Forming of contoured irradiated regions in materials such as semiconductor bodies by nuclear radiation

DETAILED DESCRIPTION The present invention provides a method of forming an irradiated region of a desired thickness, dosage and dosage gradient in a material such as semiconductor body a desired distance from a selected surface thereof.
The invention is particularly useful in tailoring irradiated regions to simulate radiation effects on material properties produced by fast neutrons of a fusion reaction, and in forming irradiated regions changing the electrical characteristics of semiconductor bodies without affecting other electrical characteristics of the body.
The method is commenced by providing a radiation beam from a given radiation source radiating particles with molecular weight of at least one (1) capable of penetrating a material wherein an irradiated region is to be formed though a selected surface to greater than the maximum desired distance of the irradiated region from the selected surface.
Preferably, such nuclear radiation source is protons or alpha particles produced by a Van de Graaff accelerator forming a substantially monoenergetic radiation beam.
Such radiation sources can be produced relatively inexpensively, and are substantially chemically and electrically inactive on irradiation into the material.
A beam modifier of a given material and nonuniform shape is formed to modify the energy of the radiation beam on transmission therethrough.
Preferably the beam modifier is made of material such as aluminum to reduce scattering and provide good resolution for a transmitted radiation beam.
The beam modifier is of a shape to form a transmitted radiation beam capable of forming an irradiated region of a desired thickness and dosage gradient in the material a given distance from the selected surface on irradiation of the material through the selected surface with the transmitted radiation beam.
Almost any reasonable distance between the irradiated region and selected surface and any reasonable thickness of the irradiated region is possible provided the radiation source emits particles of energy sufficient to penetrate to the maximum depth of the irradiated region from the selected surface