Optics: measuring and testing – By alignment in lateral direction – With light detector
Patent
1997-02-18
1999-12-14
Font, Frank G.
Optics: measuring and testing
By alignment in lateral direction
With light detector
356401, 355 53, 355 55, G01N 2186, G03B 2742
Patent
active
060024879
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an alignment method for performing alignment between each shot area on a wafer and a mask pattern on the basis of array coordinates predicted using, e.g., a statistical method, which can be applied not only to alignment in a stepper type exposure apparatus but particularly suitable for alignment between a mask pattern and each shot area on a wafer in a step and scan type exposure apparatus.
BACKGROUND ART
When a semiconductor device, a liquid crystal display device, or the like is to be manufactured by photolithography, a projection exposure apparatus (e.g., a stepper) which transfers, through a projection optical system, the pattern of a reticle as a mask on each shot area on a wafer (or a glass plate or the like) coated with a photoresist is used. In addition to a stepper type projection exposure apparatus, a step and scan type projection exposure apparatus which synchronously scans the reticle and the wafer with respect to the projection optical system to increase the exposure area without increasing the load on the projection optical system is recently becoming popular.
For example, a semiconductor device is formed by overlaying multiple layers of circuit patterns on a wafer. When the circuit patterns of the second and subsequent layers are to be projected and exposed on the wafer, alignment between each shot area on the wafer, on which a circuit pattern has already been formed, and a reticle pattern to be exposed next, i.e., wafer alignment must be accurately performed. As a highly accurate wafer alignment method for the conventional projection apparatus, an alignment method called enhanced global alignment (to be abbreviated as "EGA" hereinafter) disclosed in, e.g., Japanese Patent Laid-Open No. 61-44429 is known, in which the coordinate positions of alignment marks (wafer marks) provided to a predetermined number of selected shot areas (sample shots) on a wafer are measured, and the measurement result is subjected to statistical processing to calculate the array coordinates of each shot area on the wafer.
DISCLOSURE OF INVENTION
In the alignment method by EGA, however, the array coordinates of the shot area on the wafer are linearly calculated, and alignment is performed on the basis of the array coordinates. Nonlinear distortion in the shot area or nonlinear distortion of the wafer itself, which is caused by various wafer processes, remains as an alignment error (overlay error). For this reason, when the nonlinear distortion is particularly large, accurate alignment can hardly be performed.
The present invention has been made in consideration of the above situation, and has as its object to provide an alignment method which enables accurate alignment between each shot area and the exposure pattern of a reticle even when the shot area on a wafer, or the wafer itself has nonlinear distortion.
According to the present invention, there is provided an alignment method for performing alignment between each shot area on a substrate (W) and a pattern of a mask (R) in an exposure apparatus which transfers the pattern formed on the mask (R) onto the shot area on the substrate (W), comprising the first process (steps 101 to 107) of measuring array coordinates of predetermined reference points (22a to 22h) of a plurality of predetermined shot areas (21a to 21h) of all shot areas on the substrate (W), respectively, the second process (steps 108 and 109) of performing statistical processing of actual measurement array coordinates measured in the first process and designed array coordinates of the predetermined reference points (22a to 22h) of the plurality of predetermined shot areas (21a to 21h) on the substrate (W), thereby calculating a linear component of the actual measurement array coordinates of the predetermined reference points, the third process (step 110) of subtracting the linear component from the actual measurement array coordinates to obtain a nonlinear component, and the fourth process (step 111) of obtaining distortions of the shot areas (2
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Font Frank G.
Nikon Corporation
Smith Zandra
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