Abstract: A method for detecting phase features or phase defects on photomasks for optical lithography is described. The asymmetric imaging behavior through focus of defects or features with a phase other than 0° or 180° is used to distinguish them from other features on the mask. The mask is inspected at equally spaced positions about an optimum focus in both positive and negative directions. The images are subtracted from one another to produce a differential image of the mask. While opaque features as well as transmitting features at 0° and 180° behave identically at positive and negative defocus, thus leading to a zero-valued differential image, the focus asymmetry of phase defects and features produces a non-zero differential image from which these phase defects and features can be located.

Abstract: A method of simulating aerial images of large mask areas obtained during the exposure step of a photo-lithographic process when fabricating a semiconductor integrated circuit silicon wafer is described. The method includes the steps of defining mask patterns to be projected by the exposure system to create images of the mask patterns; determining an appropriate sampling range and sampling interval; generating a characteristic matrix describing the exposure system; inverting the matrix to obtain eigenvalues as well as the eigenvectors (or kernels) representing the decomposition of the exposure system; convolving the mask patterns with these eigenvectors; and weighing the resulting convolution by the eigenvalues to form the aerial images. The method is characterized in that the characteristic matrix is precisely defined by the sampling range and the sampling interval, such that the sampling range is the shortest possible and the sampling interval, the largest possible, without sacrificing accuracy.

Abstract: A process for creating and verifying a design of phase-shifted masks utilizing at least one phase shift region employing a computer-aided design system. A chip design is provided. A phase-shift mask design capable of producing the chip design is created. Features in a design of the phase-shifted mask that require phase shifting are located. Uncolored phase regions are created on opposite sides of the features. Proper phase termination of the phase regions is ensured based upon space constraints of a phase-shifted mask technique utilized. Phases are determined for the phase regions. Whether coloring errors and un-phase-shiftable design features exist is determined. Mask process specific overlaps and expansions are applied to the mask design to prepare designed data levels for mask manufacture. A residual phase edge image removal design is derived.

Abstract: A two-step method for eliminating transmission errors in alternating phase-shifting masks is described. Initially, the design data is selectively biased to provide a coarse reduction in the inherent transmission error between features of different phase, size, shape, and/or location. During fabrication of the mask with the modified data, residual transmission errors are then eliminated via the positioning of the edges of the etched-quartz trenches which define the phase of a given feature to a set location beneath the opaque chrome film. Application of feedback, in which the aerial image of the mask is monitored during the positioning of the etched-quartz edges, provides additional and precise control of the residual transmission error.