Low-temperature Si and Ge CVD processing was investigated unaer the cleanest possible reaction environment of SiH4, GeH4 and H2 using an ultraclean hot-wall low-pressure CVD system. Epitaxial growth can be achieved on Si substrates a't temperatures as low as 350 and 550'~ for Ge and Si, respectively. The deposition rate can be expressed by an equation similar to the Langmuir adsorption isotherm as a function of SIB4 and H2 partial pressure for Si CVD, and only GeH4 partial pressure for Ge CVD with excellent agreement. The substrate orientation dependence of the deposition rate shows that the surface reaction proceeds at adsorption sites composed of dangling bonds on the surface. It is found that the SiH4 decomposition induces nucleation on Si oxide. The nucleation rate is suppressed by the presence of GeH4 and decreases on CVD BPSG compared with Si02. Therefore, by a proper choice of deposition temperature, SiH4 and GeH4 partial pressure, as well as of the insulating oxide. 500nm-thick selective growth of Si at 850'~ and Si-Ge alloy at 550'~ could be realized. A perfect selective growth of Ge between Si and Si02 is obtained. At low surface coverages of GeH4 on Si, facets are formed due to a step-flow dominated growth mechanism. At high surface coverages, plane surfaces are obtained due to dangling bond dependent growth mechanisms.
A method for growing the high-quality strained epitaxial heterostructure of Si/Si1-x
Ge
x
/Si by low-pressure chemical vapor deposition (CVD) and the fabrication of Si1-x
Ge
x
-channel metal-oxide-semiconductor field-effect transistors (MOSFET's) with a high Ge fraction layer have been investigated. It is found that lowering of the deposition temperature of the Si1-x
Ge
x
and Si capping layers is necessary with increasing Ge fraction in order to prevent island growth of the layers. With the use of the optimized fabrication process, Si/Si1-x
Ge
x
/Si heterostructures with flat surfaces and interfaces were realized, and a high-performance Si0.5Ge0.5-channel MOSFET has been achieved with a large mobility enhancement of about 70% at 300 K and over 150% at 77 K compared with that of a MOSFET without a Si1-x
Ge
x
channel.
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T h e BzHe-and PHs-partial pressure dependence of the doping concentration of in-situ doped silicon films, deposited in the temperature range between 6 0 0 and 7500C by low pressure chemical vapor deposition has been investigated for two different substrate orientations. In addition, the influence of BzHs and PHs and their partial pressure o n the silicon growth rate has been studied. It is found that the doping concentration can b e controlled over a wide range, and that in the presence of PHs as well a s BzHe the silicon growth is reduced. In the case of boron doping, the in-situ doping has been used to fabricate delta-doped silicon layers.
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