Magazine autumn98 p35

Page 1

Best of YMS S

E

C

T

I

O

N

S

Inspection of Advanced OPC Reticles During the July 1998 YMS2, DuPont Photomask (DPI) presented its evaluation of OPC techniques and the inspection capabilities of KLA-Tencor’s new 353UV reticle inspection system. In the results, DPI emphasized the importance of OPC technology and the 353UV’s superior ability to inspect these features

Simply defined, optical proximity correction (OPC) techniques consist of incorporating features in the production of photomasks that neutralize optical distortion when a semiconductor design pattern is transferred to silicon. The value and use of OPC technology is growing because of the ongoing progression to increasingly smaller semiconductor design features. Semiconductor manufacturers are recognizing that OPC technology can extend the life of lithography steppers by extracting the maximum resolution performance possible from their equipment.

OPC addresses many issues OPC features range in complexity from simple edge jogs and line size adjustments to more complex, isolated mixed-tone features that are embedded in both the clear and chrome areas of the photomask. Serifs and hammerheads — squares and rectangles — are the most common OPC features on the photomask and are added to the end of a design line to prevent corner rounding and line-end shortening. Another technique involves adding assist features that change the way design features behave during the lithogra-

Figure 1. An oversized OPC feature can result in bridging on the wafer pattern.

phy process. For example, some OPC software packages automatically add scatter bars to isolated design features, causing those structures to print in the same manner as more dense design areas to produce a uniform result during the semiconductor manufacturing process. The features are too small to print during the lithography process, but preserve design integrity by increasing the resolution achieved by the stepper.

Monitoring the effects of OPC OPC features generated on a photomask are usually between 20 and 50 percent of the size of design features, requiring advanced production equipment to complete the manufacturing process successfully. Just as

Autumn 1998

properly implemented OPC features improve the pattern accuracy, improper OPCs can create pattern complications. For instance, a missing or under-sized serif can cause significant drawback, while oversized serifs can result in bridging on the wafer (figure 1). Inspection technology is being pushed to new levels of functionality by the use of OPC. Although these features are sub-resolution, they still must be inspected and verified. As part of a strategic alliance, DPI and KLA-Tencor are working closely together to test advanced photomask inspection technology and new software algorithms that enable pattern recognition of advanced OPC fea-

Yield Management Solutions

35


Turn static files into dynamic content formats.

Create a flipbook
Issuu converts static files into: digital portfolios, online yearbooks, online catalogs, digital photo albums and more. Sign up and create your flipbook.
Magazine autumn98 p35 by KLA Corporation - Issuu