As technology advances, the geometries of lithography processes have declined by several orders of magnitude over the past 25 years. However, one area that has remained unchanged is the cleaning process of litho tracks. These tracks are used to coat, bake, and develop wafers and transfer them to the scanner for exposing, and even small amounts of contamination transferred from the track through the wafers can cause major issues with the scanner.
One of the most common causes of particle contamination is the use of polyester wipers that were introduced almost 40 years ago. These wipers shed particles as they are used and cannot pick up developer and resist particles very efficiently, which can lead to contamination of the wafers. This can cause significant downtime and financial losses for the company.
ASML Twinscan lithography tools are highly susceptible to particle contamination, and the P-chuck/TSU is the very first transfer point where the wafer travels from track to scanner. The P-chuck is responsible for spinning the wafer to find its notch to pre-align before bringing the wafer-to-wafer stage. The TSU controls the temperature of the wafer as the P-chuck pre-aligns and moves up and down for robot grippers to pick up and drop off the wafer. Both the P-chuck and TSU have vacuum holes that clamp down the wafer during pre-aligning. If there are particles in between the P-chuck/TSU and wafer, the tool will error out for low TSU vacuum because they are not making good enough contact with each other due to those particles.
To resolve this issue, litho engineers can use Foamtec International’s PolyCHECK process to troubleshoot the root source of the particle contamination. The PolyCHECK process uses a unique combination of particle identification and analysis to determine the type and origin of the particles present on the wafers, equipment or in the cleanrooms. This information can then be used to put corrective action in place to clean the litho track and prevent further contamination.
The PolyCHECK process offers several benefits to litho engineers. It can quickly identify the root source of the particle contamination, which can save significant time and resources. It can also help to prevent future contamination incidents, which can save the company significant financial losses. Furthermore, it can be used to monitor the effectiveness of cleaning methods and to ensure that the cleanroom is meeting the required standards.
The resist polyester and polycellulose contamination captured from the P-Chuck & TSU are greater than 500 microns in size. The polyester fibers are a direct match with the wipers used in the track.
In conclusion, Foamtec International’s PolyCHECK process offers a powerful solution for troubleshooting the root source of particle contamination in litho tracks. By using this process, litho engineers can quickly identify the root source of the contamination, put corrective action in place, and prevent future contamination incidents, which can save significant time and resources for the company.
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