METHOD FOR RECONSTRUCTING A SEMICONDUCTOR TEMPLATE
The disclosed subject matter pertains to deposition of thin film or thin foil materials in general, but more specifically to deposition of epitaxial monocrystalline or quasi-monocrystalline silicon film (epi film) for use in manufacturing of high efficiency solar cells. In operation, methods are disclosed which extend the reusable life and to reduce the amortized cost of a substrate or template used in the manufacturing process of silicon solar cells. Further, methods are disclosed which provide for the conversion of a low quality starting surface into an improved quality starting surface of a silicon wafer.
1 . A method for making a thin film crystalline semiconductor substrate, said method comprising:
providing a reusable doped crystalline semiconductor template;
forming a porous semiconductor sacrificial release layer on a front side of said reusable crystalline semiconductor template;
epitaxially depositing a thin film semiconductor substrate conformally to said sacrificial release layer;
releasing said thin film semiconductor substrate from said reusable semiconductor template by separation at said porous semiconductor layer; and
epitaxially depositing a thickening layer of semiconductor material on said front side of said template, said thickening layer being a like material and having a like polarity as said template.
2 . The method of claim 1 , wherein additional device processing steps are performed after said epitaxially depositing a thin film semiconductor substrate step and prior to said releasing process step.
3 . The method of claim 1 , wherein said epitaxially depositing a thickening layer of semiconductor material is performed once after a plurality of said epitaxially depositing a thin film semiconductor substrate and subsequently releasing said thin film semiconductor substrate process cycles.
4 . The method of claim 1 , wherein said thin film crystalline semiconductor substrate is used for fabrication of a solar cell.
5 . The method of claim 1 , wherein laser processing is utilized prior to said step of releasing said thin film semiconductor substrate from said reusable semiconductor template by separation at said porous semiconductor layer.
6 . The method of claim 1 , wherein said crystalline semiconductor comprises crystalline silicon.
7 . The method of claim 6 , wherein said crystalline silicon comprises monocrystalline silicon.
8 . The method of claim 1 , wherein reusable doped crystalline semiconductor template comprises a substantially planar surface for the formation of said thin film crystalline semiconductor substrate.
9 . The method of claim 1 , wherein reusable doped crystalline semiconductor template comprises a textured surface for the formation of said thin film crystalline semiconductor substrate.
10 . The method of claim 1 , wherein reusable doped crystalline semiconductor template comprises a three-dimensional surface topography for the formation of said thin film crystalline semiconductor substrate.
11 . The method of claim 10 , wherein said three-dimensional surface topography comprises surface cavities and ridges defining the openings of said surface cavities.
12 . The method of claim 11 , wherein said step of epitaxially depositing a thickening layer of semiconductor material on said front side of said template restores said ridges to a position substantially planar to the front side edge of said template.
13 . The method of claim 1 , wherein said doped semiconductor template is lightly doped and said thickening layer of semiconductor material is more highly doped to facilitate producing said porous semiconductor material.
14 . The method of claim 1 , further comprising using bevel grinding of said template containing said epitaxially deposited thin film semiconductor substrate to define a boundary of said thin film semiconductor substrate prior to said step of releasing, thereby aiding said step of releasing.
15 . The method of claim 1 , further comprising the step polishing or grinding said thickening layer of semiconductor material from a beveled edge of said reusable semiconductor template, thereby strengthening said template.
16 . The method of claim 1 , wherein said step of epitaxially depositing a thickening layer of semiconductor material on said front side of said template is performed after it is determined the thickness of said reusable doped semiconductor template is below a predetermined threshold.
17 . The method of claim 1 , wherein said step of epitaxially depositing a thickening layer of semiconductor material on said front side of said template is performed when there exists an epitaxial layer on said front side of said reusable semiconductor template with a dopant non-suitable for porous semiconductor layer formation.
18 . The method of claim 1 , wherein said step of releasing said thin film semiconductor substrate from said reusable semiconductor template by separation at said porous semiconductor layer further comprises utilizing laser processing.
19 . A method for smoothing a wafer surface, said method comprising:
performing a saw damage removal etch on a doped wafer sliced from an ingot; and
epitaxially depositing a planarizing layer of semiconductor material on said wafer, said planarizing layer being a like material and having a like polarity as said wafer.
20 . The method of claim 19 , wherein said wafer is a monocrystalline silicon wafer.