A system for studying electron-induced surface reactions at pressures up to 10−4 Torr has been constructed. It uses the electron source of a single pass cylindrical mirror electron energy analyzer to both stimulate surface reactions and to analyze, by Auger electron spectroscopy, the surface changes brought about by those reactions. The centerpiece of the design is a small separately pumped fixed position chamber lying within the main vacuum chamber. From below, sample surfaces are brought into this chamber through a Viton-sealed opening and are positioned at the focal plane of the Auger analyzer using a rotatable z-motion manipulator. During electron-induced surface reactions at elevated pressures, the hot filament of the electron source is protected via a small 0.5-mm-diam aperture between the electron source operating at 10−8 Torr and the reaction cell operating at ∼10−4 Torr. In a second configuration, selected after the reaction cell has been pumped out, a larger aperture suitable for collecting Auger electrons is used. The sample is mounted on a rotatable off-axis stage that allows several different irradiation experiments for a single sample preparation. Test results for e-beam induced carbon deposition and etching are presented.

Electron induced carbon deposition and etching was investigated by Auger electron spectroscopy in a custom designed vacuum system. The Auger electron spectrometer was used to provide a high flux electron beam to induce reactions and to monitor surface composition. During the e-beam induced deposition or etching, the gas phase pressure was 10-4 to 10-5 Torr. Several carbon precursors: benzene, cyclohexane and propane were used for deposition. The deposition rate depended on the precursor sticking coefficient and bonding structure. Among the three precursors tested, the deposition rate of carbon was cyclohexane > benzene > propane. The e-beam induced etching of carbon films was carried out in 1 × 10-4 torr oxygen ambient and the carbon film was prepared by reactive physical vapor deposition. The etching process can be divided into three stages: bulk film, interface, and substrate. For the bulk carbon film, the decrease of film thickness varies linearly with the e-beam flux, while at the interface, the film thickness shows an exponential decay with the electron flux. For the C in the Si substrate, a very slow etching rate was observed. The etching rate for bulk carbon film was ∼ 0.1 nm/min under the experimental conditions, which is equivalent tp 2.4 × 10-27 cm3/electron. At the interfacial region, the cross section of carbon removal by electrons was ∼ 4.6 × 10-21 cm2. Based on the change of the carbon line shape at the interface, we concluded that the etching rate is related to the chemical nature of the carbon species.