Method for the post-alloy diffusion of impurities into a semiconductor

Claim 1

IN A METHOD OF FABRICATING A SOLAR CELL OUT OF A SLICE OF SEMICONDUCTOR MATERIAL HAVING FIRST AND SECOND MAJOR SURFACES WHICH CONSTITUTE THE FRONT LIGHT RECEIVING SURFACE AND THE BACK SEMICONDUCTOR SURFACE, RESPECTIVELY, OF THE FABRICATED SOLAR CELL, SAID METHOD BEING OF THE TYPE WHEREIN A P-N JUNCTION IS FORMED BY DIFFUSING A DOPANT OF A FIRST TYPE CONDUCTIVITY INTO SAID FIRST MAJOR SURFACE OF SAID SLICE OF SEMICONDUCTOR MATERIAL HAVING A SECOND TYPE CONDUCTIVITY OPPOSITE SAID FIRST TYPE CONDUCTIVITY, THE IMPROVEMENT IN SAID METHOD COMPRISING THE STEPS OF: A.PLACING A LAYER OF MATERIAL ON SAID SECOND MAJOR SURFACE OF SAID SLICE PRIOR TO THE FORMATION OF SAID P-N JUNCTION, SAID LAYER OF MATERIAL BEING CHARACTERIZED IN THAT IT WILL FORM AN ALLOY WITH THE SEMICONDUCTOR AT TEMPERATURES BELOW THE MELTING POINT OF SAID SEMICONDUCTOR MATERIAL AND IT CONTAINS ATOMS WHICH ARE DOPANT ATOMS OF SAID SECOND TYPE CONDUCTIVITY, B. HEATNG SAID SLICE WITH LAYER OF MATERIAL THEREON TO A TEMPERATURE SUFFICIENT TO CAUSE SAID MATERIAL TO ALLOY WITH SAID SEMICONDUCTOR MATERIAL AND BE IN A MOLTEN STATE AND SAID DOPANT ATOMS OF A SECOND TYPE CONDUCTIVITY TO DIFFUSE INTO SAID SLICE FROM SAID MATERIAL THEREBY FORMING A HEAVILY DOPED REGION OF SAID SECOND TYPE IN SAID SLICE NEAR SAID SECOND MAJOR SURFACE OF SAID SLICE, AND C. SUBSEQUENTLY DIFFUSING SAID DOPANT OF A FIRST TYPE CONDUCTIVITY INTO SAID FIRST MAJOR SURFACE FROM A GASEOUS MIXTURE CONTAINING ATOMS OF SAID DOPANT AT A TEMPERATURE ABOVE THE MELTING POINT OF SAID MATERIAL AND ABOVE THE ALLOYING AND MELTING POINT OF AN ALLOY OF SAID MATERIAL AND SAID SEMICONDUCTOR, WHEREIN SAID SEMICONDUCTOR SLICE IS SILICON AND SAID LAYER OF MATERIAL COMPRISES A METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, INDIUM, GALLIUM AND THALLIUM.