Experimental Study on Etching Characteristics of a Spin-Etching Method

In this paper, a spin-etching method is proposed for wafer thinning using a mixture of hydrofluoric, nitric, and acetic acids (HNA solution), and experimental studies are conducted. In the spin-etching apparatus, the silicon wafer was rotated in a Teflon bath filled with HNA solution. The etch rate of HNA spin-etching can be determined by mixture ratio; mass transfer, both through and in boundary layer; and heat transfer. When the Reynolds number of the flow on the rotating disk is below 1.8 × 10⁵, the flow is in the laminar region, and the boundary layer thickness and convective heat transfer coefficient do not vary with radius at the same rotational speed. In this study, the silicon wafer was rotated at <;60 rpm, at which the flow was in the laminar region. Nevertheless, the local etch rate varied with the radial position. To investigate spin-etching characteristics of the silicon wafer rotated in the laminar region, experimental studies on etch rate and uniformity of etch of 6-in silicon wafers as the rotational speed was varied were carried out with various HNA mixture ratios.