Light detection device, scanning probe microscope, and measurement method

Abstract

A light detection device according to the present disclosure is a light detection device in a scanning probe microscope. The light detection device according to the present disclosure comprises a photodetector (61) and an amplification unit (60). The photodetector (61) receives laser light reflected by a cantilever of the scanning probe microscope and outputs an electrical signal. The amplification unit (60) amplifies the electrical signal on the basis of a gain. In the light detection device according to the present disclosure, the gain of the amplification unit (60) is variable.

Description

Photodetection device, scanning probe microscope, and measurement method

[0001] The present disclosure relates to a light detection device, a scanning probe microscope, and a measurement method, and more particularly to a scanning probe microscope that can change the detection sensitivity and dynamic range depending on the sample to be measured.

[0002] International Publication No. 2020 / 031329 (Patent Document 1) discloses a method for observing the characteristics of a sample using a scanning probe microscope. A scanning probe microscope can measure physical properties such as the shape, attractive force, adhesive force, and hardness of a sample by measuring a force curve that represents the distance dependence of the force acting between the probe and the sample surface. Furthermore, the surface condition of the sample can be observed and analyzed by measuring and imaging the physical properties while moving the probe in the X and Y directions. From the analysis image, users can gain insights into the sample, such as the state and / or physical properties of the sample surface.

[0003] The optical lever method is known as a method for measuring the displacement of a cantilever. In this method, the cantilever is irradiated with laser light and the change in position of the reflected light is detected by a photodetector, thereby measuring the displacement of the cantilever. In the optical lever method, the larger the electrical signal generated with each unit displacement of the cantilever, the higher the detection sensitivity of the scanning probe microscope.

[0004] International Publication No. 2020 / 031329

[0005] Improving the detection sensitivity of a scanning probe microscope can sometimes reduce the dynamic range, which is the range of detectable cantilever displacement. If the cantilever displacement exceeds the dynamic range, the state or physical properties of the sample will not be reflected in the measurement results. For example, measuring a sample that is harder than expected can cause the cantilever to bend significantly, exceeding the dynamic range. In such cases, the user cannot gain insight into the state and / or physical properties of the sample surface from the measurement results obtained.

[0006] In such cases, using a cantilever that is harder than the cantilever attached to the scanning probe microscope can sometimes reduce the amount of cantilever displacement per unit force, making it possible to measure the sample. However, replacing the cantilever requires adjusting the optical axis of the laser light, and users sometimes find the task of replacing the cantilever to match the sample to be cumbersome.

[0007] The present disclosure has been made in view of the above circumstances, and its purpose is to reduce the burden on users involved in the task of replacing a cantilever in measurements using a scanning probe microscope.

[0008] A first aspect of the present disclosure is an optical detection device for a scanning probe microscope, comprising a photodetector that receives laser light reflected by a cantilever of the scanning probe microscope and outputs an electrical signal, and an amplification unit that amplifies the electrical signal based on a gain, the gain of the amplification unit being variable.

[0009] A second aspect of the present disclosure is an optical detection device for a scanning probe microscope, comprising: a beam splitter that splits laser light reflected by a cantilever of the scanning probe microscope into first and second divided lights; a first photodetector that receives the first divided light; a second photodetector that receives the second divided light; a first amplification unit that amplifies an electrical signal output from the first photodetector; and a second amplification unit that amplifies the electrical signal output from the second photodetector, wherein the gain of the first amplification unit is greater than the gain of the second amplification unit.

[0010] A third aspect of the present disclosure is a measurement method including the steps of: (a) receiving an instruction to measure a sample using a scanning probe microscope; (b) measuring the sample and obtaining a first measurement result; (c) changing the gain based on the first measurement result; (d) measuring the sample with the gain set in the changing step and obtaining a second measurement result; and (e) displaying the second measurement result.

[0011] According to the present disclosure, it is possible to reduce the burden on the user involved in the task of replacing a cantilever in measurements using a scanning probe microscope.

[0012] FIG. 1 is a schematic configuration diagram of a scanning probe microscope according to a first embodiment; FIG. 2 is a block diagram of a light detection unit; FIG. 3 is a diagram showing the state of displacement of a cantilever; FIG. 4 is a diagram showing an example of a force curve; FIG. 5 is a block diagram of a light detection unit according to a comparative example; FIG. 6 is a flowchart showing processing according to the first embodiment; FIG. 7 is a schematic configuration diagram of a scanning probe microscope according to a second embodiment; and FIG. 8 is a flowchart showing processing according to the second embodiment.

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0014] 1 is a schematic diagram of a scanning probe microscope according to embodiment 1. The scanning probe microscope 100 includes a measuring device 10, a computer 20, a display 30, and an input device 40.

[0015] The measurement device 10 is configured to be able to communicate with a computer 20 and sends the measurement results to the computer 20 .

[0016] The computer 20 processes the transmitted measurement results and notifies the user of the calculation results obtained via the display 30. The computer 20 accepts inputs such as measurement conditions via the input device 40, and controls the entire measuring device 10 in accordance with the accepted measurement conditions.

[0017] As shown in FIG. 1, the measurement device 10 includes a piezo scanner 1, a sample stage 2, a cantilever 3, a laser diode 5, a light detection unit 6, a feedback signal generation unit 7, and a scanning signal generation unit 8.

[0018] A sample S is placed on the sample stage 2. The sample stage 2 is moved in three dimensions by the piezo scanner 1. In the following description, the mounting surface of the sample stage 2 on which the sample S is placed is defined as the XY plane, and the direction perpendicular to the XY plane is defined as the Z-axis direction.

[0019] The piezoelectric scanner 1 is an example of a drive unit that moves the sample stage 2 and the cantilever 3 relative to each other. The piezoelectric scanner 1 moves the sample stage 2 in three dimensions, the X, Y, and Z directions. The piezoelectric scanner 1 includes a Z scanner 1z that moves the sample stage 2 in the Z direction based on a command voltage value Vz, and an XY scanner 1xy that moves the sample stage 2 in the X and Y directions based on command voltage values ​​Vx and Vy, respectively. Note that the drive unit only needs to move the sample stage 2 and the cantilever 3 relative to each other, and may be configured to move the cantilever 3 or both the sample stage 2 and the cantilever 3.

[0020] The cantilever 3 is disposed opposite the sample stage 2. The cantilever 3 is formed in the shape of a leaf spring. One end of the cantilever 3 is a fixed end supported by a holder (not shown). The other end of the cantilever 3 is a free end, which is disposed opposite the sample S on the sample stage 2. A probe 4 is provided on the surface of the free end of the cantilever 3 facing the sample S.

[0021] The laser diode 5 emits a laser beam L1 toward the cantilever 3. The laser beam L1 emitted from the laser diode 5 is incident on the cantilever 3 and reflected therefrom.

[0022] The light detection unit 6 detects the laser light L2 reflected by the cantilever 3. When the cantilever 3 is bent and displaced, the position at which the light detection unit 6 receives the reflected light changes. The light detection unit 6 calculates the amount of displacement (amount of deflection) of the cantilever 3 based on the position at which the laser light L2 is received, and sends the calculated amount of displacement to the feedback signal generation unit 7 and the computer 20. In this way, the computer 20 obtains the change in the amount of cantilever displacement over time. The light detection unit 6 corresponds to one example of an "optical detection device."

[0023] 2 is a block diagram showing the configuration of the light detection unit 6. Referring to FIG. 2, the light detection unit 6 includes a photodetector 61, an amplification unit 60, a comparator 68, and an A / D converter 69.

[0024] Photodetector 61 detects laser light L2 reflected by cantilever 3 and outputs an electrical signal. The light receiving surface of photodetector 61 is divided into two regions: region 611 and region 612. The position at which laser light L2 is incident moves up and down in proportion to the displacement of cantilever 3, thereby changing the difference between the amount of light incident on region 611 and the amount of light incident on region 612. Region 611 and region 612 output signals T1 and T2 according to the amount of light received, respectively. Note that the light receiving surface of photodetector 61 may be divided into three or more regions.

[0025] The amplifier unit 60 amplifies the electrical signal output from the photodetector 61. The amplifier unit 60 includes an amplifier circuit 62 and an amplifier circuit 65.

[0026] Amplification circuit 62 amplifies signal T1 output from region 611, and amplification circuit 65 amplifies signal T2 output from region 612. Amplification circuit 65 has the same configuration as amplification circuit 62, so the following description will focus on amplification circuit 62. Amplification circuit 62 has amplifier 63 and gain setting circuit 64. In amplification circuit 65, amplifier 66 corresponds to amplifier 63, and gain setting circuit 67 corresponds to gain setting circuit 64.

[0027] The amplifier 63 converts the electrical signal output from the photodetector 61 into a voltage and amplifies the converted voltage according to a gain. The amplifier 63 is, for example, an operational amplifier. The gain of the amplifier 63 is set by a gain setting circuit 64.

[0028] The gain setting circuit 64 includes a switch 641 , a switch 642 , a resistor 643 , and a resistor 644 .

[0029] The switch 641 and the resistor 643 are connected in series, and the series-connected switch 641 and resistor 643 are connected in parallel to the amplifier 63 .

[0030] The switch 642 and the resistor 644 are connected in series, and the series-connected switch 642 and resistor 644 are connected in parallel to the amplifier 63 .

[0031] The resistance values ​​of the resistors 643 and 644 determine the gain in the gain setting circuit 64. The resistance value of the resistor 643 is greater than the resistance value of the resistor 644.

[0032] In the amplifier circuit 62, feedback is applied to the amplifier 63 via a resistor 643 or a resistor 644. The gain of the amplifier circuit 62 can be set by switching the resistor connected to the amplifier 63 using a switch 641 or a switch 642.

[0033] The computer 20 controls the on / off of the switches 641 and 642. A state in which the switch 641 is on and the switch 642 is off is referred to as state 1. A state in which the switch 641 is off and the switch 642 is on is referred to as state 2. In state 1, the gain of the amplifier 63 has a value corresponding to the resistance value of the resistor 643. In state 2, the gain of the amplifier 63 has a value corresponding to the resistance value of the resistor 644. Because the resistance value of the resistor 643 is greater than the resistance value of the resistor 644, the gain in state 1 is greater than the gain in state 2.

[0034] In the amplifier circuit 65, the switch 671 corresponds to the switch 641, the switch 672 corresponds to the switch 642, the resistor 673 corresponds to the resistor 643, and the resistor 674 corresponds to the resistor 644. The resistance values ​​of the resistors 673 and 643 are configured to be equal, and the resistance values ​​of the resistors 674 and 644 are configured to be equal.

[0035] The computer 20 controls each switch so that in state 1, switch 671 is turned on and switch 672 is turned off. Furthermore, the computer 20 controls each switch so that in state 2, switch 671 is turned off and switch 672 is turned on. In this way, the gain of amplifier 63 and the gain of amplifier 66 are equal in both state 1 and state 2. The amplifier 63 converts the signal T1 to a voltage, and outputs a signal T3 amplified according to the gain to the comparator 68. The amplifier 66 converts the signal T2 to a voltage, and outputs a signal T4 amplified according to the gain to the comparator 68.

[0036] Comparator 68 receives signals T3 and T4 and outputs an electrical signal having a magnitude equal to the voltage difference between these signals.

[0037] The A / D converter 69 converts the analog signal output from the comparator 68 into a digital signal and outputs a detection signal T5. The output detection signal T5 is sent to the computer 20 and the feedback signal generator 7.

[0038] Returning to FIG. 1 , the feedback signal generating unit 7 calculates a command voltage value Vz in the Z-axis direction in accordance with instructions from the computer 20 and outputs it to the Z scanner 1z. Upon receiving a start signal from the computer 20, the feedback signal generating unit 7 calculates a command voltage value Vz so that the Z scanner 1z moves the sample stage 2 toward the cantilever 3 and then away from the sample stage 2, and outputs the command voltage value Vz to the Z scanner 1z. The feedback signal generating unit 7 controls the Z-axis position of the sample stage 2 based on the deflection amount sent from the light detecting unit 6 so that the force acting on the probe 4 from the sample S does not exceed a predetermined value. When the deflection amount sent reaches the predetermined value, the feedback signal generating unit 7 calculates a command voltage value Vz in the Z-axis direction so that the movement direction of the sample stage 2 is switched from toward the cantilever 3 to away from it, and outputs the command voltage value Vz to the Z scanner 1z. The feedback signal generating unit 7 sends the command voltage value Vz corresponding to the movement amount of the Z scanner 1z in the Z-axis direction to the computer 20. As a result, the computer 20 acquires the change over time in the amount of movement of the sample stage 2 in the Z-axis direction.

[0039] The scanning signal generating unit 8 calculates command voltage values ​​Vx and Vy in the X-axis and Y-axis directions in accordance with instructions from the computer 20 so that the sample S moves relative to the probe 4 in the XY plane, and outputs them to the XY scanner 111xy.

[0040] The computer 20 creates a force curve that indicates the relationship between the position of the sample stage 2 in the Z-axis direction and the displacement of the cantilever 3, based on the displacement of the cantilever 3 sent from the light detection unit 6 and the command voltage value Vz sent from the feedback signal generation unit 7. The computer 20 includes a processor 22, a memory 24, and an input / output I / F 26. The components within the computer 20 are configured to be able to communicate with each other via a bus.

[0041] The processor 22 is typically an arithmetic processing unit such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The processor 22 controls the operation of the computer 20 by reading and executing programs stored in the memory 24. The programs include a program that, when executed by the processor 22, causes the computer 20 to control the measuring device 10, the display 30, and the input device 40.

[0042] The memory 24 is realized by a storage device such as a ROM (Read Only Memory), a RAM (Random Access Memory), and a HDD (Hard Disk Drive). The ROM non-temporarily stores the program executed by the processor 22. The RAM temporarily stores data used by the processor 22 while the program is running, and functions as a temporary data memory used as a work area. The HDD is a non-volatile storage device. A semiconductor storage device such as a flash memory may be used in addition to or instead of the HDD. The program and / or data may be stored in an external storage device accessible by the processor 22.

[0043] The input / output I / F 26 is an interface for exchanging various types of data between the processor 22 and external devices connected to the input / output I / F 26. The external devices include a display 30, an input device 40, and the measurement device 10. The display 30 is an example of a notification unit that notifies the user of predetermined information, and displays, for example, an image for accepting input from the input device 40 and the results of calculations by the processor 22. The notification unit may also be other devices such as a speaker or a printer. The input device 40 is typically composed of a touch panel, a keyboard, a mouse, etc. The input device 40 accepts user input operations for the processor 22.

[0044] [Force Curve] The force curve will be described in detail. FIG. 3 shows the displacement of the cantilever. FIG. 4 shows an example of a force curve. FIG. 3 shows the displacement of the cantilever 3 when the sample S approaches the probe 4 in the Z-axis direction and when the sample S moves away from the probe 4 in the Z-axis direction. The horizontal axis of FIG. 4 represents the position Z of the sample stage 2 in the Z-axis direction. Since one end of the cantilever 3 on which the probe 4 is attached is a fixed end, the position Z corresponds to the vertical distance between the probe 4 and the sample S. On the horizontal axis of FIG. 4, the left direction on the paper surface represents the direction in which the distance between the probe 4 and the sample S decreases, and the right direction on the paper surface represents the direction in which the distance between the probe 4 and the sample S increases. The vertical axis of FIG. 3 represents the force F applied to the cantilever 3. The force F can be calculated by multiplying the displacement D [V] of the cantilever 3 by the spring constant K [N / m] and the sensitivity S [m / V]. The spring constant K is a physical property value of the cantilever 3 and is a constant determined by the cantilever 3. Furthermore, the sensitivity S is the sensitivity of the measurement device 10 and is determined by the measurement device 10. Therefore, the force F corresponds to the displacement amount that represents the displacement of the cantilever 3. Note that the vertical axis of the force curve may be any characteristic amount that represents the displacement of the cantilever 3, and may be the displacement D [V] of the cantilever 3.

[0045] The sensitivity S varies depending on the gain of the light detection unit 6. The sensitivity S is the value obtained by dividing the displacement [m] of the cantilever under predetermined conditions by the voltage value [V] output from the light detection unit 6. The predetermined conditions are, for example, when the sample is a hard substrate that does not deform even when the cantilever is pressed against it. An example of a hard substrate is a glass substrate.

[0046] (1) to (4) in Figure 3 correspond to (1) to (4) in Figure 4, respectively. In (1) to (4), the sample S moves toward the probe 4 and makes contact. In (4) to (6), the sample S moves away from the probe 4 and finally separates from it. In (1), the probe 4 at the tip of the cantilever 3 and the sample S are completely separated. Therefore, the cantilever 3 does not displace. In (2), the cantilever 3 receives a slight attractive force from the sample S and bends downward. This is called a jump-in. In (3), the cantilever 3 receives a repulsive force from the sample S and bends upward. In (4), the probe 4 and the sample S come into closest contact, and the repulsive force received from the sample S is at its maximum. In (5), the force received by the cantilever 3 from the sample S changes from repulsion to attraction. At (6), an adhesive force acts between the cantilever 3 and the sample S, and the attractive force from the sample S reaches a maximum. Immediately after (6), the probe 4 separates from the sample S, returning to the state of (1). This is called a jump-out.

[0047] The feedback signal generating unit 7 controls the Z-direction position of the sample stage 2 based on the displacement sent from the light detecting unit 6 so that the force that the probe 4 receives from the sample S does not exceed a predetermined set value. Therefore, the maximum repulsive force that the cantilever 3 receives is designed not to exceed a predetermined set value.

[0048] The force curve is composed of an approach curve obtained during approach when the sample S approaches the probe 4, and a release curve obtained during release when the sample S moves away from the probe 4. For ease of explanation, the following will be described taking the approach event as an example.

[0049] After the sample S and the probe 4 come into contact, if the sample S is further moved, the probe 4 is pressed against the surface of the sample S. If the surface of the sample S is sufficiently hard compared to the probe 4, the amount of movement of the sample S and the amount of displacement of the cantilever 3 will match. On the other hand, if the surface of the sample S is softer than the probe 4, the surface of the sample S will deform due to the pressing of the probe 4, and the amount of movement of the sample S and the amount of displacement of the cantilever 3 will no longer match. Therefore, the relative hardness of the sample S with respect to the hardness of the cantilever 3 can be observed from the slope a1 of the approach curve, which indicates the amount of displacement of the cantilever 3 relative to the amount of movement of the sample S. The relative hardness of the sample S with respect to the hardness of the cantilever 3 can also be observed from the slope a2 of the release curve.

[0050] [Comparative Example] A scanning probe microscope can measure the shape of a sample, its attractive force, adhesive force, hardness, and other physical properties by measuring a force curve that represents the distance dependency of the force acting between the probe and the sample surface. Furthermore, by measuring and imaging the physical properties while moving the probe in the X and Y directions, the surface condition of the sample can be observed and analyzed. From the analysis image, users can gain insight into the sample, such as the state of the sample surface and its physical properties.

[0051] The optical lever method is a well-known method for measuring the displacement of a cantilever. In this method, the cantilever is irradiated with laser light and the change in position of the reflected light is detected by a photodetector, thereby measuring the displacement of the cantilever.

[0052] In the optical lever method, a photodetector divided into two or more regions is used to detect laser light reflected by the cantilever. The electrical signal output from each region is converted into a voltage and output to a comparator. The amount of cantilever displacement is calculated based on the difference between the voltage values ​​output by the comparator. When the electrical signal output from each region is converted into a voltage, the electrical signal output from each region is amplified by the gain in the amplifier circuit. Even if the amount of cantilever displacement is the same, the output of the photodetector will be greater if the gain is greater. Therefore, by increasing the gain in the photodetector, the detection sensitivity of the scanning probe microscope will be improved.

[0053] 5 is a schematic diagram of a light detection unit 6A of a scanning probe microscope according to a comparative example. As shown in FIG. 5, the light detection unit 6A includes a photodetector 61, an amplification unit 60A, a comparator 68, and an A / D converter 69.

[0054] In the light detection section 6A, the signals T1 and T2 output from the regions 611 and 612 of the photodetector 61 are amplified in the amplifier unit 60A. The amplifier unit 60A includes an amplifier circuit 62A and an amplifier circuit 65A.

[0055] The amplifier circuit 62A includes an amplifier 63 and a gain setting circuit 64A. The gain setting circuit 64A has a resistor 644A. The signal T1 is amplified by a gain corresponding to the resistance value of the resistor 644A and converted into a signal T6.

[0056] The amplifier circuit 65A includes an amplifier 66 and a gain setting circuit 67A. The gain setting circuit 67A has a resistor 674A having the same resistance as the resistor 644A. The signal T2 is amplified with the same gain as the amplifier circuit 62A and converted into a signal T7.

[0057] Comparator 68 receives signals T6 and T7 and outputs the voltage difference between these signals.

[0058] The A / D converter 69 converts the analog signal output from the comparator 68 into a digital detection signal T8, which is sent to the computer 20 and the feedback signal generator 7.

[0059] Increasing the gain of amplifier circuits 62A and 65A, i.e., increasing the resistance values ​​of resistors 644A and 674A, can improve the detection sensitivity of a scanning probe microscope equipped with light detection unit 6A. However, there may be a limit to the difference in voltage values ​​that can be detected by comparator 68. Therefore, amplifying the electrical signals output from regions 611 and 612 and increasing the difference in voltage values ​​applied to comparator 68 may reduce the accuracy with which comparator 68 measures this difference. Increasing the gain of amplifier circuits 62A and 65A improves detection sensitivity, but may narrow the dynamic range, which is the range of detectable cantilever displacements.

[0060] For example, when measuring and acquiring a specific sample, if the sample is harder than the user expected, the cantilever may bend significantly. If the cantilever displaces beyond the dynamic range, the state or physical properties of the sample may not be reflected in the measurement results. In such cases, for example, replacing the cantilever provided in the scanning probe microscope with a harder cantilever can reduce the amount of cantilever displacement, potentially allowing the state or physical properties of the sample to be reflected in the measurement results. However, replacing the cantilever requires adjusting the optical axis, which can be a cumbersome process for users.

[0061] [Scanning Probe Microscope According to First Embodiment] Each of the amplifier circuits 62 and 65 of the light detection unit 6 of the scanning probe microscope 100 according to the first embodiment includes a plurality of resistors. By switching these resistors, it is possible to change the gain for amplifying the detected light signal in accordance with the sample to be measured.

[0062] According to the scanning probe microscope 100 of the first embodiment, when measuring a predetermined sample, if the cantilever bends beyond the dynamic range, the state or physical properties of the sample can be reflected in the measurement results by reducing the gain without replacing the cantilever, thereby reducing the burden on the user of replacing the cantilever.

[0063] Measurement using the scanning probe microscope 100 according to the first embodiment will be described below.

[0064] When an instruction to measure the sample S is received, the computer 20 controls the switches 641, 642, 671, and 672 to set the light detection unit 6 to state 1, in which the gains in the amplifier circuits 62 and 65 are large.

[0065] Next, the computer 20 moves the sample stage 2 using the piezo scanner 1, and brings the probe 4 of the cantilever 3 into contact with the sample S. The computer 20 creates a first force curve based on the output of the light detection unit 6.

[0066] The computer 20 determines whether or not the cantilever 3 detects a force equal to or greater than a predetermined value in the obtained first force curve. The force equal to or greater than the predetermined value may be a repulsive force or an attractive force.

[0067] The predetermined value may be set in advance, for example, by a company that provides the scanning probe microscope 100 or the cantilever 3. Alternatively, the predetermined value may be set in advance by a user of the scanning probe microscope 100, or the computer 20 may set the predetermined value. For example, when calculating the sensitivity S, the computer 20 determines the magnitude of the force detected when the amount of displacement of the cantilever that can be detected by the light detection unit 6 in state 1 is maximum.

[0068] When the computer 20 determines that the cantilever 3 has detected a force greater than a predetermined value in the obtained first force curve, it controls the switches 641, 642, 671, and 672 to set the light detection unit 6 to state 2 in which the gain in the amplifier circuits 62 and 65 is smaller than state 1.

[0069] Next, the computer 20 moves the sample stage 2 using the piezo scanner 1, and brings the probe 4 of the cantilever 3 into contact with the sample S. The computer 20 creates a second force curve based on the electrical signal detected by the light detection unit 6.

[0070] Thereafter, computer 20 displays the measurement results, including the created first force curve and / or second force curve, on display 30. In addition to the force curve, the measurement results include values ​​that can be derived from the force curve, such as gradient value a1, gradient value a2, and suction force.

[0071] [Flowchart] Fig. 6 is a flowchart showing a process for acquiring a force curve according to the first embodiment. The process steps shown in Fig. 6 are realized by the processor 22 executing a program stored in the memory 24. Note that the process shown in Fig. 6 is started, for example, when a user selects execution of a predetermined application.

[0072] In step S10, the computer 20 sets the position (X, Y) of the sample stage 2 to a predetermined arbitrary position (Xa, Ya).

[0073] In step S12, the computer 20 instructs the scanning probe microscope 100 to move the position of the sample stage 2 to the position set in step S10.

[0074] In step S14, the computer 20 controls the switches 641, 642, 671, and 672 to set the light detection unit 6 to state 1.

[0075] In step S16, the computer 20 executes processing to create a first force curve. Specifically, the computer 20 sends a signal to start measurement of the sample S to the feedback signal generator 7. Upon receiving the start signal, the feedback signal generator 7 moves the sample stage 2 closer to the cantilever 3. After that, based on the amount of deflection reaching a predetermined set value, the feedback signal generator 7 controls the Z scanner 1z to switch the movement direction of the sample stage 2 from a direction approaching the cantilever 3 to a direction away from the cantilever 3. The computer 20 acquires the amount of movement of the sample stage 2 and the amount of displacement of the cantilever 3 while the Z scanner 1z is driven. As a result, the computer 20 creates a force curve as shown in FIG. 3 .

[0076] In step S18, computer 20 determines whether a force equal to or greater than a predetermined value has been detected in the first force curve created in step S 16. If computer 20 determines that a force equal to or greater than the predetermined value has been detected in the first force curve (YES in step S18), computer 20 proceeds to step S20; otherwise (NO in step S18), computer 20 proceeds to step S24.

[0077] In step S20, the computer 20 controls the switches 641, 642, 671, and 672 to set the gain in the light detection unit 6 to state 2, which is smaller than state 1.

[0078] In step S22, similarly to step S14, the computer 20 executes the process for creating a force curve and creates a second force curve.

[0079] In step S24, the computer 20 displays the first force curve and / or the second force curve on the display 30. Thereafter, the computer 20 ends the force curve acquisition processing subroutine and returns the processing to the main routine.

[0080] According to the scanning probe microscope 100 of the first embodiment, if the displacement of the cantilever 3 during measurement of the sample S exceeds the detectable displacement of the cantilever 3, the dynamic range can be increased by reducing the gain of the amplification unit 60. This allows the state or physical properties of a harder sample to be reflected in the measurement results without replacing the cantilever 3. This reduces the burden on the user of replacing the cantilever.

[0081] In the first embodiment, the gain is reduced according to the hardness of the sample. However, this is not limiting and the gain may be increased according to the sample. In measurements using a scanning probe microscope, if the displacement of the cantilever is within the dynamic range, the state or physical properties of the sample are reflected in the measurement results. However, for example, if there is a first dynamic range and a second dynamic range that is smaller than the first dynamic range, and the displacement of the cantilever does not exceed the first dynamic range or the second dynamic range, the measurement results in the second dynamic range have better detection sensitivity. Therefore, for example, if the magnitude of the force detected using the first dynamic range is equal to or smaller than a predetermined value, the scanning probe microscope may be controlled to measure the sample using the second dynamic range.

[0082] In the above-described first embodiment, the computer 20 determines whether or not to perform measurement in state 2, but the user may determine whether or not to perform measurement in state 2. For example, after the user checks the first force curve displayed on the display 30, the user instructs the computer 20 to perform measurement in state 2.

[0083] In the above-described first embodiment, the computer 20 determines whether to perform measurement in state 2 based on whether a force equal to or greater than a predetermined value is detected in measurement in state 1, but the criteria for determining whether to perform measurement in state 2 are not limited to this. For example, the user may input the magnitude of the force required to measure the sample S, and the computer 20 may determine whether to measure the sample S in state 1 or state 2 based on that value. In this case, depending on the magnitude of the force input by the user, measurement in state 1 may not be performed, and only measurement in state 2 may be performed.

[0084] Furthermore, for example, it may be determined whether or not to perform measurement in state 2 based on the gradient value a1, the gradient value a2, and the value of the adsorptive force.

[0085] Although the number of settable gains is two in the first embodiment, the number of settable gains is not limited to 2. The gain setting circuit includes resistors and switches according to the number of settable gains.

[0086] In the first embodiment, the photodetector 6 does not need to have the resistors 644 and 647. In this case, the gain in state 2 is 1.

[0087] Each of the amplifier circuits 62 and 65 of the scanning probe microscope 100 may include a variable resistor instead of including multiple resistors and multiple switches. In this case, the resistance values ​​of the variable resistors in the amplifier circuits 62 and 65 are controlled by the computer 20 to be equal to each other.

[0088] In the scanning probe microscope 100 according to the first embodiment, the gain is set by the amplifier used when converting current into voltage, but this is not limiting. For example, an amplifier may be provided that receives and amplifies the signals T6 and T7, and the gain of the scanning probe microscope may be set by the gain of the amplifier.

[0089] In the first embodiment, the gain is switched after the measurement in State 1 is completed, but the timing at which the gain is switched is not limited to this. For example, the gain may be switched during the measurement in State 1. Specifically, if the magnitude of the detected force exceeds a predetermined value while the probe 4 is approaching the sample S in State 1, the gain may be switched while the probe 4 is in contact with the sample S. By doing so, it may be possible to shorten the time required to measure the sample.

[0090] In the first embodiment, the scanning probe microscope 100 has been described as acquiring a force curve, but the present invention can also be applied to imaging the unevenness of a sample surface in contact mode and dynamic mode. In this case, the amplitude of the cantilever can be changed by changing the gain. This reduces the burden on the user of replacing the cantilever.

[0091] Second Embodiment [Configuration of the Light Detector According to the Second Embodiment] In the first embodiment, a configuration has been described in which a scanning probe microscope is configured to be able to set multiple resistance values ​​in a gain setting circuit. In the first embodiment, after a measurement at a large gain, a measurement at a small gain is performed as needed. Therefore, in order to obtain force curves at two different gains, the probe needs to approach the sample twice, which may take a long time to measure the sample.

[0092] In the second embodiment, a configuration will be described in which a beam splitter splits the laser light reflected by the cantilever. In the second embodiment, each split laser light is detected by a different photodetector. Therefore, by approaching the probe to the sample once, force curves with two different gains can be obtained, which may shorten the time required to measure the sample compared to the first embodiment.

[0093] 7 is a schematic diagram showing the configuration of a photodetector 6C included in the scanning probe microscope according to the second embodiment. Referring to Fig. 7, the photodetector 6C includes a beam splitter 91, photodetectors 921 and 922, amplification units 60B and 60C, comparators 961 and 962, and A / D converters 971 and 972.

[0094] In the second embodiment, the same components as those of the scanning probe microscope 100 described in the first embodiment are denoted by the same reference numerals, and detailed description thereof will not be repeated. Furthermore, the contents described in the first embodiment can be combined with the second embodiment to the extent that they do not contradict each other.

[0095] The beam splitter 91 splits the laser beam L2 reflected by the cantilever 3 into two beams, a split beam L3 and a split beam L4.

[0096] Photodetector 921 detects split light L3, and photodetector 922 detects split light L4. The light receiving surface of photodetector 921 is divided into two areas: area 9211 and area 9212. The light receiving surface of photodetector 922 is divided into two areas: area 9221 and area 9222. The position at which laser light L2 is incident moves up and down in proportion to the displacement of cantilever 3, thereby changing the difference in the amount of light incident on each area. Areas 9211, 9212, 9221, and 9222 output signals T9 to T12 according to the amount of light received. Note that the light receiving surfaces of photodetector 921 and photodetector 922 may be divided into three or more areas.

[0097] The amplifier unit 60B amplifies the signal T9 and the signal T10 output from the photodetector 921. The amplifier unit 60B includes an amplifier circuit 931 and an amplifier circuit 932.

[0098] The amplifier circuit 931 includes a resistor 941 and an amplifier 951. The amplifier circuit 931 receives the signal T9, and outputs the amplified signal T13 in accordance with the gain set by the resistor 941.

[0099] The amplifier circuit 932 includes a resistor 942 and an amplifier 952. The amplifier circuit 932 receives the signal T10, and outputs a signal T14 amplified according to the gain set by the resistor 942.

[0100] The amplifier unit 60C amplifies the signal T11 and the signal T12 output from the photodetector 922. The amplifier unit 60C includes an amplifier circuit 933 and an amplifier circuit 934.

[0101] The amplifier circuit 933 includes a resistor 943 and an amplifier 953. The amplifier circuit 933 receives the signal T11, and outputs a signal T15 amplified according to the gain set by the resistor 943.

[0102] The amplifier circuit 934 includes a resistor 944 and an amplifier 954. The amplifier circuit 934 receives the signal T12, and outputs a signal T16 amplified according to the gain set by the resistor 944.

[0103] The resistance values ​​of the resistors 941 to 944 are configured so that the resistance value of the resistor 941 = the resistance value of the resistor 942 > the resistance value of the resistor 943 = the resistance value of the resistor 944. Therefore, the gain in each amplifier circuit is such that the gain in the amplifier circuit 931 = the gain in the amplifier circuit 932 > the gain in the amplifier circuit 933 = the gain in the amplifier circuit 934.

[0104] The comparator 961 receives the signal T13 output from the amplifier circuit 931 and the signal T14 output from the amplifier circuit 932, and outputs the voltage difference between these signals.

[0105] The A / D converter 971 converts the analog signal output from the comparator 961 into a digital detection signal T17. The output detection signal T17 is sent to the computer 20 and the feedback signal generator 7.

[0106] The comparator 962 receives the signal T15 output from the amplifier circuit 933 and the signal T16 output from the amplifier circuit 934, and outputs the voltage difference between these signals.

[0107] The A / D converter 972 converts the analog signal output from the comparator 962 into a digital detection signal T18. The output detection signal T18 is sent to the computer 20 and the feedback signal generator 7.

[0108] [Flowchart] Figure 8 is a flowchart showing a process for acquiring a force curve according to the second embodiment. The process steps shown in Figure 8 are realized by the processor 22 executing a program stored in the memory 24. The process shown in Figure 8 is started, for example, when a user selects execution of a predetermined application. In Figure 8, the same components as those in the flowchart described in Figure 6 are designated by the same reference numerals, and detailed description thereof will not be repeated.

[0109] In step S30, the computer 20 executes processing for creating a force curve. Specifically, the computer 20 sends a signal to start measurement of the sample S to the feedback signal generator 7. Upon receiving the start signal, the feedback signal generator 7 moves the sample stage 2 closer to the cantilever 3. After that, based on the amount of deflection reaching a predetermined value, the feedback signal generator 7 controls the Z scanner 1z to switch the movement direction of the sample stage 2 from approaching the cantilever 3 to moving away from it. The computer 20 acquires the amount of movement of the sample stage 2 and the amount of displacement of the cantilever 3 while the Z scanner 1z is driven. At this time, the displacement amount of the cantilever 3 is used to create a third force curve based on signal T17 and a fourth force curve based on signal T18.

[0110] In step S32, computer 20 determines whether a force greater than a predetermined value is detected in the third force curve created in step S30. If computer 20 determines that a force greater than the predetermined value is detected in the third force curve (YES in step S32), computer 20 proceeds to step S34; otherwise (NO in step S32), computer 20 proceeds to step S36.

[0111] In step S34, the computer 20 displays the fourth force curve on the display 30. Thereafter, the computer 20 ends the force curve acquisition process subroutine and returns the process to the main routine.

[0112] In step S36, the computer 20 displays the third force curve on the display 30. Thereafter, the computer 20 ends the force curve acquisition process subroutine and returns the process to the main routine.

[0113] In the photodetector unit 6C of the scanning probe microscope according to the second embodiment, laser light L2 reflected by the cantilever is split into two beams, split light L3 and split light L4, by the beam splitter 91. The gain of the amplifier circuit for the electrical signal output from the photodetector 921 that detects split light L3 is greater than the gain of the amplifier circuit for the electrical signal output from the photodetector 922 that detects split light L4. Therefore, by once approaching and releasing the probe 4 from the sample S, it is possible to create force curves with different gains.

[0114] According to the scanning probe microscope equipped with the light detection unit 6C of the second embodiment, it is possible to obtain force curves of two gains by making the probe 4 approach the sample S once. This reduces the burden on the user of replacing the cantilever, and makes it possible to shorten the time required to measure the sample compared to measurement with the scanning probe microscope 100 of the first embodiment.

[0115] Aspects It will be understood by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0116] (Item 1) An optical detection device according to one aspect is an optical detection device for a scanning probe microscope, and includes a photodetector that receives laser light reflected by a cantilever of the scanning probe microscope and outputs an electrical signal, and an amplification unit that amplifies the electrical signal based on a gain, and the gain of the amplification unit may be variable.

[0117] According to the light detection device described in paragraph 1, it is possible to reduce the burden on the user of the work of replacing the cantilever in measurements using a scanning probe microscope.

[0118] (Clause 2) In the photodetector described in clause 1, the light receiving surface of the photodetector includes a first region and a second region, the electrical signal includes a first signal output based on the amount of light irradiated onto the first region and a second signal output based on the amount of light irradiated onto the second region, the amplification unit includes a first amplification circuit that amplifies the first signal and a second amplification circuit that amplifies the second signal, and the gain of the first amplification circuit and the gain of the second amplification circuit may be equal and variable.

[0119] According to the photodetector described in paragraph 2, the signal output from each of the light-receiving surfaces of the divided photodetector is amplified by a corresponding amplifier circuit. The gains of the multiple amplifier circuits are equal and variable, so the detection sensitivity and dynamic range can be changed depending on the sample being measured. This reduces the user's burden of replacing the cantilever during scanning probe microscope measurements.

[0120] (Clause 3) In the photodetector device described in clause 1 or 2, the first amplifier circuit may include a first resistor and a second resistor having a resistance smaller than that of the first resistor, a first switch connected in series with the first resistor, a second switch connected in series with the second resistor, and a first converter connected in parallel with each of the first resistor and the second resistor and converting the first signal into a voltage value; and the second amplifier circuit may include a third resistor having a resistance equal to that of the first resistor, a fourth resistor having a resistance equal to that of the second resistor, a third switch connected in series with the third resistor, a fourth switch connected in series with the fourth resistor, and a second converter connected in parallel with each of the third resistor and the fourth resistor and converting the second signal into a voltage value.

[0121] According to the photodetector described in paragraph 3, the gain of the voltage value output by the converter that converts current into voltage is set by one or more resistors included in the amplifier circuit. At this time, by switching the switch, the resistors used in the converter can be switched, and the gain of the amplifier circuit can be changed.

[0122] (4) In the photodetector device according to any one of the first to third paragraphs, the amplification unit may include a variable resistor.

[0123] According to the photodetector described in the fourth aspect, the gain of the amplification unit can be changed by changing the resistance value of the variable resistor included in the amplification unit.

[0124] (Item 5) A photodetector according to one aspect is a photodetector for use in a scanning probe microscope, and includes a beam splitter that splits laser light reflected by a cantilever of the scanning probe microscope into a first divided light and a second divided light, a first photodetector that receives the first divided light, a second photodetector that receives the second divided light, a first amplification unit that amplifies an electrical signal output from the first photodetector, and a second amplification unit that amplifies an electrical signal output from the second photodetector, and the gain of the first amplification unit may be greater than the gain of the second amplification unit.

[0125] According to the optical detection device described in paragraph 5, in measurements using a scanning probe microscope, by approaching the probe to the sample once, the sample can be measured based on the gain determined by the first amplifier circuit and the gain determined by the second amplifier circuit.

[0126] (Item 6) In the photodetector device described in item 5, the first amplification unit may include a fifth resistor, and the second amplification unit may include a sixth resistor having a resistance value smaller than that of the fifth resistor.

[0127] According to the photodetector described in paragraph 6, a sample can be measured based on the gain determined by the fifth resistor of the first amplifier circuit and the gain determined by the sixth resistor of the second amplifier circuit.

[0128] (7) A scanning probe microscope may include the photodetector device according to any one of the 1st to 6th paragraphs.

[0129] According to the scanning probe microscope described in item 7, the burden on the user of the cantilever replacement work in measurements using the scanning probe microscope can be reduced.

[0130] (Clause 8) A measurement method according to one aspect may include the steps of receiving an instruction to measure a sample using a scanning probe microscope, measuring the sample and obtaining a first measurement result, changing a gain based on the first measurement result, measuring the sample with the gain set in the changing step and obtaining a second measurement result, and displaying the second measurement result.

[0131] According to the measurement method described in paragraph 8, the burden on the user of replacing the cantilever in measurements using a scanning probe microscope can be reduced.

[0132] (Clause 9) In the measurement method described in clause 8, the changing step may include a step of reducing the gain when the maximum value of the magnitude of the force detected in the first measurement result is equal to or greater than a first threshold value.

[0133] According to the measurement method described in paragraph 9, if the gain for the sample is large in the first measurement result, the gain can be set small and a second measurement result can be obtained. As a result, even if the user cannot obtain information about the state and / or physical properties of the sample surface from the first measurement result, the user can obtain information about the state and / or physical properties of the sample surface from the second measurement result without replacing the cantilever.

[0134] (Clause 10) In the measurement method described in clause 8, the changing step may include a step of increasing the gain when the maximum value of the magnitude of the force detected in the first measurement result is equal to or less than a second threshold value.

[0135] According to the measurement method described in paragraph 10, the second measurement result can be obtained by setting a gain higher than that of the first measurement result, thereby allowing the user to obtain the second measurement result with better detection sensitivity than the first measurement result without replacing the cantilever.

[0136] The embodiments disclosed herein are intended to be combined as appropriate within the scope of any technical inconsistency. The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the description of the above-mentioned embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0137] 1 Piezo scanner, 2 Sample stage, 3 Cantilever, 4 Probe, 5 Laser diode, 6 Light detection unit, 7 Feedback signal generation unit, 8 Scanning signal generation unit, 10 Measuring device, 20 Computer, 22 Processor, 24 Memory, 30 Display, 40 Input device, 60, 60A, 60B, 60C Amplification unit, 61, 921, 922 Photodetector, 62, 65, 931, 932, 933, 934 Amplification circuit, 63, 66, 951, 952, 953, 954 Amplifier, 64, 67 Gain setting circuit, 68, 961, 962 Comparator, 69, 971, 972 A / D converter, 91 Beam splitter, 100 Scanning probe microscope, 641, 642, 671, 672 Switches, 643, 644, 673, 674, 941, 942, 943, 944 Resistors.

Claims

1. A photodetector for a scanning probe microscope, comprising: a photodetector that receives laser light reflected by the cantilever of the scanning probe microscope and outputs an electrical signal; and an amplification unit that amplifies the electrical signal based on a gain, the gain of which is variable.

2. The photodetector according to claim 1, wherein the light receiving surface of the photodetector includes a first region and a second region, the electrical signal includes a first signal output based on the amount of light irradiated onto the first region and a second signal output based on the amount of light irradiated onto the second region, the amplification unit includes a first amplification circuit that amplifies the first signal and a second amplification circuit that amplifies the second signal, and the gain of the first amplification circuit and the gain of the second amplification circuit are equal and variable.

3. The photodetector device of claim 2, wherein the first amplifier circuit comprises a first resistor and a second resistor having a resistance smaller than that of the first resistor, a first switch connected in series with the first resistor, a second switch connected in series with the second resistor, and a first converter connected in parallel with each of the first resistor and the second resistor and converting the first signal into a voltage value; and the second amplifier circuit comprises a third resistor having a resistance equal to that of the first resistor, a fourth resistor having a resistance equal to that of the second resistor, a third switch connected in series with the third resistor, a fourth switch connected in series with the fourth resistor, and a second converter connected in parallel with each of the third resistor and the fourth resistor and converting the second signal into a voltage value.

4. The photodetector device of claim 1, wherein the amplification unit includes a variable resistor.

5. A photodetector for a scanning probe microscope, comprising: a beam splitter that splits laser light reflected by a cantilever of the scanning probe microscope into a first divided light and a second divided light; a first photodetector that receives the first divided light; a second photodetector that receives the second divided light; a first amplification unit that amplifies an electrical signal output from the first photodetector; and a second amplification unit that amplifies an electrical signal output from the second photodetector, wherein the gain of the first amplification unit is greater than the gain of the second amplification unit.

6. The photodetector device according to claim 5, wherein the first amplifying unit includes a fifth resistor, and the second amplifying unit includes a sixth resistor having a resistance value smaller than that of the fifth resistor.

7. A scanning probe microscope comprising the optical detection device according to claim 1.

8. A measurement method comprising the steps of: receiving an instruction to measure a sample using a scanning probe microscope; measuring the sample and obtaining a first measurement result; changing a gain based on the first measurement result; measuring the sample with the gain set in the changing step and obtaining a second measurement result; and displaying the second measurement result.

9. The measurement method according to claim 8, wherein the changing step includes a step of decreasing the gain when the maximum value of the magnitude of the force detected in the first measurement result is equal to or greater than a first threshold value.

10. The measurement method according to claim 8, wherein the changing step includes a step of increasing the gain when the maximum value of the magnitude of the force detected in the first measurement result is equal to or less than a second threshold value.

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