KR19980030993A - Target precise position measuring device and measuring method - Google Patents

Abstract

The present invention relates to a precise position measuring apparatus of the target and a method for measuring the same, and a light source for emitting light in order to enable accurate position alignment during overlapping exposure as well as a short alignment range; A target having an alignment mark of an aperiodic pattern diffracting light; A mask disposed between the light source and the target and engraved with a reference mark of an aperiodic pattern serving 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 measuring method by such a precision position measuring apparatus includes the steps of passing light through a mask having a reference mark of an aperiodic pattern; Injecting light passing through the mask into a target having an aperiodic pattern of alignment marks; 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 passing through the spatial filter and measuring the optical signal.

Description

Target precise position measuring device and measuring method

The present invention relates to a precise position measuring apparatus for a target and a measuring method thereof, and more particularly, to a precise position measuring apparatus and a measuring method for a target capable of measuring the precise position of the target using diffracted light.

In the exposure equipment that is essential for manufacturing flat panel displays such as semiconductor memory devices and liquid crystal display devices, which play a key role in the information society, what exactly is to align the target which is the object to be exposed to a predetermined position? More important than that.

Referring to FIG. 1, an alignment light 13 emitted from a light source (not shown) is irradiated with an alignment mark 12 formed on a target 11 that is an exposure target. Here, the alignment mark 12 is formed by arranging a plurality of reflective diffraction gratings 12a having the same width d in the horizontal and vertical directions in a row at a constant period P. The alignment light irradiated thereon Is the same width as The alignment light 13 is reflected and diffracted by the degree of overlapping with the alignment mark 12 while passing over the alignment mark 12. In this case, since the alignment mark 12 is formed on the target 11, the position of the target 11 may be aligned by measuring the change in intensity of diffracted light (arrow) diffracted by the alignment mark 12. Can be.

In such an alignment method, an alignment signal can be obtained until the alignment light 13 overlaps with the alignment mark 12 to be superimposed and separated, that is, until diffraction starts, becomes maximum, and ends. The range in which the alignment signal can be obtained can be within a range of about 2d until the alignment light 13 overlaps the separation mark 12 and then separates the alignment light 12.

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

In addition, in order to engrave a specific pattern, such as an electronic circuit, on the target, it is necessary to sequentially expose several times using a mask on which another pattern is formed. In this process, the alignment mark is easily damaged or deformed. Such damage or deformation may cause a large change in the alignment signal, resulting in different alignment positions in the overlapping exposure.

The present invention has been made to solve the above problems, to provide a precise position measuring device and a measuring method of the target capable of precise position alignment during overlapping exposure as well as a short alignment range.

1 is a view showing that the alignment light is irradiated to the alignment mark formed on the target in the conventional precision position measuring apparatus of the target, (b) is a side view of (a).

Figure 2 is a schematic configuration diagram of a precision position measuring device of the target according to the present invention.

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

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

5 is a view showing a pattern of the spatial filter shown in FIG.

6 is a light intensity graph of an alignment signal detected by the photodetector shown in FIG.

Explanation of symbols for main parts of the drawings

21 ... light source 22 ... collimator

23 ... reflectors 24 ... mask

24a ... reference mark 25 ... beam splitter

26 ... Lens 27 ... Spatial Filter

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

29 ... Photodetector 30 ... Computer

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

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

40 ... alignment signal

In order to achieve the above object, the precise position measuring device of the target of the present invention, the 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 engraved with a reference mark of an aperiodic pattern serving as a reference for alignment; A spatial filter for blocking a part of 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.

In order to achieve the above object, the precise position measuring method of the target of the present invention, the light passing through the mask having a reference mark of the aperiodic pattern; Incident light passing through the mask to a target having an aperiodic pattern of alignment marks; 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 passing through the spatial filter and measuring the optical signal.

Hereinafter, a precise position measuring apparatus and a measuring method of a target according to an embodiment of the present invention will be described in detail with reference to the drawings.

2 to 6, the precision position measuring device of the target of the present invention is provided with a light source 21 for emitting the alignment light, the collimator 22, the reflector 23 and the reference mark on the path of the alignment light The mask 24 formed is provided sequentially. On the path, there is further provided a beam separator 25 for selectively separating the light passing through the mask 24, and the lens 26 for focusing the light passing through the beam separator 25 to the target 31. Is provided. The light passing through the lens 26 is irradiated onto a target 31, which is an exposure target with an alignment mark engraved thereon, and the target 31 is placed on the XY stage 35 capable of plane movement in the X and Y directions. Lost On the other hand, the diffracted light reflected from the target 31 is reflected in a direction different from the initial optical path by the beam splitter 25, and on the optical path of the reflected light, a spatial filter which blocks and partially passes the diffracted light ( 27) is provided. Then, a lens 28 for focusing the diffracted light passing through the spatial filter 27 and a photodetector 29 for receiving the diffracted light passing through the lens 28 are provided, and the photodetector 29 is provided as described above. It is connected with the computer 30 which controls the movement of the XY stage 35. At this time, the light source 21 may be any light source as long as it can emit coherent light such as a mercury light source in which a filter is coupled to a laser light source or a mercury lamp.

Referring to Figure 3, the alignment mark formed on the target, the alignment mark (31a) is made of a reflective diffraction grating 31a 'protruding from the target, each of the diffraction grating 31a' Different rectangular shapes. When the diffraction gratings have the same horizontal and vertical ratios, the light diffracted by the alignment mark engraved on the wafer and the light diffracted by the alignment mark 24a engraved on the mask 24 in the alignment optical system overlap each other. This is because the light diffracted by the alignment mark 24a recorded in the mask 24 acts as optical noise. Therefore, the aspect ratio is changed to prevent such noise. That is, the rectangular 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 arranged at random without being mutually periodic.

Referring to Fig. 4, the reference mark engraved on the mask is described. The reference mark 24a engraved on the mask 24 is made by applying a chrome coating on a glass plate made of glass. At this time, the reference mark (24a) is a region that is not coated with chromium, the cycle in the x, y direction is also formed randomly non-periodic like the alignment mark (31a) engraved on the target (31). Here, the light is not transmitted to the portion coated with chromium, and the light is transmitted only to the reference mark 24a that is not coated. The pattern of this reference mark 24a is the same as that of the alignment mark 31a as a whole.

Referring to FIG. 5, the spatial filter 27 filters the portion of the alignment light diffracted by the alignment mark 31a. The portion indicated by the dots in the figure does not transmit light, and the transparent portion is the filter pattern 27a through which light passes. At this time, the filter pattern 27a engraved on the spatial filter 27 is formed differently from the pattern of the alignment mark 31a, in order to filter out the zero-order diffracted light reflected and diffracted by the alignment mark 31a. .

The spatial filter 27 filters zeroth-order diffraction light and passes ± first-order and ± second-order diffracted light among alignment light diffracted by the alignment mark 31a engraved on the target 31. Therefore, the light intensity of the diffracted light is changed according to the degree to which the alignment light passing through the reference mark 24a overlaps with the alignment mark 31a, and the alignment light having the pattern shape of the reference mark 24 is the alignment mark 31a. If the light does not overlap at all with the alignment light, only the reflection occurs, and thus the filter is filtered by the spatial filter 27 so that no signal is detected by the photodetector 29. And when the diffraction occurs as a little overlap, the photodetector 29 detects the alignment signal 40, as shown in Figure 6, the image of the reference mark 24a and the alignment mark 31a most accurately Diffraction occurs most when matched. In this case, the abscissa coordinate is the stage coordinate X or Y and the ordinate coordinate is the light intensity of the alignment signal. Here, if the 0th light is filtered out by the spatial filter 27 and ± 1,2th light is used as the alignment signal 40, but if it satisfies the purpose of measuring the degree of diffraction, the ± 1,2th light is filtered out. Only shading can be used as an alignment signal.

Referring to the measuring method of the precise position measuring device of the target having such a structure, the light emitted from the light source 29 is made of parallel light of a suitable size while passing through the collimator 22. This light is reflected by the reflector 23 and passes through the mask 24 and the beam separator 25 with the reference mark 24a engraved therein and then enters the target 31 with the alignment mark 31a engraved by the lens 26. The shape of the mark 24a is irradiated on the alignment mark 31a. The light is reflected by the alignment mark 31a and diffracted. At this time, diffraction occurs according to the degree of overlap of the alignment light having the pattern shape of the reference mark 24a and the alignment mark 31a, and passes through the lens 26 to the beam. Reflected by the separator 25 is incident to the spatial filter 27. In the spatial filter 27, zero-order diffracted light of the diffracted light is filtered out and only the remaining light is passed. The light is collected by the lens 28 and collected by the photodetector 29. At this time, the light intensity of the alignment signal 40 detected by the photodetector 29 is changed depending on the degree of overlap of the image of the reference mark 24a and the alignment mark 31a, so that the alignment signal 40 is most accurately overlapped. ) Value is the highest. Therefore, the position of the alignment mark 31a indicated by the alignment signal 40, that is, the position of the target 31 is found, and the XY stage 35 on which the target 31 having the alignment mark 31a engraved is placed is scanned. As a result, each coordinate of the XY stage 35 and the sampled value of the alignment signal 40 input to the computer 30 are matched 1: 1. Therefore, the position of the target 31 is found 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 analyzing the alignment signal 40 drives the XY stage 35 to position the target 31. Go to to perform the sort.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom.

As described above, in the precise position measuring apparatus of the target of the present invention, since the change of the alignment signal 40 occurs when the light passing through the mask 24 overlaps with the alignment mark 31a, the alignment performance range. Is determined by the range where the reference mark 24a and the alignment mark 31a overlap, i.e., its total size.

In addition, since the period of the reference mark 24a or the alignment mark 31a as described above is randomly arranged non-periodically, as shown in FIG. 6, the alignment signal gradually increases with the floor and the valley as shown in FIG. 6. A graph is made. Therefore, the direction in which the light intensity increases can be easily determined, so that alignment can be easily performed.

On the other hand, even if the alignment mark is damaged or dust is contaminated in the process of superimposing exposure to the target, the diffraction due to the overlap with the alignment light is performed in the entire area of the alignment mark, so that the partial alignment mark is damaged or deformed or dusted. The change of the alignment signal due to contamination by is smaller than before. This prevents the alignment position from being changed during overlapping exposure due to such damage or deformation.

Claims (12)

A light source for emitting light; A target engraved with an alignment mark in an aperiodic pattern for diffracting the light; A mask disposed between the light source and the target and engraved with a reference mark of an aperiodic pattern serving as a reference for alignment; A spatial filter for blocking a part of diffracted light reflected from the target; And a photo detector 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 coherent light, such as a laser. The apparatus of claim 1, wherein the light is coherent light made using a mercury lamp and a filter. 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. The apparatus of claim 1, wherein the alignment mark and the reference mark have the same dimension. Passing light through a mask having a reference mark in an aperiodic pattern; Incident light passing through the mask to a target having an aperiodic pattern of alignment marks; 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 that has passed through the spatial filter and measuring the optical signal. 8. The method of claim 7, wherein the light is coherent light, such as a laser. 8. The method of claim 7, wherein the light is coherent light produced using a mercury lamp and a filter. The method of claim 7, wherein the alignment mark comprises a plurality of rows and columns. The method of claim 7, wherein the reference mark comprises a plurality of rows and columns. The method of claim 7, wherein the alignment mark and the reference mark have the same dimension.