JPH01129143A - Detecting method of extraneous substance and apparatus therefor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method and apparatus for detecting a specific object on a sample, and particularly to a method for detecting a foreign object on a wafer having, for example, a fine circuit pattern on its surface. The present invention relates to a method and apparatus for detecting foreign matter suitable for detecting foreign substances.

[Conventional technology]

The conventional foreign object detection device is 2, for example, Japanese Patent Application Laid-Open No. 59-65428.
The sample 2 is placed on a stage 1 that reciprocates in the X direction as shown in Figure 4(a).

A laser beam (hereinafter referred to as illumination light) 3 is irradiated diagonally from above as indicated by an arrow, and this pattern is magnified with an objective lens 4.
The image is further enlarged by a magnifying lens 5 to form an image 6. At this time, an apparatus has been proposed in which the Fourier transform surface in the objective lens 4 is photographed using a field lens 7 to create an image 8 of the Fourier transform surface.

In this apparatus, an image 11' created by illuminating the pattern 11 on the sample 2 from obliquely above with the illumination light 3 is shown in an enlarged view in FIG. 4(b). Pattern 1 perpendicular to the direction (indicated by an arrow)
1a, foreign matter 11b, pattern corner portion 11c, pattern intersection portion lid, etc., light is scattered. Therefore, the image 12 obtained by photographing this image 11' with the field lens 7 is
As its enlarged view is shown in FIG. 4(Q), the pattern 12a, the foreign matter 12b,
Pattern corner portion 12c and pattern intersection portion 12d
When we perform Fourier transform on image 12 of shining light, the image 8
As shown in an enlarged view at 13 in FIG. 4(d), the light 13a from the pattern 11 becomes a vertical straight line in the center, and the other light 13b is scattered widely around the periphery.

The light-shielding mask 14 shown in FIG. 4(e) is applied to the center vertical
When the light from the straight line is blocked, the information of the pattern 11 is blocked, and the final image 6 is an enlarged view of the pattern 11 shown in FIG. 4(f).
5, an image 15a of a foreign object.

Image 15 of pattern intersection or pattern corner
Only b is available.

Therefore, in the case of a large foreign object, the signal thereof is larger than the signals at the pattern intersection and the pattern corner, so that the large foreign object can be detected by detecting such a large signal. However, the circuit patterns of recent semiconductor devices are becoming increasingly finer, and in such finer patterns, the signal at the pattern intersection or pattern corner is often larger than the signal from the foreign object, and the above-mentioned problems arise. The device configuration makes it difficult to detect foreign objects with such small signals.

Therefore, the conventional method is described in, for example, Japanese Unexamined Patent Publication No. 59-6536, as shown in FIGS. 5(a) and 5(b).

The detected images of the two chips 22 and 23 on the sample 21 are compared, and those appearing at the same position are determined to be signals of a pattern, a pattern corner portion, or a pattern intersection portion, and the signals of these chips are differentiated. An apparatus has been proposed that detects a foreign object by subtracting the difference signal, and if a difference signal remains, it is regarded as a foreign object signal appearing at a different position. Specifically, the image detected by the objective lens 24 is passed through the fluoroscope 28 and converted into an electrical signal by the sensor 25.
As shown in the enlarged view of FIG.
The image signal of the area 27 of No. 3 is compared with the previously stored signal, and the difference is determined to be a foreign object.

Note that 29 in FIG. 2 is an illumination lamp.

FIG. 6 is a two-dimensional representation of the image signals detected in FIG.
Area 26. It represents a part of the area 27 in the chip 23, and the 2nd screen 33 is the result of subtracting the signal of the screen 31 from the screen 32. The signal that exists in common in the 0th screen 31 and 32 (310=321.311=322)
is a pattern intersection/corner, and since the signal 323 that does not exist in common is a foreign object signal, the foreign object 34 (signal 32
3) can be detected.

In semiconductors, patterns are overlapped and exposed many times for each chip, so the overlapping state of the patterns changes from chip to chip, and the three-dimensional shape of the pattern changes little by little. Figures 7 and 35 and 36 are enlarged portions of different chips with the same pattern, but the lower layer pattern 37
．． It can be seen that the amount of positional deviation is different from that of the pattern 38 and the upper layer patterns 39 and 40.

8 to 10 are cross-sectional views 41 to 43 of the pattern and the corresponding detection signal magnitudes 44 to 43 when this part is obliquely illuminated.
46 is shown. When the positional deviation d is small as shown in FIG. 8, the detection signal 44 is large because the 9 step portion is steep, but when the positional deviation is large as shown in FIG. 10, the step portion is small and the pattern edge is smooth. Detection signal 46 is small. FIG. 9 shows an intermediate state between the two. In this way, even at similar pattern intersections/steps, the value of the detection signal changes greatly depending on the amount of positional deviation between the 9 overlaps, and in some cases, even with oblique illumination, almost no scattered light is generated. , a detection signal may not be obtained.

[Problem that the invention seeks to solve]

It cannot be said that such pattern intersections and corners cause scattered light in common between chips, so even if the signals from each chip are simply subtracted as in the conventional technology, it is not possible to accurately detect only foreign objects. Have difficulty.

The present invention eliminates these drawbacks of the prior art.

Even if pattern intersections/corners do not cause completely common scattered light between chips, the improved sensor can distinguish between foreign object signals and other normal pattern signals and correctly detect only foreign objects. The present invention provides a method and device for detecting foreign matter.

[Means for solving problems]

Since the amount of misalignment of pattern overlay differs between chips within an allowable range, it cannot be said that the pattern intersections and corners will always be at the same position between chips and will cause a common scattered light, but if the wafer Since there are more than 100 chips of the same type on the top, it is unreasonable to think that the same pattern intersections/corners in at least two of these chips may commonly generate scattered light at the same position. It's not natural. on the other hand.

When it comes to foreign objects, the probability of a foreign object existing at the same coordinates in different chips can be considered to be zero.

Scattered light does not occur on the same coordinates between chips. The present invention has been developed with this in mind, and adjacent chips are sequentially compared with each other, and coordinates where the signals do not match are stored as foreign object candidate coordinates (A). At the same time, a separate location 4 where a detection signal exists in common between at least two chips.
1 Find (B).

By removing coordinate B from coordinate A above.

The residual signal coordinate of coordinate A is determined as the foreign object coordinate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Below, the structural features of the present invention will be listed and the present invention will be explained in further detail.

First, a method for detecting foreign matter, which is the first invention, will be explained.

(1) A micro region at the same position between adjacent chips on a sample is illuminated obliquely with illumination light, and scattered light from this region is imaged by an image sensor, thereby generating image signals between the two adjacent chips. This difference signal obtained by detecting and subtracting is sequentially obtained and stored as foreign object candidate coordinates A, while at the same time image signals of minute areas at the same position of each of the adjacent chips obtained by the image sensor are The same image signals at the same position on at least two different chips are sequentially obtained and stored as common detection signal coordinates B, and the common detection signal coordinates B are accumulated from the accumulated signal of the foreign object candidate coordinates A. A residual coordinate is obtained from the foreign object candidate coordinate A by removing the signal, and this residual coordinate is detected as a foreign object presence signal. (2) A laser beam is used as the illumination light to illuminate the sample. The present invention is characterized in that a semiconductor wafer is used, and the object to be detected is a foreign object on the wafer.

Next, a foreign object detection device according to the second invention will be explained.

(1) A light source that obliquely illuminates a microscopic region on a sample, and a means for detecting scattered light from the microscopic region, which is disposed vertically above the microscopic region at least on an objective lens and its imaging plane. an optical system comprising an image sensor, and means for sequentially storing difference signals obtained by subtracting image signals of the minute regions of adjacent chips on the sample obtained from the image sensor; means for sequentially storing, as a common detection signal, the same image signal at the same position on at least two different chips among the scattered light of minute regions at the same position on the adjacent chips obtained simultaneously from the image sensor; and means for detecting a foreign object presence signal by removing the accumulated common detection signal from the differential signal.

(2) A laser light source is used as the light source, and a first
While storing the image signal of the first chip in the memory of
A second memory binarizes this signal and stores it with coordinates, and a second memory binarizes the image signal of the second chip and performs an AND with the signal of the first chip at the same coordinates of the second memory. Then, the third memory sequentially stores this signal.

(3) The optical system is characterized in that an objective lens, a field lens, a light-shielding mask, a magnifying lens, and an image pickup device are sequentially arranged with the same optical axis.

[Effect]

As mentioned above, with the conventional technology, it was only possible to detect foreign objects that caused scattered light larger than the scattered light of the pattern that occurred at pattern intersections and corners. It is now possible to detect foreign objects that generate scattered light of equal or smaller magnitude. The biggest reason for this is that the conventional method does not simply compare only the detection outputs in a minute area at the same position between two chips and treat the difference as a foreign object signal.

The present invention is characterized in that a means for accurately detecting a normal pattern signal is added. In other words,
The difference signal between the detection signals of scattered light at the same position between adjacent chips is stored as information on foreign object candidates, and at the same time, a separate pattern signal is used as a pattern signal to increase the accuracy. Accurate pattern information is obtained by accumulating only the coordinates where signals exist, and information about only the foreign object is obtained by removing this accurate pattern information from the information about the foreign object candidate. There is a possibility that normal pattern information is mixed in with the information of the above foreign object candidates in addition to pure foreign object information, and by removing this pattern information, only pure foreign object information is output in the coordinate display. be able to.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The figure shows an apparatus for detecting foreign matter on a patterned product wafer.

A small area 51 on a wafer 50 is irradiated obliquely from above with a laser beam 52 (light source not shown), this small area is magnified by an objective lens 53, and a field lens 54. Magnifying lens 55
The image sensor 56 detects the image through the image sensor 56. A light-shielding mask 57 corresponding to the light-shielding mask 14 described in FIG. 4 is provided at the position of the real image (conjugate image) on the Fourier transform surface of the objective lens 53 to remove pattern information on the wafer.

In this state, the xY stage 58 is moved in the X direction.

First, an electric circuit for determining foreign object candidate coordinates will be explained. First, switch the write side changeover switch 81 to the solid line state,
The small area 7e in the chip 61 is detected and the first memory 82
Store in. Next, the write side changeover switch 81 and the readout side changeover switch 83 are switched to the state shown by the broken line, and the detection signal of the small area 72 in the chip 62 is extracted from the signal 84.
The signal in the first memory 82 taken out from the signal line 85 (
The detection signal of the small area 71) is subtracted by the operator amplifier 86.The changeover switches 81 and 83 are switched at high speed, and the signal in the first memory 82 is sent out to the area where the blank has occurred. A signal detected by the image sensor 56 is transmitted to the signal line 84 and also stored in the first memory 82 . This is the detection signal of the small area 72, and is used for subtraction with the detection signal of the small area 73 that will be detected later.

The signal passed through the operator amplifier 86 is binarized by the operator amplifier 87, and the result is stored in a fourth memory 88 together with the coordinates within the chip and the code obtained when the signal is binarized. Here, the coordinates of the signal within the chip are determined by determining the X coordinate with a position detector (not shown) attached to the XY stage 58, and determining the Y coordinate from the pixel number of the image sensor 56. It becomes.

The signal processing situation during this time will be schematically explained using FIG. FIG. 2(a) shows the detection signal in a small area within each chip, and FIG. 2(b) shows the subtraction result binarized by the operator amplifier 87 and expressed with a sign. FIG. 3 shows the contents written in the memory 88 of foreign object candidate dust II.
(A), the subtraction result shown in FIG. 2(b) is written with the coordinates within the chip attached. The symbol - indicates that the foreign object candidate exists on the right chip (chip N1162 here), and the symbol in the symbol indicates that the foreign object candidate exists on the left chip (chip Nα6 here).
1). Naturally, the left and right chips have the same signal (chip Na61, 62
, the signal 610=620) is gone.

Returning to FIG. 1 again, an electric circuit for creating a pattern intersection/corner coordinate map will now be described. In this method, a map is created by regarding a case where a detection signal occurs at least twice at the same location within a chip as a pattern intersection/corner.

Memory 82 (detection signals of the small area 71 are stored)
The signal is binarized by an operator amplifier 91 and stored in a second memory 92. At the same time, the detection signal of the adjacent small area 72 is binarized by the operator amplifier 93, and the result is ANDed with the contents of the memory 92, and the result is stored in the third memory 94.

The signal processing situation during this time will be explained using FIGS. 2(c) and 2(d). FIG. 2(Q) shows the contents of the memory 92, which stores all the results detected by the image sensor 56 and converted into binarization.

FIG. 2(d) shows the contents of the third memory 94, which stores detection signals only when a binarized signal occurs at least twice at the same coordinates.

That is, the third memory 94 stores signals of pattern intersections and corners caused by patterns within the chip.

Returning to FIG. 1 again, the information stored in the fourth memory 88 (foreign object candidate coordinates) (A) to the information stored in the third memory 94 (pattern intersections/corners) (B)
By removing the foreign object, information 95 on the coordinates of the foreign object is obtained.

〔Effect of the invention〕

According to the present invention, it is possible to distinguish between foreign objects on a patterned sample and patterns, and it is possible to detect minute foreign objects.

When the present invention is not used, only foreign objects that generate scattered light larger than the scattered light generated at pattern intersections and corners can be detected, and in the case of wafers with multilayer patterns, 3 to 4 - Only the above foreign substances could be detected. If pattern intersections and corner portions are removed using the present invention, even in the case of a wafer on which a multilayer pattern is formed, a 1- foreign object can be detected, and the foreign object detection performance is significantly improved.

When applying the present invention, the angle of 82.92°9 shown in FIG.
Memory such as 4 is required. In Figure 1, assuming that the width of the small area 72 is 1.5m+s and the length is 10mm, the area is 1.
5+wn”. Pixel (minimum unit of image detection) is 5I
! If it is m square, the number of 9 pixels is 0.6 x 10@, and if a 1M bit (101 bits) LSI memory is used, one piece can be sufficient for recording. The first memory 82 needs to store an analog signal, and it is assumed that one signal is digitized into 64 gray levels and stored.

Six bits, that is, six IMbLSIs are required for one pixel. Also, 1st. Since the second memories 92 and 94 only need to store the binary signals, each of the second memories 92 and 94 has one IMbLSI.
Even if 0 or more are required, all of the above processing can be performed by using eight IMbLSIs, and excellent performance can be achieved with such a small electric circuit.

[Brief explanation of the drawing]

FIG. 1 is an apparatus for detecting foreign matter on a patterned wafer and a detection signal processing circuit, which is an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the processing situation inside the detection signal processing circuit, which is also an embodiment of the present invention. Figure 3 is an explanatory diagram of the format in which the contents of Figure 2(b) are stored in memory, Figure 4 is a configuration diagram of a conventional foreign matter detection device on a patterned wafer, and Figure 5 is a diagram of the conventional patterned wafer. An explanatory diagram of the operating principle of the foreign matter detection device on a wafer, FIG. 6 is an explanatory diagram of extracting only foreign matter from a foreign matter candidate map, and FIG.
The figure is an explanatory diagram of positional deviation due to overlay error during exposure of a semiconductor pattern, and FIG. 8 is a diagram showing a cross section of the pattern and a detection signal when the positional deviation is small. FIG. 9 is a diagram showing a pattern cross section and a detection signal when the positional deviation is medium, and FIG. 10 is an explanatory diagram showing a pattern cross section and a detection signal when the positional deviation is large. In fig. 1...XY stage 2...Sample wafer 4...
・Objective lens 50...Wafer 51...Small area 52...Laser beam 53...Objective lens 54...Field lens 55...Magnifying lens 56...Image sensor 61, 62, 63...
...Chip 71.72.73...Small area 81...
・Write side changeover switch 83...Readout side changeover switch 82, 92.94.88...Memory 86, 87.91.93...Operator amplifier representative patent attorney Junnosuke Nakamura Figure 2 Figure 8 Figure 9 Figure 10

Claims (1)

[Claims] 1. By obliquely illuminating a micro region at the same position between adjacent chips on a sample with illumination light, and capturing an image of scattered light from this region with an imaging device, the two adjacent chips are This difference signal obtained by detecting and subtracting the image signals of the chips is sequentially determined and stored as the foreign object candidate coordinates A, while the image signals at the same position of each of the adjacent chips obtained by the image sensor at the same time are Image signals of minute regions are taken in sequentially, and the same image signals at the same position on at least two different chips are sequentially determined and stored as common detection signal coordinates B, and the common detection is performed from the accumulated signal of the foreign object candidate coordinates A. A foreign object detection method characterized in that residual coordinates from the foreign object candidate coordinates A are determined by removing the accumulated signal of signal coordinate B, and the residual coordinates are detected as a foreign object presence signal. 2. The method for detecting foreign matter according to claim 1, wherein a laser beam is used as the illumination light, the sample is a semiconductor wafer, and the object to be detected is a foreign matter on the wafer. 3. A light source that obliquely illuminates a microscopic region on a sample, and an imaging device disposed on at least an objective lens and its imaging plane vertically above the microscopic region as means for detecting scattered light from the microscopic region. means for sequentially storing difference signals obtained by subtracting image signals of the minute regions of adjacent chips on the sample obtained from the imaging device; means for sequentially storing, as a common detection signal, the same image signals at the same position on at least two different chips among the scattered lights of microscopic regions at the same position on the adjacent chips obtained simultaneously from the elements; A foreign object detection device comprising means for detecting a foreign object presence signal by removing the accumulated common detection signal from the differential signal. 4. A laser light source is used as the light source, and the image signal of the first chip is stored in the first memory as a means for sequentially storing the same image signal at the same position on the at least two different chips as a common signal. and a second memory that binarizes this signal and stores it with coordinates;
and a third memory that binarizes the image signal of the second chip, performs an AND operation with the signal of the first chip at the same coordinates of the second memory, and then sequentially stores this signal. A foreign object detection device according to claim 3, characterized in that: 5. The optical system according to claim 3 or 4, characterized in that the optical system includes an objective lens, a field lens, a light-shielding mask, a magnifying lens, and an image sensor, which are sequentially arranged with the same optical axis. Foreign object detection device.