Method for fabricating a photovoltaic device by uniform plating on emitter-lined through-wafer vias and interconnects
Photovoltaic devices are formed by laser drilling vias through silicon substrates and, following surface preparation of the via sidewalls, plating a continuous, electrically conductive layer on the via sidewalls to electrically connect the emitter side of the cell with the back side of the cell. The electrically conductive layer can be formed on portions of a base emitter within the vias and on the back side of the substrate. Alternatively, the electrically conductive layer can be formed on a passivation layer on the via sidewalls and back side of the cell.
1. A method for fabricating a photovoltaic device, comprising:
obtaining a substrate comprising silicon and including a front side and a back side;
laser drilling a via through the substrate, the via including a sidewall;
smoothing the sidewall of the via;
forming a continuous, lightly doped emitter having a first portion on the front side of the substrate and a second portion on the sidewall of the via;
forming an electrically conductive contact pad on the back side of the substrate;
forming an antireflective coating on the first portion of the doped emitter, the second portion of the doped emitter remaining uncoated by the antireflective coating;
patterning a fine line selective emitter on the front side of the substrate, the fine line selective emitter intersecting the via and being deeper and more highly doped than the first portion of the base emitter, and
plating a continuous, electrically conductive layer on the fine line selective emitter and the second portion of the doped emitter on each sidewall of the via, thereby forming a plated via, each plated via having an axial opening, wherein plating the continuous, electrically conductive layer further includes:
plating the fine line selective emitter and the second portion of the doped emitter with nickel;
conducting a silicide anneal to form a continuous nickel silicide layer, the doped emitter having a resistivity that facilitates formation of the continuous nickel silicide layer;
removing unreacted nickel following the silicide anneal, and
plating copper over the nickel silicide layer,
whereby the continuous, electrically conductive layer of the via is electrically connected to the doped emitter.
2. The method of claim 1 , wherein the step of laser drilling the via further includes drilling from the back side of the substrate towards the front side thereof.
3. The method of claim 1 , further including etching the sidewall of the via, the step of etching the sidewall including using a hydrogen fluoride etch prior to plating the continuous, electrically conductive layer.
4. The method of claim 3 , wherein the step of etching the sidewall of the via is performed as a single sided etch from the back side of the substrate.
5. The method of claim 4 , wherein the step of laser drilling the via further includes drilling from the back side of the substrate towards the front side thereof.
6. The method of claim 1 , wherein the electrically conductive layer is plated directly on the second portion of the doped emitter.
7. The method of claim 1 , wherein the fine line selective emitter and the second portion of the doped emitter are plated simultaneously.
8. The method of claim 7 , wherein the fine line selective emitter electrically contacts the doped emitter on the sidewall of the via.