comprises the step of loading said wafer into a vacuum chamber and rapidly depressurizing said vacuum chamber.
20. The method of claim 1 , wherein a said release step further comprises a final cleaning step wherein said final cleaning step further comprises a megasonic or ultrasonic cleaning step or a mechanical precision pulling step.
21. The method of claim 1 , wherein said step of forming a buried porous semiconductor layer on a template further comprises the step of forming a buried porous silicon layer.
22. The method of claim 1 , wherein said step of forming a buried porous semiconductor layer on a template further comprises the step of forming said buried porous semiconductor layer on a silicon template.
23. The method of claim 1 , wherein forming a TFSS on said buried porous semiconductor layer further comprises the step of forming a thin-film silicon substrate.