Pattern fidelity enhancement with OPC pattern generation on laser lithography

Laser pattern generators ALTA 3500 and 3700 are widely used for 0.18 micron and above technology nodes in photomask manufacturing. They have low butting, high throughput and high position accuracy, with some weaknesses such as, corner rounding, no proximity effect correction and poor CD linearity when compared to E-beam pattern generators. Optical Proximity Correction (OPC) software was thus created to extend the productivity of laser pattern generators. For contact holes serifs are typically added at the four corners to enhance pattern fidelity. However, the serifs or scattering bars can significantly increase the data size. In our study, we generated serifs for contact holes but applied different exposure strategies: (1) lumping serifs together with the main pattern; (2) exposing serifs and main pattern separately with same dosage; (3) exposing serifs and main pattern separately with different dosages. We examined the results of each approach in terms of contact hole quality, throughput, and inspection results.