An in situ investigation of Si[sub x]Ge[sub 1-x] chemical vapor deposition by differential reflectance
An investigation of the surface kinetic processes of low pressure chemical vapor deposition (LPCVD) of Si, Ge, and Si[sub x]Ge[sub 1[minus]x] was carried out using time-resolved differential reflectance measurements. The source gas (disilane, digermane, or mixtures of these two diluted in a helium carrier) was delivered to a heated substrate by a fast-acting modulated molecular jet valve. Thin film growth was studied in the range of 400-500[degrees]C on Si and Ge (001) substrates. The kinetics of chemisorption and of by-product desorption were determined from the surface differential reflectance signal obtained using p-polarized, high-stability HeNe probe laser. Both chemisorption and by-product desorption were fond to obey first-order kinetics. Chemisorption of the parent molecules was found to be relatively efficient and weakly temperature dependent. For pure Si and Ge, by-product desorption occurred through a single first-order reaction. Two first-order desorption steps were inferred for the Si[sub x]Ge[sub 1[minus]x] alloy surfaces. These reactions are believed to be H[sub 2] desorption from Si-like and Ge-like surface sites. However, the activation energy of the more rapid of these two steps actually decreases as the Si content of the film increases. Generally, the films were of high crystalline quality and were very well aligned with the substrate. Preferential incorporation of digermane into the film produced an alloy composition that was Ge-rich relative to the gas composition. The primary accomplishment of this work is the demonstration that the active surface layer of the Si[sub x]Ge[sub 1[minus]x] system can be monitored in situ by an optical probe under typical LPCVD conditions. The results indicate that the rate-limiting step in Si or Ge LPCVD obeys simple first-order kinetics. Further work is needed to understand fully the rate-limiting surface reaction in Si[sub x]Ge[sub 1[minus]x] LPCVD.
- Research Organization:
- Tennessee Univ., Knoxville, TN (United States)
- OSTI ID:
- 7103314
- Country of Publication:
- United States
- Language:
- English
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Investigation of the kinetics of surface-limited thin film growth of SiGe alloys
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Related Subjects
360601* -- Other Materials-- Preparation & Manufacture
664200 -- Spectra of Atoms & Molecules & their Interactions with Photons-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
CHEMICAL COATING
CHEMICAL REACTION KINETICS
CHEMICAL VAPOR DEPOSITION
DEPOSITION
ELEMENTS
GERMANIUM
KINETICS
METALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
REACTION KINETICS
SEMIMETALS
SILICON
SORPTIVE PROPERTIES
SPECTRAL REFLECTANCE
SURFACE COATING
SURFACE PROPERTIES
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K