Solar cell fabrication using implantation

Abstract

A solar cell device and method of making are provided. The device includes a silicon substrate including a preexisting dopant. A homogeneous lightly doped region is formed on a surface of the silicon substrate to form a junction between the preexisting dopant and the lightly doped region. A heavily doped region is selectively implanted on the surface of the silicon substrate. A seed layer is formed over the heavily doped region. A metal contact is formed over the seed layer. The device can include an anti-reflective coating. In one embodiment, the heavily doped region forms a parabolic shape. The heavily doped regions can each be a width on the silicon substrate a distance in the range 50 to 200 microns. Also, the heavily doped regions can be laterally spaced on the silicon substrate a distance in the range 1 to 3 mm from each other. The seed layer can be a silicide. The silicon substrate can include fiducial markers configured for aligning the placement of the heavily doped regions during an ion implantation process.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to co-pending U.S. Provisional Application Ser. No. 61 / 131,687, filed Jun. 11, 2008, entitled “SOLAR CELL FABRICATION USING IMPLANTATION,” co-pending U.S. Provisional Application Ser. No. 61 / 131,688, filed Jun. 11, 2008, entitled “APPLICATIONS SPECIFIC IMPLANT SYSTEM FOR USE IN SOLAR CELL FABRICATIONS,” co-pending U.S. Provisional Application Ser. No. 61 / 131,698, filed Jun. 11, 2008, entitled “FORMATION OF SOLAR CELL-SELECTIVE EMITTER USING IMPLANTATION AND ANNEAL METHODS,” co-pending U.S. Provisional Application Ser. No. 61 / 133,028, filed Jun. 24, 2008, entitled “SOLAR CELL FABRICATION WITH FACETING AND IMPLANTATION,” and co-pending U.S. Provisional Application Ser. No. 61 / 210,545, filed Mar. 20, 2009, entitled “ADVANCED HIGH EFFICIENCY CRYSTALLINE SOLAR CELL FABRICATION METHOD,” which are all hereby incorporated by reference as if set forth herein.FIELD OF THE INVENTION[0002]The present invention relates...

AI Technical Summary

Benefits of technology

[0014]The seed layer is preferably a silicide. The seed layer can be a layer of a material including any of the materials Ni, Ta, Ti, W or Cu. The silicon substrate can include fiducial markers configured for aligning the placement of the heavily doped regions during the selective ion implantation process. The method includes using an annealing process on the silicon substrate having the homogeneous lightly doped region. Alternatively, the annealing process is used on the silicon substrate after forming the metal contact. Using annealing after forming the metal contact allows for lower temperature annealing than conventional processes. Thus allowing for the use of substrates or thin substrates on carriers that otherwise may degrade at higher temperatures.

Problems solved by technology

The use of diffusion in forming dopants on the surface of a semiconductor substrate is plagued by several problems.

One problem is excess accumulation of unactivated dopants near the surface as the dopants are driven into the bulk of the semiconductor material.

In particular, one problem encountered is the lack of utilization of the blue light as the result of formation of a “dead layer.”

Another drawback of conventional diffusion forming systems is the difficulty in laterally positioning of the dopants across the semiconductor substrate as the line widths and wafer thicknesses become smaller.

Such miniaturization is difficult or even impossible for the present methodology of diffusion and screen printing in forming solar cells.

The interface of the metal contact with the semiconductor affects the performance of the solar cell.

This heating process improves the interface, but also includes drawbacks.

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