JP3446754B2 - Micro foreign matter detection method and its detection device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detecting a minute foreign substance which detects the position of the minute foreign substance on the sample surface by irradiating the sample surface with a beam of light and observing a change in beam light caused by the minute foreign substance. The present invention relates to a detection device.

[0002]

2. Description of the Related Art It is said that the yield in the manufacture of ultra-highly integrated LSI represented by 16 Mbit-DRAM and the like is mostly caused by defects caused by foreign substances adhering to a wafer. This is because as the pattern width becomes finer, it adheres to the wafer in the manufacturing process of the previous process.
This is because minute size foreign matter, which has not been a problem in the past, becomes a pollution source. It is generally said that the size of the minute foreign matter that causes this problem is a fraction of the minimum wiring width of the ultra-high integration LSI to be manufactured.
In bit-DRAM (minimum wiring width 0.5 μm), minute foreign matters having a diameter of 0.1 μm level are targeted. Such minute foreign matters become pollutants and cause disconnection and short circuit of the circuit pattern, which greatly leads to the occurrence of defects and deterioration of quality and reliability. Therefore, the key to yield improvement is to detect minute foreign substances and to quantitatively and accurately measure, grasp, and manage the actual state of their adherence.

As a means for doing this, a foreign substance inspection apparatus has been conventionally used which can detect the presence position of minute foreign substances existing on the surface of a planar sample such as a silicon wafer. The foreign matter detection method adopted in the conventional foreign matter inspection apparatus will be described below.

A light scattering method is used as a foreign matter detection method adopted in the foreign matter inspection apparatus. The scattering intensity obtained by scanning the inside of the wafer surface with the beam light is linearly measured using a photomultiplier tube with time change, and the generation time of the scattering signal due to the light scattering from the fine particles and the wafer surface at that time are measured. This is a method for detecting foreign matter and specifying the position by associating the positions of the light beams scanning the. As a conventional foreign matter inspection device, IS manufactured by Hitachi Electronics Engineering
-2000, LS-6000 or Surfscan 6200 manufactured by Tencor, WIS-90 manufactured by Estek
There is 00 etc. Further, the measurement principle used for these foreign matter inspection devices and the device configuration for realizing the same are described, for example, in “Analysis / Evaluation Technology for High Performance Semiconductor Process” published by Realize Co.
~ Page 129 for details.

However, conventional fine particle measurement by the method using light scattering is limited by noise generated in the measurement system with respect to a scattering signal from fine particles, and noise (haze) generated on a silicon wafer due to the influence of surface roughness or the like. It is extremely difficult to detect minute foreign particles having a size of 0.10 μm or less existing on the wafer surface. This is described in detail, for example, on pages 474 to 479 of "Semiconductor Measurement Evaluation Dictionary" issued by Science Forum. Therefore, 64M, 256M, 1Gbit-DRAM that will be developed and mass-produced in the future.
Etc. (minimum wiring width 0.35, 0.20, 0.15 μm) requires management for the manufacture of ultra-highly integrated LSI 0.0
A method for detecting fine foreign matters of 7, 0.04 and 0.03 μm has not been established yet.

Further, in a particle measuring method using light scattering adopted in a conventional foreign matter inspection apparatus, a beam light for detecting a minute foreign matter is irradiated while being scanned, and the entire beam light is a sample such as a silicon wafer. Since the change in the amount of scattered light generated on the surface is detected linearly by using a detector such as a photomultiplier tube, the position of minute foreign matter should be detected with high accuracy. In this case, however, there is an error corresponding to the area of the pixel that depends on the area of the sample surface where the beam light strikes (the spot of the beam light). That is, in order to detect the position of a minute foreign substance with high accuracy, it is necessary to reduce the spot of the light beam by focusing the light beam on the surface of the sample as much as possible, but there is a limit to reducing this. . Further, when the spot of the light beam is made small, the scanning line length for measuring the entire surface of the sample becomes long, which causes a problem that the measurement time becomes long. The pixels of the existing device are usually in the area of 20 × 200 μm □. Regarding the condensing area of the laser beam possessed by the conventional foreign matter inspection device, refer to 1 of “High-performance semiconductor process analysis / evaluation technology” published by Realize Co., Ltd.
It is described in detail on pages 11-129.

In order to detect minute foreign matter having a size of 0.10 μm or less, first, it is necessary to detect with high sensitivity while maintaining a high S / N ratio without erroneously detecting the presence of minute foreign matter, and to perform positioning with high accuracy. Need to As a method for realizing this, Japanese Patent Laid-Open Nos. 8-29354 and 7-
The conventional method described in detail in Japanese Patent No. 325041 is considered to be effective. The conventional method is to irradiate the surface of the wafer with a beam of light, focus the spot of the beam of light on the microscope, magnify the scattered light with the microscope, and, within that field of view, use an image-in This is a method of observing (detecting) in a plane (two-dimensional) using a high-sensitivity CCD camera or the like equipped with a tensioner or the like. Since this conventional method detects the haze, which is noise generated on the wafer surface, in a plane, the haze detected by using the photomultiplier tube used in the conventional foreign substance inspection apparatus is By integrating scattered light that depends on minute surface roughness,
High signal is detected as haze)
The / N ratio can be secured.

FIG. 5 is a block diagram showing a conventional minute foreign matter detecting device described in each of the above-mentioned JP-A-7-325041 and JP-A-8-29354. In the figure, 1 is an XY stage, 2 is a sample (here, a silicon wafer), 3 is an Ar laser for irradiating the sample 2, 4 is a detection beam light for detecting a minute foreign substance, and 5 is reflected by the sample 2. Reflected beam light, 8 is a microscope for observing the sample 2, 9 is a CCD camera equipped with an image intensifier for photographing an image observed by the microscope 8, 1
Reference numeral 0 is a CRT that outputs the field of view of the CCD camera. The detection beam light 4 can be polarized by the polarizing plate 11. 6 and 7 are diagrams showing how the detection beam light 4 is applied to the sample 2 in FIG. 6, in which 6 is a foreign matter on the sample 2, 7 is irregularly reflected light,
12 is the spot diameter of the light beam 4.

Next, the operation will be described. First, XY
A silicon wafer 2 as a sample is set on the stage 1. It should be noted that the silicon wafer 2 as a sample is provided with highly accurate virtual coordinates on the XY stage 1 by a method based on the outer shape of the wafer such as an oriental flat or notch. The method for setting the virtual coordinates is described in detail in Japanese Patent Application No. 7-25118. Next, the beam light 4 for detection is irradiated on the silicon wafer 2 to generate the spot portion 12 in FIG. Using the microscope 8 provided in the dark field part, the spot part 1
2 is observed using the CRT 10 via the CCD camera 9. The microscope 8 is focused on the surface of the spot portion 12. In the field of view of the microscope 8 (in the spot portion 12)
If there is a foreign matter 6 in the X-Y stage coordinates (x1, y
Diffuse reflected light 7 is observed in 1) (FIG. 7). In addition,
At this time, if there is no foreign matter 6 on the spot portion 12, the detection beam light 4 is specularly reflected, so that the reflected beam light 5 cannot be observed from the dark field portion.

Next, this relationship will be supplementarily described. In the observation system shown in FIG. 7, the observation field range A of the microscope 8 installed in the dark field section covers the spot diameter 12 on the silicon wafer 2 of the detection beam light 4 with which the silicon wafer 2 is irradiated. It is written. From FIG. 7, the presence position of the foreign matter 6 inside the spot diameter 12 can be specified by observing the diffused reflected light 8 with the microscope 8 because the diffused reflected light 7 is generated on the silicon wafer 2. From the experiment, the contrast ratio between the part where the diffused reflected light 8 is not generated and the part where it is generated is very high and is clear even for foreign matter of 0.03 μm or less, and a sufficient S / N ratio can be secured. It has been confirmed. On the other hand, if the foreign matter 7 does not exist even within the same spot diameter 12, the detection beam light 4 is almost completely specularly reflected, and therefore almost nothing can be observed with the microscope 8 installed in the dark field portion. From these facts, even if the detection beam light 4 having a spot diameter 12 much larger than that of the foreign matter 6 is used, the diffused reflected light 7 by the foreign matter 6 can be observed from the microscope 8 installed in the dark field. As a result, the spot diameter is 1
The position of the foreign matter 6 in the inside 2 can be easily specified with high accuracy.

[0011]

As described above, since the conventional foreign matter detecting device is constructed so that a part of the sample can be observed, the above CCD camera is used when detecting the foreign matter on the entire surface of the sample. The method had a problem that a system capable of observing the entire surface of the sample had to be added.

The present invention has been made in order to solve the above-mentioned problems, and a method for detecting a minute foreign substance which can easily detect a minute foreign substance of 0.1 μm or less over a wide range of the entire surface of a sample in a short time. And its detection device. The term "fine foreign matter" as used herein includes dust having a particle diameter of 0.1 to 0.005 µm and not only dust but also crystal defects and scratches.

[0013]

A method for detecting minute foreign matter according to the present invention irradiates a sample surface with a beam of light, and focuses irregularly reflected light by the minute foreign matter adhering to the surface of the sample onto a spot portion of the beam of light. A fine foreign matter detection method for detecting the position of the fine foreign matter in the xy plane by observing with a CCD camera installed in the eyepiece part of the microscope in which the XY stage carrying the sample is mounted. And the XY
Do not move the stage continuously in the xy plane.
Sequential frame while overlapping some areas with the above-mentioned image pickup tube
The image is taken so that the entire surface of the sample can be observed.

[0014]

[0015]

Further, the present invention is a detection device which detects the minute foreign matter by adopting the above-mentioned minute foreign matter detecting method.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. An embodiment of the present invention will be described below with reference to the drawings. 1 is a configuration diagram showing a minute foreign matter detection device according to a first embodiment of the present invention. In the figure, 101 is the position where the diffusely reflected light is generated and XY
It is a computer for calculating the relative positional relationship of the CRT screen 100 on the stage 1, and has the same configuration as the conventional example shown in FIG. Although the observation range to be evaluated is expressed as the CRT screen 100 here, the CRT screen 100 to be observed is actually used.
Is not limited to, but the CC of the range to be evaluated
It means the entire image signal of the D camera 9. The drive of the XY stage 1 is controlled by the computer 101, and the drive range is a range in which the surface of the silicon wafer 2 can be moved sufficiently. Further, the silicon wafer 2 as a sample is given highly accurate virtual coordinates on the XY stage 1 by a method based on the outer shape of the wafer such as an oriental flat or notch.
Further, similarly to the conventional example, the spot portion 12 of the detection beam light 4 is larger than the visual field of the microscope 8.

According to the present embodiment, the XY stage 1
At a pitch below the range of the CRT screen 100 through the field of view of the microscope 8 under the control of the computer 101.
By intermittently moving in the direction, the presence or absence of the irregularly reflected light 7 by the foreign matter 6 and its position are detected. by this,
Even a minute foreign matter of 0.03 μm or less on the entire surface of the silicon wafer can be easily and quickly identified. The presence position of the foreign matter 6 detected at this time is sequentially recorded in the computer 101.

Further, in the first embodiment, since the XY stage 1 is intermittently moved in the X and Y directions, there is a time during which the XY stage 1 remains stationary and an ON / OFF time of the driving device exists. Although the measurement time becomes long, if the XY stage 1 is moved continuously, these times can be saved, and the entire surface of the silicon wafer can be inspected in a short time compared to the case where the XY stage 1 is moved intermittently. can do.

Embodiment 2. In the first embodiment, X-
When the Y stage 1 is continuously moved, an uninspectable portion occurs on the surface of the silicon wafer 2 due to the relationship between the moving speed of the XY stage 1 and the scanning speed of the CCD camera 9. The present embodiment has been made to solve this problem, and is directed to the moving direction of the XY stage 1 and the CCD.
By arranging the CCD camera 9 so that the main scanning direction of the camera 9 is substantially orthogonal and the moving direction of the XY stage 1 and the sub-scanning direction of the CCD camera 9 are opposite to each other, a portion that cannot be inspected can be minimized. It is something to reduce.

FIG. 2 is an explanatory view for explaining a minute foreign matter detecting method according to the second embodiment of the present invention. In the figure, 1
Reference numeral 10 is a scanning line of a CCD camera for detecting light. When the X-Y stage 1 is continuously moved, as shown in FIG.
As shown in (a), the main scanning direction of the scanning line 110 and X-
When the CCD camera 9 is installed so that the moving direction of the Y stage 1 is the same, the scanning line 110 is the CRT screen 100.
Is sequentially shifted (sub-scanning) from top to bottom while scanning left and right (main scanning), there is a large time difference between the upper left corner and the lower left corner of the CRT screen 100 and the image.
-Y stage 1 also moves, and the part under observation moves forward. Therefore, the area of the wafer surface detected by the CCD camera 9 in one frame of observation time becomes a rhombus, and as a result, an uninspectable portion occurs.

On the other hand, according to the present embodiment, FIG.
As shown in, the moving direction of the XY stage 1 and the scanning line 1
Since the CCD camera 9 is installed so that the main scanning direction 10 is substantially orthogonal to the moving direction of the XY stage 1 and the sub-scanning direction of the CCD camera 9 is opposite to the moving direction of the XY stage 1. On the other hand, the scanning delay time of the CCD camera 9 is shortened, and the range of the surface of the silicon wafer 2 detected by the CCD camera 9 in one frame of observation time is substantially rectangular. Therefore, although only a small portion cannot be inspected, there is no problem if the minute portion that cannot be inspected is included in the inspection area of the next frame in a marginal manner. The entire surface of the silicon wafer 2 can be completely inspected, and the existence position of the minute foreign matter can be specified.

Embodiment 3. In the second embodiment, C
The shot noise generated in the CD camera 9 may be erroneously detected as a foreign substance. The present embodiment is made to solve this.

FIG. 3 is an explanatory view for explaining a minute foreign matter detecting method according to the third embodiment of the present invention. In the figure, 107 is shot noise. The range of the CRT screen referred to here is the range that the CRT screen captures when the XY stage is stationary. As shown in the figure, X
-Moving speed v for moving the Y stage 1 continuously in the X and Y directions at a pitch below the range of the CRT screen 100.
x and vy are values obtained by dividing the width (Wx) or the width (Wy) of the screen projected by the CRT screen 100 by the time T required for the CCD camera 9 to observe one frame, that is, vx =
Wx / T (when moving the XY stage 1 in the X direction)
Alternatively, vy = Wy / T (when moving the XY stage 1 in the Y direction), which matches the speed of the scanning line of the CCD camera 9. For example, it is assumed that the foreign matter detection is started in the state (frame n) of FIG. Since the XY stage 1 moves rightward on the paper surface at the speed vx, the foreign matter 6 also moves rightward on the paper surface at the speed vx. On the other hand, the scanning line 110 is the CRT screen 10
0 Scan from the right end to the left on the paper at the speed vx. Figure 3 (b)
Indicates the state after T (time required for the CCD camera 9 to observe one frame) has elapsed from (a).
Is the moment when entering the CRT screen 100 (frame of the CCD camera 9). Scanning line 110 is shot noise 10
After detecting 7, the diffused reflected light 7 generated by the foreign matter 6 reaches the left end of the CRT screen 100, and the inspection of the frame n is completed. Next, the scan line 110 returns to the right end of the CRT screen 100 again to start the inspection of the frame n + 1. FIG. 3C shows a state after T / 2 has further elapsed from this state. Since the foreign matter 6 and the scanning line 110 approach each other at a velocity vx, the place where they contact each other (the scanning line 110 again detects diffused reflection light 7 by the foreign matter 6) is CR.
It is Wx / 2 from the end of the T screen. And scan line 1
10 reaches the left end of the CRT screen 100 and the frame n +
The inspection of No. 1 is completed, and from the state of FIG.
Inspection 2 starts. That is, for one foreign matter 6,
The irregular reflection light 7 is detected twice in the frame n and the frame n + 1, and the interval time between the detection of the two irregular reflection lights 7 is T.
/ 2. Therefore, if the interval time of the detection signals is T / 2, if the computer 101 recognizes that the irregular reflection light 7 is generated by the foreign matter 6, the foreign matter 6 can be easily detected.
It is possible to distinguish the irregular reflection light 7 and the shot noise 107. Since the direction of the straight line connecting the positions of the detection signals of the foreign matter 6 appearing on each frame screen with respect to the foreign matter 6 coincides with the moving direction of the XY stage 1, the detection by the foreign matter 6 is also performed from this. The signal and the shot noise 107 can be distinguished. As described above, according to the present embodiment, shot noise and a detection signal due to a foreign substance can be easily separated, and high S / S
An N ratio can be realized. The third embodiment described above
Then, the moving speed of the XY stage 1 is set to vx or vy.
However, if the speed is set to vx or vy or less, diffused reflected light is generated on a plurality of frames with respect to one foreign substance, and the interval time between signals of adjacent frames is measured, the same as in the third embodiment. The effect of is obtained.

Fourth Embodiment In the first to third embodiments described above, the XY stage 1 is used as the sample stage, but in the present embodiment, a rotary stage is used instead of the XY stage 1.

FIG. 4 is a block diagram showing a minute foreign matter detecting device according to a fourth embodiment of the present invention. In the figure, 21 is a rotary stage, 22 is a spindle, and 23 is a uniaxial slider. The center position of the silicon wafer 2 and the center position of the rotary stage 21 are made to coincide with each other, and the rotary stage 2
The rotation center of 1 is installed on the track of the uniaxial slider 23. The field of view of the microscope 8 is set on the trajectory along which the uniaxial slider 23 moves.

Next, the operation will be described. First, the field of view of the microscope 8 is adjusted to the center position of the silicon wafer 2 placed on the rotary stage 21. Next computer 101
The inspection is performed by intermittently rotating the spindle 22 controlled by, and intermittently moving the uniaxial slider 23 also controlled by the computer 101. In addition, the spindle 22 and the uniaxial slider 2
If 3 is continuously moved from the inner circumference to the outer circumference of the silicon wafer 2, the entire surface of the silicon wafer 2 can be efficiently inspected in a spiral shape as shown in FIG. The position can be specified easily and in a short time. At this time, the CCD camera 9 is shown in FIG.
As shown in (b), the rotation direction of the rotary stage 21 and C
If the main scanning direction of the CD camera 9 is substantially orthogonal and the rotation direction of the rotary stage 21 and the sub scanning direction of the CCD camera 9 are opposite to each other, the same effect as in the second embodiment can be obtained. To be Further, the moving speed of the uniaxial slider 23 may be gradually reduced as it moves from the inner circumference to the outer circumference, and the rotation stage 21 also reduces the rotation speed of the spindle 12 so that the field of view of the microscope 8 is reduced. If the peripheral speed of is set to vx or vy in the third embodiment, the same effect as in the third embodiment can be obtained.

In the first to fourth embodiments, X-
Although the sample 2 was moved by moving the Y stage 1, the same effect can be obtained by mounting the microscope 8 on the XY stage 1 and moving the sample 2 to fix the sample 2.

Further, in the above-described first to fourth embodiments, the description is made such that the irregular reflection light is detected on the CRT screen 100, but in reality, the image signal (scanning line) obtained from the CCD camera 9 is used. (Signal) is input to the computer 101 and then arithmetic processing is performed to make the determination.

[0030]

According to the first aspect of the present invention, the entire surface of the sample can be observed by continuously moving the sample or the microscope in the xy plane. It is possible to obtain an effect of easily inspecting and detecting minute foreign matter.

Further, according to the minute foreign matter detecting method of the present invention, since the image pickup tube is the CCD camera, the effect of highly accurately detecting the minute foreign matter can be obtained.

According to the minute foreign matter detecting method of the present invention, since the CCD camera is equipped with the image intensifier, the effect of detecting minute foreign matter with high sensitivity can be obtained.

Further, according to the minute foreign matter detecting method of the present invention, an XY stage on which a sample is mounted is provided, and the XY stage is used.
Since the entire surface of the sample can be observed by moving the Y stage in the x-axis direction or the y-axis direction,
The effect of easily inspecting the entire surface of the wafer in a short time and detecting minute foreign matter can be obtained.

Further, according to the minute foreign matter detecting method of the present invention, the moving direction of the XY stage is opposite to the moving direction of the imaging range of the image of the sample surface sequentially frame-imaged by the image pickup tube. Since the image pickup tube is installed in such a manner that the entire surface of the wafer can be inspected easily and in a short time, the effect of detecting minute foreign matter can be obtained.

[0035]

[0036]

Further, according to the minute foreign matter detecting apparatus of the present invention, since it is a detecting apparatus which detects the minute foreign matter by using the minute foreign matter detecting method according to any one of claims 1 to 8 , the surface of the silicon wafer is detected. The effect of detecting the minute foreign matter can be obtained by inspecting the entire surface easily and in a short time.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a minute foreign matter detection device according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a method for detecting minute foreign matter according to a second embodiment of the present invention.

FIG. 3 is a diagram for explaining a method for detecting minute foreign matter according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram showing a device for detecting minute foreign matter according to a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram showing a conventional minute foreign matter detection device.

FIG. 6 is a diagram for explaining a conventional method for detecting minute foreign matter.

FIG. 7 is a diagram for explaining a conventional method for detecting minute foreign matter.

[Explanation of symbols]

1 XY stage, 2 samples (silicon wafer), 3
Ar laser, 4 detection beam light, 5 reflected beam light, 6 minute foreign matter, 7 irregular reflection light, 8 microscope, 9CC
D camera, 10 CRT, 11 polarizing plate, 21 rotary stage, 22 spindle, 23 uniaxial slider, 1
01 computer

Continuation of the front page (56) Reference JP-A-10-48145 (JP, A) JP-A-2-139676 (JP, A) JP-A-61-104244 (JP, A) JP-A-7-325041 (JP , A) JP-A-8-29354 (JP, A) Patent 3287227 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 21 / 84-21 / 958

Claims (9)

(57) [Claims] 1. A sample surface is irradiated with a beam of light, and diffuse reflection light due to minute foreign matter on the sample surface is detected from a dark field portion of a microscope focused on a spot portion of the beam light, and the diffuse reflection light is detected. By observing in the field of view of the microscope, or by using an image pickup tube installed in the eyepiece part of the microscope and observing the captured image with a CRT, or by analyzing the captured image with a computer, the minute foreign matter X
-A method for detecting minute foreign matter for detecting a position in the y-plane,
An XY stage for mounting a sample is provided, and the XY stage is used.
While moving the page continuously in the xy plane.
Sequential frame imaging while overlapping some areas with the image pickup tube
And then observing the entire surface of the sample. 2. A main scanning direction in the frame imaging and
The moving directions of the XY stage are substantially orthogonal to each other.
The method for detecting minute foreign matter according to claim 1. 3. The frame imaging is the same area on the sample surface.
The process is performed a plurality of times for each region.
Or the method for detecting minute foreign matter described in 2. 4. In the plurality of frame image pickups, the adjacent
Interval of detection time of irregularly reflected light between matched frames
4. The foreign matter is detected based on
Micro foreign matter detection method. 5. It is necessary to observe one frame with the image pickup tube.
Between the frames, where T is the time
When the detection time interval of diffused reflection light is T / 2,
To recognize foreign objects based on computer processing.
The method for detecting minute foreign matter according to claim 4, characterized in that: 6. The XY stage moves in the x direction.
If the moving speed of the XY stage is Vx,
The time required to observe one frame with a tube is T,
When the width of the rame in the x direction is Wx, Vx = Wx /
6. The relationship of T is established, wherein the relationship of T is established.
The method for detecting minute foreign matter according to claim 1. Wherein said image pickup tube is a CCD camera, claims 1, characterized in that the arithmetic processing to input image signals obtained from the CCD camera to the computer
7. The method for detecting minute foreign matter according to any one of 6 to 6 . 8. The method for detecting minute foreign matter according to claim 7, wherein the CCD camera is equipped with an image intensifier. 9. A minute foreign matter detecting device for detecting a minute foreign matter by using the minute foreign matter detecting method according to any one of claims 1 to 8 .