Ozone-Water Process Removes Back-End Post-Etch Resist/Residue
Maria A. Lester, Associate Editor
-- Semiconductor International, 9/1/2000
Oxygen plasma ashing and post-ash solvent-cleaning are used widely in the industry for back-end post-etch resist and residue removal. There is a new alternative. The
HotOzone process, an ozone-water cleaning process developed by
Phifer Smith Corp. (Palo Alto, Calif.), can be used for post-contact/via oxide etch or post-metal etch resist or residue removal.
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1. 0.35 µm technology with 0.5 µm features: (a) left SEM: after metal etch; right SEM: after 1.5 min HotOzone clean; (b) left SEM: after oxide etch; right SEM: after 1.0 min HotOzone clean. (Source: Phifer Smith Corp.)
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This 50°C wet process can be integrated into a cluster tool in a single-wafer spin processor. The process performance was evaluated by the Hewlett Packard ULSI Research Laboratory (Palo Alto, Calif.)
1. The process was an attractive candidate for evaluation because it had demonstrated resist removal rates two to four times higher than competing ozone-water processes.
The researchers prepared 0.35 µm and 0.18 µm technology
post-oxide etch and post-metal etch test structures on 150 mm wafers. One set of
the four test structures was oxygen plasma ashed before the ozone-water cleaning
process, and the other set was not ashed before cleaning. Cross-section SEM
photographs taken at HP provide a preliminary assessment of the new process'
cleaning and corrosion performance. Results for the second test set (not ashed)
are shown in Figures 1 and 2. The post-etch resist and residue are removed from
the 0.35 µm post-metal etch and post-oxide etch test structures within 1.5
minutes and 1.0 minutes, respectively (Fig. 1a and 1b). Post-etch resist and
residue are removed from the 0.18 µm post-metal etch test structure within 3.0
minutes (Fig. 2a ).
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2. 0.18 µm technology with 0.25 µm features: (a) left SEM: after metal etch; right SEM: after 3.0 min HotOzone clean; (b) left SEM: after oxide etch; right SEM: after 3.0 min HotOzone clean. (Source: Phifer Smith Corp.)
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Although the post-etch
resist is removed from the 0.18 µm technology post-oxide etch test structure
within 3 minutes, the surface and sidewall polymer were only partially removed
even after the process time was extended to 5 minutes (Fig. 2b). The SEM photographs showed no evidence of metal corrosion of any of the test structures.
This cleaning process has demonstrated the potential to replace the plasma ashing and solvent cleaning processes for all but the post-oxide etch test structure with DUV resist on an organic BARC layer. Phifer Smith says work is under way to enhance the post-etch residue removal rate. The company also says it has completed an initial evaluation of the performance of the cleaning process in front-end applications with implanted resist. •
REFERENCES 1. S. Ma, R. Parker, R. Kavari, I. Leal, D.G. Boyers, and J.T. Cremer, IITC Proceedings, p. 46-48, June 2000, San Francisco.
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