Patrick R. McCurdy

A modified molecular beam instrument for the imaging of radicals interacting with surfaces during plasma processing

A new instrument employing molecular beam techniques and laser induced fluorescence(LIF) for measuring the reactivity of gas phase radicals at the surface of a depositing film has been designed and characterized. The instrument uses an inductively coupled plasma source to create a molecular beam containing essentially all plasma species. A tunable excimer pumped dye laser is used to excite a single species in this complex molecular beam.LIF signals are imaged onto a gated, intensified charge coupled device (ICCD) to provide spatial resolution. ICCD images depict the fluorescence from molecules both in the molecular beam and scattering from the surface of a depositing film. Data collected with and without a substrate in the path of the molecular beam provide information about the surface reactivity of the species of interest. Here, we report the first measurements using the third generation imaging of radicals interacting with surfaces apparatus. We have measured the surface reactivity of SiH molecules formed in a 100% SiH_4 plasma during deposition of an amorphous hydrogenated silicon film. On a 300 K Si (100) substrate, the reactivity of SiH is near unity. The substrate temperature dependence (300–673 K) of the reactivity is also reported. In addition, reactivity measurements for OH molecules formed in a water plasma are presented. In contrast to the SiH molecule, the reactivity of OH radicals is 0.55±0.05 on the surface of a Si (100) substrate.

Advances in continuous, in-line processing of stable CdS/CdTe devices

A continuous, in-line process suitable for high throughput manufacturing of CdS/CdTe photovoltaic devices has been demonstrated. Utilizing this process, devices with efficiencies of 13% has been fabricated with a low iron soda lime glass (3″×3″) with ant-reflection coatings. The process has been extended to large area devices (16″ ×16″ substrate size). After CdCl<inf>2</inf> treatment, devices showed V<inf>oc</inf> ≫ 700 mV and J<inf>sc</inf> ≫ 20 mA/cm². This performance is similar to the performance of small area devices which showed good stability. Also we have employed Spectroscopic Ellipsometry (SE) as a nondestructive tool to characterize CdS/CdTe heterojunction specifically studying the effects of chemical treatment on the optical properties of the thin-film layers.

Pulsed and continuous wave plasma deposition of amorphous, hydrogenated silicon carbide from SiH4/CH4 plasmas

Continuous wave (cw) and equivalently powered, pulsed radio frequency plasmas are used to deposit a-Si1−xCx:H films. Films produced from SiH4/CH4 and SiH4/CH4/H2 gas mixtures were analyzed with Fourier-transform infrared, x-ray photoelectron spectroscopy, scanning electron microscopy, and profilometery. Gas-phase plasma species were identified using optical emission spectroscopy. The effects of biasing (±1000 V) and grounding the substrates, pulse peak power, pulse on time and off time, and duty cycle on film composition were examined. Films deposited with cw plasmas show an increase in hydrogen incorporation compared to films deposited in the pulsed systems. In the pulsed plasmas, deposition rates depend on both the on time and off time of the plasma pulse cycle, while grounding the substrate causes a significant reduction in oxidation rates for films deposited under all conditions.

Synthesis, and measurement of structural and magnetic properties, of La1-xNaxFeO3(0.0≤x≤0.3) perovskite oxides

Abstract Polycrystalline La1-xNaxFeO3 (0.0≤x≤0.3) solid solutions were synthesized by a solution combustion method using glycine as a fuel. The combustion synthesized compounds were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), diffused reflectance (DR) in the UV-vis, and magnetic measurements. The crystal structure examined by X-ray powder diffraction indicated that the samples were single phase and crystallized in an orthorhombic (space group, Pbnm no.62) structure. The parent and sodium-substituted compounds showed canted anti-ferromagnetic behavior associated with an increase in magnetic moment as Na content increased. The changes in magnetic properties of the materials were correlated to the changes in structural features, as shown by Rietveld structural refinement of the materials.

Velocity distributions of NH2 radicals in an NH3 plasma molecular beam

Abstract Using spatially and temporally resolved LIF we have measured the velocity distributions of NH 2 molecules in an effusive NH 3 plasma molecular beam as a function of applied rf plasma power. Monte Carlo simulation methods are used to model spatial profiles of radicals in the molecular beam. The model assumes a Gaussian distribution and calculates time dependent changes in the profiles using Maxwell-Boltzmann distributions. The translational temperature increases with rf power, from 512 ± 8 K at 25 W to 664 ± 35 K at 150 W. Preliminary data on velocity profiles for NH 2 radicals scattered from a 300 K Si substrate are presented.

Comparison of Oxidation Rates for a ‐ Si1 − x C x : H Films Deposited from Pulsed and Continuous Wave RF Plasmas

Oxidation rates for hydrogenated amorphous silicon carbide (a-Si 1-x C x :H) films deposited from both pulsed and continuous wave (CW) SiH 4 /CH 4 rf (13.56 MHz) plasmas have been measured using Fourier transform infrared spectroscopy. Films deposited from CW plasmas oxidize much more rapidly than those deposited from equivalently powered pulsed plasmas. The effect of a diluent gas in the feed (He, Ar, or H 2 ) on film oxidation rates has also been investigated. With He and Ar, the CW films oxidize faster than the pulsed films. With H 2 as the diluent, however, the CW films do not oxidize as rapidly as other CW films, even after long periods of time. This is most likely the result of hydrogen radicals annealing the films through reactions with active sites on the CW films. Addition of H 2 also decreases the deposition rates in both pulsed and CW systems, suggesting H 2 contributes to the deposition reaction scheme. Additional compositional changes in the a-Si 1-x C x :H materials with addition of H 2 to the plasma feed gas are also discussed.

Influence of process conditions on the optical properties of HfO2/SiO2 coatings for high-power laser coatings

We investigate the variations that occur with changes in the number of layers and with the use of the assist beam main and assist beam energy on the morphology of HfO2/SiO2 quarter wave stacks deposited by dual ion beam sputtering. We show how the addition of sequential HfO2/SiO2 bilayers, up to eight, affects the surface roughness and micro-crystallinity of the top HfO2 layer. We also show that use of the assist source significantly smooths the surface while simultaneously reducing microcrystallinity. The HfO2/SiO2 structures are very robust and can withstand fluences in excess of 3 J/cm2 generated by 1ps pulses from a chirped amplified Ti:Sapphire laser.

Surface Interactions of Radicals During Plasma Processing of Polymers

Surface interactions of radical species were investigated using the imaging of radicals interacting with surfaces (IRIS) technique during plasma surface modification of polymers. Three plasma systems were investigated by spatially probing the laser induced fluorescence of individual radical species and determining their surface scattering coefficients, S. The behavior of CF2 moieties on polymer surfaces was studied using the fluorocarbon plasmas C2F6 and hexafluoropropylene oxide (HFPO). Three types of surface interactions were observed, surface generation of CF2 (S > 1), surface loss of CF2 (S < 1), and unit scattering (S = 1). Surface loss of CF2 was seen in HFPO plasmas, while CF2 was generated in C2F6 systems. The differences between these systems is believed to be the result of different overall surface interactions, specifically film deposition in the HFPO system and etching in the C2F6 system. Using NH3 plasmas, the surface interactions of NH2 radicals with polymers was also investigated. Here, NH2 is generated at the surface of polyethylene and polytetrafluoroethylene substrates, but is consumed on polyimide substrates. Ion effects were also investigated by placing a grounded mesh in the path of the molecular beam to remove charged species.

Effect of Chemical Treatment on the Optical Properties of a Cadmium Telluride Photovoltaic Device Investigated by Spectroscopic Ellipsometry

Spectroscopic ellipsometry has been successfully used to characterize the CdS/CdTe heterojunction solar cell deposited on TEC15 glass. The effects of copper treatment on the optical properties of a cadmium chloride treated photovoltaic device were investigated using ellipsometry. No changes in either the band gaps or critical points of CdTe layer were noticed as a result of copper treatment. The copper treated CdTe layer exhibited a higher refractive index in the visible and longer wavelengths (≤3 eV), as compared with the untreated layer. This was attributed to the increased disorder in the case of copper treated layers.

A versatile substrate heater for thermal and plasma-enhanced chemical-vapor deposition

A simple and inexpensive substrate heater that can be used in both thermal- and plasma-enhanced chemical-vapor deposition (PECVD) systems has been constructed. This heater design can be used to achieve and sustain substrate temperatures as high as 650 °C with a minimal amount of outgassing under both CVD and PECVD conditions. Substrates are heated very quickly with all but the highest temperatures achieved within 30 min. The heater is also very robust, with a lifetime of more than 30 h of continuous use under vacuum with several heating and cooling cycles. We have used this heater design to thermally deposit TiS2 from 1-methyl-1-propanethiol and TiCl4 in the temperature range of 200–500 °C. In addition, amorphous hydrogenated silicon carbide (a-Si1−xCx:H) was deposited in the temperature range of 30–570 °C using a 13.56 MHz rf plasma reactor and a modified version of the same heater.A simple and inexpensive substrate heater that can be used in both thermal- and plasma-enhanced chemical-vapor deposition (PECVD) systems has been constructed. This heater design can be used to achieve and sustain substrate temperatures as high as 650 °C with a minimal amount of outgassing under both CVD and PECVD conditions. Substrates are heated very quickly with all but the highest temperatures achieved within 30 min. The heater is also very robust, with a lifetime of more than 30 h of continuous use under vacuum with several heating and cooling cycles. We have used this heater design to thermally deposit TiS2 from 1-methyl-1-propanethiol and TiCl4 in the temperature range of 200–500 °C. In addition, amorphous hydrogenated silicon carbide (a-Si1−xCx:H) was deposited in the temperature range of 30–570 °C using a 13.56 MHz rf plasma reactor and a modified version of the same heater.