Apparatus for fabricating large-surface area polycrystalline silicon sheets for solar cell application

Abstract

A method and apparatus for forming a semiconductor sheet suitable for use as a solar cell by depositing an array of solidified drops of a feed material on a sheet support. The desired properties of the sheet fabricated with the teaching of this invention are: flatness, low residual stress, minority carrier diffusion length greater than 40 microns, and minimum grain dimension at least two times the minority carrier diffusion length. In one embodiment, the deposition chamber is adapted to form and process sheets that have a surface area of about 1,000-2,400 cm2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 is an isometric view illustrating one embodiment of a solar cell processing system of the invention;

FIG. 2 is a side cross-sectional view of the solar cell processing system according to this invention.

FIG. 3 illustrates one embodiment of a process sequence containing various process recipe steps that may be used in conjunction with the various embodiments of the cluster tool described herein;

FIG. 4A is a side cross-sectional view of deposition reactor in accordance with embodiments of the invention;

FIG. 4B is a side cross-sectional view of deposition reactor in accordance with embodiments of the invention;

FIG. 4C is a side cross-sectional view of deposition reactor in accordance with embodiments of the invention;

FIG. 5 is a side cross-sectional view of deposition reactor in accordance with embodiments of the invention;

FIG. 6 isometric view of one embodiment of the deposition chamber in accordance with embodiments of the invention;

FIG. 7 an isometric view of one embodiment of the deposition chamber in which the lid assembly has been separated and tilted at an angle relative to the crucible in accordance with embodiments of the invention;

FIG. 8 is close up view of the processing region illustrated in FIG. 5 in accordance with embodiments of the invention;

FIG. 9 is plan view of solidified drops deposited on the collection region illustrated in FIG. 8 in accordance with embodiments of the invention.

FIG. 10A is an isometric cross-sectional view of the of the deposition reactor illustrated in FIG. 4A in accordance with embodiments of the invention.

FIG. 10B is a plan view of an array of solidified drops deposited on the collection region of the sheet support assembly in accordance with embodiments of the invention;

FIG. 10C is a plan view of an array of solidified drops deposited on the collection region of the sheet support assembly in accordance with embodiments of the invention;

FIG. 10D is a side cross-sectional view of the array of solidified drops deposited on the collection region shown in FIG. 10C in accordance with embodiments of the invention;

FIG. 11 is a side cross-sectional view of re-crystallization and/or preheat chamber in accordance with embodiments of the invention.

FIG. 12 is a side cross-sectional view of cool down chamber in accordance with embodiments of the invention.

FIG. 13A illustrates a series of rectangular shaped gas flow pulses as a function of time.

FIG. 13B illustrates a series of triangular shaped gas flow pulses as a function of time.

Claims

1. An apparatus for forming a polycrystalline semiconductor sheet comprising: a deposition reactor comprising: a crucible having one or more walls that form a crucible processing region and a deposition port that is formed in one of the one or more wall, wherein the deposition port is in fluid communication with the crucible processing region;a heater in thermal communication with the crucible, wherein the heater is adapted to heat a feed material positioned in the crucible processing region to a liquid state; anda gas delivery port that are in fluid communication with a fluid source, the feed material positioned in the crucible processing region, and the deposition port; anda sheet support platen having a collection region that is positioned to receive feed material delivered through the deposition port from the crucible processing region.

2. The apparatus of claim 1, further comprising an actuator adapted position the sheet support platen relative to the deposition port formed in the one or more walls.

3. The apparatus of claim 1, further comprising a feed material loading module having a material loading region that is adapted to accept a feed material, wherein the material loading region is in communication with the crucible processing region.

4. The apparatus of claim 3, wherein material loading region is adapted to accept feed material in a solid state and deliver the feed material to the crucible processing region in a liquid state by use of a second heater that is in thermal communication with the material loading region.

5. The apparatus of claim 1, further comprising: an enclosure having one or more walls that form a vacuum processing region, wherein the deposition reactor and the sheet support are positioned within the vacuum processing region; anda vacuum pump that is in fluid communication with the vacuum processing region and is adapted to evacuate the vacuum processing region to a pressure below atmospheric pressure.

6. The apparatus of claim 1, wherein a surface of the collection region of the sheet support platen contains a material selected from a group consisting of silicon carbide, silicon nitride, boron nitride, graphite, or boron carbide.

7. An apparatus for forming a polycrystalline semiconductor sheet comprising: a deposition reactor comprising: a crucible having one or more walls that form a crucible processing region and two or more deposition ports that are formed in one of the one or more wall, wherein the two or more deposition ports are in fluid communication with the crucible processing region;a heater in thermal communication with the crucible, wherein the heater is adapted to heat a feed material positioned in the crucible processing region to a liquid state; anda plurality of gas delivery ports that are in fluid communication with one or more fluid sources, the feed material positioned in the crucible processing region, and the two or more deposition ports, wherein the at least one gas delivery port is in fluid communication with each of the two or more deposition ports;a sheet support platen having a collection region that is positioned to receive feed material delivered through the two or more deposition ports from the crucible processing region; andan actuator adapted position the sheet support platen in direction that is generally parallel to a portion of the wall that has the two or more deposition ports formed therein.

8. The apparatus of claim 7, further comprising a controller that is in communication with actuator and the one or more gas delivery sources, wherein the controller is adapted to synchronizing the motion of the sheet support platen positioned on the actuator with the flow of the fluid delivered from the one or more fluid sources to form an array of crystallites on the collection region.

9. The apparatus of claim 7, further comprising a feed material loading module having a material loading region that is adapted to accept a solid granular feed material, wherein the material loading region is in communication with the crucible processing region.

10. The apparatus of claim 9, wherein material loading region is adapted to accept feed material in a solid state and deliver the feed material to the crucible processing region in a liquid state by use of a second heater that is in thermal communication with the material loading region.

11. The apparatus of claim 7, further comprising an enclosure having one or more walls that form a reactor processing region, wherein the deposition reactor and the sheet support are positioned within the reactor processing region.

12. The apparatus of claim 11, further comprising a vacuum pump that is in fluid communication with the reactor processing region and is adapted to evacuate the reactor processing region to a pressure below atmospheric pressure.

13. The apparatus of claim 7, wherein a surface of the collection region of the sheet support platen contains a material selected from a group consisting of silicon carbide, silicon nitride, boron nitride, graphite, or boron carbide.

14. The apparatus of claim 7, wherein the diameter of at least two of the two or more deposition ports is a different size.

15. The apparatus of claim 7, wherein the two or more deposition ports are disposed in a staggered array.

16. The apparatus of claim 7, wherein the feed material is a granular solid silicon containing material that is between about 1 mm and about 3 mm in size.

17. An apparatus for forming a polycrystalline semiconductor sheet comprising: one ore more walls that forms a system processing region;a deposition reactor positioned in the system processing region, wherein the deposition reactor comprises: a crucible having one or more walls that form a crucible processing region and a deposition port that are formed in one of the one or more wall, wherein the deposition port is in fluid communication with the crucible processing region; anda heater in thermal communication with the crucible, wherein the heater is adapted to heat a feed material positioned in the crucible processing region to a liquid state;a sheet support platen positioned in the system processing region and having a collection region that is positioned to receive feed material delivered through the deposition port from the crucible processing region;a re-crystallization chamber positioned in the system processing region and having a re-crystallization processing region, wherein the re-crystallization chamber is adapted to heat at least a portion of the feed material deposited on the collection region of the sheet support platen to a desired temperature; andan actuator that is adapted position the sheet support platen in direction that is generally parallel to a portion of the wall that has the two or more deposition ports formed therein and to transfer the sheet support platen through the re-crystallization processing region.

18. The apparatus of claim 17, further comprising a pre-heat chamber that is adapted to heat at least the collection region of the sheet support to a temperature that is at or below the feed material melting temperature.

19. The apparatus of claim 17, further comprising a cool down chamber that is adapted to cool the collection region of the sheet support platen after it has been processed in the re-crystallization chamber to a temperature that is at or below about 650° C.

20. The apparatus of claim 17, further comprising a feed material loading module having a material loading region which is accessible from a position outside the system processing region and can be sealably isolated from the system processing region by use of a moveable isolation door, wherein when the material loading region is not sealably isolated from the system processing region it is in communication with the crucible processing region.

21. The apparatus of claim 17, further comprising: a vacuum pump that is adapted to evacuate the system processing region to a pressure between about 10−9 and about 700 Torr.

22. The apparatus of claim 17, further comprising: a gas source that is adapted to deliver a gas to the system processing region to achieve a partial pressure of oxygen less than about 10−11 Torr in the system processing region.

23. The apparatus of claim 17, further comprising: a load-lock chamber that is in transferable communication with the system processing region and is adapted to receive one or more of the semiconductor sheets formed on the collection region of the support plate.

24. The apparatus of claim 17, wherein the feed material is a granular solid silicon containing material that is between about 1 mm and about 3 mm in size.

25. The apparatus of claim 17, wherein the deposition reactor further comprises a gas delivery port that are in fluid communication with a fluid source, the feed material positioned in the crucible processing region, and the deposition port.