Parameter study for silicon grass formation in Bosch process

Abstract

Bosch process is one type of silicon etching technology for high-aspect ratio where silicon grass is one of the by-products. Previously, most of the studies have been focused on eliminating these silicon grasses. However, in this study, the optimized condition for obtaining silicon grasses was studied using inductively coupled plasma reactive ion etching for its potential application as silicon wires in the field of lithium ion batteries as electrodes and texturing of Si solar cells. It was found that the diameter for silicon grass was found to be proportional to the pattern size. The diameter and length of silicon grass were found to be dependent on the chuck power, duty cycle, SF6 pressure, etch/passivation time ratio, and ratio of flow rate. As chuck power decreases, the diameter and density of silicon grass increase. Low duty cycle and high chamber pressure are favorable for obtaining high density of silicon grass formation. Moreover, it was found that the relative time ratio of SF6 to C4F8 being 7:2 seems to be the optimal condition for sub-micrometer-sized grass formation. Finally, the flow rate of SF6 was found to be inversely proportional to the grass formation; the flow ratio of SF6 and C4F8 being 2:1 is the optimum condition to obtain high density of silicon grass. Overall, various parameters can be controlled in Bosch process to control the diameter and length of silicon grasses.