Abstract: A method of reducing a critical dimension (“CD”) bias between a dense pattern and an isolation pattern is disclosed. The method includes a first step of providing a mask having a dense pattern, an isolation pattern and the other area of the mask is transparent, in which mask the dense pattern has a first opaque pattern and the isolation pattern has a second opaque pattern. The second step of the method is forming a virtual pattern around the isolation pattern, in which a distance between the virtual pattern and the isolation pattern is y, and the virtual pattern has a pattern line width x. By forming the virtual pattern around the isolation pattern, the flare effect of the isolation pattern is close to that of the dense pattern, thus the CD bias between a dense pattern, and an isolation pattern is reduced, and the process window does not shrink.

Abstract: A microlithographic process is provided. First, a photoresist layer is formed over a substrate. Thereafter, a first photomask having a dense pattern thereon is set up over the photoresist layer. A first photo-exposure is carried out to transfer the dense pattern on the first photomask onto the photoresist layer. The first photo-exposure is performed using a beam of light at an energy level E1. The first photomask is removed and then a second photomask having a sparse pattern thereon is set up over the photoresist layer. A second photo-exposure is carried out to transfer the sparse pattern on the second photomask onto the photoresist layer. The second photo-exposure is performed using a beam of light at an energy level E2 such that E2 is greater than E1. Finally, the photoresist layer is chemically developed to produce a patterned photoresist layer.