Andrew Duenner Department of Mechanical Engineering, University of Texas at Austin, Austin, TX 78712 Tsung-Fu Yao Department of Mechanical Engineering, University of Texas at Austin, Austin, TX 78712 Bruno De Hoyos Department of Mechanical Engineering, University of Texas at Austin, Austin, TX 78712 Marianna Gonzales Department of Mechanical Engineering, University of Texas at Austin, Austin, TX 78712 Nathan Riojas Department of Mechanical Engineering, University of Texas at Austin, Austin, TX 78712 Michael Cullinan Department of Mechanical Engineering, University of Texas at Austin, Austin, TX 78712 A Low-Cost, Automated Wafer Loading System With Submicron Alignment Accuracy for Nanomanufacturing and Nanometrology Applications This paper introduces a low-cost, automated wafer alignment system capable of submi- cron wafer positioning repeatability. Accurate wafer alignment is critical in a number of nanomanufacturing and nanometrology applications where it is necessary to be able to overlay patterns between fabrication steps or measure the same spot on a wafer over and over again throughout the manufacturing process. The system presented in this paper was designed to support high-throughput nanoscale metrology where the goal is to be able to rapidly and consistently measure the same features on all the wafers in a wafer carrier without the need for slow and expensive vision-based alignment systems to find and measure the desired features. The wafer alignment system demonstrated in this paper consists of a three-pin passive wafer alignment stage, a voice coil actuated nesting force applicator, a three degrees-of-freedom (DOFs) wafer handling robot, and a wafer cas- sette. In this system, the wafer handling robot takes a wafer from the wafer cassette and loads it on to the wafer alignment stage. The voice coil actuator is then used to load the wafer against the three pins in the wafer alignment system and align the wafer to an atomic force microscope (AFM)-based metrology system. This simple system is able to achieve a throughput of 60 wafers/h with a positional alignment repeatability of 283 nm in the x-direction, 530 nm in the y-direction, and 398 nm in the z-direction for a total capital cost of less than $1800. [DOI: 10.1115/1.4034610] 1 Introduction In a typical semiconductor manufacturing setting, wafers are transported in cassettes by guided vehicles and loaded into or unloaded from machines by wafer handling robots [1]. The critical dimension of features patterned in modern semiconductor manufacturing processes continues to decrease without a signifi- cant impact on manufacturing throughput. As a result, a gap is emerging in the field of semiconductor metrology where few technologies are capable of in-line metrology. Recent advan- ces in microelectromechanical systems (MEMS) fabrication have enabled the realization of an entire AFM on a single MEMS chip. This MEMS-based AFM is capable of high-speed scanning of nanoscale features over micron scale areas and is small enough that it can be incorporated into manufacturing tools for in situ nanoscale measurements or into metrology platforms with multi- ple scanning probes operating on a wafer at the same time [2]. These low-cost devices dramatically reduce setup time required for AFM metrology due to the fact that they do not require the focusing of a laser on an AFM cantilever tip as is common with traditional AFM systems and do not require the inspection wafer to be loaded into a large AFM system where it is necessary to search for the spot on the wafer the user wants to inspect before a measurement can be made. Improvements in the scanning area and throughput are made possible by the MEMS-based AFMs through the incorporation of multiple AFM chips on a platform as described in Ref. [3]. The system described in this paper aims to further reduce the setup time of AFM-based metrology by ena- bling the repeatable alignment of wafers into a low cost, AFM- based metrology system in order to realize the ultimate goal of high-throughput AFM-based nanoscale metrology of semiconduc- tor wafers. This type of metrology system would enable in-line metrology of silicon wafers after a lithography or etching step in the semi- conductor manufacturing process. Currently, it is not possible to measure nanoscale features in-line with the semiconductor manu- facturing process since most nanoscale metrology methods are too slow for in-line process measurements [4]. Therefore, in semiconductor manufacturing processes, a few wafers are taken off the manufacturing line each hour and inspected using time- intensive methods such as scanning electron microscopy. This means that many defective wafers can travel through the manu- facturing process before an error is detected. In-line metrology enabled by the precision alignment methods described in this paper will help to detect these errors much quicker in the manu- facturing process and reduce the scrap rate in semiconductor manufacturing. 2 Background Transport of wafers between semiconductor manufacturing equipment is typically accomplished by wafer handling robots. Typical wafer handling robots are based on the selective compli- ance arm for robot assembly (SCARA) robot platform [5]. SCARA wafer handling robots commonly operate in a horizontal work plane with 1DOF in the vertical direction and 3DOF in the horizontal plane [5]. These wafer handling robots are typically capable of throughputs of up to 350 wafers/h and positioning repeatability on the order of 100 lm[6,7]. Coarse optical alignment of wafers is often achieved by rotating the wafer and using an optical sensor to determine the location of the wafer flat [8]. Wafers can be precisely aligned with respect to Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received June 12, 2016; final manuscript received September 1, 2016; published online October 10, 2016. Assoc. Editor: Rajiv Malhotra. Journal of Micro- and Nano-Manufacturing DECEMBER 2016, Vol. 4 / 041006-1 Copyright V C 2016 by ASME Downloaded From: http://micronanomanufacturing.asmedigitalcollection.asme.org/pdfaccess.ashx?url=/data/journals/ajmnbt/935806/ on 02/28/2017 Terms of Use: http://www.a