Semiconductor technology

A tremendous upgrowth of microelectronics, most of all further miniaturization and sophistication of integrated systems is connected with the development of fundamentally new technological processes, which are often possible only in vacuum conditions. Vacuum technological processes makes it possible not only to obtain integrated schemes with more compact item design with high level of process control, but also to reduce the prime cost of integrated schemes. Apart from that, such technologies, as a rule, are safer for the health of working personnel. Therefore diffusion doping is replaced by ion doping, photolithography — by electron-beam lithography, chemical etching — by plasm etching.

Most of these processes do not require ultra-high vacuum (as a rule, they are conducted under pressure around 10-4 Pa). On the other hand, all basic research works, connected with further development of integrated scheme technology, are usually carried out in ultra-high vacuum conditions, in order to, whenever possible, minimize the impact of uncontrolled factors. One of the methods, which is widely used at the present time in manufacturing of silicon semi-conductor structures, is epitaxy. Materials, which are hard to obtain in form of crystals, can be grown as monocrystallic layers on monocrystallic base plates. Moreover, the cristallic structures of the layer and the base plate must be similar or the same to accommodate growth of a defect-free oriented monocrystallic layer.

Most of the methods of epitaxy are based on technology of liquid phase or gas vapor high temperature deposition. In recent times a new method is widely used — molecular beam epitaxy (MBE), which is based on molecular beam condensation. Molecular beams are created in vacuum with the aid of small furnaces with a hole (Knudsen cell deposition source) and condensed on a heated base plate.

A specific feature of MBE method in comparison with other methods of growing epitaxy layers is a possibility of obtaining much smoother surfaces and interfaces. This possibility is the most essential in the process of manufacturing materials with special optic properties, used in solid lasers. Apart from that, MBE method makes it possible to obtain more precise dopant profile, to grow the layer in-situ, and to very precisely control the doping process.