JPH06229933A - Observation method - Google Patents

Abstract

PURPOSE:To obtain an image having a high contrast between a pattern being transparent for a visible light and the other part, on the occasion when an object of inspection whereon the pattern transparent for the visible light is formed is illuminated by an illuminating light, an image of the object is formed on a prescribed plane of observation and the object is observed. CONSTITUTION:An infrared light is selected from a light of a light source 1 by a filter 2 and a pattern 6 of a transparent conductive film on a glass base 7 is illiminated vertically by this infrared light through the intermediary of a relay lens 3, a half mirror 4 and an objective lens 5. A reflected light from the pattern 6 forms an image of an object of inspection on an image- sensing element 8 via the objective lens 5 and the half mirror 4. Since the reflectance of the transparent conductive film for an infrared ray is high, an image having a high contrast between the part of the pattern 6 of the transparent conductive film and the part of the glass base 7 is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an observation method suitable for observing a liquid crystal substrate or the like with an alignment system of, for example, a microscope, a defect inspection apparatus or an exposure apparatus.

[0002]

2. Description of the Related Art Conventionally, when a defect of a semiconductor element such as an LSI is inspected, the presence / absence of a defect or the type of the defect is automatically and rapidly detected based on an image pickup signal obtained by picking up an image of the semiconductor element. Defect inspection equipment is used. In general, since a semiconductor element has a fine metal pattern formed on a silicon wafer or the like, the illumination for defect inspection is epi-illumination, and visible light is used as illumination light.

Further, in an exposure apparatus used for exposing a mask pattern onto a silicon wafer or the like when a semiconductor element is manufactured by a photolithography process,
An alignment system for aligning a mask with a substrate such as a silicon wafer is provided. An observation system for detecting the position of an alignment mark formed of a metal thin film on a substrate is arranged in such an alignment system, and this alignment system detects the alignment mark using visible light.

[0004]

Recently, miniaturization of liquid crystal display elements has progressed, and liquid crystal display elements are automatically and rapidly operated based on an image pickup signal of the liquid crystal display elements as in the case of semiconductor elements. There is a demand for a defect inspection device that detects defects. However, in general, a liquid crystal display element is one in which a circuit pattern is formed on a glass substrate by a transparent conductive film transparent to visible light. Therefore, if visible light is used as the illumination light in the defect inspection, only an image with a low contrast between the glass substrate portion and the pattern portion of the transparent conductive film can be obtained, and good imaging for accurate defect inspection can be obtained. There was the inconvenience that no signal was obtained.

Liquid crystal display elements are also mass-produced by an exposure apparatus. In an alignment system for aligning a glass substrate of a liquid crystal display element with a mask, the glass substrate is exposed to visible light, for example. It is necessary to detect the position of the alignment mark formed of a transparent film. Also in this case, if visible light is used as the light for alignment, only an image with low contrast can be obtained, and the alignment accuracy is low.

In view of the above point, the present invention illuminates an object on which a pattern transparent to visible light is formed with illumination light,
When an image of the test object is formed on a predetermined observation surface and the test object is observed, it is possible to obtain an image having a high contrast between the pattern transparent to visible light and other parts. The purpose is to provide a possible observation method.

[0007]

According to the observation method of the present invention, an object on which a pattern (6) transparent to visible light is formed is illuminated with illumination light, and a predetermined observation surface (8) is illuminated. In the method of observing the test object by forming an image of the test object and photoelectrically converting the formed image, infrared rays (infrared light) are used as the illumination light. .

When the object to be inspected is epi-illuminated with the illumination light and an image of the object to be inspected is formed by the reflected light from the object to be inspected, the wavelength range of the illumination light is 1 μm to. 5 μm
Is desirable. Further, when the object to be inspected is transmitted and illuminated with the illumination light and an image of the object to be inspected is formed by the transmitted light from the object to be inspected, the wavelength range of the illumination light is set to 1 μm.
It is desirable that the thickness is m to 3 μm.

[0009]

According to the present invention, infrared rays are used as illumination light. If the test object is a liquid crystal substrate, the pattern (6) transparent to visible light is a transparent conductive film. Generally, as shown by the curves C1 and C2 in FIG. 2 showing the characteristics of the transmittance and the reflectance of the transparent conductive film, the transparent conductive film has a wavelength of about 1 μm as a boundary, and the visible light having a smaller wavelength has a higher transmittance and is reflected. Although the reflectance is low, infrared rays (infrared light) having a larger wavelength have a higher reflectance and a lower transmittance. Therefore, for example, in the case where a transparent conductive film is formed on a normal glass substrate, if infrared light is used as illumination light, the contrast between the glass substrate portion and the transparent conductive film portion will be good whether it is epi-illumination or transmitted illumination. Higher images are obtained.

When the object to be inspected is a liquid crystal substrate,
The transmittance of an ordinary glass substrate used as a substrate sharply decreases when the wavelength exceeds about 3 μm. However, in the case of epi-illumination, the contrast of an image obtained is little affected even if the illumination light is absorbed by the glass substrate portion, so infrared light having a wavelength of about 1 μm to 5 μm can be used as the illumination light.

On the other hand, when observing the liquid crystal substrate with transmitted illumination, the image becomes dark on the entire surface when the wavelength exceeds about 3 μm.
Therefore, in the case of transmitted illumination, the wavelength range of the illumination light is 1
Infrared rays of about 3 μm to 3 μm are desirable.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the observation method according to the present invention will be described below with reference to FIGS. This first embodiment deals with the case of epi-illumination. FIG. 1 shows an optical system of an observing apparatus to which the observing method of this example is applied. In FIG. 1, a dotted ray is a conjugate relation of light incident on a test object, and a solid ray is a light from the test object. Represents the conjugate relation of. As the light source 1 for illumination, an incandescent lamp or a halogen lamp that emits light including infrared rays is used.

The light emitted from the light source 1 has a wavelength of 1 μm.
The illumination light made of infrared rays that has entered the filter 2 that transmits only light in the infrared region exceeding a certain level and is emitted from the filter 2 travels to the half mirror 4 via the relay lens 3 for illumination. The illumination light reflected by the half mirror 4 passes through the objective lens 5 and illuminates an illumination area in a predetermined range on the glass substrate 7 with a substantially uniform illuminance. A transparent conductive film pattern 6 such as an ITO film is formed on the glass substrate 7,
A liquid crystal substrate is composed of the glass substrate 7 and the transparent conductive film pattern 6.

Glass substrate 7 and transparent conductive film pattern 6
The reflected light from passes through the objective lens 5 and the half mirror 4, and forms an image of the glass substrate 7 and the pattern 6 of the transparent conductive film on the image pickup surface of the image pickup device 8 such as a two-dimensional CCD. The image pickup device 8 of this example may have a sensitivity mainly to infrared rays. FIG. 2 shows general reflectance and transmittance characteristics of the transparent conductive film. As can be seen from the curve C1 showing the transmittance of FIG. 2, the transmittance of the transparent conductive film is high in the visible light region. It is small in the infrared region where the wavelength exceeds about 1 μm. On the other hand, as can be seen from the curve C2 showing the reflectance in FIG. 2, the reflectance of the transparent conductive film is low in the visible light region and the wavelength is 1 μm.
It is high in the infrared region exceeding about m.

Therefore, in this example, the illumination light has a wavelength of 1 μm.
Infrared rays exceeding about m, that is, light in a wavelength range in which the pattern 6 of the transparent conductive film has a large reflectance is used. However, when the wavelength of the illumination light exceeds approximately 3 μm, the illumination light is not absorbed and is not transmitted by ordinary glass. Therefore, the wavelength is 3 μm
When using infrared rays exceeding 1, use a special optical material such as silicon or germanium instead of ordinary glass as the optical material for the relay lens 3 for illumination, the half mirror 4 and the objective lens 5 of FIG. There is a need to. The upper limit of the wavelength that can be used as the illumination light is about 5 μm.

However, as can be seen from the curve C2 in FIG. 2, since the reflectance of the transparent conductive film is very high even with light having a wavelength of about 2 μm, the optical members such as the half mirror 4 and the objective lens 5 are made of glass, It is also possible to share the optical system with the case of using visible light as the illumination light. When the optical system is shared in this way, the filter 2 becomes unnecessary. Even if the filter 2 is not used, if the observation target is a liquid crystal substrate, visible light almost passes through the glass substrate 7 and the pattern 6 of the transparent conductive film and is discarded, so that the obtained images are almost the same.

As described above, according to this example, since the liquid crystal substrate is observed by epi-illumination using infrared rays as the illumination light, the normal glass substrate 7 portion and the transparent conductive film pattern 6 portion are observed. Therefore, the reflectance of illumination light is relatively different. Therefore, the obtained image is an ordinary glass substrate 7.
Is dark and the pattern 6 of the transparent conductive film is bright, and the image has a high contrast.

Next, a second embodiment of the present invention will be described with reference to FIG. In this example, the observation apparatus of FIG. 1 is used for transmitted illumination, and in FIG. 3, portions corresponding to those of FIG. 1 are denoted by the same reference numerals and detailed description thereof will be omitted. Figure 3
3 shows the optical system of the observation apparatus of this embodiment. In FIG. 3, light including infrared rays from the light source 1A is incident on the filter 2A, and infrared rays passing through the filter 2A pass through the relay lens 3A for illumination and the glass substrate. Illuminate 7 through. The transparent conductive film pattern 6 is formed on the glass substrate 7, and the image of the transparent conductive film pattern 6 is formed on the image pickup surface of the image pickup device 8 by the objective lens 5.

In the case of using transmissive illumination, if the wavelength of the illuminating light is about 1 μm to 3 μm, the glass substrate 7 has a high transmittance, so that good observation is possible. However, since the illumination light having a wavelength of more than 3 μm is absorbed by the glass substrate 7, it is necessary to use a silicon substrate (silicon wafer) or the like instead of the glass substrate 7. Also in this example, the relay lens 3A for illumination and the objective lens 7 can be formed of ordinary glass and can be shared with a system that uses visible light as illumination light. As can be seen from the curve C1, the transmittance of visible light to the pattern 6 of the transparent conductive film is high. Therefore, if the filter 2 is removed, noise due to transmitted light is superimposed on the image of the pattern 6 of the transparent conductive film. Therefore, in the case of transmitted illumination, it is desirable to switch and use the filter 2A depending on whether the illumination light is visible light or the infrared light.

When the illumination light is infrared light in this example, the illumination light is transmitted through the glass substrate 7 (or silicon wafer) portion and is reflected by the pattern 6 portion of the transparent conductive film. Therefore, the obtained image is a high contrast image in which the glass substrate 7 (or silicon wafer) is bright and the transparent conductive film pattern 6 is dark.

Next, a third embodiment of the present invention will be described with reference to FIGS. The present embodiment is an application of the present invention to an observation apparatus capable of switching between epi-illumination and transmitted illumination for observation, and in FIG. 4, parts corresponding to those in FIGS. Is omitted. Here, a liquid crystal substrate will be described as an observation target. In general, most liquid crystal substrates are glass substrates, and wiring is often formed on the glass substrate by a transparent conductive film that is difficult to observe with visible light. In addition, in the liquid crystal display device, apart from the pattern of the transparent conductive film, three types of color filters including a red (R) filter, a green (G) filter and a blue (B) filter are formed on a glass substrate, In most cases, the glass substrate on which the transparent conductive film pattern is formed and the glass substrate on which the color filter is formed are stacked. That is, when observing the liquid crystal substrate, it is necessary to observe not only the transparent conductive film but also any color filter among the red filter, the green filter, and the blue filter.

FIG. 5 shows an example of the transmittance and reflectance characteristics of these three types of color filters. In FIG. 5, the curves CR, CG and CB are the transmittance characteristics of the red, green and blue filters, respectively. ,
A curve C3 shows the reflectance characteristic common to the red filter, the green filter and the blue filter. FIG. 4 shows an optical system of the observation apparatus of this example. In FIG.
After passing through the dichroic filter 2B and the relay lens 3 for selecting the wavelength range of visible light or infrared light and reflected by the Huff mirror 4, the light from is incident on the glass substrate 7 through the objective lens 5. . On the other hand, the lower light source 1A
The emitted light illuminates the glass substrate 7 through the dichroic filter 2C and the relay lens 3A, which select either the visible or infrared wavelength range. Then, the color filter 10 is formed on the glass substrate 7, and the light from the color filter 10 is used as the objective lens 5.
Further, the infrared rays that have entered the dichroic mirror 9 through the half mirror 4 and are reflected by the dichroic mirror 9 are directed to the infrared ray image pickup element 8A, and the visible light that has passed through the dichroic mirror 9 is placed on the visible light image pickup element 8B. Go to An image of the test object under infrared light is formed on the infrared imaging element 8A, and an image of the test object under visible light is formed on the visible light imaging element 8B. It is imaged. In addition,
It is not necessary to use the dichroic mirror 9 to divide the optical path into two as long as it is an image pickup element that can use both infrared rays and visible light.

Next, the use of infrared rays and visible light and the use of epi-illumination and transmission illumination in this example will be described. First, regarding infrared rays and visible light, when the pattern of the transparent conductive film is formed on the glass substrate 7, infrared rays are used as the illumination light as described above. On the other hand, when the color filter 10 is formed on the glass substrate 7, visible light is used as illumination light. However, as can be seen from the reflectance characteristics of FIG. 5, when the color filter 10 is observed by epi-illumination, the reflectance is too low to obtain an image with high contrast.

On the other hand, as can be seen from the curves CR to CB in FIG. 5, the transmittances of the red filter, the green filter and the blue filter are high near their respective wavelengths (red, green and blue). Therefore, the color filter 10
In the case of observing, it is possible to obtain an image with high contrast by using transmitted illumination. However, in a liquid crystal display element (liquid crystal panel), another layer made of a metal layer may be arranged on a glass substrate, and in this case, a color filter is formed on the metal layer. Obviously, it is difficult to observe a color filter on such a metal layer using transmitted illumination. Therefore, in order to observe the color filter on the metal layer, epi-illumination is adopted, and by observing the light transmitted through the color filter and reflected on the surface of the metal layer below the color filter, the color filter is provided with high contrast. I can observe.

In FIG. 4, the dichroic filters 2B and 2C are preferably switched in accordance with the intended use in order to obtain a high-contrast image, but the dichroic filters 2B and 2C are removed. It doesn't matter. Further, as the objective lens 5 used in FIG. 4, it is desirable to use a lens whose aberration is corrected in a wide band from infrared to visible light. However, using the dichroic mirror 9,
When the image sensor is divided into the infrared image sensor 8A and the visible light image sensor 8B, the dichroic mirror 9 is used.
An optical member such as a lens for aberration correction may be inserted between the image pickup device 8A and the image pickup device 8A. Therefore, as the objective lens 5, it is possible to use an objective lens which is easy to design and relatively bright.

Further, when it is difficult to correct aberrations from visible light to infrared rays, the objective lens for visible light and the objective lens for infrared rays are exchanged by a revolver system or the like as used in a microscope, for example. You may use it. As described above, the present invention is not limited to the above embodiment,
Various configurations can be adopted without departing from the scope of the present invention.

[0027]

According to the present invention, infrared rays having a high reflectance with respect to the transparent conductive film are used as illumination light. Therefore,
When the pattern transparent to visible light is the transparent conductive film, there is an advantage that an image having a high contrast between the transparent conductive film portion and other portions can be obtained.

Further, when the object to be inspected is epi-illuminated with illumination light having a wavelength range of 1 μm to 5 μm, an image with high contrast can be obtained especially when the object to be inspected is a liquid crystal substrate. When the test object is transmitted and illuminated with illumination light having a wavelength range of 1 μm to 3 μm, a high-contrast image can be obtained particularly when the test object is a liquid crystal substrate.

[Brief description of drawings]

FIG. 1 is an optical path diagram showing an optical system of an observation apparatus to which a first embodiment of an observation method according to the present invention is applied.

FIG. 2 is a diagram showing characteristics of reflectance and transmittance of a transparent conductive film.

FIG. 3 is an optical path diagram showing an optical system of an observation apparatus to which a second embodiment of the present invention is applied.

FIG. 4 is an optical path diagram showing an optical system of an observation apparatus to which a third embodiment of the present invention is applied.

FIG. 5 is a diagram showing characteristics of reflectance and transmittance of a color filter.

[Explanation of symbols] 1,1A light source 2,2A filter 2B, 2C dichroic filter 3,3A illumination relay lens 4 half mirror 5 objective lens 6 transparent conductive film pattern 7 glass substrate 8, 8A, 8B image sensor 9 Dichroic mirror

Claims (3)

[Claims] 1. An object on which a pattern transparent to visible light is formed is illuminated with illumination light, an image of the object is formed on a predetermined observation surface, and the formed image is formed. In the method for observing the object to be examined by photoelectrically converting, an infrared ray is used as the illumination light. 2. The subject is illuminated with the illumination light by epi-illumination,
The observation method according to claim 1, wherein an image of the test object is formed by reflected light from the test object, and the wavelength range of the illumination light is set to 1 μm to 5 μm. 3. The object is transmitted and illuminated with the illumination light,
The observation method according to claim 1, wherein an image of the test object is formed by transmitted light from the test object, and the wavelength range of the illumination light is set to 1 μm to 3 μm.