Double-sided reusable template for fabrication of semiconductor substrates for photovoltaic cell and microelectronics device manufacturing
This disclosure presents manufacturing methods and apparatus designs for making TFSSs from both sides of a re-usable semiconductor template, thus effectively increasing the substrate manufacturing throughput and reducing the substrate manufacturing cost. This approach also reduces the amortized starting template cost per manufactured substrate (TFSS) by about a factor of 2 for a given number of template reuse cycles.
1. A method for making a pair of monocrystalline thin-film silicon substrates, said method comprising:
providing a monocrystalline silicon wafer;
patterning a first surface and a second surface of said monocrystalline silicon wafer with a resist layer having a hexagonal pattern;
etching said monocrystalline silicon wafer, thereby producing a set of structural surface topography features on said first surface and said second surface, said structural surface topography features comprising a plurality of isolated hexagonal posts;
removing said resist layer from said monocrystalline silicon wafer; and
cleaning said first surface and said second surface of said monocrystalline silicon wafer, said monocrystalline silicon wafer comprising a double-sided reusable template;
producing a first porous silicon layer on said first surface and a second porous silicon layer on said second surface of said double-sided reusable template via an anodic etching process, said porous silicon layers having a crystallinity consistent with said double-sided reusable template;
epitaxially depositing a first monocrystalline thin-film silicon substrate on said first porous silicon layer and a second monocrystalline thin-film silicon substrate on said second porous silicon layer, said monocrystalline thin-film silicon substrates having a crystallinity consistent with said porous silicon layers;
separating said first and said second monocrystalline thin-film silicon substrates from said first and said second porous silicon layers.
2. The method of claim 1 , wherein said first porous silicon layer comprises a first porous silicon bilayer having at least two different porosities, and said second porous silicon layer comprises a second porous silicon bilayer having at least two different porosities.
3. The method of claim 1 , wherein said first porous silicon layer comprises a first graded porosity layer, and said second porous silicon layer comprises a second graded porosity layer.
4. The method of claim 1 , wherein said monocrystalline thin-film silicon substrates comprise in-situ doped monocrystalline thin-film silicon substrates.
5. The method of claim 4 , wherein each of said in-situ doped monocrystalline thin-film silicon substrates comprises a front-surface field layer and a base layer for a photovoltaic solar cell.
6. The method of claim 4 , wherein each of said in-situ doped monocrystalline thin-film silicon substrates comprises a front-surface field layer, a base layer, and an emitter layer for a photovoltaic solar cell.
7. The method of claim 1 , further comprising the step of heating said double-sided reusable template in an atmosphere of hydrogen after producing said first and said second porous silicon layers in situ and prior to said epitaxial depositing step.
8. A method for making a pair of monocrystalline thin-film silicon substrates, said method comprising:
providing a monocrystalline silicon wafer;
producing a thermally grown silicon oxide layer on a first surface and a second surface of said monocrystalline silicon wafer;
patterning said first surface and said second surface of said monocrystalline silicon wafer with a resist layer comprising large squares and small squares, said large and small squares being aligned to a <110> direction of said monocrystalline silicon wafer;
transferring said pattern of large squares and small squares to said silicon oxide layer;
anisotropically etching said monocrystalline silicon wafer, thereby producing a set of structural surface topography features on said first surface and said second surface, said structural surface topography features comprising a plurality of square pyramidal cavities;
removing said resist layer from said monocrystalline silicon wafer; and
cleaning said first surface and said second surface of said monocrystalline silicon wafer, said monocrystalline silicon wafer comprising a double-sided reusable template;
producing a first porous silicon layer on said first surface and a second porous silicon layer on said second surface of said double-sided reusable template via an anodic etching process, said porous silicon layers having a crystallinity consistent with said double-sided reusable template;
epitaxially depositing a first monocrystalline thin-film silicon substrate on said first porous silicon layer and a second monocrystalline thin-film silicon substrate on said second porous silicon layer, said monocrystalline thin-film silicon substrates having a crystallinity consistent with said porous silicon layers;
separating said first and said second monocrystalline thin-film silicon substrates from said first and said second porous silicon layers.
9. The method of claim 8 , wherein said first porous silicon layer comprises a first porous silicon bilayer having at least two different porosities, and said second porous silicon layer comprises a second porous silicon bilayer having at least two different porosities.
10. The method of claim 8 , wherein said first porous silicon layer comprises a first graded porosity layer, and said second porous silicon layer comprises a second graded porosity layer.
11. The method of claim 8 , wherein said monocrystalline thin-film silicon substrates comprise in-situ doped monocrystalline thin-film silicon substrates.
12. The method of claim 11 , wherein each of said in-situ doped monocrystalline thin-film silicon substrates comprises a front-surface field layer, a base layer, and an emitter layer.
13. The method of claim 8 , further comprising the step of heating said double-sided reusable template in an atmosphere of hydrogen after producing said first and said second porous silicon layers.