JPH07260705A - Flaw detection system - Google Patents

Abstract

PURPOSE: To provide a substrate defect inspection method and a device thereof suitable for inspection during a production process. CONSTITUTION: A substrate 10 provided with a regular pattern such as a grid is arranged on one side of a lens 12. Light with intense coherency is radiated to the substrate 10. A Fourier transformation body of the pattern is formed on a focal plane 14 of the lens 12. The inspection of the Fourier transformation body provides information related to the presence of a defect in the pattern.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method and apparatus for detecting substrate defects. A particular field of the invention is the inspection of thin film coated flat substrates used in electronics, although the invention is not limited to such applications.

[0002]

BACKGROUND OF THE INVENTION Coating thin films on flat materials to enhance or modify performance is a common industrial process. The material to be coated may be rigid or flexible. The thin film may be transparent, semi-transparent, or opaque. The coating may be either single layer or multiple layers. It may also be patterned by either etching or lift-off techniques. The coating may be applied by any vacuum technique such as physical vapor deposition or another method such as spin coating a liquid.

[0003]

[Problems to be Solved by the Invention]

Whatever coating method is used, the product performance of the coated product is often due to pinholes and other microscopic defects within, below, or above the film. Be lowered. Although the product to be coated is thinly processed at a high speed,
Conventional inspection methods are too slow and in-process inspection is not possible. Typical conventional inspection methods rely on image processing performed by a video camera that provides data to a computer that analyzes the image. Another inspection method is to scan with a laser beam and detect backscattered light. This latter method is not compatible with patterned substrates.

For example, in the manufacture of dynamic matrix liquid crystal displays, current technology has a device assembly production rate of approximately one minute per processing step. It seems that this speed can be reduced to a manufacturing speed of about 1 unit in 10 seconds. However, there are 2 image analysis inspection systems available today.
The inspection time of min / cm ² unit is required, and therefore, the image analysis inspection system needs to increase the inspection speed by about 3 digits (1000 times) so as to enable the inspection in the process.

It is an object of the present invention to overcome or alleviate the above drawbacks and to provide a system which is well suited for in-process inspection.

[0007]

According to the present invention, a method of inspecting a substrate comprises irradiating a substrate with light having a high degree of coherence, forming a Fourier transform body of the substrate irradiated with the light, It is characterized in that light detection is performed on the Fourier transform plane of the dynamic system.

From another aspect, the present invention provides a substrate positioning device for holding a substrate at a predetermined position, a light source of high-coherence light, and irradiation of a high-coherence light beam on the substrate at the predetermined position. An apparatus for inspecting a substrate is provided, which comprises an optical device for forming a Fourier transform body of the substrate irradiated with light, and a detection device located on a Fourier transform surface of the optical device.

[0009]

A grating or other substrate having a regular pattern is placed on one side of the lens. The substrate is irradiated with intense coherent light. A Fourier transform of the pattern is formed on the focal plane of the lens. Inspection of the Fourier transform provides information regarding the presence or absence of pattern defects. This information does not depend on the movement of the pattern within the field of view.

[0010]

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings. FIG. 1 shows Fourier transforms for various optical signals, FIG. 2 is a schematic diagram showing the principle underlying the invention, and FIG. 3 is a schematic diagram of an apparatus according to one embodiment of the invention. 4, FIG. 4 is a schematic diagram of a device modified from the embodiment of FIG. 3, and FIGS. 5 and 6 are schematic diagrams of devices of two further embodiments.

Referring to FIGS. 1 and 2, the principles underlying the present invention will first be described. When an object is illuminated with light of high coherence and that light is passed through the lens, the spatial amplitude distribution in the back focal plane of the lens is the Fourier transform of the spatial amplitude distribution of the object. The object may be located in several positions with respect to the lens and the Fourier transform body may appear in several positions with respect to the lens. In the most common arrangement, the object is placed in the front focal plane so that the Fourier transform appears in the rear focal plane.

FIG. 1 shows a Fourier transform body for various optical signals. The Fourier transform shown in the figure is the luminance spectrum (int
It is noteworthy that the phase spectrum information does not appear, recording the intensity spectrum). In fact, conventional optical detection methods cannot detect any phase. The phase gives information about the position. For example, even if the object in A is moved, the Fourier transform body in B remains on the same plane. This means that whatever movement of the object occurs in the field of view, the pattern in the focal plane of the conversion lens always stays exactly in the same place.

FIG. 2 shows in principle one application of the above. A perfect, defect-free grating 10 is placed on one side of the lens 12, and when the grating is illuminated by coherent light, its Fourier transform appears in the focal plane on the opposite side of the lens. A photographic plate is then placed on the focal plane, exposed and developed to form a photographic negative of the Fourier transform image. If this negative is placed in the focal plane, as shown at 14 in FIG. 2, in the case of a perfect (non-defective) test piece, no light will pass through the negative 14 and go to the detector 16. .

This state does not change regardless of the movement of the test piece 10 within the visual field. When a defect appears in the field of view, the Fourier transform image is slightly modified and some light passes through the negative 14 and is detected by the detector 16. The detected signal is the same for the same defect whether the defect is moving or stationary in the field of view.

In fact, it is not necessary to use a photographic negative for the majority of two-dimensional structures. As shown in the grid example, a simple crosshair device is sufficient. Also, a multi-point detector or an array of multiple detectors can be used instead of a single-point detector.

FIG. 3 shows the implementation of the present invention in detail. Coherent light is produced by laser light source 20 and passed through an optical beam optimizer 22. What is desired for best performance is that the output of the beam, shown at 24, is of a fixed optical form with light intensity outside the central beam spot negligible. The beam optimizer 22 may comprise any device known per se for this purpose.

The beam is reflected 90 ° at 26 and 28. This is purely for layout conveniences and does not affect the basic sensing mechanism. The substrate 30 to be inspected is the reflector 2
6 and 28, and is Fourier transformed by a high quality Fourier transform lens 32. Importantly, lens reflections, scatter, and aberrations are minimized so that each of these elements contributes directly to the final signal level as a noise source.

The Fourier transform of the substrate to be tested is 3
Appears at 4. The inspection is done at this location, but for convenience the Fourier transform is reimaged at 36 or 38 by optical components such as lens 40 and / or beam splitter 42. . The function of imaging performed by these optical components is purely to move the position of the Fourier transform image, not to transform the Fourier transform image back into an image occupying space. It is important to pay attention. In this way, the photodetection of the Fourier transform body is located on the Fourier transform plane, and the code 4
4 by a physical beam stop or combination of amplitude and / or phase filters and components such as photodiodes, photomultipliers, and primary and 2D video cameras.

In addition to the above photodetectors, format multi-component pho
to detector) can be used. This detector, commonly referred to as a "wedge-ring" detector, allows the detection and discrimination of different Fourier transform images. Different types of defects give rise to Fourier transform images of different shapes, spreads and periodicities. With the use of a properly configured wedge ring detector, a suitable software algorithm can be used to identify the Fourier Transform image and thus identify the shape and size of the defect.

Some substrates and thin films are not transparent. The device described above may also be modified as shown in Figure 4 to provide for reflected light for detection. The reflector 26 has been replaced with the substrate 30A to be inspected and the rest of the part is essentially the same.

It is possible to scan the area of the substrate to be inspected by moving the substrate in the X and Y directions in the plane of the substrate itself by means of a suitable mechanical device. FIG. 5 shows another device in which the scanning is partially optical.

Referring to FIG. 5, coherent light from the laser light source and beam optimizing component 50 passes through the semi-reflective surface 52 and reaches the scanning mirror 54. Scanning mirror 5
4 may be of a rotating polygonal type as shown, an oscillating planar type, or any other suitable form. The rays then enter the collector lens 56,
Proceed to substrate 58, and back reflector 60. The collector lens 56 is provided with a curved focal plane. The rays then return along the optical path to the semi-reflective surface 52, where some of the signal goes to the image processor, indicated at 62. For clarity, the Fourier transform lens and the individual optical components comprising the image stop, filter, detector and image reconstruction optics are not shown.

Thus, in the apparatus of FIG. 5, the substrate is optically scanned in the X direction, but scanning in the Y direction may be performed by linear movement of the substrate. The device is therefore suitable for applications where the substrates are transported along conveyors and the like.

It is clear that scanning in the X and Y directions can be achieved optically, for example using a second polygon mirror at right angles to the first polygon mirror.

FIG. 6 shows yet another inventive version that replaces the use of an amplitude and / or phase filter that removes regular information with interference between signals from two regions adjacent to the substrate.

Referring to FIG. 6, a laser and beam refining optics, generally designated 64, is shown.
eam refining optics) emits a coherent ray 66 which is split by a beam splitter 68 into two rays 70 and 7.
It is divided into two. The reflected light beam 72 is directed by the reflecting mirror 74 in a direction parallel to the transmitted light beam 70 with a small distance from the transmitted light beam 70. The spacing between the two rays must be small compared to the characteristic spacing of substrate and / or film changes that it is not desired to detect. Such changes include, for example, the slowly varying thickness of the substrate.

One of the rays, in this example ray 72, is passed through a phase adjuster 78 such that the phase difference between the rays is an odd multiple of π radians. Then rays 70, 72
Is passed through the sample substrate 76 and then through the Fourier transform lens 80. The resulting Fourier transform is superposed in the focal plane 82 and is the net signal displaying only the spatial frequencies that differ depending on the examination area of the substrate 76. Assuming that the probability of the same defect occurring in two adjacent regions is negligible, these signals indicate a defect. Therefore, the removal of common mode noise improves the SN ratio of the system.

In addition to the fact that the two rays are completely spatially separated, the two rays can be substantially superposed, in which case the defect is not immediately detected because the defect during scanning is It can be understood that it is only when the illuminances of two rays are equal.

The recombining of both rays occurs before or after passing through the Fourier transform lens, and the device for separating and / or recombining both rays is not limited to beam splitters and mirrors, but is universal. Bollaston without Wolla
It is understood that optical components such as a ston) prism are also included.

In the system described above, the filter may be computer generated. The filter may also be holographic. In any case, it may be generated by the system itself for reuse within the system in test mode.

Not only is the system capable of detecting the presence or absence of defects, it is possible to classify defects by size, density or distribution.

[0032]

As described above in detail, according to the present invention, the substrate is irradiated with light having a high degree of coherence,
By forming the Fourier transform body of the substrate irradiated with the light and detecting the light on the Fourier transform plane of the optical system, it is possible to provide an inspection system suitable for the inspection in the manufacturing process.

[Brief description of drawings]

FIG. 1 shows Fourier transforms for various optical signals.

FIG. 2 is a schematic diagram showing the principle underlying the present invention.

FIG. 3 is a schematic diagram of an apparatus of one embodiment of the present invention.

FIG. 4 is a schematic view of a device obtained by partially modifying the embodiment shown in FIG.

FIG. 5 is a schematic diagram showing another embodiment.

FIG. 6 is a schematic diagram showing another embodiment.

[Explanation of symbols]

10 Lattice, Test Piece 12 Lens 14 Negative 16 Detector 20 Laser Light Source 22 Optical Beam Optimizer 24 Beam Output 26 Reflector 28 Reflector 30, 30A Substrate 32 Fourier Transform Lens 34 Fourier Transform 40 Lens 42 Beam Splitter 44 Components such as physical beam stop and primary and two-dimensional video camera 50 Components for optimizing laser light source and beam 52 Semi-reflective surface 54 Scanning mirror 56 Collector lens 58 Substrate 60 Back reflector 62 Image processor 64 Laser And beam refining optical element 66 light beam 68 beam splitter 70, 72 light beam 76 substrate 78 phase adjuster 80 Fourier transform lens

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 21/66 C 7630-4M

Claims (19)

[Claims] 1. A method comprising: irradiating a substrate with light having a high degree of coherence, forming a Fourier transform body of the substrate irradiated with the light, and performing light detection on a Fourier transform plane of an optical system. Board inspection method. 2. The substrate inspection method according to claim 1, wherein the substrate is patterned. 3. The method for inspecting a substrate according to claim 2, wherein light is spatially filtered on a Fourier transform plane to attenuate regular information generated by the existence of the pattern. 4. The method for inspecting a substrate according to claim 3, wherein the filtering is performed by a phase or amplitude filter or a holographic filter. 5. The method for inspecting a substrate according to claim 4, wherein the filter is formed by exposing a photographic plate on a Fourier transform surface to a light-irradiated defect-free master sample. 6. The method according to claim 3, wherein the filtering is performed by causing a light beam from the target region to interfere with a light beam from a region adjacent to a test piece different from the light beam from the target region. Board inspection method. 7. The method of inspecting a substrate according to claim 1, wherein the substrate is irradiated with reflected light. 8. The method of inspecting a substrate according to claim 1, wherein the substrate is irradiated with light that is transmitted therethrough. 9. The method of inspecting a substrate according to claim 4, wherein the filter is generated by a computer. 10. A substrate positioning device for holding a substrate at a predetermined position, a light source of light having a high degree of coherence, and a substrate positioned at the predetermined position is irradiated with a light beam of a high degree of coherence. An apparatus for inspecting a substrate, comprising: an optical device for forming a Fourier transform body of the substrate; and a detection device located on a Fourier transform surface of the optical device. 11. The substrate inspection device according to claim 10, wherein the detection device includes a filter positioned on a Fourier transform plane. 12. A patterned filter, characterized in that the filter is a phase or amplitude filter patterned to attenuate the regular information caused by the presence of the patterned pattern on the substrate. The board inspection apparatus according to claim 11, which is used for board inspection. 13. The photographic negative of claim 12, wherein the filter comprises a photographic negative created by exposing a photographic plate located in the substrate positioner to a light-illuminated, defect-free master sample. Board inspection device. 14. The substrate inspection apparatus according to claim 11, wherein the filter is a holographic filter. 15. The board inspection apparatus according to claim 11, wherein the filter is generated by a computer. 16. The portion of the substrate that is exposed to the high coherence ray beam, and the detection device includes a portion of the substrate adjacent to the substrate that has a different high coherence ray beam that is different from the light beam emitted to the one portion of the substrate. The apparatus for inspecting a substrate according to claim 10, further comprising: a device for irradiating the substrate and a device for forming an interference pattern of the two light rays on a Fourier transform surface. 17. The apparatus for inspecting a substrate according to claim 10, further comprising a device for performing relative scanning between the light beam and the substrate in one dimension or two dimensions. 18. The apparatus for inspecting a substrate according to claim 17, wherein the scanning device includes at least one scanning mirror. 19. The substrate inspection apparatus according to claim 18, wherein a single scanning mirror includes a device that performs beam scanning in the X direction and moves the substrate in the Y direction.