SYSTEM AND METHOD FOR FABRICATING THIN-FILM PHOTOVOLTAIC DEVICES
Described are a system and a method for depositing a thin film on a substrate. In some embodiments, the system includes a substrate transport system to transport a plurality of discrete substrates, such as glass substrates or wafers, along a closed path. The system also includes a metal deposition zone, a selenization zone and a cooling chamber each disposed on the closed path. During transport along the closed path, the metal deposition zone deposits a layer of a composite metal onto the discrete substrates and the selenization zone selenizes the layer of the composite metal. The cooling zone cools the discrete substrates prior to a subsequent pass through the metal deposition zone and the selenization zone.
1 . A system for depositing a thin film on a substrate, comprising:
a substrate transport system to transport a plurality of discrete substrates along a closed path;
a metal deposition zone disposed on the closed path and configured to deposit a layer of a composite metal onto the discrete substrates during passage through the metal deposition zone;
a selenization zone disposed on the closed path to receive the discrete substrates after passing through the metal deposition zone; and
a cooling chamber disposed along the closed path to receive the discrete substrates after passing through the selenization zone, the cooling chamber configured to cool the discrete substrates prior to a subsequent pass of the discrete substrates through the metal deposition zone and the selenization zone.
2 . The system of claim 1 wherein the metal deposition zone is a sputtering zone.
3 . The system of claim 2 wherein the sputtering zone comprises a plurality of magnetrons, the system further comprising a target material for each of the magnetrons, each of the target materials having a composition comprising one of copper indium gallium, copper gallium and copper indium.
4 . The system of claim 3 wherein the target material for each magnetron in one of the sputtering zones has a composition that is different from a composition of the target material for each of the other magnetrons in the sputtering zone.
5 . The system of claim 1 wherein the layer of the composite metal is a copper indium gallium layer.
6 . The system of claim 1 wherein the selenization zone comprises:
a selenization furnace;
a first selenium trap disposed between the metal deposition zone and the selenization furnace; and
a second selenium trap disposed between the selenization furnace and the cooling chamber.
7 . The system of claim 6 wherein the selenization furnace is configured to maintain a temperature in a range of approximately 250° C. to 600° C.
8 . The system of claim 6 further comprising:
a first low conductance aperture disposed between the metal deposition zone and the first selenium trap; and
a second low conductance aperture disposed between the second selenium trap and the cooling chamber.
9 . The system of claim 6 wherein the first and second selenium traps are differentially pumped.
10 . The system of claim 6 wherein the selenization furnace has a heater comprising a plurality of zones each having a temperature that is independently controlled.
11 . The system of claim 1 further comprising:
a load mechanism disposed along the closed path to load the discrete substrates onto the substrate transport system; and
an unload mechanism disposed along the closed path to remove the discrete substrates from the substrate transport system.
12 . The system of claim 1 wherein the discrete substrates comprise glass substrates.
13 . A system for depositing a thin film on a substrate, comprising:
a substrate transport system to transport a plurality of discrete substrates along a path having a load end and an unload end;
a plurality of metal deposition zones disposed on the path, each metal deposition zone configured to deposit a layer of a composite metal onto the discrete substrates during passage through the metal deposition zone;
a plurality of selenization zones, each selenization zone disposed on the path to receive the discrete substrates after passing through a respective one of the metal deposition zones; and
a plurality of cooling zones, each cooling zone disposed on the path to receive the discrete substrates after passing through a respective one of the selenization zones.
14 . The system of claim 13 further comprising:
a load mechanism disposed at the load end of the path to load the discrete substrates into the substrate transport system; and
an unload mechanism disposed at the unload end of the path to remove the discrete substrates from the substrate transport system.
15 . A method of depositing a thin film on a substrate, the method comprising:
(a) depositing a layer of a composite metal onto a discrete substrate during transport through a metal deposition zone;
(b) transporting the discrete substrate to a selenization zone;
(c) depositing a selenium layer onto the layer of the composite metal during transport of the discrete substrate through the selenization zone;
(d) heating the discrete substrate during transport through the selenization zone to selenize the layer of the composite metal;
(e) determining if the layer of the composite metal deposited onto the discrete substrate is a last deposition layer;
(f) repeating steps (a) to (d) if a determination is made that the layer of the composite metal deposited onto the discrete substrate is not the last deposition layer.
16 . The method of claim 15 further comprising cooling the discrete substrate after step (e) if a determination is made that the layer of the composite metal deposited onto the discrete substrate is not a last deposition layer.
17 . The method of claim 15 wherein the layer of the composite metal comprises a copper indium gallium layer.
18 . The method of claim 17 wherein a plurality of layers of the composite metal are deposited and wherein a relative composition of copper, indium and is different for at least two of the layers.