JPH0437922B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an automatic pattern defect inspection method, and in particular to a method and method for detecting defects from complex and fine patterns such as circuit patterns formed on LSI wafers. This is related to the device.

[Background of the invention]

Fine patterns formed on LSI wafers are made of multiple thin film layers made of different materials. For this reason, the defects include pattern shape defects caused by poor planar shape of the layer, and hue defects or density unevenness defects caused by abnormal layer thickness. Humans can detect these defects by visually observing them with a microscope.
However, in order to perform this automatically, it is necessary to separately detect pattern shape information and hue or shading information. Pattern shape information is originally based on pattern edges having steps, and dark field illumination is effective for efficiently detecting this. However, with dark-field illumination, only the edge portions are detected, and the hue and shade within the smooth pattern cannot be detected. On the other hand, bright-field illumination can detect hue and density unevenness, but pattern edges are also detected at the same time, and attempting to separate this information requires extensive image processing, making it impractical.

[Purpose of the invention]

The purpose of the present invention is to solve the problems of the prior art as described above, and to solve the problems of the prior art, it is an object of the present invention to solve pattern shape defects caused by shape defects such as chips that occur in the top layer transparent thin film pattern on a substrate forming a multilayer fine circuit pattern such as an LSI wafer. And, to provide a method and device for detecting fine pattern defects, which can separate and detect hue defects or shade unevenness defects caused by an abnormality in the film thickness of the layer without performing extensive image processing. It is in.

[Summary of the invention]

That is, in order to achieve the above-mentioned object, the present invention provides a method for forming a multi-layer microcircuit pattern from the surface of the cut-off portion of the uppermost transparent thin film pattern to approximately the same location on the uppermost transparent thin film pattern on the substrate on which the multilayer fine circuit pattern is formed. In order to increase the amount of reflected light and make the difference in the uppermost layer transparent thin film pattern visible, first illumination light consisting of S-polarized light is irradiated from an oblique direction to perform dark-field illumination, and a wavelength different from that of the first illumination light is applied. The second illumination light is irradiated from a substantially vertical direction, passes through the uppermost transparent thin film pattern, is reflected by the surface of the lower layer of the uppermost transparent thin film pattern, and is transmitted through the uppermost transparent thin film pattern. Bright field illumination is performed so as to vary according to the film thickness of the uppermost transparent thin film pattern, and the first reflected light and the second illumination light are emitted from the difference part of the uppermost transparent thin film pattern caused by the first illumination light. The second reflected light that passes through the uppermost transparent thin film pattern and is reflected on the surface of the lower layer of the uppermost transparent thin film pattern is focused through the objective lens, and the first
The reflected light image and the second reflected light image are separated based on the difference in wavelength and detected by each image detector, and the first reflected light image obtained by one of the image detectors is The image signal is compared with the first reference image signal to detect a shape defect in the uppermost layer transparent thin film pattern based on the mismatch signal of the outline indicating the difference, and the second reflected light obtained from the other image detector is detected. A second image signal based on an image is compared with a second reference image signal to detect a defect due to a film thickness variation of the uppermost layer transparent thin film pattern using a difference image signal indicating a change in shade or hue. A method and apparatus for detecting pattern defects.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. Figure 1 shows a dark-field illumination system including a light source 1, a condenser lens 2, a narrow band filter (wavelength λ ₁ ) 3 for selecting the wavelength for dark-field illumination, a ring-shaped aperture slit 4, a ring-shaped mirror 5, and a paraboloid. concave mirror 6,
In addition, a bright field illumination system includes a light source 7, a condenser lens 8, a wavelength selection filter 9, and a circular aperture slit 1.
0, a half mirror 11, an objective lens 12 as an imaging system, a wavelength separation mirror (for example, a dichroic mirror) 13, and a dark field image detection image sensor 1
4, bright field image detection image sensor 15, binarization circuit 16, memory 17, image comparison circuit 18, binarization circuit 19, memory 20, image comparison circuit 21, determination section 22, XY table 23, feed motor 24, It is composed of a table control circuit 25 and an overall control circuit 26.

An object to be inspected, for example, an LSI wafer 27, is accurately positioned and fixed on the XY table 23 in advance. Positioning and fixing mechanisms are not shown. The pattern on 27 is illuminated in dark field and bright field. The dark field illumination is limited to a wavelength λ by a filter 3, and is illuminated onto the pattern from an oblique direction around the pattern by a parabolic concave mirror 6. Bright field illumination is limited to light that does not include the wavelength λ by a filter 9, and is passed through a half mirror 11 to the objective lens 1.
2. It is illuminated from above. The pattern is magnified by the objective lens 12, and a dark-field image with a wavelength λ is formed on the image sensor 14, and a bright-field image with a wavelength other than λ is formed on the image sensor 15. Wavelength and optical path separation in the imaging system is performed by a thin film mirror 13.

Assume that there is a pattern shown in FIG. 9 on the LSI wafer 27. FIG. 9a is a plan view of the pattern, and FIG. 9b is a sectional view taken along the dashed line in a. That is, there is a thick surface layer of SiO ₂ around it, and the SiO ₂ layer is extremely thin only in the pattern area.
Here, the part indicated by A is a defect in which a part of the pattern shape is missing, that is, the contour shape is abnormal, and the part indicated by B is a defect in which the thickness of the SiO ₂ layer is locally thick. A pattern shape defect like A is detected as an abnormality in the planar shape of the pattern edge. On the other hand, in the case of a defect such as B in which the thickness of the transparent thin film is abnormal, the planar shape of the pattern edge is not abnormal at all, but the brightness and hue of the planar image change.
This occurs because the amount of transmitted light changes due to a change in the thickness of the thin film, or because the interference color due to the interference of reflected light from the surface and bottom surface of the thin film changes with the change in thickness. Although FIG. 9 shows an example of a single layer pattern, similar defects occur in multilayer patterns as well. Now, when this wafer pattern is detected, 14
A dark-field illumination image as shown in FIG. 2a is formed on the imaging plane. That is, the pattern edges are detected brightly, and the other substantially smooth surfaces are detected darkly. FIG. 2b shows an example of the video signal on the dashed line shown in the center of a, and the edges are bright and clearly detected. Therefore, in the binarization circuit 16,
When the image is binarized using the binarization threshold value V _TH1 shown by the chain line in FIG. On the other hand, a bright field illumination image as shown in FIG. 3a, for example, is formed on the imaging plane 15. That is, the smooth surface of each pattern has shading determined by the properties of the pattern.
In the example shown in FIG. 3, there is an abnormality in the pattern film thickness to the right of the bone-like pattern, and the shading changes. This part is defective. FIG. 3b shows the video signal on the dashed-dotted line in FIG. 3a, and the output is slightly reduced at the defective portion. The threshold value V _TH2 is set so that this part is detected as dark (value 0), and when the pattern is binarized, the pattern part with almost uniform brightness is set to a value 1, and the value 1 is set so that this part is detected as dark (value 0). A binary pattern is obtained in which the value 0 is set at the edge, the edge, and its surroundings.

FIG. 4 shows an LSI wafer as an example of an object to be inspected. On the wafer 27, LSI chips 28 are repeatedly arranged in alignment. When linear image sensors are used as the image sensors 14 and 15, the image sensors have a field of view as shown by the solid line 29 in FIG.
Move like. Therefore, the detection patterns are sequentially stored in the memories 17 and 20, and the pattern signal at the same position one chip before the top of the pattern being detected is read out. Therefore, comparison circuit 1
At steps 8 and 21, the pattern being detected and the pattern at the same position of the pattern one chip before are compared, and when a mismatch exists, the defect determining section 22 is notified of the presence of the mismatch, its size, and position. When the defect determination unit is notified from 18 or 21 of the existence of a mismatch having a size greater than a preset value,
The position is stored as a defect position. A circuit for outputting the defect position, defect size, etc. is not particularly shown. The overall control circuit 26 controls the sequence of the above-described operations. As described above, in this embodiment, the contour shape and shading information of a pattern can be simultaneously detected separately and automatically inspected using dark field illumination and bright field illumination.

Although a linear image sensor is used in this embodiment, a two-dimensional image sensor may be used, and the XY table may be fed in steps or continuously, and pulsed light emission may be used as the illumination light source. Further, in this embodiment, the detected image is binarized and compared as a binary image, but it may be converted into a multivalued image using an A/D converter and compared as a multivalued image. In addition, in this example, a comparison inspection with the previous chip was exemplified, but this can also be done with comparison inspection between repeated patterns within one chip, comparison inspection between two wafers, and non-defective pattern information that can be prepared in advance such as a design pattern. It may also be a comparative test.

FIG. 5 shows another embodiment of the invention.
The dark field illumination system consists of a light source 1, a condenser lens 2, a filter 3 with wavelength λ, and a ring-shaped slit 3 that also serves as a polarizing plate.
1. It is composed of a ring-shaped mirror 5 and a parabolic concave mirror 6, and provides uniform dark-field polarized illumination to the target surface from the surrounding area. The polarization is S-polarized light (vibration parallel to the surface to be inspected). The bright field illumination system includes two light sources 32 and 33 with wavelength components λ' and λ'' different from the wavelength λ, a condenser lens 34, and a narrow band filter 3 with a wavelength λ'.
5. Narrow band filter 36 for wavelength λ'', half mirror 37 for combining λ' and λ'', circular aperture slit 10,
It is composed of a half mirror 11. The detection system includes an objective lens 12 and a mirror 3 for separating bright field and dark field illumination lights.
8. This is a separation mirror 39 that transmits only the wavelength λ, reflects λ' and λ'', and separates the bright field illumination light into λ' and λ''.
λ′ narrow band filter 40, λ″ narrow band filter 4
1. It is composed of an image sensor 42 for bright field λ' and an image sensor 43 for bright field λ''. The determination circuit section includes an A/D converter 44, a memory 45, a hue extraction circuit 46, an image comparison circuit 47, 48, a determination section 22, an XY table 23, a feed motor 24, a table control circuit 25, and an overall control circuit 26.

As shown in FIG. 6, the polarizing plate/ring-shaped slit 31 can be divided and combined to provide almost uniform S-polarized dark field illumination around the area. S
The reason why polarized light is used is that it is effective in detecting the top layer pattern of a multilayer complex pattern with good contrast. FIG. 10 shows the structure of a dynamic RAM as an example of a wafer multilayer pattern. That is, data line 49 is A, word line 5
0 is made of polycrystalline silicon, and a storage area consisting of an electrode 51 also made of polycrystalline silicon and an inversion layer region of a P substrate 52 is laid out directly below the data line 49 in the data line direction. Note that an insulating film is formed between the word line 50 and the data line 49. Consists of many types of layers like this
In order to inspect the pattern of each layer of an LSI wafer, it is necessary to inspect whether the uppermost layer has been formed correctly each time it is formed, and the detection of the uppermost layer meets this purpose. The principle behind this is that, as shown in Figure 7, S-polarized light has a higher reflectance than P-polarized light; in other words, much of the light illuminated on a multilayer pattern is reflected from the surface, making the pattern edge of the top layer obvious. be. The dark-field illumination image is detected by the image sensor 14 and compared with the dark-field illumination image at the same position of the pattern one chip before by 45 and 47. This point is the same as the first embodiment.

On the other hand, with bright-field illumination, two wavelengths λ' and λ'' are set in advance to make it easier to detect color changes in the target pattern.
λ'', and the images are detected by image sensors 42 and 43, respectively.The hue extraction circuit 46 does not need to extract the hue accurately, but only needs to be able to detect subtle changes in tone of the multilayer thin film.Generally, thin films are bright. Field illumination produces interference colors as shown in Fig. 8, and the spectral reflectance thereof varies depending on the film thickness t.Therefore, if two wavelengths λ' and λ'' are selected that have prominent characteristics, each Assuming that the output at wavelength is V(λ') and V(λ''), the change in color tone can be made apparent by finding V(λ')/V(λ''). Here V(λ″)
<V When _TH3 , by not performing division and setting the output to zero, it is possible to prevent false detection in dark areas such as pattern edges, and it is possible to bring about the same effect as the first embodiment in terms of density changes. can. At step 46, the above processing is performed. 45 and 46 have the same functions as in the first embodiment, and detect discrepancies in hue and shade changes, which can be recognized as defects at 22.

Also in the second embodiment, the additional items in the first embodiment (two-dimensional image sensor and variations of the comparison target) hold true. Further, in the second embodiment, the case where two wavelengths of λ' and λ'' are used is illustrated, but a method of detecting the three primary colors of blue, red, and green and determining the phase angle of the color may also be used. Alternatively, it may be a method that uses a wavelength light source, cuts only the wavelength λ, and detects images of multiple wavelengths using a plurality of image sensors.

〔Effect of the invention〕

As explained above, according to the present invention, the first reflected light image from the difference part of the uppermost layer transparent thin film pattern by the first illumination light consisting of S-polarized light and the uppermost layer transparent thin film pattern by the second illumination light. The second reflected light image reflected from the surface of the lower layer of the uppermost layer transparent thin film pattern is separated based on the difference in wavelength and detected by each image detector. The first image signal based on the first reflected light image and the first
A shape defect in the uppermost layer transparent thin film pattern is detected by comparing the reference image signal with the reference image signal of the contour part indicating the difference part, and a second reflected light image obtained from the other image detector is detected. By comparing the image signal and the second reference image signal and detecting defects due to film thickness variations in the top layer transparent thin film pattern using the difference image signal indicating changes in density and hue, multilayer microcircuits such as LSI wafers can be detected. In the uppermost transparent thin film pattern on the substrate where the pattern is formed, we can determine whether the defect is due to an abnormal contour or a variation in the film thickness.
The simple configuration allows for high-speed separation and inspection, provides feedback to process conditions, investigates the cause of defects, and produces products such as semiconductors with high yield.

[Brief explanation of drawings]

Figure 1 is an overall configuration diagram for explaining one embodiment of the present invention, Figure 2 is a diagram for explaining pattern detection status and binarization in dark-field illumination, and Figure 3 is a diagram for explaining pattern detection status in bright-field illumination. 4 is a diagram illustrating the detection field of view and the detection sequence in the embodiment, FIG. 5 is an overall configuration diagram illustrating another embodiment of the present invention, and FIG. 6 is a diagram explaining the binarization. is a diagram explaining a specific example of the ring-shaped polarizing plate in the embodiment of FIG. 5, FIG. 7 is a diagram explaining the difference in the reflection characteristics of S-polarized light and P-polarized light, and FIG. 8 is a diagram explaining the interference color of the thin film. Figure 9a shows the spectral reflectance characteristics for
Plan view showing the pattern on the LSI wafer, Figure 9b
is a cross-sectional view of FIG. 9a, and FIG. 10 is a diagram showing the structure of a dynamic RAM as an example of a wafer multilayer pattern. 1...Light source, 2...Condenser lens, 3...
Narrowband filter, 4...ring-shaped opening slit,
5... Ring-shaped mirror, 6... Parabolic concave mirror, 7...
...Light source, 8...Condenser lens, 9...Wavelength selection filter, 10...Circular aperture slit, 11...
...Half mirror, 12...Objective lens, 13...
Wavelength separation mirror, 14...Dark field image detection image sensor, 15...Bright field image detection image sensor,
16... Binarization circuit, 17, 20... Memory, 1
8, 21... Image comparison circuit, 22... Judgment unit, 2
7...LSI wafer.

Claims (1)

[Scope of Claims] 1. Increase the amount of light reflected from the surface of the cut-off portion of the uppermost transparent thin film pattern at substantially the same location on the uppermost transparent thin film pattern on the substrate on which the multilayer fine circuit pattern is formed. In order to make the difference in the uppermost layer transparent thin film pattern visible, the first
Dark-field illumination is performed by irradiating illumination light from an oblique direction, and second illumination light having a different wavelength from the first illumination light is irradiated from a substantially perpendicular direction to transmit through the uppermost transparent thin film pattern to perform dark field illumination. Bright field illumination is performed so that the amount of reflected light reflected from the surface of the lower layer of the upper transparent thin film pattern and transmitted through the uppermost transparent thin film pattern changes according to the film thickness of the uppermost transparent thin film pattern, and The first reflected light from the difference part of the uppermost transparent thin film pattern caused by the illumination light and the second reflected light from the surface of the lower layer of the uppermost transparent thin film pattern through the uppermost transparent thin film pattern caused by the second illumination light. The reflected light is collected through an objective lens, and a first reflected light image and a second reflected light image are
The first image signal obtained by the first reflected light image obtained by one of the image detectors is compared with the first reference image signal, which is separated based on the difference in wavelength and detected by each image detector. A shape defect in the top layer transparent thin film pattern is detected based on a mismatch signal of a contour portion indicating a difference, and a second image signal and a second reference image signal are generated based on a second reflected light image obtained from the other image detector. 1. A method for detecting defects in fine patterns, characterized by detecting defects due to variations in film thickness of an uppermost layer transparent thin film pattern using a difference image signal indicating a change in shade or hue by comparing the two. 2. Increase the amount of light reflected from the surface of the cut-off portion of the top-layer transparent thin-film pattern on the top-layer transparent thin-film pattern on the substrate on which the multilayer fine circuit pattern is formed, so that the cut-off portion of the top-layer transparent thin-film pattern is increased. a dark-field illumination optical system that irradiates first illumination light consisting of S-polarized light from an oblique direction in order to make the The amount of light transmitted through the uppermost transparent thin film pattern is reflected by the surface of the lower layer of the uppermost transparent thin film pattern, and then transmitted through the uppermost transparent thin film pattern.The uppermost transparent thin film A bright field illumination optical system that irradiates almost the same spot on the pattern from a substantially perpendicular direction, and a first illumination light that irradiates with the dark field illumination optical system from the difference part of the uppermost transparent thin film pattern. The second beam is illuminated by the reflected light and the bright-field illumination optical system.
an objective lens for condensing second reflected light reflected from the surface of the lower layer of the uppermost transparent thin film pattern through the uppermost transparent thin film pattern caused by the illumination light; and a first reflected light obtained through the objective lens. a separation detection optical system that separates the image and a second reflected light image based on the difference in wavelength and forms the images on respective image detectors for detection; A first image signal based on a first reflected light image obtained by a detector is compared with a first reference image signal, and a shape defect in the top layer transparent thin film pattern is detected based on a mismatch signal of a contour portion indicating a difference portion. At the same time, a second image signal based on a second reflected light image obtained from the other image detector is compared with a second reference image signal, and a difference image signal indicating a change in density or hue is used to detect the top layer transparent thin film. 1. A defect detection device for fine patterns, comprising: defect detection means for detecting defects due to variations in film thickness of a pattern.