Negative resist profiles of close-spaced parallel and isolated lines: experiment, modelling and simulation

• Published in: Microelectronic engineering 1999-02, Vol.45 (1), p.71-84
• Main Authors: Karafyllidis, I., Hagouel, P.I., Neureuther, A.R.
• Format: Article
• Language: English
• Subjects: Applied sciences; Cellular automata; Electronics; Etching; Exact sciences and technology; Microelectronic fabrication (materials and surfaces technology); Photolithography; Resists; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
• ISSN: 0167-9317; 1873-5568
• DOI: 10.1016/S0167-9317(98)00283-4

We present a series of experiments for a cluster of parallel lines and an isolated one on Shipley SNR-248 negative resist coated Si wafers using a stepper and a Deep Ultra Violet source at 248 nm. The profiles obtained show that if the parallel lines are close-spaced they do not open up completely. We use the cellular automata model in order to simulate this effect. We attribute this effect to the change of the {developer–developer products} solution into a viscous one due to the presence of slowly diffusing dissolved resist molecules and free (dissolved) resist chunks in close proximity in the developer. This effectively reduces the development speed. The effect that we observe experimentally is a direct result of the thermodynamics of quasi-irreversible processes applied to a viscous continuous medium. The physics are incorporated in our model. Development depends on volume effects in addition to the “surface” etching phenomenon. The simulation results are in very good agreement with the experimental ones. This effect is expected to be pronounced in 193 nm photolithography and below and, therefore, the model presented here may contribute to the design of new low wavelength resists.