Patent ID: 7550355

Claim:
A method, comprising: obtaining a silicon layer having a plurality of regions distributed in a same first plane, wherein each region is separated from a neighboring region by a respective trench in the silicon layer, and wherein each region has first, second, third, and fourth sidewalls that together define a boundary of a rectangular surface and that is each also a side of one of the trenches; causing the silicon layer and a boron ion source to be oriented with respect to each other at a first relative orientation; while the silicon layer and the ion source are at the first relative orientation, directing ions into the silicon layer in a direction having a first angular component that, when measured in the first plane with respect to the first sidewall, is 45 degrees; causing the silicon layer and the ion source to be oriented with respect to each other at a second relative orientation different from the first relative orientation; while the silicon layer and the ion source are at the second relative orientation, directing ions into the silicon layer in a direction having a second angular component that, when measured in the first plane with respect to the second sidewall, is 45 degrees; causing the silicon layer and the ion source to be oriented with respect to each other at a third relative orientation different from the first and second relative orientations; while the silicon layer and the ion source are at the third relative orientation, directing ions into the silicon layer in a direction having a third angular component that, when measured with respect to the third sidewall within the plane parallel to the first plane, is 45 degrees; causing the silicon layer and the ion source to be oriented with respect to each other at a fourth relative orientation different from the first, second, and third relative orientations; and while the silicon layer and the ion source are at the fourth relative orientation, directing ions into the silicon layer in a direction having a fourth angular component that, when measured with respect to the fourth sidewall within the plane parallel to the first plane, is 45 degrees, thereby producing a boron concentration in a bottom of each of the trenches that is on average twice that of a boron concentration in each of the first, second, third, and fourth sidewalls.