Photomask Lithography


The demand for smaller and more uniform features on photomasks is rapidly increasing. The complexity of these patterns is also increasing with the need for optical proximity correction and phase shifting structures. These complex mask features demand unprecedented accuracy in pattern placement and dimensional control. We have conducted research designed to model and optimize the process for laser pattern generation by improving resolution and process latitude for 365 nm optical pattern generators. Lithographic simulation and photomask manufacturing trials have demonstrated sub-0.30 micron spaces in I-line resists using the ALTA 3500.

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257 nm Resist Development

Our photoresist models are currently being expanded to formulate a resist for a new 257 nm optical pattern generator. A non-chemically amplified resist is being developed from a 2,1,4 diazonaphthoquinone/ novolak resist system. Diazonaphthoquinone (DNQ)/ novolak resists have not been used for DUV Integrated Circuit (IC) applications mainly due to the low sensitivity and the strong absorbance of the DNQ photoactive compound (PAC) at 248 nm. However, a 2,1,4 DNQ based resist has been characterized that bleaches at 257 nm and inhibits novolak. The photoproduct of the 2,1,4 DNQ PAC is much more transparent at 257 nm than 248 nm. Novolak resin is too strongly absorbing for use in formulating efficient 248 nm resists, but novolak has an absorbance minimum at 257 nm that provides transparency similar to poly (hydroxystyrene).

An exposure system using a 257 nm frequency doubled Ar laser system has been constructed to study the resist photokinetics. Dill exposure parameters (A, B and C) have been extracted for a 2,1,4 DNQ/ novolak based resist. Dissolution rate measurements have been made with a DRM developed at the University of Texas at Austin. Simulation is used to determine the optimal resist absorption, bleaching, dose and dissolution properties to maximize resolution. Manufacturing trials are now in progress to evaluate our non-chemically amplified 257 nm resist.