Michelle T. Schulberg

Hydrogen desorption from chemical vapor deposited diamond films

Temperature programmed desorption was used to measure the desorption kinetics of hydrogen and its isotopes from chemical vapor deposited diamond surfaces. The desorption spectra are surprisingly simple considering the polycrystalline nature of the sample, exhibiting a single peak at ∼1300 K for a heating rate of 6 K/s. There is no isotope effect to the desorption, and neither the position of the peak maximum nor the peak width change with increasing hydrogen coverage. The maximum surface coverage achieved is approximately one monolayer. The spectra can be represented by a single peak first order desorption model, yielding kinetic parameters of Ea=51 kcal/mol and ν=5×107 s−1. An alternate model of multiple desorption sites with a Gaussian‐distributed population gives kinetic parameters of Ea,mean=82 kcal/mol, ν=9×1012 s−1, and σ (the width of the Gaussian distribution)=3 kcal/mol. A comparison to desorption from low‐index natural diamond surfaces is presented.

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.

Characterization of chemically amplified resists for soft x‐ray projection lithography

Sensitivity, lithographic performance, photoabsorption, and photodesorption of chemically amplified novolac‐based resists have been studied at an exposure wavelength of 140 A and are compared to poly(methylmethacrylate) (PMMA). Monochromatic exposures of the resists AZ PF514, AZ PN114, and SAL 601 yielded D0.9 values of 2.5–3 mJ/cm2 for 0.25 μm thick films. Contrast values ranged from 3 for AZ PN114 to 5 for SAL 601. Photoabsorption measurements of supported AZ PN114 films at 140 A yield an absorption coefficient of 4.4±0.1 μm−1. Photodesorption of fragment ions induced by 140 A radiation has been studied in PMMA and AZ PN114 using time‐of‐flight mass spectrometry. It is found that H+, CH2+, CH3+, H2O+, CHO+, C3H5+, and COOCH3+ dominate the ion mass spectra photodesorbed from PMMA, while H+, CH3+, H2O+, and CHO+ dominate the ion mass spectra for AZ PN114. The mass‐integrated ion desorption yield from AZ PN114 is three times less than that measured for PMMA per photon or 90 times less when expressed per ex...

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.

Temperature programmed desorption of hydrogen and deuterium from CVD diamond samples

The desorption kinetics of H{sub 2}, HD, and D{sub 2} from a CVD- grown diamond sample have been measured using temperature programmed desorption. The sample was exposed to hydrogen and deuterium at {approximately}100K. Molecular hydrogen does not react with the diamond surface but atomic hydrogen chemisorbs. The sample is then heated to 1500 K at a rate of 6 K/s. The hydrogen desorption spectrum from these polycrystalline specimens is surprisingly simple, consisting of a single peak near 1270 K for all coverages studied. The width of the desorption peak is {approximately}100K. Neither the width nor the peak maximum shift with increasing hydrogen coverage. The is no isotope effect to the desorption. No other desorption products (water, small hydrocarbons) are detected. Kinetic parameters can be extracted from these spectra, and these can be compared to hydrogen desorption from natural diamond single crystal surfaces. These parameters can be used to model diamond growth processes.

Chemically amplified soft-x-ray resists: sensitivity, resolution, and molecular photodesorption.

The sensitivity, ion photodesorption, and lithographic performance of selected novolac-based chemically amplified resists have been studied at an exposure wavelength of 140 Å. Flood exposures of the resits AZ PF514, AZ PN114, and SAL 601 yield D(0.9) values of 2.5-3.5 mJ/cm(2) for 0.25-µm-thick films. Contrast values range from 3 for AZ PN114 to 5 for SAL 601. Photodesorption of fragment ions induced by 140-Å radiation has been examined in AZ PN114 by using time-of-flight mass spectrometry and compared with poly(methylmethacrylate) (PMMA). Mass-integrated ion desorption yields from AZ PN114 are found to be ∼ 90 times less per exposure than from PMMA. Soft-x-ray projection imaging in AZ PF514 and SAL 601 has been characterized by use of a multilayer-coated 20 × Schwarzschild objective and a transmissive Ge/Si mask illuminated by a laser plasma source.