JP3345936B2 - Scanner for confocal scanning optical microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask, a reticle,
In a confocal scanning optical microscope used for measuring the line width of a pattern drawn on a wafer, etc., a scanner for scanning a sample is designed to perform highly reliable measurement in two orthogonal directions. is there.

[0002]

2. Description of the Related Art A confocal scanning optical microscope is constructed as, for example, a confocal scanning laser microscope, and is used as a mask, reticle, or wafer dimension inspection apparatus to measure the line width of a pattern drawn on a mask, reticle, or wafer. And used to measure overlay accuracy. FIG. 2 shows a principle diagram of the confocal scanning laser microscope. The laser light 12 emitted from the laser oscillator 10 is
The light is reflected by the mirror 14, squeezed by the lens 16, and passed through the pinhole 18. The laser beam 12 that has passed through the pinhole 18 passes through the beam splitter 20 and passes through the objective lens 22.
And irradiates the sample 24 (mask or reticle or wafer). The laser light reflected by the surface of the sample 24 is reflected by the beam splitter 20, passes through the pinhole 26, and is received and amplified by the photomultiplier tube 28.

When a dimensional inspection is performed, the position of the focal point F of the laser beam is fixed below the pattern 30 (or above the pattern 30) as shown in FIG. Then, while the sample 24 is scanned in the X-axis direction at a high frequency by the scan controller 32, the sample 24 is slowly moved in the Y-axis direction on the X and Y stages. At this time, when the beam spot passes below the pattern 30 as in (a), all the reflected light passes through the pinhole 26, and the output of the photomultiplier tube 28 increases. On the other hand, when the beam spot is passing over the pattern 30 as shown in (b), the reflected light is not focused at the position of the pinhole 26 and is largely blocked. The output will be smaller. Therefore, by sequentially drawing on the television monitor 34 with a brightness corresponding to the output of the photomultiplier tube 28 in synchronization with the scan by the scan controller 32, the image 3 of the pattern 30
6 is displayed on the television monitor 34. When the operator moves the cursor to an arbitrary position on the image 36, the pattern width at that position is automatically measured.

A specific example of a conventional confocal scanning laser microscope for wafers using the above principle (SScan manufactured by SiScan)
iScanIIA) will be described. FIG. 3 is a block diagram of the apparatus. This confocal scanning laser microscope 40 for wafers
Are composed of an optical module 42 and a workstation 44, and are connected to each other by a signal cable 45. The optical module 42 has an X, Y stage 48 mounted on a base 46 supported by an air suspension, and a scanner 50 mounted thereon. The sample is attached to the scanner 50 by being chucked by vacuum suction.
A focusing device 52 is disposed above the scanner 50, and converges the laser light emitted from the laser head 54 with the objective lens 22 and irradiates the sample on the scanner 50. The optical system shown in FIG. 2 is housed in the laser head 54. Further, a television camera 56 with a zoom lens is disposed downwardly adjacent to the laser head 54,
It is used to take an image near the laser irradiation position on a sample (wafer). Under the base 46, an electric circuit chassis 58, an indicator 60 such as a vacuum for chuck, a power supply 62 for laser, and a robot control for setting a sample on the scanner 50 and removing the sample after inspection from the scanner 50. A device 62 and the like are provided.

On the other hand, the work station 44 includes an operator's operation panel 64, a television monitor 66, and a printer 6.
8. A control device 70 including a CPU and the like are provided so that all the optical modules 42 can be operated from the workstation 44. On the television monitor 66, an observation image by a laser microscope, an image by a television camera 56, and the like are displayed.

FIG. 4 shows a system configuration of the confocal scanning laser microscope 40 for a wafer shown in FIG. The sample (wafer) 24 is conveyed onto the scanner 50 by the wafer handling robot 72 and chucked. The laser beam 12 from the laser oscillator 10 is emitted from the objective lens 22 via the optical system shown in FIG. The reflected light is received by a photodetector 28 (such as a photomultiplier tube).

Computer 7 of workstation 44
Reference numeral 6 controls each unit via the bus 77. That is, the wafer handler control unit 82 drives the robot 72 to carry out and carry in the sample 24. Further, the X, Y stage motor control unit 78 drives the X, Y stage 78 to position a desired inspection location on the sample 24 within the scan range of the laser light 12. In addition, the Z-axis focus control unit 80 moves the objective lens 22 in the up-down direction to focus on a pattern below or above the pattern on the sample 24. When focus is achieved, the height of the objective lens 22 is fixed there.

[0008] The scan control and synchronization circuit 84 performs readout of scan waveforms and synchronization control as scan control. The line scan waveform memory 86 stores a scan waveform such as a sine wave, and reads out the stored scan waveform at a high speed (for example, 2 kHz) according to a command from the scan control and synchronization circuit 84. The read scan waveform is converted into an analog waveform by a D / A converter 88, and the actuator (voice coil motor, piezoelectric element, etc.) of the scanner 50 is driven in the X-axis direction via an amplifier 90, Scan the light irradiation position. The scanning speed is maintained at a specified speed by speed feedback.

The output of the photodetector 28 is converted into a digital signal by an A / D converter 94 via an amplifier 92.
The pixel timing and synchronization circuit 96 is for obtaining the correspondence between the detection information of the photodetector 28 continuously obtained in each scan and the position on the X axis, and the data sequentially output from the A / D converter 94. In response to this, an address on one scan line is given and taken into the line scan pixel memory 98. The line scan distortion memory 100 corrects the spatial distortion of the scan waveform so that an accurate pattern is taken into the memory 98.

Scanning is performed while slowly moving the Y-axis of the X, Y stage 48 at a constant speed.
The data is sequentially taken into the memory 102, whereby X,
A pattern image in a desired range on the Y plane is displayed on the display area of the image monitor 104 on the television monitor. In the display area of the graphic monitor 106 on the television monitor, a photodetector detection waveform in the X-axis direction at the Y-axis position indicated by the cursor on the image monitor 104 is displayed. The pattern width is a value obtained by counting the number of pixels of the pattern stored in the video display memory 102 in the range indicated by the cursor on the image monitor 104 and averaging the count value at each position in the Y-axis direction within the cursor. Is automatically calculated, and the result is displayed on a television screen as a numerical value.

[0011]

In the conventional apparatus, since scanning is performed by vibrating in the X-axis direction and slowly moving in the Y-axis direction, as shown in FIG. When extending in the Y-axis direction, each pattern 30 crosses each scan in the X-axis direction, so that information on the width of each pattern 30 is obtained for each scan. However, as shown in FIG. 5B, when the pattern 30 on the sample 24 extends in the X-axis direction, the operation of crossing the pattern 30 in the width direction is performed by moving in the Y-axis direction. Information on the width of each pattern 30 can be obtained only in degrees. For this reason, the reliability of the measured value of the line width of the pattern 30 obtained by averaging the number of pixels in the width direction is high in FIG. 5A, but low in FIG. 5B. Occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a confocal scanning optical microscope capable of solving the problems in the conventional technique and performing highly reliable measurement in two orthogonal directions.

[0013]

According to the present invention, there is provided a first stage driven in a first axial direction using a piezoelectric element as an actuator, and a piezoelectric element serving as an actuator on the first stage while holding a sample. a second stage which is driven in a second axis direction orthogonal to the first axis, said first
When an oscillating voltage is applied to the actuator of the stage,
Both gradually to the actuator of the second stage
Applying a voltage that changes to the
Applying an oscillating voltage to the actuator
Gradually changes to the actuator of the first stage.
Can be driven either by applying a changing voltage
Actuator driving means .

[0014]

According to the present invention, since the piezoelectric elements driven in two orthogonal directions are provided, the piezoelectric elements in the direction perpendicular to the direction of the pattern to be measured are vibrated, so that the pattern is scanned every scan. , Information on the line width can be obtained so that highly reliable measurement can be performed for patterns in any direction.

[0015]

FIG. 1 is a plan view showing one embodiment of the present invention.
The XY scanner 110 has a spring 1 inside a quadrilateral outer frame 112 fixed on an XY stage.
14, 118 via the inner frame of the quadrilateral
(The first stage) is movably supported in the Y-axis direction. A spring 1 is provided inside the inner frame 118.
A square support base 124 (second stage) is movably supported in the X-axis direction via the bases 20 and 122. The sample is placed and supported on the support table 124 by vacuum suction or the like.

A frame 1 is provided between the frames 112 and 118.
A piezoelectric element 126 for driving the Y-axis 18 in the Y-axis direction, and a speed sensor for detecting the moving speed of the frame 118 in the Y-axis direction (a method in which a coil is attached to one side and a magnet is attached to the other side to detect an induced voltage of the coil) Etc.) 128 are attached.

A piezoelectric element 130 for driving the support 124 in the X-axis direction is provided between the frame 118 and the support 124.
And a speed sensor 132 for detecting the moving speed of the support base 124 in the X-axis direction. Piezoelectric element 1
The reference numeral 30 can be composed of a piezoelectric ceramic element such as PZT (trade name).

With the above configuration, the piezoelectric elements 126, 13
By driving any one of the zeros with the oscillating voltage, the support 124 on which the sample is placed can be vibrated in the Y-axis direction or the X-axis direction. The movement in the other axis direction orthogonal to the vibration direction is performed by applying a voltage that gradually changes at a constant gradient to the other piezoelectric element, or by moving the XY stage supporting the XY scanner 110. It can be performed by driving.

FIG. 6 shows an embodiment of a control device for a confocal scanning laser microscope equipped with the XY scanner 110 shown in FIG.
Shown in An X stage 48 is supported on the base 46 so as to be movable in the X-axis direction with a movement width of, for example, 200 mm, and a Y stage 49 is supported so as to be movable in the Y-axis direction with a movement width of, for example, 200 mm. An XY scanner 110 is provided on the Y stage 49 in the X-axis direction and the Y-axis direction, for example, 200 times each.
It is movably supported with a movement width of μm. A sample is placed and supported on a support 124 (FIG. 1) of the XY scanner 110 while being held by a mask holder 140 (an auxiliary tool for holding the sample 24).

A laser beam 12 emitted from a laser oscillator 10 passes through a beam splitter 20, a pinhole 18, and a mirror 14, and is converged by an objective lens 22 to form a sample 24.
(Masks, reticles, wafers, etc.). The laser beam reflected by the surface of the sample 24 is reflected by the mirror 14, passes through the pinhole 18, is reflected by the beam splitter 20 and the mirror 26, and is received and amplified by a photodetector 28 (photomultiplier tube or the like). You.

When the line width of the pattern on the sample 24 is measured, the host computer of the workstation sends positional information of the measurement point to the stage control 142 via the bus 77. This allows the stage control 142 to control the X-axis stage servo amplifier 144 and Y
X stage 4 via axis stage servo amplifier 146
8. The Y-stage 49 is driven to position a corresponding portion on the sample 24 at a position immediately below the objective lens 22.

The waveform memory 148 stores, for example, a sine waveform as a waveform for vibrating in one axial direction during scanning, and a waveform changing at a constant gradient, for example, as a waveform for moving at a constant speed in the other axial direction. Have been. The scanner control 150 reads out these waveforms and applies a vibration waveform voltage to the piezoelectric element in the axial direction selected by a command from the host computer among the two axes of the XY scanner 110 via the scanner servo amplifier 152. Then, a voltage having a waveform that changes at a constant gradient is applied to the other piezoelectric element. Thereby, scanning is performed for a predetermined range of the measurement location. The moving speed in both X and Y directions at the time of scanning is the speed sensor 132,1.
The specified speed is maintained by speed feedback based on the speed detection at 28.

The light receiving signal obtained from the photodetector 28 at the time of scanning is input to the data acquisition circuit 152, and the pattern axis is measured through the same processing as in FIG. That is, referring to FIG. 4, the output of the photodetector 28 is converted into a digital signal by the A / D converter 94 via the amplifier 92. The pixel timing and synchronization circuit 96 gives an address on one scan line to the data sequentially output from the A / D converter 94 and takes it into the line scan pixel memory 98. Then, the contents of the memory 98 are sequentially taken into the video display memory 102 for each scan in the X-axis direction, whereby a pattern image in a desired range on the X, Y plane is displayed on the image monitor 104 on the television monitor. Is displayed in the display area. Also, the graphic monitor 1 on the television monitor
In the display area 06, the scan waveform at the position indicated by the cursor on the image monitor 104 is displayed.
The pattern width is calculated by counting the number of pixels in the width direction of the pattern stored in the video display memory 102 in the range indicated by the cursor on the image monitor 104 and automatically averaging the count value in the cursor. Then, the result is displayed on a television screen as a numerical value.

The manner in which line width measurement is performed on a pattern in each direction by the laser microscope 134 shown in FIG. 6 will be described.
FIG. 7 shows a case where the pattern extends in the Y-axis direction. In this case, the pattern is slowly moved in the Y-axis direction at a constant speed while vibrating in the X-axis direction. As a result, when the pattern image 36 is obtained on the television monitor 34, the cursor 160 is positioned at a desired position. Then, the average value of the number of pixels for each scan in the cursor 160 is automatically calculated and displayed.

FIG. 8 shows a case where the pattern extends in the X-axis direction. In this case, the pattern is slowly moved at a constant speed in the X-axis direction while vibrating in the Y-axis direction. As a result, when the pattern image 36 is obtained on the television monitor 34, the cursor 160 is positioned at a desired position. Then, the cursor 16
The average value of the number of pixels for each scan within 0 is automatically calculated and displayed. According to this, since line width information is obtained for each scan in both the X-axis direction and the Y-axis direction, highly accurate measurement can be performed.

[0026]

[Modification] In the above embodiment, the movement in the direction orthogonal to the vibration direction was performed by the XY scanner 110.
It can also be performed on the stages 48 and 49.

The position of the inspection point is determined by the XY stages 48 and 49.
XY scanner 100 after rough positioning with
It is also possible to control the voltage applied to the piezoelectric elements 126 and 130 for precise positioning. This voltage is given as an offset voltage even during scanning. The present invention can also be used for applications other than line width measurement.

[0028]

As described above, according to the present invention, since the piezoelectric element driven in two orthogonal directions is provided, the piezoelectric element in the direction orthogonal to the direction of the pattern to be measured is vibrated. By doing so, line width information can be obtained across the pattern for each scan, so that highly reliable measurement can be performed for patterns in any direction.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 is a principle diagram of a confocal scanning laser microscope.

FIG. 3 is a configuration diagram of a conventional confocal scanning laser microscope.

FIG. 4 is a block diagram showing a system configuration of the confocal scanning laser microscope 40 of FIG.

FIG. 5 is a diagram showing a conventional line width measuring method.

FIG. 6 is a control block diagram showing one embodiment of a laser microscope provided with the XY scanner of FIG. 1;

FIG. 7 is a diagram showing a situation when a line width of a pattern in a Y-axis direction is measured by the laser microscope of FIG. 6;

8 is a diagram showing a situation when the line width of a pattern in the X-axis direction is measured by the laser microscope of FIG.

[Explanation of symbols]

24 sample 110 XY scanner (scanner) 118 frame (first stage) 124 support base (second stage) 126, 130 piezoelectric element 134 confocal scanning laser microscope (confocal scanning optical microscope) 150, 152 Scanner control, scanner servo amplifier (actuator driving means) Y 1st axis X 2nd axis

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01B 9/00-11/30 102 G01B 21/00-21/32 G02B 21/00-21/36 G12B 5 / 00

Claims (1)

(57) [Claims] A first stage driven in a first axial direction by using a piezoelectric element as an actuator; and a sample holding a sample, wherein the piezoelectric element is used as an actuator on the first stage and orthogonal to the first axis. An oscillating voltage is applied to a second stage driven in a second axial direction and the actuator of the first stage.
And the actuation of the second stage
Applying a gradually changing voltage to the
Applying an oscillating voltage to the actuator of the second stage
And the actuator of the first stage
Drive by either applying a gradually changing voltage
A confocal scanning optical microscope, comprising: