Optical apparatus for defect and particle size inspection

What is claimed is:

1. A defect inspecting apparatus comprising:

a stage used for mounting a substrate serving as an object of inspection and having circuit patterns created thereon and used for moving said substrate;

an illumination optical system for radiating an illumination slit-shaped beam from a light source to said substrate in a direction inclined at a predetermined gradient relative to the direction of a line normal to said inspected substrate with its longitudinal direction oriented almost perpendicularly to a direction of a movement of said stage, and has an optical element having a shape of at least a portion of a conical surface for shaping said radiated illumination beam;

a detection optical system for receiving a scattered light reflected by a defect such as a foreign particle existing on said substrate illuminated by said illumination optical system and converting said received light into a detection signal by using an image sensor; and

an image-signal processing unit for extracting a signal indicating a defect such as a foreign particle on the basis of said detection signal output by said image sensor employed in said detection optical system.

2. A defect inspecting apparatus according to claim 1 wherein said image-signal processing unit comprises:

a criterion setting means which sets a criterion on the basis of a variation computed from said detection signal output by said image sensor employed in said detection optical system from locations at which the same circuit patterns are naturally created or positions in close proximity to said locations; and

a signal extracting means which extracts a signal indicating a defect such as a foreign particle from said detection signal output by said image sensor employed in said detection optical system on the basis of the criterion set by said criterion setting means.

3. A defect inspecting apparatus according to claim 1 wherein said image-signal processing unit has a means which extracts a signal indicating a defect such as a foreign particle from said detection signal on the basis of a criterion set for each of a variety of areas constituting said circuit pattern.

4. A defect inspecting apparatus according to claim 1, wherein an optical axis in said detection optical system is substantially perpendicular to said substrate serving as the object of the inspection.

5. A defect inspecting apparatus according to claim 1 wherein, in said illumination optical system, said light source is a laser light source.

6. A defect inspecting apparatus according to claim 1 wherein said illumination optical system is provided with an optical subsystem for radiating an illumination white-color light from a direction inclined with respect to a normal line.

7. A defect inspecting apparatus according to claim 1 wherein a spatial filter is provided in said detection optical system.

8. A defect inspecting apparatus according to claim 1 wherein said image sensor employed in said detection optical system is a TDI (Time Delay Integration) sensor.

9. A defect inspecting apparatus according to claim 1 wherein an optical axis in said detection optical system is inclined with respect to a line normal to said substrate serving as an object of inspection.

10. A defect inspecting apparatus according to claim 1, wherein said illumination beam radiated by said illumination optical system is a DUV (Deep Ultra-Violet) beam.

11. A defect inspecting apparatus according to claim 1, wherein said illumination optical system has said radiating direction inclined at a predetermined gradient on a surface with respect to a group of main straight lines of said circuit patterns.

12. A defect inspecting apparatus comprising:

an illumination optical system which is used for radiating an illumination beam to a surface of an object of inspection in a direction inclined at a predetermined gradient from the direction of a line normal to said surface and is provided with an optical element with a shape of at least a portion of a conical surface for shaping said illumination beam radiated in at least a direction in a surface of said object of inspection;

a detection optical system including an image sensor for receiving a light reflected by said object of inspection and for converting said received light into a detection signal; and

an image-signal processing unit for processing said detection signal output by said detection optical system.

13. A defect inspecting apparatus according to claim 12, wherein an optical axis in said detection optical system is substantially perpendicular to said substrate serving as the object of the inspection.

14. A defect inspecting apparatus according to claim 12 wherein, in said illumination optical system, said light source is a laser light source.

15. A defect inspecting apparatus according to claim 12, wherein said illumination optical system is provided with an optical subsystem for radiating an illumination white-color light from a direction inclined with respect to a normal line.

16. A defect inspecting apparatus according to claim 12, wherein a spatial filter is provided in said detection optical system.

17. A defect inspecting apparatus according to claim 12, wherein said image sensor employed in said detection optical system is a TDI (Time Delay Integration) sensor.

18. A defect inspecting apparatus according to claim 12, wherein an optical axis in said detection optical system is inclined with respect to a line normal to said substrate serving as an object of inspection.

19. A defect inspecting apparatus according to claim 12, wherein said illumination beam radiated by said illumination optical system is a DUV (Deep Ultra-Violet) beam.

20. A defect inspecting apparatus comprising:

an illumination optical system for radiating an illumination light to a surface of an object of inspection on which a plurality of patterns with substantially identical shapes are laid out;

a detection optical system including an image sensor for receiving light reflected by said object of inspection and for converting said received light into a detected image signal; and

an image signal processing unit used for processing said detected image signal output by said detection optical system, comprising

a size specifying means which specifies a size of a defect; and

a control means which controls the power of said illumination optical system in accordance with said defect size specified by said size specifying means.

21. A defect inspecting apparatus according to claim 20, wherein said image-signal processing unit comprises:

a criterion setting means which sets a criterion on the basis of a variation computed from said detection signal output by said image sensor employed in said detection optical system from locations at which the same circuit patterns are naturally created or positions in close proximity to said locations; and

a signal extracting means which extracts a signal indicating a defect such as a foreign particle from said detection signal output by said image sensor employed in said detection optical system on the basis of the criterion set by said criterion setting means.

22. A defect inspecting apparatus according to claim 20, wherein said image-signal processing unit has a means which extracts a signal indicating a defect such as a foreign particle from said detection signal on the basis of a criterion set for each of a variety of areas constituting said circuit pattern.

23. A defect inspecting apparatus according to claim 20, wherein an optical axis in said detection optical system is substantially perpendicular to said substrate serving as the object of the inspection.

24. A defect inspecting apparatus according to claim 20 wherein, in said illumination optical system, said light source is a laser light source.

25. A defect inspecting apparatus according to claim 20, wherein said illumination optical system is provided with an optical subsystem for radiating an illumination white-color light from a direction inclined with respect to a normal line.

26. A defect inspecting apparatus according to claim 20, wherein a spatial filter is provided in said detection optical system.

27. A defect inspecting apparatus according to claim 20, wherein said image sensor employed in said detection optical system is a TDI (Time Delay Integration) sensor.

28. A defect inspecting apparatus according to claim 20, wherein an optical axis in said detection optical system is inclined with respect to a line normal to said substrate serving as an object of inspection.

29. A defect inspecting apparatus according to claim 20, wherein said illumination beam radiated by said illumination optical system is a DUV (Deep Ultra-Violet) beam.

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BACKGROUND OF THE INVENTION

The present invention relates to a defect testing apparatus and a defect testing method for inspecting a state of generation of defects such as foreign particles in a fabrication process such as a semiconductor fabrication process, a liquid-crystal-display fabrication process and a print-board fabrication process wherein a defect such as a foreign particle generated in a process to create a pattern on a substrate to produce an object is detected and analyzed in order to determine a countermeasure.

In the conventional semiconductor fabrication method, a foreign particle existing on a semiconductor substrate also known as a wafer causes a defect such as poor insulation of a wire or a short circuit. Furthermore, in the case of a miniaturized semiconductor device, an infinitesimal foreign particle existing in a semiconductor substrate results in poor insulation of a capacitor or destruction of typically a gate oxide film. These foreign particles are introduced to get mixed with a semiconductor material in a variety of states due to a variety of causes. For example, a foreign particle is generated by a movable part of a transportation apparatus or a human body. A foreign particle can also be generated as a result of a chemical reaction in processing equipment using a process gas or mixed with chemicals or a raw material.

Likewise, if a foreign particle is introduced to get mixed with a pattern, causing some defects in a process to fabricate a liquid-crystal display device, the resulting display device is not usable. The process to fabricate a print board is in the same situation. That is to say, a mixed foreign particle causes a poor connection and a short circuit in a pattern.

One technique for detecting a foreign particle on a semiconductor substrate of this type is disclosed in Japanese Patent Laid-open No. Sho 62-89336 and referred to hereafter as publication 1. According to this prior art, a laser beam is radiated to a semiconductor substrate. If a foreign particle is stuck to the semiconductor substrate, the foreign particle will generate scattered beams which can then be detected and compared with a result of inspection for a semiconductor substrate of the same type inspected immediately before. In this way, a difference in inspection result can be detected and used to eliminate a pattern defect. As a result, a foreign particle and a defect can be detected with a high degree of sensitivity and a high degree of reliability. Another publication referred to hereafter as publication 2 is disclosed in Japanese Patent Laid-open No. Sho 63-135848. According to this publication, a laser beam is radiated to a semiconductor substrate. If a foreign particle is stuck to the semiconductor substrate, the foreign particle will generate scattered beams which can then be detected. A detected beam generated by a foreign particle is analyzed by using an analysis technique such as laser photo luminescence or a secondary X-ray analysis (XMR).

In addition, as a technology for detecting a foreign particle, there is also known a technique whereby a coherent beam is radiated to a wafer, and the beam reflected by repetitive patterns on the wafer is removed by a spatial filter to emphasize light components generated by a foreign particle or a defect which does not exhibit repetitiveness. In this way, a foreign particle or a defect can be detected.

A technology disclosed in Japanese Patent Laid-open No. Hei 1-117024 is referred to hereafter as publication 3. According to this publication, in a foreign particle inspecting apparatus, a beam is radiated to a circuit pattern on a wafer in a direction forming an angle of 45 degrees with respect to a group of main straight lines of the circuit pattern and a 0th-order diffracted beam from the group of main straight lines is introduced into the aperture of an objective lens. The disclosure also includes a description which states that, according to publication 3, a beam from any group of straight lines other than the group of main straight lines is shielded by a spatial filter.

In addition, other publications related to apparatuses and methods for detecting defects such as foreign particles are disclosed in Japanese Patent Laid-open No. Hei 1-250847, Japanese Patent Laid-open No. Hei 6-258239, Japanese Patent Laid-open No. Hei 6-324003, Japanese Patent Laid-open No. Hei 8-210989 and Japanese Patent Laid-open No. Hei 8-271437 and referred to as publications 4, 5, 6 7 and 8 respectively.

With the teachings of publications 1 to 8 mentioned above, however, it is impossible to detect a defect such as an infinitesimal foreign particle on a substrate, on which repetitive patterns coexist with non-repetitive patterns, at a high speed, with ease and with a high degree of sensitivity.

To put it in detail, the teachings of publications 1 to 8 have a problem of a substantially reduced sensitivity (increased minimum dimensions of a detected foreign particle) in the case of a part of the substrate other than the repetitive portion such as memory cells.

In addition, the teachings of publications 1 to 8 also have a problem of a substantially reduced sensitivity in the case of an oxide film which passes a radiation beam.

Moreover, the teachings of publications 1 to 8 also have a problem of inability to detect a defect such as an infinitesimal foreign particle.

Furthermore, in the case of the teachings of publications 1 to 8, a mass-production build-up line or a pilot line and a mass-production line of a semiconductor production process are not distinguished from each other. That is to say, inspection equipment used in the mass-production build-up work is also used in a mass-production line without change in spite of the fact that it is necessary to detect generation of a foreign particle on the mass-production line early, to efficiently determine a countermeasure for the detected foreign particle.

At any rate, the conventional defect inspecting apparatus is large in size and has such a configuration that the apparatus must be installed independently. For this reason, in order to inspect a foreign particle and a defect, it is necessary to transport a semiconductor substrate, a liquid-crystal-display substrate or a print substrate which has been processed along the mass-production line to a place at which the defect inspecting apparatus is installed. That is to say, it takes time to transport the substrate and to inspect the substrate for a foreign particle and a defect. As a result, complete inspection is difficult. In addition, it is hard to carry out such sampling inspection at a sufficiently high frequency.

Further, a defect inspecting apparatus with such a configuration requires an operator.

SUMMARY OF THE INVENTION

It is thus an object of the present invention addressing the problems described above to provide a defect inspecting apparatus and a defect inspection method capable of inspecting a defect such as an infinitesimal foreign particle on an inspected substrate containing repetitive patterns, non-repetitive patterns and non-patterns which coexist with each other at a high speed and with a high degree of precision.

It is another object of the present invention to provide a defect inspecting apparatus and a defect inspection method which allow a high-efficiency substrate fabrication line to be constructed by implementation of complete inspection and sampling inspection at a sufficiently high frequency.

It is still another object of the present invention to provide a defect inspecting apparatus and a defect inspection method which are capable of inspecting also a defect such as an extremely infinitesimal foreign particle having a size of the order of 0.1 .mu.m or smaller at a high speed and with a high degree of sensitivity by effectively utilizing the light quantity of a Gaussian beam generated by an ordinary inexpensive light source such as a laser-beam source.

It is a further object of the present invention to provide a defect inspecting apparatus and a defect inspection method which are capable of inspecting also a defect such as an extremely infinitesimal foreign particle having a size of the order of 0.1 .mu.m or smaller at a high speed and with a high degree of sensitivity by effectively utilizing the light quantity of a Gaussian beam generated by typically a laser-beam source and by resolving a problem of a lack of illumination at regions surrounding an area on a substrate being inspected due to a decrease in MTF at locations separated away from an optical axis in a detection optical system.

It is a still further object of the present invention to provide a defect inspecting apparatus capable of inspecting a defect such as a real foreign particle by setting the level of a threshold value at a proper degree of sensitivity without substantially increasing the amount of generated false information wherein the threshold value is used as a criterion as to whether or not a defect exists in a variety of circuit-pattern areas in the device structure laid out on a substrate being inspected.

It is a still further object of the present invention to provide a defect inspecting apparatus capable of inspecting a defect such as a foreign particle with a specified size to be detected by setting the level of a threshold value used as a criterion as to whether or not a defect exists for the size of the defect to be detected in a variety of circuit-pattern areas in the device structure laid out on a substrate being inspected.

It is a still further object of the present invention to provide a defect inspecting apparatus capable of inspecting a defect such as a foreign particle by allowing the size of the defect existing in a variety of circuit-pattern areas in the device structure laid out on a substrate being inspected to be inferred.

It is a still further object of the present invention to provide a semiconductor-substrate fabricating method for fabricating a semiconductor substrate at a high efficiency and, hence, at a high yield.

In order to achieve the objects described above, the present invention provides a defect inspecting apparatus and a defect inspection method adopted by the defect inspecting apparatus comprising: a stage for mounting and moving an inspected substrate with a circuit pattern created thereon; an illumination optical s