Nanoscale materials processing electron beam-induced etching of silicon and silicon dioxide /

by 1976- Randolph, Steven Jeffrey

Both silicon and silicon dioxide can be etched with an electron beam in the presence of a xenon difluoride atmosphere in a process known as electron beam-induced etching (EBIE). In order to study the EBIE process, a Hitachi S-3500N scanning electron microscope (SEM) was modified to accept a vapor delivery system. Evidence has been presented regarding the fundamental mechanisms by which EBIE occurs, as well as the microscope variables that effect the etch process. The effects of beam current and beam energy on the EBIE process were examined for both materials. On silicon, it was observed that the increased current had little effect on the etch rate. In contrast, high current enhanced the etch rate of silicon dioxide. For both materials, increased beam energy resulted in a decrease in process efficiency, which is consistent with the known decrease in interaction cross-sections at high energy. It was proposed that the mechanism for the silicon etch process involved the enhancement of a reaction in which a volatile SiF 4 species was formed from two SiF 3 molecules. In the case of silicon dioxide, the rate limiting mechanism is more unclear, but is proposed to be initially limited by the electron stimulated desorption of oxygen from the SiO 2 matrix. Microscope variables have a profound effect on the etched features. Increased probe current resulted in lower resolution due to the increased condenser lens setting and larger probe size. Experiments performed at high energies, which correspond to smaller probe size, resulted in higher feature resolution. It was also determined that an optimal scan rate exists at which the etch process is most efficient. iv