KR0183658B1 - Parts position measuring apparatus and measuring method therefor - Google Patents

Abstract

The present invention relates to an apparatus for accurately measuring a target and a method of measuring the same, and more particularly, to an apparatus and method for precise position measurement of a target, comprising: a light source for emitting light in order to enable precise alignment during overlay exposure as well as a wide alignment range; A target engraved with an alignment mark of an aperiodic pattern that diffracts light; A mask disposed between the light source and the target and having a reference mark of an aperiodic pattern as a reference of alignment; A spatial filter for blocking a part of the diffracted light reflected from the target; And a photodetector for receiving diffracted light having passed through the spatial filter and photoelectrically converting the optical signal. The method of measuring with the precision position measuring device includes passing light through a mask having a reference mark of an aperiodic pattern; Introducing light passing through the mask into a target having an alignment mark of an aperiodic pattern; Passing diffracted light reflected from the target through a spatial filter to block a portion of the diffracted light; Receiving the diffracted light passing through the spatial filter and measuring the optical signal.

Description

Precision Positioning Device of Target and Method of Measuring It

The present invention relates to an apparatus for accurately measuring a target and a measuring method thereof, and more particularly, to a target precision position measuring apparatus and a measuring method thereof that can measure a precise position of a target using diffracted light.

In an exposure apparatus, which is essentially used for manufacturing a flat panel display such as a semiconductor memory device or a liquid crystal display device, which plays a key role in an information society, it is necessary to precisely align a target, which is an object to be exposed, More important than that.

Referring to FIG. 1, alignment light 13 emitted from a light source (not shown) is irradiated onto an alignment mark 12 formed on a target 11 as an object to be exposed. Here, the alignment marks 12 are formed by arranging a plurality of reflection type diffraction gratings 12a having the same width (d) in the horizontal and vertical directions in a line at a constant period (P) . This alignment light 13 is reflected by the degree of overlapping with the alignment mark 12 as it passes over the alignment mark 12 and varies in degree of diffraction. At this time, since the alignment mark 12 is formed on the target 11, the position of the target 11 is aligned by measuring the intensity change of the diffracted light (arrow) diffracted by the alignment mark 12 .

In such an alignment method, an alignment signal can be obtained until the alignment light 13 overlaps with the alignment mark 12 and overlaps and is separated, that is, diffraction is started, maximum is reached, and end is reached. The alignment performance range from which the alignment signal can be obtained is possible within a range of about 2d until the alignment light 13 is superimposed on and separated from the alignment mark 12. [

However, in general, the alignment mark is formed in a very small range compared to the size of the target, and furthermore, the width d of the alignment mark is very small. Therefore, in order to perform the above-described precision alignment, a prealignment is required to move the position of the alignment mark 12 within the measurement range.

Further, in order to engrave a specific pattern such as an electronic circuit on a target, it is necessary to sequentially and repeatedly perform overlap exposure using a mask having another pattern formed thereon. In this process, the alignment mark is liable to be damaged or deformed. Such damage or deformation may cause a large change in the alignment signal, resulting in different alignment positions during overlap exposure.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a device for precise position measurement of a target capable of precise alignment during overlay exposure as well as a wide alignment range and a measurement method thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing alignment light that is irradiated onto an alignment mark formed on a target in a conventional precision position measuring apparatus for a target, and FIG. 1 (b) is a side view of FIG.

2 is a schematic block diagram of an apparatus for precise position measurement of a target according to the present invention.

Fig. 3 is a view showing an alignment mark of the target shown in Fig. 2, wherein (a) is a front view, and Fig. 3 (b) is a side view of Fig.

Fig. 4 is a view showing a reference mark of the mask shown in Fig. 2, wherein (a) is a front view, and (b) is a side view of (a).

5 shows a pattern of the spatial filter shown in Fig.

Fig. 6 is a graph of the light intensity of the alignment signal detected by the photodetector shown in Fig. 2; Fig.

DESCRIPTION OF THE REFERENCE NUMERALS

21 ... light source 22 ... collimator

23 ... reflector 24 ... mask

24a ... reference mark 25 ... beam separator

26 ... Lens 27 ... Spatial filter

27a ... filter pattern 28 ... lens

29 ... photodetector 30 ... computer

31 ... target 31a ... alignment mark

31a '... reflective grating 35 ... X-Y stage

40 ... Sort signal

According to an aspect of the present invention, there is provided an apparatus for accurately positioning a target, comprising: a light source for emitting light; A target engraved with an alignment mark of an aperiodic pattern for diffracting the light; A mask disposed between the light source and the target and having a reference mark of an aperiodic pattern as a reference for alignment; A spatial filter for blocking a part of the diffracted light reflected from the target; And a photodetector for receiving the diffracted light having passed through the spatial filter and photoelectrically converting the optical signal.

According to an aspect of the present invention, there is provided a method of accurately positioning a target, the method comprising: passing light through a mask having a reference mark of an aperiodic pattern; Introducing light through the mask into a target having an alignment mark of an aperiodic pattern; Passing the diffracted light reflected from the target through a spatial filter to block a part of the diffracted light; And receiving the diffracted light having passed through the spatial filter to measure the optical signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an apparatus for measuring a precise position of a target according to an embodiment of the present invention and a measuring method thereof will be described in detail with reference to the drawings.

2 to 6, the apparatus for accurately positioning a target according to the present invention is provided with a light source 21 for emitting alignment light. A collimator 22, a reflector 23, and a reference mark And a mask 24 formed thereon are sequentially provided. Also provided on the path is a beam splitter 25 for selectively separating the light that has passed through the mask 24 and a lens 26 for focusing the light that has passed through the beam splitter 25 onto the target 31, Respectively. Light that has passed through the lens 26 is irradiated onto a target 31 which is an object to be exposed with an alignment mark engraved. The target 31 is placed on an XY stage 35 capable of performing plane motion in X and Y directions It is. On the other hand, the diffracted light reflected by the target 31 is reflected by the beam splitter 25 in a direction different from the initial optical path. On the optical path of the reflected light, a spatial filter (not shown) 27 are provided. A lens 28 for focusing the diffracted light having passed through the spatial filter 27 and a photodetector 29 for receiving diffracted light having passed through the lens 28 are provided, And is connected to a computer 30 that controls the motion of the XY stage 35. [ At this time, the light source 21 may be any light source as long as it can emit interference light, for example, a laser light source or a mercury light source combining a filter with a mercury lamp.

3, the alignment mark 31a is composed of a reflection type diffraction grating 31a 'protruding from the target, and the horizontal and vertical ratio of each diffraction grating 31a' And have a different rectangular shape. This is because the light diffracted by the alignment mark engraved on the wafer and the light diffracted by the alignment mark 24a engraved in the mask 24 in the alignment optical system are superposed when the aspect ratio of each diffraction grating has the same value, This is because the light diffracted by the alignment mark 24a recorded in the mask 24 acts as optical noise. Therefore, the horizontal and vertical ratios are different in order to prevent such noise. That is, the rectangular-shaped diffraction grating 31a 'is arranged long in the horizontal and vertical directions to form the alignment mark 31a. The alignment marks 31a made of such diffraction gratings 31a 'are not arranged periodically but randomly.

Referring to the reference mark engraved in the mask with reference to FIG. 4, the reference mark 24a engraved on the mask 24 is made by chrome coating the glass plate with glass. In this case, the reference mark 24a is an area without chromium coating, and the period in the x and y directions is formed irregularly randomly as in the case of the alignment mark 31a on the target 31 as well. Here, light is not transmitted through the portion coated with chromium, and light is transmitted only through the reference mark 24a, which is an uncoated portion. The pattern of the reference mark 24a is the same as the pattern of the alignment mark 31a when viewed as a whole.

Referring to FIG. 5, the spatial filter 27 serves to filter out a part of the alignment light diffracted by the alignment mark 31a. In the drawing, a dotted portion is a filter pattern 27a through which light is not transmitted, and a transparent portion is a filter pattern 27a through which light is transmitted. At this time, the filter pattern 27a engraved in the spatial filter 27 is formed differently from the pattern of the alignment mark 31a in order to filter the 0th-order diffracted light reflected by the alignment mark 31a .

The spatial filter 27 filters the 0th order diffracted light in the alignment light diffracted by the alignment mark 31a engraved on the target 31 and passes the ± 1st order and ± 2nd order diffracted light therethrough. Therefore, the light intensity of the diffracted light according to the degree to which the alignment light having passed through the reference mark 24a overlaps with the alignment mark 31a is changed. When the alignment light having the pattern shape of the reference mark 24 is incident on the alignment mark 31a, The alignment light is only reflected, so that all of the light is filtered by the spatial filter 27, so that no signal is detected in the photodetector 29. 6, an alignment signal 40 is detected. When the phase of the reference mark 24a and the alignment mark 31a are the most accurately detected, Diffraction occurs most often when matched. At this time, the abscissa is the stage coordinate (X or Y) and the ordinate is the light intensity of the alignment signal. In this case, if the zero-order light is filtered by the spatial filter 27 and the ± 1, 2-order light is used as the alignment signal 40, if the purpose of measuring the degree of diffraction is met, Only shading can be used as an alignment signal.

The light emitted from the light source 29 passes through the collimator 22 and is made into parallel light of an appropriate size. This light is reflected by the reflecting mirror 23 and passes through the mask 24 and the beam separator 25 engraved with the reference mark 24a and is incident on the target 31 on which the alignment mark 31a is engraved by the lens 26, The shape of the mark 24a is irradiated onto the alignment mark 31a. This light is reflected and diffracted by the alignment mark 31a. At this time, diffraction occurs depending on the degree of overlap of the alignment mark 31a with the alignment light having the pattern shape of the reference mark 24a, Is reflected by the separator (25) and is incident on the spatial filter (27). In the spatial filter 27, the 0th-order diffracted light is filtered to pass only the remaining light, and the light is condensed by the lens 28 and condensed by the photodetector 29. At this time, the light intensity of the alignment signal 40 detected by the photodetector 29 changes according to the degree of overlap of the alignment mark 31a with the phase of the reference mark 24a, and the alignment signal 40 ) Value is the highest. That is, the position of the alignment mark 31a indicated by the alignment signal 40 is found, that is, the position of the target 31. When the alignment mark 31a scans the XY stage 35 on which the target 31 is placed, The coordinates of the XY stage 35 and the sampled values of the alignment signal 40 input to the computer 30 are matched at a ratio of 1: 1. Therefore, the position of the target 31 is calculated by calculating the position of the alignment mark 31a indicated by the alignment signal 40 through a signal processing process. The alignment signal 40 incident on the photodetector 29 is photoelectrically converted and input to the computer 30 and the computer that analyzes the alignment signal 40 drives the XY stage 35 to move the target 31 to a desired position To perform alignment.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

As described above, in the apparatus for accurately positioning the target of the present invention, since the change of the alignment signal 40 occurs from when the light passing through the mask 24 is superimposed on the alignment mark 31a, Is determined by the range in which the reference mark 24a and the alignment mark 31a overlap, that is, the total size thereof.

In addition, since the reference marks 24a and the alignment marks 31a are randomly and non-periodically arranged, the alignment signal according to the degree of overlapping has a floor and a valley and gradually increases . Therefore, the direction in which the light intensity increases can be easily determined, and the alignment can be easily performed.

On the other hand, even if the alignment marks are damaged or dust is contaminated in the process of performing the overlapping exposure on the target, the diffraction due to the overlapping with the alignment light occurs in the entire area formed by the alignment marks, The variation of the alignment signal due to the contamination by the electrode is smaller than that in the prior art. Therefore, such damage or deformation prevents the alignment positions from being different in the overlapping exposure.

Claims (12)

A light source for emitting light; A target engraved with an alignment mark of an aperiodic pattern for diffracting the light; A mask disposed between the light source and the target and having a reference mark of an aperiodic pattern as a reference for alignment; A spatial filter for blocking a part of the diffracted light reflected from the target; And a photodetector for receiving the diffracted light passing through the spatial filter and photoelectrically converting the optical signal. The apparatus of claim 1, wherein the light is interference light such as a laser. The apparatus according to claim 1, wherein the light is an interference light produced by using a mercury lamp and a filter. 2. The apparatus of claim 1, wherein the alignment mark comprises a plurality of rows and columns. The apparatus of claim 1, wherein the reference mark comprises a plurality of rows and columns. 2. The apparatus of claim 1, wherein the alignment mark and the reference mark have the same dimensions. Passing light through a mask having a reference mark of an aperiodic pattern; Introducing light through the mask into a target having an alignment mark of an aperiodic pattern; Passing the diffracted light reflected from the target through a spatial filter to block a part of the diffracted light; And receiving the diffracted light having passed through the spatial filter to measure the optical signal. 8. The method of claim 7, wherein the light is an interference light such as a laser. 8. The method of claim 7, wherein the light is an interference light produced by using a mercury lamp and a filter. 8. The method of claim 7, wherein the alignment mark comprises a plurality of rows and columns. 8. The method of claim 7, wherein the reference mark comprises a plurality of rows and columns. 8. The method of claim 7, wherein the alignment mark and the reference mark have the same dimensions.