MULTI-LAYER BARRIER FOR METALLIZATION
A solar cell can include a substrate, a semiconductor region disposed in or above the substrate, and a conductive stack that includes a first conductive region, a multi-layer barrier region, and a second conductive region.
1 . A solar cell, comprising:
a substrate;
a semiconductor region disposed in or above the substrate; and
a conductive contact disposed on the semiconductor region, the conductive contact comprising:
a first conductive region disposed on the semiconductor region,
a first barrier region disposed on the first conductive region,
a second barrier region disposed on the first barrier region, and
a second conductive region disposed over the second barrier region.
2 . The solar cell of claim 1 , wherein the first barrier region includes a refractory metal.
3 . The solar cell of claim 1 , wherein the first conductive region includes aluminum and the second conductive region includes copper.
4 . The solar cell of claim 1 , wherein the first and second barrier regions each have a thickness of approximately 30 nm or less.
5 . The solar cell of claim 1 , wherein the first barrier region includes molybdenum.
6 . The solar cell of claim 1 , wherein the second barrier region includes a nickel-vanadium alloy.
7 . The solar cell of claim 1 , wherein a thickness of the first barrier region is different than a thickness of the second barrier region.
8 . The solar cell of claim 1 , further comprising a third barrier region disposed on the second barrier region, wherein the second conductive region is disposed on the third barrier region.
9 . The solar cell of claim 1 , wherein the conductive contact is on a back side of the solar cell opposite a sunny side of the solar cell.
10 . The solar cell of claim 1 , further comprising additional metal disposed on the second conductive region.
11 . A solar cell, comprising:
a monocrystalline silicon substrate;
a semiconductor region disposed in or above the monocrystalline silicon substrate; and
a conductive stack comprising:
a first conductive layer disposed on the semiconductor region;
a plurality of diffusion-barrier conductive layers disposed on the first conductive layer; and
a second conductive layer disposed on the plurality of diffusion-barrier conductive layers.
12 . The solar cell of claim 11 , wherein the plurality of diffusion-barrier conductive layers comprises a layer of molybdenum and a layer of nickel-vanadium alloy.
13 . The solar cell of claim 11 , wherein a thickness of a first one of the plurality of diffusion-barrier conductive layers is different than a thickness of a second one of the plurality of diffusion-barrier conductive layers.
14 . The solar cell of claim 11 , wherein a combined thickness of the plurality of diffusion-barrier conductive layers is less than approximately 20 nm.
15 . The solar cell of claim 11 , further comprising plated metal disposed on the conductive stack.
16 . A method of fabricating a solar cell, the method comprising:
forming a first conductive region on a semiconductor region disposed in or above a substrate;
forming a multi-layer barrier region on the first conductive region;
forming a second conductive region over the multi-layer barrier region.
17 . The method of claim 16 , further comprising:
annealing the first conductive region, multi-layer barrier region, and second conductive region at a temperature in a range of less than approximately 450° C.; and
patterning the annealed first conductive region, multi-layer barrier region, and second conductive region.
18 . The method of claim 17 , wherein said patterning includes etching the first conductive region, multi-layer barrier region, and second conductive region with a single etchant.
19 . The method of claim 16 , further comprising:
annealing the first conductive region, multi-layer barrier region, and second conductive region;
applying a patterned plating resist to the annealed first conductive region, multi-layer barrier region, and second conductive region;
plating a metal onto the first conductive region, multi-layer barrier region, and second conductive region to form a plurality of metal contacts; and
etching portions of the first conductive region, multi-layer barrier region, and second conductive region between the plurality of metal contacts.
20 . The method of claim 16 , wherein said forming the multi-layer barrier region comprises forming a first barrier layer to inhibit diffusion to or from the first conductive region that includes aluminum and forming a second barrier layer to inhibit diffusion to or from the second conductive region that includes copper.