Critical review of the epitaxial growth of semiconductors by rapid thermal chemical vapor deposition

Abstract

Rapid thermal processing, which was originally developed for implant annealing, has been extended to the epitaxial growth of semiconductors. Early work in this field featured the homoepitaxial growth of silicon. Abrupt doping profiles have been demonstrated for both boron and arsenic doped layers using conventional dichloro silane (DCS)/hydrogen chemistries. Minimum doping concentrations approaching 10 12 cm −3 have been demonstrated when growing over lightly doped substrates. Gas phase autodoping limits the minimum dopant concentration over more heavily doped substrates. Due to the temperature difference between the wafer and the walls, rapid thermal epitaxy has also been used to demonstrate the in-situ production of integrated device structures such as MOSFETs. Numerous authors have demonstrated the heteroepitaxial growth of strained layers of GeSi on Si, normally from the DCS/germane/hydrogen chemistry. The presence of germane dramatically increases the growth rate. This may be related to the ability of germane to produce reactive sites on the epi surface. The presence of arsine in the growth ambient shifts the growth activation energy back toward that of pure silicon. Numerous devices have been demonstrated with these films. Most common are the NPN heterojunction bipolar transistor and enhanced mobility p-channel FETs. These devices are natural applications of the technology because of the large valence band discontinuity. Growth of layers on strain relieved GeSi have led to the demonstration of PNP and n-channel devices. Optoelectronic devices have also been demonstrated, but the devices are not direct gap. Finally carbon incorporation can be used to reduce the strain. To some extent this provides the ability of decoupling strain and germanium mole fraction. The addition of small amounts of carbon dramatically increases the critical layer thickness.