Next, the effect of the C value and the mechanism to achieve the normal water injection were evaluated. Figure 5 shows the water injection from the Type-B nozzle observed using the blue-colored ink tracer. The C value was 2.5 mm. Figure 5(e) is a schematic of the water path in the Type-B nozzle. The water coming from the right side entrance is divided into two paths, such as Paths I and II. The water following Path II goes through the space between the inner tube and the outside tube. The water following Path I reaches the left end of the nozzle and turns back to enter the space between the inner tube and the outside tube. Thus, the water following Path I approaches the center pinholes of #4-8 earlier than that following path II to the same pinholes.
Figure 4. Water injection from Type-A nozzle observed using blue-co- lored ink tracer.
Figure 5. Water injection from Type-B nozzle observed using blue-colored ink tracer. The C value was 2.5 mm. (a), (b), (c) and (d) are sequential changes in tracer position. (e) Schematic of water path.
Figure 6. Water injection from Type-B nozzle observed using blue-colored ink tracer. The C value was 3.5 mm. (a), (b), (c) and (d) are sequential changes in tracer position. (e) Schematic of water path.
Figure 5(a) shows the tracer motion during the early stage. A dense image of the blue-colored ink existed at the pinholes of #1-3. A very slight blue color could be observed at #5, #6 and #7, while no tracer existed at #8-11. Figure 5(b) shows the tracer position after the time at Figure 5(a). The blue contrast at the positions between #1 and #7 is denser than that in Figure 5(a). Additionally, the blue color at positions #8-11 slightly appeared. Next, in Figure 5(c), the blue color contrast was much denser than that in Figure 5(b). The further dense contrast was totally observed in Figure 5(d). Based on the tracer motion, the water motions following Paths I and II are assumed to be distinguished using the dotted line. The high contrast of the blue color came from the right end to the dotted line. Afterwards, the high contrast of the blue color came from the left end to the dotted line. The meeting point coming from Paths I and II is the position indicated using the dotted line, because the blue color contrast was significantly different between positions #7 and #8 in Figure 5(c).
In Figure 6, the water motion can be evaluated following the method similar to that in Figure 5. The blue color contrast sequentially intensified, pinhole by pinhole, from both sides of the Type-B nozzle, from Figure 6(a) to Figure 6(d). The water flow following Path I meets with that following Path II at the position between #6 and #7. The meeting point in Figure 6 slightly shifted to the center of the Type-B nozzle, rather than that in Figure 5. Thus, the C value of 3.5 mm is considered to be better than that of 2.5 mm from the viewpoint of symmetry.
In order to evaluate the water velocity profile in detail, Figure 7 shows the calculation for the Type-B nozzle. The water velocity was normalized using those in the center region. In Figure 7(a) and Figure 7(b), the C value is 3.5 mm and 2.5 mm, respectively. The D value of 12 mm and 10 mm is indicated using the circle and triangle, respectively.
In Figure 7(a) and Figure 7(b), the water velocities shown using the circles and triangles are overlapped. Thus, the D value, that is, the inner tube diameter does not cause a significant difference. However, in Figure 7(b), the pinhole giving the maximum velocity by the D value has a position nearer the center than that by the 10 mm. Thus, the D value of 12 mm is expected to produce a symmetrical velocity profile along the Type-B nozzle, even when the C value significantly changes.
Next, the C value, that is, the left end clearance between the inner tube and the outside tube was evaluated. Figure 7(b) shows that the water velocity at the pinhole position #11 is significantly lower than those at the other positions. In contrast, the water
Figure 7. Calculation of normalized water velocity injected from Type-B nozzle. The C value is (a) 3.5 mm and (b) 2.5 mm. The D value of 12 mm and 10 mm is indicated by circle and triangle, respectively.
velocity profile in Figure 7(a) is flatter than that in Figure 7(b). Thus, the C value of 3.5 mm was employed in this study.
4.3. Water Flow Using Type-B Nozzle
In addition to the water velocity evaluation at the pinhole, the entire water flow generated by the Type-B nozzle was observed and evaluated in the bath, as shown in Figure 8. In order to evaluate the water velocity profile generated by the nozzle, specifically, concerning the tracer motion between the wafers, the tracer motion observed from the right side was the focus. Because the T-region indicated using the dotted line is the position outside of the bath, used to add the tracer, the blue color in this region was not related to the water flow in the bath. Figures 8(a)-(c) show the time sequence of the tracer; while Figure 8(d) shows a schematic of the water motion. Immediately after the tracer injection, as shown in Figure 8(a), the highest tracer position was the center region where the six wafers were arranged, as shown in Figure 8(d). In Figure 8(b) and Figure 8(c), the tracer went up faster in the center region than in the other region. Additionally, the tracer distribution was symmetrical to the center of the bath. Based on the tracer motion shown in Figure 8, the symmetrical water injection profile in the normal direction was recognized to be successfully achieved by the Type-B nozzle.
Because all the entire dimensions of the Type-B nozzle are exactly the same as those of the Type-A, the Type-B nozzle produces no deterioration in the other condition for removing small particles and contaminations including the grinding waste.
For a silicon wafer wet cleaning bath, a dual-tube-type water injection nozzle was studied, based on theoretical calculations and experiments. A thin inner tube was simply installed and its position was optimized in order to generate a counter flow. Such a simple design could make the water injection direction normal and the water velocity profile symmetrical along the nozzle. The water flow in the wet cleaning bath, observed using blue-colored ink as the tracer, showed the fast upward water stream through the
Figure 8. Observed tracer motion sequentially shown versus time, (a), (b) and (c). (d) is a schematic of the tracer motion. The T-region indicated by the dotted line is where to add the tracer.
array of six wafers when the nozzle developed in this study was placed at the bottom of the bath. Because the outside dimension of the nozzle caused no change, the water flow was simply improved with no trade-off by this study.