Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Reexamination Certificate
2002-08-30
2004-06-01
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
C356S620000, C430S022000, C355S043000
Reexamination Certificate
active
06744512
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a position measuring apparatus which measures position information of a mark formed on an object such as a wafer or glass plate, or a mask or reticle, in a manufacturing process of semiconductor devices, liquid crystal display devices or the like, and an exposure apparatus which carries out alignment of an object, using the position information of the mark obtained by the position measuring apparatus, to expose a pattern formed on the mask or the reticle onto the wafer or the glass plate.
BACKGROUND ART
In manufacturing of devices such as semiconductor devices or liquid crystal display devices, an exposure apparatus is used to repetitively perform projection and exposure of a fine pattern image formed on a photo-mask or a reticle (hereinafter generally referred to as a “reticle”) onto a substrate such as a semiconductor wafer or a glass plate, to which a photosensitizer such as a photo resist has been applied. When projection exposure is to be performed, it is necessary to precisely align the position of the substrate and the position of a pattern image formed on the reticle. The exposure apparatus has an alignment device for performing this alignment. The alignment device comprises an alignment sensor for detecting the position of an alignment mark formed on the substrate, and a control system for performing alignment of the substrate based on the position of the alignment mark detected by the alignment sensor.
Since the surface condition (roughness level) of the substrate, being an object to be measured, changes in the manufacturing process of semiconductor devices or liquid crystal display devices, it is difficult to accurately detect the position of the substrate by one alignment sensor. Therefore, a different sensor is generally used according to the surface condition of the substrate. Main alignment sensors include an LSA (Laser Step Alignment) type, an FIA (Field Image Alignment) type, and an LIA (Laser Interferometric Alignment) type. The outline of these alignment sensors will be described below.
The LSA type alignment sensor is an alignment sensor which irradiates a laser beam onto an alignment mark formed on the substrate, and measures the position of the alignment mark, using the diffracted and scattered light, and has been heretofore widely used for semiconductor wafers in various manufacturing steps. The FIA type alignment sensor is one which performs position measurement by illuminating an alignment mark, using a light source having a wide wavelength bandwidth such as a halogen lamp, and performs image processing of the image of the alignment mark obtained by the illumination result, and is effective for measurement of asymmetric marks formed on an aluminum layer or on the surface of a substrate. The LIA type alignment sensor is one which irradiates laser beams having a slightly different wavelength from two directions, makes the two diffracted light generated as a result thereof interfere with each other, and detects the position information of the alignment mark from the phase of the interfered light. This LIA type alignment sensor is effective, when used for alignment marks having a low difference in level, or a substrate having a large surface roughness.
The position information detector includes a TTL (Through The Lens) type which detects the position information of a mark on a substrate via a projection optical system, an off-axis type which directly detects the position information of a mark on a substrate, without using the projection optical system, and a TTR (Through The Reticle) type which observes a substrate and a reticle at the same time via the projection optical system, and detects the relative position thereof. When alignment of the reticle and the substrate is performed by using these position information detectors, a baseline quantity, which is a spacing between the measurement center of the position information detector and the center (exposure center) of the projected image of a pattern on the reticle, is determined in advance. Then the amount of misalignment of the mark from the measurement center is detected by the position information detector, and the substrate is shifted by a distance obtained by correcting this amount of misalignment by the baseline quantity, to thereby accurately align the center of a section area (shot area) set on the substrate with the exposure center. The shot area is then exposed by the exposure light. The baseline quantity may change gradually in the process of holding and using the exposure apparatus. If a so-called baseline change, being a change in the baseline quantity, occurs, the alignment accuracy (superposition accuracy) decreases. Therefore, it is necessary to regularly carry out a baseline check for accurately measuring the spacing between the measurement center of the position information detector and the exposure center.
One example of the overall operation of the exposure apparatus will be outlined below.
Before a substrate is carried to the exposure apparatus, the position information of a mark formed on a reticle is detected by a reticle position information detector, and position adjustment of the reticle is performed based on the position information. The substrate is then carried to the exposure apparatus, and the position information of a mark formed on the substrate is detected by a substrate position information detector. The substrate is then shifted by a distance obtained by correcting the amount of misalignment indicated by the position information of the substrate by the baseline quantity, within a plane perpendicular to the optical axis of the exposure light, based on the position information of the mark formed on the substrate, to thereby align the relative positions of the reticle and the shot area formed on the substrate. After this, and the exposure light is irradiated onto the reticle, to expose on the substrate the image of a pattern formed on the reticle.
Incidentally, the mark formed on the substrate is, for example, as shown in FIG.
12
.
FIG. 12
is a diagram showing one example of a mark formed on the substrate for position measurement. In
FIG. 12
, a mark
100
is one where rectangular mark elements
101
having a longitudinal direction are arranged substantially parallel in the longitudinal direction of each mark element
101
, with a predetermined interval, for example, several &mgr;ms, in a direction orthogonal to the longitudinal direction. Therefore, the mark
100
shown in
FIG. 12
has a construction such that the surface position changes periodically with respect to the direction orthogonal to the longitudinal direction of the mark elements
101
, that is, in the direction indicated by reference symbol
102
in the figure.
The alignment sensor detects periodical changes of the surface position to measure the position information of the mark
100
. For example, the FIA type alignment sensor detects an edge position of the mark elements
101
, by performing image processing with respect to image information in which a signal strength (brightness of the image) changes according to the periodic change of the surface position, and measures the position information of the mark
100
(for example, position information indicating the central position of the mark
100
), based on the detected edge position. When the position information of the mark
100
is to be measured by performing image processing, if image information having a sufficient strength cannot be obtained, the position information cannot be measured with high accuracy. Therefore, amplification is carried out by an AGC (Automatic Gain Control) circuit or the like, and it is set such that the strength of the image information so as to become a strength within a certain range.
Measurement processing of the position information by the FIA type alignment sensor will be described in detail below.
FIG. 13
is a diagram for explaining the position information measurement processing by the FIA type alignment sensor. The FIA type alignment sensor includes an image pic
Lauchman Layla
Oliff & Berridg,e PLC
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