Apparatus and methods for uniformly forming porous semiconductor on a substrate
This disclosure enables high-productivity controlled fabrication of uniform porous semiconductor layers (made of single layer or multi-layer porous semiconductors such as porous silicon, comprising single porosity or multi-porosity layers). Some applications include fabrication of MEMS separation and sacrificial layers for die detachment and MEMS device fabrication, membrane formation and shallow trench isolation (STI) porous silicon (using porous silicon formation with an optimal porosity and its subsequent oxidation). Further, this disclosure is applicable to the general fields of photovoltaics, MEMS, including sensors and actuators, stand-alone, or integrated with integrated semiconductor microelectronics, semiconductor microelectronics chips and optoelectronics.
1. An apparatus for producing porous semiconductor on a plurality of semiconductor wafers, comprising:
an electrolyte-filled chamber, said chamber operable to open and close, and forming a seal when closed;
an anode disposed at a first end of said chamber;
a cathode disposed at an opposite end of said chamber, said anode and said cathode coupled to electrical circuitry capable of providing an electrical power comprising electrical voltage and current;
an array of a plurality of semiconductor wafers arranged between said anode and said cathode in a tunnel, said tunnel having substantially the same diameter as said wafers, each of said wafers held in place by a wafer clamp securing the surface edge of said wafer and sealing the fluid filled compartment formed between each of said wafers with said tunnel; and
said anode and said cathode each having a region size smaller than the diagonal dimension of said wafer, said anode and said cathode each facing a respective dome shaped wall adjacent to a respective backside wall of said chamber and away from said array of said plurality of semiconductor wafers.
2. The apparatus of claim 1 , further comprising transducers positioned in said electrolyte-filled chamber to dislodge byproduct gas bubbles from the surface of said wafers with sonic energy.
3. The apparatus of claim 2 , wherein said transducers are positioned to said wafer clamps.
4. The apparatus of claim 1 , wherein said electrical circuitry is operable to allow for dissipation of byproduct gas from the surface of said wafers by pulsating electrical current during anodization.
5. The apparatus of claim 1 , wherein said semiconductor wafers are crystalline silicon wafers.
6. The apparatus of claim 1 , wherein byproduct gas is hydrogen gas.
7. The apparatus of claim 1 , wherein said wafer clamp comprises a first inner layer for minimal edge wrap-around and a second outer harder flexible layer providing a seal around said wafer edge.