JP2794764B2 - Defect inspection equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection apparatus that performs a defect inspection of a reticle (synonymous with a mask) provided for LSI manufacture, for example, and particularly observes an inspection object. The present invention relates to a defect inspection device having an observation optical system.

[Prior Art] FIG. 2 shows a configuration of an optical system of a conventional reticle defect inspection apparatus. Here, the observation optical system includes an objective lens 103 to 105 that is switched as necessary, an image sensor IS2, and the image sensor IS2.
It comprises an adjustment lens 108 for adjusting the upper observation area and the like, and includes an eyepiece 110 for visual observation and a splash mirror 107.

The reticle R2 of the object to be inspected is illuminated from below by the transmitted illumination light source BL2.
6. The image is enlarged and input to the image sensor IS2 via the adjustment lens 108, and the image is output to the television monitor M2.

The inspection apparatus incorporates an automatic focusing mechanism that automatically adjusts the distance between the inspection object and the objective lens 104 optimally. The automatic focus detection optical system includes a focus detection device FS2, a chromatic aberration correction lens 11 inserted according to replacement of the objective lens.
2. It is composed of a dichroic mirror 111 that reflects infrared light and transmits visible light, a half mirror 106, and an objective lens 104.
Detect the distance between them. This distance is automatically adjusted by means not shown.

The light for focus detection (in this case, infrared light) is a focus detection device
The light is emitted from the FS2, reflected by the dichroic mirror 111 and the half mirror 106, reflected by the inspection object through the objective lens 104, guided backward through the same path, and guided to the focus detection device FS2.

As described above, three objective lenses (103 to 105) are mounted according to three types of observation magnifications, and are configured to be switched according to the application. In other words, a wide field of view is required during alignment, so a low-magnification objective lens
At the time of the reticle R2 inspection, the objective lens 104 is switched to the medium magnification objective lens 104, and if a high magnification is required, the objective lens 105 is switched to the high magnification objective lens 105.

At this time, the field of view of the image sensor IS2 is readjusted by the adjustment lens 108, and the chromatic aberration correction lens 112 is replaced to correct axial chromatic aberration generated in the automatic focus detection optical system.

[Problems to be Solved by the Invention] In the above-described conventional visual inspection apparatus, it is necessary to switch the objective lens according to the observation magnification, and it is necessary to correct the automatic focus detection optical system by the chromatic aberration correction lens. Further, since the objective lens switching mechanism is located directly above the object to be inspected, dust is generated from a sliding portion of the machine during the switching operation and adheres to the object to be inspected, causing a new contamination problem.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a defect inspection apparatus that does not require switching of an objective lens and that can easily change an observation magnification.

[Means for Solving the Problems] A defect inspection apparatus according to claim 1 of the present application includes a light source unit that supplies illumination light to an inspection object, and observation of the inspection object based on observation light from the inspection object. In a defect inspection apparatus having an observation optical system that forms an image at a predetermined magnification, the observation optical system is fixed to the defect inspection apparatus, has a constant magnification, and forms an image with an infinity objective lens. An objective lens system including an image lens, and an objective lens system for converting the observation image captured by the objective lens system to a predetermined magnification, which is disposed behind the intermediate image of the object to be inspected formed by the objective lens system. A variable power optical system, a split optical system that separates focus detection light from the observation light, and an automatic operation that operates by detecting a positional relationship between the objective lens system and the object to be inspected by the focus detection light. And a focusing mechanism.

A defect inspection apparatus according to a second aspect is the defect inspection apparatus according to the first aspect, wherein the split optical system is disposed between the objective lens system and the variable power optical system. It is.

A defect inspection apparatus according to a third aspect is the defect inspection apparatus according to any one of the first and second aspects, wherein the split optical system is disposed between the infinity objective lens and the imaging lens. It is characterized by being performed.

A defect inspection apparatus according to a fourth aspect is the defect inspection apparatus according to any one of the first to third aspects, wherein the light for focus detection is light in a wavelength range different from the observation light,
The split optical system has a dichroic mirror.

A defect inspection apparatus according to claim 5, and claims 1 to 3.
Wherein the light for focus detection is infrared light, and is transmitted through the split optical system and guided to the automatic focusing mechanism. .

[Operation] In the defect inspection apparatus of the first aspect, the objective lens system is fixed at a fixed magnification, and when changing the observation magnification, the magnification is changed by the variable magnification optical system provided separately without switching the objective lens system. Changes are made. Therefore, it is possible to prevent the generation of dust that contaminates the test object when the magnification is changed. In addition, since the objective lens system includes an infinity objective lens and an imaging lens, even if an optical element such as a mirror is inserted between the infinity objective lens and the imaging lens, the effect of the insertion is minimized. Therefore, the degree of freedom in designing the entire optical system can be increased. Further, since the variable power optical system is disposed behind the intermediate image formed by the objective lens system, the image formed by the imaging lens is changed in magnification, and the variable power optical system is further moved from the objective lens. It is possible to further reduce the contamination of the object to be inspected, simplify the design of the variable power optical system and the like, and prevent the deterioration of the imaging characteristics due to the variable power. Further, the positional relationship between the objective lens system and the object to be inspected is detected by the light for focus detection separated by the split optical system, and the auto-focus mechanism detects the distance between the objective lens and the object to be inspected based on the distance detection result. Automatically adjust the distance to optimal.

In the defect inspection apparatus according to the second aspect, since the split optical system is disposed between the objective lens system and the variable power optical system, the automatic focusing mechanism is operated at a constant detection magnification using the objective lens system. Can be.

In the defect inspection apparatus according to the third aspect, the light from the object to be inspected is converted into a parallel light beam by the infinity objective lens,
An image of the inspection object is formed at the rear focal position of the imaging lens by the imaging lens. Further, since the split optical system is disposed between the infinity objective lens and the imaging lens, a parallel light beam enters the split optical system.

In the defect inspection apparatus according to the fourth aspect, the light for focus detection is light in a wavelength range different from the observation light, and the split optical system has a dichroic mirror, so that focus detection and observation can be performed in parallel. .

In the defect inspection apparatus according to the fifth aspect, since the light for focus detection is infrared light and passes through the split optical system and is guided to the automatic focusing mechanism, the split optical system can be easily manufactured.

[Embodiment of the Invention] Fig. 1 shows a configuration of an optical system of a defect inspection apparatus for a reticle R, which is an embodiment of a visual inspection apparatus according to the present invention.
In the present embodiment, the objective lens, which has conventionally been switched and used according to the required magnification, is replaced with a single infinite objective lens 3 having a field of view required for alignment and a numerical aperture required for inspection and observation. The magnification is changed by a variable magnification relay lens 11 installed behind the image formed by the imaging lens 9.

The observation optical system of the present embodiment includes a fixed infinite objective lens 3, an imaging lens 9, a dichroic mirror 4 that transmits infrared light and reflects visible light, a variable magnification relay lens 11, an image sensor IS, and the like. , A bounce mirror for visual observation 12
And an eyepiece 13.

The reticle R is illuminated from below by the transmitted illumination light source BL, and the observation light from the inspection target (circuit pattern) on the upper surface of the reticle R is captured by the objective lens 3, reflected by the dichroic mirror 4, passes through the half mirror 7, An image is formed on the target 10 by the imaging lens 9. This image is magnified to an appropriate magnification by the variable power relay lens 11 and input to the image sensor IS.
The image is output to the television monitor M, and the reticle R is inspected.

When it is necessary to determine whether the abnormality on the screen of the television monitor M is a defect or dust, the epi-illumination light source RL and the half mirror 7 illuminate the reticle R from above, and the bouncing mirror 12 is inserted into the optical path. Then, visual observation of the abnormality is performed from the eyepiece 13.

This inspection apparatus incorporates an automatic focusing mechanism for automatically adjusting the distance between the reticle R and the objective lens 3 automatically. The focus detection optical system includes a focus detection device FS, an imaging lens 5, a dichroic mirror 4 (transmits infrared light and reflects visible light), and an objective lens 3.

The focus detection device FS projects a pattern for focus detection on the reticle R by infrared light using an infrared light emitting LED. The focus detection device FS captures the reflected light of the infrared light on the surface of the reticle R, splits the light by an internal beam splitter,
An image of a focus detection pattern is formed. Focus detector FS
Is to detect the focus state from this image.

Infrared light, which is light for focus detection, is emitted from the focus detection device FS, passes through the imaging lens 5, the dichroic mirror 4, and the objective lens 3, is reflected by the reticle R, and travels backward on the same path to focus. It is led to the detection device FS.

The focus detection device FS detects the distance between the reticle R and the objective lens 3, and this distance is automatically adjusted by means not shown.

In the present embodiment, the objective lens 3 is an infinite system, but it can be configured as a finite system as in the prior art.

In the present embodiment, since the optical system to the focus detection device FS is separated immediately after the objective lens 3 by the dichroic mirror 4, the overall structure is simplified and the dichroic mirror can be easily manufactured (infrared ray). The light transmission type is easier to manufacture than the visible light transmission type). However, as before, an infrared light reflection type dichroic mirror was used,
It is also possible to configure an optical system only with a half mirror.

[Effects of the Invention] As described above, the defect inspection apparatus of the present invention can reduce the generation of dust contaminating the inspection object.
In addition, since the objective lens system includes the infinity objective lens and the imaging lens, the degree of freedom in designing the entire optical system can be increased. In addition, since the variable power optical system is disposed behind the intermediate image formed by the objective lens system, the variable power optical system can be further separated from the objective lens to reduce contamination of the object to be inspected, The design of the system and the like can be simplified, and it is possible to prevent the imaging characteristics from deteriorating due to zooming. Furthermore, since the autofocus mechanism performs focus adjustment, the observer can immediately observe without performing focus adjustment by himself.

Further, when the split optical system is disposed between the objective lens system and the variable power optical system, the automatic focusing mechanism can have a simple structure that operates at a constant magnification. That is, complicated adjustment such as insertion and replacement of the chromatic aberration correcting lens used for focus detection at the time of changing the magnification is not required. In addition, the number of focus targets corresponding to the objective lens is reduced, and the structure and operation of the entire automatic focusing mechanism are simplified. Further, since the observation optical system and the optical system of the automatic focusing mechanism share components such as an objective lens, the total number of components is reduced, and the operation accuracy of the automatic focusing mechanism is improved.

In particular, when the split optical system is disposed between the infinity objective lens and the imaging lens, mirrors inserted into the observation optical system (portions denoted by reference numerals 4, 7, and 12 in the embodiment).
This has the effect of preventing asymmetric chromatic aberration from occurring.

Furthermore, when the light for focus detection is light in a wavelength range different from the observation light and the splitting optical system has a dichroic mirror, or when the light for focus detection is infrared light and passes through the splitting optical system and is automatically focused. When guided to the mechanism, the defect inspection apparatus can be made suitable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of an optical system of a reticle inspection apparatus according to one embodiment of the present invention. FIG. 2 is a configuration diagram of an optical system of a reticle inspection apparatus according to a conventional example. [Description of Signs of Main Parts] 3 ... Objective lens, BL ... Transmission illumination light source 4 ... Dichroic mirror, R ... Reticle 7 ... Half mirror, FS ... Focus detection device 9 ... Imaging lens, IS …… Imaging element 11 …… Resizing lens

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 21/84-21/91 G02B 21/00-21/36

Claims (5)

(57) [Claims] 1. A light source unit for supplying illumination light to a test object, and an observation optical system for forming an observation image of the test object at a predetermined magnification based on the observation light from the test object. Wherein the observation optical system is fixed to the defect inspection device and has a fixed magnification, and an objective lens system including an infinity objective lens and an imaging lens. A variable-magnification optical system for converting the observation image captured by the objective lens system to a predetermined magnification, which is disposed on the rear side of the intermediate image of the inspection object to be formed, and light for focus detection from the observation light 1. A defect inspection apparatus, comprising: a split optical system that separates an object; and an automatic focusing mechanism that operates by detecting a positional relationship between the objective lens system and the object to be inspected using the light for focus detection. 2. The defect inspection apparatus according to claim 1, wherein said split optical system is disposed between said objective lens system and said variable power optical system. 3. The defect inspection apparatus according to claim 1, wherein the split optical system is disposed between the infinity objective lens and the imaging lens. 4. The apparatus according to claim 1, wherein the light for focus detection is light in a wavelength range different from that of the observation light, and the split optical system has a dichroic mirror. The defect inspection device according to the item. 5. The auto-focus mechanism according to claim 1, wherein the light for focus detection is infrared light, and is transmitted through the split optical system and guided to the automatic focusing mechanism. Described defect inspection apparatus.