JPS6269614A - Projection exposure device - Google Patents

Abstract

PURPOSE:To enable any photosignals to be correctly detected constantly by a method wherein a processor to detect the relative position of a reticle or a mask to a wafer by processing any output signals from a photoreceiving element selected by a photoreceiving element selection means. CONSTITUTION:The step difference structure of patterns in each exposure process and the kinds or coated thickness etc. of photoresist coated on wafer surface are changeable. Therefore, when the image formation shapes of photosignals received from wafer marks are changed, a photoreceiving element selection means 15 selects an optimum photoreceiving element 16a so that photosignals may be detected correctly just like in case the positions of photosignals are deflected. The deflections in the vertical direction can be corrected by means of comparing the level of signals detected by a photoreceiving element group 16 corresponding to photosignal selection windows W1 and W2 to shift the optimum photoreceiving element group 16a to the lower signal level side likewise the deflections in the right and leftside directions can be corrected as to the photoreceiving element group 16 corresponding to the other photosignal selection windows W3 and W4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a projection exposure apparatus for transferring a reticle pattern or a mask pattern onto a wafer, and in particular to a through-the-lens (TTL) type position exposure apparatus using a projection optical system. The present invention relates to a projection exposure apparatus that performs alignment.

[Backbone of the invention 1 Generally, in a projection exposure apparatus for manufacturing T-SR or Vl-8r, a reticle pattern (or mask pattern) is projected onto a wafer through a projection lens with a reduction magnification of 115 or 1/10. At this time, the same pattern is repeatedly exposed on one wafer. Therefore, −
Before each exposure, it is necessary to measure and align the relative positions of the reticle and wafer through a projection lens. In order to automatically perform this operation, the reticle and wafer require marks for alignment, that is, reticle marks and wafer marks. Moreover, usually LSI, V
In the LSI manufacturing process, the alignment and exposure steps are performed multiple times, so a plurality of alignment marks are often sequentially created at different positions from the marks used in the previous process.

In general, there are two types of projection lenses for projection exposure equipment: a double-telecentric type and a single-telecentric type.The principal ray on the side of the reticle projection image is incident perpendicularly to the wafer surface in both the double-telecentric type and the single-telecentric type. , the chief ray on the reticle side is perpendicular to the reticle surface in the case of the double-telecentric type, whereas in the case of the single-telecentric type, it has an inclination that deviates from perpendicular to the reticle surface at image heights other than the optical axis. The slope changes depending on the image height.

Therefore, conventionally, a single-telecentric lens is used as a projection lens,
When detecting the optical signal of a wafer mark through a lens to detect the relative position of the reticle and wafer, if the image height of the wafer mark changes, the principal ray on the reticle side will deviate from perpendicular to the reticle plane at image heights other than the optical axis. Since the inclination changes depending on the image height, the optical axis position of the optical signal incident on the optical signal selection means of the wafer mark changes, making it impossible to detect the optical signal correctly.

Also, both TV I on the projection lens? Even when detecting the optical signal of a wafer mark through the lens using a wafer lens, if the lens has a telecentricity error, if the image height of the wafer mark changes, the light of the optical signal incident on the optical signal selection means will change. Since the axis position changes by the amount of the telelens error, the disadvantage is that the imaging position of the optical signal relative to the optical signal selection means shifts, making it impossible to detect the correct optical signal, similar to when a single-telecenter type lens is used. there were.

Furthermore, in each exposure process, the step structure of the pattern and the type or coating thickness of the photoresist applied to the wafer surface change, so that the diffraction state of the optical signal obtained from the wafer mark also changes. As a result, the image formation shape of the optical signal from the wafer that enters the photoelectric conversion means changes as well, so that the optical signal selection means cannot correctly detect the optical signal.

[Objective of the Invention 1] The present invention eliminates the drawbacks of the prior art described above, and improves optical signal formation according to variations in the optical signal imaging position due to the telecentricity characteristics of the projection lens or due to differences in the surface structure of the wafer, etc. Is it in a photoelectric conversion means consisting of a large number of light-receiving elements arranged in a grid according to the image shape?

Based on the concept of selecting only the signal of a specific light-receiving element, regardless of the imaging position and shape of the optical signal,
It is an object of the present invention to provide a projection exposure apparatus that can always correctly detect optical signals.

[Description of Examples] Hereinafter, the present invention will be described in more detail based on Examples.

Figure 4 shows a state in which the optical axis of the optical signal of the wafer mark and the optical axis of the alignment optical system are aligned in a device that detects the optical signal of the wafer mark through a projection lens in order to detect the relative position of the reticle and the wafer. .

After the alignment light emitted from the laser 1 passes through the lens 2, it passes through the polygon mirror 3, the mirror 4, and the objective lens 5.
The light is irradiated onto the reticle 6 through.

The reticle 6 is provided with marks for alignment with the wafer 8 , and the alignment light that has passed through the reticle 6 is illuminated through a projection lens 7 onto a wafer mark provided in a scribe area of the wafer 8 .

Incidentally, the sample holder 8 is placed on the sample stage 9. The reflected light from the wafer mark, that is, the optical signal from the wafer mark passes through the projection lens 7 and passes through the same path as the incident light to the mirror 4.
, and is guided by the mirror 4 to a different optical path from that at the time of incidence, passes through the lens 10, and converts the selected light into an electrical signal. The light enters the photoelectric conversion means 12. By electrically processing the output of this photoelectric conversion means, the relative position between the reticle 6 and the wafer 8 is detected.

FIG. 5 shows the positional relationship between the optical signal and the optical signal selection means 11, and $1 to S4 are optical signals whose directionality is determined according to the shape of the wafer mark. W1 to W4 are optical signal selection windows, which are arranged according to the imaging position and directionality of the optical signal. The case shown in the figure shows a state in which the relative position between the optical signal selection means and the optical axis of the optical signal is optimal, and the optical signal is detected correctly.

When the image height of the wafer mark is changed from the image height at which the optical axis of the optical signal of the wafer mark and the optical axis of the alignment optical system coincide with each other as explained in FIG. The optical axis position of the optical signal of the wafer mark incident on the selection means 11 changes. As a result, the optical signal imaging position relative to the optical signal selection means 11 is shifted, making it impossible to correctly detect the optical signal. 6th
The figure shows a state in which the optical signal imaging position is shifted with respect to the optical signal selection means 11 in this way.

FIG. 1 shows a schematic block configuration of a projection exposure apparatus according to an embodiment of the present invention. In the figure, 13 is a multi-separate type photoelectric conversion means having a light receiving surface with a large number of light receiving elements arranged in a grid pattern, 14 is an arithmetic processing means for calculating the relative position between the reticle 6 and the wafer 8, and 15 is an optimum light receiving surface. This is a light receiving element selection means for selecting an element. Here, the optimum light-receiving element is the reticle 6 among the many light-receiving elements arranged in a grid pattern.
A light-receiving element that correctly calculates the relative position of the wafer 8. Note that other symbols are the same as in FIG. 4.

This embodiment shows the case where the wafer mark is changed from the image height a shown in FIG. 4 to the image height . Therefore, the optical axis of the optical signal from the wafer mark changes as shown by the broken line due to the telecentricity characteristic of the projection lens 7. The figure also shows that the optical axis position of the optical signal entering the separate photoelectric conversion means 13 is probably shifted by ΔY compared to the state shown in FIG. This indicates the state in which the In this embodiment, in order to correctly detect the relative position between the reticle 6 and the wafer 8 even if there is a deviation in ΔY, the difference from the conventional device shown in FIG. The means 13 has a light receiving surface in which a large number of light receiving elements (photoelectric conversion elements) are arranged in a grid pattern,
The optimum light-receiving element can be arbitrarily selected from these light-receiving elements by the light-receiving element selection means 15 using J:. That is, the separate type photoelectric conversion means 13 serves both as the photoelectric conversion means 12 and the optical signal selection means 11 of the conventional example, and therefore the optical signal selection means 11 shown in FIG. 4 is unnecessary in this embodiment. It becomes.

FIG. 2 shows that the multi-segment light-receiving element 16 captures the optical signal in an optimal state when the optical axis of the optical signal of the wafer mark and the optical axis of the alignment optical system match as shown in FIG. 4. FIG. 3 is a diagram in which the separate photoelectric conversion means 13 captures the optical signal in an optimal state when the optical axis of the optical signal shown in FIG. 1 is shifted by ΔY. In these figures, each grid square is an individual light-receiving element 16, and the black portion is the optimal light-receiving element (group) selected by the light-receiving element selection means 15 to optimally capture the optical signal. 16a,
b. The arithmetic processing means 14 receives the selection information of the optimum light receiving element 16a from the light receiving element selection means 15, and
Only the output signal from the selected optimal light receiving element 16 is processed to calculate the relative position between the reticle or mask and the wafer. In this way, even if the optical axis of the optical signal is shifted by ΔY as shown in FIG. It can always be detected correctly regardless of the situation.

In addition, if the image formation shape of the optical signal 411 from the wafer mark changes due to the step structure of the pattern in each exposure process and the type or coating thickness of the photoresist applied to the wafer surface, it is necessary to select the light receiving element. Since the means 15 selects the optimum light receiving element 16a according to the image formation shape,
The optical signal can be detected correctly as in the case where the position of the optical signal is shifted.

Thereafter, hair alignment is performed and exposure is performed in a conventional manner.

In the above embodiment, whenever the image height is changed, the light receiving element selection means 15 selects the optimum light receiving element 1.
It is necessary to select 6a. This means, for example, that the optimum light-receiving element group 16a is selected from the optical signal selection windows W1 to W1 in FIG. 5 or FIG.
4]), the method disclosed by the present applicant in Japanese Patent Application No. 60-24519 as a method for correcting the position of the optical signal selection means 11 is applied. be able to. That is, the magnitude of the signals detected by the light receiving element groups 16 corresponding to the optical signal selection windows W+ and W2 in FIG. 5 of the present application are compared and the optimum light receiving element group 16a is moved to the one with the smaller signal level. : The vertical deviation can be corrected, and the horizontal deviation can be corrected in the same way for the light receiving element groups 16 corresponding to the optical signal selection windows W3 and W4.

In addition, information on the optimum light receiving element 16a is input in advance to a control system (not shown) based on the known telecentricity error design value of the projection lens 7, and the selection of the optimum light receiving element 16a is made according to the image height of the wafer mark. This may be done automatically.

Furthermore, if the image formation shape of the optical signal changes as described above, it is possible to use a standard sample and input the optimum arrangement of the light receiving cables 16a corresponding to the image formation shape into a control system (not shown) in advance. good.

[Effects of the Invention] As explained above, according to the present invention, even if there is a change in the imaging position of the optical signal of the wafer mark due to the telecentricity characteristic of the projection lens or the telecentricity error, the difference in the wafer surface structure etc. Even if there is a change in the image formation shape of the optical signal due to the change in shape, the light receiving element selection means can select the optimum light receiving element according to the change. It becomes possible to achieve high alignment accuracy.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic diagram of a projection exposure apparatus according to an embodiment of the present invention, and FIGS. Figure 4 shows the optimum light receiving element and the optical signal optical axis and alignment 1 of the
Wafer mark light 1 when the optical axes of the optical systems match
Figure 5 is a diagram explaining the No. 8 detection, Figure 5 is a diagram showing the positional relationship between the optical signal and the optical signal selection means, and Figure 6 is a diagram showing a state in which the optical signal imaging position is shifted with respect to the optical signal selection means. It is a diagram. 1... Laser, 2... Lens, 3...
・Polygon mirror, 4... Mirror, 5... Objective lens, 6... Reticle, 7... Projection lens,
8... Wafer, 9... Sample stage, 1
0... Lens, 11... Optical signal selection means, 12.
...Photoelectric conversion means, 13... Multi-type photoelectric conversion means, 14... Arithmetic processing means, 15... Light receiving element selection means, 16... Light receiving elements, 16a, b...
Optimal light receiving elements, 81-84, 81'-84'...
Optical signal, W1 to W4... Optical signal selection window.

Claims (1)

[Claims] A projection optical system for transferring a pattern image of a reticle or mask onto a wafer, and a multi-type photoelectric conversion means having a light receiving surface in which a large number of light receiving elements are arranged in a grid pattern. an alignment optical system for detecting a relative alignment signal between the wafer and the wafer;
a light-receiving element selection means for selecting an arbitrary light-receiving element according to the imaging position and image-forming shape of an optical signal incident on the multi-different type photoelectric conversion means; and an output signal of the light-receiving element selected by the light-receiving element selection means. 1. A projection exposure apparatus comprising: arithmetic processing means for calculating a relative position between a reticle or a mask and a wafer by arithmetic processing.