C. Bater

Ammonia as a precursor in electron‐enhanced nitridation of Si(100)

Electron beam-enhanced nitridation of Si(100) using ammonia as a precursor at 110 K was studied with electron-stimulated desorption, XPS, AES and high-resolution electron energy-loss spectroscopy (HREELS). Hydrogen ion kinetic energy distributions from adsorbed ammonia exhibited a component from NH 3 (a) at 7.8 eV, from NH 2 (a) at 5.4 eV and from H(a) at 4 eV. Formation of the nitride following electron beam irradiation of adsorbed ammonia was shown by both N 1s at 398 eV and Si 2p at 102 eV in XPS spectra. From HREELS spectra following electron beam irradiation, we are able to show that the electron beam is highly effective in removal of hydrogen from NH x (a) (x = 3,2) and from the silicon surface. Electron-stimulated desorption of adsorbed hydrogen and dissociation of adsorbed NH x (x = 3,2) are believed to be responsible for enhanced nitridation. Nitride can also form on the surface by irradiating the surface in an ammonia environment at 110 K. A nitride growth rate of 1 A min -1 was obtained from the bulk Si LVV AES signal intensity attenuation.

Effects of low-energy electron irradiation on submonolayer ammonia adsorbed on Pt(111)

The effects of electron impact on ammonia-covered Pt(111) have been studied using temperature-programmed desorption (TPD) and electron-stimulated desorption (ESD). For coverages below one monolayer, ammonia adsorbs on the surface in two distinct TPD states: the α-state is broad and desorbs over the temperature range 150-350 K, and the β-state appears as a sharper peak at 150 K. The β-state was seen to be damaged by electron-beam impact much more readily than the α-state, resulting in the formation of atomically adsorbed N on the surface. The mass 28 recombinative nitrogen desorption TPD peak appearing at 550 K exhibited second-order desorption kinetics, further confirming the presence of atomically adsorbed nitrogen. The ESD kinetic energy distributions (KEDs) were obtained for m/e = 1 amu, which exhibited broad peaks generally. The H + KEDs were analyzed using empirical curve fits, with the resulting conclusion that the H + KEDs contain contributions from at least three different hydrogen-containing surface species. We believe that these three H + KED peaks are due to ESD from adsorbed NH 3 , NH 2 and H. The ESD cross-section for NH 3 removal was measured in three different ways, all of which were found to be in general agreement, and which gave an averaged cross-section value of Q lot = 4 x 10 -17 cm 2 .

Observation of a novel electron beam effect: electron-stimulated associative desorption

We observed diatomic hydrogen and nitrogen desorbing from Pt(111) surfaces covered with multilayer ammonia at 120 K during electron irradiation at 600 eV. Experiments were conducted to verify that the source of H2(g) and N2(g) species was indeed the electron-irradiated ammonia multilayer. This effect, which we describe as electron-stimulated associative desorption (ESAD), has not been previously reported.

Adsorption studies of digermane and disilane on Ge(100)

Adsorption studies of digermane (Ge 2 H 6 ) and disilane (Si 2 H 6 ) on Ge(100) are reported. Temperature-programmed desorption (TPD) experiments suggest the existence of two hydrogen adsorption states in the submonolayer regime for both digermane and disilane. The TPD spectra observed for disilane on Ge(100) are qualitatively similar to previous studies of disilane adsorbed on thin epitaxial layers of germanium on Si(100). These spectra show the existence of an α-state arising from the germanium monohydride and a β 1 -state arising from a silicon monohydride. The two-peak structure observed in the hydrogen TPD spectra for digermane on Ge(100) suggests the existence of both germanium monohydride and germanium dihydride, about which there is disagreement in the literature. However, high-resolution electron energy-loss spectroscopy and low-energy electron diffraction provide additional evidence for the existence of both germanium hydrides on the digermane/Ge(100) system. Kinetic energy distributions of electronically desorbed H + and hydrogen removal cross-sections obtained through electron-stimulated desorption are also presented for both systems.

Investigation of electron-stimulated desorption of nitrogen from Pt(111)

Abstract The effects of electron-beam irradiation of molecular adlayers of N 2 on Pt(111) are investigated. N + was seen desorbing from the surface, but no N − . The electron-stimulated desorption cross-section for removal of adsorbed N 2 was found to be greatest at a 150 eV beam energy, and the current-density averaged value for this cross-section was determined to be σ = 6.7 × 10 −17 cm 2 . Dissociative adsorption of N 2 molecules was not seen following electron bombardment of molecular N 2 adlayers on Pt(111). However, chemisorbed N atom deposition was observed when the sample was negatively biased.

Electron beam‐enhanced oxynitridation of Si(100) by NO adsorption

The adsorption of NO on Si(100) and the electron irradiation effects of an NO-covered surface were studied by XPS, AES, high-resolution electron energy-loss spectroscopy (HREELS), temperature-programmed desorption (TPD) and electron-stimulated desorption (ESD). Nitric oxide both molecularly and dissociatively adsorbs on Si(100) at 110 K. The molecular and dissociative adsorption occurred simultaneously, and reached saturation. The thermal desorption of molecularly adsorbed NO (NO(a)) peaks at -200 K. Thermal dissociation of NO(a) was not detected from heating. Electron irradiation of Si(100) in an NO environment gave a dramatic decrease in the elemental Si LVV signal at 92 eV in AES. This indicates the formation of a silicon oxynitride overlayer by electron-stimulated dissociation of NO(a). The overlayer thickness exhibited a linear dependence on the electron irradiation/NO exposure time. An oxynitride growth rate of 0.02 nm min -1 was obtained.

Observation of an enhanced N 1s shake-up satellite on nitrided Si(100) and correlation with N bonding geometry

Abstract Si(100) dosed with NO and thermally nitrided with ammonia was investigated by X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS) for a wide range of temperatures. A 410-eV peak was observed in the N 1s XPS spectrum region. It is proposed to be an enhanced shake-up satellite of the N 1s photoelectrons. The temperature dependence of both this peak and HREELS data suggests that precursor silicon nitrides such as planar and pyramidal Si3N species as well as Si3N4 can form at different temperatures.

H- ESD observed from β-state NH3 adsorbed on Pt(111)

Abstract H− ions were detected from ammonia covered Pt(111) surfaces. We found that H− electron-stimulated desorption (ESD) ions can only be detected when adsorbed β-state ammonia is present on the Pt(111) surface. The H− kinetic energy distributions (KEDs) obtained from Pt(111) surfaces covered with adsorbed β-state ammonia exhibit a very narrow peak appearing at 3 eV with a FWHM of less than 1 eV. The total removal cross-section measured from H− ESD ion-yield curves is in good agreement with the total removal cross-section obtained from H+ ESD ion-yield measurements and other measurements, which are described elsewhere (C. Bater, J.H. Campbell, J.H. Craig Jr., Surf. Interface Anal. 26 (1998) 97). A total removal cross-section of 5.6×10−17 cm2 was obtained from the H− ESD ion-yield curves obtained in this work.