The Effect of Slurry pH and Particle Size on LiTaO3 Polishing
Abstract –The demand of LiTaO3 (LT) wafer mainly used as substrate of SAW (Surface Acoustic Wave) filter device has been quite increasing in recent years. From the viewpoint of LT wafer’s productivity in the polishing process, high removal rate and good recycle stability are required for slurry to eliminate generated damages in the previous process. In this study, the effect of pH and particle size in the slurry on the removal rate and the polishing stability of LT wafer were investigated. We found out that acid slurry containing large particle can achieve high removal rate with good recycle stability. The balance of pH and particle size would be taken advantage of polishing other hard brittle or chemically stable materials such as sapphire, silicon carbide and gallium compounds.
INTRODUCTION
LT is one of the ceramics materials mainly used as the substrate of SAW filter device that can distinguish an electric signal of specific frequency. In recent years, in addition to the market growth of smartphones, demand is rapidly expanding due to the large increase in the number of devices mounted on each smartphone because of high speed and large capacity of transmission. Under such circumstances, improvement of productivity is desired. LT wafer should be polished as well as typical substrates like silicon, sapphire and silicon carbide in order to eliminate the damage occurred at previous process. The features of the LT wafer are different from others, for example, thinner thickness, brittleness and high chemical stability.[1] As these features, polishing condition of LT wafer is generally so mild that removal rate can not be raised easily. One of the key factors to improve the removal rate effectively is polishing slurry. Typical one is composed of a normal colloidal silica with a pH adjuster,[2] but it can’t realize a sufficient polishing performance with respect to both a high removal rate and good stability. In this study, the effect of pH and particle size in the slurry on the removal rate and the polishing stability of LT wafer were investigated, and we propose a suitable area that can keep the balance of pH and particle size with respect to high removal rate with good stability.
EXPERIMENTS
The effect of slurry pH on removal rate was evaluated by using slurries containing 20wt% silica abrasives. Mean particle size was 122nm and slurry pH was controlled by hydrochloric acid and potassium hydroxide from 3 to 9. Removal rate was calculated by weight loss of 15 minutes polishing. Polishing conditions are shown in Table 1.
