JPS60182734A - Inspecting device for pattern - Google Patents

Abstract

PURPOSE:To improve the efficiency of inspection while facilitating work by obtaining combined focal images to each layer and inspecting several circuit pattern when a plurality of the layers to which the circuit patterns are each connected are laminated on a light-transmitting body to be inspected and these patterns are inspected by using an optical system. CONSTITUTION:A light-transmitting body to be inspected is constituted by a semiconductor such as a semiconductor wafer 1, and a plurality of layers 1a-1c to which circuit patterns 2a-2c are each connected are laminated on the wafer 1. Optical system beams are projected from the surface of the wafer 1 in order to decide acceptable or defective patterns 2a-2c, but the focal surface of an optical system is changed at that time and the combined focal image of the pattern 2a is detected first. Accordingly, focal images with other patterns 2b and 2c are dimmed, and only the pattern 2a is made clear. The same operation is conducted to the pattern 2b and successively the pattern 2c, and acceptables or defectives are extracted and inspected regarding all patterns.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a pattern inspection method that can effectively inspect patterns formed at different positions in the depth direction of a transparent inspection object such as a semiconductor wafer. Regarding equipment.

[Technical background of the invention and its problems]

In the manufacturing process of semiconductor devices, silicon (Sl
), etc., to visually observe circuit patterns formed on semiconductor wafers to inspect the quality of the circuit patterns, and also to test the quality of the manufacturing process. However, recently, the circuit pattern of semiconductor devices is LSI.
Circuit patterns, as typified by JZ, are becoming increasingly complex, and circuit patterns are being formed over multiple layers. For this reason, visual inspection of circuit patterns has become extremely difficult.

That is, conventionally, pattern inspection of semiconductor devices is performed by visually observing the pattern formed on the semiconductor device using a microscope, but since the focusing range (depth of field) of the optical system of the microscope is extremely narrow, When the optical system is focused on a certain layer to be inspected, images of other layers become blurred due to the focus shift. Therefore, when inspecting the pattern of a semiconductor device over multiple layers, it is necessary to adjust the focus of the optical system and visually observe the circuit patterns of each layer. It was necessary to investigate the interrelationships. However, in this case, only the image of the focused layer is clear, and if the images of other layers are blurred, the blurred image will probably be an eyesore compared to the focused image, so the pattern inspection is difficult. was extremely difficult.

[Purpose of the invention]

The present invention has been made in consideration of these circumstances, and its purpose is to improve the effectiveness of each circuit pattern formed over multiple layers of a translucent test object such as a semiconductor wafer. The object of the present invention is to provide a highly practical pattern inspection device that can perform inspections in a variety of ways.

[Summary of the invention]

The present invention focuses an optical system on a plurality of positions in the depth direction of a transparent object to be inspected to respectively image the object to be inspected,
The focused points (elements) of each of the focused focal planes of each of these stripes are extracted, and the pattern of each focal position of the object to be inspected is inspected from the images of these focused points.

〔Effect of the invention〕

Thus, according to the present invention, the focal position of the optical system is adjusted to each layer to be inspected of the object to be inspected, and only the image of the focused plane is obtained from each strip of the object to be inspected whose focal positions are aligned. Since the pattern is inspected after extraction, it becomes possible to easily and efficiently inspect the pattern of the object to be inspected. In other words, since pattern inspection is performed by removing unnecessary image components that cause so-called blurring from the image of the object to be inspected other than the focused plane, it is possible to clearly capture the pattern to be inspected on the object to be inspected. , its practical effects are enormous.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

1 and 2 illustrate the basic inspection principle of the present invention. For example, a semiconductor wafer 1, which is a light-transmitting object to be inspected, has circuit patterns 2a, 2b, and 2c formed over a plurality of layers 1a, 1b, and 1c, respectively.

These circuit patterns 2a, 2b, and 2c are formed in each layer 1a, lb, and 1c of the semiconductor wafer 1 according to the functionality required for the semiconductor element. Pattern 2a, 21+, 2
The focus of the optical system of the microscope IVl mirror for inspecting c is focused on each layer 1a, Ib, lc of the semiconductor wafer 1 on which the circuit patterns 2a, 2b, 2c are formed according to the CAD information, which is the specification 51 of the semiconductor element, for example. are adjusted to each.

That is, the optical system of the microscope is focused on a plurality of circumferential positions where the circuit patterns 2a, 21) and 2c are formed in the depth and thickness direction of the semiconductor wafer 1, respectively.

As shown in FIGS. 2(a) to (C), each strip of the semiconductor wafer 1 seen by the optical system focused on each of these sets 1a, 11+, and 1c is at its focused point. It consists of a clear image on the plane and a so-called blurred image at a position deviated from the focused plane. Specifically, in the image of the semiconductor wafer 1 shown in FIG. 2(a) when focusing on the upper surface (layer 1a) of the semiconductor wafer 1, a clear image of the circuit pattern 2a can be obtained, and the other layer 1 of
The images of the circuit patterns 2b and 2c at positions b and 1c become blurred and unclear. Therefore, from this one image, the 19 components that are blurred and blurred are removed by filtering, etc., and only the image of the focused plane is extracted. Then, the pattern of the semiconductor wafer 1 is inspected based on the focused image. be exposed.

FIG. 3 is a schematic diagram of a pattern inspection apparatus according to an embodiment of the present invention, which performs pattern inspection of an object to be inspected in this manner. Semiconductor wafer 1, which is the object to be inspected, is on stage 1
1 and used for pattern image detection by a microscope 12. Is microscope 12 the optical system? 2a is adjusted by an autofocus mechanism 13 to focus on a predetermined position in the depth direction of the semiconductor wafer 1 on the stage 11. The image of No. 1 is photo-electrically converted and read by the TV camera 14. Focusing of the optical system 12a on the semiconductor wafer 1 by the autofocus mechanism 13, and the stage 1 on which the semiconductor wafer 1 is placed.
The positional control of the optical system 12a of No. 1 is performed under the control of the central control section 1G based on the C and AD information related to the manufacturing of the semiconductor wafer 1 stored in the CAD information memory 15. In addition, the position control of the stage 11 is...
The stage drive 34i1 is controlled by the stage control section 17 which receives the focusing completion signal from the mechanism 13.
8, but instead of moving the stage 11, the position on the optical system 12a side may be controlled to move.

Therefore, the image of the semiconductor wafer 11 seen by the TV camera 14 (an image focused on the formation layer of the circuit pattern to be inspected) is transmitted to the A/D converter 1.
9 and is digitally encoded and stored in the image memory 20. The image data of the semiconductor wafer 11 stored in the image memory 20 is supplied to a filter circuit 21 and subjected to image processing, and image components other than the in-focus plane are removed, that is, image components that are blurred are removed. Only the focused image of the focal plane that has been brought into focus is extracted and rewritten in the image memory 20. This filter circuit 2
The focused image extraction process according to No. 1 is performed, for example, by performing two-dimensional Fourier transform on the image taken by the TV camera 14 of the semiconductor wafer 1, extracting only its high frequency components, and then performing two-dimensional inverse Fourier transform on the component. be exposed. By this processing, since the image component that is deviated from the focal plane and has caused so-called blur has a low frequency component, the image component other than the in-focus plane that has caused the blur is removed.

The image of the focused plane of the semiconductor wafer 1 at the focal position of the optical system 12a extracted in this way is transmitted to the binarization circuit 22.
After being converted into a binary image via the memory selection circuit 23
are selectively written into the image memories 24a, 24b to 2411 corresponding to a plurality of focal positions set in the optical system 12a, respectively.

The above processing is performed by adjusting the focus of the optical system 12a for each layer on which a circuit pattern is formed on the semiconductor wafer 1, and the focused image at each focal position of the semiconductor wafer 1 is stored in the image memory 24a.
, 24b to 2411, respectively.

The display control circuit 25 selectively reads out the images of the focused planes stored in the image memories 24a, 241) to 24n under the control of the central control unit 16, and displays the images on the display 26. are doing. Visual inspection of the circuit patterns of each layer of the semiconductor wafer 1 is performed from this displayed image. Further, each focused plane image stored in the image memories 24a, 24b to 24n is read out to a pattern matching circuit 27 under the control of the central control section 16, and
Pattern inspection is performed by comparing the design circuit pattern of each layer stored in the D information memory 15. This pattern matching is performed by aligning the focused image and the designed circuit pattern, which is CAD information, with each other, then subtracting between the two patterns, and measuring the area of the difference. In this case, when the area where the difference occurs is equal to or larger than a predetermined threshold value, this may be determined as an abnormality.

Thus, according to the present apparatus configured in this manner, circuit patterns formed on each of the plurality of layers of the semiconductor wafer 1, which is a translucent inspection object, can be extracted as focused images of each layer. Therefore, it is possible to accurately inspect the pattern without being affected by a so-called blurred image caused by a defocus. Moreover, in this way, the circuit patterns of each layer of the semiconductor wafer 1 can be clearly extracted and inspected by aligning the focus according to the CAD information, so the inspection efficiency is very good.
It is also easy to automate it.

Therefore, its practical advantages are enormous.

Note that the present invention is not limited to the embodiments described above. For example, a color display may be used to distinguish and display focused images at each focal position of the object to be inspected using different display colors. Further, the focused image seen as described above and the designed circuit pattern indicated by the CAD information may be displayed in a superimposed manner.

Further, in the above-described embodiment, the image of the focal plane is extracted by filtering processing in the spatial frequency domain, but so-called digital filtering processing in which neighborhood calculation is performed for each pixel may also be performed. Furthermore, images of a large number of focal positions are collected at fine intervals in the depth direction of the object to be inspected, and each part of each of these images is checked to determine whether or not each part is in focus. Patterns may also be extracted. In this case, the in-focus position may be determined by, for example, examining changes in image density at a plurality of focal positions of the portion to be inspected. Alternatively, each image may be Fourier transformed for each portion to be inspected, and the focal point position may be determined by determining the focal plane where the power of the high frequency component is maximum. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams for explaining the principle of pattern extraction of a focused plane according to the present invention, and FIG. 3 is a schematic diagram of a pattern inspection apparatus according to an example of the present invention. 1... Semiconductor wafer (object to be inspected), 2a, 2b, 2
c...Circuit pattern, 11...Stage, 12...
・Microscope, 12a...Optical system, 13...O1~・
Low focus, 14...TV camera, 15...C
AD information memory, 16... Central control unit, 17... Stage control unit, 18... Stage drive view side, 19...
・A/D converter, 20... Image memory, 21... Filter circuit, 22... 2 +ffi conversion circuit, 23...
- Memory selection circuit, 24a, 24b to 24n... Image memory, 25... Display control circuit, 2G... Screenplay, 27... Pattern matching circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] (1) The focal position of an optical system for obtaining an image of a translucent test object is set at a plurality of locations in the depth direction of the test object, and the optical system means for respectively capturing images of the object to be inspected under the plurality of focal alignment conditions of the system; means for extracting focused images of each focused plane of each of these lines; A pattern inspection apparatus comprising means for inspecting the pattern of the object to be inspected from focused images having different focal planes. (2) The plurality of focal positions of the optical system set in the depth direction of the object to be inspected are comprised of positions of the pattern forming layer according to the design specifications of the object to be inspected. (3) The means for obtaining a focused image of each focal plane involves filtering the image of the object to be inspected taken through the optical system to remove image components that deviate from the focal plane. The pattern inspection device according to claim 1. (4) The means for inspecting the pattern of the object to be inspected compares the focused image with pattern information based on the design specifications of the object to be inspected. The pattern inspection apparatus according to claim 1, which is for carrying out the inspection.