AVS 59th Annual International Symposium and Exhibition
    Plasma Science and Technology Tuesday Sessions
       Session PS2-TuM

Paper PS2-TuM11
Challenges for Sub 20nm STI Etch

Tuesday, October 30, 2012, 11:20 am, Room 25

Session: Advanced FEOL/Gate Etching 2
Presenter: H. Zhou, Applied Materials Inc.
Authors: H. Zhou, Applied Materials Inc.
X. Ji, Applied Materials Inc.
S. Srinivasan, Applied Materials Inc.
J. He, Applied Materials Inc.
X. Hua, Applied Materials Inc.
D. Heo, Applied Materials Inc.
J. Choi, Applied Materials Inc.
A. Khan, Applied Materials Inc.
A. Agarwal, Applied Materials Inc.
S. Rauf, Applied Materials Inc.
Correspondent: Click to Email
With the feature size scaled down below 20nm, the plasma etching technology for shallow trench isolation (STI) becomes very challenging. The aspect ratio of the isolation trench can be as high as 20:1, and the space CD variation from double patterning is no longer negligible. Advanced processes and hardware are then required for the sub 20nm STI etch to minimize the depth loadings, i.e. intra-cell loadings. First approach is to trim the mask at the beginning to reduce the aspect ratio of the mask. With trimmed mask, the intra-cell loading is reduced. Second approach is realized with pulsed plasma. The period of pulsed plasma is ~ms, which is comparable to the residence times of typical plasma etch conditions. During the off cycle, the radicals/ions/byproducts have extra time to move out of the trench or act on the sidewall independently, and the sidewall polymer deposition is better managed. The advantage of pulsed plasma has been demonstrated with both 13MHz and 2MHz bias frequencies. Synchronized pulsed plasma etching has shown at least 40% improvement on CD-dependent depth loading than continuous wave plasma process. Moreover, 2MHz bias frequency also helps to round the trench bottom with higher energized ions. Another challenge for sub 20nm STI etch is profile control at extreme edge. Because of the plasma sheath bending effect, extreme edge trenches tend to tilt toward the wafer center. This issue can be fixed with a novel improvement of bottom electrode, which also improves the depth uniformity across the wafer. The ion flux with the novel bottom electrode is more uniform, in particular at the extreme edge locations. Compared to the standard electrode, the center to extreme edge trench depth variation has been reduced from 14.55% to 4.42% with the novel bottom electrode. Challenges for sub 20nm STI etch also include in-situ etching and line bending prevention, which will be also discussed.