JP2002043209A - Device and method for projection alignment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and method for projection alignment, which can improve the throughput of base line measurement. SOLUTION: The wafer stage 11 of the projection aligner does not move and, accordingly, the aligner can shorten processing time, because the position of a wafer stage 11 when a wafer 1 is loaded and unloaded on and from the stage 11 is the same as that of the stage 11 when the base line measurement is made by means of an off-axis alignment optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus and a projection exposure method for projecting and exposing a pattern formed on a reticle onto a wafer held on a wafer stage.
In particular, the present invention relates to a projection exposure apparatus and a projection exposure method for performing a baseline check using an off-axis alignment optical system provided at a position distant from the optical axis of the projection optical system.

[0002]

2. Description of the Related Art A projection exposure apparatus is used as a means for forming a wiring pattern of a semiconductor integrated circuit. In a projection exposure apparatus, a reticle (mask) on which a wiring pattern is formed is disposed above a wafer on which a photosensitive layer is formed, and the exposure pattern is transferred to the wafer by irradiating exposure light from above the reticle.

[0003] Regarding alignment of a wafer and a reticle in a projection exposure apparatus, an off-axis method in which an alignment optical system is arranged at a position different from the exposure position without using a projection optical system to perform alignment, and an exposure method in which a projection optical system is used. An on-axis method for performing alignment at the same position as the position is known.

Further, when performing alignment between a reticle and a wafer, a baseline amount, which is the distance between the measurement center of the alignment sensor and the center of the projected image of the reticle pattern (exposure center), is obtained in advance. Then, the alignment sensor detects the amount of displacement of the alignment mark from the measurement center, and moves the wafer by a distance corrected for the amount of displacement by the baseline amount, whereby the center of the shot area is accurately aligned with the center of exposure. You. However, since the amount of the baseline may gradually change in the process of using the exposure apparatus, a baseline check for accurately measuring the interval between the measurement center of the alignment sensor and the exposure center is periodically performed.

Next, a conventional reduction projection exposure apparatus will be described with reference to FIGS. In the conventional reduction projection exposure apparatus, as shown in FIGS. 4 and 5, the wafer exchange position A and the baseline measurement position B are separated from each other, and the wafer stage 11 holding the wafer 1 is moved to the wafer exchange position A.
And a base line measurement position B. The wafer stage 11 has a wafer vertical drive mechanism 12 that chucks the wafer 1 and moves up and down in the vertical direction.
Is provided. The first fiducial marks 13a and 13b and the second fiducial mark 1
The plate 13 provided with 3c is attached.

[0006] The wafer exchange position A
A wafer loading arm 14 that reciprocates between a position distant from the stopped wafer stage 11 and a position above the wafer vertical drive mechanism 12 is disposed. The wafer 1 is loaded and unloaded on the wafer stage 11 by lowering and raising the wafer vertical drive mechanism 12.

On the other hand, a reduction projection lens 21 and an off-axis alignment optical system 22 are arranged adjacent to each other at a baseline measurement position B. The reduction projection lens 21 transmits the exposure light L radiated from the light source 23 to the wafer stage 11
The wafer 1 loaded thereon is subjected to reduced projection exposure. As the exposure light L, for example, Kr having a wavelength of about 248 nm
An F excimer laser is used. The off-axis alignment optical system 22 has the first reference mark 13
a glass plate or an off-axis microscope with a target mark (not shown) serving as a reference when aligning the reference marks 13a and 13b and the second reference mark 13c (neither is shown)
Is provided. Further, the optical axis of the off-axis alignment optical system 22 is parallel to the optical axis of the reduction projection lens 21.

[0008] An illumination optical system 24, an illumination stop 25, and a reticle 26 are arranged between the light source 23 and the reduction projection lens 21. The reticle 26 is provided with a reticle mark (not shown). Reticle 26
A sensor (not shown) for an alignment mark is arranged above. The light source 23 and the illumination optical system 2
4, and between the illumination stop 25 and the reticle 26, reflection mirrors 27, 27 for deflecting the optical axis of the exposure light L are arranged.

Next, a method for forming a wiring pattern on the wafer 1 by the projection exposure apparatus configured as described above will be described. First, in the first step, as shown in FIG.
The wafer 1 is loaded on the wafer stage 11. When the wafer 1 is loaded onto the wafer stage 11, the wafer 1 is held by the wafer loading arm 14 as shown by a virtual line in FIG.
As shown by the solid line in FIG.
4 moves to a wafer exchange position above the wafer vertical drive mechanism 12. Next, as shown in FIG. 4B, the wafer up-down drive mechanism 12 moves up to chuck the wafer 1, and
As shown in (c), the wafer up-down drive mechanism 12 descends to load and hold the wafer 1 on the wafer stage 11.

In the next second step, as shown in FIG. 5, the wafer stage 11 is moved in the direction of the arrow to the baseline measurement position B to perform baseline measurement. In the third step, alignment measurement is performed. In the fourth step, a step-and-repeat exposure for irradiating the wafer 1 with the exposure light L emitted from the light source 23 is performed. In the last fifth step, as shown in FIG. 4, the wafer stage 11 returns from the baseline measurement position B to the wafer exchange position A, the wafer vertical drive mechanism 12 moves up, and the wafer 1 is moved by the wafer loading arm 14. Unloaded from stage 11.

In the baseline measurement in the second step, (1) the wafer stage 11 is moved from the wafer exchange position A to the baseline measurement position B, and (2) the wafer stage 11 is moved at the baseline measurement position B. Calm down,
(3) Baseline measurement between the position of the reticle 26 and the off-axis alignment optical system 22 is performed. (4) The wafer stage 11 moves from the baseline measurement position B to the alignment start position, and the origin of the off-axis alignment is (5) that the wafer stage 11 is settled at the alignment start position.
Two operations are performed.

In the step (3), the baseline measurement between the position of the reticle 26 and the off-axis alignment optical system 22 is performed by using the first reference marks 13a and 13a on the wafer stage 11.
13b, the second reference mark 13c, and the reticle mark on the reticle 26. Wafer stage 1
The first reference marks 13 a and 13 b on the first stage 1 are detected by a sensor for an alignment mark above the reticle 26 simultaneously with the reticle mark on the reticle 26 via the reduction projection lens 21, and The relative position between the reference marks 13a, 13b and the reticle mark on the reticle is measured. The shift amount and the rotation amount can be obtained from the first reference marks 13a and 13b arranged on the left and right. The second reference mark 13c is detected by the off-axis alignment optical system 22. The above three fiducial marks 13a, 13b,
Baseline measurement of the position of the reticle 26 and the off-axis alignment optical system 22 is performed from the measurement result of 13c.

A projection exposure apparatus and an exposure method having an off-axis alignment optical system are disclosed in Japanese Patent Laid-Open No. 11-166.
810, JP-A-11-168062, JP-A-11-195606, and the like.

In the projection exposure apparatus disclosed in Japanese Patent Application Laid-Open No. H11-166810, a reference mark that matches a reticle mark on a reticle and a reference mark that matches a detection center point of an off-axis alignment optical system include a wafer stage. It is characterized in that it is provided on a reference plate formed together therewith. The projection exposure method disclosed in Japanese Patent Application Laid-Open No. H11-168062 is characterized in that a reference mark which can be simultaneously detected by both an alignment system and an off-axis alignment optical system is provided on a wafer stage to measure a baseline. JP-A-11-19560
The projection exposure method disclosed in Japanese Patent Application Laid-Open No. H06-15764 is characterized in that two reference marks are measured almost simultaneously while the wafer stage is stopped. Either projection exposure apparatus and projection exposure method can make baseline measurement highly accurate.

[0015]

In the process of baseline measurement in a conventional projection exposure apparatus, there is a problem that the processing capability is low because five operations are performed.

That is, in the baseline measurement process,
(1) 1.5 seconds for the wafer stage 11 to move from the wafer exchange position A to the baseline measurement position B, (2) 0.05 seconds for the wafer stage 11 to settle at the baseline measurement position B, (3) ) The time for performing the baseline measurement is 0.3 seconds, (4) the time for the wafer stage 11 to move from the baseline measurement position B to the alignment start position is 0.5 seconds, and (5) the wafer stage 11 is settled at the alignment start position. The time to perform is 0.05 seconds. Therefore, in the baseline measurement, one wafer 1
Takes 2.4 seconds.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to provide a projection exposure apparatus and a projection exposure method that improve the processing performance in baseline measurement.

[0018]

A projection exposure apparatus according to the present invention comprises a wafer stage for holding a wafer, a reticle on which a predetermined pattern is formed, and an illumination optical system for irradiating the reticle with exposure light from a light source. A projection optical system for projecting and exposing a pattern formed on the reticle onto a wafer held by the wafer stage, and an off-axis alignment optical system provided at a position distant from the optical axis of the projection optical system Wherein the position of the wafer stage when loading and unloading the wafer and the position of the wafer stage when baseline measurement is performed by the alignment optical system are the same position. Things.

The wafer stage has a first reference mark for detecting a relative position with respect to a mark provided on a reticle, and a second reference mark for detecting a position with the alignment optical system. May have.

The first reference mark may be detected simultaneously with the mark on the reticle via a lens of the projection optical system by an alignment mark detection sensor provided above the reticle.

According to the projection exposure method of the present invention, a step of loading a wafer on a wafer stage, a step of measuring a baseline by an off-axis type alignment optical system at a position of the wafer stage when the wafer is loaded,
It is characterized by having.

The baseline measurement may be performed for each of a plurality of wafers, or may be performed for each of the wafers.

According to the present invention, the position of the wafer stage when loading and unloading the wafer is the same as the position of the wafer stage when measuring the baseline by the alignment optical system. In addition, the processing time can be reduced without moving the wafer stage.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a projection exposure apparatus according to an embodiment of the present invention will be described with reference to the drawings. However,
The same parts as those in the related art are denoted by the same reference numerals, and the detailed description is omitted.

The projection exposure apparatus according to the embodiment of the present invention is characterized in that the wafer exchange position A and the baseline measurement position B are at the same position, and the wafer stage 11 does not move for the baseline measurement. . Other configurations are the same as the conventional one.

Next, a method of forming a wiring pattern on the wafer 1 by the projection exposure apparatus according to the embodiment of the present invention will be described.

In the projection exposure method according to the present invention, a wiring pattern is formed on the wafer 1 by the first to fifth steps as in the conventional case. In the first step, the wafer 1 is held by the wafer loading arm 14 as shown by the imaginary line in FIG. 1A, and the wafer loading arm 14 is moved by the wafer vertical drive mechanism 12 as shown by the solid line in FIG.
To the wafer exchange position A above the wafer. Then, FIG.
As shown in FIG. 2B, the wafer up / down driving mechanism 12 moves up to chuck the wafer 1, and as shown in FIG. 2B, the wafer up / down driving mechanism 12 moves down to load the wafer 1 on the wafer stage 11. .

In the next second step, the wafer stage 11
Is moved, the baseline measurement is performed at the wafer exchange position A. In the third step, alignment measurement is performed. In the fourth step, a step-and-repeat exposure for irradiating the wafer 1 with the exposure light L emitted from the light source 23 is performed. In the last fifth step, the wafer 1 on the wafer stage 11 is unloaded by the wafer loading arm 14.

In the baseline measurement in the second step, (1) the baseline measurement between the position of the reticle 26 and the off-axis alignment optical system 22 is performed, and (2) the wafer stage 11 is aligned from the wafer exchange position A. The three operations of moving to the start position and (3) setting the wafer stage 11 at the alignment start position are performed.

The processing time of the baseline measurement in the second step is as follows: (1) The time of the baseline measurement is 0.3
Seconds, (2) the time for the wafer stage 11 to move from the wafer exchange position A to the alignment start position is 0.5 seconds, and (3) the time for the wafer stage 11 to settle at the alignment start position is 0.05 seconds. 0.85 seconds processing time.

In the conventional projection exposure apparatus, the processing time for the baseline measurement is 2.4 seconds. Therefore, the difference between the processing time of the baseline measurement between the projection exposure apparatus of the present invention and the conventional projection exposure apparatus is 2.4−0.85 = 1.55 seconds, and the processing time is reduced.

The conventional and the projection exposure apparatus according to the present invention can process about 200 wafers per hour. Therefore, the processing time for one wafer 1 is 36 seconds. When the baseline is checked for each wafer 1, the projection exposure apparatus of the present invention is (1.55 sec / 36 sec) × 100 = 4.3% as compared with the conventional projection exposure apparatus.
Even the processing capacity is improved. By performing the baseline measurement every time, accuracy is improved and reliability of the projection exposure apparatus is improved.

The baseline measurement may be performed periodically. For example, in the case of performing a baseline check every three images using the conventional and the projection exposure apparatus of the present invention, the projection exposure apparatus of the present invention can be compared with the conventional projection exposure apparatus by ｛1.
The processing capacity is improved by 55 / (36 × 3-2.4 × 2)｝ 100 = 1.5%.

The present invention is not limited to the above-described embodiment, and various changes can be made within the scope of the technical matters described in the claims.

[0035]

According to the present invention, the position of the wafer stage when loading and unloading a wafer is the same as the position of the wafer stage when the baseline is measured by the alignment optical system. In measurement, the processing time can be reduced without the wafer stage moving. Therefore, the productivity of forming a wiring pattern on a wafer is improved, and the cost of a product can be reduced.

[Brief description of the drawings]

1A and 1B are explanatory views for explaining a projection exposure method according to the present invention, wherein FIG. 1A is a schematic plan view and FIG. 1B is a schematic front view.

2A and 2B are explanatory diagrams for explaining a projection exposure method according to the present invention, wherein FIG. 2A is a schematic plan view and FIG. 2B is a schematic front view.

FIG. 3 is a configuration diagram schematically showing a projection exposure apparatus.

4A and 4B are explanatory views for explaining a conventional projection exposure method, wherein FIG. 4A is a schematic plan view, and FIGS. 4B and 4C are schematic front views.

5A and 5B are explanatory views for explaining a conventional projection exposure method, wherein FIG. 5A is a schematic plan view and FIG. 5B is a schematic front view.

[Explanation of symbols]

 1: Wafer 11: Wafer stage 13a: First fiducial mark 13b: First fiducial mark 13c: Second fiducial mark 21: Reduction projection lens 22: Off-axis alignment optical system 26: Reticle A: Wafer exchange position B: Baseline measurement position L: exposure light

Claims (6)

[Claims] 1. A wafer stage for holding a wafer, a reticle on which a predetermined pattern is formed, an illumination optical system for irradiating exposure light from a light source to the reticle, and a pattern formed on the reticle on the wafer stage. A projection optical system having a projection optical system for projecting and exposing to a wafer held by a projection optical system, and an off-axis type alignment optical system provided at a position distant from the optical axis of the projection optical system; A projection exposure apparatus, wherein the position of the wafer stage when unloading is the same as the position of the wafer stage when baseline measurement is performed by the alignment optical system. A first reference mark for detecting a relative position with respect to a mark provided on a reticle; and a second reference mark for detecting a position with the alignment optical system. 2. The projection exposure apparatus according to claim 1, comprising: 3. The apparatus according to claim 2, wherein the first reference mark is detected simultaneously with a mark on the reticle via a lens of the projection optical system by an alignment mark detection sensor provided above the reticle. The projection exposure apparatus according to claim 2. 4. A step of loading a wafer on a wafer stage, and a step of measuring a baseline by an off-axis type alignment optical system at a position of the wafer stage when the wafer is loaded. Projection exposure method. 5. The projection exposure method according to claim 4, wherein the baseline measurement is performed for each of a plurality of wafers. 6. The projection exposure method according to claim 4, wherein said baseline measurement is performed for each wafer.