JPS60254109A - Optical device - Google Patents

Abstract

PURPOSE:To optimize lighting to a body and to obtain an image with high resolving power by providing an optical path for lighting the body and an optical path of reflected light from the body independently, and photodetecting selectively scattered light from a pattern in a specific direction of the body. CONSTITUTION:The pattern is formed of a group of lines perpendicular to a wafer 1 and a group of slanting lines crossing them at 45 deg.. Light beam from a white light source 12 is made into parallel light through a condenser lens 13, and the parallel light is passed through a stop 11 and reflected by a holded mirror 10 slanted by 45 deg. to form an image on the wafer 1 through a holed lens 14. The lens 14 and an objective lens 2 are arranged coaxially and the pattern on the wafer 1 is inputted to the photoelectric converter 15 of a video camera, etc. The stop 1 is rotated according to the direction of lines on the wafer 1. Consequently, only scattered light and diffracted light from current lines reach the video camera 15 to easily find a defect on the wafer 1. This device suits to pattern check on ICs and LSIs.

Description

[Detailed Description of the Invention] (Background of the Invention) The present invention relates to a device that provides illumination suitable for photoelectric detection and observation to a target object, and in particular, to a device that provides illumination suitable for photoelectric detection and observation, and particularly for illumination that has a specific directionality, such as an integrated circuit pattern such as an IC or LSI. This device is suitable for photoelectric detection and observation of objects.

(Description of Prior Art) Most lines of integrated circuit patterns are composed of vertical lines or horizontal lines for advantages in circuit design or drawing. Furthermore, when inserting memory cells, wiring patterns, or patterns for auto-alignment, it is limited to six diagonal lines of ±45 degrees.

Systems that handle such IC or LSI pattern information and perform image processing include, for example, automatic alignment between masks and wafers, masks and semiconductor exposure equipment, or wafers and processing equipment, and defect inspection systems for mask and wafer patterns. .

In the field of IC, LSI, etc., objects of interest are masks or reticles and bars on which patterns are formed. However, when attempting to optically detect a pattern, there is a clear difference between the former two and a wafer. That is, the former two have a structure in which a thin film of chromium or chromium-chromium oxide is patterned and placed on a transparent glass substrate. Therefore, optically, the pattern portion has only a binary state of transmission or non-transmission, and high-contrast pattern detection can be easily performed. On the other hand, since the wafer is an opaque material and is itself a reflective object, it has the disadvantage that it is difficult to obtain images with good contrast. It is well known that a sufficient S/N ratio cannot be obtained when wafers are detected using the normal bright field method, and therefore a method of detecting under dark field illumination is adopted.

Conventionally, an invention proposed for this type of use is Japanese Patent Application No. 57-210908 "Detection Optical System", and the optical system described in this application has apertures that are conjugate to each other in the system, and By devising the shape of the diaphragm aperture, vertical lines can be selectively detected, and horizontal lines can be selectively detected.

The operation based on this configuration will be explained in more detail using FIG. 1. Reference numeral 1 is a wafer having an integrated circuit pattern of fine irregularities, 2 is a microscope objective lens, 3 is a beam splitter 14 for branching an optical path, and 5 is an aperture stop. An illumination light flux coming from a light source (not shown) located at a position conjugate with the pupil of the objective lens 2 passes through an aperture 4, becomes a hollow light flux, and illuminates the object 1 with diagonally shaded light. The light scattered by the object 1 passes through the aperture 5 and becomes imaged light 6 and is detected. Light that is specularly reflected without being scattered is cut off by the aperture 5. The apertures 5 and 6 are connected in a conjugate relationship by the objective lens 2.

One of the limitations of this optical system is that the objective lens itself is used as the illumination system. And the illumination light is applied to the outside, that is, from the NA(
Even though a light beam with a large numerical aperture (numerical aperture) is used, what is actually detected is the small inner NA area, so dark field detection is performed at the expense of resolution.

In addition, there are other limitations in lens design, such as the need to provide a margin for the illumination light to pass through each lens of the objective lens, and the fact that illumination is transmitted through the objective lens itself, which tends to cause flare.

(Object of the Invention) An object of the present invention is to enable a large NA luminous flux to be used for detection.

Further, this has the advantage of reducing flare with a simple optical system, enabling accurate detection corresponding to the directionality of the pattern, and using white light, which has the effect of mitigating the harmful effects of interference.

(Description of the Embodiment) Before entering into the description of the configuration of the embodiment, the angular distribution of the luminous flux will be explained using FIGS. 2(a) and 2(b). FIG. 2(a) is a three-dimensional representation of a light beam diverging from a certain point A, and FIG. 2(b) is a two-dimensional representation of its angular distribution. The angular distribution shown in FIG. 2(b) is realized on the focal plane of the objective lens 2 in FIG. Although the present invention does not pass illumination light through an objective lens, it is possible to detect a pattern in a specific direction by limiting the angular distribution of illumination light and detection light with respect to point A to be observed. Features.

Figure 3 (a) shows the angular distribution of the optical system that detects the horizontal line, and the diffracted light from the horizontal line is in the vertical direction (the direction of the white arrow).
heading to Further, as shown in FIG. 3(c), the diffracted light from the vertical line is directed in the left and right directions.

If the filament is illuminated with the illumination light of the inner cone in FIG. 2(a), diffracted light or scattered light will exist between the outer cone and the inner cone.

In the configuration of the embodiment described later, on the contrary, illumination is performed from between the outer and inner cones, and reflected light passes through the inner cones.

Therefore, the angular distribution of illumination light for extracting diffracted light or scattered light from the horizontal line in FIG. 3(a) must exist within the hatched area in FIG. 3(b). The circle in the middle of the figure is the range of angular distribution in which the imaging optical system captures the light flux. As can be seen from this figure, the angular distribution of the illumination system that detects a pattern in a specific direction can be determined by drawing a tangent with a direction perpendicular to the pattern direction to the angular distribution of the light flux captured by the imaging optical system. You can

Figure 3 (C) shows the relationship between the illumination light and the imaging light for the pattern in the vertical direction, (e) in the -45° direction, and (g) in the +45'' direction. It is sufficient that the angular distribution of the illumination optical system is within the angular distribution of the applied part.As shown in Figure 3, there is a book that allows you to easily determine the angular distribution of illumination light when detecting only a pattern in a specific direction. can.

FIG. 4(a) shows the range of angular distribution of the illumination system required when detecting only horizontal patterns. The angular distribution of the illumination system only needs to fall within the hatched area. The range of the angular distribution of the illumination light that detects only patterns in the vertical direction or ±45'' direction can be easily adjusted by rotating Fig. 4(a). Also, Fig. 4(b) shows the vertical line. , is the angular range of the illumination system required when detecting only lines in the ±456 directions without detecting horizontal lines.

The illumination method according to the invention can be easily applied to all conventional dark field illumination methods. As a typical example, FIG. 5 shows an example in which a ring mirror 10 is used to illuminate the objective lens barrel from outside, and FIG. 6 shows an example in which a fiber bundle is attached to the objective lens barrel.

In FIG. 5, reference numeral 1 denotes a wafer, and a pattern consisting of a group of lines in orthogonal directions and a group of diagonal lines forming 456 lines with these lines is provided. 2 is an objective lens. Reference numeral 10 denotes a ring mirror, which is obliquely installed near the pupil of the objective lens 2, and whose orthogonal shadow has a circular aperture. Reference numeral 11 denotes a diaphragm, which has an aperture corresponding to the hatched area in FIG. 4(a) and is rotated intermittently every 45", or has an aperture corresponding to the hatched area in FIG. 4(b). Therefore, fixed or intermittent rotation is selected as appropriate depending on the application.

Reference numeral 12 denotes an illumination light source, which is preferably a white light source, but may also be a monochromatic light source. 13 is a condenser lens; 14 is a perforated lens having an aperture in the center; the perforated lens 14 is disposed coaxially with the objective lens 2. In this example, Koehler illumination is used in which the light beam of the illumination light source 12 is once imaged near the pupil of the perforated lens 14 by the condenser lens 13 to illuminate the wafer 1, but a critical illumination method may also be used. The aperture 11 satisfies a substantially conjugate relationship with the pupil of the objective lens 2 with respect to the perforated lens 14 and the objective lens 2 when the surface of the wafer 1 is a mirror surface. 15 is a photoelectric converter such as a video camera, which images the pattern of the wafer 1 through the objective lens 2; The signal from the video camera 15 is displayed on a video receiver (not shown) or subjected to electrical processing and displayed. In addition, if it is necessary to determine the range of angular distribution of the illumination system more precisely, the ring mirror 10
It is preferable to arrange a relay optical system between the aperture 11 and the aperture 11.

With the above configuration, if the rotation angle of the aperture 11 is selected in accordance with the directionality of the pattern on the wafer 1, for example, the vertical direction, the horizontal direction, or the 45° direction, each time, the filament with the selected directionality is The wafer 1 is illuminated with an illumination light flux such that only the diffracted light and scattered light of the wafer 1 reaches the video camera 15. In this case, if there is a defect on the wafer 1, the defect will cause scattered light regardless of the angular distribution of the illumination light, so a light spot that does not communicate with other filaments will appear on the screen of the image receiver and be discovered. This is determined by mutual comparison with the video signals of other chips above.

Further, when used in a mark detection system for auto-alignment, the aperture 11 is fixed in accordance with the direction of the striations forming the mark, and the mark is illuminated with illumination light having an optimal angular distribution. Therefore, even if illumination light is incident on a region other than the mark, the scattered light from this region will not reach the photoelectric converter 15, improving the S/N ratio.

FIG. 6 shows the main part of another embodiment. Here, a branched optical fiber bundle 20 is arranged in place of the diaphragm 11, ring mirror 10, and perforated lens 14 shown in FIG. 5, and performs dark field illumination. 21 is an illumination light source, and 22 is an elliptical mirror for condensing light. The elliptical mirror 22 focuses the light from the illumination light source 21 onto the input end of the optical fiber bundle 20.

Branch ends 20a, 20e of optical fiber bundle 20
The other parts are arranged around the objective lens 2 facing inward so that the illuminated parts overlap. If the angle distribution provided by these branch ends is circular, the branch ends 20a to 20h may be arranged as shown in FIG. Here 20a and 20
The fiber combination e corresponds to horizontal line detection, the combination 20b and 2Of corresponds to the pattern in the +45” direction, 20C and 20g correspond to the vertical line, and 20d and 20h correspond to the detection of the pattern in the 1456 direction. By selecting an arbitrary combination of fibers using the shutter 23 or the like, it is possible to specify a pattern in a direction desired to be detected.

Of course, the shape of the fiber 20 and the shape of the diaphragm 11 shown in FIG. 5 can be set arbitrarily, so the angular distribution can be set in consideration of the amount of light, crosstalk between each pattern, etc.

Furthermore, although only the case of a reflective object has been shown up to FIG. 6, the present invention can be easily applied to the case of a transparent object such as a mask. In Fig. 8, 30 is the objective lens for the illumination optical path, and 31 is the fifth objective lens.
It is a diaphragm similar to the diaphragm 11 shown in the figure. An illumination light flux coming from a light source (not shown) passes through an illumination objective lens 30 to provide dark field illumination.

The hatched light flux indicates the light flux that illuminates any one point in the illuminated area. Since this light flux is given an angular distribution according to the direction of the filaments of the mask 1', only the diffracted light of the filaments oriented in the specified direction passes through the objective lens 2 and is used for detection.

(Effects of the Invention) According to the present invention described above, it is possible to perform optimal illumination according to the target object, and it is also possible to use an optical system with a large numerical aperture for detection and observation, thereby obtaining a high-resolution image. There is an effect that can be done.

This also increases detection accuracy, which has the advantage of increasing subsequent operation speed and reducing malfunctions. Since the structure of the optical system is relatively simple, there is almost no increase in cost or assembly effort.

[Brief explanation of drawings]

FIG. 1 is an optical cross-sectional view of a prior example. FIGS. 2(a) and 2(b) are diagrams for explaining the angular distribution of the luminous flux. Figure 3(a)(c)
(e) (g) are diagrams showing the diffraction direction, (b) (d) (f
) and (h) are diagrams showing the angular distribution of illumination light. Figure 4(a) (
b) is a diagram showing the angular distribution of illumination light. FIG. 5 is an optical sectional view showing an embodiment of the present invention. FIG. 6(a) is an optical sectional view of another embodiment, and FIG. 6(b) is a perspective view of the constituent members. FIG. 7 is an explanatory diagram of the arrangement of the constituent members. FIG. 8 is an optical sectional view showing another embodiment. In the figure, 1 is a wafer, 2 is an objective lens, 10 is a ring mirror, 11 is an aperture, 12 is an illumination light source, 14 is a perforated lens, 20 is an optical fiber bundle, 23 is a shutter, 3o is an objective lens for illumination, 31 is the aperture. Applicant Canon Co., Ltd. Kabuto 3 items (L) (c) (e) (El) Almost 4 rin (α) (b) 5th shoe Figure 6 1 ゛) (″

Claims (1)

[Claims] (1) A device comprising an illumination system that illuminates an object without passing through an objective lens that contributes to image formation of the object, and a light receiving system that receives light coming from the object through the objective lens, the apparatus comprising a pattern of the object in a predetermined direction. An optical device comprising: means for imparting an angular distribution to illumination light from the illumination system so that the light reception system selectively receives scattered light from the illumination system.