Characterization of the morphology and composition of commercial negative resists used for lithographic processes

We present a spectroscopic and microscopic characterization of the chemical composition, structure, and morphology of two commercial negative resists using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). For this purpose, films of a novolak-based resist (ma-N 2400) and hydrogen silsesquioxane (HSQ) are treated under different conditions (temperature, deep ultraviolet (DUV) exposure, CHF₃ plasma). Topographic AFM images show that both heating and DUV exposure strongly affect the surface morphology of as-prepared ma-N 2400 resist films. These different treatment conditions also lead to decreasing roughnesses, which indicates structural reorganization. Furthermore, the decrease of the photoactive compound (bisazide) in the ma-N 2400 resist films, observed in FTIR spectra, suggests cross-linking of the resist after CHF₃ plasma treatment, heating, or DUV exposure. XPS measurements on different CHF₃ plasma-treated surfaces reveal that a structurally homogeneous fluorine-containing polymer is generated that is responsible for an enhanced etch resistance. FTIR measurements of HSQ films show a correlation between the degree of HSQ cross-linking and baking time.     

Relations between theT 0 values of bulk and quantum-well GaAs

A simple calculation of the threshold current densityJ _th of quantum-well and bulk GaAs lasers shows that it is proportional to the temperatureT in the first case and toT ^3/2 in the second case. As a consequence theT ₀ value of quantum-well GaAs is 3/2 times larger than for the bulk material. Moreover, we get a further doubling ofT ₀ for a one-dimensional quantum-well wire. These results are independent on the magnitude ofJ _th and hold also for other laser materials, provided that the Auger recombination is negligible as in GaAs.     

Coulomb effects in an optically excited electron-hole plasma of a disordered semiconductor

In this paper we extend the work of Altshuler and Aronov [1] on the effect of Coulomb interaction in disordered metals to the case of an optically generated quasi-equilibrium electron-hole plasma in a disordered semiconductor in view of its possible implications for nonlinear optics. The nonlinearity considered here arises through the optically excited plasma density. The plasma is bipolar and not necessarily degenerate as in the metallic case. The density of states and the optical spectra due to freecarrier interband transitions are numerically computed in the presence and in the absence of the Altshuler-Aronov Coulomb-disorder singularity.     

Studien über Schutzkolloide. Zehnte Reihe: Saponin als Schutzkolloid

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