International Business Machines Corporation

Lockheed Martin Corporation

Richard A Ferguson

Lars W Liebmann

Alfred K Wong

Mark Alan Lavin

William John Adair

David V Horak

Steven J Holmes

Mark Charles Hakey

Robert K Leidy

Allen H Gabor

Scott Marshall Mansfield

Song Peng

David S O'Grady

Ronald M Martino

William H Ma

William Hsioh-Lien Ma

Thomas Harold Newman

Ronald Michael Martino

A method of forming a photolithographic mask layout with Sub-Resolution Assist Feature (SRAF) elements on a mask for correcting for proximity effects for a pattern imaged comprising the steps of developing a layout of mask features for printing main pattern features. Provide a table of SRAF element data including spacing of main pattern features and SRAF elements, applying SRAF elements to the mask layout as a function of spacing of main pattern features and SRAF elements, legalizing the SRAF elements as a function of style options, and providing a target pattern comprising a modified layout for the mask, identifying problem edge segments of an SRAF element of the target pattern at risk of causing a printing defect, applying a selected bias to the problem edge segments to modify the pattern where there are areas of SRAF element loss, and providing an output of a modified pattern with modified SRAF elements removing the areas of SRAF element loss. The system can provide SRAF elements to the mask layout as a function of spacing of main pattern features and SRAF elements may be based on data from the SRAF table; or the system can applying model based OPC for exposure dose values based on data from the SRAF table.

Binary OPC for assist feature layout optimization

A technique is described, based on concepts of halftone printing, for controlling feature dimensions in a printed image at increments smaller than the smallest addressable unit of the template used to produce that image. Accordingly, photomasks may be fabricated to yield images with sizes differing from a nominal width by increments which are small fractions of the minimum template size or pixel size. A template fabricated according to this technique includes a feature having one or more edges, and a first array and a second array of shapes (protrusions or indentations) disposed on the edges. The first and second arrays have respective segmentation periods; the first and second segmentation periods are different. Each array is formed of a plurality of identical shapes repeating at every corresponding segmentation period, each shape having a predetermined length and a predetermined width. The shapes (protrusions or indentations) in the first array and the second array may have different lengths, in addition to the two arrays having different segmentation periods; a line feature on a template will thus appear asymmetric with respect to both the length and period of the shapes along the edges of the feature.

Asymmetric halftone biasing for sub-grid pattern adjustment

A method of creating a pattern for a mask adapted for use in lithographic production of features on a substrate. The method comprises initially providing a mask pattern of a feature to be created on the substrate using the mask. The method then includes establishing target dimensional bounds of the pattern, determining simulated achievable dimensional bounds of the pattern, comparing the target dimensional bounds of the pattern to the simulated achievable dimensional bounds of the pattern, and determining locations where the simulated achievable dimensional bounds of the pattern differ from the target dimensional bounds of the pattern. In its preferred embodiment, the feature is an integrated circuit to be lithographically produced on a semiconductor substrate.

Process window based optical proximity correction of lithographic images

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&deg; or 180&deg; 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&deg; and 180&deg; 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. By comparing the locations on the mask for which a non-zero differential image is obtained with the designed data for the mask, the phase defects can be sorted from the phase features and the absence of phase features can be detected. Additional image processing can be applied to verify the integrity of the phase features. The differential image inspection technique can be implemented on existing optical inspection tools by employing a two-pass inspection performed at positive and negative defocus in sequence. In addition, a new apparatus with parallel inspection optics is described for inspecting the mask at positive and negative focus simultaneously.

Detection of phase defects on photomasks by differential imaging

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. The method of generating aerial images of patterns having large mask areas provides a speed improvement of several orders of magnitude over conventional approaches.

Kernel-based fast aerial image computation for a large scale design of integrated circuit patterns

A method for forming square shape images in a lithographic process is disclosed wherein a first plurality of lines running in a first direction is defined in a first, usually sacrificial, layer, and then a second resist is defined wherein the lines run in an intersecting pattern to those of the first layer, thereby creating cornered images wherever the first and second layer intersect and in the open areas between the lines. Methods are proposed for developing the square intersecting areas and the square angle areas defined by the openings. Additionally, a photomask is disclosed in which the length and width of the cornered images are independently patterned using the two-exposure process.

Method for forming cornered images on a substrate and photomask formed thereby

A method for determining if an undesirable feature on a photomask will adversely affect the performance of the semiconductor integrated circuit device that the mask is being used to create. The method includes inspecting the photomask for undesirable features and analyzing the designed features close to the defects. This analysis is performed on lithographic images that represent the image that is transferred onto the semiconductor wafer by the lithography process. This analysis takes into account the effect of variations that are present in the lithography process. Through knowledge of the effects of variations in mask critical dimension of a feature on the lithographic image of that feature, the analysis results in the assignment of an equivalent critical dimension error to the defect. This equivalent critical dimension error is then compared to the mask critical dimension error specification to determine whether or not the defect will adversely affect the device.

Method of determining the printability of photomask defects

Method for forming cornered images on a substrate and photomask formed

A focus monitor for establishing best focus of a lithographic system in semiconductor wafers. The focus monitor has a phase region having a first phase and a slot disposed within the phase region having a gap size indicative of a defocus level of the lithographic system.

Focus monitor for alternating phase shifted masks

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.

Exact transmission balanced alternating phase-shifting mask for

A lithographic patterning method and mask set using a phase shift trim mask having mask dimensions increased in block size so as to remove previous exposure defects.

Lithographic patterning method and mask set therefor with light field

A process of phase edge lithography is employed in the manufacture of very large scale integrated (VLSI) chips in which chrome images are biased on a phase edge of a phase shift mask (PSM) and the mask overexposed to compensate for the positive bias. This overexposure eliminates any residual images from the phase edge mask with minimum impact to the desired images. This simple process results in a trim-less phase edge process that takes advantage of the improved resolution and process latitude of phase edge PSMs while avoiding layout impacts caused by a trim mask or other phase edge elimination methods.

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Pleasant Valley, NY, United States of America

Richard A Ferguson