Process for resurf diffusion for high voltage MOSFET
View Patent ↗A starting wafer for high voltage semiconductor devices is formed by implanting arsenic into the top surface of a p type silicon substrate wafer to a depth of about 0.1 micron. A N type non-graded epitaxial layer is then grown atop the substrate without any diffusion step so that the arsenic is not intentionally driven. Device junction are then diffused into the epitaxially grown layer.
1. A starting wafer for containing semiconductor junctions having voltage ratings in excess of 600 volts, said wafer comprising:
a P-type substrate;
an unmasked blanket arsenic implant of depth less than 0.3 microns formed uniformly across and in a top surface of said substrate; and
an N-type junction-receiving epitaxial layer deposited atop said arsenic implant formed in the surface of said substrate, said arsenic implant being diffused only due to subsequent diffusions which form junctions in said N-type junction-receiving epitaxial layer and acting as a buffer layer to the doping of said epitaxial layer from said P-type substrate.
2. The wafer of claim 1 , wherein said arsenic implant is increased in thickness to less than about 5 microns by subsequent diffusions into said epitaxial layer.
3. The wafer of claim 1 , wherein said P substrate is boron doped and has a resistivity of 70 ohm cm, and said arsenic implant has a resistivity defined by an implant dose of about 1.3E12 atoms per square cm.
4. The wafer of claim 2 , wherein said P substrate is boron doped and has a resistivity of 70 ohm cm, and said arsenic implant has a resistivity defined by an implant dose of about 1.3E12 atoms per square cm.
5. The wafer of claim 3 , wherein said epitaxial layer is phosphorus doped and has a thickness of less than about 5 micrometers and a resistivity of about 1.0 ohm cm.
6. The wafer of claim 4 , wherein said epitaxial layer is phosphorus doped and has a thickness of less than about 5 micrometers and a resistivity of about 1.0 ohm cm.
7. The wafer of claim 1 , wherein said arsenic implant has less than the charge in said epitaxial layer and contains about 40% of the total charge in the implant and the epitaxial layer.
8. The wafer of claim 1 , wherein the total charge in said epitaxial layer and said arsenic implant is in about a 60 to 40 ratio.