JPH06105168B2 - Thin film pattern detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention detects the thin film pattern by irradiating the sample surface on which the thin film pattern is formed with light and detecting the reflected light or transmitted light thereof. In particular, the present invention relates to an apparatus suitable for detecting a thin film pattern on a sample in which reflected light or transmitted light causes an interference phenomenon due to an optical effect of a thin film formed on a sample surface.

<Prior Art> In recent years, various devices for optically detecting a thin film pattern formed on a substrate have been used in the fields of semiconductor device manufacturing, liquid crystal display device manufacturing, and the like.

For example, in the case of a proximity exposure apparatus used in a photolithography process, a substrate and a photomask arranged in proximity to the substrate are irradiated with visible white light through an objective lens of a microscope, and each reflected light is received and detected. By detecting the relative positional relationship between the alignment mark previously formed on the substrate and the mask alignment mark on the photomask, and correcting the relative positional deviation, Are aligned.

<Problems to be Solved by the Invention> However, like a liquid crystal display device, a substrate on which a transparent electrode film pattern is formed on a glass substrate and a photoresist, particularly a positive photoresist, is applied thereon. In the case of exposing, the light reflected at the photoresist surface, the interface between the photoresist and the glass substrate, the surface of the transparent electrode film pattern, the interface between the transparent electrode film pattern and the glass substrate interferes with each other, and Since the intensity of the interference light changes according to the variation in the film thickness of the photoresist and the film thickness of the transparent electrode film pattern, the contrast of the observed image decreases and the transparent electrode film pattern can be accurately detected. There is a problem in that it does not exist or the pattern shape is erroneously detected. Such a problem may occur not only in the substrate for the liquid crystal display device as described above but also in the substrate on which another thin film pattern is formed.

The present invention has been made in order to solve such a problem, and an optical effect of a thin film formed on the surface of a sample causes an interference phenomenon in reflected light or transmitted light on the sample. An object of the present invention is to provide a thin film pattern detection apparatus which can improve the contrast of an observed image when detecting a thin film pattern and can detect the thin film pattern easily and accurately.

<Means for Solving Problems> The present invention has the following configuration in order to achieve such an object.

That is, the first device according to the present invention is a device that detects the thin film pattern by irradiating the sample surface on which the thin film pattern is formed with light and detecting the reflected light or transmitted light thereof. The wavelength band of the light to be transmitted is set by the wavelength band shifting means, the contrast of each image is detected based on the image data in each wavelength band, and the wavelength band that gives the desired contrast is obtained from that, and the received light is detected. Is for controlling the wavelength band shifting means so that the wavelength band is in this wavelength band.

Further, the second device according to the present invention sets the wavelength band of the light received and detected by the wavelength band shifting means, divides the image data in each wavelength band into a plurality of blocks, and positions them correspondingly. With respect to the blocks of each group, each block having a desired contrast is detected, and the blocks are combined to obtain one observation image.

Hereinafter, the principle common to the present invention will be described by taking the case of detecting a transparent electrode film pattern on a glass substrate coated with a positive photoresist film as an example.

FIG. 10 is a sectional view of a sample S having a thin film pattern formed thereon.

In the figure, reference numeral 1 is a glass substrate, 2 is a transparent electrode film pattern formed on the glass substrate 1, and 3 is a positive type photoresist film applied to the glass substrate 1. The reflectance of the sample S irradiated with the illumination light L ₀ for observation is as follows.

(1) The reflectance at the portion where the transparent electrode film pattern 2 is not formed (hereinafter referred to as the photoresist film portion) is the same as the reflected light L ₁ from the surface of the photoresist film 3 (boundary surface with air). , Is determined by the intensity of the interference light with the reflected light L ₂ from the boundary surface between the photoresist film 3 and the glass substrate 1.

(2) The reflectance at the portion where the transparent electrode film pattern 2 is formed (hereinafter referred to as the transparent electrode film portion) is the same as the reflected light L ₃ from the surface of the photoresist film 3 (boundary surface with air). , The intensity of the interference light between the reflected light L ₄ from the interface between the transparent electrode film pattern 2 and the photoresist film 3 and the reflected light L ₅ from the interface between the transparent electrode film pattern 2 and the glass substrate 1 .

Assuming that the respective refractive indices are constant, the respective reflectances are determined by the thickness of the transparent electrode film pattern 2 and the photoresist film 3, and the wavelength of the light received and detected.

FIG. 11 shows the spectral reflectance at the photoresist film portion. However, the reflectance is shown assuming that the reflectance of the glass substrate is 1, and the same applies to FIGS. 12 to 14 described later.

As is clear from FIG. 11, the reflectance is high at the wavelength where the phases of the reflected light L ₁ and the reflected light L ₂ are intensifying, and conversely, the reflectance is low at the wavelength where the phases are weakening. Further, when the film thickness of the photoresist film 3 changes, the position of the peak of the spectral reflectance curve shown in the same figure moves to the left and right, and its synchronization also changes.

On the other hand, although not shown in FIG. 10, the spectral reflectance when there is only the transparent electrode film pattern 2 on the glass substrate 1 (when there is no photoresist film 3) is as shown in FIG. .

As is clear from FIG. 12, the transparent electrode film pattern 2
Since the film thickness is about 10 to 40 nm, the peak of the spectral reflectance curve as shown in Fig. 11 does not appear in the so-called visible region, and the reflectance monotonically increases as the wavelength becomes shorter. Is. In this case, the change in the thickness of the transparent electrode film pattern 2 appears as a change in the rate of increase in reflectance.

Qualitatively, the spectral reflectance curve of the portion where the photoresist film 3 is present on the transparent electrode film pattern 2 (transparent electrode film portion) is qualitatively obtained by combining the curves of FIG. 11 and FIG. The curve A is shown by the solid line in FIG. The chain line B shown in FIG. 13 shows the curve of the spectral reflectance of the photoresist film portion shown in FIG. 11 for reference.

As is clear from FIG. 13, the curve A of the transparent electrode film part
In comparison with the curve B of the photoresist film, the change in reflectance is large on the short wavelength side, and the average value of reflectance is also large.

The intersection of the curve A and the curve B means that the reflectance of the transparent electrode film portion may be higher or lower than the reflectance of the photoresist film portion depending on the wavelength band. ing. Further, at the wavelength where the curve A and the curve B intersect, there is no difference in the reflectance between the two portions, which means that the contrast cannot be obtained.

Further, the peak positions and periods of the curves A and B change according to the film thicknesses of the photoresist film 3 and the transparent electrode film pattern 2, and such a change not only occurs between different substrates, It also occurs within the same substrate.

By the way, the average value (hereinafter, referred to as the average reflectance) of the spectral reflectance of the transparent electrode portion (or the photoresist film portion) is the curve A (or the curve B) between the wavelength bands of the light received and detected. It can be known by integrating with. That is, the area surrounded by the curve A (or the curve B), the horizontal axis, and the both ends of the wavelength band of the light received and detected indicates the average reflectance in that wavelength band.

From this, according to the conventional device that does not have means for shifting the wavelength band, the wavelength band of the light received and detected is fixed in the visible region of 400 nm to nm as shown in FIG. 13, for example. It can be understood that there is no large difference in average reflectance between the curve A and the curve B, and it is difficult to optically detect the transparent electrode pattern 2 as a difference in contrast.

On the other hand, as shown by the shaded area in FIG. 13, when the light received and detected is shifted to an appropriate wavelength band on the short wavelength side, the average reflectance of the curve A of the transparent electrode film portion is It is considerably higher than that of the curve B of the part. This means that the transparent electrode film portion is observed brighter than the photoresist film portion.

Next, the bandwidth of the received and detected light, which has not been mentioned in the above description, will be described.

If the bandwidth of the detected light is set too wide,
Since the difference in average reflectance between the transparent electrode film portion and the photoresist film portion, that is, the contrast becomes small, it is not preferable to widen the band width too much. On the other hand, if the band width is set too narrow, the influence of the variation in the film thickness of the thin film pattern becomes large. Hereinafter, description will be given with reference to FIG.

When the band width is set to be considerably narrow as indicated by the diagonal lines in the figure, in a certain area on the substrate, for example, as shown in FIG. 14 (a), the average reflectance of the curve A is equal to the average reflectance of the curve B. Since the reflectance is considerably higher than the reflectance, the transparent electrode film pattern 2 can be clearly observed. However, as mentioned above,
Even within the same substrate, there are variations in the film thickness of the transparent electrode film pattern 2 and the photoresist film 3, so the peaks or periods of the curves A and B change.

For example, in another region in the same substrate, the curves A and B are
It is assumed that the curves A ′ and B ′ are changed as shown in FIG. 14 (b). In this case, when observed with light having the same wavelength band as in FIG. 14 (a), there is almost no difference between the average reflectance of the curve A ′ and the average reflectance of the curve B ′, and the contrast is lowered, resulting in a transparent electrode film pattern. 2 cannot be detected optically. Therefore, in such a case, the transparent electrode film pattern 2 is changed by shifting the wavelength band of the light received and detected to the wavelength band surrounded by the two-dot chain line as shown in FIG. 14 (b).
Can be observed.

From the above, even if interference occurs in the reflected light, if the wavelength band of the light received and detected is shifted to an appropriate place, the contrast of the observed image becomes high and the transparent electrode film pattern 2 is optically It turns out that it can be detected.

<Operation> According to the first device of the present invention, the contrast detection means maximizes the contrast in the imaging region.
Since the wavelength band shifting means for shifting the wavelength band of the reflected light or the transmitted light detected by the received light is controlled, for example, even if the film thickness of the thin film pattern varies in each imaging region, the contrast is always good. A thin film pattern is detected.

In addition, according to the second device, the image obtained for each wavelength band is divided into a plurality of blocks, respectively, and blocks that give a desired contrast are combined to form one observation image. Even if there is a variation in the film thickness of the thin film pattern within the imaging region, the thin film pattern is detected in a good state.

<Examples> Examples of the present invention will be described below with reference to the drawings.

Basic Configuration of Thin-Film Pattern Detection Device Before describing the device according to the present invention, the basic configuration of the thin-film pattern detection device will be described for easy understanding. FIG. 1 is a schematic diagram showing the basic configuration of a thin film pattern detection apparatus.

In the figure, reference symbol S is a sample having a thin film pattern formed thereon, and is, for example, a liquid crystal display element substrate as shown in FIG.

The basic thin film pattern detection device includes, for example, a light source 10 that irradiates visible light, a wavelength band shift unit 12, an observation optical system 14, an image pickup unit 16 that receives and detects reflected light. As the imaging unit 16, for example, a two-dimensional CCD camera or the like is used. The image pickup unit 16 is connected to a monitor TV or the like (not shown).

The wavelength band shift unit 12 has a mechanism for selecting the light L ′ having an appropriate wavelength band from the irradiation light L from the light source 10.

Hereinafter, a configuration example of the wavelength band shifting unit 12 will be described with reference to FIGS. 2 to 4.

FIG. 2 is an example of a configuration using a plurality of bandpass filters. In this configuration example, the rotary plate 18 that is rotationally driven intermittently
By attaching a plurality of band filters 20a, 20b, ... Which respectively pass lights of different wavelength bands, an arbitrary band filter can be set in the optical path of the irradiation light L.

According to this example, the operator operates the rotary plate 18 while watching the monitor TV or the eyepiece to confirm the contrast of the observed image for each of the bandpass filters 20a, 20b ,. The bandpass filter that obtains

FIG. 3 shows an example using a prism monochromator. In this configuration example, the light L emitted from the light source 10 is emitted through the entrance slit 22, the concave mirror 24, the prism 26, the reflecting mirror 28, the prism 26, the concave mirror 24, the reflecting mirror 30, and the exit slit 32. There is. The prism 26 is configured to be swingable, and the light L ′ in a desired wavelength band is emitted from the exit slit 32 by changing the swing angle.

According to this example, like the example described in FIG. 2,
Prism 26 for best contrast
The swing angle of is set.

The exit slit 32 shown in the figure is configured so that the slit width can be arbitrarily changed. Therefore, for example, after setting the swing angle of the prism 26,
Even better contrast can be obtained by setting the slit width of the exit slit 32 to an appropriate width.

Further, in this example, the prism 26 is configured to be swingable so as to change the wavelength band of the emitted light L ', but instead of fixing the prism 26, the entire exit slit 32 is configured to be horizontally movable. The output light L ′ can also be
The wavelength band of can be changed.

Further, each part of this example can be modified variously, and for example, the irradiation light L from the light source 10 may be directly incident on the prism 26.

FIG. 4 shows an example using a diffraction grating monochromator. In this example, the diffraction grating 34 is configured to be swingable so that the wavelength band of the emitted light L'is shifted. Other configurations and operations are similar to those of the example shown in FIG.

As described above, in the basic thin film pattern detection apparatus shown in FIG. 1, when the variation in the film thickness of the thin film pattern formed on the sample S is relatively small, the operator does not perform the wavelength band so frequently. Since it is not necessary to operate the shift unit 12, the present apparatus having a basic configuration is suitable for such a sample S.

Embodiment of First Device FIG. 5 is a schematic configuration diagram of an embodiment according to the first device of the present invention. In the figure, the parts designated by the same reference numerals as those in FIG. 1 have the same configuration as the basic device described above, and therefore, the description thereof is omitted here.

The feature of this embodiment is that the image signal output from the image pickup unit 16 is converted into a digital signal by the A / D converter 36 and is taken into the microcomputer 38 so that the contrast of the observed image is maximized. 38 to control the wavelength band shift unit 12.

The microcomputer 38 has an input / output interface 4
0, CPU (Central Processing Unit) 42, ROM (Read Only
Memory) 44 and RAM (Random Access Memory) 46. R
The AM 46 corresponds to image data storage means in the configuration of the present invention, and the CPU 42 corresponds to contrast detection means and control means in the configuration of the present invention.

The operation will be described below with reference to the operation flowchart shown in FIG.

In this embodiment, within the range of the central wavelengths λ _{1 to} λ _N of the emitted light L ′ from the wavelength band shift unit 12 (for example, within the visible light region).
Then, the wavelength is changed at a constant wavelength interval (for example, 10 nm interval).

First, the emitted light L ′ having the central wavelength λ ₁ is emitted from the wavelength band shift unit 12. The image data of the sample S detected by the imaging unit 16 at this time is taken into the microcomputer 38 via the A / D converter 36 and stored in the RAM 46 (step S1). FIG. 7 schematically shows the image data stored in the RAM 46, and the hypotenuse area in the figure corresponds to the image data of the thin film pattern formed on the sample S.

When the image data is loaded into the RAM 46, first, the absolute value of the difference between the image data between the adjacent pixels in the X direction is sequentially calculated (step S2). Then, an addition value δ _X i (i = 1 to n: n is the number of pixels in the X direction) of absolute values of differences in the X direction is calculated for each row (step S3), and the sum Σδ _X of the addition values δ _X i is calculated. i is calculated (step S4).

Next, in the same manner as in the X direction, the absolute value of the difference between adjacent pixels in the Y direction is obtained (step S5), and the addition value δ _Y i (i = 1 to m: m is the number of pixels in the Y direction) (step S6), and the sum Σδ _Y i of these added values δ _Y i is obtained (step S7). Then, the above Σ
The sum of δ _X i and Σδ _Y i is calculated (step S8).

When step S8 is completed, it is confirmed whether the wavelength of the outgoing light L'is the final wavelength λ _N (step S9). If it is not λ _{N, the} wavelength band shifting unit 12 is controlled to change the wavelength band to the next wavelength band. Shift to the wavelength band (λ _{2 in} this case) (step S10),
Return to step S1, perform the processing up to step S8,
Σδ _X i + Σδ _Y i in ₂ is obtained.

Similarly, for each wavelength up to λ _N , Σδ _X i + Σδ _Y i
Ask for. FIG. 8 is a distribution chart of Σδ _X i + Σδ _Y i corresponding to the respective wavelengths λ _{1 to} λ _N , obtained in this way.

When it is confirmed that the processing at the wavelength λ _N is completed (step S9), the process proceeds to step S11, and the maximum value is obtained from the respective Σδ _X i + Σδ _Y i from λ _{1 to} λ _N (step S9).
S12). Then, the wavelength band shift unit 12 is controlled so that the wavelength λ _MAX corresponds to the maximum value (step S12).

As described above, according to this embodiment, since the wavelength band shift unit 12 is controlled so that the contrast in the imaging region is maximized, the operator shifts the wavelength band for each sample or each observation position in the sample. It is not necessary to operate the section 12, the work efficiency can be improved, and it is suitable for an automatic thin film pattern detection apparatus.

The means for detecting the contrast in the imaging region is not limited to the above-described example, and various modifications can be made. For example, among the image data in a certain wavelength band, a plurality of pixels having a large value are selected from the higher order and the average value is calculated, while a plurality of pixels having a smaller value are selected from the lower order and the average value is calculated. However, the difference between these average values may be used as the maximum contrast of the image.

Example of Second Device According to the above-described example of the first device, it is suitable for detecting a thin film pattern of a sample having a small film thickness variation in the imaging region, but it is not uniform in the imaging region. In the case of a large sample, the contrast is lowered at any position in the image pickup area, and it is difficult to detect all patterns in the image pickup area.

The second device described below is suitable for such a sample.

The schematic configuration of the embodiment of the second device is similar to that of the device shown in FIG. The CPU 42 is the second
It corresponds to the block detecting means and the image synthesizing means in the apparatus.

The operation of this embodiment will be described below.

First, as described in the embodiment of the first device, the wavelength band of the outgoing light L'from the wavelength band shifting unit 12 is sequentially shifted to λ ₁ to λ _N , and the image data of each wavelength band is stored in the RAM 46. .

Next, each image data is divided into a plurality of blocks as shown in FIG. In this example, the block is divided into 16 blocks Δ1i to Δ16i (i = 1 to N: N is the number of wavelength bands for which transition is set).

Then, a block of each group corresponding to a position, for example, Δ
_{1 1, Δ1 2, ...,} Δ1i, ..., for .DELTA.1 _N, and performs the same processing as described above contrast calculation process calculates the contrast of each block, the block having among them, the maximum contrast .DELTA.1 Detect _MAX .

Hereinafter, similar processing is performed for the blocks of each group of Δ2i to Δ16i to obtain the block Δ2i having the maximum contrast.
To detect the _{MAX ~Δ16 MAX.}

Each block detected in this way Δ1 _MAX ~ Δ16 _MAX
To synthesize one image. FIG. 9 (b) shows
An image synthesized in this way is shown.

According to the second embodiment of the present invention, the entire thin film pattern in the imaging region can be clearly detected even if the film thickness varies greatly in the imaging region.

In each of the embodiments of the basic device and the first device described above, the light L emitted from the light source 10 is incident on the wavelength band shift unit 12 so that the wavelength band of the light L ′ emitted from the wavelength band shift unit 12 is changed. And the wavelength band of the reflected light received and detected by the image pickup unit 16 is changed by this. However, the wavelength band shift unit 12 causes the wavelength of the reflected light in the optical path of the reflected light from the sample S. The band may be directly displaced.

Further, the wavelength band shifting means in the present invention is not limited to the wavelength band shifting unit 12 as described in FIGS. 2 to 4, but may shift the spectral emissivity instead of the wavelength band shifting unit 12, for example. The same effect can be obtained by using or combining an available light source, an imaging unit capable of changing the spectral sensitivity characteristic, and an observation optical system capable of changing the spectral characteristic.

Further, the wavelength band shifting means in the present invention does not necessarily need to shift the band width of the outgoing light L ', like the exit slit 32 shown in FIGS. 3 and 4, and the band width can be changed. It may be fixed to an appropriate width.

Further, in the above-described embodiments, the so-called coaxial incident illumination type illumination system has been described as an example, but the present invention can also be applied to an illumination system that uses general reflection illumination that is not coaxial.

Furthermore, in the embodiment, the case where the reflected light from the sample surface is detected has been described, but the present invention can be applied to an apparatus that detects the thin film pattern on the sample surface by detecting the transmitted light of the sample. it can.

Further, the present invention is not limited to the exposure device for the liquid crystal display device,
It goes without saying that it can be applied to all devices for optically detecting a thin film pattern.

<Effects of the Invention> As is apparent from the above description, according to the first device of the present invention, the wavelength band shifting unit is configured to maximize the contrast in the imaging region based on the signal from the imaging unit. Since it is controlled, the contrast of the detected image automatically becomes the optimum state, which is convenient for improving the efficiency of the work of detecting the thin film pattern and automatically detecting the thin film pattern.

Further, according to the second device of the present invention, the image data of each wavelength band is divided into a plurality of blocks, and the blocks having the desired contrast are detected from the blocks of each group corresponding to the position. Since an image is created by synthesizing these blocks, the entire pattern can be detected with good contrast even if there is a large variation in the film thickness of the thin film pattern in the imaging region.

[Brief description of drawings]

FIGS. 1 to 4 are explanatory views of a basic thin film pattern detection apparatus. FIG. 1 is a schematic configuration diagram thereof, FIG. 2 is a first configuration example of a wavelength band shifting unit, and FIG. Second wavelength band shift unit
Configuration Example, FIG. 4 is a third configuration example of the wavelength band shifting unit. 5 to 8 are explanatory views of an embodiment according to the first device of the present invention. FIG. 5 is a schematic configuration diagram thereof, FIG. 6 is an operation flowchart, and FIG. 7 is an explanatory diagram of image data. , FIG. 8 is a diagram for explaining the wavelength band selecting operation. FIG. 9 is an explanatory diagram of image data processing in the embodiment according to the second device of the present invention. 10 to 14 are views for explaining the constitution of the present invention, FIG. 10 is a sectional view of a substrate in which a transparent electrode film pattern is covered with a photoresist film, and FIG. 11 is a glass substrate. Spectral reflectance characteristic diagram when there is only photoresist film in
The figure shows the spectral reflectance characteristic diagram when there is only the transparent electrode film on the glass substrate, Fig. 13 shows the spectral reflectance characteristic diagram when the transparent electrode film pattern is covered with a photoresist film, and Fig. 14 shows the illumination light. FIG. 5 is an explanatory diagram showing a change in spectral reflectance when the wavelength band of is set too narrow. S …… Sample 2 …… Transparent electrode film pattern 12 …… Waveband shift part 16 …… Imaging part 38 …… Microcomputer 46 …… RAM

Claims (2)

[Claims] 1. An apparatus for detecting the thin film pattern by irradiating a sample surface on which a thin film pattern is formed with light and detecting the reflected light or the transmitted light thereof, wherein the reflected light or the transmitted light is detected. A wavelength band shifting unit that shifts the wavelength band of light, an imaging unit that receives reflected light or transmitted light from the sample surface to image the sample surface, and for each wavelength band that is set to shift by the wavelength band shifting unit. An image data storage unit that stores each image data obtained from the image pickup unit; a contrast detection unit that detects the contrast of each image based on the image data of each wavelength band stored in the image data storage unit; From the contrast of the image corresponding to each wavelength band, find the wavelength band that gives the desired contrast, and the reflected light or transmitted light is So that, the detection device of the thin film pattern, characterized in that a control means for controlling said wavelength band shifting means. 2. A device for detecting the thin film pattern by irradiating a sample surface on which a thin film pattern is formed with light and detecting the reflected light or the transmitted light thereof, the reflected light or the transmitted light being detected. Wavelength band shifting means for shifting the wavelength band of light, imaging means for receiving reflected light or transmitted light from the sample surface to image the sample surface, and for each wavelength band set to be shifted by the wavelength band shifting means The image data storage means for storing each image data obtained from the image pickup means, and the image data of each wavelength band stored in the image data storage means are divided into a plurality of blocks and correspond in position. For each group of blocks, a block detection unit that detects a block having a desired contrast, and a desired block detected by the block detection unit. Detection device of the thin film pattern comprising the image synthesizing means for synthesizing a plurality of blocks having a contrast.