JPH11288869A - Measuring method for distortion of lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a measuring method in which the accuracy of a measured value for every measuring point is increased and in which the distortion of a lens can be measured in a short time by a method, wherein the exposure of a pattern, for measurement which is stepped and moved is executed in the number of several times in the same point and an image distortion generated in a projection optical system in a measured value based on plural exposures measured. SOLUTION: A measuring pattern which is formed by a resist 12 in a measuring point is a box mark 13. For example, an inside pattern part is exposed by a field whole-face exposure operation, and an outside pattern part is exposed by a stepping exposure operation. The box mark 13 is formed in such a way, that its exposure is performed several number of times at several fractions of an exposure amount. The outside pattern part is formed of a plurality of resist latent images corresponding to a stepping exposure operation for each time. When the latent images are developed, one resist pattern is formed. The patent images which are average and from which the effects of distortion is removed are formed on a resist layer by the plural number of times for the exposure operation. The box mark 13 by the resist pattern from which a distortion is removed after their developing operation is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring lens distortion, and more particularly to a method for measuring lens distortion of a projection optical system used for manufacturing semiconductor devices.

[0002]

2. Description of the Related Art Conventionally, when manufacturing a semiconductor device or the like, a projection exposure apparatus for exposing a pattern image of a reticle to a wafer coated with a photoresist through a projection optical system has been used. The allowable range of the imaging characteristics required for the projection optical system of this projection exposure apparatus is extremely strict, and among the imaging characteristics, the lens distortion characteristics of the projection optical system (including the magnification error and the distortion of the projected image including the distortion). Image characteristic) is adjusted to be the best.

FIG. 3 is an explanatory view showing an exposure method associated with a conventional lens distortion measuring method. FIG. 4 shows box marks formed by the exposure method of FIG.
(A) is a plan view and (b) is a cross-sectional view.

As shown in FIG. 3, when performing lens distortion measurement, for example, 10 or more shots (in the figure, 9 shots are shown for the sake of convenience) over the entire field on the wafer 1, and several shots are taken for each shot. Stepping exposure involving ten stepping movements is performed. The stepping exposure is performed because it is necessary to form a reference point for each measurement point 2 having an exposure field distortion. That is, as shown in FIG. 4, a box mark (Box Mark) 4 formed by the resist 3 at the measurement point 2
Causes distortion in the outer pattern portion (see (a)).

As described above, the reference point is formed by performing the stepping exposure. However, since the stepping error actually exists, the position of the reference point is shifted by one exposure. In order to eliminate this effect, it is actually sufficient to form a set of reference points (shot over the entire field) that is ten times or more the number of exposures at one time, and obtain a lens distortion for each of them and perform averaging. Accuracy cannot be obtained.

In the case of such a conventional exposure method, since the number of all measurement points is determined by (the number of measurement points in each shot) × (the number of shots), it is inevitable that the measurement requires a long time. Was.

The following method is known as a similar lens distortion measuring method. For example, the method for measuring image distortion of a projection optical system disclosed in Japanese Patent Application Laid-Open No. 01-068926 discloses a method in which after exposing a plurality of first patterns to a resist layer of a photosensitive substrate through a projection optical system, only a second pattern is exposed. The exposure area is limited by a reticle blind or the like so that the exposure can be performed, and based on the design layout of the first pattern, the photosensitive substrate is moved by a fixed amount, and the second pattern is overlaid and exposed to the latent image of the first pattern. The amount of distortion of the projection optical system is measured by measuring the latent images of the first pattern and the second pattern. The method of evaluating an exposure apparatus disclosed in Japanese Patent Application Laid-Open No. 07-219243 discloses a method of performing multiple exposure of an evaluation mark on a plurality of regions on a photosensitive substrate by driving a stage. The position is being measured.

[0008] The distortion measurement method disclosed in Japanese Patent Application Laid-Open No. 08-078309 discloses a method of exposing a test reticle pattern onto a wafer and then performing a second exposure at a position shifted in the x direction on the wafer. The third exposure is performed at a position shifted in the y direction. The displacement amount of the box-in-box mark image formed by the multiple exposure, that is, the distortion difference is measured, the value of the weight given to each distortion difference is determined, and the weight is added using the determined weight to obtain the distortion. Find the X component.

The method of measuring lens distortion disclosed in Japanese Patent Application Laid-Open No. 09-015098 is disclosed in US Pat.
One semiconductor substrate is subjected to sequential exposure processing under a plurality of different optical conditions to generate a developed semiconductor substrate, and the developed semiconductor substrate is used to measure lens distortion under a plurality of different optical conditions. A lens distortion difference between a plurality of optical conditions is determined by directly comparing and collating lens distortion measurement values under each optical condition. Tokuhei 06-066637
In the method of manufacturing a semiconductor device disclosed in Japanese Patent Application Laid-Open Publication No. 9-209, a pattern for checking electrical characteristics of each chip is arranged at a plurality of locations separated from each other, and variations in the electrical characteristics of the plurality of checking patterns are reduced. By measuring
The distribution of exposure in the chip is monitored.

[0010]

However, in each of the above measuring methods, etc., the measured values for averaging are obtained by one measurement, and the measured values at each measuring point are all It is based on measured values. Therefore,
In order to obtain sufficient accuracy by averaging, as shown in the above-described conventional exposure method, individual measurement points (the number of measurement points in each shot) or the number of target fields including the individual measurement points (the number of shots) Number), and it was inevitable that the measurement would take a long time.

An object of the present invention is to provide a lens distortion measuring method which does not require a long time for measurement by increasing the accuracy of the measured value at each measuring point.

[0012]

In order to achieve the above object, a method for measuring lens distortion according to the present invention comprises:
A lens distortion measurement method for exposing a measurement pattern and measuring image distortion generated in a projection optical system is characterized in that exposure involving stepping movement is performed by multiple exposures at the same point.

With the above arrangement, the exposure of the measurement pattern accompanied by the stepping movement is performed by a plurality of exposures at the same point, and the image distortion generated in the projection optical system is measured by the measurement value based on the plurality of exposures. Is done. For this reason, the accuracy of the measurement value at each measurement point can be improved, and a lens distortion measurement that does not require a long time for the measurement can be performed.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram showing an exposure method associated with a lens distortion measuring method according to an embodiment of the present invention. As shown in FIG. 1, when performing lens distortion measurement for exposing a measurement pattern and measuring image distortion generated in a projection optical system, a field of at least one shot (one shot is shown in the figure) is placed on a wafer 10. Full-surface exposure and stepping exposure involving dozens of stepping movements for each shot are performed. By this stepping exposure, several tens of measurement points 11 are included in one shot.
Are formed (only five locations are shown in the figure).

In the stepping exposure, the exposure amount is set to a fraction of the conventional value, and the number of exposure times is several times the conventional single exposure value, that is, a plurality of exposures at the same point. A stepping movement is performed during the plurality of exposures. Such an exposure method is performed under the control of an exposure control unit provided in a projection exposure apparatus (not shown). Note that the total exposure amount in the multiple exposures is approximately the same as the resist sensitivity in the conventional exposure method.

FIGS. 2A and 2B show box marks formed by the exposure method of FIG. 1, wherein FIG. 2A is a plan view for explaining exposure and FIG. 2B is a plan view for explaining after development. As shown in FIG. 2, the measurement pattern formed by the resist 12 at the measurement point 11 is a box mark (Box Mark) 13 that is generally used for overlay displacement measurement including distortion measurement ((b) )), As an example, the inner pattern portion is
The outer pattern portion is exposed by stepping exposure. Conversely, the inner pattern portion may be exposed by stepping exposure, and the outer pattern portion may be exposed by overall field exposure.

Since this box mark 13 is formed by performing a plurality of stepping exposures at a fractional exposure amount, as shown in the outer pattern portion, a plurality of stepping exposures corresponding to each time stepping exposure are performed. It is formed by a resist latent image (see (a)), but when this is developed, one resist pattern is formed (see (b)).

That is, a latent image is formed in the resist layer by averaging and eliminating the influence of distortion by a plurality of exposures. After completion of the exposure, development is performed to remove the influence of the distortion. A box mark 13 is formed by the resist pattern.

Therefore, when forming a reference point by performing stepping exposure, in order to eliminate the influence of a stepping error, a set of reference points (fields) which is ten times or more the number of exposures (one time) as in the prior art is used. It is not necessary to form an entire shot), and by performing at least one shot of the entire field exposure and several tens of stepping exposures for this shot, a sufficiently accurate measurement value at each measurement point 11 can be obtained. .

As a result, (the number of measurement points in each shot) ×
In the number of measurement points 11 determined by (the number of shots),
The number of shots is greatly reduced compared to the prior art, and the measurement time can be greatly reduced to, for example, one tenth or less, and a lens distortion measurement method that does not require a long time for measurement becomes possible. In addition, the number of stepping exposure shots is not different from the conventional one, and the exposure amount for one shot is greatly reduced, so that the exposure time of the wafer can be greatly reduced. In addition, since the number of stepping exposure shots and the number of shots on the entire field can be increased, these can be further increased to enable high-precision lens distortion measurement.

The above-mentioned exposure method, in addition to the lens distortion measurement method, relates not only to variation but also to an absolute value, such as illumination telecentricity, determination of a baseline offset amount of an alignment sensor, and stability of a lens controller in long-time continuous exposure. Can also be applied.

The measurement is not limited to the box mark, but may be a diffraction pattern used in an exposure apparatus.

Further, exposure of the entire field may be performed by a plurality of exposures at the same point, similarly to the grid point (measurement point) serving as a reference. In this case, it is possible to obtain the effect of general averaging of the dispersion of the demonstration itself and its measurement accuracy.

[0025]

As described above, according to the present invention,
Exposure of the measurement pattern with stepping movement is performed by multiple exposures at the same point, and the measured value based on the multiple exposures measures the image distortion generated in the projection optical system. The accuracy of the value can be increased, and a lens distortion measurement that does not require a long time for the measurement can be performed. In addition, the number of stepping exposure shots is not different from the conventional one, and the exposure amount for one shot is greatly reduced, so that the exposure time of the wafer can be greatly reduced. In addition, since the number of stepping exposure shots and the number of shots on the entire field can be increased, these can be further increased to enable high-precision lens distortion measurement.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an exposure method associated with a lens distortion measurement method according to an embodiment of the present invention.

FIGS. 2A and 2B show box marks formed by the exposure method of FIG. 1, wherein FIG. 2A is a plan view illustrating exposure and FIG. 2B is a plan view illustrating development.

FIG. 3 is an explanatory diagram showing an exposure method associated with a conventional lens distortion measurement method.

4A and 4B show box marks formed by the exposure method of FIG. 3, wherein FIG. 4A is a plan view and FIG. 4B is a cross-sectional view.

[Explanation of symbols]

 10 Wafer 11 Measurement point 12 Resist 13 Box mark

Claims (6)

[Claims] 1. A lens distortion measuring method for exposing a measurement pattern and measuring image distortion generated in a projection optical system, wherein an exposure accompanied by a stepping movement is performed by a plurality of exposures at the same point. Measuring method. 2. The lens distortion measuring method according to claim 1, wherein a total of the exposure amounts in the plurality of exposures is about a resist sensitivity. 3. The lens distortion measuring method according to claim 1, wherein the exposure accompanied by the stepping movement is combined with at least one shot of the entire field exposure. 4. The lens distortion measuring method according to claim 3, wherein the exposure accompanied by the stepping movement is performed at each measurement point of the field overall exposure. 5. The measurement pattern is formed by a box mark, and an inner pattern portion is exposed by the entire field exposure, and an outer pattern portion is exposed by the exposure accompanied by the stepping movement.
The lens distortion measurement method described in 1. 6. A lens distortion measuring apparatus for exposing a measurement pattern and measuring image distortion generated in a projection optical system, comprising an exposure control means for performing an exposure accompanied with a stepping movement by a plurality of exposures at the same point. Characteristic lens distortion measurement device.