ABSTRACT CTS-9623450 This project addresses the importance of inelastic and reactive scattering in the etching of semiconductors. Experiments are proposed with a recently invented hypersonic neutral beam of fluorine atoms with translational energies in the 3-25 eV regime for fundamental studies of the gas-surface dynamics occurring during steady-state etching of silicon and etching studies of submicron features in silicon in order to understand how neutral beams etch. The effort is based on recent results from profile evolution modeling and experiments with flourine atom beams with translational energies between 3 and 18 eV. Anisotropic etching of silicon at room temperature with fluorine chemistry (no sidewall deposition) is demonstrated as a proof of the capabilities of such beams. This has been possible because of direct reactions occurring at the high translational energies employed. Collision-induced desorption (CID) has been implicated as the mechanism responsible for the increased desorption rate of fluorinated silicon moieties from the SiFx layer at the higher energies. Rapid removal of the SiF3 product in the CID mode enables rapid fluorination of the exposed surface, which increases fluorine utilization and, in turn, results in a reduction of the thermally desorbing unreacted fluorine-atom flux. Reduction of scattered fluorine to the sidewalls dramatically improves anisotropy. Fundamental measurements of the energy and flux of unreacted F atoms and reaction products (SixFy) leaving the SiFx layer during etching are made. Moreover, similar measurements are performed on the silicon dioxide surface. Silicon dioxide is ubiquitous on today's wafers (e.g., as a hard mask, gate oxide, etc.) and scattering on its surface will also affect profile evolution. Besides improving fundamental understanding of gas-surface dynamics, these measurements provide for a description of the physics and chemistry of the interaction, which is incorporated into a Monte Carlo simulator of profile evolution. Preliminary calculations based on detailed scattering experiments on SiFx are shown to capture profile peculiarities such as the so-called "microtrenching", that is, the appearance of grooves at the bottom of etched features. The model is improved to describe pattern-dependent etching, three-dimensional effects, and the roughness appearing on etched surfaces. By including microstructure charging and ion deflection effects, the applicability of the profile simulator is enhanced, enabling its combination with plasma reactor models (developed by others) for designing the etch tools for the next generation of ultrahigh-density semiconductor devices. Etching experiments are also performed to support the model and verify predictions of profile peculiarities. Understanding the origin of predicted and observed deviations from the ideal anisotropic profile is expected to enable control over the final profile. Electrical damage studies on gate oxides of MOS devices are done as a demonstration of the potential of the technique. Finally, upon perfection of the technique, fabrication of quantum-confined and photonic bandgap structures is attempted. In order to integrate research with education in chemical engineering, the relation between classical chemical engineering concepts and modern electronic material processing techniques is exposed. As an example, special topics are offered in the undergraduate thermodynamics class, such as equilibrium in plasmas and surface thermodynamics, which are not traditionally covered. An introductory plasma experiment is planned for the undergraduate laboratory with hands-on experience in diagnostics. Extended research projects are also offered to undergraduates in the P.I.'s laboratory to enhance their appreciation of experimental science. At the graduate level, in addition to a course on electronic materials processing, plans are made to offer a new course on beam modification of surfaces, which is based on results and understanding obtained from this proposed research. ***
