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Overlay Control Strategy for 45/32nm RD and Production Ramp Up Tuan-Yen Yua;Jun-Hung Lina;Yong-Fa Huanga;Chien-Hao Chen a;Chun-Chi Yua; Chin-Chou Kevin Huangb;Chien-Jen Huangb, David Tienb a

b

United Microelectronics Corp. (UMC); Tainan,Taiwan, R.O.C. KLA-Tencor Corporation; 1 Technology Drive, Milpitas, CA 95035, U.S.A.

ABSTRACT The tight overlay budgets required for 45nm and beyond makes overlay control a very important topic. High order overlay control (HOC) is becoming an essential methodology to remove the immersion induced overlay signatures. However, to implement the high order control into dynamic APC system requires FA infrastructure modification and a stable mass production environment. How to achieve the overlay requirement before the APC-HOC system becomes available is important for RD environment and for product early ramp up phase. In this paper authors would like to demonstrate a field-by-field correction (FxFc) or correction per exposure (CPE) methodology to improve high order overlay signature without changing current APC-linear control system. Keywords: overlay metrology, high order, FxFc, CPE, APC, process control.

1. INTRODUCTION High order overlay component has been becoming a significant factor in 45nm or beyond for overlay control1-4. Lithography engineer could improve the high order overlay component by implementing scanner high order alignment or zone alignment while wafer was on scanner stages. However, scanner throughput reduction is the price to be paid. Many studies have been pointing to high order control (HOC) to satisfy the tighter overlay control in the mass production environment. Automatic process control (APC) then is essential requirement for production HOC. However, to implement APC-HOC requires (1) mature process condition and (2) extensive modifications of factory automation (FA) system. The critical production ramp-up phase is not mature (by definition), and extensive FA modifications are always painful. In this paper, the authors demonstrate a methodology that is effective, independent of these two conditions. The field-by-field correction (FxFc) or so called correction per exposure (CPE) method has been shown to produce significant overlay control results5, without any APC or FA changes from traditional linear control. The simplest FxFc method is to use raw overlay data from every field of the wafer and generating a FxFc lookup table, then send and store the lookup table into scanner for a period of time until the FxFc table is out of date. Problems for this “raw overlay data” are: (1) it requires all fields to be measured, (2) it includes linear systematic component which is to be corrected by the current APC, and (3) it requires high frequency update in a range from every few lots to once per week. To search for improvement for the “raw overlay data” FxFc problems, authors investigated an alternative FxFc method by analyzing non-linear high order signature instead of the “raw overlay data.” The alternative “non-linear high order signature” FxFc method still requires every field in the wafer to be measured. The authors’ goal is to (1) provide a significant and reliable correction for production lots, (2) as early as possible in the production ramp cycle, (3) while maintaining current APC-linear correction system, and (4) minimizing the frequency of updating the FxFc lookup table. While investigating the feasibility of “non-linear high order signature” FxFc method, two fundamental questions must be answered: (1) the number of lots required to generate a reliable signature lookup table, and (2) the frequency with which the lookup table must be refreshed/updated. These questions will be answered in this paper through a systematic long term data study.

Metrology, Inspection, and Process Control for Microlithography XXIV, edited by Christopher J. Raymond, Proc. of SPIE Vol. 7638, 76382K · © 2010 SPIE · CCC code: 0277-786X/10/$18 · doi: 10.1117/12.846569

Proc. of SPIE Vol. 7638 76382K-1 Downloaded from SPIE Digital Library on 01 Apr 2010 to 192.146.1.254. Terms of Use: http://spiedl.org/terms


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