| The techniques of silicon micromachining developed by the microelectronics industry are increasingly being used to fabricate a wide variety of microelectromechanical systems (MEMS). As the geometry of MEMS becomes more complicated, new chemical etching techniques need to be developed in order to meet technological demands. This thesis describes three separate investigations into different aspects of site-specific surface chemistry.; In the first investigation, micromachined test patterns are used to perform orientation-dependent kinetic studies on the etching of silicon in aqueous KOH solutions. Standard models of chemical reactivity cannot accurately describe the observed kinetics. Temperature-dependent macroscopic etch rates exhibit non-Arrhenius behavior, and empirical rate laws do not fit the observed concentration dependence. The disagreements with standard models are attributed to the multisite nature of surface etching reactions. Deuterium substitution reduces the etch rate of all surfaces in the Si[110] zone. This kinetic isotope effect is attributed to the rate-limiting breaking of Si-H bonds. The kinetic studies show that surfaces in the Si(110) zone are divided into four regions of similar reactivity: vicinal Si(100), vicinal Si(110), and two types of vicinal Si(111).; In the second investigation, a new technique was developed for fabricating nanoperiodic surfaces with periodicities of 2–100 nm. By selectively etching dislocations at the interface of two twist-bonded Si(100) surfaces, a periodic array of hillocks is produced. The etch rates of tilt- and twist-dislocations are compared. Both types of dislocations etch at very similar rates, even though their calculated strain field energies differ by two orders of magnitude. This observation contradicts long-held assumptions about dislocation etching.; In the third investigation, nanofabricated arrays of silicon nanodots were used to study nanostructure-directed anodic etching. These experiments suggested that the current density, not the voltage, was the morphology-determining parameter of porous silicon formation. Removal of the porous silicon layer by both KOH etching and a combination of thermal oxidation and selective oxide etching revealed that the nanostructures had been preserved at the bottom of the porous silicon layer. This preservation of the arrays was attributed to the formation of bulk-silicon nanopillars within a porous silicon medium. |
