JPH10270350A - Projection exposure apparatus and projection exposure method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection exposure apparatus which is able to eliminate pattern transfer errors caused by deformation of a reticle, while controlling the thickness and weight of the reticle. SOLUTION: A projection exposure apparatus 1 comprises holders 13 for a reticle R, an illumination optic system 11 for illuminating the reticle R, a projection optic system PL for permitting light which has passed through the reticle R to be image-formed on a sensitive substrate W and a holding means WS for the sensitive substrate W. The error factors ascribed to deformation of the reticle R when the reticle has been held by the holders 13, are corrected on designing of the projection optic system PL.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an original plate (reticle, reticle,
The present invention relates to a projection exposure apparatus and a projection exposure method for projecting and exposing a pattern on a mask or the like (hereinafter referred to as a reticle). In particular, the present invention relates to a projection exposure apparatus and a projection exposure method that can eliminate a pattern transfer error caused by deformation of a reticle.

[0002]

2. Description of the Related Art The prior art will be described using a projection exposure apparatus for semiconductor wafers as an example. FIG. 6 is a side view schematically showing a configuration of a conventional semiconductor wafer projection exposure apparatus. The projection exposure apparatus 101 has an illumination optical system 11 that irradiates the reticle R with illumination light IL from above. The reticle R is held on its side by a reticle holder 13 serving as holding means. Reticle holder 13 is placed on reticle stage RS. A semiconductor circuit pattern is drawn on the lower surface Ra of the reticle R, and is patterned when the illumination light IL passes below the reticle R.

[0003] Exposure light that has passed through reticle R passes through projection optical system PL provided below reticle stage RS, and a wafer W placed below projection optical system PL is exposed.
Is formed on the resist coating surface Wa on the upper surface of the substrate. Projection optical system P
In L, the pattern is reduced to 1/5 (an example) and transferred onto the wafer W. Wafer W is fixed on wafer stage WS via a vacuum chuck (not shown). The wafer stage WS is driven by a Z-axis in a direction parallel to the optical axis of the projection optical system PL and an X-axis, a Y-axis in a plane perpendicular to the optical axis, and θ around the Z-axis, and moves the wafer W to a desired position. Position.

The reticle R is a thin plate made of quartz, and a Cr thin film is deposited on a lower surface thereof. Its dimensions are 5,6 inches wide, ie 127 mm, 152 mm,
It is 0.09 inches or 2.3 mm thick and 0.25 inches or 6.4 mm thick. FIG. 7 is a plan view showing a planar configuration of a general reticle. The central portion of the reticle R is a pattern portion 33 on which a semiconductor circuit pattern is formed. In the peripheral portion 31 around the pattern portion 33, a pellicle frame sticking portion 32 exists at the innermost side. Here, a frame for attaching a thin organic film called a pellicle for preventing adhesion of dust covering the pattern portion 33 is attached. The outside of the pellicle frame pasting section 32, that is, the left and right in FIG.
Or, there is an alignment mark AM.

[0005]

As shown in FIG. 6, the center of the reticle R held as described above is bent downward by a maximum of several μm due to its own weight. The deflection itself becomes an error in the focus direction, and the reticle R
The pattern shifts outward toward the left and right ends of 0.01μ
Generates distortion errors on the order of m.

When the reticle holding section 13 is a vacuum chuck, even if the reticle is bent by its own weight, if the holding section is flat, a correcting force acts on the reticle, and the amount of bending is reduced. However, due to the recent decrease in the depth of focus due to the increase in the NA of the projection lens and the demand for further improvement of the overlay accuracy due to the reduction in the line width, the residual deformation amount of the reticle after correction has become a level that cannot be ignored. I have.

As described above, the size of a reticle for exposing a semiconductor wafer has changed from a 5-inch reticle to a 6-inch reticle. At this time, the thickness of the reticle is set to 0 to reduce an error caused by the reticle deformation.
The thickness was increased from 09 inches to 0.25 inches. In view of future technology trends of semiconductor devices, a larger exposure field is required than at present, and a further increase in reticle size is expected. Estimating the focus direction and distortion error with the currently expected next-generation reticle size of 9 inches gives a focus error of 0.01 μm.
In order to satisfy the tolerance of 0.005 .mu.m, a thickness of about 0.5 inch is required. However, a 9-inch reticle is actually used.
Considering an exposure apparatus of about 2000, a scan exposure apparatus that performs exposure while moving a reticle and a wafer in synchronization with each other is considered to be general. When performing the scanning exposure, if the thickness of the reticle is large, the weight increases accordingly, which may cause a problem in fixing the reticle. further,
Increasing the number of processed sheets per unit time, that is, the throughput, exists as a strong demand for the exposure apparatus,
Conversely, the reticle weight may be limited. Under such circumstances, the thickness of the reticle is determined taking into account both the required thickness determined from the deflection and the required thickness determined from the throughput. In that case, the ideal thickness is not necessarily the ideal thickness from the viewpoint of the deflection. It does not become. Therefore, there is a possibility that the target values of the focus error and the distortion error cannot be achieved.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a projection exposure apparatus and a projection exposure method capable of suppressing a pattern transfer error caused by deformation of a reticle while suppressing the thickness and weight of the reticle.

[0009]

In order to solve the above-mentioned problems, a projection exposure apparatus according to the present invention comprises an original plate holder, an illumination optical system for illuminating the original plate, and a light passing through the original plate on a sensitive substrate. What is claimed is: 1. A projection exposure apparatus comprising: a projection optical system for forming an image; and a means for holding a sensitive substrate, wherein an error factor caused by deformation of the original plate due to its own weight when the original plate is held in a holder is caused by a design of a projection lens. Is corrected. Instead of (or together with) correcting the error in the lens design, an adjustment mechanism for the projection lens may be provided to correct the error when adjusting the apparatus.

[0010] The projection exposure method of the present invention is a projection exposure method for projecting a pattern on an original plate onto a sensitive substrate and transferring the pattern onto the substrate; Error factors caused by deformation due to the weight of the
The correction is performed in the design of the projection lens.

That is, a focus error, a distortion error, and the like, which are expected to be caused by the deflection of the reticle, are corrected in advance when designing or adjusting the reticle. Therefore, even when a thin reticle is used, a pattern transfer error caused by deformation of the reticle can be eliminated.

In the projection exposure method of the present invention, first, exposure or measurement is performed using a reference original plate to determine an error caused by deformation of the original plate due to its own weight, and a projection optical system is used to cancel the error. It is preferable to adjust the lens and then perform the actual exposure. In this case, since an error is obtained and corrected at the time of adjustment, an error caused by the reticle chuck portion can also be obtained and the correction can be performed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a specific description will be given with reference to the drawings. FIG. 1 is a partially sectional side view schematically showing a configuration of a projection exposure apparatus according to one embodiment of the present invention. The projection exposure apparatus 1 has an illumination optical system 11 for applying illumination light IL to the reticle R from above. Reticle R is held by reticle holder 13 on its side. Reticle holder 13
Is placed on the reticle stage RS. A semiconductor circuit pattern is drawn on the lower surface Ra of the reticle R,
It is patterned when the illumination light IL passes below the reticle R. Note that the exposure apparatus 1 of the present embodiment is of a scanning type in which the reticle stage RS and the wafer stage WS are exposed while relatively scanning the projection optical system PL therebetween.

Exposure light passing through reticle R passes through projection optical system PL provided below reticle stage RS, and wafer W placed below projection optical system PL.
Is formed on the resist coating surface Wa on the upper surface of the substrate. Projection optical system P
In L, the pattern is reduced to 1/5 and transferred onto the wafer W. Wafer W is fixed on wafer stage WS via a vacuum chuck (not shown). The wafer stage WS has a Z-axis parallel to the optical axis of the projection optical system PL, an X-axis in a plane perpendicular to the optical axis, a Y-axis, and θ around the Z-axis.
To position the wafer W at a desired position.

At the uppermost stage of the projection optical system PL, a correction lens 15 having an inverted kamaboko-shaped cross section in which the reticle holder 13 has a flat upper surface and a lower surface is depressed in an R-shape when viewed in the cross-sectional direction in the state of FIG. Is arranged. This correction lens 15
Has a rectangular (parallel band) cross section in the longitudinal direction of the reticle holder 13 (the direction perpendicular to the paper surface of FIG. 1). The shape of the correction lens 15 is designed to correct an error due to the deflection of the reticle R, and the pattern image of the reticle R projected on the wafer W is accurate.

FIG. 2 is a flowchart showing a procedure for designing the projection optical system of FIG. First, the reticle size (width, thickness) is determined (51). Next, the shape of the portion holding the reticle is determined (52). As shown in FIG. 7, the reticle holding unit 7 is provided with an exposure pattern unit 33 actually used for exposure and various alignment marks and the like used for reticle positioning and the like outside the pellicle frame pasting unit 32. Is provided. The pellicle frame attachment position is determined in consideration of the exposure field, the aperture ratio of the projection lens, the size of foreign matter that may adhere, the working distance of the foreign matter inspection machine, the pellicle frame dimensional accuracy, the pellicle frame attachment accuracy, etc. It is determined.

When the position of holding the reticle in the holder and the method of holding the reticle, such as using a vacuum chuck or simply placing it, are determined, the amount of deflection of the reticle is calculated (53). The finite element method provided by commercially available software can also be used for calculating the amount of deflection. Next, the focus and distortion errors that occur when the pattern is exposed on the wafer surface are determined from the bending state (5).
4). This error is compared with an allowable value (55). If the error exceeds the allowable value (NO), the obtained focus and distortion errors are fed back to the design of the projection lens and redesigned (56). Generally, in the design of a projection lens, the design is advanced so as to reduce the aberration to zero. However, in reality, an error has occurred because the reticle is bent as a fixed offset as described above. In the present embodiment, an error generated as a constant value is inversely given as an aberration at the time of designing the projection lens, so that the design is performed so as to be corrected in the exposure result. The error after the redesign is calculated again (54), and when the error becomes equal to or less than the allowable value (YES), the process ends.

FIG. 3 is a partial sectional side view schematically showing a configuration of a projection exposure apparatus according to another embodiment of the present invention.
The feature of the projection exposure apparatus 1 'in FIG. 3 is that the correction lens 2 which is non-rotationally symmetric about the optical axis is provided in the upper stage of the projection optical system PL.
1 and 25 and their rotating mechanisms 23 and 27. The correction lens 21 and the correction lens 25 can be independently rotated around the optical axis by rotation mechanisms 23 and 27, respectively. By moving the rotation mechanisms 23 and 27 during adjustment, the position adjustment can be performed by rotating the non-rotationally symmetric correction lenses 21 and 25 around the optical axis. Rotating mechanism 23, 27
As a specific example, each of the rotation mechanisms 23 and 27 is provided with a plurality of holes into which a rod for adjustment can be inserted in a direction perpendicular to the optical axis direction. Then, the adjuster rotates the rod around the optical axis to change the optical relative relationship between the correction lenses 21 and 25, so that the combined vector can be directed in a desired direction.

FIG. 4 is a flowchart showing a procedure for adjusting the projection optical system of FIG. In the present embodiment, the reticle size is determined (61), and the shape and position of the holding unit (6).
The steps up to 2), the calculation of the amount of bending (63), and the calculation of the amount of error caused by bending (64) are common to the first embodiment. However, the difference is that the estimated error is considered as an offset in the adjustment of the projection lens. In other words, the design of the projection lens itself is performed so that the aberration is minimized, but the projection lens is driven to the specified value when adjusting the lens. As a method of the adjustment, in addition to the type of rotating the aspherical symmetric lens as shown in FIG. 3, a certain offset from the design value may be added to the distance between the lenses.

FIG. 5 is a flowchart showing a procedure according to another embodiment for adjusting the projection optical system of FIG. In this embodiment, in the processing / assembly of the projection lens (71), the projection lens is adjusted using the design value. Next, the deflection component of the reticle is obtained by a method such as exposure (72). Give feedback to the run-in target value.
As a method of separating the error due to the deflection of the reticle and other components, for example, the data of the wavefront of the projection lens is obtained without using the reticle, the aberration of the lens itself is obtained, and the reticle for performance evaluation is further obtained. Is measured using a coordinate measuring instrument or the like. At the time of evaluation of an image on which the reticle pattern is projected, an aberration component of the projection optical system and a reticle error component are removed to extract a component caused by the deflection of the reticle, and the component is adjusted to reduce the error to zero. This is because, if the correction is performed using only the result of printing in normal production, if the reticle used for adjustment and the reticle used for producing the actual device are different from each other, the error may increase. After the projection lens adjustment (74), the exposure (72) is performed again to measure the error (73). If the error is equal to or less than the allowable value (YES), the adjustment ends.

[0021]

As is apparent from the above description, according to the present invention, even when the reticle is bent, the error can be fed back to the design of the projection lens in advance to accurately expose the device pattern. Becomes possible. Further, even when the design of the projection lens is not changed, the exposure of the device pattern can be accurately performed by giving an amount for correcting the error as the target value of the lens adjustment.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional side view schematically showing a configuration of a projection exposure apparatus according to one embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure for designing the projection optical system of FIG.

FIG. 3 is a partial sectional side view schematically showing a configuration of a projection exposure apparatus according to another embodiment of the present invention.

FIG. 4 is a flowchart illustrating a procedure for adjusting the projection optical system of FIG. 2;

FIG. 5 is a flowchart showing a procedure according to another embodiment for adjusting the projection optical system of FIG. 2;

FIG. 6 is a side view schematically showing a configuration of a conventional semiconductor wafer projection exposure apparatus.

FIG. 7 is a plan view showing a planar configuration of a general reticle.

[Explanation of symbols]

Reference Signs List 1 projection exposure apparatus 11 illumination optical system 13 reticle holder 15 correction lens IL illumination light R reticle RS reticle stage PL projection lens W wafer WS wafer stage 21 first correction lenses 23, 27 rotating mechanism 25 second correction lens 31 peripheral part 32 Pellicle frame pasting part 33 Pattern part 35 Holding part AM Alignment mark

Claims (4)

[Claims] 1. A projection exposure system comprising: an original plate holder; an illumination optical system for illuminating the original plate; a projection optical system for forming an image of light passing through the original plate on a sensitive substrate; and a photosensitive substrate holding means. A projection exposure apparatus, wherein an error factor caused by deformation of the original plate due to its own weight when the original plate is held in the holder is corrected in the design of the projection lens. 2. A projection exposure system comprising: an original plate holder; an illumination optical system for illuminating the original plate; a projection optical system for forming an image of light passing through the original plate on a sensitive substrate; and a photosensitive substrate holding means. A projection exposure apparatus, comprising: a projection optical system adjusting mechanism for correcting an error factor caused by deformation of the original plate due to its own weight when the original plate is held by the holder. 3. A projection exposure method for projecting a pattern on an original onto a sensitive substrate and transferring the pattern onto the substrate; wherein the original is held by the original and deformed by its own weight. A projection exposure method, wherein the error factor is corrected in the design of the projection lens. 4. The projection exposure method according to claim 3, wherein:
First, exposure or measurement is performed using a reference original plate to determine an error caused by deformation of the original plate due to its own weight, a projection lens of a projection optical system is adjusted to cancel this error, and then actual exposure is performed. Characteristic projection exposure method.