Masanori Shinohara

Oxidation processes on the H2O-chemisorbed Si(100) surface studied by in-situ infrared spectroscopy

Abstract The oxidation processes on the Si(100)-(2×1) surface during exposure to H 2 O and subsequent thermal annealing were investigated using in-situ infrared absorption spectroscopy in the multiple internal reflection geometry. Exposure to H 2 O results in the oxidation of Si–Si bonds (dimer bond and backbonds) even at room temperature. Upon annealing up to 500°C the dimer bond is cleaved to produce dihydride Si (Si–H 2 ), and the backbonds are attacked by atomic oxygen released from the surface Si–OH species to produce intermediate oxidation species such as SiH 2 (SiO). We demonstrate that most of the hydride species are driven out from the surface by annealing up to 500°C, but an intermediate oxidation species (SiH(O 3 )) persists up to 600°C. A model of wet oxidation is presented in which dissociation of water molecules, attack of the Si–Si bonds by atomic oxygen and hydrogen and hydrogen desorption are involved in the oxidation.

Infrared spectroscopy study of adsorption of silane on Si(001)

Abstract We used infrared absorption spectroscopy in the multiple internal reflection geometry to investigate the adsorption of SiH 4 on the Si(0xa00xa01)(2×1) surface. Comparing infrared data with the density functional cluster calculation, we show that at low hydrogen coverage the silane molecule dissociatively adsorbs on Si(0xa00xa01)(2×1) to populate a dihydride (SiH 2 ) at the bridge site between two adjacent dimers and monohydride species; monohydrides are formed by terminating the unsaturated dangling bonds of dimers by hydrogen atoms released from the silane molecule. We suggest that at high hydrogen coverage, silane adsorbs onto a single dimer to generate monohydride and sylil groups (–SiH 3 ). We also demonstrate that the dihydride species that is initially generated by silane adsorption, decomposes to monohydride species even at room temperature.

Infrared study of adsorption and thermal decomposition of Si2H6 on Si(100)

Sumario We have investigated the adsorption and thermal decomposition of disilane on Si(100) (2×1) using infrared absorption spectroscopy. We demonstrate that at room temperature, disilane dissociatively adsorbs onto the surface with the dimer bond unbroken, to produce mono-, di-, and tri-hydride species. At low coverages, the disilane molecule adsorbs on the surface without breaking the Si–Si bond of the molecule. Thermal annealing following room-temperature adsorption of disilane produces a hydrogen-terminated adatom dimer (HSi–SiH) and an isolated monohydride species. We suggest that these hydride species are generated through the rupture of the substrate dimer bonds. Hydrogen desorption from the isolated monohydride occurs at much lower temperature than that from the adatom dimer.

Infrared study of carbon incorporation during chemical vapor deposition of SiC using methylsilanes

Abstract We use infrared absorption spectroscopy (IRAS) in the multiple internal reflection geometry to investigate the carbon incorporation during chemical vapor deposition of SiC on Si(1xa00xa00) using methylsilanes, SiH x (CH 3 ) 4− x ( x =1–3). We have measured IRAS spectra in the Siue5f8H stretching vibration region of the Si(1xa00xa00) surface that was dosed with methylsilanes at temperatures ranging from 300 to 500°C. IRAS data demonstrate that at temperatures below 400°C, methylsilane is thermally decomposed to form a doubly occupied dimer (DOD, ue5fbHSi–SiHue5fb) and a mixed adatom dimer (ue5fbHSi–SiHue5fb). At higher temperatures, carbon atoms that are released from the methyl group, attack the backbonds of surface Si atoms to generate amorphous carbon-incorporated layers that include Si atoms having two or three C atoms bound to them. It is found that the carbon incorporation is enhanced with the increase of the number of methyl groups of methylsilane.

Hydrogen adsorption and desorption processes on Si(100)

The hydrogen adsorption and desorption processes on the Si(100)(2×1) surface were investigated using in-situ infrared absorption spectroscopy in the multiple internal reflection geometry. It is demonstrated that the distribution of hydride species (SiH, SiH2, and SiH3) significantly changes during adsorption of atomic hydrogen and desorption of molecular hydrogen. At the initial stages of hydrogen adsorption, the monohydride Si (Si–H) and dihydride Si (Si–H2) are populated, with Si–H being dominant. For higher hydrogen exposures the dihydride and trihydride Si are formed. Thermal annealing causes hydrogen to desorb from the hydride species. For annealing temperature up to approximately 400°C, the trihydride Si is etched away, producing a H-terminated surface which consists of monohydride (SiH) and dihydride (SiH2) species. We demonstrate that the conversion from the monohydride to the dihydride phase occurs during thermal annealing.

Adsorption and decomposition of methylsilanes on Si(100)

Abstract We have investigated in-situ the adsorption and thermal decomposition of methylsilanes, SiH x (CH 3 ) 4− x ( x =1–3), on Si(100)(2×1), using infrared absorption spectroscopy (IRAS) in the multiple internal reflection geometry. IRAS spectra revealed that at initial stages of adsorption, monohydride (–SiH) and CH 3 -substituted hydride species (–SiH x (CH 3 ) 3− x ) are generated with monohydride species being dominant. We suggest that upon room temperature adsorption of methylsilanes, breaking of the Siue5f8H bonds of methylsilane is favored over that of the Siue5f8C bonds. It is found that the dissociative adsorption of SiH 3 (CH 3 ) exhibits the second-order kinetics. Due to thermal annealing, surface species –SiH x (CH 3 ) 3− x are thermally decomposed to generate surface Siue5f8H and Siue5f8C bonds, and subsequently H 2 desorption from the Siue5f8H bonds occurs.

Si2H6 adsorption and hydrogen desorption on Si(100) investigated by infrared spectroscopy

Abstract The adsorption and decomposition of disilane on Si(100)(2×1) was investigated using in-situ infrared (IR) absorption spectroscopy. The IR data demonstrate that upon room-temperature adsorption, disilane dissociatively adsorbs on the unsaturated dangling bonds of dimers with the dimer bonds unbroken, to produce mono-, di-, and tri-hydride species. At low coverages, dissociative adsorption without breaking of the Siue5f8Si bond of Si 2 H 6 is favored. Thermal annealing following room-temperature disilane adsorption produces the doubly-occupied adatom dimers (DOD, HSiue5f8SiH) and isolated monohydride species. These hydride species are generated via the rupture of dimer bonds of the substrate. Hydrogen desorption from the isolated monohydride site occurs at lower temperatures than from the DOD site.

PHOTOEMISSION STUDY OF THE METAL DEPOSITION ON THE (NH4)2SX-TREATED GAAS(100) SURFACE AT ROOM TEMPERATURE

Abstract We have used synchrotron radiation photoemission spectroscopy to investigate the chemical interactions and atomic intermixing at metal/GaAs interfaces during deposition of Au and In onto GaAs(100) surfaces that are chemically treated in (NH 4 ) 2 S x and in H 2 SO 4 . For the Au deposition onto the (NH 4 ) 2 S x -treated surface, alloy formation and metal segregation at interfacial regions are significantly suppressed as compared to the Au deposition onto the H 2 SO 4 -treated surface. On the other hand, for In deposition, the In adatoms strongly interact with the (NH 4 ) 2 S x -treated surface to generate a thin layer of In x Ga 1− x As alloy on which the In overlayer is formed in a layer-by-layer fashion. We found that Au reacts with the H 2 SO 4 -treated surface to generate AuGa alloy, but In does not interact appreciably with the surface, leading to the island growth of the In overlayer.