Paper PS2-FrM7
Investigation of Bottom Profile Degradation Mechanism in Extremely High-Aspect-Ratio Feature Etching

Friday, October 24, 2008, 10:20 am, Room 306

As the half-pitch of DRAM design rule advances beyond the 50 nm, precistion plasma etching will be required to realize extremely high aspect ratio feature of over 30. According to the shrinkage of pattern CD and narrowing pattern pitch size, many kinds of profile degradations that occur especially at around bottom area, such as, bottom distortion, twisting, shortage of bottom CD, have been observed. We assume that the mechanism of these etching profile degradations has closely connection with the combination of mask profile deformation, charge-up phenomenon, and the change of etch-front condition at bottom region. In order to diminish these profile degradations, we investigated the mechanism in terms of mask profile deformation effect with using ultra-high-frequency ECR (UHF-ECR) plasma etching system.¹ In this study, we used trench pattern to evaluate the degree of pattern deformation quantitatively as a function of pattern depth. Also, direct observation of etched pattern sidewall with using atomic-force-microscopy (AFM) was applied to clarify the relationship between bottom distortion and mask (necking) profile. The ratio of line width roughness (LWR) to line edge roughness (LER) that estimated from top view observation of etched sample after etch-back process decreased with increasing pattern depth and it means that pattern deformation becomes to ‘wiggling’ mode at deeper area. On the other hand, AFM observation of etched sidewall revealed that mask (necking) roughness is transferred to the bottom region and amplified drastically. As a result, we confirmed that using the mask of low degree of deformation is effective to diminish the bottom distortion.

(1) K. Yokogawa, N. Negishi, S. Yamamoto, K. Suzuki, and S. Tachi, 1997 Dry Process Symp., pp. 379-383.