JPH06163346A - Gap measurement method - Google Patents

Abstract

PURPOSE:To measure a mask-to-wafer gap accurately by measuring a difference between a focal point of a direct imaging to a target mark attached to a measurement object and a second measurement object and a focal point to a high- order mirror image obtained by multiple reflection. CONSTITUTION:At first, a mask 1 is focused to a target mark M on a wafer 2 at a position fairly far from a designated gap by a metallic microscope 20. Focusing is performed by picking up a microscopic image by a CCD camera 8 and an image is adjusted to be maximum by an image treatment device 10. Then, a metallic microscope tube 7 is moved downward by a value twice a designated gap and movement of the mask 1 is finished when it is focused to a mirror image of the target mark M. Gap adjustment is finished in this way. Since the difference between the focal point of a target mark M on the wafer 2 and the focal point of a mirror image reflected once at a rear of the mask 1 is twice a gap interval, a half the acquired difference in focal points is a gap G.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gap measuring method, and more particularly to a gap measuring method for measuring a mask-wafer gap suitable for use in the field of a proximity exposure apparatus. In recent years, for example, IC (In
integrated circuit), LSI (Large Scale Integrated)
circuit) and other semiconductor integrated circuits have become highly integrated, so that exposure apparatuses, which are bases for semiconductor integrated circuit fabrication, are also required to have high accuracy.

By the way, when the mask and the wafer are brought into close contact with each other, a pattern defect occurs due to adhesion of dust to the mask and peeling of the resist from the wafer, resulting in a decrease in device manufacturing yield.
Since the mask is also damaged and the life thereof is shortened, the recent apparatus is configured so that the mask and the wafer are spaced from each other even during exposure. This is called proximity exposure to distinguish it from the original contact exposure.

However, if the mask and the wafer are spaced apart from each other, the resolution is unavoidable due to Fresnel diffraction at the edge of the mask pattern. The standard of resolution is (λd) ^1/2
(Λ: exposure wavelength, d: distance between mask and wafer). If d is large, damage to the mask and the resist film is reduced, but the resolution is also lowered, so there is a compromise. That is,
The mask-wafer gap value in the proximity exposure of the IC is set so as to suppress the decrease in the resolution of the resist pattern mainly due to the diffraction phenomenon due to the mask pattern to a value not more than the value allowed in the IC design. The gap value decreases with the miniaturization of the
The gap value required to form a resist pattern of 0.2 μm or less when an X-ray of about Å is used is 2
0 to 30 μm or less, and set value accuracy is 0.5 μ
A value of m or less is required.

Therefore, in order to carry out proximity exposure of an IC with high resolution, it is necessary to accurately measure between the mask and the wafer and to accurately match the required gap value.

[0005]

2. Description of the Related Art As a conventional gap measuring method of this type, for example, there is a method applied to a proximity exposure apparatus as shown in FIG. In FIG. 3, 1 is a mask, 2 is a wafer, 3 is a wafer stage, 4 is a mask ring, 5 is a mask Z stage, 6 is a microscope barrel stage, 7 is a metal microscope barrel, 8 is a CCD camera, and 9 is a control circuit. Reference numeral 10 is an image processing apparatus, and 11 is a stage controller.

FIG. 5 is an enlarged view of a main part of FIG. 4, and in FIG.
Reference numeral 12 is a laser diode, 13 is a focusing lens, and 14 is a CCD sensor. In the above configuration,
Laser light is irradiated from the laser diode 12 onto the mask 1 surface, and when the laser light obliquely incident from the upper left side in FIG. 5 is imaged on the mask surface 1, the laser light reflected on the mask 1 surface (in FIG. 5) , Indicated by a solid line) and a laser beam that is transmitted through the mask 1 surface and reflected by the wafer 2 surface (indicated by a chain line in FIG. 5), and is disposed at a position facing the laser diode 12. Interference fringes are detected on the CCD sensor 14 thus formed.

In this case, the pitch T of the interference fringes is determined by the mask 1
Since it depends on the gap distance G between the mask 1 and the wafer 2, the gap distance G between the mask 1 and the wafer 2 is measured by measuring the pitch T of the interference fringes by a predetermined signal processing method.
Is required.

[0008]

However, in such a conventional gap measuring method, the CCD sensor 14 detects the interference generated by the laser light emitted from the laser diode 12 to the mask 1 and the wafer 2. Therefore, in order to obtain the gap distance G, a space for securing the optical path of the laser light is required.

That is, in such a method, the mask-
In some cases, it cannot be realized due to the effect of the alignment mechanism between the wafers, and in particular, the alignment mechanism performs the alignment by applying the image processing method to the metallographic image of the alignment mark on the mask-wafer. As shown in FIG. 6, the microscope objective lens 15 blocks the optical path of the interference light, and there is a problem that such a positioning mechanism cannot coexist with the above-mentioned gap measuring mechanism. there were.

[Object] Therefore, an object of the present invention is to provide a gap measuring method for accurately measuring a mask-wafer gap without being affected by the alignment mechanism.

[0011]

In order to achieve the above object, a gap measuring method according to the present invention comprises a first measuring object which partially transmits a light beam and a first measuring object which is arranged at a predetermined distance from the first measuring object. A gap measuring method for measuring a distance between two measurement objects, by the imaging optical system for forming an image at an arbitrary focal position, the first measurement object, or the second measurement object The focus position when directly imaged on the attached target mark is measured, and the image is formed on a higher-order mirror image obtained by multiple reflection between the first measurement object and the second measurement object. The focus position at that time is measured, and the distance between the first measurement target and the second measurement target is determined based on the difference between the measured focus positions and the dimensionality of the mirror image formed by multiple reflection. It is configured to measure.

In this case, it is effective that the first measurement object is a mask, the second measurement object is a wafer, and the imaging optical system is a metal microscope in a proximity exposure apparatus.

[0013]

According to the present invention, the imaging optical system measures the focus position when an image is directly formed on the target mark attached to the first measurement object or the second measurement object. The focus position when imaged on a higher-order mirror image obtained by multiple reflection between the measurement target and the second measurement target is measured, and the difference between each measured focus position and the multiple reflection form an image. The distance between the first measurement target and the second measurement target is measured based on the dimension number of the mirror image.

This is because the difference between the focal positions measured by the above-mentioned method is an integral multiple of the distance between the first measurement object and the second measurement object, and this value is formed by multiple reflection. This is because it matches the number of dimensions of the mirror image. That is, the distance between the first measurement object and the second measurement object is accurately measured without being affected by the structure of the alignment mechanism.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 and 2 are diagrams showing an embodiment of the gap measuring method according to the present invention, and FIG. 1 is a schematic diagram of a proximity exposure apparatus to which the gap measuring method of the present invention is applied. First, the configuration will be described.

In FIG. 1, the same numbers as the numbers given to the conventional example shown in FIG. 3 indicate the same parts. The exposure apparatus of this embodiment is roughly classified into a metal microscope section 20 and a control section 2.
1, the metal microscope unit 20 is provided with a stage 3, a mask ring 4, a mask Z stage 5, a microscope barrel stage 6, and a metal microscope barrel 7 on the upper side, and a control unit 21 includes a CCD camera 8, a control circuit 9, The image processing apparatus 10 and the stage controller 11 are provided.

In the figure, M is a target mark formed on the wafer 2. In the above configuration, the microscope image of the target mark M on the wafer 2 is analyzed in the image processing apparatus through the CCD camera, and the analysis result is fed back to the stage control system. In this system, in addition to gap alignment, a series of pre-exposure treatments such as focus alignment and mask-wafer alignment are performed.

The operation will be described below with reference to FIG. First, the mask 1 is preset at a position far away from the designated gap, and the target mark M on the wafer 2 is focused by the metallographic microscope. Focusing of the metallographic microscope is performed by taking a metallographic image of the target mark M with a CCD camera, and then detecting a peak of the image by the image processing apparatus 10 so that the peak intensity becomes maximum and the vertical position of the metallographic microscope 10 is adjusted. Is adjusted.

Next, while observing the metallographic microscope image, the metallographic microscope barrel 7 is moved downward by a value that is twice the specified gap, and the mask 1 is moved at the point where the mirror image of the target mark M is in focus. The gap adjustment is completed. That is, as shown in FIG. 2A, the focus position of the target mark M on the wafer 2 observed by the metallographic microscope and the mirror image once reflected on the back surface of the mask 1 as shown in FIG. Since the difference from the focus position is twice the gap interval, the distance of half of the obtained difference in focus position is the gap G, which is not affected by the structure of the alignment mechanism. The gap between the wafers is accurately measured.

Even when the target mark M is formed on the mask 1, as shown in FIG.
The difference between the focal position of the target mark M on the mask 1 observed by a metallographic microscope and the focal position of the mirror image once reflected on the surface of the wafer 2 as shown in FIG. Therefore, the distance of half of the difference between the obtained focal positions is the gap G, and similarly to the above case, the gap between the mask and the wafer is not affected by the structure of the alignment mechanism. Accurately measured.

As described above, in this embodiment, in the gap measuring method using the metallurgical microscope in the proximity exposure apparatus, the gap can be easily measured using the same system as that used for alignment. In principle, the mask
Since a high-order mirror image due to multiple reflections can be created between the wafers,
Gap measurement can also be performed based on this higher-order mirror image, but the above embodiment has been described taking the case where a secondary mirror image is used to obtain the focal position of the target mark as an example.

This is because the signal strength decreases as the order increases, so a secondary mirror image is used to prevent deterioration of accuracy due to the signal strength shortage, but measures against the signal strength shortage are taken. If a sufficient signal strength is obtained, the gap is not limited to the above embodiment, and the gap may be measured using, for example, a mirror image of the third order or higher.

[0023]

According to the present invention, the imaging optical system measures the focus position when the image is directly formed on the target mark attached to the first measurement object or the second measurement object. The focal position of the high-order mirror image obtained by multiple reflection between the measurement target and the second measurement target is measured, and the difference between the measured focus positions and the mirror image formed by multiple reflection. The distance between the first measurement object and the second measurement object can be measured based on the number of dimensions.

Therefore, the distance between the first measurement object and the second measurement object can be accurately measured without being affected by the structure of the alignment mechanism.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a proximity exposure apparatus to which a gap measuring method of the present invention is applied.

FIG. 2 is a diagram for explaining a gap measuring method according to the present embodiment.

FIG. 3 is a diagram for explaining a gap measuring method according to another embodiment.

FIG. 4 is a schematic diagram of a proximity exposure apparatus to which a gap measuring method of a conventional example is applied.

FIG. 5 is an enlarged view of a main part for explaining a gap measuring method of a conventional example.

FIG. 6 is a diagram for explaining a problem of the conventional example.

[Explanation of symbols]

 1 Mask 2 Wafer 3 Wafer Stage 4 Mask Ring 5 Mask Z Stage 6 Stage for Microscope Cylinder 7 Metal Microscope Cylinder 8 CCD Camera 9 Control Circuit 10 Image Processing Device 11 Stage Controller 12 Laser Diode 13 Focusing Lens 14 CCD Sensor 15 Microscope Objective Lens G Gap interval T Pitch M Target mark

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03F 9/02 H 9122-2H

Claims (2)

[Claims] 1. A gap measuring method for measuring a distance between a first measuring object which partially transmits a light beam and a second measuring object arranged at a predetermined distance from the first measuring object. With an imaging optical system that forms an image at an arbitrary focus position, the focus position when directly imaged on the target mark attached to the first measurement object or the second measurement object is determined. Along with the measurement, the focus position when an image is formed on a high-order mirror image obtained by multiple reflection between the first measurement target and the second measurement target is measured, and the difference between the measured focus positions is measured. And the gap between the first measurement object and the second measurement object based on the number of dimensions of the mirror image formed by multiple reflection. 2. The first measurement object is a mask, the second measurement object is a wafer, and the imaging optical system is a metallographic microscope in a proximity exposure apparatus. Gap measurement method.