Yukio Kiba

Improvement of pattern collapse issue by additive-added D.I water rinse process: II

Reduction of critical dimension in lithography technology is aggressively promoted. At the same time, further resist thickness reduction is being pursued to increase the resolution capabilities of resist. However, thin film has its limitation because of etch requirements etc. As that result, the promotion of reduction results in increasing the aspect ratio, which leads to pattern collapse. It is well known that at drying step in developing process the capillary effect operates the photoresist pattern. If the force of the capillary effect is greater than the aggregation force of the resist pattern, the pattern collapse is generated. And the key parameters of the capillary effect are the space width between patterns, the aspect ratio, the contact angle of the D.I water rinse and the surface tension of rinse solution. Among these parameters the surface tension of rinse solution can be controlled by us. On the other hand, weve already reported that the penetration of TMAH and D.I water into the resist plays an important role on the lithographic latitude. For example, when we use the resist which TMA ion can be easily diffuse into, D.I water and TMA ion which are penetrated in the resist decreases the aggregation force of resist pattern and causes the pattern collapse even by the weak force against resist pattern. These results indicate that the swelling of photoresist by TMA ion and water is very important factor for controlling the pattern collapse. Currently, two methods are mainly tried to reduce the surface tension of rinse solution: SCF (Super Critical Fluid) and addition of additive to D.I water rinse. We used the latter method this time, because this technique has retrofittability and not special tool. And in this evaluation, we found that the degree of suppressing pattern collapse depends on the additive chemistry or formulation. With consideration given to process factors such as above, we investigated what factors contribute to suppressing pattern collapse for each resist platform when using additive-added rinse solutions. This report describes the results of our examinations and discussions of the pattern collapse mechanism.

Improvement of the resist pattern collapse

In this study, we investigated resist pattern collapse during the resist development process. We evaluated the effect of a simple improvement such as rinse-liquid sequencing and rinsing using surfactants. First, we controlled the wafer spinning speed during the rinse-liquid flow step to reduce liquid flow shock. Using this approach, we obtained a 110-nm L/S (line and space) structure with no pattern collapse. However, this technique has only a small effect on preventing pattern collapse with sub-100-nm devices. By using a rinse process with a surfactant, we could control pattern collapse with 100-nm L/S or smaller patterns. Finally, we have succeeded in controlling pattern collapse of 70-nm L/S patterns (aspects ratio of 4.6) using a surfactant during the rinse process. These two simple methods are a significant improvement over conventional rinse processes. These process improvements are available for 90-nm (and smaller) design rules and are applicable for a single layer resists.

Application of diluted developer solution (DDS) process to 193-nm photolithography process

Along with the trend of reducing the critical dimension in photolithography, exposure wavelength has been shortened from 248nm to 193nm. Resin structures of resist including their chemical characteristics have been altered from PHS to acrylate polymer. On the other hand, 2.38wt% TMAH developer solution is widely used, which was optimized at the time of 436nm resist process. However, since the resist backbone and chemical characteristics of 193nm resist are different from that of 436nm resist. So, TMAH concentration of 2.38wt% is not necessarily the best value for 193nm process and may even worsen the process latitude. Therefore, we have studied improvement of the process latitude such as CD uniformity, pattern defect, and dissolution mechanism of 193nm resist in developer solution, by applying Diluted Developer Solution (DDS) on 193nm resist process.