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"Tuned reticle enhancements optimized for process response"

Semiconductor FabTech Article

Vol. 33 Q1-2007

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The design alternatives of any reticle enhancement feature are shown to have a measurable impact on the size and response stability of the process window

• Process windows optimization means more than selecting focus and dose.

• Every reticle feature enhancement can influence both the size and the stability of the process window response

• What exposure conditions minimize the process impact of local MEEF sensitivity?

• What are the exact pattern sensitivities of each feature as process conditions and the exposure environment changes?

• Do simulations take into account all reticle and wafer process variation?

• Going beyond process simulation response, how can I make the right decisions for reticle feature design performance tuned to my process?

Abstract

ITRS roadmap history details the growing complexity of device design and the latest device-manufacturer’s techniques for tuning their process for each new design generation. In spite of the current desire to incorporate techniques termed “Design for Manufacture” (DFM) into manufacturing, simulations and the design cycle do little more than optimize feature quality for ideal exposure conditions while testing for shorts, opens and overlay problems over process variations.

The manufacturing linkage method in the DFM simulation is performed by the adaptation of a technique unchanged in the last 30 years, the “Process Window analysis”. With this methodology recent successes seen in chip-design have not taken their share of the burden of technology advancement. The lack of adequate manufacturing awareness in the designs coupled with materials design problems for EUV technology recently redirected industry’s path into critical layer splitting termed “Double Patterning”

Design optimization by simulation focuses on feature layout optimization for resolution. Design solutions that take advantage of the full potential spectrum of mask-feature alternatives to increase functional process-space and simplify setup in manufacturing do not exist since there is no method of feedback. A mechanism is needed that can quantify design performance robustness, with mask-contributions, to variations in the user’s specific manufacturing process.

In this study, a Process Behavior Model methodology is presented for the analysis of feature profiles and films to derive the relative robustness of response to process variations for alternative OPC designs. Analysis is performed without regard to the specific mechanics of the design itself. The design alternatives of each OPC feature are shown to be strong contributors not only to resolution and depth-of-focus but also to the stability of final image response; that is the ability of the feature profile to remain at optimum under varying conditions of process exposure excursion.

A method of extracting the systematic component of each feature’s design-iteration is derived providing the ability to quantify the specific OPC response sensitivity to changes in the exposure and process films as well as drift introduced by the tools of the exposure set.

Keywords: Lithographic Friendly Design, Double Patterning, DFM, Bossung, ACLV, Process Behavioral Models, metrology, stability, matching, photomask, simulation, proximity, response

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