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How to Select the Proper Cleanroom Wiper for Photolithography Track Wet Cleans

by | Jan 30, 2023

In photolithography modules, keeping TEL tracks clean is critical in preventing contamination in the ASML DUV TWINSCAN scanner. Contamination in the scanner can lead to two main scenarios: low vacuum in the P-chuck and TSU and wafer table flatness issues on the wafer table. Using PolyCHECK, we have established that the resist and polyester particle and fiber contamination from polyester wipers are the majority of contamination transferred from the track to the scanner. To prevent these issues, it is crucial to employ a wiper with the durability to resist particle shedding and the absorbency to capture and remove resist residue on the clean coaters and hot plates inside the TEL Lithius tracks.

20x exposure of MiraWIPE and polyester wiper after both were used to clean the coater.

Polyester fiber collected from the wafer table in the scanner using PolyCHECK

Polyester fiber and residue collected from the coater with the PolyCHECK Process

Using FTIR analysis, we helped the engineer confirm that the fiber contamination found on the coater and scanner originated from the polyester wipers that were previously used to clean the tools.

The P-chuck and TSU are the first transfer point for wafers out of the track and into the scanner. The vacuum holes in the P-chuck and TSU are used to clamp down the wafer during pre-alignment, but if there are particles between the wafer and the P-chuck/TSU, the tool will error out for low vacuum. Most of the time, the source of the contamination is the track, which can lead to several hours of downtime, including the initializing of the tool. To prevent this issue, a cleanroom wiper should have high absorbency and particle removal properties to thoroughly clean the track and avoid backside contamination.

TEL Lithius Track Coaters

Dry photoresist flakes are easily cleaned with MiraWIPE.

When the wafer is successfully pre-aligned, it is moved to a wafer table where it is measured and scanned. A sensor monitors the flatness of the wafer table, and if there is a hotspot, the flatness will go off. This is caused by backside contamination of the wafer, which is most likely introduced from the track. When the SPC chart consistently sees flatness out of spec, the tool will be taken down, and an ASML engineer will manually remove the wafer and clean the wafer table with a dry stone. A cleanroom wiper should be able to clean the track and prevent backside contamination effectively.

MiraWIPE enables stubbornly adhered resist stains on the coater to be cleaned efficiently.

Coating bowls with resist stains can be cleaned at the track.

In conclusion, the ideal characteristics for a cleanroom wiper for cleaning TEL tracks in photolithography modules should have ultra-low fiber shedding, high absorbency and particle removal properties to prevent backside contamination of wafers. This will prevent issues with the P-chuck and TSU, and wafer table flatness reducing downtime and ensuring the ASML DUV TWINSCAN scanner operates at its maximum potential.

MiraWIPE 256 is production-proven in the most advanced foundries to reduce post pm particle counts and improve re-cleans due to particle failure. MiraWIPE 256 has greatly improved scanner uptime by allowing operators to more thoroughly and completely clean the track.

MiraWIPE 256

PolyCHECK FM Identification Process

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