JP2003075364A - Device and method for inspecting defect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain detection precision of a defect from being lowered by reflection of irradiated light due to an image-focusing lens or the like, when the defect is detected by irradiation of the light, in a photomask formed with fine patterns. SOLUTION: A light-reflection preventing film is provided between a photomask substrate of an inspection object and a photodetector for detecting transmission light transmitted through the photomask substrate to remove a noise such as reflected light, and the defect is detected at high precision thereby.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect detecting device and a defect detecting method for detecting a defect by irradiating light. More specifically, the present invention relates to a photomask defect detection device and a defect detection method used in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art With the miniaturization of semiconductor circuits, the size of defects allowed on a photomask substrate is becoming smaller and smaller due to the shortening of the exposure wavelength, making it difficult to detect defects. Further, by using a phase shift mask such as a halftone type phase shift mask or a Levenson type phase shift mask, it has become possible to realize miniaturization of semiconductor circuits without shortening the exposure wavelength.
Along with the miniaturization of the pattern of the semiconductor circuit, the pattern of the photomask for transferring the pattern is also miniaturized, and the defect size allowed relative to the pattern formed on the photomask becomes smaller.

As defects that occur on the photomask substrate, there are defects in which the constituent material of the light-shielding film adheres to a region where it is not necessary to form the light-shielding film on the transparent substrate (hereinafter, black defect).
There is a pinhole defect (hereinafter, white defect) in which a part of the light shielding film is missing. The black defect has a light transmitting region around the defect and is easily transmitted with light, and the transmitted light is reduced only in the defect portion, so that the defect can be detected more easily than the white defect. In particular, in order to detect a minute white defect or the like, improvement in the sensitivity of defect detection of the photomask defect inspection device has been improved by shortening the inspection wavelength and reducing the detection size of the photoelectric conversion element. .

[0004]

However, with white defects such as pinhole defects, when the size of the defect is less than the inspection wavelength, the amount of transmitted light sharply decreases. Therefore, in order to detect a white defect, it is important to have a technique for capturing the transmitted minute light with a photoelectric conversion element. At this time, it is often difficult for the photoelectric conversion element to detect the low light amount that has passed through the minute white defect. In particular, when the light detection sensitivity of the photoelectric conversion element is increased, light other than light that has passed through the white defect is detected by the photoelectric conversion element, and it is difficult to detect only the transmitted light from the white defect. become.

Further, the transmitted light that has passed through the white defect may be reflected by an imaging lens before being detected by the photoelectric conversion element, and stray light may be generated. At this time, the signal when the transmitted light for detecting the shape and size of the white defect is detected and the signal when the stray light is detected are mixed in the photoelectric conversion element. Therefore, it is difficult to distinguish a signal for detecting a white defect from a signal due to noise such as stray light, and it is often difficult to accurately detect a minute white defect.

Further, the defect detection due to the shortening of the inspection wavelength requires a drastic change of the optical system such as the light source, the lens and the photoelectric conversion element due to the change of the inspection wavelength, resulting in an increase in equipment cost. Further, as the detection size of the photoelectric conversion element is reduced, the number of scans for inspecting the entire photomask is increased with the reduction of the capture area, which is a region that can be scanned at one time in the defect detection apparatus using the scanning method. This increases the defect inspection time.

Therefore, the present invention is a defect detecting apparatus and a defect detecting method capable of detecting a defect by irradiating light, and in the defect detecting apparatus, the light which has passed through the defect can be accurately detected by the light detecting section. And a defect detection method.

[0008]

A defect detecting apparatus of the present invention is a defect detecting apparatus for detecting defects by irradiating an inspection object with light and preventing reflection of transmitted light which has passed through the inspection object. It is characterized by having antireflection means for In the defect detection device, by providing an antireflection film of light between the photomask and the photodetector provided to detect the defect of the photomask, not only black-based defects but also minute white-based defects are detected. can do.

Further, by forming an antireflection film of light on an imaging lens for forming an image of the transmitted light which has passed through the white defect on the photodetector, only the light transmitted through the white defect is detected by the photodetector. It can be detected, and the generation of noise due to stray light or the like can be suppressed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A defect detecting apparatus and a defect detecting method to which the present invention is applied will be described in detail with reference to the drawings.

FIG. 1 is a schematic view showing an example of the structure of a defect detecting device. The defect detection apparatus of this example includes a light source 1, a condenser lens 2, an imaging lens 4, a photoelectric conversion element 5, and an antireflection film 6. A photomask 3 which is an inspection object is mounted on a photomask defect detection device including these components,
The defects formed on the photomask 3 are detected.

The light source 1 can use light having a short wavelength such as ultraviolet rays for detecting fine defects, but is not limited to ultraviolet rays, and light having an appropriate wavelength can be used depending on the size of the defect to be detected. You can choose. Moreover, you may use these laser beams. In addition, for detection of defects in photomasks used for forming fine circuit patterns, such as halftone type phase shift masks and Levenson type phase shift masks, it is possible to use light with a short wavelength such as ultraviolet rays. It is applied.

The condenser lens 2 is a convex lens used for condensing the light emitted from the light source 1 and irradiating the inspection area of the photomask 3 with the light. In particular, the accuracy of defect detection can be improved by using a lens having a large numerical aperture in order to increase the resolution in defect detection.

The antireflection film 6 is an object to be inspected, and transmitted light which has passed through the photomask substrate 3 on which a pattern is formed is reflected on the surface of the imaging lens 4, and the light is reflected on the photomask substrate 3. It is provided to prevent the light from re-entering the imaging lens 4 after being irradiated. In the defect detection device of this example, between the imaging lens 4 and the photomask substrate 3,
A plate-shaped antireflection film 6 is provided using a material that hardly reflects the transmitted light that has passed through the photomask substrate 3. The present invention is not limited to this, and it is also possible to form an antireflection film by forming a material having light transmittance as a base material and forming an antireflection film on the surface of a plate having a flat surface. As a material for forming the antireflection film 6, a fluoropolymer or the like used as a dustproof film of a photomask can be used. Furthermore, a multilayer film is formed by a vapor deposition method on a glass substrate or the like that transmits light in the wavelength range of the light emitted from the light source,
An antireflection film can also be formed. When the wavelength of light used for defect detection is changed, the selectivity of the wavelength of light that can be used for defect detection is also improved by using the antireflection film with the structure of the multilayer film changed.

The imaging lens 4 transmits the light transmitted through the photomask substrate 3 and the antireflection film 6 into the photoelectric conversion element 5.
It is an optical lens used to form an image. The photoelectric conversion element 5 is formed on the photomask substrate 3 by changing the intensity of light imaged on the photoelectric conversion element 5 when the image is formed on the photoelectric conversion element 5 by the imaging lens 4 into a current value. It is an element that visualizes the pattern shape. As the photoelectric conversion element 5, for example, a photomultiplier tube, a photodiode or the like can be used. A defect on the photomask substrate 3 can be detected by comparing the pattern formed on the photomask substrate 3 which is an inspection object with the image detected by the photoelectric conversion element 5.

Next, a defect detecting method using the defect detecting apparatus of this example will be described. First, the light emitted from the light source 1 is focused by the condenser lens 2 and applied to the inspection area on the photomask substrate 3. At this time, a part of the surface of the photomask substrate 3 is irradiated with light, the light irradiation region is sequentially moved, and by repeating this, the entire region on the photomask substrate 3 can be inspected. Further, it is possible to inspect a wide area by collectively exposing the photomask substrate 3.

Next, the transmitted light that has passed through the photomask substrate 3 passes through the antireflection film 6 and enters the imaging lens 4.
At this time, a part of the transmitted light is reflected on the surface of the imaging lens 4. Most of a part of the reflected transmitted light is absorbed by the antireflection film 6 and does not enter the imaging lens 4 again. Therefore, when the light reflected by the imaging lens 4 enters the imaging lens 4 again and reaches the photoelectric conversion element 5, the contrast of the image of the pattern formed on the photomask substrate 3 is imaged on the photoelectric conversion element 5. Is hardly reduced. In particular, when the size of a white defect in which a part of the pattern on the photomask substrate 3 is missing is very small, the amount of transmitted light that passes through the white defect is small and noise such as reflected light is present. Since it becomes difficult to detect a minute white defect, it becomes possible to increase the defect detection accuracy by eliminating reflected light.

The brightness of the light imaged on the photoelectric conversion element 5 is
It is converted into a current value and recognized as an image of the pattern formed on the photomask substrate 3. Defects are detected by comparing this image with the image of a defect-free pattern.

In particular, when inspecting a photomask having a fine pattern such as a halftone type phase shift mask or a Levenson type phase shift mask, the light and dark pattern of light detected by the photoelectric conversion element 5 is used. It is important to detect with good contrast. Therefore, by reducing noise such as reflected light generated when the photomask substrate 3 is inspected, it is possible to clearly detect the image of the pattern shape formed on the photomask substrate, and to detect even fine defects. It is possible to improve the detection accuracy.

FIG. 2 is a schematic view showing another example of the structure of the defect detection apparatus, which is an image forming lens 14 on which a light source 11, a condenser lens 12, a photoelectric conversion element 15 and an antireflection film 16 are formed.
Composed of. The photomask 13 which is the inspection object is arranged in the photomask defect detection apparatus including these components, and the defect formed on the photomask 13 is detected.

The light source 11 can use light having a short wavelength such as ultraviolet rays for detecting fine defects, but is not limited to ultraviolet rays, and light having an appropriate wavelength can be used depending on the size of the defect to be detected. You can choose. Moreover, you may use these laser beams. Also, like halftone type phase shift mask and Levenson type phase shift mask,
In order to detect defects in a photomask used for forming a fine circuit pattern, it is particularly applicable to use light having a short wavelength such as ultraviolet light.

The condenser lens 12 is a convex lens which is used for condensing the light emitted from the light source 1 and irradiating the inspection area of the photomask 3 with the light. In particular, the accuracy of defect detection can be improved by using a lens having a large numerical aperture in order to increase the resolution in defect detection.

The image forming lens 14 is an optical lens used for forming an image on the photoelectric conversion element 5 of the transmitted light that has passed through the photomask substrate 3 and the antireflection film 6. An antireflection film 16 is formed on the surface of the imaging lens 14 on the photomask 13 side. The antireflection film 16 is formed by coating the surface of the photomask 13 with a material that hardly reflects light, and can be formed of, for example, a fluoropolymer. Further, a multilayer film may be formed by a vapor deposition method on a glass substrate or the like that transmits light in the wavelength range of light emitted from a light source to form an antireflection film. When the wavelength of light used for defect detection is changed, the selectivity of the wavelength of light that can be used for defect detection is also improved by using the antireflection film with the structure of the multilayer film changed.

The photoelectric conversion element 15 changes the intensity of the light imaged on the photoelectric conversion element 5 into a current value when the transmitted light is imaged on the photoelectric conversion element 15 by the imaging lens 14. It is an element for imaging the pattern shape formed on the substrate 13. As the photoelectric conversion element 15, for example, a photomultiplier tube, a photodiode or the like can be used. A defect on the photomask substrate 13 can be detected by comparing the pattern formed on the photomask substrate 13 as the inspection object with the image detected by the photoelectric conversion element 15.

[0025]

EFFECTS OF THE INVENTION In a defect detecting apparatus for detecting a defect by irradiating light, it is possible to detect a defect with high accuracy by reducing noise incident on a photoelectric conversion element which is a photodetector. In particular, when detecting minute white defects formed in a fine pattern such as a photomask, the antireflection film prevents the reflected light generated in the optical path from the light source to the photoelectric conversion element that is the photodetector. By doing so, it is possible to detect a defect with high accuracy in a low light amount of transmitted light that passes through a white defect without using a short-wavelength light source.

Furthermore, by providing an antireflection film on the defect detection device, the defect detection device can be made simple in structure, and minute white defects can be detected with high accuracy without adding a great deal of cost to the defect detection device. It becomes possible to do.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of the structure of a defect detection device of the present invention.

FIG. 2 is a schematic view showing another example of the structure of the defect detecting device of the present invention.

[Explanation of symbols]

1, 11 light source 2,12 condenser lens 3, 13 Photomask substrate 4, 14 Imaging lens 5, 15 Photoelectric conversion element 6, 16 Anti-reflection film

Claims (12)

[Claims] 1. A defect detection apparatus for irradiating an inspection object with light to detect a defect, comprising a reflection preventing means for preventing reflection of transmitted light transmitted through the inspection object. Detection device. 2. The defect detecting apparatus according to claim 1, wherein the inspection object is a photomask. 3. The defect detection device according to claim 1, wherein the transmitted light is detected by a photodetector. 4. The defect detection device according to claim 3, wherein the photodetector is a photoelectric conversion element. 5. The defect detecting apparatus according to claim 3, further comprising an image forming means for forming an image of the transmitted light transmitted through the inspection object on the photodetector. 6. The defect detecting apparatus according to claim 5, wherein the image forming means is an optical lens. 7. The antireflection means is provided between the inspection object and the photodetector.
The defect detection device described. 8. The defect detecting apparatus according to claim 5, wherein the antireflection means is provided in the image forming means. 9. The defect detecting apparatus according to claim 1, wherein the antireflection means is an antireflection film. 10. The defect detection device according to claim 9, wherein the antireflection film is a fluoropolymer film. 11. A defect detecting method for detecting a defect by irradiating an inspection object with light and detecting transmitted light which has passed through the inspection object, wherein reflection of the transmitted light is prevented. Detection method. 12. The defect detecting method according to claim 11, wherein reflection of the transmitted light is prevented between the inspection object and a photodetector for detecting the transmitted light.