JP2621179B2 - Alignment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an alignment method for a projection exposure apparatus,
In particular, the present invention relates to a method for correcting a telecentric state determined by an alignment optical system and a projection optical system.

[Prior Art] Hereinafter, an example of an alignment method according to a conventional technique will be described with reference to FIG. FIG. 1 shows a projection exposure apparatus which is currently used relatively frequently. First, an exposure optical system will be briefly described.

In the figure, exposure light emitted from an exposure illumination system 10 forms an image on a reticle R and a wafer W via a projection lens 12 configured on both sides telecentric, and the reticle R
Is projected onto a wafer W placed on the wafer stage 14 by projection exposure.

 Next, the alignment optical system will be described.

Laser alignment light LA output from a laser light source (not shown) is emitted through a laser light transmission system 16, is reflected by a half mirror 18, and is incident on an objective lens 20.

The alignment light LA transmitted through the objective lens 20 transmits through the harbing 22 arranged at the pupil position, and further passes through the objective lens 24.
After being transmitted, the light is reflected by the mirror 26 and enters the reticle R. On reticle R, reticle mark RM (not shown) for alignment is formed.

Here, the objective lens 20, the harving 22, the objective lens
The alignment optical system of the apparatus is constituted by the mirror 24 and the mirror 26, and the alignment optical system includes a reticle mark RM.
In addition, it is configured to be movable in two-dimensional directions of X and Y according to the position of a wafer mark WM to be described later. Also, Harving 22
Is precisely controlled by an encoder (not shown) so that a telecentric state (hereinafter referred to as a telecentric state) of the alignment optical system with respect to the projection lens 12 can be arbitrarily changed in both the S and M directions by changing the angle. Has become.

Next, the alignment light LA irradiated with the reticle R passes through the projection lens 12 and reaches the wafer mark WM on the wafer stage 14 in a telecentric state. Wafer mark
The WM is arranged at the same height as the surface of the wafer W. Further, the alignment light LA is configured to scan on the reticle mark RM and the wafer mark WM. The wafer stage 14 is configured to be movable in three X, Y and Z axes, and the position of the wafer stage 14 in the X and Y directions is controlled by an interferometer 28.

On the other hand, the detection light from each alignment mark of the reticle mark RM and the wafer mark WM returns to the half mirror 22 as scattered light, returns to the same optical path as the incident light, enters the half mirror 22, and passes through the half mirror 22 to generate photoelectric light. Each mark position is detected by the detector 30.

Next, the overall operation of the above-described related art will be described.

First, the reticle R is loaded into the apparatus, the alignment optical system is moved to the position of the reticle mark RM of the reticle R, and the wafer mark 14 is moved to the image forming position of the reticle mark RM on the wafer W surface by the movement of the wafer stage 14. To move. Then, the alignment optical system and the projection lens 12 are aligned in a telecentric state in advance.

After the telecentric state as described above, the laser
Alignment light LA from a laser light source (not shown)
And the alignment light emitted from the laser light transmission system 16
LA is incident on the reticle mark RM by the respective actions of the optical elements of the half mirror 18, the objective lens 20, the harving 22, the objective lens 24, and the mirror 26.

Next, a reticle mark RM (not shown) and a wafer mark
The WM is scanned with the alignment light, the return light from both alignment marks is received by the photoelectric detector 30, and the position of each alignment mark is detected. Then, based on the information obtained by the photoelectric detector 30, the reticle R
And the wafer W are relatively aligned. Thereafter, when the position of the reticle mark RM (not shown), that is, the position of the alignment optical system changes when the reticle R is exchanged, the telecentric state between the alignment optical system and the projection lens 12 is changed due to the spherical aberration of the projection lens 12. It changes according to the position of the reticle mark RM. For this reason, based on the telecentric map information created in advance,
The angle of 22 is adjusted to correct the telecentric state.

The telecentric map is created by setting positions at appropriate intervals (for example, 1 mm) in the exposure area of the reticle R to be used, and calculating the amount of deviation of the telecentric state due to movement of the alignment optical system corresponding to these positions. Further, the angle is determined by obtaining the angle of the harving 22 at which a predetermined telecentric state is obtained from these deviation amounts.

[Problems to be Solved by the Invention] However, in the above-described prior art, the measurement error of the telecentric state when creating the telecentric map, the accuracy of mechanical reproducibility of the optical components when the alignment optical system is moved, and the like. There is a problem that it is difficult to maintain the telecentric state with high accuracy.

The present invention has been made in view of such a point, and an object of the present invention is to provide an alignment method capable of correcting a telecentric state determined by an alignment optical system and a projection lens with high accuracy.

[Means for Solving the Problems] The alignment method according to the present invention detects an alignment mark provided on both a substrate and a mask via a projection optical system having a telecentric configuration, and detects the detected alignment mark. In the alignment method of a projection exposure apparatus that performs relative alignment between a mask and a substrate based on the position information, an error component from a telecentric state determined by the alignment optical system and the projection optical system is applied to both the substrate and the mask. A technical point is that measurement is performed based on the position of the provided alignment mark, and correction is performed on the light transmission system side to a predetermined telecentric state determined by the alignment optical system and the projection optical system based on the measured error component. And

[Operation] In the present invention, since the telecentric state is directly corrected at the mark position at which the substrate and the mask are aligned, even when the alignment optical system moves, it is not affected by a mechanical error, and accurately at an arbitrary position. It can be corrected to a predetermined telecentric state.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Since the configuration of the apparatus is the same as that of the above-described conventional technique, the details are omitted, and the operation and action will be described in detail with reference to the flowchart of FIG.

First, the reticle R is loaded into the apparatus, the reticle R is aligned at a predetermined position, the alignment optical system is moved to the position of the reticle mark RM of the reticle R, and the reticle mark is moved by moving the wafer stage 14.
The wafer mark WM or a reference mark (not shown) on the wafer stage 14 is moved to an image forming position on the wafer W surface of the RM. Then, the alignment optical system and the projection lens 12 are aligned in advance in a telecentric state by adjusting the angle of the harving 22.

After the telecentric state as described above, the laser
The alignment light LA emitted from the half mirror 18, half mirror 18,
The light enters the reticle mark RM (not shown) formed on the reticle R by the action of each of the optical elements of the objective lens 20 and the pupil of the projection lens 12 conjugated with the harving 22, the objective lens 24 and the mirror 26. Then, the wafer mark WM is radiated through the projection lens 12 to obtain a state as shown in FIG.

Then, both marks are scanned in the X direction with the spot light SP, and further scanned in the Y direction perpendicular to (A) at a position as shown in FIG.
By such an operation, as shown in FIG. 4, a detection signal corresponding to the edge portion of each alignment mark is detected in both X and Y directions as a light intensity corresponding to the scan position, and the relative position of both marks is detected. Is detected.

Next, based on the signal obtained as shown in FIG. 4, the X-direction displacement ΔX of the mutual horizontal displacement between the reticle mark RM and the wafer mark WM is calculated. , And similarly, ΔY is obtained as the amount of deviation in the Y direction.

Then, the wafer stage 14 is sequentially moved by a predetermined amount in the Z direction, and scanning of the spot light SP in both the X and Y directions at both marks is performed several times, and the values of the deviation amounts ΔX and ΔY in the Z direction are calculated. Ask for each.

FIG. 5 shows the relationship between the deviation amount ΔX or ΔY and the position in the Z direction, and the error in the telecentric state can be accurately determined based on the inclination of the graph based on the best focus position. That is, the state where the graph of FIG. 5 is perpendicular to the Z direction is the telecentric state. Note that Δ
Similar data is obtained for Y in the same manner.

Next, based on the data in FIG. 5, an error from a preset telecentric state is calculated in both the X and Y directions. Then, based on this value, the angle of the harving 22 is controlled via an encoder (not shown) in both the sagittal direction and the meridional direction of the field of view of the projection lens 12 to correct a predetermined telecentric state.

Note that the detection and correction of the error from the telecentric state as described above may be performed only once, but when repeated, the accuracy of the telecentric state is further improved.

Thereafter, the reticle R and the wafer W for the shadow lens 12
The projection exposure is performed while the relative alignment is performed. Then, when the position of the reticle mark RM changes due to the reticle R exchange, the reticle state is corrected to the telecentric state by the same method as described above.

Thus, in the above embodiment, the reticle R
Immediately after alignment, the telecentric state is detected and corrected at the alignment mark position, so that it is always accurate without being affected by the error of the telecentric map estimated by the estimation, the mechanical reproducibility of the alignment optical parts, and the change over time. This has the effect that correction can be made to a predetermined telecentric state.

The present invention is not limited to the above embodiment. In the above embodiment, the correction of the telecentric state in both the sagittal and meridional directions (X and Y directions) with respect to the projection lens 12 of the alignment optical system is performed by one harbing 22. However, similar effects can be obtained even if different sabbing and meridional directions are used.

Further, although the error of the telecentric state is obtained by the detection signals from both the reticle mark RM and the wafer mark WM (or the reference mark), it is also possible to use only the detection light from the wafer mark WM alone. In this case, it is sufficient to use only the value b in FIG. 4 and obtain the difference in the Z direction.

Further, it is also possible to use the above-mentioned prior art and this embodiment together. If the detection range in the Z direction shown in FIG. 5 is narrowed based on the telecentric map and the telecentric state is corrected, the measurement is performed. The time can be reduced.

[Effects of the Invention] As described above, according to the present invention, since the telecentric state is measured and corrected at the alignment position, the telecentric state can be corrected very accurately at any position.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention and a conventional technique, and FIGS. 2, 3, 4, and 5 are explanatory views showing the operation of the embodiment. "Explanation of Signs of Main Parts" 12 Projection lens, 18 Half mirror, 20, 24 Objective lens, 22 Harving, 26 Mirror, R, Reticle, W ... Wafer, LA ... ... Alignment light. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] An alignment mark provided on both a substrate and a mask is detected through a projection optical system having a telecentric configuration, and a relative position between the mask and the substrate is determined based on the detected position information of the alignment mark. In an alignment method of a projection exposure apparatus that performs a general alignment, an error component from a telecentric state determined by the alignment optical system and the projection optical system is measured based on the position of an alignment mark provided on both the substrate and the mask, An alignment method comprising: correcting a predetermined telecentric state determined by the alignment optical system and the projection optical system on the light transmitting system side based on the measured error component.