KR20040110079A - Optical illumination system of pattern inspection using line CCD - Google Patents

Abstract

PURPOSE: An optical illumination system for inspecting a pattern using a line CCD is provided to improve an optical efficiency by using a spherical lens. CONSTITUTION: An optical illumination system of inspecting fine patterns using a line CCD(3) employs a coaxial image forming scheme and hides a half of a lens using a mirror. The optical illumination system uses a line light source formed with LED arrangement or optical fiber. The optical illumination system irradiates the fine patterns to be inspected. The optical illumination system uses a spherical lens(8) as a cylinder lens. A cylinder lens(9) is realized by cutting a cylinder rode in two. The cut surface of the cylinder rode is polished so that a volume of the optical illumination system is reduced.

Description

Optical illumination system of pattern inspection using line CCD

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system and an illumination method used in an LCD, a PDP, a PCB, and an apparatus for inspecting defects of various fine patterns, and to an illumination method for efficiently illuminating a portion to be inspected from a light source and an image forming method.

Referring to (a) of the conventional general operating principle, a plurality of LEDs for use as a light source are listed, or after injecting light into an optical fiber in a halogen lamp, etc. By reflecting the light to the LCD substrate (2) through the illumination lens system (5), and the optical splitter (7) used to illuminate the LCD substrate (2) to be examined by pattern), and the fine pattern image passes through the imaging lens system 4 and the light splitter 7 and forms an image on the line CCD. In addition, Fig. 1B shows a case where the optical splitter 7 is outside the lens system. As shown in the figure, an illumination method in which the optical axis of the illumination system is the same as the optical axis of the imaging system is generally referred to as coaxial illumination.

The disadvantage of this coaxial illumination method is that the splitter 7 generally reflects 50% of the light and transmits 50% of the light, so the light emitted from the first light source must pass through the splitter twice to reach the CCD. Therefore, only 25% of the amount of light can be used, and the light efficiency is much reduced. Therefore, there is an inefficient problem of using a higher power light source. In addition, if the optical splitter is used in the commonly used imaging lens, chromatic aberration occurs due to the glass material used as the material for the optical splitter, and the performance of the imaging lens is degraded. It is difficult to use general lenses only by using only lenses that are designed.

In addition, FIG. 2 illustrates the inclined light rather than the coaxial light of the conventional method, but the light efficiency is higher than that of the coaxial light method of FIG. 1, but when the glass substrate is inspected, the image of the fine pattern on the first surface is immediately After reflecting from the backside of the substrate (second surface) to the image formed by the imaging lens and reflected on the back side of the substrate, the image formed is superimposed like a shadow, and has become a stumbling block to secure a clear image. As described above, the conventional method has a large amount of light loss in the case of coaxial illumination and a special lens has to be manufactured. In the case of oblique illumination, a clear image cannot be obtained by the shadow image reflected from the backside of the substrate.

On the other hand, in the configuration of the illumination optical system, as shown in FIG. 6, only the cylinder lens is used to reflect the light emitted from the substrate to the outside, thereby reducing the amount of light entering the imaging optical system, and consequently reducing the uniformly illuminated area. Therefore, in order to compensate for this phenomenon, it was necessary to use a large illumination length and a cylinder lens.

In the case of coaxial lighting, the loss of light is large, and in the case of oblique lighting, in order to compensate for the disadvantage that a shadow image occurs, the present invention proposes an optical system having a feature to compensate for the above two disadvantages by suggesting a new structure of the optical system.

In addition, as a component constituting the illumination optical system conventionally had a disadvantage in that the light efficiency is reduced by using only the cylinder lens, but by using the spherical lens according to the present invention to improve the light efficiency and illumination uniformity.

1 is a block diagram of a conventional coaxial lighting method

(A) Configuration diagram when the optical splitter is inside the lens system

(B) Schematic diagram when light splitter is in front of lens system

2 is a block diagram of a conventional external oblique lighting method

3 is a diagram illustrating a new coaxial illumination and imaging method according to the present invention.

Figure 4 is a schematic view of the new stock lighting and imaging method according to the present invention

5 is a block diagram of a conventional scattered light illumination method of the present invention and similar structure

6 is an optical path diagram of a conventional method for implementing line lighting using a cylinder lens;

(A) Optical path diagram with cylinder lens in vertical direction

(B) Optical path diagram with cylinder lens in horizontal direction

7 is an optical path diagram of a method using a spherical lens and a cylinder lens to realize efficient line illumination.

(A) Optical path diagram with cylinder lens in vertical direction

(B) Optical path diagram with cylinder lens in horizontal direction

Figure 8 is an internal structure diagram of an illumination system using a cylinder rod cut in half for implementing the present patent

(A) Method using concave mirror

(B) How to use convex lenses

9 is a structural diagram combined with an illumination system and an imaging system to implement the present patent

(A) If CCD is in the stockpile of the imaging lens

(B) If there is a CCD on the axis of the imaging lens

<Description of the symbols for the main parts of the drawings>

1: light source (LED or optical fiber), 2: inspection substrate, 3: line CCD

4: imaging lens, 5: illumination lens, 6: reflecting mirror, 7: splitter

8: spherical lens, 9: cylinder lens, 10: spherical mirror

Hereinafter, described in detail with reference to the accompanying drawings.

Referring to FIG. 3, in the general imaging optical system, a light source illuminating the substrate 2 passes through the entire aperture of the imaging lens 4 to form an image on the CCD 3. However, in the present invention, since the mirror 6 is inclined to the right 50% of the aperture of the imaging lens system to illuminate through the mirror, the amount of light entering the imaging lens is reduced by 50%. That is, the light emitted from the light source 1 passes through the illumination lens 5 and then reflects from the mirror 6 located on the right under the imaging optical 4 to illuminate the substrate 2 underneath and to have a good reflectance. By satisfying the law of reflection, the reflected light is imaged on the CCD 3 through the left 50% semicircle aperture of the imaging lens 4. The optical structure has a light efficiency of 50%, but can obtain twice the light efficiency as compared to the conventional coaxial lighting method that uses a light splitter twice. In addition, there is an advantage that can be used as it is a conventional imaging lens.

Another invention is a non-axis illumination method, and the conventional method is to form a fine pattern on the optical axis of the imaging lens (4), so whether the coaxial illumination or oblique illumination system, the line CCD (3) position of the imaging lens (4) Was on the optical axis. However, the method proposed in FIG. 4 is such that the position of the line CCD 3 is not on the optical axis of the imaging lens but on a non-axis that is slightly off the optical axis.

The basic principle of this method is that in FIG. 3, the angles of the left light a and the right light b passing through the left side of the lens are symmetrical to each other. However, the left light a 'of FIG. It is inclined by twice as much as the left ray (a) of FIG. 3, and (b ') is a vertical angle. In other words, by analyzing the characteristics of the imaging lens (b ') to calculate the vertical axis position and the relative position of the line CCD (3) to calculate the position of the line CCD (3).

In addition, the lower side light (b ") of the illumination system is to illuminate the substrate vertically after the reflection from the mirror (6), and the upper side light (a") is opposite to the left side light (a ') after the reflection on the mirror and the same angle To illuminate the substrate 2.

In this way, 100% of the total amount of light can be used by completely eliminating the loss of light, which is a disadvantage of the conventional method. Also, the imaging lens generally used can be used as it is, and the shadow image generated from the backside of the substrate is also reflected. It can be completely eliminated.

In FIG. 5, a conventional lighting system having a structure similar to the present study will be described. 5 is an optical system for detecting a fine pattern engraved on an opaque object with a PCB or the like. However, the present invention is an illumination system used in a device for detecting a fine pattern engraved on a transparent object such as a glass substrate. The difference between the two methods is that the present invention is an optical system to which the law of transmission reflection is applied, but the optical system of FIG. 5 is a scattered light optical system. In other words, the reflected light path after the illumination is directed toward the outside of the lens, so the light coming into the lens is light scattered from the object. Therefore, such devices must use high power light sources. In other words, the structure looks similar, but the fundamental principle is fundamentally different.

On the other hand, since line CCD is used, line lighting should be performed. As for the method for implementing such line lighting, the conventional method uses a cylinder next to a line light source 1 composed of an optical fiber or an LED array as shown in FIG. The only disadvantage of this method is that the light rays f, g, h, etc. reflected from the glass substrate are reflected outwards, so they do not enter the imaging lens system.

As a result, the center of the substrate becomes uniform illumination from the camera's point of view, but there is a disadvantage in that the uniform illumination is not possible in the periphery. In order to solve this disadvantage, as shown in (b) of FIG. 6, a light source 1 and a cylinder lens 9 that are much larger than the area to be examined should be used.

In order to solve the above disadvantages, the present invention uses a spherical lens as a method of adding a spherical lens 8 as shown in FIG. 7 and places a light source near the front focal point of the spherical lens 8. If the light rays d, d ', d ", etc. emitted from the center are allowed to pass through the spherical lens and run parallel to the optical axis, then the light rays c, c', c" emitted from the upper part of the light source are emitted from the lower part of the light source. Incident light is emitted at an symmetrical angle with the emitted light rays e, e ', and e ". The illumination system structure has a higher light source and a smaller size than the illumination system using only the cylinder lens of FIG. You have an advantage.

The structure for suitably applying to a system using the principles of FIG. 7 may be the same as FIG. 8. It is better to configure the illumination system in parallel with the imaging lens in order to improve spatial constraints and mounting, and the structure for realizing it may have a structure that reflects the optical path twice as shown in FIG. 8.

8A shows an example of applying a cylinder lens and a spherical glass lens which cut the cylinder rod in half and totally reflect at the cutting plane, and in FIG. 8B, an optical system using a reflection mirror instead of a spherical lens. Is showing.

FIG. 9A shows the structure of the entire optical system in which the non-axis imaging system of FIG. 4 and the illumination system of FIG. 8A are combined, and in FIG. 9B, the optical axis of the imaging system is slightly tilted to form the center of the CCD. The structure of the optical system applied to the optical axis of the lens system is shown. Although the structure of the optical system is inclined, the illumination condition satisfies the conditions of vertical illumination and vertical imaging, so that the shadow phenomenon of the pattern reflected from the back side pointed out as a disadvantage of the inclined illumination structure in FIG. 2 does not appear.

According to the present invention, the optical efficiency can be improved by 2 and 4 times, respectively, while using a general imaging optical system rather than an imaging optical system specifically designed to use the optical separator 7.

In addition, by using spherical lenses in the illumination optical system, it is possible to realize uniform illumination in a wide area with a small size light source and a cylinder lens.

Claims (6)

In the illumination method of the optical system for inspecting a fine pattern using a line CCD, a coaxial imaging method is used as shown in FIG. 3, but a half of the lens is covered and ordered using a mirror. In the illumination / imaging method of an optical system for inspecting a fine pattern using a line CCD, a non-axis illumination method is used, as shown in FIG. ) And oblique (a ") illumination and inspection by placing the line CCD on the stockpile As shown in FIG. 7, the spherical lens 8 and the cylinder lens 9 are simultaneously used in the illumination optical system, thereby increasing the light efficiency and reducing the size of the component. 4. The optical system and light source of claim 3, wherein the light beam emitted from the center of the line light is emitted in parallel with the optical axis after passing through the spherical lens (d, d ', d "). Illumination system that allows vertically emitted rays c ', d', and e 'to converge to the center of the illumination area The illumination system according to claim 3, wherein the cylinder lens is used as the structure shown in Fig. 8, the cross section obtained by cutting the cylinder rod is used as the total reflection surface, and the spherical surface of the cylinder is used as the structure in which the light passes twice. An illumination optical system using a spherical mirror 10 instead of the spherical lens 8 of the illumination optical system and having a structure as shown in FIG.