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Characterization of Photolithographic Tooling by use of an X-Y Coordinate System

IP.com Disclosure Number: IPCOM000045594D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 15K

Publishing Venue

IBM

Related People

Babinski, JP: AUTHOR

Abstract

DISCUSSION. Today the standard technique for characterizing a photo tool utilizes the conventional mask/wafer contact set, the assumption being that the wafers are true one-to-one reproductions of the mask. In most cases this assumption is valid, but only to the accuracy that wafers can be measured using the standard vernier-type structure.

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Characterization of Photolithographic Tooling by use of an X-Y Coordinate System

DISCUSSION.

Today the standard technique for characterizing a photo tool utilizes the conventional mask/wafer contact set, the assumption being that the wafers are true one-to-one reproductions of the mask. In most cases this assumption is valid, but only to the accuracy that wafers can be measured using the standard vernier-type structure.

The procedure using the contact set is as follows: The mask is loaded into the tool and allowed to acclimate to a preset mask temperature. Then the corresponding resist-coated oxide wafers (with the first level pattern contacted printed from the test mask and etched into the oxide) are loaded into the tool, an alignment is made with the same pattern as the first level, but shifted in one direction so as to form the vernier-type test structure. After the wafers are developed, they are manually read using a microscope. A total of 9 sites along the X-Y axis of the tool are read per wafer and 10 wafers are usually run. An average is calculated site by site of the individual data points and plotted. From this plot, local distortion (i.e., site by site) and tool magnification errors are analyzed.

The X-Y coordinate technique makes use of a special 1X distortion mask and uses the mask house X-Y measurement system for making all measurements.

The required target reference for the X-Y measurement system (XYMS) is stepped onto a 1X mask in a predetermined array. The mask is then loaded onto the XYMS (backside vacuum clamped), and each target in the array is measured in both the X and Y direction. From this data the centers of the targets are calculated and plotted as a (X(m), Y(m)) coordinate system. This information now becomes the footprint of the X-Y distortion mask. The mask is now loaded into the exposure tool to be characterized and allowed to acclimate to a preset mask temperature after which a predetermined number of blank resist-coated oxide wafers are loaded into the tool and exposed. After developing and etching the wafers, the etched targets are measured on the XYMS. Again, the center of the targets is calculated and plotted as a (Xw1 approaches i, Yw1 approaches i, where i=number of wafers) coordinate system.

From the data from all the wafers (X(wi), Y(wi)) an average (mean) per site is calculated (X(w), Y(x)). From this average the mask data (X(m), Y(m)) is subtracted and the resulting (DX, DY) is used to analyze such tool parameters as tool distortion (site by site) and tool magnification. To obtain within tool repeatability the individual wafer datasets (Xw1 approaches i, Yw1 approaches i) are subtracted (site by site) from the calculated wafer mean (X(ww), Y(ww)). A frequency plot is then made of the resulting data, and a 3 sigma value for both the X and Y p...