KR102637333B1 - Wafer inspection optics system - Google Patents

Abstract

The present invention relates to a wafer inspection optical system. More specifically, the present invention relates to a wafer inspection optical system, and more specifically, a wide area of scattered light outside the NA of the objective lens among the scattered light emitted from the wafer by oblique incident illumination is collected in one place using a reflector to accept various defect signals of the wafer. This relates to a wafer inspection optical system that can significantly improve wafer inspection performance.

Description

Wafer inspection optics system

The present invention relates to a wafer inspection optical system. More specifically, the present invention relates to a wafer inspection optical system, and more specifically, a wide area of scattered light outside the NA of the objective lens among the scattered light emitted from the wafer by oblique incident illumination is collected in one place using a reflector to accept various defect signals of the wafer. This relates to a wafer inspection optical system that can significantly improve wafer inspection performance.

Semiconductor devices are manufactured by performing various treatments on silicon wafers. In the semiconductor manufacturing process, in the process of forming a pattern on a silicon wafer, pattern defects or defects that are different from the normal part may be unintentionally formed, leading to malfunction of the semiconductor device. Therefore, it is important to improve yield by detecting defects or pattern defects that are different from the normal part in the pattern on the wafer during manufacturing in-line and feeding the results back to the semiconductor manufacturing process.

A pattern inspection device (defect inspection device) is a device that detects defects on a semiconductor wafer as position information. The coordinate information of the detected defect is used to acquire an enlarged image of the defect using an observation device such as a review SEM (scanning electron microscope). Review Images acquired from SEM are used to identify defect types, and the results are used for condition management of the manufacturing process, etc. For example, by methods such as monitoring the frequency distribution of the number of defects for each defect type.

Wafer inspection systems are required to improve sensitivity to particles, anomalies and other defect types while maintaining overall inspection speed (wafers per hour). Dark-field illumination optical inspection systems typically utilize laser light to illuminate the wafer in a specific pattern, i.e. individual dots, lines or areas, and collection optics to direct the scattered light to a set of corresponding sensors. Use (collection optics).

Figure 1 schematically shows a conventional dark field wafer inspection system 3. In the conventional system 3, a light source 5 oblique incident light toward the surface of the wafer 4, and the wafer Scattering light scattered from the surface of (4) is collected by the objective lens (6) to form an image, and imaging processing is performed by the computing subsystem (7).

At this time, as shown, the scattered light from the wafer surface is scattered over a wide area, but only the scattered light within a certain angle is incident on the objective lens, so there is a problem that inspection performance is deteriorated when using the conventional system. .

Korean Patent Publication No. 2020-0128602

The present invention was developed to solve the above problems. Among the scattered light emitted from the wafer by oblique incident illumination, the scattered light in a wide area beyond the NA of the objective lens is collected in one place using a reflector, thereby reducing various defect signals on the wafer. The purpose is to provide a wafer inspection optical system that is acceptable and can greatly improve wafer inspection performance.

A wafer inspection optical system according to an example of the present invention includes a light source that irradiates light at a predetermined angle toward a target surface of a wafer; an objective lens for receiving scattered light scattered from the target surface of the wafer; and a reflector that reflects at least a portion of the scattered light scattered from the target surface of the wafer and makes it incident on the objective lens.

The reflector may be an elliptical reflector having a first focus and a second focus.

The reflector may be arranged such that the second focus is located at the target surface of the wafer.

A pinhole may be provided at the location of the first focus.

The angle of incidence at which the reflected light reflected from the reflector is incident on the pinhole may be within the numerical aperture of the objective lens.

There may be a plurality of reflectors.

The plurality of reflectors includes a first reflector located opposite the light source when the optical system is viewed from above, and a second reflector located at a predetermined distance from the first reflector along the circumferential direction of the first reflector. may include.

The reflector may have an arc shape centered on the target surface when the optical system is viewed from above.

The center of the reflector may be located on the same line as the light source and the target surface, and the center angle of the reflector may be less than 180 degrees.

The center of the reflector is located on the same line as the light source and the target surface, and the center angle of the reflector may be greater than 180 degrees.

It may further include an objective lens driving unit that moves the objective lens in the vertical direction.

The objective lens driving unit may move the objective lens in the vertical direction so that the distance between the objective lens and the first focus and the distance between the first focus and the second focus are the same.

It may further include a reflector driver that adjusts at least one of the position and angle of the reflector.

The reflector driver may be capable of moving the reflector up and down and tilting the angle of the reflector.

The reflector may be a flat reflector.

It may further include an objective lens driving unit that adjusts the angle of the objective lens, and the objective lens driving unit may adjust the angle of the objective lens so that reflected light reflected from the reflector is incident perpendicularly toward the objective lens.

It may further include a reflector driver that adjusts at least one of the position and angle of the reflector.

The reflector driver may be capable of moving the reflector up and down and tilting the angle of the reflector.

According to the present invention, among the scattered light emitted from the wafer by oblique incident illumination, scattered light in a wide area beyond the NA of the imaging optical system is collected in one place using a reflector, making it possible to accept various defect signals of the wafer, thereby improving inspection performance. can be greatly improved.

1 is a diagram schematically showing a conventional dark field wafer inspection system.
Figure 2 is a diagram schematically showing a wafer inspection optical system according to an example of the present invention.
Figure 3 is a view of the reflector viewed from the side.
Figure 4 is a perspective view of a reflector.
Figure 5 is a diagram to explain the size and shape of the reflector.
FIG. 6 is a view of the optical system of FIG. 2 viewed from above.
Figures 7, 8, and 9 are diagrams showing various embodiments of a reflector.
Figure 10 is a diagram to explain the size and shape of the reflector.
Figure 11 is a diagram showing the optical system of Figure 2 again.
Figure 12 is a diagram schematically showing a wafer inspection optical system according to another example of the present invention.
FIG. 13 is a three-dimensional diagram showing the optical path of FIG. 12.

Hereinafter, the present invention will be described with reference to the attached drawings.

2 schematically shows a wafer inspection optical system according to an example of the present invention, wherein the optical system 10 includes a computer subsystem 12 of the wafer inspection system and is configured to inspect the surface of the wafer 11. This may apply to some optical elements of a wafer inspection system.

The wafer 11 may be placed on a stage (not shown), and the stage may include a chuck. The chuck may be an edge-engaging chuck, a vacuum chuck, or an air bearing chuck, and a single chuck may support multiple wafer diameters (e.g., 300 mm and 450 mm) or a single substrate diameter. . The stage can be moved in the x, y, and z directions, and can be simultaneously or selectively switched in the θ direction.

The computer subsystem 12 is a component that detects defects on the wafer using the output of an image sensor (not shown), and the computer subsystem may be any suitable known computer system.

This optical system 10 is a detection optical system for collecting images on the surface of a wafer and transmitting them to an imaging optical system such as an image sensor. As shown, it largely consists of a light source 100, an objective lens 200, and a reflector 300. may include.

The light source 100 irradiates light at a predetermined angle toward the surface of the wafer, more specifically, the target surface (T) of the wafer, and may be, for example, a pulse laser. The target surface (T) may refer to a specific area of part of the wafer surface or the entire wafer surface, and the position of the target surface on the wafer surface may be changed by driving the stage. The light emitted from the light source 100 may be obliquely incident on the surface of the wafer at a predetermined angle toward the surface of the wafer, and such oblique incident illumination 101 collides with the test object, that is, the surface of the wafer. may be scattered.

The objective lens 200 is configured to receive scattered light 102 scattered from the target surface (T) of the wafer. The objective lens 200 may be positioned on the upper part of the wafer surface in a direction perpendicular to the surface of the wafer. there is. The light receiving angle of the objective lens 200 may be determined by the numerical aperture (NA) of the objective lens.

Below, we will look at the optical system according to an example of the present invention.

2 to 10 are diagrams of a reflector according to an example of the present invention. As shown, in the optical system of this example, the reflector 300 may be configured as an elliptical mirror.

Figure 3 is a view of the reflector viewed from the side, and Figure 4 is a perspective view of the reflector. As shown, the reflector may have a first focus (f1) and a second focus (f2), and the first focus (f1) and The second focus f2 may be formed as a part of an ellipse with two vertices c and -c.

At this time, the reflector 300 may be arranged so that the second focus f2 is located on the target surface T of the wafer, and the reflector 300 may be positioned so that the objective lens 200 is located at the position of the first focus f1 correspondingly. (300) may be arranged. By arranging the reflector in this way, the scattered light incident on the reflector among the scattered light scattered from the target surface can be reflected by the reflector and concentrated on the objective lens. Accordingly, the objective lens is a point collector that condenses the light to one point. function can be performed.

In this way, the elliptical reflector 300 uses the two focuses of the elliptical equation to converge light from one focus to another focus, and the curvature of the elliptical reflector is determined by the focal length (2c) or free space (2c) of the objective lens. It can be applied depending on. For example, when the free space 2c is 30 mm, the reflector becomes an elliptic function of a and b that satisfies 900 = b ² - a ² , and the curvature of the reflector can be determined based on this.

In addition, since the scattered light 102 scattered from the surface of the wafer radiates in different orders depending on the frequency of the wafer pattern, the size and shape of the elliptical reflector 301 are determined by determining the angle or focus of the desired order of light. It can be determined according to the NA of the objective lens. Figure 5 is a diagram for explaining the size and shape of the reflector. Depending on the NA of the objective lens, the reflector 300 of the present invention has a low angle and order, such as the reflector on the left in the drawing, or the reflector on the right in the drawing. It can be configured to have a high angle and order as follows.

Referring again to FIG. 2, the optical system 10 may be provided with a pinhole 400 at the position of the first focus f1. More specifically, the pinhole 400 may be formed in a structure in which a region on the plate penetrates, and may be placed below the objective lens 200. As the pinhole 400 is provided, some of the scattered light 102 scattered from the surface of the wafer can be blocked from being directly incident on the objective lens 200, and is further reflected by the reflector 300 to reach the first focus f1 ) can help ensure that the reflected light 103 collected is incident within the NA of the objective lens.

Meanwhile, as described later with reference to FIG. 10, the optical system 10 may further include an objective lens driving unit 200A that moves the objective lens 200 in the vertical direction, and the objective lens 200A is driven by the driving unit 200A. When (200) is moved upward from the position of the first focus f1, only the pinhole 400 may be located at the position of the first focus f1, and at this time, the optical system 10 is separated from the reflector 300. The angle of incidence of the reflected light 103 that is reflected and incident on the pinhole 400 may be configured to be smaller than the NA of the objective lens.

FIG. 6 is a view of the optical system viewed from above. As shown, the reflector 300 may be formed in the shape of an arc centered on the target surface T when viewed from above. One reflector may be provided, one reflector may be positioned to face the light source, and the center of the reflector may be positioned on the same line as the light source and the target surface.

The scattered light 102 may be scattered in all directions centered on the target surface (T). In this case, the scattered light 102 corresponds to dark field illumination by oblique incident lighting 101, so the light source 100 opposite to the light source 100 The intensity of the scattered light 102 is greatest in the area, that is, the area horizontal to the direction of movement of the oblique incident lighting 101, and as the angle formed with the direction of progress of the oblique incident lighting 101 increases, the intensity of the scattered light 102 increases. may gradually become smaller.

Here, the present invention can obtain the brightest scattered light by installing the reflector 300 to face the light source 100, and the center of the reflector 300 is located on the same line as the light source 100 and the target surface (T). By doing so, symmetrical information about the target surface (T) can be obtained.

Furthermore, the present invention provides not only dark field illumination in an area opposite the light source 100, that is, an area horizontal to the direction of progress of the oblique incident illumination 101, but also an area forming a predetermined angle with the direction of progress of the oblique incident illumination 101. Dark-field illumination (dark dark-field) can be further utilized.

More specifically, Figure 7 is a diagram showing an optical system using a plurality of reflectors. As shown, the present invention may be provided with a plurality of reflectors 300, and the plurality of reflectors 300 are positioned to face the light source. It may include a first reflector 301 and a second reflector 302 disposed at a predetermined angle with the direction in which the oblique incident light 101 travels. The second reflector 302 may be positioned at a predetermined distance from the first reflector 301 along the circumferential direction of the first reflector 301, and at least one second reflector 302 may be provided. Additionally, the first reflector 301 and the second reflector 302 may each have the same size and shape. In this way, as not only the first reflector 301 but also the second reflector 302 is provided, more diverse information about the target surface T of the wafer, especially information in the dark dark-field region, can be obtained. .

Unlike further providing a second reflector 302 in addition to the first reflector 301, the present invention can be configured to have the same effect by extending one reflector 300 in the circumferential direction. Figures 8 and 9 are diagrams showing a reflector extending in the circumferential direction, where the central angle (θ) of the reflector 300 is formed to be smaller than 180 degrees as shown in Figure 8, or the central angle (θ) of the reflector 300 is formed as shown in Figure 9. This can be formed to be greater than 180 degrees. Meanwhile, although not shown, the design can of course be changed in such a way that the reflector is completely extended in the circumferential direction to form a complete circle, and a penetrating structure through which light can pass is installed at a certain portion.

The example of FIGS. 8 and 9 has the advantage of being simpler to construct and install than the example of FIG. 7, and the example of FIG. 7 has the advantage of being able to fine-tune each reflector compared to the example of FIGS. 8 and 9.

FIG. 10 is a diagram illustrating the optical system of FIG. 2 again. As shown, the optical system 10 may further include an objective lens driving unit 200A that moves the objective lens 200 in the vertical direction.

The objective lens driving unit 200A operates the objective lens 200 so that the distance between the objective lens 200 and the first focus f1 and the distance between the first focus f1 and the second focus f2 are the same. can be moved up and down. In other words, the arrangement of this optical system can be changed by the objective lens driving unit so that the distance (S) from the pinhole to the objective lens corresponds to the distance (2c) between the two focal points of the reflector (T = 2c).

Furthermore, referring again to FIG. 5, the optical system 10 may further include a reflector driver 300A that adjusts at least one of the position and angle of the reflector 300, and in this case, the reflector driver 300A is a reflector ( 300) can be moved up and down, and the angle of the reflector 300 can be tilted. That is, the driver 300A can adjust the position of the reflector 300 up and down by moving the reflector 300 up and down, and adjust the opposing angle of the reflector 300 by tilting the reflector 300 separately or simultaneously. Accordingly, even when the specifications of the wafer's target surface, light source, objective lens, etc. change, the arrangement of the reflector can be changed to optimize it.

Below, we will look at an optical system according to another example of the present invention.

FIG. 11 is a diagram schematically showing a wafer inspection optical system according to another example of the present invention, and FIG. 12 is a diagram illustrating the optical path of FIG. 11 in three dimensions. As shown, in the optical system 10 of this example, the reflector 300 This may consist of a planar reflector.

The flat reflector 300 may be made of a square or circular shape, and the size of the flat reflector may be determined according to the order to be incident and the NA of the objective lens, similar to the elliptical reflector described above.

Meanwhile, the optical system of this example may also further include an objective lens driving unit 200A. However, unlike the objective lens driving unit 200A of the previous example that moves the objective lens 200 in the vertical direction, the objective lens driving unit of this example ( 200A) can adjust the angle of the objective lens 200 so that the reflected light 103 reflected from the reflector 300 is incident perpendicularly toward the objective lens 200.

In addition, together with the objective lens driver 200A, the reflector driver 300A described in the previous example may be further provided, and the reflector driver 300A moves the reflector 300 up and down and simultaneously or selectively moves the reflector 300. The angle of (300) can be tilted. According to the optical system 10 of this example, optimization under various conditions can be possible by appropriately adjusting the objective lens driver 200A and the reflector driver 300A.

As explained above, the scattering profile of the light irradiated to the defects of the wafer in the wafer inspection system can be formed in various forms and have different energy densities depending on the angle and location of the collected light, so the sensitivity of the detector is very high. This may vary, but according to the present invention, scattered light from a wide area beyond the NA of the objective lens can be collected in one place using a reflector, and by using this, various defect signals can be accepted, greatly improving inspection performance.

Above, embodiments of the present invention have been described with reference to the attached drawings, but those skilled in the art will understand that the present invention can be implemented in other specific forms without changing the technical idea or essential features. You will understand that it exists. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

10: Wafer inspection optical system
100: light source
101: Four incident lighting
102: Scattered light
103: reflected light
200: Objective lens
200A: Objective lens driving unit
300: reflector
300A: Reflector driving unit
400: Pinhole
11: wafer
T: target surface
12: Computer system

Claims (18)

A light source that irradiates light at a predetermined angle toward the target surface of the wafer;
an objective lens for receiving scattered light scattered from the target surface of the wafer; and
It includes a reflector that reflects at least a portion of the scattered light scattered from the target surface of the wafer and makes it incident on the objective lens,
The reflector is an elliptical reflector having a first focus and a second focus,
The second focus of the reflector is positioned to be located on the target surface of the wafer,
If the light reflected from the reflector is called reflected light, the reflected light is concentrated at the first focus,
Wafer inspection optics.
delete delete According to paragraph 1,
A wafer inspection optical system, wherein a pinhole is provided at the position of the first focus.
According to clause 4,
An angle of incidence at which the reflected light reflected from the reflector is incident on the pinhole is within the numerical aperture of the objective lens.
According to paragraph 1,
A wafer inspection optical system including a plurality of reflectors.
According to clause 6,
The plurality of reflectors are,
When looking at the optical system from above,
a first reflector positioned opposite the light source;
A wafer inspection optical system comprising a second reflector positioned at a predetermined distance from the first reflector along a circumferential direction of the first reflector.
According to paragraph 1,
The reflector is,
When looking at the optical system from above,
A wafer inspection optical system in the form of an arc centered on the target surface.
According to clause 8,
The center of the reflector is located on the same line as the light source and the target surface,
A wafer inspection optical system, wherein the central angle of the reflector is less than 180 degrees.
According to clause 8,
The center of the reflector is located on the same line as the light source and the target surface,
A wafer inspection optical system, wherein the central angle of the reflector is greater than 180 degrees.
According to paragraph 1,
An objective lens driving unit that moves the objective lens in the vertical direction. A wafer inspection optical system further comprising a.
According to clause 11,
The objective lens driving unit
A wafer inspection optical system that moves the objective lens in the vertical direction so that the distance between the objective lens and the first focus and the distance between the first focus and the second focus are the same.
According to paragraph 1,
A wafer inspection optical system further comprising a reflector driver that adjusts at least one of the position and angle of the reflector.
According to clause 13,
The reflector driving unit,
A wafer inspection optical system capable of moving the reflector up and down and tilting the angle of the reflector.
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