Water Motion over a Wafer Surface Rotating in a Single-Water Wet Cleaner

Abstract

Water motion over a 200-mm diameter wafer surface rotating in a single-wafer wet cleaner was studied, using the water flow visualization technique with a video camera and blue-colored ink as the tracer. When the tracer was injected from the wafer center, it was seen to symmetrically spread over the rotating wafer surface from its center to the edge. The radial velocity of the water showed a negligibly small change over the wafer surface except at its center area. The water layer thickness in the rotation rate range between 500 and 1400 rpm was approximately 0.1 mm; it gradually decreased with the increasing rotation rate. The tracer injected from non-center positions showed that the water flow tended to be localized in the peripheral region of the wafer, particularly at the high rotation rates.The process of fabricating semiconductor silicon microelectronic devices requires a very clean silicon surface. Because various contaminants are present during the device fabrication, they must be removed by cleaning techniques, such as wet cleaning using a single-wafer-type and a batch-type wet cleaner. 1,2 The single-wafer wet cleaner using wafer rotation has various advantages, such as no cross-contamination between the wafers and a small footprint. 1 In order to study and optimize the wet cleaning process condition from the viewpoint of the transport phenomena and the chemical reaction, the fluid flow on and around the rotating wafer surface should be clarified. 3,4 Thus, the water motion and etch rate were studied by many researchers 3,5 based on numerical calculations. For further developing the numerical calculation model, the water motion should be clarified by experiment using a fluid visualization technique.In this study, the typical water motion over a wafer surface rotating in a single-wafer wet cleaner was studied by the flow visualization technique using a blue-colored ink tracer and a video camera. The water velocity and the water layer thickness were evaluated when the water was injected at the wafer center. Additionally, the water motion injected from positions other than the wafer center was studied. Figure 1 shows the single-wafer wet cleaner used in this study. This cleaner uses a 200-mm diameter wafer rotating at the rate of 100-1400 rpm in a cylindrical-shaped vessel. Water was supplied through a tube from the pump, and was injected downward from the water nozzle normal to the wafer surface at the flow rate of 1 l/min. After the injection, the water was transported along the wafer surface from the injected position to the wafer edge, then finally sputtered off from the wafer edge to the outside. ExperimentalIn order to obtain the water motion, the mass transport should be directly visualized and traced. For this purpose, a water-soluble colored ink can be a suitable tracer, because it is perfectly dissolved and transported with the water. Additionally, the ink is harmless and very low cost.At a specified time after starting the water injection for forming a steady state of water flow, 1 cm 3 of the blu...

Numerical calculation model of a single wafer wet etcher using a swinging nozzle

“…2(b) was assumed. This assumption is reasonable, because the water injected from the non-center nozzle has been shown to exist axi-symmetrically in the region farther out from the nozzle position [2]. Additionally, this inlet model involves low calculation cost, because the periodical boundary condition is applicable, similar to that shown in Fig.…”

“…The HF aqueous solution flow and its surface chemical reaction were numerically calculated, as an extension of our previous study [2]. As shown in Fig.…”

“…For preparing a very clean silicon surface avoiding unnecessary contamination, a single wafer wet etching method has been widely used in the semiconductor silicon industry [1][2][3]. Particularly, for fabricating a silicon-on-insulator (SOI) wafer by the wafer-bonding technique using two silicon wafers [4][5][6][7], a very clean and flat surface of silicon dioxide film for the buried oxide layer is necessary.…”

“…Although the silicon dioxide film thickness uniformity can be adjusted by various oxidation process conditions [7], it should still be effectively improved after the oxidation. For this purpose, the single wafer wet etching method [1][2][3]8] is a useful technique. Particularly the single wafer wet etching method [1][2][3] has a function for choosing the region to be deeply etched on the wafer, by means of adjusting the motion of swinging nozzle which injects the etchant.…”

“…Thus, in our previous study [2], the water motion, such as the water velocity and the water layer thickness, was measured using a tracer method and calculated using computational fluid dynamics. However, the previous study was limited to a simple geometry, having the water nozzle fixed at the wafer center, without any chemical reaction.…”