Establishing a Link Between Carbon Concentration and Contact Angle on HMDS Surfaces

Hexamethyldisilizane (HMDS) is commonly used as a photoresist adhesion promoter for semiconductor applications. The wafer surfaces are typically hydrophilic and HMDS is usually coated onto the surface to ensure adhesion during develop and wet etch, and also serves as a repellent to unwanted water molecules. The vapor deposition of HMDS is utilized for this process, and an optimum amount of exposure is required for effective priming. Water contact angle measurements are typically used to verify the presence and quality of the HMDS, but this is an offline measurement, time-intensive, and exposes personnel to potential hazards. For this work, in-line XPS characterization was explored as an alternative to contact angle. XPS measurements were correlated with contact angle results to obtain a "magic" carbon concentration that can be used to monitor HMDS effectiveness. The C concentration and contact angle both increases with HMDS exposure times but plateaus at ~20 seconds for bare Si wafer and ~30 seconds for SiO
2
/Si surfaces. The correlation between the two results show linear relationship on both surfaces within the dispense times of 10-40 seconds. The optimum results were utilized for the HMDS coating and the total C % were monitored as defense line for HMDS-related issues. In conclusion, this study demonstrates the effectivity in the use of XPS as an alternative HMDS test, allowing for faster and inline measurements without the risk of chemical exposure.