Molecular Beam Epitaxy:
The molecular beam epitaxy (MBE) is based on evaporation. In MBE, the film is evaporated and deposited one layer at a time. In the process, no chemical reactions are considered. Instead of that the evaporation of silicon and other dopant is carried out under ultra high vacuum (UHV) pressures of the orders of 10-8 to 10-10 Torr • The through put is slow. The growth rate is also very slow typically, 0.01 to 0.3 gm/min.
The molecular beam epitaxy is carried out under temperature ranging between 6009C to 9009C which is comparatively low temperature. As this process is very expensive, it is, extensively used in only special applications such as Ga As technology, silicon on insulator (SIC) and silicon on sapphire (SOS).
Advantages of MBE Over CVD Process
- MBE is low temperature process which is advantageous for VLSI
- While preparing thin layers using MBE process, auto.cloping and autodiffusion both are minimized.
- The MBE process can be used for generating complicated doping profiles as it regulates the amount of dopant.
- As MBE process is based on the evaporation of silicon and the dopants, hence no chemical reactions are involved in it.
- For MBE process safety precautions are not required extensively as compared to those required in CVD process.
Disadvantages of MBE Process
- For overall perfect and pure film, it is necessary to maintain a very low pressure of the order of 10-10 Tor, which is slightly difficult.
- This process is very expensive as compared to CVD process.
- The growth rate in MBE process is 0.01 – 0.3 gm/min which is very small compared to the growth rate of 1 µm/min in CVD process.