JP3257010B2 - Pattern inspection method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an appearance inspection apparatus for detecting defects in a pattern to be inspected, and more particularly to a pattern detection and comparison method and apparatus suitable for inspecting the appearance of a pattern on a semiconductor wafer or a liquid crystal display.

[0002]

2. Description of the Related Art Conventionally, this type of inspection apparatus is disclosed in
As described in Japanese Patent No. 192943, while moving the pattern to be inspected at a constant speed, an image of the pattern to be inspected is detected by an image sensor such as a line sensor, and the position of the detected image signal and the image signal delayed by a certain time are detected. The mismatch is recognized as a defect by correcting the deviation at predetermined time intervals and comparing them. As a line sensor,
One-dimensional CCD line sensor and recently time delay integration type
(Time Delay Integration) A CCD image sensor is used, and an image of a target pattern is detected through an objective lens having a relatively high magnification. Note that the TDI image sensor has a structure in which a plurality of one-dimensional image sensors are two-dimensionally arrayed.
By adding to the output of the three-dimensional image sensor,
This is to increase the amount of detected light.

[0003]

However, in such a configuration, it is impossible to determine whether the defect detected as mismatch is a foreign substance or a non-foreign substance such as a shape defect. If the detected defect is a foreign substance, appropriate measures such as cleaning of the apparatus can be taken to cope with the generation of the foreign substance.

When the target pattern is a multi-layer pattern, each layer overlaps and has a high step and unevenness. As a result, a high-magnification objective lens has an insufficient depth of focus, and a narrow range for forming an image on an image sensor. There is a drawback that only the pattern is detected as an image, and most of the others are blurred. Therefore, according to the conventional method, only a part of the focused pattern is accurately inspected, and most of the other patterns that are not focused have low defect detection sensitivity, so that highly reliable inspection cannot be realized. Was.

An object of the present invention is to provide a visual inspection method and apparatus capable of identifying a detected defect as a foreign substance and inspecting it.

Another object of the present invention is to perform a highly reliable inspection on a single-layer or multi-layer pattern, so that a high-level pattern can be accurately focused even on a high-level pattern, and a high-sensitivity image can be detected. It is an object of the present invention to provide a visual inspection method and an apparatus for realizing a simple comparison.

[0007]

For this reason, the present invention has achieved the above object by realizing the following concept.

After the defect is detected, the detected defect position is inspected by the foreign matter detecting means. Based on this detection result, it is determined whether the defect is a foreign substance.

The defect detection has a structure in which a plurality of one-dimensional image sensors are arranged two-dimensionally, and the output of each one-dimensional image sensor is delayed for a predetermined time to obtain an adjacent one-dimensional image of the same position of an object. An image sensor called a TDI image sensor having a function of adding the output of the image sensor is used. The image sensor is disposed obliquely, a pattern is formed on the image sensor by a confocal imaging optical system, and the output signal is compared with a reference signal.

According to the above-mentioned and / or method, a high-precision image is detected to detect a defect, and whether or not a foreign substance is detected at the detected position.

[0011]

According to the above-described means, not only defect detection but also foreign matter detection is performed, so that only foreign matter can be extracted and detected.
Therefore, it can be determined whether the defect is a foreign substance. Furthermore, since foreign matter detection is performed only at the detected defect position, the detection conditions and the like can be optimized and foreign matter can be detected with higher accuracy compared to the conventional foreign matter inspection performed on the entire sample surface. Therefore,
The determination as to whether or not there is a foreign substance can be performed with higher reliability.

According to the above, each one-dimensional image sensor inside the TDI image sensor forms an image at a slightly different position (Z position) in a direction perpendicular to the optical axis. For this reason, even if the target has a high step or unevenness, the target forms an image on any one-dimensional image sensor surface, and as a result, a clear, large-amplitude signal output is obtained. The presence or absence of a defect is reflected in the value of any one-dimensional image sensor output. The clear large-amplitude signal and other blurred small-amplitude signals are added by the signal addition function of the TDI image sensor. These added signals are compared, but one of the one-dimensional image sensor output signals capturing the defect has a large amplitude without blurring and a large difference from a normal part. It is possible to detect the presence. As a result, even in a multilayer pattern in which each layer overlaps and has irregularities, high-precision pattern detection focused on each layer and high sensitivity can be compared in a short time. Therefore, the defect detection performance can be significantly improved as compared with the related art.

[0013]

Embodiments of the present invention will be described below. FIG. 10 is a pattern inspection apparatus showing one embodiment of the present invention. FIG.
In the above, the LSI wafer 1 as the pattern to be inspected can be detected by the image sensors 5 and 54 via the objective lens 4, and the LSI wafer 1 is scanned by the XY table 6 in a direction orthogonal to the scanning of the image sensors 5 and 54, ie, By moving in the X direction, the pattern to be inspected can be detected as a two-dimensional image. Note that L
The SI wafer 1 is illuminated by an illumination lamp 3.
The output image signal of the image sensor 5 is input to a defect detection means 60 described later in detail, and a defect on the wafer is detected. The output of the defect detection means 60 is defect information such as a defect position. When a defect is detected, the XY table 6 is positioned at the defect position based on the defect position information.

At the defect position, foreign matter is detected at the detected defect position by the foreign matter detection means 62 described later in detail. When the foreign matter is detected, it is determined that the previously detected defect is a foreign matter. If no foreign matter is detected, it is determined that the previously detected defect is a shape defect or discoloration. In the above example, the defect detection and the foreign substance detection are performed using the common XY table 6, but may be performed separately using different XY tables.

FIG. 11 is a diagram for explaining the configuration and operation of the defect detection of the present invention in detail. In the figure, the wafer 1 is irradiated with S-polarized laser light at an angle ψ by S-polarized lasers 52a and 52b. ψ is about 1 degree. Here, the polarized light that oscillates perpendicularly to the plane formed by the irradiation laser light and the normal to the wafer is called S-polarized light, and the polarized light that oscillates parallelly is called P-polarized light. At this time, among the circuit patterns on the wafer having low steps, the scattered light does not change its polarization direction and proceeds toward the objective lens 4 with the S-polarized light shown by the solid line. Since the polarization direction of the laser light hitting the stepped circuit pattern changes, the laser light contains a large amount of P-polarized light components indicated by dotted lines. Therefore, a polarizing plate 53 for blocking S-polarized light is provided behind the objective lens 4, and light passing through the polarizing plate 53 is detected by the image sensor 54, thereby detecting foreign matter and scattered light from a circuit pattern edge having a high step. The scattered light signal is converted into a digital signal by the A / D converter 55.
The detected signal and the signal at the corresponding position of the adjacent chip are detected, stored in the image memory 56, and compared with this signal. These signals are aligned by the alignment circuit 57, and the difference signal is detected by the difference signal detection circuit 58. Since the scattered light signal from the edge of the circuit pattern having a high step is commonly included in the two signals, the difference signal includes only the scattered light signal from the foreign matter. The difference signal is binarized by the binarization circuit 59 to detect foreign matter. Therefore, not only defect detection but also foreign matter detection is performed, so that only foreign matter can be extracted and detected. Thereby, it can be determined whether the defect is a foreign substance. Furthermore, since foreign matter detection is performed only at the detected defect position, it is possible to optimize the detection conditions, for example, the above angle 上 記, and to detect only foreign matter more accurately than in the conventional foreign matter inspection performed on the entire sample surface. it can. In the above example, since the comparison is made between the position determined to be defective and the position determined to be normal, it is possible to more reliably determine whether or not a foreign substance exists.

FIG. 1 is a diagram for explaining in detail the configuration and operation of the defect detection of the present invention. In FIG.
Is a time delay integration type CCD
The TDI image sensor has a structure in which a plurality of one-dimensional image sensors are arranged two-dimensionally, and the output of each one-dimensional image sensor is imaged at the same position of an object after a predetermined time delay. The detected light quantity is increased by adding the output of the one-dimensional image sensor to the output. TDI image sensors of this type include those manufactured by Darsa Corporation of Canada and those manufactured by Reticon Corporation of the United States. The TDI image sensor 5 is arranged at an angle θ with respect to a plane perpendicular to the optical axis, as shown in FIG.
The tilt direction is the longitudinal direction (Y direction) of the internal one-dimensional image sensor with the center of the TDI image sensor as a fulcrum.
And the direction orthogonal to The tilt amount is an amount corresponding to the unevenness of the target. The scanning of the one-dimensional image sensor, for example, inside the TDI image sensor arranged at such an inclination is made coincident with the scanning in the Y direction, whereby the LSI wafer 1 which is the pattern to be inspected is made one-dimensional via the objective lens 4. In addition to enabling detection, the XY table 6
By moving the wafer 1 in a direction orthogonal to the main scanning of the TDI image sensor 5, that is, in the X direction, the pattern to be inspected can be detected as a two-dimensional image. X
A linear scale 8 is mounted on the Y table 6,
The actual position of the wafer can be accurately detected. A timing generation circuit 9 generates a start timing signal indicating a pixel from the output signal of the linear scale 8, and the TDI image sensor 5 is driven by this start timing signal every time the TDI image sensor 5 moves a predetermined distance. For example, if the pixel size is 0.1
If it is 5 μm, a start timing signal is generated every time the wafer moves by 0.15 μm in the X direction, and the image sensor is driven.

In the above configuration, the one-dimensional image sensors 5-1 to 5-m inside the TDI image sensor are slightly different from each other in the direction perpendicular to the optical axis (Z position) as shown in FIG. The TDI image sensor is arranged at an angle in order to form an image on the TDI image sensor. At this time, a rotating disk 35 having a pinhole and an optical path length conversion element 36 are arranged in front of the TDI image sensor. The rotating disk 35 has a large number of pinholes, for example, 200,000, and rotates the disk at high speed. The diameter of the pinhole is, for example, 20 microns. This pinhole acts as a confocal. That is, the illumination light passing through the pinhole forms an image on the pattern, and the reflected light from the pattern focuses on the pinhole. When the disk rotates at a high speed, a pattern is formed at all positions on the TDI image sensor. The optical path length conversion element 36 is provided for each one inside the TDI image sensor.
A different optical path length is given to the three-dimensional image sensor. The one-dimensional image sensor 5-k forms an image on the upper surface of the A layer at time Ti by the rotating disk 35 and the optical path length conversion element 36. When the LSI wafer 1 moves in the X direction,
At time Tj, an image is formed on the adjacent one-dimensional image sensor at a position shifted from the upper surface of the layer A in the Z direction, that is, out of focus. In this case, the amount of light detected by the function of the confocal point is not focused on the pinhole, but is interrupted by the pinhole and becomes small. In this way, the same position (X position) of the target is detected at each of the one-dimensional image sensors at a position slightly shifted in the Z direction, and the pattern without focus does not contribute to the detection signal. If the target has high steps or irregularities,
Since the object forms an image on the surface of the one-dimensional image sensor, a clear, large-amplitude signal output is obtained, and the presence or absence of a defect is reflected in the output value of any one-dimensional image sensor. All these signals are added by the signal addition function of the TDI image sensor. If the target is a three-layer pattern as shown in FIG. 3A, and if there is a pattern defect in the lowermost layer, conventionally, for example, only the intermediate layer is focused, and as shown in FIG. Although only the pattern of the layer has a large contrast of the detection signal waveform, in the present invention, all three layers show the same contrast. Therefore,
Conventionally, when there is a defect in the lower layer, the contrast was small as shown in FIG. 3B and the difference from the normal part was not clear. However, in the present invention, the difference from the normal part was clear as shown in FIG. Can be

In FIG. 1, the TDI image sensor 5 outputs, for example, eight image signals in parallel. These plurality of output signals are output from the delay memory 7 to the wafer 1 by one.
Delay by the amount of time to move for chips. Thereby, TD
The output signal of the I image sensor 5 and the output signal of the delay memory 7 correspond to the image signals of the adjacent chips 2a and 2b. The plurality of output signals are compared in parallel for each channel, and defects are detected at high speed. Next, processing contents for one channel will be described. Image signal edge detection circuit 11
Input to a and 11b to detect the pattern edge of the pattern to be inspected. The edge detection circuits 11a and 11b are equipped with a differential operator for detecting, for example, a dark pattern edge. Then, the detected pattern edges are binarized by the binarization circuits 12a and 12b. Next, 22 is a mismatch detection circuit,
The configuration is as shown in FIG. That is, the mismatch detection circuit
Reference numeral 22 denotes a TD for converting the image signal from the output of the
Shift register for delaying one scan of I image sensor
26 × 26 pixels and 2 × 7 × 7 pixels (arbitrary range) by serial-in / parallel-out shift registers 27a-27g
Cut out a dimensional local image. The outputs of the other binarization circuit 12b are the same as the shift registers 28a to 28c and 2
9, the output of which is synchronized with the center position of the two-dimensional local image. Next, the shift register
EXOR circuits 30a to 30n take the exclusive OR of the output of 29 and each bit output of the local image to detect unmatched pixels, and the counters 31a to 30n calculate the number of unmatched pixels. Each of the counters 31a to 31n is cleared to zero every N scans of the TDI image sensor 5, and the value is read immediately before the counter to read out the area M × N of the product of the number M of pixels of the TDI image sensor 5 and the number N of scans. The unmatched pixels within are indicated. Each bit output of the local image is ± 3 with respect to the output of the shift register 29 in the X and Y directions.
Since the pixels are shifted by one pixel within the range of pixels, the counters 31a to 31n count the number of mismatched pixels in each shift amount when the ± 3 pixel input pattern is shifted in the X and Y directions. . Therefore, if a counter having a characteristic value of the number of mismatched pixels such as a minimum value or a minimum value is checked, it is possible to perform optimal alignment with small image mismatch. Of course, a counter in which the number of mismatched pixels is smaller than a predetermined value may be obtained, and a counter that satisfies the counter may be determined as the optimum position.

As described above, when the counters 31a to 31n are X,
When the number of mismatched pixels in each shift amount when shifting the ± 3 pixel input pattern in the Y direction is counted, the value counted by the minimum value detection circuit 32 is read, and a counter having a minimum value or a minimum value is selected. The TDI image sensor 5 outputs shift amounts 34a and 34b for scanning in the Y direction and shift amounts 33a and 33b for scanning in the X direction perpendicular to the Y direction.

Reference numerals 23a and 23b denote delay circuits, and the number M of pixels of the internal one-dimensional image sensor of the TDI image sensor 5 is M.
And the register in an area M × N corresponding to the product of the number of scans of the TDI image sensor 5 and the number of scans N required for alignment, so that the outputs from the binarization circuits 12a and 12b are delayed. I have.

Reference numeral 24 denotes a positioning circuit. As shown in FIG. 5, shift amounts 33a and 33b for scanning the TDI image sensor 5 in the X direction from the minimum value detection circuit 32 are input to a selection circuit 35. In this case, the selection circuit 35 selects an optimum shift position from the outputs of the one delay circuit 23a and the shift registers 36a to 36f for delaying by one scan of the TDI image sensor 5, and inputs the selected shift position to the registers 37a and 37b. Is done. The selection circuits 38a and 38b select the optimum shift position of the TDI image sensor 5 in the Y direction from the shift amounts 34a and 34b when the TDI image sensor 5 scans in the Y direction from the minimum detection circuit 32. . Therefore, a local image corresponding to the shift position where the amount of mismatch is minimum or minimum is extracted from the outputs of the selection circuits 38a and 38b. From the output of the other delay circuit 23b, the shift register 3
Using the outputs of 9a to 39c and 40, the shift register 29
An image is synchronously extracted at a position delayed by the same amount as the output of (see FIG. 4). In this state, the local images output from the selection circuits 38a and 38b are at the optimal shift positions without positional deviation with respect to the local images output from the shift register 40.

When the optimum shift position is determined in this manner, the defect judging circuit 25 regards the inconsistency that appears in common as a defect. FIG. 6 shows the defect determination circuit 25 described above. The figure shows the case of two shift positions. The EXOR circuit detects a mismatch between the output of the selection circuit 38a and the output of the shift register 40, and at the same time, the output of the output shift register 40 of the selection circuit 38b. The EXOR circuit 43 detects the inconsistency, and the AND of the output of the EXOR circuit 42 is calculated by the AND circuit 44. Then, the decision unit 45 decides whether or not the output signal of the AND circuit 44 is defective according to the size and outputs it.

As described above, the edge detection circuit 11, the binarization circuit 12, the mismatch detection circuit 22, the delay circuit 23, the positioning circuit 24, the defect determination circuit 25, and the like can detect a defect for each channel. It is. In this example,
Processing is completely independent for each channel, but can be shared. FIG. 7 shows an example of an inspection apparatus having a common alignment.
In the pattern inspection apparatus shown in FIG. 7, in the mismatching pixel number detecting circuit 48 for each of the channels 2 to 8, the counter 31 calculates the number of mismatching pixels for each channel as shown in FIG. At 47, these are summed by an adder 46 as shown in FIG. 8, and the output of the adder 46 is processed by a minimum value detection circuit. In this case, since a wider range of images can be handled, the accuracy of positional deviation correction is improved. This is particularly effective for inspecting places where the pattern density is small. Channels 1, 2, 7, and 8 are configured as described above, and otherwise, the delay circuit 23, the alignment circuit 24,
Mismatch detection may be omitted as only the defect determination circuit 25.

In the above embodiment, the binarization circuit 12
We explained defect detection using digitized images,
In FIGS. 1 and 7, the binarization circuit 12 may be set to thru to detect defects using the grayscale image itself. (FIGS. 1, 7
Are connected like dotted lines. In this case, the binarization circuit 12
Are connected only to the mismatch detection circuit 22. In this case, a region having a large difference in shading is regarded as a defect.
With such a configuration, a signal of a defect different from that of a normal portion can be detected with higher accuracy. Further, in practice, each one-dimensional image sensor causes a slight magnification error (Y position) due to image formation in a direction orthogonal to the moving direction, but this error is also canceled out by the comparison, which is a problem. No. in this way,
Although the TDI image sensor is intended to increase the amount of detected light, it is extremely effective in increasing the depth of focus. As a result, even when a multi-layer pattern in which each layer overlaps and has irregularities is formed, the focus of each layer can be reduced. Highly accurate pattern detection and high sensitivity can be compared. In particular, fine defects can be detected in any layer. Therefore, the defect detection performance can be significantly improved as compared with the related art.

Although the above has been described in detail with reference to the embodiments, individual components can be realized by existing techniques. The foreign matter detecting means may be a method other than the embodiment as long as foreign matter can be detected. In addition, although the method of inspecting using two TDI image sensors has been described, the present invention is also applicable to a method of comparing and inspecting images detected simultaneously using two TDI image sensors.

[0026]

As described above, since not only defect detection but also foreign substance detection is performed, only foreign substances can be extracted and detected from defects. Therefore, it can be determined whether the defect is a foreign substance. Furthermore, since foreign matter detection is performed only at the detected defect position, the detection conditions and the like can be optimized and foreign matter can be detected with higher accuracy compared to the conventional foreign matter inspection performed on the entire sample surface.
Therefore, it is possible to more reliably determine whether or not a foreign substance exists.

In addition, even in the case of a multilayer pattern in which each layer is overlapped and has irregularities, it is possible to detect a focused high-precision pattern and compare the sensitivity with each other. Can be provided. In particular, fine defects can be detected in any layer.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the configuration and operation of defect detection according to the present invention.

FIG. 2 is a diagram showing a confocal imaging relationship by a TDI image sensor.

FIG. 3 is a diagram illustrating an example of a detection signal waveform.

FIG. 4 is a diagram illustrating a mismatch detection circuit;

FIG. 5 is a diagram showing an alignment circuit.

FIG. 6 is a diagram illustrating a defect determination circuit.

FIG. 7 is a diagram illustrating a pattern inspection apparatus according to another embodiment.

FIG. 8 is a diagram illustrating a mismatch detection circuit;

FIG. 9 is a diagram illustrating a mismatched pixel number detection circuit.

FIG. 10 is a diagram illustrating a pattern inspection apparatus according to an embodiment of the present invention.

FIG. 11 is a diagram for explaining the configuration and operation of foreign matter detection according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wafer, 2 ... Chip, 3 ... Illumination light, 4 ... Objective lens, 5 ... TDI image sensor, 6 ... Stage, 7 ... Delay memory, 8 ... Linear scale, 9 ... Timing generation circuit, 11 ... Edge detection circuit, 12 binarization circuit, 22 mismatch detection circuit, 23 delay circuit, 24 alignment circuit, 25 defect determination circuit, 26 to 29 shift register, 30 EXOR circuit, 31 counter, 32 minimum value Detection circuit, 35: pinhole, 36: optical path length conversion element, 36, 37, 39, 40: shift register, 45: determiner, 46: adder, 47: mismatch detection circuit, 48: mismatch detection pixel number detection circuit 52: S-polarized laser, 53: Polarizer, 54: Image sensor, 55: A / D converter, 56: Image memory, 57: Positioning circuit, 58: Difference signal Detection circuit, 59 ... binarization circuit, 60 ... defect detecting means, 62 ... foreign substance detecting means.

Continuation of the front page (72) Inventor Takashi Hiroi 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref. Hitachi, Ltd. Production Technology Laboratory (56) References JP-A-3-278553 (JP, A) JP-A-3 JP-A-156947 (JP, A) JP-A-3-85742 (JP, A) JP-A-61-253448 (JP, A) JP-A-62-220840 (JP, A) (58) Fields investigated (Int. . ^7, DB name) H01L 21/66 G01B 11/30 G01N 21/956

Claims (8)

(57) [Claims] 1. A pattern inspection method for inspecting defects of a pattern to be inspected, the objective les defects of the inspection pattern
Detected by the first detection system via the lens, and the detected defect is again detected via the objective lens based on the position information of the defect.
Te detected by the second detection system, the shape deleting該再degree detected defect
A pattern inspection method characterized by discriminating between a defect and a foreign substance . 2. A pattern inspection method for inspecting a defect of a pattern to be inspected, wherein the pattern to be inspected is irradiated with light.
The reflected light from the pattern to be inspected by irradiation of
The light is condensed through the first sensor and detected by the first sensor, and the first sensor
Processing the detected signal by the support to detect the defect of the inspection pattern, the object on the basis of the position information of a defect the detected
The reflected light from the inspection pattern is collected through a lens and
A pattern inspection method, wherein the detected defect is detected again by using the second sensor, and the type of the defect is identified using information of the detected defect. 3. The first sensor and the second sensor.
Are both TDI image sensors
The pattern inspection method according to claim 2 . 4. The TDI image sensor according to claim 1, wherein the plurality of signals are a plurality of signals.
4. The pattern according to claim 3, wherein the patterns are output in parallel.
Inspection method . 5. A pattern inspection apparatus for inspecting a defect of a pattern to be inspected, wherein said pattern is inspected through an objective lens using a first image sensor.
From the obtained first image of the pattern to be inspected,
A first defect detecting means for obtaining information of defects over emissions, first
Before based on information of the defect obtained by the detection by the defect detecting means
The pattern to be inspected is changed to a second image through the objective lens.
The inspection target page obtained by imaging using a page sensor.
A second defect detecting means for detecting the turns of the second image the defect again, and defect identification means for identifying a type of the defect have use the detected defect information again in the second defect detecting means A pattern inspection apparatus, comprising: 6. A pattern inspection apparatus for inspecting a defect of a pattern to be inspected, comprising: a defect detecting means for detecting a defect of the pattern to be inspected via an objective lens to obtain positional information of the defect; A foreign matter defect extracting means for detecting the detected defect again through the objective lens based on the position information of the defect obtained by the means and extracting a foreign matter defect from the defects, and extracting the foreign matter defect by the foreign matter defect extracting means A pattern inspection apparatus comprising: a defect identification unit that identifies a defect detected by the defect detection unit using the information on the detected foreign particle defect into a foreign particle defect and another defect. 7. The first image sensor and the second image sensor.
That the image sensor is a TDI image sensor
The pattern inspection apparatus according to claim 5, wherein: 8. The TDI image sensor includes a plurality of signals.
The pattern inspection apparatus according to claim 7, wherein the pattern inspection apparatus outputs the pattern inspection data in parallel .