EPITAXIAL WAFER HAVING A HEAVILY DOPED SUBSTRATE AND PROCESS FOR THE PREPARATION THEREOF
This invention generally relates to a process for suppressing silicon self-interstitial diffusion near the substrate/epitaxial layer interface of an epitaxial silicon wafer having a heavily doped silicon substrate and a lightly doped silicon epitaxial layer. Interstitial diffusion into the epitaxial layer is suppressed by a silicon self-interstitial sink layer comprising dislocation loops.
1 . A process for preparing an epitaxial silicon wafer, the process comprising:
forming a layer of dislocation loops in a highly doped single crystal silicon substrate, the highly doped silicon substrate being the slice of an ingot grown by the Czochralski method having a central axis, a front surface and a back surface that are generally perpendicular to the central axis, a circumferential edge joining the front and back surfaces, a radius extending from the central axis to the circumferential edge, a resistivity of less than 5 mΩ*cm; and wherein the dislocation loops do not extend to the front surface; and
depositing an epitaxial silicon layer on the front surface of the highly doped silicon substrate to form the epitaxial silicon wafer, the epitaxial layer having a resistivity of greater than about 10 mΩ*cm.
2 . The process of claim 1 wherein the dislocation loops are formed by an ion implantation of the highly doped single crystal silicon substrate and an anneal of at least about 750° C.
3 . The process of claim 2 wherein the implanted ions are selected from the group consisting of silicon, germanium, helium, neon, argon, xenon, and a combination thereof.
4 . The process of claim 2 wherein the ion implantation is carried out at an energy level of at least about 30 keV.
5 . The process of claim 2 wherein the ion implantation step implants at least about 6×10 13 atoms/cm 2 .
6 . The process of claim 2 wherein the anneal is carried out for at least about 3 seconds.
7 . The process of claim 1 wherein the highly doped silicon substrate comprises an N-type dopant.
8 . The process of claim 7 wherein the highly doped silicon substrate comprises a dopant selected from the group consisting of P, As, Sb, and combinations thereof.
9 . The process of claim 1 wherein the highly doped silicon substrate comprises a P-type dopant.
10 . The process of claim 9 wherein the highly doped silicon substrate comprises a dopant selected from the group consisting of B, Al, Ga, and combinations thereof.
11 . The process of claim 1 wherein the epitaxial layer comprises an N-type dopant.
12 . The process of claim 11 wherein the epitaxial layer comprises a dopant selected from the group consisting of P, As, and combinations thereof.
13 . The process of claim 1 wherein the epitaxial layer comprises a P-type dopant.
14 . The process of claim 13 wherein the epitaxial layer comprises a dopant selected from the group consisting of B, Al, Ga, and combinations thereof.
15 . The process of claim 1 wherein the epitaxial layer is deposited to a thickness of at least about 5 cm.
16 . The process of claim 1 further comprising depositing a layer of polysilicon on the back surface of the highly doped single crystal silicon substrate before the annealing step.
17 . The process of claim 1 wherein the layer is at a depth of at least about 100 Å from the front surface of the highly doped silicon substrate.
18 . The process of claim 1 wherein the layer of dislocation loops has a concentration of at least about 1×10 8 loops/cm 2 .
19 . The process of claim 1 wherein the layer of dislocation loops has a radial width of at least about 10% of the radius.