Research Papers

A Low-Cost, Automated Wafer Loading System With Submicron Alignment Accuracy for Nanomanufacturing and Nanometrology Applications

[+] Author and Article Information
Andrew Duenner, Tsung-Fu Yao, Bruno De Hoyos, Marianna Gonzales, Nathan Riojas, Michael Cullinan

Department of Mechanical Engineering,
University of Texas at Austin,
Austin, TX 78712

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.

J. Micro Nano-Manuf 4(4), 041006 (Oct 10, 2016) (8 pages) Paper No: JMNM-16-1027; doi: 10.1115/1.4034610 History: Received June 12, 2016; Revised September 01, 2016

This paper introduces a low-cost, automated wafer alignment system capable of submicron 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 cassette. 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.

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Fig. 6

Free-body diagram for turntable calculations

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Fig. 5

CAD rendering of wafer handling robot

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Fig. 4

Rotary axis exploded view

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Fig. 3

Flowchart of loading operation: (a) wafer in cassette, (b) handling system grabs wafer, (c) wafer transportation, (d) wafer release and flexure preload to put into alignment mechanism, and unloading operation (e) flexure release, (f) handling system grabs wafer, (g) wafer transportation, and (h) back to cassette

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Fig. 2

Wafer alignment system

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Fig. 1

Arrangement of three constrain pins in passive wafer alignment system

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Fig. 7

(Left) Measurement spots (1–6) for capacitance probes on reference block showing coordinate axis of the measurements and (right) schematic of capacitance probe setup relative to the measurement block and the wafer that is loaded into the system

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Fig. 8

Error budget coordinate frames

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Fig. 9

(Left) Kinematic coupling consists of a Vee-block and truncated ball ensuring position repeatability between capacitance probe fixture and alignment mechanism (right) capacitance probe fixture in use

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Fig. 10

(Left) Translational and (right) rotational error distribution with outliers

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Fig. 11

(Left) Translational error versus (right) rotational error trial with outliers eliminated

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Fig. 12

Low-cost misalignment detector



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