NEXAFS Measurements of the Surface Chemistry of Chemically Amplified Photoresists

• Main Authors: Jablonski, Erin L, Lenhart, Joseph L, Sambasivan, Sharadha, Fischer, Daniel A, Jones, Ronald L, Lin, Eric K, Wu, Wen-li, Goldfarb, Dario L, Temple, Karen, Angelopoulos, Marie, Ito, Hiroshi
• Format: Conference Proceeding
• Language: English
• ISSN: 0094-243X

Near edge x-ray absorption fine structure (NEXAFS) spectroscopy was used to quantify the surface composition profile (top 1 nm to 6 nm) of model chemically amplified photoresists with various photo-acid generators. These materials are prone to interfacial and surface chemical changes that cause deviations in the desired lithographic pattern such as T-topping and closure. If interfacial excess or depletion of the photo-generated acid occurs, either from atmospheric contamination, evaporation, or segregation within the film, the resulting compositional heterogeneity will affect the interfacial photoresist structure, composition, and deprotection kinetics. A significant technical challenge lies in measuring the surface composition and extent of reaction with depth resolution at interfaces. Electron yield NEXAFS allows measurement of the surface chemical composition, particularly for carbon, fluorine, oxygen, and nitrogen. When exposed to vacuum ultraviolet x-rays (soft x-rays), the top surface of the material releases electrons that can be measured with a high pass grid analyzer electron yield detector. By varying the negative voltage bias at the entrance grid to the electron yield detector, it is possible to differentiate the kinetic energy of electrons escaping from depths up to 6 nm into the film. This measurement capability becomes increasingly important with the drive towards sub-100 nm lithography. As the photoresist film thickness continually decreases and the interfacial regions dominate the behavior of the material, it is crucial to understand both their physical and chemical nature.