In such a known method the target may be, for example, a semiconductor disc which is locally provided with a coating not permeable to ions and in which implanted zones are created in the places having no coating. In general the implanted doses should be as homogeneous as possible throughout the semiconductor disc.
In known methods of implanting ions the ion beam describes a pattern in the form of a zig-zag line over the target, which line extends from one side of the pattern to the other side while descending at a small angle, travels from there back to the first side while descending at the same angle, and so on. Such a beam pattern exhibits disadvantages. Near the sides of the pattern where the line returns at an acute angle, the surface with which the ion beam impinges on a semiconductor disc will overlap in the return stroke as a part of the already implanted "line". This overlap causes locally a larger implantation dose, hence inhomogeneity. Furthermore the beam will cover the whole pattern a number of times, for example in an up and down direction, so as to ultimately achieve a desired implantation dose of the target. In the known method, when a full pattern has been covered and a return pattern is described, the beam will not follow the lines of the preceding pattern, but the lines of the return pattern are slightly shifted. So these lines will locally intersect the lines of the preceding pattern and in these areas a larger implantation dose than elsewhere will also be formed, which is a further cause of inhomogeneity.
USPTO Backgrounds
USPTO Backgrounds