534 IEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING, VOL. 18, NO. 4, NOVEMBER 2005 Real-Time Lithography Registration, Exposure, and Focus Control—A Framework for Success Mani Janakiram and Scot Goernitz Abstract—Intel factories are being challenged by an increasingly diverse product and technology mix. Semiconductor manufac- turers have successfully leveraged advanced process control (APC) for overlay and critical dimension (CD) in the lithography module. Trends are continuously corrected through in-line metrology feedback, keeping the process on target. Applying an APC system suitable for litho control in high-volume manufacturing has re- sulted in significant improvement in registration capability and potential for better exposure focus and CD control. Index Terms—Advanced process control (APC), critical dimen- sion (CD), exposure focus CD control, overlay, run-to-run control, scanner registration control. I. INTRODUCTION L ITHOGRAPHY process control is a critical step in the semiconductor manufacturing process. As we migrate to 65-nm semiconductor technologies, process control is be- coming more and more complex, and with the progression toward smaller feature sizes the specifications are getting tight, demanding a better litho process control. Manual process control at Intel has succeeded through a rigorous approach to tool/process matching as dictated by copy exactly needs. How- ever, this approach is labor intensive, requiring considerable time to monitor statistical process control (SPC) charts and make manual feedback corrections to the appropriate litho tool parameters. In addition, it is reactive by nature and no longer suitable for advanced technologies that have more demanding process specifications. Before the proposed algorithm was implemented, lithography layer owners used a critical dimension (CD) scanning electron microscopy (SEM)-generated Bossung curve to determine the best dose and focus window. A registration (Reg) tool was used to perform a matrix calculation to break down measured overlay error vectors into base field and grid components [1]. Overlay, in simple terms, is defined as the misalignment, in nanometers, be- tween the current and the previous litho layer. AltReg is a mod- eling program that is used to determine overlay components and to provide quantitative information on field and wafer compo- nents. Zavecz et al. [2] have indicated that overlay errors are a function of the current process-step exposure and the history of the individual lot’s exposure sequences. Coupled with the use of SPC charts, this data is supplied to the lithography process tool to keep the CD and Reg on target. This technique involved Manuscript received March 07, 2005. The authors are with Intel Corporation, Chandler, AZ 85226 USA (e-mail: mani.janakiram@intel.com; scot.goernitz@intel.com). Digital Object Identifier 10.1109/TSM.2005.858496 Fig. 1. Overlay and SRC definition. a substantial amount of work, but it was required for successful litho processing. Scanner registration control (SRC) refers to adjusting align- ment settings on the scanner, based on feeding back data pro- duced in AltReg. Scanner adjustments are made to xshift, yshift, field rotation, field skew, xmag, ymag, xscale, yscale, wafer ro- tation, and wafer skew (see Fig. 1). SRC adjustments are now made using automated process control (APC) algorithms such as exponential weighted moving average (EWMA). The data from AltReg is used to determine if these adjust- ments are the correct AltReg error component coefficients for these variables. These coefficients are computed for each wafer, and this data is passed to the APC system as wafer level data. CD control monitors structure size and determines how closely devices can be placed. Contributing factors for CD control are mainly exposure and focus. Fig. 2 shows the difference between overexposure and underexposure. Dose adjustments are made to control the width dimensions of the various structures [6]. A defocus parameter is calcu- lated as the difference between the wall slopes for the line and space structures. This provides an indicator of defocus (i.e., the relative focus offset with respect to best focus). This parameter turns out to be independent of dose adjustments (based on the response surface models presented later). The earlier approach used for APC solution development was based on one application at a time with each application having its own data base, integration, and separate platform. In order to streamline the APC application development, an APC framework was developed that facilitates a standard approach to implementing APC applications, since the applications can be developed independently of the need to develop a sup- porting database (that stores necessary process and equipment 0894-6507/$20.00 © 2005 IEEE