1. Field of the Invention
The invention is concerned with apparatus for patterning surfaces by selective removal of surface material.
2. Description of the Prior Art
The manufacture of miniaturized electromagnetic signal processing devices depends to a large extent on methods for patterning layers of metallic, semiconducting, and insulating materials. Such patterning may be carried out chemically by so-called wet etching with a suitable agent in the presence of a mask. The mask prevents contact between the etchant and portions of the layer being etched and thereby prevents underlying areas of the layer from being etched away. Alternatively, patterning may be effected by sputter-etching or by ion-milling as disclosed in U.S. Pat. No. 3,860,783. This latter method utilizes a wide-aperture beam of ions, parallel to within .+-.5.degree., in conjunction with masking techniques analogous to those used in wet etching. Portions of the layer exposed to the ion beam are eroded in this case due to transfer of momentum from the ions to the particles constituting the exposed surface rather than by chemical reaction. The ion beam is produced by means of an ion gun in which a suitable gas such as argon is ionized by electron impact and in which the ions so produced are accelerated by means of a stationary electric field. To prevent chemical interaction between the gas and the layer being etched, it is advantageous to choose one of the noble gases as etchant gas; however, reactive gases such as oxygen have also proven effective.
Ion milling allows patterning circuit elements of widths of as little as one micron and uniform to within 0.05 micron. While the process is basically suited for the manufacture of small, reliable, inexpensive microminiature communications devices such as high-frequency, transistors, diffraction gratings, and magnetic bubble memories, commercial exploitation has been hampered due to the limited capacity of available ion milling apparatus.