Abstract A novel method for producing very high concentrations of semiconductor dopants in silicon by a diffusion process. The concentration of dopant achievable by the present invention approaches the solid solubility limit of the dopant material. First an undoped layer of material, typically silicon dioxide, is deposited over one or both of the planar surfaces of a silicon substrate of a particular conductivity type. Next a second layer of doped silicon dioxide is deposited over the first layer, the dopant therein being of a conductivity type opposite of that of the silicon wafer. A third layer of undoped silicon dioxide is then deposited over the second layer. Next, the substrate of silicon, with the three layers deposited thereon, is heated to a temperature which causes the diffusion of some dopant into the upper region of the silicon substrate. The three layers of silicon dioxide are then stripped off, and three fresh layers are deposited. The heating step is repeated, ''''pumping,'''' by diffusion, more dopant into the silicon substrate from the fresh source. The process can be repeated, thereby enabling the concentration of dopant in the silicon substrate to approach the solid solubility limit. This invention also contemplates growing the layers of silicon dioxide by controlled oxidation of the substrate, instead of by depositing them.
The method of claim 1 wherein said wafer is of P conductivity type, said glass is silicon dioxide and said dopant is a material which, when diffused into said wafer, cause said region thereof to be of N conductivity type.
Claim 2
Independent Claim
260 words
A method of producing high concentrations of dopant in silicon comprising the steps of: a. providing a wafer of silicon of a first conductivity type, said wafer having planar surfaces; b. heating said wafer in an oxidizing atmosphere at a temperature in the range from 1,000* to 1,250* C until a first layer of silicon dioxide is grown on each of said planar surfaces, said first layer having a thickness in the range from 100 - 1,000 Angstroms; c. introducing a dopant into said oxidizing atmosphere while heating said wafer at said temperature until a second layer of doped silicon dioxide is formed over each of said first layers, some of said dopant diffusing through said first layers into said wafer and causing a region thereof to be of a second conductivity type opposite that of said first conductivity type, said second layer having a thickness in the range from 500 - 2,000 Angstroms; d. removing said dopant from said atmosphere and continuing said heating at said temperature until an undoped third layer of silicon dioxide is grown over each of said second layers while said dopant therein continues to diffuse into said region of said wafer, said third layer having a thickness in the range from 100 - 1,000 Angstroms; e. removing substantially all of said first, second and third layers of silicon dioxide by etching said wafer with hydrofluoric acid; f. repeating said steps (b), (c), (d) and (e) at least once in said order until said dopant in said region of said wafer reaches a desired concentration.