As the feature size continues to decrease well below 100nm, the relative width variation along the resist depth dimension, compared to the feature size, becomes larger. The actual sidewall shape may significantly deviate from the target shape. In order to have a better control over the sidewall shape, one needs to consider the exposure variation along the depth dimension (in addition to the lateral dimensions) in proximity effect correction. A true 3-D proximity effect correction scheme which is based on the 3-D exposure model has been developed. One of the implementations of the 3-D schemes employs a resist development simulation to obtain correction results leading to more realistic resist profiles.