Optical inspection device and control method thereof

Abstract

Provided are an optical inspection device that can be miniaturized and that can quickly control the amount of irradiated light according to the size of foreign matter, and a control method thereof. This optical inspection device comprises: a light source that generates irradiation light with which a sample is irradiated; a light quantity adjustment unit that adjusts the quantity of the irradiation light; a voltage switching unit that switches a voltage applied to the light quantity adjustment unit; an optical sensor that measures scattered light from the sample and generates a measurement signal; and a control unit that controls each unit. The voltage switching unit includes a first high voltage source that outputs a first voltage, a second high voltage source that outputs a second voltage different from the first voltage, an attenuation circuit that outputs an attenuation voltage obtained by attenuating the first voltage, and a switch that applies the second voltage or the attenuation voltage to the light quantity adjustment unit. The control unit controls the attenuation circuit on the basis of the measurement signal.

Description

Optical inspection device and control method thereof

[0001] The present invention relates to an optical inspection device that detects foreign matter in a sample by irradiating the sample with light and measuring the light scattered from the sample, and a control method for the same.

[0002] Optical inspection equipment, along with electron microscopes, is used to inspect semiconductor devices, which are becoming increasingly miniaturized. Optical inspection equipment detects foreign particles by measuring the scattered light from a sample irradiated with light. Detecting tiny foreign particles requires increasing the amount of irradiated light, but large foreign particles may explode if they absorb the irradiated light, so it is preferable to quickly control the amount of irradiated light according to the size of the foreign particle.

[0003] Patent Document 1 discloses a method for predicting the presence or absence of foreign matter based on the measurement results of the previous circumference when a sample is spirally scanned with irradiation light, and for reducing the amount of irradiation light if a foreign matter is predicted to be present. It also discloses that a driver circuit for switching the voltage applied to an optical modulation element that increases or decreases the amount of irradiation light uses MOS transistors to quickly switch and control multiple voltages generated in each of a number of high-voltage generation circuits.

[0004] International Publication No. 2016 / 121756

[0005] However, in Patent Document 1, insufficient consideration is given to miniaturization of the optical inspection device. Because the high-voltage generation circuit has a transformer, it is difficult to miniaturize an optical inspection device that includes a large number of high-voltage generation circuits.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical inspection device that can be miniaturized and that can quickly control the amount of light irradiated according to the size of foreign matter, and a control method for the same.

[0007] In order to achieve the above object, the present invention provides an optical inspection device comprising a light source that generates illumination light to be irradiated onto a sample, a light intensity adjustment unit that adjusts the amount of the illumination light, a voltage switching unit that switches the voltage applied to the light intensity adjustment unit, an optical sensor that measures scattered light from the sample and generates a measurement signal, and a control unit that controls each unit, wherein the voltage switching unit has a first high voltage source that outputs a first voltage, a second high voltage source that outputs a second voltage different from the first voltage, an attenuation circuit that outputs an attenuated voltage that attenuates the first voltage, and a switch that applies either the second voltage or the attenuated voltage to the light intensity adjustment unit, and the control unit controls the attenuation circuit based on the measurement signal.

[0008] The present invention also provides a control method for an optical inspection device that includes a light source that generates illumination light to be irradiated onto a sample, a light intensity adjustment unit that adjusts the amount of the illumination light, a voltage switching unit that switches the voltage applied to the light intensity adjustment unit, an optical sensor that measures scattered light from the sample and generates a measurement signal, and a control unit that controls each unit, wherein the voltage switching unit has a first high-voltage source that outputs a first voltage, a second high-voltage source that outputs a second voltage different from the first voltage, an attenuation circuit that outputs an attenuated voltage that attenuates the first voltage, and a switch that applies either the second voltage or the attenuated voltage to the light intensity adjustment unit, and the control unit controls the attenuation circuit based on the measurement signal.

[0009] According to the present invention, it is possible to provide an optical inspection device and a control method thereof that can be miniaturized and that can quickly control the amount of irradiated light in accordance with the size of foreign matter.

[0010] FIG. 1 is a diagram showing an example of the overall configuration of an optical inspection device according to the first embodiment; FIG. 2 is a diagram showing an example of the configuration of a light intensity adjustment unit; FIG. 3 is a diagram showing an example of the configuration of an attenuation circuit; FIG. 4 is a diagram explaining adjustment of the scanning path and the intensity of irradiation light by irradiation light; FIG. 5 is a diagram showing an example of the processing flow of the first embodiment; FIG. 6 is a diagram showing an example of the processing flow for setting the intensity of irradiation light for the next cycle; FIG. 7 is a diagram giving a supplementary explanation about changing the intensity of irradiation light based on the measured value and the intensity of irradiation light; FIG. 8 is a diagram giving a supplementary explanation about changing the intensity of irradiation light based on the measured value and the intensity of irradiation light;

[0011] An embodiment of an optical inspection device according to the present invention will now be described with reference to the accompanying drawings. The optical inspection device measures scattered light generated by irradiating a sample with light, and detects foreign matter in the sample based on the obtained measurement values.

[0012] An example of the overall configuration of the optical inspection apparatus of Example 1 will be described with reference to Fig. 1. The optical inspection apparatus includes a light source 101, a light intensity adjustment unit 102, a sample stage 103, an optical sensor 104, a voltage switching unit 110, and a control unit 120. A sample 100 such as a semiconductor wafer is held on the sample stage 103.

[0013] The light source 101 generates irradiation light that is irradiated onto the sample 100. The irradiation light generated by the light source 101 is, for example, an ultraviolet laser.

[0014] The light intensity adjustment unit 102 adjusts the amount of irradiation light generated by the light source 101. For example, irradiation light generated by the light source 101 with an intensity P0 is adjusted by the light intensity adjustment unit 102 to an intensity C·P0, and is irradiated onto the sample 100. Here, C is a transmittance between 0 and 1. Details of the light intensity adjustment unit 102 will be described later with reference to FIG. 2.

[0015] The optical sensor 104 measures scattered light generated by irradiation of the sample 100 held on the sample stage 103 with irradiation light, and generates a measurement signal. The generated measurement signal is sent to the control unit 120, where it is converted into a measurement value of the scattered light. Note that while the sample 100 is being irradiated with the irradiation light, the sample stage 103 moves horizontally while rotating the sample 100, causing the surface of the sample 100 to be spirally scanned by the irradiation light, thereby measuring the scattered light at each point on the surface of the sample 100. Since the measurement value of the scattered light at a point where a foreign object is present is larger than that at a point where no foreign object is present, foreign objects can be detected based on the measurement value of the scattered light. Furthermore, since the measurement value of the scattered light increases as the size of the foreign object increases, the size of the foreign object can be calculated based on the measurement value of the scattered light.

[0016] The voltage switching unit 110 has a first high-voltage source 111, a second high-voltage source 112, an attenuation circuit 113, and a switch 114, and switches the voltage applied to the light amount adjustment unit 102. The first high-voltage source 111 is a high-voltage generating circuit that outputs a first voltage V1. The second high-voltage source 112 is a high-voltage generating circuit that outputs a second voltage V2 that is different from the first voltage V1.

[0017] The attenuation circuit 113 is connected to the first high-voltage source 111 and outputs an attenuated voltage obtained by attenuating the first voltage V1. For example, the first voltage V1 output from the first high-voltage source 111 is attenuated to (1-α)·V1 by the attenuation circuit 113. Here, α is an attenuation factor greater than or equal to 0 and less than or equal to 1, and (1-α)·V1 is the attenuation voltage. Details of the attenuation circuit 113 will be described later with reference to FIG. 3.

[0018] The switch 114 is connected to the attenuation circuit 113 or the second high-voltage source 112, and applies either the attenuation voltage (1-α)·V1 or the second voltage V2 to the light amount adjustment unit 102. That is, when the switch 114 is connected to the attenuation circuit 113, the attenuation voltage (1-α)·V1 is applied to the light amount adjustment unit 102, and when the switch 114 is connected to the second high-voltage source 112, the second voltage V2 is applied to the light amount adjustment unit 102.

[0019] Although the voltage switching unit 110 can apply a large number of voltages to the light intensity adjustment unit 102, it only has two high voltage generation circuits, the first high voltage source 111 and the second high voltage source 112, which makes it possible to miniaturize the optical inspection device.

[0020] The control unit 120 is, for example, a general-purpose computer, which controls the operation of each unit, and determines the presence or absence of a foreign object and calculates the size of the foreign object based on the measurement signal transmitted from the optical sensor 104. A storage device, a display device, and an input device may be connected to the control unit 120. The storage device stores various programs, data, measurement signals, etc. The display device displays the results of the determination of the presence or absence of a foreign object and the calculation results of the size of the foreign object. The input device allows the user to input data, etc.

[0021] An example of the configuration of the light intensity adjustment unit 102 will be described using Figure 2. The light intensity adjustment unit 102 has a Pockels cell 201 and a polarizing plate 202. The Pockels cell 201 is an element that rotates the polarization direction of incident irradiation light in accordance with the applied voltage. The polarizing plate 202 is a plate with many slits, which transmits light in the direction in which the slits extend and absorbs light in the direction in which the slits are aligned. Note that the slit direction, which is the direction in which the slits extend, is perpendicular to the direction in which the slits are aligned.

[0022] The Pockels cell 201 rotates the polarization direction of the irradiated light, thereby changing the amount of light transmitted through the polarizing plate 202. Specifically, when the angle between the polarization direction of the irradiated light and the slit direction is 0 degrees, the irradiated light passes through the polarizing plate 202, resulting in a transmittance C=1. As the angle increases, C decreases, and when the angle is 90 degrees, C=0. That is, by switching the voltage applied to the light intensity adjustment unit 102, which includes the Pockels cell 201 and the polarizing plate 202, between the attenuation voltage (1-α)·V1 or the second voltage V2, the amount of irradiated light irradiated onto the sample 100 can be adjusted quickly. Furthermore, by controlling the attenuation voltage (1-α)·V1 output from the attenuation circuit 113, the amount of irradiated light irradiated onto the sample 100 can be adjusted more precisely. It is preferable that the attenuation voltage (1-α)·V1 be controlled quickly.

[0023] An example configuration of the attenuation circuit 113 will be described using Fig. 3. The attenuation circuit 113 illustrated in Fig. 3(a) includes three resistors R1, R2, and R3 connected in series and a voltage dividing switch 301. Terminals are provided at both ends of each of the resistors R1, R2, and R3. That is, terminals T1 and T2 are provided at both ends of the resistor R1, terminals T2 and T3 are provided at both ends of the resistor R2, and terminals T3 and T4 are provided at both ends of the resistor R3. A first voltage V1 is applied to terminal T1, and terminal T4 is at ground potential. The number of resistors connected in series is not limited to three.

[0024] Voltage dividing switch 301 is connected to one of terminals T1 to T4 in response to instructions from control unit 120, and outputs an attenuated voltage (1-α)·V1. The attenuation factor α is determined by the terminal to which it is connected, with α=0 for terminal T1, α=R1 / R0 for terminal T2, α=(R1+R2) / R0 for terminal T3, and α=1 for terminal T4. Here, R0=R1+R2+R3. Voltage dividing switch 301 is, for example, a high-voltage switching element that can switch the connected terminals in about 100 ms, allowing the attenuated voltage (1-α)·V1 to be controlled at high speed.

[0025] 3B includes a resistor R, an NMOSFET 302, and a voltage division control unit 303. A first voltage V1 is applied to one end of the resistor R, and the NMOSFET 302 is connected to the other end.

[0026] NMOSFET 302 functions as a variable resistor because its drain-source resistance Rds changes in response to the gate-source voltage Vgs applied by voltage division control unit 303, and is connected between resistor R and ground potential. An output terminal that outputs an attenuated voltage (1-α)·V1 is provided at the connection point between resistor R and NMOSFET 302. The attenuation factor α is determined by the resistance Rds, and is given by α=R / (R+Rds).

[0027] The voltage division control unit 303 controls the gate-source voltage Vgs according to the difference between the target voltage transmitted from the control unit 120 and the attenuation voltage (1-α)·V1. The voltage division control unit 303 may be equipped with a DAC (Digital to Analog Converter) or a high-speed operational amplifier. The inclusion of a DAC can improve the resolution of the gate-source voltage Vgs and can also make the voltage division control unit 303 more compact. The inclusion of a high-speed operational amplifier can also quickly control the attenuation voltage (1-α)·V1. Instead of the NMOSFET 302 and the voltage division control unit 303, a high-voltage variable resistor whose resistance value is controlled by the control unit 120 may be used.

[0028] The attenuation circuit 113 shown in FIG. 3 is configured by a resistor and a switch, and therefore can control the attenuation voltage (1-α)·V1 at high speed.

[0029] The adjustment of the scanning path and the intensity of the irradiation light by the irradiation light will be described using FIG. 4 . While the irradiation light is irradiating the sample 100, the sample stage 103 moves horizontally while rotating the sample 100, so that the surface of the sample 100 is spirally scanned by the irradiation light. In FIG. 4( a), a spiral scanning path 400 is shown by a dotted line. Note that by defining the radial direction of the sample 100 as the r axis and the circumferential direction as the θ axis, the coordinates on the surface of the sample 100 can be expressed as (r, θ). Furthermore, since the sample stage 103 moves Δr in the horizontal direction during one rotation of the sample 100, the distance between the spiral trajectories is Δr. Furthermore, the irradiation field 401 formed on the surface of the sample 100 by the irradiation of the irradiation light is an ellipse with its major axis in the radial direction of the sample 100.

[0030] FIG. 4B shows an example of the distribution of the irradiated light intensity P on the r-axis at θ = θ0, where a foreign object is present, showing a light intensity distribution 402 for the Nth rotation and a light intensity distribution 403 for the N+1th rotation. The irradiated light intensity P is a distribution, such as a Gaussian distribution, in which the irradiated light intensity is greatest at the center of the irradiation field 401 and decreases toward the edge. Because the measured value of scattered light at a point where a foreign object is present is greater than at a point where no foreign object is present, a foreign object can be detected based on the measured value of scattered light even if the foreign object is present at the base of the light intensity distribution 402 for the Nth rotation, i.e., at the edge of the irradiation field 401 where the irradiated light intensity is small. A foreign object detected at the Nth rotation may explode if exposed to a greater irradiated light intensity at the N+1th rotation than at the base of the light intensity distribution 402 for the Nth rotation. Therefore, if a foreign object is detected at the Nth rotation, the explosion of the foreign object can be avoided by lowering the irradiated light intensity, as in the light intensity distribution 403 for the N+1th rotation. Furthermore, if the measured value of scattered light in the N+1th rotation is extremely reduced compared to the measured value in the Nth rotation, and it can be determined that the center of the irradiation field 401 in the N+1th rotation has passed over a foreign object, the amount of irradiation light in the N+2th rotation can be increased to reduce the possibility of overlooking a minute foreign object. The amount of irradiation light is controlled by the attenuation voltage (1-α)·V1 and the second voltage V2 that the voltage switching unit 110 applies to the light amount adjustment unit 102.

[0031] An example of the processing flow of the first embodiment will be described step by step with reference to FIG.

[0032] (S501) The control unit 120 irradiates the starting point of the sample 100 with irradiation light and measures the scattered light at the starting point. Note that in order to avoid the explosion of foreign matter when foreign matter is present at the starting point, the amount of irradiation light irradiated at the starting point is gradually increased from the minimum level and is set to the maximum level if no foreign matter is present at the starting point. The starting point may be the center of the sample 100 as shown in FIG. 4A or the edge of the sample 100.

[0033] (S502) The control unit 120 sets the amount of light to be irradiated for the next rotation based on the scattered light measurement value S. Details of the processing of S502 will be described later using FIGS.

[0034] (S503) The control unit 120 controls the sample stage 103 to move the sample stage 103 horizontally while rotating the sample 100 once.

[0035] (S504) The control unit 120 acquires the measurement value S of the scattered light during one rotation of the sample 100. That is, the rotation angle θ and the measurement value S of the scattered light are associated with each other.

[0036] (S505) The control unit 120 determines whether or not the entire sample 100 has been measured. That is, if the starting point is the center of the sample 100, it determines whether or not scanning has been completed up to the edge of the sample 100, and if the starting point is the edge of the sample 100, it determines whether or not scanning has been completed up to the center of the sample 100. If the entire sample 100 has been measured, the processing flow ends, and if not, the processing returns to S502.

[0037] According to the processing flow explained using Figure 5, the amount of irradiation light for the next rotation is set based on the measurement value S of scattered light for one rotation obtained when the surface of the sample 100 is spirally scanned with irradiation light, thereby avoiding explosion of foreign matter and reducing the chance of missing minute foreign matter.

[0038] An example of the processing flow of S502 will be described step by step with reference to FIG.

[0039] (S601) The control unit 120 determines whether or not there is a measurement value S equal to or greater than the threshold value Th1. If there is no measurement value S equal to or greater than the threshold value Th1, the process proceeds to S602; if there is, the process proceeds to S603. The threshold value Th1 is the lower limit of scattered light when a minute foreign object is present in the irradiation field 401 of the irradiation light. In other words, if the measurement value S is equal to or greater than the threshold value Th1, a foreign object is present in the irradiation field 401.

[0040] (S602) The control unit 120 maintains the amount of irradiation light. That is, the amount of irradiation light in the (N+1)th rotation is set to be the same as the amount of irradiation light in the Nth rotation.

[0041] (S603) The control unit 120 changes the amount of irradiated light based on the measurement value S and the amount of irradiated light.

[0042] The processing of S603 will be further explained using FIG. 7 . If the amount of irradiation light P in the Nth rotation is constant at Ph as shown in FIG. 7A, and the measurement value S of scattered light measured at that time is equal to or greater than the threshold value Th1 near θ1 as shown in FIG. 7B and reaches a peak value S1 at θ1, the amount of irradiation light P in the N+1th rotation is changed as shown in FIG. 7C. That is, the amount of irradiation light P in the N+1th rotation is reduced from Ph to Pl1 near θ1 where a foreign object is present, and Ph is maintained outside the vicinity of θ1. The value of Pl1 used in the N+1th rotation is set based on the amount of irradiation light Ph in the Nth rotation and the peak value S1 of the measurement value S. For example, if the upper limit of scattered light that can prevent foreign object explosion is threshold value Th2, Pl1 can be calculated using the following formula:

[0043] P11=K·Ph·Th2 / S1 (Equation 1), where K is a coefficient previously determined by experiment or simulation. If the peak value of the measurement value S in the Nth rotation is S_N, the amount of light irradiated in the Nth rotation is P_N, and the amount of light irradiated in the N+1th rotation is P_N+1, then Equation 1 can be generalized as follows:

[0044] P_N+1=K P_N Th2 / S_N (Equation 2) The process of S603 will be further explained with reference to Figure 8. If the irradiation light intensity P for the N+1th rotation is set to P11 near θ1 as shown in Figure 8(a) and to Ph other than near θ1, and the measurement value S of the scattered light measured at that time is equal to or greater than threshold value Th1 near θ1 as shown in Figure 8(b) and has a peak value S11 at θ1 that is extremely lower than S1, the irradiation light intensity P for the N+2th rotation is changed as shown in Figure 8(c). That is, because the peak value S11 is extremely lower than S1, it is determined that the center of the irradiation field 401 for the N+1th rotation has passed over a foreign object, and so the irradiation light intensity P for the N+2th rotation is increased from P11 to P12 near θ1 where the foreign object is present. The value of Pl2 used in the N+2th cycle can be calculated by substituting P_N+1=Pl2, P_N=Pl1, and S_N=S11 into (Equation 2) using the following equation.

[0045] Pl2=K·Pl1·Th2 / S11 (Equation 3) The processing flow described using FIG. 6 allows the amount of light irradiated for the next rotation to be appropriately set based on the measurement value S of scattered light obtained during one rotation of the sample 100, thereby preventing foreign matter from exploding and reducing the chance of tiny foreign matter being overlooked.

[0046] Another example of the processing flow of S502 will be described using Fig. 9. Fig. 9 shows the processing flow when multiple foreign particles are lined up in the circumferential direction of the sample 100, and is obtained by adding S901 to S903 between S601 and S603 in Fig. 6. Steps S901 to S903 will be described.

[0047] (S901) The control unit 120 determines whether or not there are multiple peaks equal to or greater than the threshold value Th1. That is, in S901, it is determined whether or not there are multiple foreign particles lined up in the circumferential direction of the sample 100. If there are multiple peaks representing the number of foreign particles lined up in the circumferential direction of the sample 100, the process proceeds to S902; if there are not multiple peaks, the process skips to S603.

[0048] (S902) The control unit 120 determines whether the adjacent angle, which is the angle between adjacent peaks, is less than the angle threshold θth. The angle threshold θth is a value set based on the control speed of the attenuation circuit 113 and the rotation speed of the sample 100, so in S902, it is determined whether the change in the amount of irradiated light will be in time between foreign objects adjacent in the circumferential direction of the sample 100. In other words, if the adjacent angle is less than the angle threshold θth, it is determined that the change in the amount of irradiated light will not be in time. If the adjacent angle is less than the angle threshold θth, the process proceeds to S903; if not less than the angle threshold θth, the process skips to S603.

[0049] (S903) The control unit 120 compares the measurement values ​​S of adjacent peaks and selects the higher one. The selected higher measurement value S is used to change the amount of irradiated light in S603. In other words, if the change in the amount of irradiated light cannot be made in time between foreign particles adjacent in the circumferential direction of the sample 100, the amount of irradiated light is set to avoid explosion of foreign particles that are more likely to explode.

[0050] The processing of S901, S902, S903, and S603 will be further explained using Fig. 10. If the amount of irradiation light P in the Nth rotation is constant at Ph as shown in Fig. 10(a) and the measurement value S of scattered light measured at that time is as shown in Fig. 10(b), the amount of irradiation light P in the (N+1)th rotation will be changed as shown in Fig. 10(c).

[0051] Specifically, the measurement value S of the scattered light for the Nth rotation has peaks equal to or greater than the threshold value Th1 at each of θ1, θ2, and θ3, and since there are multiple peaks, processing proceeds from S901 to S902. Next, the adjacent angle θ2-θ1 between θ1 and θ2 is compared with the angle threshold value θth, and since θ2-θ1≧θth, processing skips from S902 to S903 for the measurement value S at θ1. Meanwhile, the comparison result of the adjacent angle θ3-θ2 between θ2 and θ3 with the angle threshold value θth is θ3-θ2<θth, and therefore processing proceeds from S902 to S903 for the measurement values ​​S at θ2 and θ3. Then, in S903, the peak value S2 at θ2 is compared with the peak value S3 at θ3, and since S2<S3, peak value S3 is selected. Finally, in S603, the amount of irradiation light is changed from Ph to P11 based on S1 near θ1, and the amount of irradiation light is changed from Ph to P13 based on the selected S3 near θ2 and θ3. As a result, the amount of irradiation light P in the (N+1)th rotation becomes as shown in FIG.

[0052] 9, the amount of light irradiated for the next rotation can be appropriately set based on the measurement value S of scattered light obtained during one rotation of the sample 100, thereby preventing foreign matter from exploding and reducing the risk of overlooking minute foreign matter. Furthermore, even when multiple foreign matter are lined up in the circumferential direction and the amount of light irradiated between the foreign matter cannot be changed in time, foreign matter explosion can be avoided.

[0053] Incidentally, when the rotation speed of the sample 100 is constant, the distance scanned by the irradiated light per unit time varies depending on the radial position of the sample 100. Specifically, as illustrated in FIG. 11 , an outer scanning path 1101 is longer than an inner scanning path 1102. As a result, when the amount of irradiated light is constant, the amount of irradiated light per unit area and unit time inside the sample is higher than that outside the sample. The difference in the amount of irradiated light per unit area and unit time between the inside and outside of the sample causes a difference in the temperature rise of the sample 100, which may cause deformation of the sample 100.

[0054] Therefore, control may be performed so that the amount of irradiation light is greater on the outside than on the inside of the sample 100. More specifically, the amount of irradiation light may be controlled in proportion to the distance from the center of the sample 100. Alternatively, the rotation speed of the sample 100 may be controlled in inverse proportion to the distance from the center of the sample 100 while keeping the amount of irradiation light constant. By such control, deformation of the sample 100 can be suppressed.

[0055] The above describes the embodiments of the present invention. The present invention is not limited to the above embodiments, and the components can be modified and embodied without departing from the spirit of the invention. Furthermore, multiple components disclosed in the above embodiments may be combined as appropriate. Furthermore, some components may be omitted from all the components shown in the above embodiments.

[0056] Sample 100, light source 101, light intensity adjustment unit 102, sample stage 103, optical sensor 104, voltage switching unit 110, first high voltage source 111, second high voltage source 112, attenuation circuit 113, switch 114, Pockels cell 201, polarizing plate 202, voltage dividing switch 301, NMOSFET 302, voltage dividing control unit 303, scanning path 400, irradiation field 401, light intensity distribution for the Nth rotation 402, light intensity distribution for the N+1th rotation 403, outer scanning path 1101, inner scanning path 1102.

Claims

1. An optical inspection device comprising a light source that generates illumination light to be irradiated onto a sample, a light intensity adjustment unit that adjusts the amount of the illumination light, a voltage switching unit that switches the voltage applied to the light intensity adjustment unit, an optical sensor that measures scattered light from the sample and generates a measurement signal, and a control unit that controls each unit, wherein the voltage switching unit has a first high voltage source that outputs a first voltage, a second high voltage source that outputs a second voltage different from the first voltage, an attenuation circuit that outputs an attenuated voltage that attenuates the first voltage, and a switch that applies either the attenuated voltage or the second voltage to the light intensity adjustment unit, and the control unit controls the attenuation circuit based on the measurement signal.

2. An optical inspection device according to claim 1, wherein the attenuation circuit has a plurality of resistors connected in series and a voltage divider switch connected to one of the terminals on both ends of the resistors, and the control unit controls the voltage divider switch.

3. An optical inspection device according to claim 1, wherein the attenuation circuit has a variable resistor and a voltage division control section that controls the resistance value of the variable resistor, and the control section controls the voltage division control section.

4. An optical inspection device according to claim 3, wherein the variable resistor is an NMOSFET, and the voltage division control section controls the source-gate voltage of the NMOSFET based on the difference between a target value transmitted from the control section and the output value of the attenuation circuit.

5. An optical inspection device according to claim 1, further comprising a sample stage that holds the sample and moves horizontally while rotating the sample, and wherein the control unit sets the amount of irradiation light for the next rotation based on the measurement value of scattered light measured during one rotation of the sample.

6. An optical inspection device according to claim 5, wherein the control unit maintains the amount of irradiated light if the measurement value is less than a threshold value, and if the measurement value is equal to or greater than the threshold value, changes the amount of irradiated light based on the measurement value and the amount of irradiated light when the measurement value was obtained.

7. An optical inspection device according to claim 5, characterized in that, when there are multiple peaks for which the measurement value is equal to or greater than a threshold value and the adjacent angle between adjacent peaks is less than an angle threshold value, the control unit changes the amount of irradiated light based on the higher measurement value between the adjacent peaks.

8. An optical inspection device according to claim 1, further comprising a sample stage that holds the sample and moves horizontally while rotating the sample, and the control unit sets the amount of irradiation light for the next rotation based on the measurement value of scattered light measured during two rotations of the sample.

9. An optical inspection device according to claim 1, further comprising a sample stage that holds the sample and moves the sample horizontally while rotating it, and wherein the control unit increases the amount of light irradiated on the outside of the sample more than on the inside.

10. An optical inspection device according to claim 9, wherein the control unit makes the amount of irradiated light proportional to the distance from the center of the sample.

11. A control method for an optical inspection device comprising a light source that generates illumination light to be irradiated onto a sample, a light intensity adjustment unit that adjusts the amount of the illumination light, a voltage switching unit that switches the voltage applied to the light intensity adjustment unit, an optical sensor that measures scattered light from the sample and generates a measurement signal, and a control unit that controls each unit, wherein the voltage switching unit has a first high voltage source that outputs a first voltage, a second high voltage source that outputs a second voltage different from the first voltage, an attenuation circuit that outputs an attenuated voltage that attenuates the first voltage, and a switch that applies either the second voltage or the attenuated voltage to the light intensity adjustment unit, and the control unit controls the attenuation circuit based on the measurement signal.

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