Patent ID: 7939418

Claim:
A partial implantation method to implant dopant ions at different densities into a center region and a peripheral region defined in a wafer by means of a circular boundary line, the method comprising: defining a first region at an upper side of a horizontal line as a tangent line of the circular boundary line and a second region at a lower side of the horizontal line; implanting dopant ions at a first density into a first implantation zone as a remaining part of the first region except for a specific part of the first region close to the horizontal line, at a second density different from the first density into a second implantation zone as a remaining part of the second region except for a specific part of the second region close to the horizontal line, and at a third density between the first and second densities into a third implantation zone as remaining part of the wafer except for the first and second implantation zones; and repeatedly implanting the ions while intermittently rotating the wafer within an angular range of 360°, wherein a slope of the density of dopants in the third implantation zone can be adjusted by varying the area of a least one of the first and second implantation zones.