Robert M. Robertson

Atom- and radical-surface sticking coefficients measured using resonance-enhanced multiphoton ionization

Sticking coefficients γ of neutral transient species at ambient temperature were measured using in situ resonance enhanced multiphoton ionization (REMPI) of the transients in a low pressure reactor at mTorr pressure. The value of γ for I on a stainless steel surface was 0.16, whereas γ for CF3 free radical on the same surface was 0.5 was found for highly vibrationally excited CF3 containing 5900 cm−1 of internal energy and for SiH2 containing 7000 cm−1 of internal energy. The surface was stainless steel in the former case and a carbon‐containing Si and H surface in the latter case.

Sticking coefficient of the SiH2 free radical on a hydrogenated silicon‐carbon surface

The sticking coefficient of SiH2 on a hydrogenated silicon‐carbon surface is measured in a low‐pressure pulsed‐photolysis experiment. Thermal and vibrationally excited SiH2 are created by infrared multiphoton decomposition of n‐butylsilane. The first‐order wall loss rates of the radicals are determined from the time dependence of the resonance‐enhanced multiphoton ionization signal. The sticking coefficients of SiH2 (∼0.1) and vibrationally hot SiH2 (>0.5) are determined from the measured first‐order loss rate constants and the calculated wall collision rate constant.

Reaction probability for the spontaneous etching of silicon by CF3 free radicals

The spontaneous thermal etching of silicon by CF3 free radicals has been studied in a very‐low‐pressure photolysis reactor. The radical is produced by infrared multiphoton dissociation of either hexafluoracetone or CF3 I, and is allowed to react with a temperature‐controlled silicon sample (560–745 K). Mass spectrometry is used to measure the extent of dissociation of the precursor gas and the formation of product molecules, C2 F6 and SiF4 . The etch rate of the silicon is determined from the SiF4 production. Resonance‐enhanced multiphoton ionization of CF3 is used to determine the density and time history of the radical in the reactor. The measurements of the etch rate and CF3 density are combined to derive the reaction probability. CF3 etches silicon much more slowly than F atoms and at a rate comparable to molecular F2 . A carbon layer, that is deposited on the silicon by the radicals, inhibits, but does not stop, further etching. Experiments on the etching of silicon by F2 were performed both to valid...

[3+2] resonance enhanced multiphoton ionization of I and Br formed from the infrared multiphoton decomposition of CF3I and CF3Br

Resonance enhanced multiphoton ionization (REMPI) has been used to study the products of the infrared multiphoton decomposition (IRMPD) of CF3I in a very low‐pressure photolysis (VLPΦ) cell. The strongest REMPI signals are due to the ground state I(2P3/2) and the spin–orbit excited state I*(2P1/2). The origins of I and I* were determined from the time and IR laser fluence dependences of the REMPI signal. I* is formed by visible single photon dissociation of vibrationally excited CF3I and by visible multiphoton dissociation of I2 and thermal CF3I. The ionization efficiency of I has been determined relative to NH3 for our probe laser conditions, and the sticking coefficient of I with gold surfaces has been determined. The REMPI spectra of the products of the IRMPD of CF3Br is also presented.

Kinetics of surface reactions of CF3 radicals

The kinetics of reactions of CF3 radicals on various substrate materials has been studied in a gold‐coated, stainless‐steel, very‐low‐pressure photolysis (VLPΦ) cell as a function of temperature and radical concentration. The substrate materials were gold, stainless steel, copper, copper oxide, and silica. The CF3 radicals were generated from CF3I by IR‐multiphoton decomposition. The reaction products observed with a mass spectrometer included HF, CO, CO2, COF2, SiF4, and C2F6. Rate constants were obtained as a function of temperature. CF3 reacted most rapidly on copper oxide surfaces; the other metal surfaces were less reactive, and the silica surfaces were least reactive. Previous studies from this laboratory that had reported the reaction of CF3 on fused silica are reinterpreted as reactions of CF3 on the stainless‐steel heater assembly.