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When using KrF resists, a peculiarity in critical dimensions (CDs) called developer nozzle traces is often observed (figure 2). We have determined and solved the cause of this problem. We calculated the flow rate of the developer solution per unit area at various points on a wafer, which was dispensed using a conventional nozzle (Figure 1). We discovered that the flow rate per unit area varied significantly across a wafer. We determined that areas of the wafer getting high developer flow rates had narrower CDs than other areas. We concluded that the cause of developer nozzle traces was due to a flow rate imbalance. We examined in detail the correlation between the amount of developer solution dispensed on a wafer and the line width, and found that the line width was narrowed when the amount of developer dispensed was 0.4 ml/cm2 or greater (Shipley UV6) (figure 7). From this result, it appears that the nozzle traces are related to the distribution of flow rate and that of CD. In addition, the profile of the top of the pattern differs depending on the developer flow rate. At high rates, the profile becomes rounded while at lower rates the profile is rectangular. Taking all of these observations into consideration, we invented a nozzle that dispenses developer uniformly over an entire wafer. The opening of this nozzle is slit-like in shape and extends over the entire wafer diameter. For full puddle formation, the nozzle dispenses developer solution while scanning linearly across a wafer. The wafer is stationary and does not rotate during this process. This nozzle system dispenses a uniform volume of developer per unit area over an entire wafer (figure 10). In order to achieve good puddling, developer dispense rate and nozzle scan rate have been optimized to minimize the movement of developer solution. At this time, the amount of developer dispensed over the wafer surface was 0.2 ml/cm2. We evaluated CD measurements using this nozzle and obtained very slight CD variation within a wafer 3 sigma = 6nm 180nm L/S (figure 14). Finally we found out that making the dispense flow rate of the developer solution equal and low per unit area is critical for CD control. By reducing the flow rate of the developer, the profile of the feature becomes rectangular compared to when using a conventional nozzle (figure 13).
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