James A. O’Neill

Rotationally resolved hot atom collisional excitation of CO2 0001 and 0002 stretching vibrations by time‐resolved diode laser spectroscopy

A tunable infrared diode laser has been used to monitor the time‐resolved absorption of rovibrationally excited CO2 molecules produced in collisions with fast hydrogen atoms from the 193 nm excimer laser photolysis of H2S. Nascent relative rotational population distributions were measured for the 0001 and 0002 vibrational states in CO2 following collisional excitation. The nascent distributions for both of these states were found to be significantly displaced from the 300 K Boltzmann distribution with peaks at J=31 and J=34 for 0001 and 0002, respectively. An approximate diffusion treatment for the mass transport of fast moving hydrogen atoms out of the region of the diode laser probe beam was developed and used to obtain approximate absolute scattering cross sections. Sufficient energy is available in the H/CO2 collision process to excite 0001 rotational states with J greater than 140. The fall‐off in excitation probability for J>31 is ascribed to the small impact parameter necessary to produce vibration...

IR diode laser study of vibrational energy distribution in CO2 produced by UV excimer laser photofragmentation of pyruvic acid

Time domain absorption spectroscopy using a tunable, infrared diode laser has been used to monitor the vibrational excitation of CO2 produced in the 193 nm excimer laser photolysis of gas phase pyruvic acid (CH3COCOOH). Nascent vibrational populations were measured in the following ten vibrational states of CO2: 0000, 0110, 0220, 0330, 0440, 0001, 0002, 0003, 0111, and 0221. Approximately 97% of the CO2 photoproduct is observed to be directly formed in the vibrational ground state. The remaining molecules are formed with a significant degree of vibrational excitation, having mode temperatures T(ν2)=1800±150 K, T(ν3)=3700 ±1000 K, T(ν2+ν3)=2000±400 K. The present experimental data suggest that the 193 nm photolysis may proceed through more than a single dissociation channel and involve a number of different photofragments.

Diode laser probe of CO2 vibrational excitation produced by collisions with hot deuterium atoms from the 193 nm excimer laser photolysis D2S

The 193 nm excimer laser photolysis of D2S in D2S/CO2 mixtures produces fast deuterium atoms (ETR∼2.2 eV) which vibrationally excite CO2 molecules via inelastic translation–vibration/rotation (T–V/R) energy exchange processes. A high resolution (10−3 cm−1) cw diode laser probe was used to monitor the excitation of ν3 (antisymmetric stretch) and ν2 (bend) vibrations in CO2. The present results are compared with previous experiments involving hot hydrogen atom excitation of CO2 in H2S/CO2 mixtures as well as with theoretical calculations of the excitation probability. The probability for excitation of a ν3 quantum in CO2 is about 1%–2% per gas kinetic D/CO2 collision. Bending (ν2) quanta are produced about eight times more efficiently than antisymmetric stretching (ν3) quanta. The thermalization rate for cooling hot D atoms below the threshold for production of a ν3 vibrational quantum corresponds to less than 2 D*/D2S collisions or 15 D*/CO2 collisions.

Rotationally resolved hot atom collisional excitation of CO2(0001) by time‐resolved diode laser spectroscopy

A tunable infrared diode laser was used to study the nascent rotationa distribution of CO2 molecules produced directly in the 0001 excited state as a result of collisions with  hot  hydrogen atoms formed in the UV photolysis of H2S.(AIP)

Insitu infrared diagnostics of particle forming etch plasmas

In situ Fourier transform infrared absorption techniques are employed to characterize the gas‐phase plasma species and etch products present in halocarbon containing plasmas which produce particles. A correlation is demonstrated between the distribution of these species and the extent of particle formation as measured by laser light scattering. The effects of the presence of silicon and the addition of oxygen on both the plasma species distribution and the degree of light scattering are also characterized. Additionally, x‐ray photoelectron spectroscopy (XPS) and infrared (IR) microscopic techniques are employed to determine the chemical composition of the particulate material which is found on the silicon wafer after etching.

Ultraviolet laser‐induced ion emission from silicon

Si and Ge ion ejection is observed to occur from clean silicon and germanium surfaces upon excimer laser irradiation at fluences (0–150 mJ/cm2) well below that necessary to cause thermionic emission or melting of the substrate. Quadrupole mass spectrometric techniques were employed to for the detection of emitted positive ions. Laser intensity dependent measurements were performed at 193, 248, and 351 nm to elucidate the laser fluence and photon energy threshold behavior of each of the charged species.

Collisional excitation of CO2(0111) by hot hydrogen atoms: Alternating intensities in state‐resolved vibrational, rotational, and translational energy transfer

Time domain tunable diode laser absorption spectroscopy has been used to measure rotationally resolved transient absorption line shapes and nascent rotational populations for CO2 molecules excited into the (0111) vibrational state by collisions with translationally hot hydrogen atoms. The even rotational levels are more heavily populated than the odd levels, in agreement with propensity rules derived earlier by Alexander and Clary. The nascent populations and transient linewidths are interpreted in terms of a theoretical model that lends insight into the H–CO2 collision dynamics. The cross section for exciting (0111) is ∼0.23 times the cross section for exciting (0001), and ∼0.38 times the cross section for exciting (1000).

Infrared absorption spectroscopy for monitoring condensible gases in chemical vapor deposition applications

In situ infrared absorption spectroscopy is used to monitor the delivery of condensible gases in chemical vapor deposition (CVD) systems. A Fourier transform infrared (FTIR) spectrometer has been configured to enable simultaneous measurements of the concentrations of multiple gases which are critical to the performance of CVD processes. In the deposition of silicon dioxide (SiO2) films using tetraethylorthosilicate (TEOS) and ozone (O3), IR measurements of the concentration of gas‐phase TEOS closely track the deposition rate of SiO2. In doped oxide deposition processes, the percentage of phosphorous in the film is predicted from infrared measurements of the concentration of the dopant precursor gas [trimethylphosphene (TMP)]. These capabilities provide improved control of the delivery of condensible gases in CVD systems without the use of test wafers, and they enable the detection of failures in the gas delivery system in real time.

SURFACE PHOTOCHEMISTRY OF DIVALENT METAL ALKYLS ON SIO2

Metal‐alkyl molecules adsorbed on chemically prepared silicon surfaces have been studied using infrared total‐internal reflection and ultraviolet transmission spectroscopies, temperature‐programmed desorption spectroscopy (TPD), and mass spectroscopy of laser induced desorption (LID) products. For chemisorbed species, the surface hydroxyl groups have been shown to be the prime adsorption sites. In addition, we determined the identity of the chemisorbed species and their fragments under ultraviolet photodissociation. Surface photodissociation was observed to be strongly wavelength dependent at 193 and 248 nm.

Infrared internal reflection studies of the surface photochemistry of dimethylcadmium on silicon

An infrared spectroscopic technique employing the principle of total internal reflection has been used to examine the UV‐induced surface photochemistry of dimethylcadmium on chemically altered silicon surfaces. Fourier transformed infrared spectra of both chemically and physically adsorbed molecules were recorded on oxidized and hydrogen ‘‘passivated’’ silicon surfaces (SiO2 and SiH) upon exposure to excimer laser radiation at 193 and 248 nm. By monitoring changes in the infrared spectrum of adsorbed dimethylcadmium during the irradiation process, insight into the role of the surface in the photodissociation of the adspecies is obtained.