Patent ID: 7820475

Claim:
A method of forming active diffusion regions in a back side contact solar cell, the method comprising: forming a first set of dopant sources on a back side of a wafer to be processed into a solar cell, the wafer having a front side configured to face the sun during normal operation of the solar cell, the back side being opposite the front side; selectively depositing a second set and a third set of dopant sources over the first set of dopant sources, the second and third set of dopant sources having different polarity, the second set of dopant sources being selectively deposited in a first set of openings through the first set of dopant sources, the third set of dopant sources being selectively deposited in a second set of openings through the first set of dopant sources, the first set of dopant sources being formed thicker than the second set of dopant sources and the third set of dopant sources; performing a diffusion step to diffuse dopants from the first set of dopant sources to form a first set of active diffusion regions of the solar cell, dopants from the second set of dopant sources to form a second set of active diffusion regions of the solar cell, and dopants from the third set of dopant sources to form a third set of active diffusion regions of the solar cell; and exposing what are left of the first, second and third sets of dopant sources after the diffusion step to an etchant to remove portions of what are left of the third and second sets of dopant sources in a self-aligned etch process to form contact openings to the second and third sets of active diffusion regions without completely removing what are left of the first set of dopant sources.