One of the main requirements for Si-based ultrasmall devices is atomic-order control of process technology. Here we show the concept of atomically controlled processing for group IV semiconductors based on atomic-order surface reaction control. By ultraclean low-pressure chemical vapor deposition using SiH 4 and GeH 4 gases, high-quality low-temperature epitaxial growth of Si, Ge, and Si 1Àx Ge x with atomically flat surfaces and interfaces on Si (100) is achieved, and atomic-order surface reaction processes on group IV semiconductor surface are formulated based on a Langmuir-type surface adsorption and reaction scheme. In in-situ doped Si 1Àx Ge x epitaxial growth on the (100) surface in a SiH 4 -GeH 4 -dopant (PH 3 , or B 2 H 6 or SiH 3 CH 3 )-H 2 gas mixture, the deposition rate, the Ge fraction and the dopant concentration are explained quantitatively assuming that the reactant gas adsorption/reaction depends on the surface site material and that the dopant incorporation in the grown film is determined by Henry's law. Self-limiting formation of 1-3 atomic layers of group IV or related atoms in the thermal adsorption and reaction of hydride gases on Si(100) and Ge (100) is generalized based on the Langmuir-type model. Si or SiGe epitaxial growth over N, P or B layer already-formed on Si(100) or SiGe(100) surface is achieved. Furthermore, the capability of atomically controlled processing for advanced devices is demonstrated. These results open the way to atomically controlled technology for ultralarge-scale integrations.

By ultraclean low-pressure chemical vapor deposition (CVD) using SiH4 and GeH4 gases, low-temperature epitaxial growth of Si/Si1- x Ge x /Si heterostructures at high Ge fractions on Si(100) is achieved. The deposition rate and Ge fraction are controlled by the SiH4 and GeH4 partial pressures and the deposition temperature. Atomically flat surfaces and interfaces for the heterostructures containing Si0.8Ge0.2, Si0.5Ge0.5 and Si0.3Ge0.7 layers are obtained by deposition at 550, 500 and 450° C, respectively. Cross-sectional transmission electron microscope (TEM) images and Raman spectra show that these samples have excellent epitaxial qualities. It is also found that the Si0.5Ge0.5-channel metal-oxide-semiconductor field-effect transistor (MOSFET) has the highest peak field-effect mobility. Moreover, the atomic-layer growth of Si and Ge is achieved by the separation of surface adsorption and reaction of reactant gases. The adsorption processes of SiH4 and GeH4 are found to be described by the Langmuir adsorption-type equation.

We report the observation of self-limited layer-by-layer etching of Si by alternated chlorine adsorption and low energy Ar+ ion irradiation using an ultraclean electron-cyclotron-resonance plasma apparatus. The etch rate per cycle increased with the chlorine supplying time and saturated to a constant value of about 1/2 atomic layer per cycle for Si(100) and 1/3 for Si(111), which was independent of the chlorine partial pressure in the range of 1.3–6.7 mPa. These results indicate that etching was determined by self-limited adsorption of chlorine. Moreover, the chlorine adsorption rate was found to be described by a Langmuir-type equation with an adsorption rate constant k=83 and 110 (Pa s)−1 for Si(100) and Si(111), respectively.

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