The behavior of the photoresist between contact holes during the thermal flow process was investigated. When the photoresist width was smaller than 200 nm, the amount of shrinkage of the contact hole increased almost linearly with the photoresist width between contact holes. However, the amount of shrinkage was saturated and rarely changed with the photoresist width when the resist width was larger than 400 nm. We examined three models to investigate this phenomenon. The first one is the simple one-dimensional model, and the second one is the viscoelastic model with constant fluid viscosity. The third one is the viscoelastic model for the Bingham fluid. We calculated the amount of shrinkage of the contact hole vs the photoresist width, and the values calculated using the viscoelastic model for the Bingham fluid was consistent with the measured values. We also synthesized a contact-hole image by expanding this one-dimensional model to two dimensions. The average total hole radius error between the measured and the synthesized image was less than 7 nm, and the calculated image was almost the same as the measured one. We concluded that the viscoelastic model for the Bingham fluid is adequate for describing the photoresist behavior in the thermal flow process. (c) 2007 The Electrochemical Society.