JPH095023A - Super fine displacement detector - Google Patents

Abstract

PURPOSE: To provide a super fine displacement detector in which positioning of an optical system can be done easily and which has high detection precision. CONSTITUTION: Light rays of a light source 3 are projected to an object 2 whose displacement is to be detected. A waveguide device 10 provided with at least one linear grating coupler 12 is set at a position where reflected light rays from the object 2 are to be received. The intensity of guided light rays of the grating coupler 12 is detected by a detector. Consequently, the inclination of the object 2 can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detector for detecting a minute displacement of an object, and more particularly to a detector suitable for detecting a displacement of a cantilever of an atomic force microscope.

[0002]

2. Description of the Related Art An atomic force microscope is known as a means for measuring the surface shape of an object to be measured. The atomic force microscope measures the surface shape by scanning the surface of the object to be measured with a point, that is, a stylus. When the stylus is brought as close as possible to the surface of the object to be measured and the electron cloud of atoms on the surface of the object to be measured is brought into contact with the electron cloud of atoms at the apex of the stylus, a repulsive interatomic force is generated between these atoms. Occurs. A three-dimensional shape of the object to be measured is obtained by bending the force detecting cantilever to which the stylus is attached by this atomic force and measuring the amount of displacement.

Force Detection Various methods are known as a minute force detecting means for detecting a minute displacement of the cantilever, and the optical lever method is known as the most general of them. This is because the force detection cantilever is arranged at an appropriate angle (20 to 30 °) with respect to the object to be measured, and the light from the light source is guided to the upper surface of the tip of the force detection cantilever by a lens and an optical fiber. 2 reflected light
This is a configuration in which a detector such as a split photodiode is used for detection. The deflection of the force detection cantilever can be detected by the position of the reflected light spot detected by the detector. The optical lever type micro force detector has an advantage that the structure is simple, but on the other hand, an optical path connecting three points of a light projecting portion, a cantilever, and a reflecting portion is provided in a limited space of the microscope apparatus. It is necessary to secure space.

Further, the micro-force detector disclosed in Japanese Patent Laid-Open No. 4-83138 is provided with an optical waveguide and a grating on a cantilever, makes light incident on the optical waveguide to propagate, and causes the propagated light to be emitted from the grating. The emitted light is detected by the detector. The deflection of the cantilever is detected by the position of the light spot detected by the detector. This micro-force detector has a structure in which the light propagating through the waveguide on the cantilever is emitted toward the detector. Therefore, as compared with the optical lever method, the space of the optical path connecting the light projecting section and the cantilever is secured. No need.

[0005]

The above-mentioned conventional optical lever type micro-force detector is composed of a light projecting portion, a cantilever, and a detecting portion.
It is necessary to align the optical path with high accuracy so as to connect the constituent parts. Since the area of the tip of the cantilever and the area of the detection surface of the detection unit are very small, it is necessary to perform alignment with high accuracy at the cantilever position. This work
It is extremely troublesome and there is a problem that the detection sensitivity easily changes due to the accuracy of this alignment.

Further, the micro force detector disclosed in Japanese Patent Laid-Open No. 4-83138 detects the deflection of the cantilever according to the position of the light spot on the detection surface of the detector, so that the alignment between the grating and the detector is accurate. It is similar to the optical lever method in that it must be done frequently. This alignment is troublesome, and if the accuracy is low, the detection sensitivity easily fluctuates.

Further, an optical lever system and Japanese Patent Laid-Open No. 4-83
The micro force detectors described in Japanese Patent No. 138 are each configured to detect the deflection of the cantilever based on the displacement of the light spot position on the detection surface of the detector. Therefore, in order to accurately detect the deflection of the cantilever, It is necessary to increase the distance between the cantilever and the detector so that the displacement of the light spot position becomes large. Therefore, there is a problem that a large space is required to improve the detection accuracy.

It is an object of the present invention to provide a micro force detector which enables easy positioning of an optical system and has high detection accuracy.

[0009]

In order to achieve the above object, the present invention has a light source for irradiating an object whose displacement is to be detected with light and a position for receiving reflected light from the object. A microdisplacement detector comprising at least one grating coupler, an optical waveguide for propagating light incident on the grating coupler, and a detector for detecting the intensity of light propagating in the optical waveguide. .

[0010]

[Operation] The light emitted from the light source is reflected by the object,
The reflected light is applied to the grating coupler. The light applied to the grating coupler excites the guided light of the optical waveguide. At this time, the intensity of the guided light excited in the optical waveguide depends on the incident angle of the light with which the grating coupler is irradiated. Therefore, the angle at which the reflected light enters the grating coupler can be detected by detecting the intensity of the guided light in the waveguide with the detector. Thereby, the inclination angle of the object can be detected.

As described above, according to the present invention, since the intensity of guided light of the optical waveguide depends on the incident angle of the light to the grating coupler, the distance between the object and the grating coupler is irrelevant. Therefore, the inclination of the object can be detected accurately. Therefore, since the grating coupler and the waveguide can be arranged in the vicinity of the object, alignment can be facilitated and a compact micro displacement detector can be provided.

[0012]

An embodiment of the present invention will be described with reference to the drawings.

The structure of an atomic force microscope equipped with a minute displacement detector according to an embodiment of the present invention will be described with reference to FIGS. 1, 2 and 3.

First, the structure of the small displacement detector of this embodiment will be described. The configuration of the entire atomic force microscope will be described later.

The micro-displacement detector of the present embodiment has an optical axis 301
A laser light source 3 and a collimator lens 4 are provided in this order on the top, and light is emitted to an object whose displacement is to be detected. In this embodiment, the object is the cantilever 2 of the atomic force microscope probe 8. As shown in FIG. 1, the cantilever 2 is generated by the atomic force between the tip of the probe 7 at the tip and the sample 214.
Bend upwards or downwards.

A waveguide device 10 having a linear grating coupler is arranged on the optical axis of the reflected light from the cantilever 2. The linear grating coupler is a coupler that excites the guided light in the waveguide by the collimated light propagating in the space and couples the light propagating in the space to the waveguide.

The structure of the waveguide device 10 will be further described.

As shown in FIGS. 2 and 3, an n-type Si substrate 1
01, a waveguide layer 103 made of SiN is formed via a buffer layer 102 made of SiO ₂ .
Two types of linear grating couplers 11 and 12 are arranged on the waveguide layer 103. The linear grating couplers 11 and 12 are formed by arranging linear convex portions made of SiN at a constant pitch.
The pitch of the grating coupler 11 is different from the pitch of the grating coupler 12. These pitches are predetermined. This pitch will be described later.

Further, on the substrate 101, p-type regions 104 and 105 formed by impurity diffusion are formed. The buffer layer 102 is removed from the p-type regions 104 and 105, and the buffer layer 102 is processed into a tapered shape around the buffer layer 102. The waveguide layer 103 includes the p-type region 10
It is in contact with 4, 105. In addition, the waveguide layer 103 includes
Through holes are provided on the p-type regions 104 and 105, and electrode films 106 and 107 are arranged inside the through holes so as to contact the p-type regions 104 and 105. Further, an electrode film 108 is arranged on the back surface of the substrate 101 so as to face the electrode films 106 and 107, respectively. These form the light receiving elements 32 and 33.

The waveguide type lens 2 is provided on the waveguide layer 103 between the linear grating coupler 11 and the light receiving element 32.
1 is arranged. The waveguide lens 21 is formed in a shape such that the light that enters the waveguide layer 103 from the grating coupler 11 and that propagates through the waveguide layer 103 is focused on the light receiving element 32. Similarly, between the linear grating coupler 12 and the light receiving element 33, the light that enters the waveguide layer 103 from the linear grating coupler 12 and propagates therethrough,
A waveguide lens 22 for condensing light is arranged on the light receiving element 33. The waveguide lenses 21 and 22 are made of SiN.

A differential amplifier 111 is connected to the substrate 101 as shown in FIG. In the differential amplifier 111, the output of the light receiving element 32 and the output of the light receiving element 33 are
It is input by the wirings 302 and 303, respectively. The output of the differential amplifier 111 is output by the wiring 304. An electrode 305 is attached to the tip of the wiring 304. The electrode 305 is in contact with the electrode 315 of the holder that supports the waveguide substrate 101, and the wiring 3 on the holder side.
It is electrically connected to 16.

In the waveguide device 10, the reflected light 401 from the cantilever 2 is reflected by the linear grating coupler 1.
It is arranged so that the light amount is equal to 1 and 12.

Next, the operation of the small displacement detector of this embodiment will be described.

As shown in FIG. 1, the laser light emitted from the light source 3 is collimated by the collimator lens 4 and irradiated toward the tip of the cantilever 2. The reflected light from the cantilever 2 is applied to the linear grating couplers 11 and 12 formed on the waveguide substrate 101.

The reflected light 401 applied to the linear grating coupler 11 excites the guided light of the waveguide layer 103. The guided light 402 propagates through the waveguide layer 103 and reaches the light receiving element 32. At this time, the waveguide type lens 21 moves the guided light 4
02 is condensed toward the light receiving element 32 in the substrate surface direction. As shown in FIG. 3, the waveguide layer 103 includes the light receiving element 3
2 is in contact with the p-type region 105, and the guided light 402 is
It is absorbed in the p-type region 105. Thereby, the light receiving element 3
A photocurrent corresponding to the intensity of the guided light 402 flows between the two electrodes 107 and 108.

Similarly, the linear grating coupler 12
The reflected light applied to the
And guided light 403 reaches the light receiving element 33. A photocurrent corresponding to the intensity of the guided light 403 flows through the light receiving element 33.

At this time, the linear grating coupler 1
The amount of light excited into the waveguide layer 103 by the components 1 and 12, that is, the incident coupling efficiency is determined by the pitch of the grating couplers 11 and 12 and the angle of the incident reflected light.

This will be further described.

In FIG. 1, when the angle formed by the reflected light from the cantilever 2 and the surface of the waveguide device is the incident angle θ, the maximum incident coupling efficiency η _e is obtained at the incident angle θ _e that satisfies the phase matching condition. To be The incident angle θ _e is θ that satisfies (Equation 1). Fig. 4 shows the relationship between the incident angle θ and the coupling efficiency η.
Shown in

[0030]

[Equation 1]

Here, N _s is the refractive index of the substrate, N is the effective refractive index of the optical waveguide layer 103, λ is the wavelength of light, and p is the pitch of the grating couplers 11 and 12.

When the incident angle deviates from the angle θ _{e which} satisfies the phase matching condition by Δθ, the incident coupling efficiency η decreases. η
/ Η _e is given by (Equation 2).

[0033]

[Equation 2]

However, L is the coupling length of the linear grating coupler.

As can be seen from FIG. 4, the coupling efficiency η at which the reflected light from the cantilever 2 enters the waveguide layer 103.
Becomes maximum when the incident angle θ _e satisfies the phase matching condition, and monotonically decreases on both sides of the incident angle θ _e .

From (Equation 1), it is understood that the incident angles θ _{e of the} gratings having different pitches are different.

As is clear from (Equation 1), instead of changing the pitch, for example, the pitch is the same, and the refractive index of the material loaded as the grating is different to change the phase matching condition. Good.

In this embodiment, the guided lights 402 and 403 coupled to the waveguide layer 103 by the linear grating couplers 11 and 12 are the light receiving elements 32 and 33, respectively.
The detected light intensity is proportional to the coupling efficiency of the linear grating coupler. In the present embodiment, the linear grating coupler 1 is configured so that the output curves of the light receiving elements 32 and 33 intersect each other as shown in FIG.
Determine the pitch of 1 and 12. When the incident angle satisfying the phase matching condition of the linear grating coupler 11 is θ _e1 and the incident angle satisfying the phase matching condition of the linear grating coupler 12 is θ _e2 , the differential amplifier 111 determines the output difference between the light receiving elements 32 and 33. By the determination, the output of the differential amplifier 111 becomes substantially linear in the range of θ _e1 to θ _e2 as shown in FIG. Therefore, the differential amplifier 1 corresponding to the incident angle θ in the range of θ _e1 to θ _e2
11 outputs can be obtained. Therefore, the output signal of the differential amplifier 111 corresponding to the displacement detection signal of the cantilever can be obtained.

Next, the overall structure of the atomic force microscope for detecting the displacement of the cantilever by the above-mentioned minute displacement detector will be described with reference to FIG.

In the atomic force microscope, a coarse movement mechanism 211 for coarsely moving a sample 214 on a supporting frame 215, and a piezo actuator 21 for scanning the sample 214 with respect to the probe 8.
2, the drive mechanism 203 for driving the probe 8, and the illumination device 202 in which the light source 3 and the collimator lens 4 are stored are attached. The drive mechanism 203 further includes
A holder 204 is attached.

The holder 204 supports the probe 8 and the waveguide device 10. As shown in FIG. 1, the probe 8 includes a cantilever 2, a support portion 6 that supports the cantilever 2 in a cantilevered manner, and a probe 7 arranged at the tip of the cantilever 2.

The illuminating device 202 in which the light source 3 and the collimating lens 4 are stored and the waveguide device 10 constitute the minute displacement detector as described above.

Further, the coarse movement mechanism 211, the piezo actuator 212, the drive mechanism 203, and the illumination device 202 are connected to a control device 307 for controlling these operations. In addition, the control device 307 includes a differential amplifier 111 connected to the waveguide device 10 via the holder 204.
Is input. The control device 307 has a display device 3 for displaying an uneven image of the detected sample surface 214.
10 are connected.

The structure of the holder 204 will be further described.

The holder 204 includes a protrusion 311 and a leaf spring 3.
12, the probe 8 is sandwiched, and the probe 8 is tilted and supported with respect to the sample 214. Further, the waveguide substrate 101 is sandwiched by the protruding portion 313 and the leaf spring 314, and the waveguide substrate 101 is supported at a position close to the upper portion of the probe 8. The protrusion 313 has an electrode 315 for contacting the electrode 305 of the waveguide substrate 101, and an electrode 31.
The wiring 316 connected to the wiring 5 is arranged. Wiring 31
6 is connected to the control device 307, so that the output of the differential amplifier 111 of the small displacement detector is input to the control device 307.

Since the operation of the atomic force microscope is already well known, it will be briefly described here.

The drive mechanism 203 and the coarse movement mechanism 211 are operated by the control device 307 to operate the probe 7 of the probe 8.
Are moved to the observation position of the sample 214. Next, the controller 307 operates the piezo actuator 212 to scan the sample 214 with respect to the sample 214. At this time, the cantilever 2 of the probe 8 bends upward or downward due to the atomic force between the sample 214 and the probe 7. This amount of deflection is detected by the above-mentioned minute displacement detector.

Specifically, the cantilever 2 is irradiated with light from the light source 3 of the illumination device 202, and the reflected light is reflected by the linear grating coupler 1 formed on the waveguide substrate 101.
The light receiving element 3 is made to enter the waveguide layer 103 from the light receiving elements 1 and 12.
It is detected at 2, 33. The differential amplifier 111 outputs the output difference between the light receiving elements 32 and 33. The output of the differential amplifier 111 depends on the incident angle of reflected light. The output of the differential amplifier 111 is output from the electrode 305 of the waveguide substrate 101 to the holder 20.
4 via the electrode 315 and the wiring 316
It is taken in by 07. The control device 307 receives the output of the differential amplifier 111 and the piezo actuator 212.
The display device 310 is caused to display image information corresponding to the position information of the sample 214 obtained from the movement amount of.

The small displacement detector of this embodiment uses the effect that the amount of light incident on the linear grating couplers 11 and 12 depends on the incident angle of the reflected light. Therefore, the detection accuracy does not depend on the distance between the detection unit and the cantilever unlike the conventional optical lever method. Therefore, even if the linear grating couplers 11 and 12 are arranged close to the cantilever 2, a small change in the reflection angle can be accurately detected.
Therefore, the space occupied by the minute displacement detector can be reduced. As a result, the atomic force microscope equipped with the micro-displacement detector of the present embodiment can detect irregularities of the sample with high accuracy, and the space occupied by the detector is small. Therefore, the combination with other optical systems such as a stereomicroscope becomes easy.

Further, in the small displacement detector of the present embodiment, it is sufficient that the linear grating couplers 11 and 12 are evenly irradiated with the reflected light, and the positions of the object and the grating are close to each other. In addition, there is an advantage that the alignment becomes easier as compared with the case where the detection is performed at the position of the light spot of the reflected light.

As shown in FIG. 2, the waveguide device 10
Can be formed by monolithically integrating a linear grating coupler, a waveguide, a light receiving element, and a waveguide lens on a Si substrate, and therefore can be manufactured very compactly and easily. Further, in the present embodiment, the chip manufactured by a separate process is mounted as the differential amplifier 111, but it is of course possible to build it together with the light receiving element on the Si substrate.

Further, in this embodiment, since the two linear grating couplers 11 and 12 having different pitches are used to obtain the difference in the incident light amount between the two, it is possible to obtain a wide incident angle range as shown in FIG. , An output signal proportional to the incident angle can be obtained. Therefore, the detection range of the displacement of the object is wide.

However, the present invention is not limited to the one having two grating couplers,
It is also possible to set the range in which the coupling efficiency of one linear grating coupler monotonically decreases as shown in FIG. 4 as the detection range. If you have one grating,
Since a differential amplifier is also unnecessary, there is an advantage that the configuration is simple.

Further, in FIG. 6, an output signal proportional to the incident angle is shown, but depending on the pitch of the grating,
The output signal may be curved. In this case, the incident angle can be accurately detected by measuring the relation between the incident angle and the output signal in advance and providing a circuit for obtaining the incident angle from the output signal using this relation.

Further, in the structure of the holder 204 of FIG. 1, since the waveguide device 10 and the probe 8 can be easily removed, a plurality of waveguide devices 10 having different pitches of the grating couplers are prepared and the cantilevers are prepared. By exchanging the waveguide device 10 in accordance with the range of displacement, the displacement can be detected more accurately.

It is also possible to form the probe 8 from Si and form a linear grating coupler on the probe 8 as shown in FIG. The light emitted from the light source 3 is directly applied to the linear grating couplers 11 and 12 through the collimator lens 4, and the linear grating coupler 11 and 12 are incident at an incident angle corresponding to the deflection of the cantilever 2.
12 to the optical waveguide layer 103. In the case of the configuration of FIG. 8, it is only necessary to align the linear grating couplers 11 and 12 and the light source 3, and there is an advantage that the alignment becomes easier. Further, there is an advantage that the linear grating couplers 11 and 12 having an optimum pitch can be formed in advance according to the detection range of the cantilever 2.

In addition, in this embodiment, 1
One waveguide layer 103 is arranged, and in this waveguide layer 103,
2 incident from the linear grating couplers 11 and 12
The waveguide layer 1 is configured to propagate two lights respectively.
03, linear grating couplers 11 and 12
Of course, it is also possible to dispose two channel type waveguides that connect the light receiving element and the light receiving elements 32 and 33.

[0058]

As described above, the micro-displacement detector of the present invention can easily position the optical system and can detect the change of the incident angle according to the displacement of the object with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a minute displacement detector according to the present embodiment.

FIG. 2 is a block diagram showing the configuration of the waveguide device 10 of FIG.

3 is a partial cross-sectional view of the waveguide device 10 of FIG.

FIG. 4 is a graph showing the incident angle dependence of the coupling efficiency between the linear grating coupler and the waveguide.

5 is a linear grating coupler 11, 12 of FIG.
3 is a graph showing the incident angle dependence of the outputs of the two light receiving elements.

6 is a graph showing a difference signal between outputs of two light receiving elements in FIG.

FIG. 7 is a block diagram showing the configuration of an atomic force microscope equipped with the small displacement detector according to the present embodiment.

FIG. 8 is a partial cross-sectional view of a probe equipped with a linear grating coupler.

[Explanation of symbols]

2 ... cantilever, 3 ... light source, 4 ... collimating lens,
6 ... Support part, 7 ... Probe, 8 ... Probe, 10 ... Waveguide device, 11, 12 ... Linear grating coupler, 2
1, 22 ... Waveguide lens, 32, 33 ... Light receiving element, 11
1 ... Differential amplifier, 212 ... Piezo actuator, 21
4 ... Sample, 204 ... Holder, 302, 303, 304 ...
Wiring, 305, 315 ... Electrode, 316 ... Wiring.

Claims (11)

[Claims] 1. A light source for irradiating an object whose displacement is to be detected with light, at least one grating coupler arranged at a position for receiving reflected light from the object, and light guided by the light incident on the grating coupler. A micro-displacement detector having an optical waveguide in which wave light is excited and a detector for detecting the intensity of guided light propagating in the optical waveguide. 2. The grating coupler according to claim 1, wherein the grating coupler includes two grating couplers having different phase matching conditions, and the detector detects a difference in intensity of guided light excited by each of the two grating couplers. A small displacement detector characterized by: 3. The phase matching condition of the two grating couplers according to claim 2, wherein the incident angle dependence curves of the coupling efficiency between the grating coupler and the optical waveguide intersect each other. A small displacement detector. 4. The micro-displacement according to claim 1, wherein the grating coupler is a linear grating coupler configured by arranging linear patterns on an optical waveguide periodically at an equal pitch. Detector. 5. A flexible plate portion having a needle-shaped portion at its tip, a sample table for supporting a sample at a position close to the tip of the needle-shaped portion, the needle-shaped portion and the sample. A driving unit for relatively scanning, a light source for irradiating the flexible plate with light, and a detection unit for detecting reflected light from the flexible plate, wherein the detection unit is At least one grating coupler arranged at a position for receiving reflected light from the flexible plate, an optical waveguide in which guided light is excited by light incident on the grating coupler, and intensity of guided light propagating in the optical waveguide. Atomic force microscope having a detector for detecting. 6. A flexible plate portion having a needle-shaped portion at its tip, a sample stand for supporting a sample at a position close to the tip of the needle-shaped portion, the needle-shaped portion and the sample. A drive unit for relatively scanning, a light source for irradiating the flexible plate with light, and a detection unit for detecting the light with which the flexible plate is irradiated, the detection unit: An optical waveguide mounted on the flexible plate, at least one grating coupler formed in the optical waveguide to excite guided light of the optical waveguide by light from the light source, and propagates through the optical waveguide And a detector that detects the intensity of the guided light. 7. An optical waveguide layer arranged on a substrate, two grating couplers arranged on the optical waveguide layer and having different phase matching conditions, and incident on the optical waveguide layer by the two grating couplers. A waveguide device, comprising: two light-receiving elements provided on a substrate for detecting light respectively. 8. The waveguide device according to claim 7, further comprising a detector for determining a difference between outputs of the two light receiving elements on the substrate. 9. The waveguide device according to claim 7, wherein the substrate is a semiconductor substrate, and the light receiving element is formed by diffusing impurities into the semiconductor substrate. 10. The optical waveguide layer according to claim 9,
A waveguide device, wherein the waveguide device is arranged on a portion of the light-receiving element in which impurities are diffused. 11. A probe having a flexible plate portion, a needle-shaped portion arranged at one end of the plate portion, and a support portion that cantilever-supports the other end of the plate portion, the probe comprising: Is provided on a substrate for detecting an optical waveguide, two grating couplers arranged on the waveguide and having different phase matching conditions, and light incident on the waveguide by the two grating couplers, respectively. And two light receiving elements that are mounted on the plate, and the two grating couplers are arranged on the plate.