JPH10209004A - Reduced projection aligner and method of forming pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably correct the projection magnification and eliminate the magnification error in an overlay exposure. SOLUTION: The aligner having a reticle 11 for projection exposure of a pattern from a reticle 12 on a wafer 14 through a reduced projection lens 13 comprises an optical element 17 disposed between the reticle 11 and the lens 13 or between the lens 13 and the wafer 14 for correcting the reduced projection magnification. The magnification errors of the optical shot and base pattern are previously measured or calculated and, based on this result, the optical element 17 is replaced or removed to change the magnification correction value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor manufacturing apparatus, and more particularly to a reduction projection exposure apparatus and a pattern forming method used in a fine pattern forming step.

[0002]

2. Description of the Related Art With the recent increase in the degree of integration of semiconductor integrated circuits, finer circuit patterns are required.
A transistor having a size of 35 μm or less is required. At present, as the fine processing technology, i-line (wavelength 365) of a mercury lamp is used.
nm) as an exposure light source, and recently, a KrF excimer laser beam (wavelength: 248 nm) has been used.
m) has also begun to be used as an exposure light source.

Further, with the miniaturization of patterns, a high resolution and a high overlay accuracy are required.
Generally, the overlay accuracy is required to be about 1/4 or less of the minimum design rule. As a cause of the overlay deviation,
Device factors such as stage accuracy and distortion difference, and process factors such as deterioration of the position measurement mark shape and wafer expansion and contraction are considered. Above all, the expansion and contraction of the wafer caused by the stress caused by the deposition and heat treatment of the thin film may reach 10 ppm or more, which is now serious as a magnification error between the base and the exposure shot.

As a countermeasure, a wafer expansion / contraction ratio calculated from a deviation between a measurement result of two or more position measurement marks formed on a wafer and a design value thereof is set as an expansion / contraction ratio of an exposure shot. A method of changing the projection magnification of a reduction projection lens has been proposed (Japanese Patent Laid-Open No. 4-10 / 1994).
No. 7465).

[0005]

However, the above method has the following problems. First, since there is a design limitation in correcting the projection magnification of the reduction projection lens, it is only possible to correct at most about 10 ppm.

Second, there is insufficient magnification control accuracy when changing the projection magnification of the reduction projection lens, and exposure cannot be performed at a stable projection magnification.

An object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a reduced projection exposure apparatus and a pattern forming method that can stably correct a projection magnification.

[0008]

In order to achieve the above object, a reduced projection exposure apparatus according to the present invention is a reduced projection exposure apparatus for projecting and exposing a pattern on a reticle onto a wafer via a reduced projection lens. The optical element is provided between the reticle and the reduction projection lens or between the reduction projection lens and the wafer, and corrects a reduction projection magnification.

The optical element is provided so as to be replaceable or insertable.

A reduced projection exposure method according to the present invention is a pattern forming method for projecting and exposing a pattern on a reticle onto a wafer via a reduced projection lens. To form

The magnification correction value is changed by replacing or inserting or removing the optical element.

Further, the magnification error between the exposure shot and the underlying pattern is measured or calculated in advance, and the magnification correction value is changed based on the result.

[0013]

The magnification correcting optical element 41 provided in the optical path between the reticle and the projection lens is an afocal lens as shown in FIG.
Similarly, as shown by an optical path 42, the light is emitted as a parallel light beam. The principal ray bundle of the two telecentric projection optical systems parallel to the optical axis is emitted as a ray bundle parallel to the optical axis whose lateral magnification has changed. As a result, the projection magnification of the exposure shot can be changed. A plurality of types of non-focusing lenses having different lateral magnifications in which the curvature of the lens surface is changed are prepared, and the projection magnifications of the exposure shots are variously changed by exchanging or inserting and removing them.

Although the above is a strict description of both telecentric projection optical systems, many reduction projection exposure apparatuses in which the reticle side is not completely telecentric. In such a case, it is not always necessary to use an optical element of an afocal lens, and it is also possible to perform magnification correction using a parallel plate glass or the like as an optical element.

In this case, since the refractive indexes of air and glass are different, the insertion of the parallel flat glass changes the effective optical path length between the reticle and the projection lens. This is equivalent to moving the reticle in the optical axis direction, and the projection magnification is corrected. In this case, the magnification correction amount can be changed by, for example, changing the thickness of the parallel plate glass, and the fabrication of the optical element becomes easy.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a projection exposure apparatus according to the present invention.

In the figure, an illumination light source and an illumination optical system 11 are shown.
Is irradiated on the reticle 12. The exposure light having passed through the reticle 12 is projected and exposed on a wafer 14 held on a wafer stage 15 via a reduction projection lens 13.

At the time of the overlay exposure, the position of the alignment mark on the wafer 14 is measured using the off-axis alignment system 16, and the shot array correction value calculated based on the result is fed back to the wafer stage 15. To perform alignment.

The projection magnification correcting optical element 17 used in the present invention is provided between the reticle 12 and the reduction projection lens 13 (or between the reduction projection lens 13 and the wafer 14) and corrects the reduction projection magnification. It is. The optical element 17 for optical element magnification correction is an afocal system (afo
cal) lens, and the presence of the optical element 17 causes the incident parallel light beam to change in lateral magnification by the optical element 17 and is emitted as a parallel light beam. The chief ray bundle of both telecentric projection optical systems parallel to the optical axis is emitted as a ray bundle parallel to the optical axis whose lateral magnification has changed, so that the projection magnification of the exposure shot can be changed. A plurality of types of non-focusing lenses having different lateral magnifications in which the curvature of the lens surface is changed are prepared, and the projection magnifications of the exposure shots are variously changed by exchanging or inserting and removing them. 1
8 shows the optical path of the principal ray when the optical element 17 is not provided.

The optical element 17 is provided so as to be exchangeable or removable by an optical element exchange mechanism 20. The optical element exchange mechanism 20 is not limited to an automatic one, but may be one that manually exchanges or inserts and removes the optical element 17.

(Embodiment 1) Next, a method of forming an overlay displacement measurement pattern according to the present invention will be described.
As shown in FIG. 2A, a resist layer 21 is formed by exposing the first layer on the resist-coated wafer 14 without using the optical element 17 using a KrF excimer laser as an irradiation light source.

Subsequently, as shown in FIG. 2B, the wafer 14 is formed using the resist pattern 21 as an etching mask.
Is etched by about 200 nm.

Next, as shown in FIG. 2C, the resist pattern 21 is removed, and thereafter, as shown in FIG. 2D, a polysilicon film 22 is deposited to a thickness of about 800 nm on the entire surface of the wafer by the CVD method.

Next, as shown in FIG.
4. Apply resist to off-axis alignment system 1
After the shot alignment is corrected by global alignment using No. 6, exposure of the second layer is performed without using the optical element 17 similarly to the first layer, and a resist pattern 23 is formed.

The pattern shown in FIG. 2E formed by the above-described process is the pattern 33 for measuring overlay deviation shown in FIG. 3, and is formed at two places in the exposure shot as shown in FIG. I have. Exposure was performed using the shot 31 of the first layer and the shot 32 of the second layer, and as a result of measuring the misalignment of the two points, the wafer was elongated by the deposition of the polysilicon film, and a magnification error of about 8.2 ppm was generated. It turned out to be happening.

In the first embodiment of the present invention, based on the result of the above-described measured magnification error, an optical element 17 designed to enlarge the lateral magnification of the principal ray by the magnification error is used. Second on the wafer on which
The pattern is formed by exposing the layer. Optical element 17
When the patterns were formed by superimposition using the method, the displacement of the pattern due to the superposition was measured. As a result, almost no magnification error was observed.

(Embodiment 2) FIG. 2 described in Embodiment 1
On the wafer (c), a silicon nitride film was deposited to a thickness of 100 nm, 200 nm, and 300 nm, respectively, by a CVD method (referred to as wafers A, B, and C, respectively). When the expansion and contraction rates of these wafers were roughly estimated by stress analysis,
Wafers A, B, and C were 1.7 ppm and 3.4 ppm, respectively.
ppm, 5.1 ppm.

In the second embodiment of the present invention, based on the results of the above-described measured magnification errors, three types of designs designed to reduce the horizontal magnification of the principal ray corresponding to the reduction rate of each of the wafers A, B, and C are provided. The exposure of the second layer was performed using each of the optical elements 17 in the same manner as in the first embodiment, and the overlay deviation was measured. As a result, almost no magnification error was observed for any of the wafers.

In the above description, only the case where a magnification error occurs due to wafer expansion and contraction caused by a process has been described, but the present invention is not limited to this case. For example, it is of course possible to correct a magnification component of a distortion difference between different exposure apparatuses or different illumination conditions.

(Embodiment 3) The same study as in Embodiments 1 and 2 was performed under different illumination conditions for the exposure of the first and second layers. However, in the present embodiment, the thin film shown in FIG. 2D is not deposited, and the second film is directly deposited on the wafer shown in FIG.
The resist pattern of the layer is formed. The illumination condition of the first layer was σ = 0.3, and the illumination condition of the second layer was σ = 0.8. The magnification component of the distortion difference between these two illumination conditions is 3.4 ppm.

In the third embodiment of the present invention, based on the result of the above-described measured magnification error, an optical element 17 designed to enlarge the lateral magnification of the principal ray by the magnification component of the distortion difference is used, and the second layer is used. And the overlay deviation was measured. As a result, almost no magnification error was observed, and the overlay accuracy was greatly improved.

[0032]

As described above, according to the present invention, stable correction of the projection magnification can be performed, and the overlay accuracy can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a process of forming an overlay displacement measurement pattern according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating an overlay displacement measurement pattern according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a magnification correcting optical element used in the projection exposure apparatus according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11 illumination light source and illumination optical system 12 reticle 13 projection lens 14 wafer 15 wafer stage 16 off-axis alignment system 17 magnification correcting optical element 18 optical path without optical element 19 optical path with optical element 20 optical element exchange mechanism Reference Signs List 21 first layer resist pattern 22 polysilicon film 23 second layer resist pattern 31 first layer shot 32 second layer shot 33 overlay misalignment measurement pattern 41 magnification correcting optical element 42 optical path

Claims (5)

[Claims] 1. A reduction projection exposure apparatus for projecting and exposing a pattern on a reticle onto a wafer via a reduction projection lens, comprising an optical element, wherein the optical element is disposed between the reticle and the reduction projection lens. Alternatively, a reduction projection exposure apparatus is provided between the reduction projection lens and the wafer and corrects a reduction projection magnification. 2. The reduction projection exposure apparatus according to claim 1, wherein the optical element is provided so as to be exchangeable or removable. 3. A pattern forming method for projecting and exposing a pattern on a reticle onto a wafer via a reduction projection lens, wherein the pattern is formed by correcting a reduction projection magnification by an optical element. Forming method. 4. The pattern forming method according to claim 3, wherein the magnification correction value is changed by replacing or inserting / removing the optical element. 5. The pattern forming method according to claim 3, wherein a magnification error between the exposure shot and the base pattern is measured or calculated in advance, and the magnification correction value is changed based on the result.