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Method to Characterize the Stability of a Step and Repeat Lithographic System

IP.com Disclosure Number: IPCOM000043915D
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Bureau, L: AUTHOR [+2]

Abstract

The first order overlay parameters of photorepeater array generation as a function of X, Y table position have been studied. The estimated parameters are found to fluctuate against either row or column position of the X, Y table. The fluctuations represent influences of higher order overlay parameters not included in the current overlay model; thus, they point out some precautions to be exercised in the estimation the first order overlay parameters. The experimental procedure used in this study offers a simple and useful way to study the photorepeater overlay characteristics using small dimensional measurement data and to make two-dimensional standard containing angular information. The overlay performance of a lithographic system has to be strictly controlled in order to manufacture high performance VLSI circuits.

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Method to Characterize the Stability of a Step and Repeat Lithographic System

The first order overlay parameters of photorepeater array generation as a function of X, Y table position have been studied. The estimated parameters are found to fluctuate against either row or column position of the X, Y table. The fluctuations represent influences of higher order overlay parameters not included in the current overlay model; thus, they point out some precautions to be exercised in the estimation the first order overlay parameters. The experimental procedure used in this study offers a simple and useful way to study the photorepeater overlay characteristics using small dimensional measurement data and to make two-dimensional standard containing angular information. The overlay performance of a lithographic system has to be strictly controlled in order to manufacture high performance VLSI circuits. Better understanding of the lithographic system overlay behavior will enable one to better control the tools, thus improve the circuit performance. A lot of studies have been conducted on improving the lithographic system overlay tolerance. The experiment described below will provide one with a simple and effective way for photorepeater overlay performance characterization. The results obtained in the experiment will allow one to isolate and study the characteristics of some of the higher order overlay parameters not easily obtainable by other existing methods. Moreover, two- dimensional metrology standard containing angular information can also be made using the method described in the experiment. This technique may be used to characterize the Mann 3696 photorepeater function of X, Y table positions. The technique is set out in the steps below with reference to the Mann unit. Step 1: Both X, Y axes laser interferometer reading set to zero, i.e., (X 1, Y 1) =OE(0, 0). Using the photorepeater to step an array of patterns (array 1) using the 10X pattern shown in Fig. 1 at time t1 . The cross patterns in the 10X mask shown in the figure are only examples of patterns. They can be replaced by any other similar patterns which can be used for dimensional measurement. One pattern should be placed at the center of the 10X mask and others placed symmetrically to the center of the 10X mask, as shown in the figure. Step 2: Without physically touching the mask substrate on the X, Y table, offset the table origin by the amount of (WX, WY) from the table origin where array 1 was stepped, i.e., (X 2, Y 2) =OE(WX,OEWY). Follow the procedure as in Step 1, step array 2 at time t2 . The two adjacent array patterns are shown in Fig. 2. The machine parameters, such as the orthogonality and stepping pitch of X, Y table or camera (lens) parameters, can be changed before stepping the succeeding array...