column of ions 25 the coil assembly 31 constitutes the primary element in a cyrogenic pumping tower between the column of ions 25 and the coils assembly 31 are baffles 51 which serve to protect the coil assembly 31 and to prevent the coil assembly 31 from disturbing the narrow beam of plasma when the narrow beam of plasma 25 enters the deposition chamber ions remaining the narrow beam of ions deposit upon a target 53 thus forming a layer or a semiconductor device since it is desired that ultimately the semiconductor materials be used outside the device 1 the semiconductor materials such as the silicon should be removable from the target area there are several methods of accomplishing this 1 a semi permanent or temporary layer of a material to which the silicon does not adhere may be placed over the target area an example of this type of material would be boron nitrite depending upon the interface temperature the boron nitrite will decompose to some extent and the boron will diffuse into the silicon film deposited on the boron nitrite this results in heavy doping which renders the bottom surface of the silicon conducting approximately 10 3 ohms cm this permits the bottom surface to act as a back conductor for a semi conductor device which will be formed from the semiconductor material 2 the silicon can be deposited on a reusable.