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Detection of photo resist residue on advanced gate layers using optical scattering and advanced analysis techniques Scott Ku*a, Ying-Hsueh Chang Chiena, C.M Yangb Taiwan Semiconductor Manufacturing Company, 8, Li-Hsin Rd. 6. Science-base Industrial Park, Hsin-Chu, Taiwan 300-77, R.O.C. a Elvis Wang , Damian Chena, Chris Youngb, Kevin Sunb, Jack Yanb, Prasanna Digheb, Avinash Saldanhab, David Feilerb b KLA-Tencor Corporation, One Technology Drive, Milpitas, CA, USA 95035 a

ABSTRACT Detection of resist residue and organic contamination after photo resist strip and wafer clean early in the high K/metal gate (HK/MG) manufacturing process flow is critical as it has been known to significantly impact yield. This residue, when exposed to subsequent thermal process steps, transforms into solid hard spot(s), and can then be detected by a wafer inspection tool, but unfortunately it is too late to take corrective action. A unique process control solution to detect the presence of residues was developed using advanced analysis of an optical scattering inspection of a litho checkerboard pattern. The presence of residue was then validated with film thickness measurements. Keywords: HK/MG, Surfscan SP2, SURFmonitor, fluorescence, photo resist residue, checkerboard

1. INTRODUCTION As CMOS scaling continues below 45nm, conventional silicon oxide technologies cannot sustain equivalent oxide thickness (EOT) and leakage current requirements set in the International Technology Roadmap for Semiconductors [1]. Due to the limitation of physical thickness scaling and high tunneling current, next-generation CMOS devices require the introduction of high-K and metal gate electrodes to reduce gate leakage and poly depletion [2, 3]. The manufacturing infrastructure for high-k and metal gate stacks is reasonably mature. On the reliability front, however, much work remains to be done. Dual metal gate CMOS integration steps require multiple wet etch process steps to separate two different metal gates within transistors on the same wafer [4]. Integration schemes as well as wet etch chemistries must be developed to completely remove the first metal gate material without damaging the underlying gate dielectric. Photo resist material specific for high K/metal gate (HK/MG) layers must be chosen carefully and effective resist strip processes have to be developed and extensively characterized as incomplete removal of the photo resist leads to the presence of residue. Detection of such resist residue after Cap2 resist cleaning step is critical as it has been known to impact yield and affect device performance. This residue, when exposed to subsequent thermal process steps, transforms into solid hard spot(s), and can then be detected by an inspection tool, but this is unfortunately too late. A unique and innovative process control solution was developed to detect the presence of residue. This solution uses a simple litho checkerboard wafer layout; the Surfscan SP2 wafer inspection tool, which measures the optical scattering from the wafer’s surface; and, SURFmonitor, a process signature and metrology proxy add-on module for the Surfscan SP2. In this study, the litho checkerboard technique involved creating wafers where some of the regions of the wafer were left un-exposed and some regions were exposed with a line space pattern. These wafers were then inspected on the above mentioned optical scattering tool and the data was analyzed using SURFmonitor Overlay Differential Analysis (SODA) and Regions of Interest (ROI) techniques. These analyses indicated the presence of resist residues on the exposed and un-exposed regions of the wafers. These results were validated with film thickness measurements conducted by an optical film metrology (OFM) tool. OFM can be used to monitor for resist residue after the cleaning step, but the discrete sampling strategy used can miss Metrology, Inspection, and Process Control for Microlithography XXIV, edited by Christopher J. Raymond, Proc. of SPIE Vol. 7638, 76383F · © 2010 SPIE · CCC code: 0277-786X/10/$18 · doi: 10.1117/12.847797

Proc. of SPIE Vol. 7638 76383F-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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