Silicon Nitride Surface Preparation to Prevent Photoresist Blister Defects

C. Cheung, K. Luo, D.Li, P. Ngo, L. Dang, J. Uyeda, J. Wang, M. Barsky
Microelectronics, Northrop Grumman Space Technology, Redondo Beach, CA  90278
Phone: (310) 813-8365 Fax: (310) 813-3301  Email: chi.cheung@ngc.com

Preparation of silicon nitride (SiN) surface prior to photoresist coating is primarily performed to improve the resist adhesion to SiN and/or to clean the SiN surface.  Common industry practices include using oxygen plasma clean or priming the SiN surface with Hexamethyldisilazane (HMDS).  The state of the SiN surface has been observed to be a factor in the formation of blisters in the photoresist (PR) following exposure with ultra-violet (UV) light.  The PR blister defects may impact visual yield by as much as 30%.  Hydrogen plasma and methane plasma were found to be the most effective SiN surface treatments to prevent the formation of PR blister defects.  In this paper, the theory for the formation of the PR blister defect will be presented.  Alternative SiN surface preparation methods to prevent blister defects will also be discussed.  

Keywords:  Adhesion, blister, HMDS, hydrogen plasma, oxygen descum, photoresist defect, process yield, silicon nitride

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