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Optimization of mask-rule-limited Optical Proximity Correction Disclosure Number: IPCOM000029093D
Original Publication Date: 2004-Jun-15
Included in the Prior Art Database: 2004-Jun-15
Document File: 4 page(s) / 47K

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Disclosed is modification of Optical Proximity Correction in order to satisfy mask rules constraints.

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YOR820020617 Louis J Percello/Watson/IBM Mark Lavin, Emanuel Gofman

Optimization of mask-rule-limited Optical Proximity Correction

Disclosed is modification of Optical Proximity Correction (OPC) in order to satisfy certain technology limitations. OPC is the technique of applying transformations to the geometric shapes of a VLSI design to compute the corresponding shapes on a photomask that will be used to fabricate integrated circuit (IC). Those transformations compensate for systematic shape-transforming effects of the photolithographic patterning process. The objective of OPC is to fully compensate for those effects so that the shapes on the wafer are as similar as possible to the original designed shapes. In many cases, however, that objective is tempered by additional constraints on the shapes, such as "mask rules", which should be obeyed, so that a photomask can be produced by mask house. It is the objective of the current invention to provide a means for performing OPC, subject to mask rules limitations, which best achieves the intended compensating effect.

OPC tools are usually divided into two categories: Rule-based OPC, in which the transformations from design or "target" shape to mask shape are specified in terms of a set of transformation rules, and model-based OPC, in which the mask-to-wafer shape transformations are represented by a mathematical model and the design-shape-to-mask transformation is performed by incremental solving the inverse problem (what mask shape would yield a wafer shape equivalent to the design shape). OPC tools of both categories typically use a common approach to representing the design and target shapes. The current invention is applicable to both approaches.

The following is a description of the model-based OPC function implemented in the Niagara shape-processing software system:
1). The boundary of each target shape is broken up into a chain of segments. This chain of segments is used as the starting point for the output of model based OPC, the mask shapes that will best approximate the target shape on the wafer.
2). That initial version of the mask shapes is refined through a specified number of iterations. In each iteration, the mask is partially corrected by shifting each segment inward or outward, while maintaining its original orientation.
3). Within a single iteration, each segment is shifted as follows: First, the model-based simulator uses the current version of the mask plus the model to determine where each segment would appear in the simulated wafer image. Next, the difference between the simulated position and the position of the segment on the target are compared; the result is sometimes called edge placement error. Next, based on the edge placement error and other parameters, the segment of the mask is shifted inward or outward in an attempt to reduce the error.
4). The objective of the correction i...