JP2002228421A - Scanning laser microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive scanning laser microscope with a film thickness measuring function which requires only small memory capacity for image data and does not require highly accurate high resolution in Z-axis drive. SOLUTION: The scanning laser microscope comprises both a holding base 7 capable of inclining a sample 8 placed in such a way as to be orthogonal to the optical axis of laser light and holding the sample 8 in an inclined state and an operation part 5d for receiving light from the sample 8 held at the holding base 7 by an optical detector 15 and performing operations for obtaining the thickness of the sample 8 on the basis of a luminance signal from the sample 8 outputted from the detector 15 and the angle θ of inclination of the sample 8 when the luminance signal is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning laser microscope for measuring a film thickness on a substrate surface of a semiconductor wafer.

[0002]

2. Description of the Related Art Transparent or translucent thin films are sometimes formed on the surface of a substrate such as a semiconductor wafer. However, if the thickness of these thin films varies, a predetermined size can be obtained as a product. There may not be. For this reason, conventionally, a scanning laser microscope is often used as a measuring device for measuring the thickness of a thin film of a sample as described above.

According to a film thickness measuring apparatus using a scanning laser microscope, a sample on which a thin film is formed and an objective lens are moved with high accuracy in the optical axis direction, and the sample is irradiated with laser light via the objective lens. The luminance data corresponding to the reflected light from the sample is detected, and the surface to be measured (for example, the thin film surface and the substrate surface (the boundary surface between the thin film and the substrate)) is detected based on the change in the luminance data. The thickness of the thin film is measured by determining the dimension between the surfaces to be measured.

Some samples have a plurality of thin films formed on a substrate. In order to detect a measurement target surface (for example, a thin film surface, a boundary surface between different thin films, and a substrate surface) of each layer in such a sample, for example, JP-A-8-2108
As described in Japanese Patent Publication No. 18, while the laser beam is point-scanned or line-scanned in one direction or scanned in a plane in a two-dimensional direction, the position of the objective lens is shifted by a predetermined distance in the optical axis (Z-axis) direction. The brightness data corresponding to the reflected light from the sample side is continuously detected, and each measurement target surface is detected from the position where the brightness data is maximum in the continuous brightness data. .

[0005]

Problems to be Solved by the Invention
When the film thickness is measured by the apparatus described in Japanese Patent Application Laid-Open No. 8-108, the luminance data corresponding to the reflected light from each measurement target surface obtained by the irradiation of the laser light is stored in a memory together with the Z position information at the time of the acquisition. In the above-described measurement for finding the peak position where the luminance data is maximum in the continuous luminance data as described above, it is necessary to obtain the peak position from the acquired luminance data and the film thickness based on the peak position. Therefore, the memory must store all the luminance data and all the Z position information corresponding to the luminance data. In particular, when two-dimensionally scanning a laser beam, there is a problem that the storage capacity of the memory must be increased.

Further, in the above-described measuring method, since the sample and the objective lens are relatively moved in the Z-axis direction, the driving resolution of the Z-axis directly affects the measuring accuracy of the film thickness in order to obtain the film thickness. . For this reason, the Z-axis drive resolution needs to be sufficiently high and high-resolution with respect to the required measurement accuracy, and there is a problem that the apparatus becomes expensive.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and requires a small memory capacity for image data, a high-precision Z-axis drive resolution, and an inexpensive film. An object of the present invention is to provide a scanning laser microscope with a thickness measuring function.

[0008]

According to the first aspect of the present invention,
A laser light source, an objective lens for condensing laser light emitted from the light source on a sample, a scanning unit for relatively scanning the laser light condensed by the objective lens on the sample, A scanning microscope comprising: a light-shielding member disposed at a position conjugate to a light-condensing position condensed by a lens; and a photodetector that receives light from the sample via the light-shielding member and outputs a luminance signal. A holding table that can tilt the sample placed so as to be orthogonal to the optical axis of the laser beam, and that can hold the sample in an inclined state, and the sample held by the holding table. From the sample, and calculates the thickness of the sample based on the luminance signal from the sample output from the detector and the tilt angle of the sample when the luminance signal is measured. And an arithmetic unit that performs It is characterized in. .

The invention according to claim 2 is characterized in that the holding table is an inclined stage.

According to a third aspect of the present invention, the scanning means includes:
A light deflection member is used, and the sample is scanned with the laser light.

According to a fourth aspect of the present invention, the scanning means includes:
An XY stage is used, and the sample is scanned with the laser light by moving the XY stage.

According to a fifth aspect of the present invention, the light shielding member is
It is a pinhole.

According to a sixth aspect of the present invention, there is provided a monitor for displaying a luminance signal output from the photodetector as luminance information, and for obtaining a thickness of the sample based on the luminance information displayed on the monitor. Indicating means for indicating a surface to be measured.

[0014] The invention according to claim 7 is characterized in that the arithmetic section performs arithmetic processing based on a correction coefficient corresponding to a refractive index of the sample.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.

The laser light emitted from the laser light source 1 is
The light is reflected by the mirror 2, passes through the half mirror 3, and enters the two-dimensional scanning mechanism 4. The two-dimensional scanning mechanism 4 is controlled by a control unit 5a of a computer 5 (central processing unit).
This is for two-dimensional scanning with laser light. The laser light from the two-dimensional scanning mechanism 4 two-dimensionally scans the entire area of the measurement target surface of the sample 8 placed on the tilt stage 7 via the objective lens 6 movable in the optical axis direction.

The tilt stage 7 is mounted on an XY stage 9. The XY stage 9 is connected to an XY axis driving mechanism 10 controlled by the control unit 5a of the computer 5. Further, the tilt stage 7 is connected to the computer 5 (central processing unit) by an observation condition input unit 11 (for example, a keyboard, a mouse, or the like). The sample 8 can be tilted by a predetermined angle by the tilt stage drive mechanism 12 by the control unit 5a. Further, in addition to the tilt angle of the tilt stage 7, the magnification of the objective lens 6, the gain of the photodetector 15 described later, and the scanning range of the two-dimensional scanning mechanism 4 can be input to the observation condition input unit 11.

The reflected light from the sample 8 is condensed by the objective lens 6, reflected by the half mirror 3 via the two-dimensional scanning mechanism 4, and collected by the imaging lens 13 at the position of the pinhole 14. It emits light and is detected by the photodetector 15.
Since the pinhole 14 is arranged at a position conjugate with the focal position of the objective lens 6, only the light of the focused portion on the sample 8 is detected by the photodetector 15.

The focusing operation of the laser beam on the sample 8 is performed by controlling the Z-axis driving unit 17 by the Z-axis driving mechanism 16 connected to the control unit 5a of the computer 5 to move the objective lens 6 to the optical axis. By moving in the direction
Only the light in the focused portion on the sample 8 is detected by the photodetector 15.
Is detected by The signal detected by the photodetector 15 is
The image is captured by the image input unit 5b of the computer 5 (central processing unit) in synchronization with the two-dimensional scanning of the laser light, and is displayed on the monitor 18 as a two-dimensional image.

Here, the objective lens 6 is moved in the direction of the optical axis to change the focal position of the laser beam. However, the present invention is not limited to this. For example, the drive in the Z-axis direction is enabled. The XY stage 9 may be used.

Further, the computer 5 internally measures the dimensions of the observation site on a microscope image (two-dimensional image) obtained under the observation conditions set by the observation condition input unit 11 and displayed on the monitor 18. An image processing unit 5c having a function is provided. The image processing unit 5c further includes a calculation unit 5d that performs various calculation processes on the measurement results measured by the image processing unit 5c.

FIG. 2A schematically shows a state in which the sample 8 is observed using a scanning laser microscope having the structure shown in FIG.

The sample 8 described here is one in which one layer of a transparent thin film is formed on a semiconductor substrate, and is mounted on an XY stage 9 while being tilted by an angle θ by a tilting stage 7. Have been.

The laser light from the laser light source 1 is transmitted by the two-dimensional scanning mechanism 4 through the objective lens 6 to X, Y as shown by arrows on the thin film surface 8a and the substrate surface 8b as the measurement target surfaces of the sample 8. Scan with a spot light in the direction. Then
Light reflected from the sample 8 is detected by the photodetector 15. The reflected light detected by the photodetector 15 is more reflected light from the thin film surface 8a and the substrate surface 8b where the spot light is focused than the reflected light from the spot where the spot light is not focused. In effect, only the reflected light from the portion where the spot light is focused on the thin film surface 8a and the substrate surface 8b is detected by the photodetector 15.

Therefore, the reflected light detected by the photodetector 15 is, as shown in FIG.
The light reflected on the in-focus surface and the light reflected on the in-focus surface of the substrate surface 8b are displayed as lines on the observation screen on the monitor 18 and observed. FIG. 2C shows the luminance distribution of the signal of the photodetector 15 in the AA section of FIG. 2A, where the horizontal axis represents the position in the X direction and the vertical axis represents the luminance of the signal. I have.

FIG. 3 is an example of an observation screen measured when the thickness of the thin film formed on the substrate surface 8b is uneven, and the substrate is represented by a straight line. The thin film surface 8a having unevenness in film thickness with respect to the surface 8b is displayed on the observation screen as a meandering line.

2 (A), 2 (B), 2 (C) and FIG. 3, W indicates that the spot light is the thin film surface 8a and the substrate surface 8a.
The line width of W is measured by the image processing unit 5c of the computer 5.

Therefore, when the thickness of the thin film of the sample 8 is represented by t, it is expressed by the following equation.

T = W · sin θ (W is the line width and θ is the tilt angle of the sample) where θ is the tilt angle of the tilt stage 7 specified by the observation input unit 11 and is a known value. Therefore, if the calculation of the above equation is performed by the calculation unit 5c of the computer 5, the thickness t of the thin film can be obtained.

Next, a modification of the first embodiment will be described.

In the first embodiment, two lines due to the reflected light on the thin film surface and the substrate surface can be observed on the same observation screen on the monitor 18, and the image processing unit 5c of the computer 5
Was used to measure the distance (line width) W between the two lines. However, the present invention is not limited to this. For example, as shown in FIG. The optical axis may be fixed, and the XY stage may be driven in XY so that the laser beam scans the sample, and the value of W may be obtained from the moving distance of the XY stage 9.

In the first embodiment, the sample 8 is
Although one thin film is formed, the number of thin film layers is not limited to one. When two thin film layers are used, three lines representing the observed surface to be measured are three lines, and three thin films are used. The number of lines representing the measurement target surface to be observed is four, and the thickness of each thin film can be measured by measuring the line width between the lines.

According to the first embodiment, the following effects can be obtained.

Since the thickness of the thin film on the surface of the sample can be easily measured without scanning the objective lens in the optical axis direction (Z-axis direction), the storage capacity of the memory for storing the luminance information can be reduced. . Further, it is sufficient to drive the Z-axis as long as focusing can be performed, and the driving resolution of the Z-axis does not affect the measurement accuracy. Furthermore, by appropriately setting the magnification of the objective lens and the tilt angle θ of the tilt stage, it is possible to measure film thicknesses of various dimensions.

The tilt angle θ of the tilt stage is preferably changed according to the sample or the measurement time.
When trying to measure the thickness of a very thin film,
By reducing the tilt angle θ of the tilt stage, the line-to-line distance W between the thin film surface and the substrate surface can be increased, so that accurate film thickness measurement can be performed.

In the above-described embodiment, a sample in which one layer of a thin film is formed on a substrate has been described. It can measure the film thickness between the interface and the interface between the thin film and the substrate (interface). If you want to measure a sample with multiple thin films stacked and shorten the measurement time, By increasing the tilt angle θ of the tilt stage, the distance W between the thin film surface and the substrate surface can be shortened to shorten the measurement time.

A second embodiment will be described with reference to FIG.

Since the configuration of the scanning laser microscope is the same as that of the first embodiment, the same reference numerals are given and the description is omitted. This embodiment uses a computer 5 to measure the thickness of the thin film more accurately than in the first embodiment.
Only the calculation method in the calculation unit 5d is different.

In FIG. 5, the sample 8 has a transparent thin film having a relative refractive index n formed on a substrate surface. Sample 8
Is mounted on the XY stage 9 while being tilted by θ by the tilt stage 7. The reflected light from the point S on the thin film surface 8a is collected by the objective lens 6, and forms a line Sm on the right side of the observation screen of the monitor 18. The light reflected from the point Q on the substrate surface 8b is refracted because it crosses the optical path from the inside of the thin film to the observation atmosphere, and on the observation screen of the monitor 18, as if reflected from the point P in the drawing. Will be observed. Therefore, this reflected light is reflected on the monitor 1
A line Pm on the left side of the observation screen 8 is formed.

At this time, according to the law of refraction, sinα = nsinβ... Where T is the distance between OPs and t is the distance between OQs. tanα / tanβ) · T Further, assuming that the measured value of the dimension (line width) between each line on the observation screen is W, the distance T between OPs is expressed by the following equation.

T = W · sin θ... Therefore, the actual film thickness t to be measured can be represented by t = (tan α / tan β) · W · sin θ from the formulas and formulas.

Since α in the above equation varies depending on the tilt angle θ of the tilt stage 7 and the numerical aperture (NA) of the objective lens 6, W is determined with respect to a known film thickness t. It is measured and the value of (tanα / tanβ) is experimentally obtained. Then, this value is calculated by the arithmetic unit 5 of the computer 5.
The unknown film thickness can be measured more accurately by storing it in the memory unit d and performing the calculation of the equation in the calculation unit 5d.

According to the second embodiment, the following effects can be obtained.

When measuring the thickness of the thin film, correction can be made according to the refractive index of the thin film, so that accurate measurement of the film thickness can be performed.

The present invention is not limited to the film thickness measurement described in the above embodiment, but can be applied to the measurement of a step on the substrate surface other than the measurement of a thin film. In addition, the present invention is not limited to a laser scanning microscope, but can be applied to any microscope having a confocal optical system. Further, as the two-dimensional scanning mechanism, besides scanning the sample by vibrating two mirrors, a disk having a number of spiral holes is used, and the sample is rotated by rotating such a disk. You can also scan.

Further, the aperture member uses a pinhole in the above-described embodiment, but is not limited to this. For example, a slit can be used, and an acousto-optical element can be used as the scanning means. Even when light from the sample cannot be received in the pinhole, not only the same effect as in the above-described embodiment can be obtained by combining the slit and the line sensor, but also the use of an acousto-optic element. As a result, the time required for scanning can be further reduced.

In the above-described embodiment, the sample is scanned with a laser beam using, for example, a galvanomirror, and the sample is moved with an XY stage with respect to the laser beam, so that the sample is scanned with the laser beam. Although only the scanning type has been described, the present invention is not limited to this. For example, a scanning unit that scans a laser beam and a scanning unit that moves a sample are combined. And moving the sample in the Y direction on the XY stage so that the laser beam scans the sample in the Y direction.

In the above-described embodiment, the measurement value W can be manually specified for the two-dimensional image displayed on the monitor. However, a threshold value is set in advance and the measurement value W is output from the photodetector. The position where the luminance signal exceeds the threshold value may be determined to be the substrate surface or the thin film surface, and the film thickness may be automatically measured.

Further, it is possible to more accurately measure the film thickness by correcting the field curvature caused by the change of the focus position of the laser beam between the center position of the objective lens 6 and the peripheral position of the objective lens 6. Become. More specifically, in addition to the measurement sample, a reference sample is measured at a predetermined tilt angle θ before measurement before measurement, and the film thickness data including the field curvature data obtained from the reference sample is illustrated by the computer 5. The field curvature data can be corrected from the film thickness data obtained by measuring the measurement sample, and accurate film thickness measurement can be realized.

Further, a storage means for storing the film thickness data of a normal thin film including an error (hereinafter referred to as comparison data) in the above-described film thickness measuring apparatus, and a comparison means stored in the storage means. Comparing the data with the measured film thickness data, and providing a comparing means for judging that the film thickness of the sample thin film is abnormal when the film thickness data greatly exceeds or falls below the comparison data. Thus, for example, it is possible to realize a system that efficiently determines whether the semiconductor wafer substrate is good or bad.

In addition, since the film thickness can be measured only by performing two-dimensional scanning (XY scanning) with a two-dimensional scanning mechanism without driving the Z-axis, the detection speed is reduced as compared with the film thickness measurement performed by driving the Z-axis. Can be improved.

[0053]

According to the present invention, there is provided an inexpensive scanning laser microscope with a film thickness measuring function, which requires a small memory capacity for image data and does not need to have high Z-axis drive resolution and high resolution. Can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a scanning laser microscope according to a first embodiment of the present invention.

FIGS. 2A and 2B are diagrams illustrating a state of observation of a thin film according to the first embodiment of the present invention. FIG. 2A is a diagram schematically illustrating an observation state of a thin film, and FIG. FIG. 2C is a diagram illustrating an image, and FIG.

FIG. 3 is a diagram showing an image on a monitor when unevenness has occurred in the thickness of a thin film in the first embodiment of the present invention.

FIG. 4 is a view for explaining a modification of the first embodiment of the present invention.

FIG. 5 is a diagram schematically illustrating a method of measuring a film thickness of a thin film according to a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 laser light source 4 two-dimensional scanning mechanism 5c image processing unit 5d calculation unit 6 objective lens 7 tilt stage 8 sample 9 XY stage 15 photodetector 18 monitor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA30 CC19 DD06 DD07 FF04 GG04 JJ02 JJ25 LL13 LL28 LL30 LL57 LL61 MM03 MM16 PP12 PP24 QQ25 QQ31 RR06 SS02 SS04 SS13 2H052 AA08 AC04 AC15 AC34 AD06 AD19 AF22 AF23

Claims (7)

[Claims] 1. A laser light source, an objective lens for converging laser light emitted from the light source on a sample, and scanning for relatively scanning the sample on the sample with the laser light condensed by the objective lens Means, a light-shielding member disposed at a position conjugate to the light-converging position converged by the objective lens, and a light detector that receives light from the sample via the light-shielding member and outputs a luminance signal. In the scanning microscope having the above, while the sample placed so as to be orthogonal to the optical axis of the laser beam can be tilted, and a holding table that can hold the sample in an inclined state, The light from the sample held is received by the photodetector, and the sample is output based on the luminance signal from the sample output from the detector and the tilt angle of the sample when the luminance signal is measured. To calculate the thickness of A scanning laser microscope comprising a calculation unit. 2. The scanning laser microscope according to claim 1, wherein said holding table is a tilt stage. 3. A scanning laser microscope according to claim 1, wherein said scanning means uses a light deflecting member, and scans said sample with said laser light. 4. The scanning apparatus according to claim 1, wherein said scanning means uses an XY stage, and scans said sample with respect to said laser beam by moving said XY stage. Type laser microscope. 5. The scanning laser microscope according to claim 1, wherein said light shielding member is a pinhole. 6. A monitor for displaying a luminance signal output from the photodetector as luminance information, and a measurement target surface for obtaining a thickness of the sample based on the luminance information displayed on the monitor is designated. 2. The scanning laser microscope according to claim 1, further comprising an instruction unit. 7. The scanning laser microscope according to claim 1, wherein the calculation unit performs calculation processing based on a correction coefficient corresponding to a refractive index of the sample.