The reaction of silicon with atomic hydrogen by modulated molecular beam mass spectrometry
The gas-solid reaction of single crystal silicon, Si(111), and atomic hydrogen were studied in an uhv chamber with an atomic hydrogen beam produced by thermally dissociating molecular hydrogen in a tungsten oven at 2500/sup 0/K. Silicon was not etched by molecular hydrogen but interacted very strongly with atomic hydrogen to produce the volatile silicon tetrahydride, SiH/sub 4/, and molecular hydrogen by recombination of surface-absorbed H atoms. The silicon surface was characterized by in situ Auger electron spectroscopy (AES). The temperature was 300/sup 0/K to 1000/sup 0/K in most tests, with some data above 1000/sup 0/K. The equivalent beam intensity at the target ranged between 10/sup 15/ to 10/sup 17/ atoms cm/sup -2/ sec/sup -1/, and the chopping frequency was varied from 20 Hz to 900 Hz. The apparent reaction probabilities and the phase lags of the SiH/sub 4/ and H/sub 2/ products were measured as functions of these experimental variables. Approximately 50% of the incident H atoms recombined on the surface and were re-emitted as molecular hydrogen. The SiH/sub 4/ reaction probability was highest at room temperature (approx. =3%), and decreased with increasing temperature up to about 1000/sup 0/K. At 1100/sup 0/K, where Si(111) changes surface structure from Si(111)-7 x 7 to Si(111)-1 x 1, the production of SiH/sub 4/ was a minimum, and increased with further increase in temperature. No reaction was observed with an oxidized silicon surface, and oxygen surface concentrations above 1% had a significant effect on reducing the strength of the reaction. The mechanism involves saturation of the surface dangling bonds by atomic hydrogen, formation of SiH and SiH/sub 2/ surface complexes, and reaction with a weakly-bound overlayer of hydrogen. The weakly bound hydrogen is mobile. It diffuses into the bulk and reacts with the SiH/sub 2/ complex to form SiH/sub 4/. Stepwise rate constants were determined.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 5553842
- Report Number(s):
- LBL-24382; ON: DE88005260
- Resource Relation:
- Other Information: Thesis (Ph.D.). Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
HYDROGEN
CHEMICAL REACTIONS
SILANES
CHEMICAL REACTION YIELD
SILICON
ATOMS
CHEMICAL REACTION KINETICS
MASS SPECTROSCOPY
MODULATION
MOLECULAR BEAMS
MONOCRYSTALS
RECOMBINATION
BEAMS
CRYSTALS
ELEMENTS
HYDRIDES
HYDROGEN COMPOUNDS
KINETICS
NONMETALS
ORGANIC COMPOUNDS
ORGANIC SILICON COMPOUNDS
REACTION KINETICS
SEMIMETALS
SILICON COMPOUNDS
SPECTROSCOPY
YIELDS
400201* - Chemical & Physicochemical Properties
656003 - Condensed Matter Physics- Interactions between Beams & Condensed Matter- (1987-)