Duane A. Outka

The adsorption of H-atoms on polycrystalline β-silicon carbide

The adsorption of atomic hydrogen on a polycrystalline β-silicon carbide (SiC) surface has been studied using temperature-programmed desorption (TPD). Atomic hydrogen adsorbs on this surface, whereas molecular hydrogen does not. Upon heating, the hydrogen recombines and desorbs as H2, producing two peaks in the TPD spectrum at 975 and 1130 K. The unusually broad width of the desorption peaks is attributed to a distribution of surface binding energies for hydrogen atoms. The desorption spectra are fit using a model that assumes two adsorption sites and a Gaussian distribution of binding energies. The average activation energies derived for the two peaks are 63 and 72 kcal/mol.

The adsorption of hydrogen chloride on polycrystalline β-silicon carbide

The reactivity of HCl, a by-product of SiC chemical vapor deposition (CVD) from chlorine-containing precursors, is of particular interest because it has been reported that addition of HCl inhibits the SiC CVD process. In this study, HCl adsorption on polycrystalline β-SiC was examined with Auger electron spectroscopy and temperature-programmed desorption (TPD). HCl adsorbs readily on SiC at 300 K with an initial sticking probability of 0.11 and forms a strong bond with an activation energy for desorption of 64 kcal/mol. The only product detected by TPD is HCl, which desorbs in a peak centered at 1010 K. No silicon- or carbon-containing desorption products are found, demonstrating that HCl does not etch the SiC surface under these conditions. HCl inhibition of SiC CVD can be accounted for qualitatively with a surface site-blocking mechanism.

Mechanistic studies of the isotopic-exchange reaction between gaseous hydrogen and palladium hydride powder

Abstract A detailed mechanism for the isotopic-exchange reaction between gaseous hydrogen and solid palladium hydride is developed which extends previous models for this reaction by specifically including surface reactions. The modeling indicates that there are two surface-related processes that contribute to the overall rate of exchange: the desorption of hydrogen from the surface and the exchange between surface hydrogen and bulk hydrogen. This conclusion is based upon measurements in a flow reactor in which Raman spectroscopy was used to analyze the output of the reactor. This data was used to develop a computer model for the exchange process. In addition, measurements examining the effect of small concentrations of carbon monoxide were helpful in elucidating the mechanism. Carbon monoxide reversibly inhibits certain steps in the exchange; this slows the overall rate of exchange and changes the distribution of products from the reactor.

Extreme ultraviolet resist and mirror characterization: Studies with a laser plasma source

A monochromatized laser‐produced plasma source of extreme ultraviolet (XUV) radiation has been used to study resists and reflective multilayers for use in projection x‐ray lithography. We report the characterization of near‐edge x‐ray absorption fine structure (NEXAFS) spectra, exposure sensitivity, and contrast of selected polysilane resists at photon energies near 100 eV, where projection x‐ray lithography is being developed. We find absorption resonance features in the NEXAFS spectra which we assign based on ab initio quantum chemical calculations to excitation into Si–Si and Si–C σ* orbitals. Using monochromatized XUV exposures on the Si–Si σ* resonance at 105 eV, followed by solvent dissolution development, we have measured the exposure sensitivity curves of these resists. We find sensitivities in the range of 600–3000 mJ/cm2 and contrasts in the range from 0.5–1.4, depending on the polysilane side chain. Exposure sensitivity measurements have also been performed below the edge at 92 eV where we find...

Aspects of nitrogen surface chemistry relevant to TiN chemical vapor deposition

NH3 is an important component of many chemical vapor deposition (CVD) processes for TiN films, which are used for diffusion barriers and other applications in microelectronic circuits. In this study, the interaction of NH3 with TiN surfaces is examined with temperature programmed desorption (TPD) and Auger electron spectroscopy. NH3 has two adsorption states on TiN: a chemisorbed state and a multilayer state. A new method for analyzing TPD spectra in systems with slow pumping speeds yields activation energies for desorption for the two states of 24 kcal/mol and 7.3 kcal/mol, respectively. The sticking probability into the chemisorption state is ∼0.06. These results are discussed in the context of TiN CVD. In addition, the high temperature stability of TiN is investigated. TiN decomposes to its elements only after heating to 1300 K, showing that decomposition is unlikely to occur under CVD conditions.

The adsorption of atomic hydrogen on tellurium and formation of H2Te

Abstract The adsorption of hydrogen on a polycrystalline tellurium surface has been studied with temperature programmed desorption. Atomic hydrogen adsorbs on a tellurium surface and reacts to form H 2 Te. Molecular hydrogen, in contrast, does not adsorb or react with tellurium at temperatures down to 80 K. When a tellurium surface which has been exposed to atomic hydrogen is heated, two desorption products are observed, H 2 and H 2 Te. The H 2 Te desorbs in three peaks at 130, 150, and 270 K. The H 2 desorbs in two peaks at 150 and 270 K. The desorption peaks at 270 K for both H 2 and H 2 Te are unusually broad with a half-width of 80 K, and standard kinetic analysis of these peaks yields unusual desorption parameters. Overall, the adsorption of hydrogen on tellurium is similar to hydrogen adsorption on other covalent solids and differs in several respects from hydrogen adsorbed on metal surfaces.

Soft x-ray resist characterization: studies with a laser plasma x-ray source

Little work has been performed to characterize the exposure sensitivity, contrast, and tone of candidate resists for photon energies between 100-300 eV, the range in which projection soft x-ray lithography will be developed. We report here the characterization of near-edge x-ray absorption fine structure (NEXAFS) spectra, exposure sensitivity, contrast, and post-exposure processing of selected polysilane resists at photon energies close to the Si L2,3 absorption edge (100 eV). We find absorption resonance features in the NEXAFS spectra which we assign to excitation into Si-Si and Si-C *orbitals. Using monochromatized XUV exposures on the Si-Si cs* resonance at 105 eV, followed by solvent dissolution development, we have measured the exposure sensitivity curves of these resists. We find sensitivities in the range of 600-3000 mJ/cm2 and contrasts in the range from 0.5 - 1.4, depending on the polysilane side chain. We have also performed exposure sensitivity measurements at 92 eV, below the edge. Sensitivity decreases slightly compared to 105 eV exposures and the saturation depth and contrast both increase, as expected. We find also that exposing resist films to oxygen after XUV exposure, but before development, increases the sensitivity markedly.

The interaction of HCl with polycrystalline {beta}-SiC: Evidence for a site-blocking mechanism for HCl inhibition of SiC CVD

Ceramic components fabricated from SiC are of considerable practical interest, with applications in heat management, turbine engines, and aerospace. Chlorine-containing precursors are attractive for chemical vapor deposition (CVD) of SiC because they are less hazardous and more economical than silane precursors. The reactivity of HCl, a by-product of these reactions, on SiC is of particular interest because it has been reported that HCl inhibits SiC CVD, but the mechanism for this inhibition has not been identified. In this work the adsorption of HCl on polycrystalline {beta}-SiC was examined with Auger Electron Spectroscopy (AES) and Temperature Programmed Desorption (TPD). HCl adsorbs readily on SiC, with an initial sticking probability of 0.1 at 300 K, and forms a strong bond, with an activation energy for desorption of 64 kcal/mol. The only product detected by TPD is HCl, which desorbs in a peak centered at 1,010 K. There are no Si- or C-containing desorption products, demonstrating that HCl does not etch SiC under TPD conditions. These results are consistent with a site-blocking mechanism for HCl inhibition of SiC CVD, but not with an etching mechanism.

The Reactivity of HCI and Methyltrichlorosilane with Silicon Carbide Surfaces

This work explores the reactivity of HCl and methyltrichlorosilane (MTS) with polycrystalline {beta}-silicon carbide (SiC) surfaces using temperature-programmed desorption (TPD) and Auger electron spectroscopy. HCl is a corrosive gas that inhibits SiC deposition. The results show that HCl is a corrosive gas that inhibits SiC deposition. The results show that HCl is adsorbed by SiC, forming a stable surface chloride that could inhibit SiC deposition. TPD shows that chlorine desorbs as HCl or SiCl{sub 4}, confirming that HCl can etch SiC surfaces. Desorption is rate-limited by the breaking of Si-Cl bonds. MTS is also adsorbed by SiC; its desorption is similar to that of HCl.

X-Ray Lithography Studies of Polysilane using a Laser Plasma X-Ray Source

A laser-generated plasma source on monochromatized soft x-rays has been used to study the x-ray lithographic resist properties of poly(cyclohexylmethysilane-co-dimethysilane). X-ray absorption spectra near the Si L/sub 2,3/ edge of unexposed samples were measured to guide the choice of exposure photon energy. We find that poly(cyclohexyl-methylsilane-co-dimethylsilane) exhibits positive tone at x-ray energies near 105 eV (Si 2p resonance), a sensitivity of 1000 mJ/cm/sup 2/ and a contrast of 1.5. Sensitivity is found to increase markedly when exposed samples are held in air before development. Using simple wire mesh masks, estimates of the minimum achievable linewidth have been made. 17 refs., 4 figs.