JPS61240103A - Optical minute displacement meter - Google Patents

Abstract

PURPOSE:To facilitate the setting of a displacement meter to the register in a detection head having high dissolving power and to enable automatic measurement, by together providing a minute displacement meter having a wide measuring range in coaxial relation to a minute displacement having high resolving power and simultaneously measuring the same measuring point by a plurality of minute displacement meters. CONSTITUTION:The reflected beam from a specimen 6 is guided to the outside by the polarizing beam splitter 3 of a minute displacement meter and a beam splitter 30 is provided between the splitter 3 and a beam splitter 7. A part of the reflected beam from the specimen 6 through the splitter 30 is incident to a quartering photosensor 23 from a cylindrical lens 21 to form an image thereon and the focus error signal from the sensor 23 is processed by a differential amplifier 33 and a compensation circuit 34 to control a stage driving motor 37. The reflected beams divided by the splitter 7 are respectively applied to critical angle prisms 8, 9 and the signals thereof are applied to bisecting photosensors 31, 32. The signals from said sensors 31, 32 are processed by differential amplifier systems 38, 39 and an adder circuit 40 and applied to a displacement sensor 44 through a displacement output apparatus 40.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical micro-displacement needle that measures the surface roughness, micro-displacement (vertical displacement), etc. of a workpiece in a non-contact manner.

[Conventional technology]

Recently, optical micro-displacement meters have been used as non-contact optical measuring instruments to measure surface roughness and micro-displacement of workpieces.
Focus detection methods have been attracting attention as they have the potential to reduce the size of the device, and these methods include those using critical angle methods, astigmatism methods, and the like.

First, as an example of a method using the critical angle method, there is a method shown in FIG. 11, for example. This means that the infrared laser beam from the laser diode 1 passes through the collimator lens 2. Polarizing beam splitter 3. The sample 6 passes through the λ/4 plate 4° objective lens 5.
The light projected upward and reflected is 5. λ/4 plate 4. Polarized beam splinter 3. The light passing through the beam splitter 7 enters a critical angle prism 8 or 9, and is reflected by the critical angle prism 8 or 9 so that the light enters two photodiodes 10°11 or 12.13 (see FIG. 12), respectively. It is configured. When the measurement surface of the sample 6 becomes the focal point of the objective lens 5, the light reflected from the measurement surface becomes a parallel beam of light by the objective lens 5 and enters the critical angle prism 8 or 9, but at this time, the incident light If the critical angle prism 8 or 9 is set so that the incidence is exactly near the critical angle, two photodiodes 10. The same amount of light reaches '11 or '12.13 as shown in FIG. 12(b).

In addition, when the measurement surface is located closer to the objective lens 5 than the focal point, the reflected light becomes a divergent light after passing through the objective lens 5 and enters the critical angle prism 8 or 9, but at this time, the incident angle is different on both sides of the optical axis. Because of the difference, the light on the side that does not satisfy the conditions for total reflection exits the prism 8 or 9, and the light on the side that satisfies the conditions for total reflection is totally reflected.
), only a small amount of light reaches photodiode 10 or 12, and sufficient light reaches photodiode II or 13. Also, if the measurement surface is located further from the objective lens 5 than the focal position, the above is reversed.
As shown in FIG. 12(C), sufficient light reaches the photodiode 10 or 12, and only a small amount of light reaches the photodiode 11 or 13. Therefore, by reading the output difference between each of the two photodiodes 10.11 or 12.13 and scanning by moving the sample 6,
It is possible to measure the surface roughness, minute displacement, etc. of the measurement surface.

Furthermore, as an example of an apparatus using the astigmatism method, there is one shown in FIG. 13, for example. This is because the laser light from the laser light source 14 passes through the spatial filter 15 and enters the polarizing beam splitter 16, and then the λ/4 plate 17. Objective lens 18
The reflected light is projected onto the sample 19 through the objective lens 18. λ/4 plate 17. Polarized beam splinter 16.
Cylindrical lens 2 passes through beam splinter 20
1 or 22, and the cylindrical lens 21 or 2
The light beams condensed to produce astigmatism by 2 are configured to be incident on detectors 23 or 24 (see FIG. 14) each consisting of four photodiodes 25.26° and 27.28°. . Since this optical system has astigmatism, when a point image from the laser light source 14 is incident on the measurement surface of the sample 19, it is reflected by the measurement surface and then sent to the detector 23.
Or, the shape of the point image formed on 24 is the 14th point image before and after the focal point.
It changes as shown in Figures (al, (bl, and c)).

The image is detected by the photodiodes 25, 26, 27.28, and the calculation (Vzs+Vzt) - (Vz6+Vzs) is read in the row -y.By moving and scanning the sample 19, the surface of the measurement surface is detected. Roughness, minute displacement, etc. can be measured. However, Vi is the output of detector i.

[Problems to be solved by the present invention]

The optical micro-displacement meter using the critical angle method as described above can have a high resolution of up to InII+, but the linearity in the relationship between displacement and output is within a range of ±1 μm at most. Therefore, there was a problem in that the detection head had to be placed within a range of only 2 μm in a microwave when making measurements. Further, if the surface of the object to be measured has irregularities of ±1 μm or more, the measurement surface will be out of the measurement range, which causes the problem that automatic measurement cannot be performed.

Further, although the optical micro-displacement meter using the astigmatism method as described above has a wide measurement range of several tens of micrometers or more, it has a problem of low resolution.

In view of the above problems, it is an object of the present invention to provide an optical micro-displacement meter that has high resolution, allows easy setting of the detection head within the measurement range, and also enables automatic measurement. .

[Means and effects for solving the problems] The optical minute displacement meter according to the present invention has a high-resolution minute displacement meter and a minute displacement meter with a wide measurement range installed coaxially, as shown in FIG. Either measure the same measurement point with multiple micro-displacement meters at the same time, or expand the measurement range of a high-resolution micro-displacement meter in a time-sharing manner as shown in Figure 5 to measure the same measurement point across multiple measurement ranges. The measurement points are measured almost simultaneously, and the resulting displacement detection signal over a wide measurement range is used to center the detection head. The relative position with respect to the sample mounting stage is controlled.

〔Example〕

Hereinafter, the present invention will be described in detail based on each of the illustrated embodiments, with the same reference numerals assigned to the same members as in the conventional example described above.

Figures 1 to 3 respectively show the optical system, processing circuit, and displacement detection signal of the first embodiment of the optical micro-displacement meter according to the present invention. A beam splitter 30 is installed between the splitter 3 and the beam splitter 7 to guide a certain amount of reflected light from the sample 6 to the outside, and a cylindrical lens 21 is installed on the tip axis of the beam splitter 30 to split the light into four parts. The image is formed on 23. Note that 31 and 32 are two-part photosensors arranged behind the critical angle prisms 8 and 9, respectively.

Further, the output signal of the four-division photosensor 23 is sent to the operational amplifier 33. Power amplifier 35 for servo via compensation circuit 34
stage 3 is reached by the output signal of the power amplifier 35.
It is designed to control a servo motor 37 for driving up and down (Z-axis direction) of No. 6.

On the other hand, the output signals of the two-split photosensors 31 and 32 reach an adder circuit 40 via operational amplifier systems 38 and 39, respectively, and are outputted to a displacement output device 42 via a compensation circuit 41. or,
The stage 36 is also driven in the X-axis direction by an X-axis stage drive system 43, and its displacement is detected by a displacement sensor 44 and sent to a displacement output device. Note that 45 is a detection head that includes the optical system shown in FIG.

Since the first embodiment is configured as described above, a part of the reflected light from the sample 6 is guided outside by the beam splinter 30, and is imaged on the four-division photosensor 23 by the cylindrical lens 21. The signal is generated based on the principle of the astigmatism method. The focus error signal obtained by the four-division photosensor 23 is sent to a differential amplifier 33.
The signal is processed by the compensation circuit 34 and input to the power amplifier 35, and the stage drive servo motor 37 is controlled by the output signal of the power amplifier 35. Therefore, the point being measured using a high-resolution micro-displacement meter using the critical angle method is
At the same time, the measurement is being performed using a minute displacement meter with a wide measurement range using the astigmatism method, and if the detection head 45 is set at approximately the center of the measurement range using the displacement detection signal, the measurement range is wide. Easy to set up.

In addition, by feeding back using this displacement detection signal, the relative position between the sample 6 on the stage 36 and the detection head 45 can always be maintained within the measurement range of the high-resolution minute displacement needle, so that the If the stage 36 is driven in the X-axis direction while the axial position is monitored by the displacement sensor 44, and the Z-axis direction is measured using the critical angle method, even a sample with large surface irregularities that change slowly can be measured with high resolution. It can be measured automatically.

It goes without saying that if the output of the compensation circuit 34 is sent to the displacement output device 42 as shown by the dotted line in FIG. 2, it is possible to simultaneously output the large uneven structure on the surface of the sample 6. Therefore, for the sample 6 with the surface texture as shown in FIG. Therefore, the output of the compensation circuit 41 is as shown in FIG.
As shown in FIG. 2, the signal is only from the minute irregularities on the surface of the sample 6.

The displacement output device 42 adjusts and adds the levels and phases of these two human forces, converts them into an output signal that accurately represents the surface texture as shown in Figure 2+d), and outputs it externally using a CRT display 1 recorder or other means. Display to. or,
It goes without saying that the two synchronized output signals may be displayed individually, or only the signal shown in FIG. 2(b) or TCI may be output. Alternatively, the detection head 45 may be used.

FIG. 4 shows the optical system of the second embodiment, which differs from the first embodiment in that the cylindrical lens 21 is used as the imaging lens 46, and the quarter-divided photosensor 23 is used as the PSD (semiconductor device detection element) 47. Replace beam splitter 3
This embodiment is the same as the first embodiment except that a fixed optical path limiting member 48 for controlling the luminous flux by half is provided between the lens 0 and the imaging lens 46.

Incidentally, the imaging lens 46 is arranged to form an image of the light onto the PSD 47.

Since this second embodiment is configured as described above, half of the cross section of the light beam taken out laterally by the beam splinter is blocked by the optical path limiting member 48, and the remaining light beam is imaged on the PSD 47. . Since the remaining light flux is off-axis light, its imaging position moves in accordance with the position of the sample 6 in the optical axis direction. By detecting this movement, the same effects as in the first embodiment can be obtained. Incidentally, instead of the PSD 47, a two-segment photosensor as shown in Japanese Patent Laid-Open No. 58-217909 may be used.

5 to 7 show optical systems of the third embodiment, respectively.

The area around the optical path limiting member and the processing circuit are shown, and in the first embodiment of this lever, the cylindrical lens 21 is replaced with an imaging lens 46, the four-part photosensor 23 is replaced with a PSD 47, and the collimator lens 2 and polarizing beam splinter 3 are replaced. The second embodiment is the same as the first embodiment except that an optical path limiting member 49 which can be inserted into and removed from the optical path is provided between the optical paths. The optical path limiting member 49 may be a chopper or a liquid crystal shutter as shown in FIG.
There are many types that use solenoids.

Further, the synchronization signal of the optical path limiting member 49 is output from the sensor 50 (FIG. 6), and after passing through the correction circuit 51 of FIG. 7, is input to the sampling circuits 52, 53. Differential amplifier 33. The outputs of the differential amplifier systems 38, 39 are sampled, and the outputs are further passed through low-pass filter circuits 55, 56, 57, respectively, to the compensation circuits 34. The signal is returned to the adder circuit 40.

Since the third embodiment is configured as described above, when the optical path limiting member 49 is not inserted into the optical path, the entire range of the light beam can be used, so the operation is the same as that of a normal high-resolution minute displacement meter. . On the other hand, when the optical path limiting member 49 is inserted into the optical path, half of the luminous flux is restricted, and as shown in FIG. The image is taken out and imaged onto the PSD 47 by the action of the imaging lens 46. Focus detection is then performed using the same principle as automatic focus adjustment using the light cutting method. Therefore, in this embodiment, the function as an original high-resolution minute displacement meter and the function as an automatic focus detection device using the optical cutting method occur in a time-division manner.

If this continues, the resolution and measurement range will change in a time-division manner, so the correction circuit 51 performs phase and level correction on the output signal from the sensor 50, as shown in FIG. By sampling the signals from the differential amplifier 33 and the differential amplifiers 38 and 39, respectively, and passing them through low-pass filter circuits 55, 56, and 57, the time-divided information is time-averaged. Therefore, if the stage 36 is driven slowly enough in the X-axis direction (actually, if it is not slow enough, the vibrations will be large and it will be useless).

), a high-resolution micro-displacement meter and a micro-displacement meter with a wide measurement range exist almost simultaneously, and as a result, the same measurement point is measured almost simultaneously with the two measurement ranges. Therefore, in addition to the first embodiment, setting the detection head within the measurement range becomes easier and automatic measurement becomes possible. In addition, in FIG. 6, the optical path limiting member (chopper) 4
9 is detected by the sensor 50, the optical path limiting member 49 may be rotated by a step motor, and the drive pulse of the step motor may be input to the correction circuit 51.

8 to 10 show optical systems of the fourth embodiment, respectively.

The area around the optical path limiting member and the displacement-output relationship are shown.
This is a conventional optical path limiting member resolution minute displacement meter that utilizes critical angle characteristics, except that an optical path limiting member 58 that can be inserted and removed in the optical path is disposed between the collimator lens 2 and the polarizing beam splitter 3. It is the same as a displacement meter. The optical path limiting member 58 has a central opening 59 as shown in FIG. 9, and has the effect of leaving a part of the central luminous flux concentrically with respect to the total luminous flux, and the size of the central opening 59 can be set arbitrarily. It can be set. Specifically, a liquid crystal shutter is used to block light except for the central opening 59 when a driving pulse is received, and to allow the entire luminous flux to pass through when the driving pulse does not come. As long as it has the same function, an iris diaphragm from a camera, etc. may be used, or a pinhole plate with various opening sizes may be installed in a replaceable or removable manner. .

Since the fourth embodiment is configured as described above, when no driving pulse comes to the optical path limiting member 58 and the entire luminous flux passes through it, it performs the same function as a conventional high-resolution minute displacement meter, and also limits the optical path. When a driving pulse comes to the member 58,
The beam diameter is limited, and as a result, the NA of the objective lens 5 is reduced, and as shown in FIG. 10, the sensitivity to displacement is increased and the measurement range is expanded. By performing this in a time-sharing manner and performing the same processing as in the third embodiment, the same effects as in the other embodiments can be obtained.

Incidentally, in each of the above embodiments, two minute displacement meters are actually configured, but three or more may be configured.

〔Effect of the invention〕

As mentioned above, the optical micro-displacement optical diameter according to the present invention has extremely important practical advantages in that while it has high resolution, it is easy to set the detection head within the measurement range and automatic measurement is also possible. have. It also has the advantage that multiple measured values can be obtained synchronously.

[Brief explanation of the drawing]

Figures 1 to 3 are diagrams showing the optical system, processing circuit, and displacement detection signal of the first embodiment of the optical minute displacement meter according to the present invention, and Figure 4 is a diagram showing the optical system of the second embodiment. , FIGS. 5 to 7 are diagrams showing the optical system, the area around the optical path limiting member, and the processing circuit, respectively, of the third embodiment, and FIGS. 8 to 10 are diagrams showing the optical system, the area around the optical path limiting member, respectively, of the fourth embodiment. Figures 11 and 12 are diagrams showing the conventional optical system and the light reception state on the photodiode using the critical angle method, and Figures 13 and 14 are diagrams showing the displacement-output relationship, respectively. FIG. 7 is a diagram showing another conventional optical system using an astigmatism method and a light receiving state on a photodiode. ■... Laser diode, 2... Collimator lens, 3... Polarizing beam splitter, 4... λ
/4 plate, 5...objective lens, 6...sample, 7...
99. Beam splinter, 8.9... Critical angle prism, 21... Cylindrical lens, 23...
Quadrant photo sensor, 33...Differential amplifier, 34...
...Compensation circuit, 35...Power amplifier, 36...
... Stage, 37 ... Servo motor for stage drive, 38.39 ... Differential amplifier system, 40 ... Addition circuit, 41 ... Compensation circuit, 42 ... Displacement output Device, 43...X-axis direction stage drive system, 44...
...Displacement sensor, 46...Imaging lens, 47...
・PSD, 48.49... Optical path limiting member, 50...
...Sensor, 51...Correction circuit, 52.53.54
...Sampling circuit, 55.56.57...
Low-pass filter circuit, 58... Optical path limiting member, 5
9... Center opening. Figure 11 Figure 2 Figure 3 Figure 4: I! Figure 5 Off Figure S Figure 111 Figure 12 Procedural amendment (voluntary) 29 Title of invention Optical minute displacement meter 4, generation
196 Shinbashi 5, Minato-ku, Tokyo 105
, Contents of the amendment (11 "Fig. 2" on page 10, lines 2 and 6 of the specification are corrected as "Fig. 3 1." (2) "Fig. "Optical minute displacement optical diameter" is corrected to "Optical minute displacement meter J." (3) Figure 1O is corrected as attached.

Claims (2)

[Claims] (1) An optical micro-displacement meter that is constructed by installing a high-resolution micro-displacement meter and a micro-displacement meter with a wide measurement range on the same axis, so that multiple micro-displacement meters simultaneously measure the same measurement point. (2) An optical micro-displacement meter that expands the measurement range of a high-resolution micro-displacement meter in a time-division manner so that multiple measurement ranges can measure the same measurement point almost simultaneously.