Chapter 5 - Silicon Molecular Beam Epitaxy: Capabilities and Trends

Abstract

This chapter discusses the capabilities and trends of silicon molecular beam epitaxy (Si MBE). Si MBE is a maturing technology that is capable of growing high-quality layers at low temperature. The category Si MBE includes the growth of all the silicon-based compounds, such as silicon–germanium (Si-Ge) alloys, and silicides, such as nickel disilicide (NiSi 2 ) and cobalt disilicide, on silicon (CoSi 2 ). It also includes the growth of other materials, such as calcium fluoride ( CaF 2 ), on Si substrates. The chapter describes the principles of silicon and germanium growth by MBE, that is, the growth system design, capabilities for n - and p -type doping, and recent device applications. An epitaxial growth of silicon and related materials can be achieved by impinging atomic, molecular, or ionized beams onto a moderately heated typically between 550 and 850°C silicon substrate. MBE involves the evaporation of the pure elemental material onto the substrate surface. An established technique, that is, chemical vapor deposition (CVD) uses Si- or Ge-based molecular species that decompose on the surface before being incorporated. The growth of high-quality layers by MBE at low temperature demands an impurity-free environment. Thus, ultra-high-vacuum (UHV) techniques that correspond to base pressures of about 6 × 10 -9 Pa are used to ensure that contamination will not impede the crystal growth. The UHV conditions limit Si MBE to single-wafer throughput. The main advantages of Si MBE are based on its tremendous flexibility. It is an excellent tool for the investigation of novel electronic devices. Discrete IMPact ionization avalanche transit-time (IMPATT) diodes have already been produced by Si MBE and are available on the microelectronics market.