An Investigation on The Effect of Surface Tension and Gravity on The Profile of Photoresist in Reflow Process

• Main Authors: Yung-Shun Hsu, 許泳順
• Other Authors: 蔡志成
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/12868057608335271028

碩士 === 國立中興大學 === 機械工程學系所 === 94 === Photoresist has been widely used for forming patterns in different scales. When it solidifies from melting condition, for example by the reflow process, its profile deforms due to surface tension and gravity. This research is aimed to investigate the influence of surface tension and gravity on the profile of photoresist in thermal reflow process. Theoretical analysis based on the interaction between surface tension and gravity of liquid droplet is first investigated. The result showed that the height to diameter ratio (h/D), or the sag ratio, of the liquid droplet is affected by the Bond number (Bo), a number defined as the ratio of gravity to surface tension. The sag ratio is not affected at small Bo but it decreases as Bo increases if Bo is over the critical number. Based on the analysis, the critical number for the AZ4620 photoresist on a silicon substrate is 1, corresponding to the critical radius of droplet R=2500μm. When the size of the droplet is less then the critical size, the profile is mainly controlled by the surface tension and thus the sag ratio is about the same regardless the size. The profile, in contrast, is highly affected by the gravity if the size of the droplet is larger then the critical size. The sag ratio decreases exponentially with respect to Bo in this case. Experiments are also designed and conducted to verify the analysis. Experimental result showed that the sag ratio of the photoresist reduces to 0.065 from 0.095 when Bo increases from 0.005 to 0.192. The results showed that the trend is consistent to the theoretical model. Although the difference between experimental results and theoretical analysis needs further investigation, the critical size based on the analysis provides a reasonable base for photoresist forming.