Curvilinear mask handling in OPC flow

Abstract

The edge-based optical proximity correction (OPC) has been serving the industry for more than 20 years with few changes the mask geometry. In the past 10 years, ILT pioneers created the curvilinear mask using alternate algorithms. The two approaches differ so much that the experiences in conventional OPC do not easily translate to the use of ILT, and vice versa. We report a new approach to curvilinear masks that follows the conventional OPC workflow. It creates and manipulates the curvilinear shapes by generalizing the edge-based OPC to vertices. Conventional OPC techniques, including dissection, classification, target point placement, etc., remain as central roles. Full-chip correction results are included to demonstrate the good performance of the curvilinear mask for both contact and line/space patterns. The analysis of critical patterns shows that the curvilinear OPC lifts the mask rule check restriction to the mask shape that limits Manhattan OPC. The turnaround time of creating the curvilinear mask is around two times than that of the Manhattan mask.

Curvilinear mask metrology: what is the equivalent critical dimension?

“…The first barrier—the ability to write curvilinear mask patterns in a practical time frame—has been removed recently by introduction of multi-beam mask writers, which can write any shape without time penalty 20 , 21 . The second barrier—full-chip ILT—has also been removed, by applying GPU acceleration and a stitchless full-chip approach 22 , 23 …”

“…A Bezier curve is a parametric curve used in computer graphics and related fields. A set of discrete “control points” defines a smooth, continuous curve by means of a formula, 23 as shown in Fig. 5.…”

“…5. Instead of moving the sampling point in the segment OPC, control points are moved in the curvilinear OPC 23 (Fig. 6).…”

“…Curvilinear OPC represents the curve segment with a Bezier curve and moves the curve with the control points of the Bezier curve (Source: Synopsys Ref. 23). …”

“…(a) In curvilinear OPC, the curves are moved by control points and (b) in edge segment OPC the segments are moved by sampling points (Source: Synopsys Ref. 23). Red contour is the curve mask pattern, and green contour is the simulated wafer pattern.…”