JP2015172538A - Surface profile measuring apparatus, and light-transmissive object thickness measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To speedily determine the timing at which the intensity of interference light reaches a peak without changing the measurement accuracy, in a device for measuring the surface profile of an object or the thickness of a light-transmissive object by optical coherence tomography.SOLUTION: The peak intensity of a light reception signal corresponding to the intensity of interference light is made substantially constant, by changing the focal position of a measuring beam emitted from an optical head 20 synchronously with the variation in optical length by an optical length variable apparatus 40. A detection level lower than the peak intensity of the light reception signal is appropriately set, and the timing at which the light reception signal reaches a peak is detected, as an optical length variation by the optical length variable apparatus 40 or as an elapsed time from a predetermined timing, by a data processor 70 on the basis of two crossing timings at which the light reception signal crosses the detection level.

Description

  The present invention relates to an apparatus for measuring the surface profile of an object by optical coherence tomography (OCT), and an apparatus for measuring the thickness of a translucent object by optical coherence tomography.

  Optical coherence tomography divides low-coherence light into two parts, one of which is incident on the object to be measured and reflected, and the other is reflected by a mirror as the reference light. This is a technique for inspecting an inspection object by changing the optical path length of light or reference light and measuring the intensity change of interference light with respect to the change amount of the optical path length. This technique is often used to detect a cross-sectional image of the human body (especially the fundus), but as shown in Patent Document 1 or Patent Document 2 below, interference light is used for each measurement light irradiation position. It is also possible to detect the timing at which the intensity of the light reaches a peak as time or an optical path length change amount, and measure the profile of the object surface and the thickness distribution of the translucent object. In this method, as shown in Patent Document 2 below, as a device for changing an optical path length (hereinafter referred to as an optical path length variable device), there are a mirror that forms an angle of 90 ° on a disk and an angle of 90 °. By using a device that arranges prisms or retroreflectors (hereinafter collectively referred to as triangular reflectors) and rotates the disk to reflect light by the triangular reflectors, high-speed sweeping is possible, and the object surface profile In addition, the thickness distribution of the translucent object can be measured at high speed. Further, as shown in Patent Document 2 below, if the measurement light is collected by an objective lens, a minute value can be obtained, and a signal corresponding to the intensity of the interference light is A / D converted. If digital data of instantaneous values are acquired and the timing at which the intensity of the interference light peaks is obtained by program processing, the focal position of the measurement light with respect to the surface of the measurement object fluctuates or the reflectance of the measurement object changes. Thus, even if the peak intensity of the interference light changes, measurement can be performed with high accuracy.

Special table 2003-534540 gazette JP 2013-221811 A

  However, there is a problem in that the method for obtaining the peak timing by processing the digital data of the instantaneous value has a problem that it takes time until the value is obtained because the number of data is large. For this reason, even if the speed of the measurement is increased by increasing the rotation speed of the disk of the optical path length variable device and moving the irradiation position of the measurement light, the data processing takes time and cannot be increased as expected. There is a problem.

  The present invention has been made to solve this problem, and an object of the present invention is to provide an apparatus for measuring the surface profile of an object by optical coherence tomography and an apparatus for measuring the thickness of a transparent object without changing the measurement accuracy. An object of the present invention is to provide an apparatus capable of obtaining the timing at which the intensity of the interference light reaches a peak at a high speed and increasing the measurement speed.

  In order to achieve the above object, the present invention is characterized in that, in an apparatus for measuring a surface profile of an object to be measured by optical coherence tomography, a measurement light objective lens is used in synchronization with a change in optical path length by an optical path length variable device. An optical path length variable device for changing the focal position in the direction of the optical axis of the measurement light and the target peak timing corresponding to the surface of the measurement object at which the intensity of the received light signal corresponding to the intensity of the interference light peaks. This is a means to detect the change in the optical path length due to or the elapsed time from the predetermined timing, and a detection level smaller than the intensity of the received light signal at the target peak timing is set, and two intersection timings at which the received light signal intersects the detected level are detected. The peak timing detector detects the target peak timing from the two detected intersection timings. It lies in the fact that with the door.

  According to this, since the focal position of the measurement light changes in the optical axis direction of the measurement light in synchronization with the change in the optical path length, the measurement light and the measurement light on the surface of the measurement object regardless of the position of the measurement object surface. When the optical path lengths of the reference light are equal, the measurement light is focused on the surface of the measurement object, and the peak intensity of the interference light, that is, the peak intensity of the received light signal is substantially constant. Therefore, if a detection level smaller than the peak intensity is appropriately set and two crossing timings at which the received light signal crosses the detection level are detected, the target peak timing corresponding to the surface of the measurement object can be accurately obtained from this. . Since the target peak timing is obtained from the two intersection timing data, the data processing can be completed in a short time, and the measurement can be performed at high speed.

  Further, another feature of the present invention is provided with a peak signal intensity detecting means for detecting the intensity of the received light signal at the target peak timing, and the peak timing detecting means has a difference between the detected two intersection timings within a preset allowable range. If not, the detection level is reset based on the signal intensity detected by the peak signal intensity detection means.

  According to this, even if the reflectance of the surface is different for each measurement object or the reflectance of the surface of the measurement object is different for each location, the detection level can be set to an appropriate value. Therefore, measurement can be performed at high speed without changing the measurement accuracy.

  Another feature of the present invention is that the focus position changing means sets a start timing and an end timing to start changing the focus position of the measurement light based on the target peak timing detected by the peak timing detection means. If the difference between the latest target peak timing detected by the peak timing detection means after setting and the target peak timing at the time of setting the start timing and end timing is not within the allowable value, start based on the latest target peak timing. It is to reset the timing and end timing.

  According to this, since the range in which the focus position of the measurement light is changed in synchronization with the change in the optical path length can be limited to only the upper and lower minute ranges centered on the surface of the measurement object, Such a load can be minimized.

  Another feature of the present invention is that a relay lens is provided in which the measurement light enters and exits before the measurement light is incident on the objective lens, and the focal position changing means has one of the relay lenses in the optical axis direction of the measurement light. This means that it is a means for driving.

  According to this, since the focus position can be changed faster than the objective lens is driven in the optical axis direction to change the focus position of the measurement light, the measurement can be performed at a higher speed.

  Furthermore, the present invention can also be applied to an apparatus for measuring the thickness of a translucent object by optical coherence tomography. In this case, the following points are different from the apparatus for measuring the surface profile described above. First, since the measurement light is reflected from the front and back surfaces of the measurement object, the peak timing detection means corresponds to the first target peak timing corresponding to the front surface of the measurement object and the back surface of the measurement object. Means for detecting a second target peak timing, wherein a detection level smaller than the intensity of the received light signal at the second target peak timing is set, and the first two crossing timings at which the received light signal crosses the detection level; The second two intersection timings are detected, the first target peak timing is detected from the detected first two intersection timings, and the second target peak timing is detected from the detected second two intersection timings Is a point. The detection level is made smaller than the intensity of the received light signal at the second target peak timing because the measurement light reflected back from the back surface of the measurement object is smaller than the measurement light reflected back from the surface, and the peak intensity is This is because the second target peak timing is smaller than the first target peak timing.

  The second difference is that the peak signal intensity detection means detects the intensity of the received light signal at the second target peak timing, and the peak timing detection means sets the difference between the detected second two intersection timings in advance. The point is that the detection level is reset based on the signal intensity detected by the peak signal intensity detecting means when it is not within the allowable range.

  The third difference is that the focus position changing means sets the start timing for starting the change of the focus position of the measurement light based on the first target peak timing detected by the peak timing detection means, and the peak timing. Based on the second target peak timing detected by the detection means, an end timing for ending the change of the focus position of the measurement light is set, and after the setting, the latest first target peak timing and start detected by the peak timing detection means The difference between the first target peak timing at the time of timing setting or the difference between the latest second target peak timing detected by the peak timing detection means and the second target peak timing at the end timing setting is an allowable value. When not within, start timing based on the latest first and second target peak timing Is that the re-setting the end timing. The other points are the same as the apparatus for measuring the surface profile of the measurement object.

1 is an overall configuration diagram of a surface profile measuring apparatus to which the present invention is applied. It is the figure which contrasted and showed the optical path length variation | change_quantity with respect to a rotation angle, and the intensity | strength of the drive signal of the lens with respect to a rotation angle. It is the figure which showed visually the method of detecting the timing when the intensity | strength of interference light becomes a peak. It is a flowchart of the program executed by the distance calculation circuit in the data processing device of the surface profile measuring device. It is a flowchart of the program performed by the controller of a surface profile measuring apparatus. It is a flowchart of another program executed by the controller of the surface profile measuring apparatus. It is a block diagram of the data processor in the modification of the surface profile measuring apparatus to which this invention was applied. In the translucent object thickness measuring device to which the present invention is applied, the optical path length change amount with respect to the rotation angle is compared with the intensity of the lens driving signal with respect to the rotation angle.

(First embodiment)
Hereinafter, as a first embodiment of the present invention, a surface profile measuring apparatus to which the present invention is applied will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of a surface profile measuring apparatus to which the present invention is applied. The surface profile measuring device includes a measuring unit 10, an optical head 20, an optical path length varying device 40, a stage driving device 50, a data processing device 70, various circuits and a computer device 90, and is placed on the stage 51 of the stage driving device 50. This is a device for measuring the surface profile of the measured object OB. When the operator places a measurement object OB on the stage 51 and then inputs a measurement start command from the input device 92 of the computer device 90, the controller 91 of the computer device 90 and the distance calculation circuit 75 of the data processing device 70 are operated. The surface profile of the measurement object OB is automatically executed by the program to be executed, and the measurement result is displayed on the display device 93 of the computer device 90. Hereinafter, each device will be described.

  The stage driving device 50 includes a stage 51 for mounting and fixing the measurement object OB, an X-direction feed motor 52 for moving the stage 51 in the X direction (left and right in FIG. 1), and the stage 51 in the Y direction (FIG. 1). , A Y-direction feed motor 53 that moves in the direction perpendicular to the paper surface is provided. The X direction and the Y direction are one direction parallel to the mounting surface of the stage 51 and are orthogonal to each other. The stage driving device 50 includes a screw feed mechanism 54 connected to the output shaft of the X-direction feed motor 52 and a screw feed mechanism (not shown) connected to the output shaft of the Y-direction feed motor 53, respectively. The XY stage moves the stage 51 in the X direction and the Y direction by rotating 52 and 53.

  In the X-direction feed motor 52, an encoder 52a that detects the rotation of the motor 52 and outputs a rotation signal representing the rotation is incorporated. This rotation signal is a pulse train signal that alternately switches between a high level and a low level every time the X-direction feed motor 52 rotates by a predetermined minute angle, and has a phase of π / 2 to identify the rotation direction. It consists of the shifted A phase signal and B phase signal. The rotation signal is output to the X direction feed motor control circuit 62 and the X direction position detection circuit 64.

  The X direction position detection circuit 64 counts up or down the number of pulses of the rotation signal from the encoder 52a in accordance with the rotation direction of the X direction feed motor 52, detects the X direction position of the stage 51 from the count value, A signal representing the direction position (hereinafter simply referred to as the X position) is output to the controller 91. Since the X position represents the relative position of the stage 51 in the X direction with respect to the optical head 20 described later, it is treated as the X coordinate value of the measurement light irradiation position irradiated from the optical head 20 to the measurement object OB. The irradiation position of the measurement light is a position where the optical head 20 can collect and irradiate the measurement light, and it does not matter whether the measurement light is actually irradiated on the measurement object OB.

  The initial setting of the count value in the X-direction position detection circuit 64 is performed according to an instruction from the controller 91 when the power is turned on. That is, the controller 91 instructs the X-direction feed motor control circuit 62 to move the stage 51 to the X-direction limit position and the X-direction position detection circuit 64 to perform initial setting when the power is turned on. In response to this instruction, the X direction feed motor control circuit 62 rotates the X direction feed motor 52 to move the stage 51 to the X direction limit position. This X direction limit position is a drive limit position in the X direction of the stage 51 driven by the X direction feed motor 52. The X-direction position detection circuit 64 continues to input the rotation signal from the encoder 52a while the stage 51 is moving. When the stage 51 reaches the X-direction limit position and the rotation of the X-direction feed motor 52 stops, the X-direction position detection circuit 64 detects the stop of the rotation signal input from the encoder 52a and sets the count value to “0”. Reset to. At this time, the X-direction position detection circuit 64 outputs a signal for stopping output to the X-direction feed motor control circuit 62, whereby the X-direction feed motor control circuit 62 outputs a drive signal to the X-direction feed motor 52. Stop output. Thereafter, when the X-direction feed motor 52 is driven, the X-direction position detection circuit 64 counts up or down the number of pulses of the rotation signal in accordance with the rotation direction of the X-direction feed motor 52, and the count value The X position of the stage 51 is calculated based on the above and a digital signal representing the X position is continuously output to the X direction feed motor control circuit 62 and the controller 91.

  Similarly, an encoder 53 a that detects the rotation of the motor 53 and outputs a rotation signal representing the rotation is also incorporated in the Y-direction feed motor 53. Similar to the encoder 52a in the X-direction feed motor 52, this rotation signal is a pulse train signal that alternately switches between a high level and a low level each time the Y-direction feed motor 53 rotates by a predetermined minute angle. It consists of an A-phase signal and a B-phase signal that are out of phase by π / 2. This rotation signal is output to the Y-direction feed motor control circuit 63 and the Y-direction position detection circuit 65.

  The Y-direction position detection circuit 65 counts up or down the number of pulses of the rotation signal from the encoder 53a according to the rotation direction of the Y-direction feed motor 53, detects the Y-direction position of the stage 51 from the count value, and Y A digital signal representing a directional position (hereinafter simply referred to as a Y position) is output to the controller 91. Since the Y position represents the relative position of the stage 51 in the Y direction with respect to the optical head 20, the Y position is treated as a Y coordinate value of the irradiation position of the laser light irradiated from the optical head 20 to the measurement object OB.

  The initial setting of the count value in the Y-direction position detection circuit 65 is performed by an instruction from the controller 91 when the power is turned on, as in the X-direction position detection circuit 64. That is, when an initial setting is instructed from the controller 91, the Y-direction feed motor control circuit 63 rotates the Y-direction feed motor 53 to move the stage 51 to the Y-direction limit position. When the Y-direction position detection circuit 65 detects that the stage 51 has reached the Y-direction limit position and the input of the rotation signal from the encoder 53a is stopped, the Y-direction position detection circuit 65 resets the count value to “0” and feeds the Y-direction feed. An output stop signal is output to the motor control circuit 63. Thereafter, the Y-direction position detection circuit 65 counts up or down the number of pulses of the rotation signal in accordance with the rotation direction of the Y-direction feed motor 53, calculates the Y position of the stage 51 based on the count value, and calculates the Y position. Is continuously output to the Y-direction feed motor control circuit 63 and the controller 91.

  The X-direction feed motor control circuit 62 drives and controls the X-direction feed motor 52 according to an instruction from the controller 91 to move the stage 51 to the designated X position. Specifically, when the X position is input from the controller 91, the X direction feed motor control circuit 52 controls the rotation of the X direction feed motor 52 using the X position input from the X direction position detection circuit 64, and the X direction The X-direction feed motor 52 is rotated until the X position input from the position detection circuit 64 becomes equal to the X position input from the controller 91. Further, the X-direction feed motor control circuit 62 drives and controls the X-direction feed motor 52 in accordance with an instruction from the controller 91 to move the stage 51 at a preset speed in the positive direction or the negative direction. Specifically, when the moving direction (positive direction or negative direction) is input from the controller 91, the X-direction feed motor control circuit 52 sets the number of pulses per unit time of the rotation signal input from the encoder 52a. And the rotation of the X-direction feed motor 52 is controlled so that the moving direction becomes the input direction.

  The Y-direction feed motor control circuit 63 also drives and controls the Y-direction feed motor 53 according to an instruction from the controller 91 to move the stage 51 to the designated Y position. Specifically, the Y-direction feed motor control circuit 63 receives the Y position input from the Y-direction position detection circuit 65 from the controller 91 when the Y position is input from the controller 91, as in the X-direction feed motor control circuit 62. The Y-direction feed motor 53 is rotated until it becomes equal to the Y position. Further, the Y-direction feed motor control circuit 63 drives and controls the Y-direction feed motor 53 according to an instruction from the controller 91 to move the stage 51 at a preset speed in the positive direction or the negative direction. Specifically, when the moving direction (positive direction or negative direction) is input from the controller 91, the Y-direction feed motor control circuit 63 sets the number of pulses per unit time of the rotation signal input from the encoder 53a. And the rotation of the Y-direction feed motor 53 is controlled so that the moving direction becomes the input direction.

  The measurement unit 10 includes a laser light source 11, a collimating lens 12, a condenser lens 13, an optical coupler 14, and a light receiving sensor 15. The laser light source 11 is composed of a super luminescent diode (SLD) or LED, and emits low-coherence laser light by a voltage and current input from the laser driving circuit 8. When a laser irradiation start command is input from the controller 91, the laser drive circuit 8 outputs a voltage and current having a set intensity so that laser light having a set intensity is emitted from the laser light source 11. This low-coherence laser beam is characterized in that when the two branched laser beams interfere, the intensity of the laser beam after interference becomes extremely large only when the optical path lengths of the two branched laser beams are equal. Have. The collimating lens 12 converts the low-coherence laser light from the laser light source 11 into parallel light, and the condensing lens 13 condenses the parallel light from the collimating lens 12 and makes it incident on the optical fiber 16. In this case, the focal length of the condenser lens 13 is set so that the laser beam incident on the optical fiber 16 is totally reflected in the optical fiber 16. The laser light incident on the optical fiber 16 is guided to the optical coupler 14.

  The optical coupler 14 divides the laser light incident through the optical fiber 16 into two, makes one incident on the optical fiber 31 leading to the optical head 20, and the other incident on the optical fiber 32 leading to the optical path length varying device 40 described later. Let Hereinafter, the laser light incident on the optical fiber 31 is referred to as measurement light, and the laser light incident on the optical fiber 32 is referred to as reference light. Further, the optical coupler 14 branches the reflected light of the measurement light guided from the optical head 20 via the optical fiber 31 and the reflected light of the reference light guided from the optical path length varying device 40 via the optical fiber 32 into two. Each of them is guided to the light receiving sensor 15 through the optical fiber 17. In this embodiment, the outgoing light and the reflected light are branched into two using the optical coupler 14, but the outgoing light and the reflected light are converted into parallel light having a small cross-sectional diameter, and a beam splitter is used. You may branch into two.

  The light receiving sensor 15 outputs a signal having a magnitude representing the intensity of the received laser beam. In this case, since the two reflected lights incident on the light receiving sensor 15 interfere and the laser light has low coherence, the signal output from the light receiving sensor 15 is a distance from the reflection position of the measurement object OB to the optical coupler 14. The intensity increases only when the distance from the reflection position (fixed reflector 46) of the optical path length varying device 40 to the optical coupler 14 matches.

  The optical head 20 includes a collimating lens 21, relay lenses 22 and 23, and an objective lens 24. The collimating lens 21 converts the measurement light emitted from the optical fiber 31 into parallel light and guides it to the relay lens 22. The relay lenses 22 and 23 collect the incident measurement light and then convert it into a substantially parallel light and guide it to the objective lens 24. The objective lens 24 collects the incident measurement light and irradiates the measurement object OB. The relay lens 22 is provided with an actuator 25. When the actuator 25 is driven, the relay lens 22 is driven in the optical axis direction of the measurement light. As a result, the degree of parallelism of the measurement light emitted from the relay lens 23 changes, and the focal position of the measurement light by the objective lens 24 changes in the direction of the optical axis of the measurement light and in the direction perpendicular to the surface of the measurement object OB. Since the actuator 25 is driven by a signal output from a signal generation circuit 26 described later and amplified by an amplification circuit 27, the focus position of the measurement light by the objective lens 24 is set to an intended position by a signal output from the signal generation circuit 26. be able to.

  The optical path length varying device 40 includes a disk-like plate 41 that is rotationally driven by a spindle motor 44, and the disk-like plate 41 has four triangular reflectors 42 arranged at intervals of 90 ° in the circumferential direction. Each of the triangular reflectors 42 is composed of two reflectors whose reflecting surfaces intersect each other at an angle of 90 degrees, and is fixed to the disk-shaped plate 41 so that the reflecting surfaces are perpendicular to the disk-shaped plate 41. ing. Then, the combined vector of the normal vectors of each pair of reflecting surfaces of each triangular reflector 42 is set in the direction in which the disk-shaped plate 41 rotates. Further, the triangular reflector 42 reflects the incident reference light and reverses the incident reference light (in a direction parallel to the optical axis of the incident reference light and opposite to the incident reference light). The reference light is emitted, and the optical axis of the incident reference light is set to be parallel to a plane perpendicular to both reflection surfaces of the two reflectors (the upper surface of the disk-shaped plate 41). .

  The reference light emitted from the optical fiber 32 is converted into parallel light having a minute cross-sectional diameter by the collimating lens 43 and is incident on the triangular reflector 42 of the optical path length varying device 40. The reference light reflected by the triangular reflector 42 is incident on the reflecting surface of the fixed reflector 46 perpendicularly, with the optical axis parallel to that of the incident light and traveling in the opposite direction. The fixed reflector 46 reflects the incident reference light, and the reference light again enters the triangular reflector 42. Since the fixed reflector 46 does not change the optical axis of the reference light and the traveling direction is reversed, the optical axis of the reference light incident again on the triangular reflector 42 is the same as the optical axis of the reference light incident first. Yes, the direction of travel is opposite. Then, the reference light reflected again by the triangular reflector 42 does not change its optical axis position, and its traveling direction is opposite and is collected by the collimating lens 43 and then enters the optical fiber 32. That is, the reference light emitted from the optical fiber 32 enters the optical fiber 32 as reference light having the same optical axis position and a reverse traveling direction in the optical path length varying device 40. In the present embodiment, the triangular reflector 42 is composed of two reflectors whose reflecting surfaces intersect each other at an angle of 90 degrees. However, in the optical fiber 32, the optical axes of the outgoing laser light and the incident laser light. The retroreflector which is a triangular reflector obtained by intersecting three reflecting surfaces with an angle of 90 degrees may be used as the triangular reflector 42 as long as the positions are the same.

  The spindle motor 44 is drawn in the same plane as the disk-shaped plate 41 in FIG. 1, but in reality, the rotation axis of the spindle motor 44 is at the center position of the disk-shaped plate 41 and perpendicular to the surface of the disk-shaped plate 41. . The spindle motor 44 is driven and controlled by the spindle motor control circuit 47 to rotate the disk-like plate 41 at a constant rotational speed. The spindle motor 44 incorporates an encoder 44a that detects the rotation of the motor 44, that is, the disk-shaped plate 41, and outputs a rotation detection signal indicating the rotation. This rotation detection signal repeats an index signal Index generated every time the rotation position of the disk-like plate 41 reaches the reference rotation position, and a high level and a low level by a predetermined minute rotation angle, and is mutually phased by π / 2. It is composed of a pair of pulse train signals φA and φB which are shifted from each other. The spindle motor control circuit 47 starts to operate in response to a command from the controller 91, and controls the rotation of the spindle motor 44 so that the number of pulses per unit time of the pulse train signals φA and φB from the encoder 44a becomes a preset value. Thereby, the disk-shaped plate 41 rotates at the set rotational speed. The index signal Index and the pulse train signals φA and φB generated from the encoder 44a are input to a rotation angle detection circuit 73 and a signal generation circuit 26 of the data processing device 70 described later.

  When the disk-like plate 41 rotates, the position where the reference light is reflected by the triangular reflector 42 changes, but the optical axis position when the reference light is emitted from the optical fiber 32 and the optical axis position when the light is incident remain the same. However, the optical path length of the reference light from the exit from the optical fiber 32 to the incidence changes. As a result, the signal intensity corresponding to the received light intensity output from the light receiving sensor 15 is changed from the reflection position of the measurement object OB to the optical coupler 14 when the disc-shaped plate 41 is at a certain rotational position in one triangular reflector 42. And the distance from the reflection position (fixed reflector 46) of the optical path length varying device 40 to the optical coupler 14 become a peak.

  The signal generation circuit 26 starts to operate in response to an operation command from the controller 91, converts the peak value data of the signal stored as digital data in the memory in the circuit into an analog signal, and outputs the analog signal. The crest value data is stored for one rotation of the disk-like plate 41 of the optical path length varying device 40, and when the index signal Index is input from the encoder 44a, the head digital data is converted from an analog signal and output. This output is performed every time the number of pulses of the pulse train signal input from the encoder 44a reaches a predetermined number. That is, the intensity of the output signal of the signal generation circuit 26 with respect to the rotation angle of the disc-like plate 41 is determined, and the focal position of the measurement light by the objective lens 24 changes according to the signal output from the signal generation circuit 26 as described above. Therefore, when the disk-shaped plate 41 rotates once, the focus position of the measurement light changes in a certain manner. Since the peak value data of the signal stored in the memory of the signal generating circuit 26 is the focal position at the position of the optical path length of the measurement light equal to the optical path length of the reference light for each rotation angle of the disc-like plate 41, This is a peak value corresponding to the intensity of a signal for driving the relay lens 22. Therefore, when this peak value data is output as an analog signal for every predetermined number of pulses of the pulse signal input from the encoder 44a, amplified by the amplifier circuit 27 and supplied to the actuator 25, the focus of the measurement light The position changes so that the optical path length of the measurement light at the focal position becomes equal to the optical path length of the reference light. That is, the focal position changes in synchronization with the change in the optical path length.

  Visually, when the disk-shaped plate 41 of the optical path length varying device 40 rotates and the rotation angle changes from 0 to 360 °, the optical path length of the reference light changes as shown in FIG. At this time, the signal output from the signal generating circuit 26 changes as shown by the thin line in FIG. 2B, and the relay lens 22 is driven based on this signal, so that the measurement is performed to follow the change in the optical path length. The focal position of the light changes. Note that the thin line in FIG. 2B is the case where the focal position is changed in synchronization with all the changes in the optical path length of the reference light, and the thick line is the case where the focal line is changed only for a necessary period. When the drive signal intensity is input from the distance calculation circuit 75 described later, the signal generation circuit 26 receives the drive signal intensity input from the peak value data (data corresponding to the thin line) of the signal stored as digital data in the memory in the circuit. To generate peak value data (data corresponding to a thick line) using data in which only the intensity within the set range is stored, and thereafter output this data. As a result, the focal position changes in synchronization with the change in the optical path length only in the upper and lower minute ranges centered on the surface of the measurement object OB. This point will be described in detail later. Further, how to obtain the peak value data of the signal stored in the memory of the signal generating circuit 26 will be described in detail later.

  The data processing device 70 includes an amplification circuit 71, a detection circuit 72, a rotation angle detection circuit 73, a rotation angle output circuit 74, a distance calculation circuit 75, a timing designation circuit 76, a peak hold circuit 77, and a level setting circuit 78. The amplifying circuit 71 receives a signal having an intensity corresponding to the received light intensity output from the light receiving sensor 15, and outputs a signal amplified with a set amplification factor to the detecting circuit 72. Hereinafter, a signal output from the amplifier circuit 71 is referred to as a light reception signal. The detection circuit 72 has a detection level set by a set value of the signal intensity input from the level setting circuit 78 described later, and outputs a detection signal when the input light reception signal crosses the set detection level. Visually, the change in the intensity of the received light signal with respect to the change in the rotation angle of the disk-like plate 41 (change in the optical path length) is a waveform as shown in FIG. become. As described above, the peak position is a timing at which the optical path lengths of the measurement light and the reference light become equal. The detection circuit 72 is set to a detection level indicated by a dotted line in FIG. 3, and outputs a detection signal at a timing when the signal intensity indicated by a dot in FIG. 3 intersects the detection level. Since the timing at which the signal crosses the detection level when the peak occurs in the signal exists twice from the bottom to the top and from the top to the bottom, the detection signal is output twice.

  The rotation angle detection circuit 73 receives the index signal Index and the pulse train signals φA and φB output from the encoder 44a, and outputs the count value of the number of pulses of the pulse train signal from when the index signal is input as digital data. When the index signal is input, the count value is always set to zero. The value obtained by dividing the count value by the count value immediately before the index signal is input (the maximum value of the count value) and multiplying by 360 ° is the rotation angle, but the maximum value of the count value is a constant, and the count value is It may be regarded as the rotation angle itself. When the rotation angle output circuit 74 receives the digital data of the rotation angle (count value) from the rotation angle detection circuit 73 and receives the detection signal from the detection circuit 72, the digital calculation of the rotation angle input at that timing calculates the distance. Output to the circuit 75. Therefore, the rotation angles at the two timings indicated by the points in FIG. The rotation angle output circuit 74 receives the operation start command from the controller 90 and outputs the rotation angle data to the distance calculation circuit 75 until the change amount of the input rotation angle data reaches a set value. If no detection signal is input from the detection circuit 72 during this period, the latest input rotation angle data and data indicating NG are output. Accordingly, it is possible to detect a problem that the reflectance of the surface of the measurement object OB is small and the peak intensity of the light reception signal is small and does not cross the detection level of the detection circuit 72.

  The distance calculation circuit 75 stores the relationship of the change amount of the optical path length with respect to the rotation angle (count value) in the memory. When the operation start command is input from the controller 91, the program of the flow shown in FIG. Hereinafter, it demonstrates along this flow. The program starts in S200, and 0 is added to the distance Db in S202. The distance Db will be described later. In S204 to S208, it waits for two rotation angle data to be input from the rotation angle output circuit 74, and if it is input, it determines "Yes" in S204, and calculates the distance D from the two rotation angle data P1, P2 in S214. To the controller 91. In S214, an intermediate value between the two rotation angle data is obtained as the rotation angle at the peak of the signal, and the distance obtained by multiplying the change amount of the optical path length with respect to the obtained rotation angle by 1/2 from the relationship stored in the memory. Calculate as D. The distance D is a distance from the reference position where the amount of change in the optical path length of the reference light is zero. However, since the surface profile of the measurement object OB is a change in the distance D, the reference position can be set to an arbitrary position. it can. Further, the reason why the change amount of the optical path length is multiplied by 1/2 is that the measurement light is reflected and returned by the surface of the measurement object OB, so that twice the distance D corresponds to the change amount of the optical path length. .

  If the reflectance of the surface of the measurement object OB is uniform and approximately constant for each measurement object OB, the focus position of the measurement light changes in synchronization with the optical path length of the reference light, so that the peak of the received light signal The detection level of the detection circuit 72 is always an appropriate value with respect to the intensity, and measurement is possible only by the processing of S204 to S208 and S214. However, the reflectance of the surface of the measurement object OB is not uniform, and the reflectance may be different for each measurement object OB, and the focal position of the measurement light is synchronized with the change in the optical path length of the reference light. In order to limit the change to the necessary range, the program performs other processing.

  While waiting for two rotation angle data to be input from the rotation angle output circuit 74 in S204 to S208, when the latest rotation angle data and data indicating NG are input from the rotation angle output circuit 74, in S206, “ In step S210, the rotation angle data Pn input from the rotation angle output circuit 74 is output to the timing designation circuit 76. As will be described later, this output is a command for resetting the detection level set in the detection circuit 72. As described above, the rotation angle output circuit 74 outputs the latest rotation angle data and data indicating NG because the peak intensity of the light reception signal is small and the detection level set in the detection circuit 72 does not intersect the light reception signal. Is the case.

In addition, after the process of S214, the following two processes are performed before returning to the process of S204 to S208 (a process of waiting for input of two rotation angle data).
A process of determining whether the difference between the latest distance D and the previously stored distance Db is within an allowable value, and when not within the allowable value, a process of outputting a drive signal corresponding to the distance D to the signal generating circuit 26 (S216 to S220).
A command to determine whether the relationship between the peak intensity of the received light signal and the detection level set in the detection circuit 72 is appropriate, and to instruct the timing designation circuit 76 to reset the detection level set in the detection circuit 72 if it is not appropriate Is output (S222 to S226).

  Since the distance Db is set to 0 at the measurement start time, the processing of S216 to S220 is determined as “Yes” in S216 and is always executed. That is, at the start of measurement, the focus position of the measurement light is changed in all ranges in synchronization with the change in the optical path length of the reference light. However, after the distance D is first measured, a signal is created in S218. Since the drive signal intensity corresponding to the distance D is input to the circuit 26, the change in the focus position of the measurement light thereafter is only the upper and lower minute ranges centered on the surface of the measurement object OB. As described above, the distance calculation circuit 75 stores the relationship of the change amount of the optical path length with respect to the rotation angle in the memory. Further, this relationship and the rotation angle and signal peak value data stored in the signal generation circuit 26 are stored. The relationship between the amount of change in the optical path length and the peak value data of the signal is stored, and the peak value data of the signal when the value twice the distance D is applied to the amount of change in the optical path length is obtained. , And output to the signal generation circuit 26 as drive signal intensity. Visually, when a point indicated by a black dot in FIG. 2 (a) is detected as an optical path length change amount (distance D × 2) at which the received light signal reaches a peak, a point indicated by a black dot in FIG. 2 (b) Is output to the signal generation circuit 26. As described above, when the drive signal intensity is input, the signal generation circuit 26 generates peak value data corresponding to the thick line in FIG. 2B, and thereafter outputs this data. When the drive signal strength is output to the signal generation circuit 26 in S218, the distance D enters the distance Db in S220. Henceforth, as long as the latest distance D does not change from the allowable value with respect to the distance Db in S216. It is determined as “No”, and the processing of S218 and S220 is not executed. That is, unless the position of the surface of the measurement object OB changes significantly, the drive signal intensity is not output to the signal generation circuit 26. However, if the position of the surface of the measurement object OB changes significantly, the surface of the measurement object OB may not enter the change range of the focus position of the measurement light, so “Yes” is determined in S216. In S218, the drive signal strength is output to the signal generation circuit 26, and in S220, the latest distance D is input as the distance Db.

  The processing of S222 to S226 determines whether or not the difference between the two rotation angle data P1 and P2 input from the rotation angle output circuit 74 in S222 and S224 is within the allowable range. This is a process of outputting P1 to the timing designating circuit 76. As will be described later, this output is a command for resetting the detection level set in the detection circuit 72. The peak intensity of the received light signal and the detection level set in the detection circuit 72 cannot be directly compared, but the rotation angle data P1, as the peak intensity of the received light signal becomes larger than the detection level set in the detection circuit 72. Since the difference in P2 increases, it is determined from the difference between the rotation angle data P1 and P2 whether the relationship between the peak intensity of the received light signal and the detection level set in the detection circuit 72 is appropriate. That is, when the difference between the rotation angle data P1 and P2 is larger than the upper limit value, the peak intensity of the received light signal is too larger than the detection level set in the detection circuit 72, and “Yes” is determined in S222. Go to. Further, when the difference between the rotation angle data P1 and P2 is smaller than the lower limit value, the peak intensity of the received light signal is too close to the detection level set in the detection circuit 72, and “Yes” is determined in S224. Determine and go to S226. In step S226, the rotation angle data P1 is output to the timing designation circuit 76. This output is a command for resetting the detection level set in the detection circuit 72. As described above, the detection level is also obtained when the peak intensity of the received light signal is smaller than the detection level set in the detection circuit 72 (when the rotation angle data P1 and P2 are not input even if the rotation angle changes by a predetermined angle). Is output to the timing designating circuit 76.

  When a stop command is input from the controller 91 during the processing of S204 to S208 (processing for waiting for the input of two rotation angle data), the distance calculation circuit 75 determines “Yes” in S208, and goes to S212. The execution of is terminated. Therefore, during the period from when the operation start command is input from the controller 91 to when the stop command is input, a peak is generated in the received light signal every time the optical path length of the reference light changes and becomes equal to the measurement light, and the optical path at the peak position 1/2 of the long change amount is continuously input to the controller 91 as the distance D. Meanwhile, the change range of the focus position of the measurement light and the detection level set in the detection circuit 72 are made appropriate.

  The timing designation circuit 76 stores the rotation angle groups (A1, A2), (B1, B2), (C1, C2), (D1, D2) shown in FIG. 2, and the rotation angle Pn from the distance calculation circuit 75 is stored. Alternatively, when the rotation angle P1 is inputted, the rotation that comes next to the inputted rotation angle among the stored rotation angle groups (A1, A2), (B1, B2), (C1, C2), (D1, D2). Select an angle pair. Then, when the rotation angle input from the rotation angle detection circuit 73 becomes the first rotation angle of the selected rotation angle group, a start signal is output to the peak hold circuit 77. When the rotation angle input from the rotation angle detection circuit 73 becomes the rotation angle after the selected rotation angle group, a stop signal is output to the peak hold circuit 77. Thereby, a start signal and a stop signal are output to the peak hold circuit 77 at the timing when the change in the optical path length starts and the timing when the change in the optical path length ends. Note that the respective rotation angles of the rotation angle groups (A1, A2), (B1, B2), (C1, C2), (D1, D2) are shown in FIG. 2 from the range of the surface of the measurement object OB that can be considered. It may be set narrower than the range.

  The peak hold circuit 77 is a circuit provided with an A / D converter in a general peak hold circuit composed of an operational amplifier, a resistor, a diode, a capacitor, and the like. The peak hold circuit 77 receives the light reception signal from the amplifier circuit 71 when the start signal is input from the timing designation circuit 76, and stops the input of the light reception signal when the stop signal is input. Then, the intensity of the light receiving signal at the timing when the light receiving signal starts to be input from the amplifier circuit 71 is converted into digital data by the A / D converter in the circuit and output to the level setting circuit 78. Further, a signal having a strength equal to the peak strength of the received light signal during the input period (peak-held signal) is converted into digital data by the A / D converter in the circuit and output to the level setting circuit 78, and the peak-held signal is output. clear.

  The level setting circuit 78 multiplies the difference between the peak intensity of the received light signal input as digital data from the peak hold circuit 77 and the ground level (the intensity of the received light signal when no peak occurs) by a preset ratio. A value obtained by adding the ground level to the obtained value is output to the detection circuit 72 as a signal intensity. The detection circuit 72 sets the detection level with the input signal intensity as described above. Thus, when a command (rotation angle Pn or P1) for resetting the detection level is output from the distance calculation circuit 75, the detection level of the detection circuit 72 is reset.

  The computer device 90 includes a controller 91, an input device 92, and a display device 93. The controller 91 is an electronic control device mainly composed of a microcomputer including a CPU, ROM, RAM, a large capacity storage device, etc., and executes various programs stored in the large capacity storage device to execute a surface profile measurement device. Control the operation. The input device 92 is connected to the controller 91 and is used by an operator to input various parameters, work instructions, and the like. The display device 93 is connected to the controller 91 and performs a display that visually informs the operator of various setting situations, operating situations, measurement results, and the like.

The peak value data of the signal that is stored in the memory of the signal generation circuit 26 and changes the focal position of the measurement light in synchronization with the change in the optical path length may be obtained by performing the following.
(1) An operation start and operation stop command output to the peak hold circuit 77, a peak hold value input from the peak hold circuit 77, and a rotation angle input from the rotation angle detection circuit 73 are input to the controller 91 and each circuit. The rotation angle value and the peak hold value (the peak value of the received light signal) can be obtained from the display on the display device 93.
(2) A reflector whose reflection surface whose height position can be varied is placed on the stage 51, and the stage 51 is moved so that the reflector is irradiated with the measurement light from the optical head 20, and the laser driving circuit 10 is moved. Is operated to irradiate the reflector with measurement light.
(3) The disk-shaped plate 41 is set to a certain rotation angle Θ (n).
(4) The signal generating circuit 26 outputs a signal I (m) having a constant intensity. The peak hold circuit 77 is operated to change the height of the reflector in a certain direction, and the peak hold value (the peak value of the received light signal) output from the peak hold circuit 77 is obtained.
(5) The signal intensity I (m) output from the signal generating circuit 26 is changed, and the operation (4) is performed with a plurality of signal intensity I (m). When the relationship between the peak hold value (the peak value of the received light signal) and the signal intensity I (m) is drawn, a curve close to a normal distribution is obtained. The signal intensity I (n) at the peak position is the signal intensity at which the optical path length at the focal position of the measurement light is equal to the optical path length of the reference light at the rotation angle Θ (n) of the disc-like plate 41.
(6) The operations of (3) to (5) are performed at a plurality of rotation angles Θ (n) of the disc-like plate 41, and the relationship of the signal intensity I (n) to the rotation angle Θ (n) at 0 to 360 ° is expressed. obtain. The obtained relationship is the peak value data stored in the memory of the signal generation circuit 26.

  Hereinafter, the operation method of the surface profile measuring apparatus configured as described above will be described in accordance with a program executed by the controller 91. The operator turns on the power of the surface profile measurement device, places the measurement object OB on the stage 51, and then sets the X position, the Y position, and the measurement end position as measurement start positions on the measurement object OB from the input device 92. Input X position and Y position, and input measurement start command. If the measurement start position and measurement end position stored in the memory of the controller 91 are used as they are, it is not necessary to input the measurement start position and measurement end position. When the measurement start command is input from the input device 92, the controller 91 starts the program of the flow shown in FIG. 5 in S100.

  In S102, 1 is entered in the value A representing the moving direction in the X direction. As will be described later, when the value A is 1, the X direction is the positive direction, and when the value A is -1, the negative direction is the negative direction. Next, in S104, the controller 91 outputs the X and Y positions, which are measurement start positions, to the X direction feed motor control circuit 62 and the Y direction feed motor control circuit 63 so that the measurement light is irradiated to the measurement start position. The movement of the stage 51 is started. In step S106, an operation start command is output to the laser drive circuit 8, the spindle motor control circuit 47, and the signal generation circuit 26. As a result, the measurement object OB is irradiated with the measurement light, the optical path length varying device 40 changes the optical path length of the incident reference light and returns it, and the relay lens 22 is driven in the optical axis direction to focus the measurement light. The position changes in synchronization with the change in the optical path length, and the light reception signal output from the amplifier circuit 71 is a signal that generates a peak when the disk-shaped plate 41 is at a certain rotational position.

  Next, in step S108, the controller 91 determines that the X position and the Y position input from the X direction position detection circuit 64 and the Y direction position detection circuit 65 are the X position and the Y position that are the measurement start positions (the irradiation position of the measurement light is Wait until the measurement start position is reached. Then, when the X position and the Y position become the measurement start position, the process goes to S110 to output an operation start command to the rotation angle detection circuit 73, the rotation angle output circuit 74, and the distance calculation circuit 75. As a result, the rotation angle detection circuit 73 outputs the rotation angle of the disk-shaped plate 41. When the rotation angle output circuit 74 receives a signal from the detection circuit 72, the rotation angle detection circuit 73 outputs the rotation angle input at the input timing, and the distance calculation circuit. 75 starts the program of the flow shown in FIG. As a result, data of the distance D is input to the controller 91 at regular intervals, and the signal output from the signal generation circuit 26 is only in a very small range where the focal position of the measurement light is centered on the surface of the measurement object OB. Thus, the signal changes in synchronization with the change in the optical path length.

  Next, the controller 91 starts the program of the flow shown in FIG. 6 in S112. Thereafter, the controller 91 executes the flow program shown in FIG. 5 and the flow program shown in FIG. 6 in parallel. The program of the flow shown in FIG. 6 is a program that performs a process of storing a pair of the X position and the Y position at the same timing as the distance D output from the distance calculation circuit 75, but the description thereof will be described later. The program of the flow shown in FIG.

  The controller 91 waits for the detection signal to be input from the detection circuit 72 in S114, and starts moving in the Y direction in S116. In S118, A = 1 is initially determined as “Yes”, and the process proceeds to S120. Go and start moving in the positive direction of the X direction. The reason for waiting for the detection signal to be input is that when the distance calculation circuit 75 starts to operate, the reflectance of the measurement object OB is low, and the peak intensity of the light reception signal does not exceed the detection level set in the detection circuit 72. It is because there is sex. Since the movement in the Y direction is one direction, when the movement is started in S116, the movement is performed at a constant speed to the measurement end position in the Y direction. On the other hand, in the X direction, the movement in which the positive direction and the negative direction are alternately changed is performed in the processing of S118 to S134. After the movement is started, the X position is captured in S128, and the processing of S124 to S130 is continued until the X position reaches the measurement end position which is the stop position. When the X position reaches the measurement end position, S130 “Yes” is determined at S132 and the process proceeds to S132. At S132, the movement in the positive direction of the X direction is stopped. At S134, A becomes −1 and the process returns to S118, and “No” is determined at S118. Go to S122 and start moving the X direction in the negative direction. Then, the processes of S124 to S130 are continued until the X position becomes the measurement start position which is the stop position. When the X position becomes the measurement start position, “Yes” is determined in S130 and the process proceeds to S132. Thus, the movement in the negative direction of the X direction is stopped, A becomes 1 in S134, and the process returns to S118. And it goes to S120 and starts the movement to the positive direction of the X direction again. Thereafter, this process is continuously performed, and movement in which the positive direction and the negative direction are alternately changed is performed in the X direction. During this time, the Y position is fetched in S124, and it is determined in S126 whether the Y position is the measurement end position. However, since it takes time until the Y position becomes the measurement end position, it is continuously determined as “No” in S126.

  In this way, the measurement light irradiation position moves alternately in the positive and negative directions in the X direction at high speed, and the Y direction moves in the positive direction at low speed. Then, when the Y position reaches the measurement end position, “Yes” is determined in S126 and the process proceeds to S136. In S136, stop commands are output to the X-direction feed motor control circuit 62 and the Y-direction feed motor control circuit 63. The movement in the direction and the Y direction is stopped. Next, the program of the flow of FIG. 6 executed in parallel in S138 is stopped, and an operation stop command is output to the rotation angle detection circuit 73, the rotation angle output circuit 74, and the distance calculation circuit 75 in S140. Stop operation. In S142, an operation stop command is output to the laser drive circuit 8, the spindle motor control circuit 47, and the signal generation circuit 26 to irradiate the measurement light, rotate the disk-shaped plate 41, and move the relay lens 22 in the optical axis direction. The drive is stopped and the execution of the program is terminated in S144.

  At this time, the memory of the controller 91 stores a large number of data in which the distance D, the X position, and the Y position are set by executing the program of the flow of FIG. Hereinafter, description will be made along the program of the flow of FIG. The program of the flow shown in FIG. 6 starts at S300 together with the start command at S112 as described above. By repeating the processing of S302 and S314, it waits for the detection signal to be input from the detection circuit 72. When it is input, it is determined as “Yes” in S302 and proceeds to S304. In S304 and S306, the X-direction position detection circuit 64, Y The X position and Y position input from the direction position detection circuit 65 are captured. In step S308, the process waits for the distance D input from the distance calculation circuit 75 and returns to step S302. Thereafter, this repetition is repeated until a stop command is issued in S138 described above. Strictly speaking, the timing at which the detection signal is input is not the timing at which the light reception signal reaches its peak, but the timing at which the light reception signal first intersects the detection level. There is a gap, but this gap is negligible.

  When a stop command is issued in S138, most of the program in the flow of FIG. 6 is when the process of waiting for input of a detection signal is performed in S302 and S314. Therefore, “Yes” is determined in S314 and S316 is executed. End the program execution with. However, there is a slight possibility that a stop command is issued while the distance calculation circuit 75 outputs the distance D after inputting the detection signal. At this time, since the distance D is not input, “Yes” in S308. Is no longer determined. Therefore, also when waiting for the distance D input from the distance calculation circuit 75 in S308, the presence / absence of a stop command is determined in S310. If there is a stop command, “Yes” is determined in S310 and S312 is determined. End the program execution with.

  When the controller 91 finishes executing the program of the flow of FIG. 5 and FIG. 6, the surface profile of the measurement object OB is stored using data in which the distance D, X position and Y position are stored. An image is created and displayed on the display device 93. Also, numerical values representing the degree of surface irregularities such as average surface roughness (Ra), root mean square surface roughness (RMS), in-plane maximum height difference (Rmax), etc. may be calculated and displayed together. . The operator can evaluate the degree of unevenness on the surface of the measurement object OB by looking at the displayed result.

  As can be understood from the above description, in the first embodiment, in the apparatus for measuring the surface profile of the measurement object OB by optical coherence tomography, the measurement light is synchronized with the change in the optical path length by the optical path length variable device 40. Are provided with a signal generation circuit 26, an amplification circuit 27, and an actuator 25 that change the focal position of the objective lens 24 in the optical axis direction of the measurement light. Further, as a circuit for detecting the target peak timing corresponding to the surface of the measurement object OB at which the intensity of the received light signal corresponding to the intensity of the interference light reaches a peak as the optical path length change amount by the optical path length varying device 40, A detection level smaller than the peak intensity is set, and a detection circuit 72, a rotation angle detection circuit 73, and a rotation angle output circuit 74 that detect two intersection timings at which the received light signal intersects the detection level, and the detected two intersection timings A distance calculation circuit 75 for calculating peak timing is provided. According to this, since the focal position of the measurement light changes in the optical axis direction of the measurement light in synchronization with the change in the optical path length, the optical path lengths of the measurement light and the reference light are independent of the position of the surface of the measurement object OB. Are equal, the measurement light is focused on the surface of the measurement object OB, and the peak intensity of the received light signal is substantially constant. Therefore, if a detection level smaller than the peak intensity is appropriately set and two crossing timings at which the received light signal crosses the detection level are detected, the target peak timing corresponding to the surface of the measurement object OB can be accurately obtained from this. it can. Since the target peak timing is obtained from the two intersection timing data, the data processing can be performed in a short time, and the measurement can be performed at high speed.

  Further, the first embodiment includes the timing designating circuit 76 and the peak hold circuit 77 for detecting the intensity of the received light signal at the target peak timing, and the distance calculation circuit 75 sets the difference between the two detected intersection timings in advance. When it is not within the allowable range, the level setting circuit 78 resets the detection level set in the detection circuit 72 based on the signal strength detected by the timing designation circuit 76 and the peak hold circuit 77. . According to this, even if the reflectance of the surface is different for each measurement object OB or the reflectance of the surface of the measurement object OB is different for each place, the detection level set in the detection circuit 72 is set. Can be set to an appropriate value, so that measurement can be performed at high speed without changing the measurement accuracy.

  In the first embodiment, the signal generation circuit 26 ends with the start timing for starting the change of the focal position of the measurement light based on the signal intensity corresponding to the target peak timing input from the distance calculation circuit 75. When the difference between the latest target peak timing calculated by the distance calculation circuit 75 after setting and the target peak timing corresponding to the signal intensity output to the signal generation circuit 26 is not within the allowable value, the latest timing is set. The signal intensity corresponding to the target peak timing is output to the signal generation circuit 26, and the signal generation circuit 26 resets the start timing and the end timing. According to this, the focus position of the measurement light can be changed in synchronization with the change in the optical path length so that the focus position of the measurement light can be changed only in the upper and lower minute ranges centered on the surface of the measurement object OB. Therefore, the load applied to the actuator 25 can be minimized.

  In addition, another feature of the present invention is that relay lenses 22 and 23 from which the measurement light enters and exits before the measurement light enters the objective lens 24 are provided. This is done by driving in the optical axis direction of the measurement light. According to this, since the focus position can be changed faster than the objective lens 24 is driven in the optical axis direction to change the focus position of the measurement light, measurement can be performed at a higher speed.

  The first embodiment can be variously modified without departing from the object of the present invention. In the above embodiment, the rotation angle detected by the rotation angle detection circuit 73 from the index signal output from the encoder 44a and the pulse train signal (the disk-shaped plate 41) The timing at which the received light signal reaches a peak is obtained from the rotation angle. However, since the disk-shaped plate 41 is rotated at a constant rotation speed under the control of the spindle motor control circuit 47, the rotation angle can be obtained from the time after the input of the index signal. Therefore, in the data processing device 70, the rotation angle detection circuit 73 and the rotation angle output circuit 74 are replaced with a time measurement circuit 73 ′ and a time output circuit 74 ′ as shown in FIG. In the above embodiment, what is set as the rotation angle may be changed to time by dividing the rotation angle by the rotation speed. In this case, only the index signal Index is input as the signal output from the encoder 44a, the time measuring circuit 73 ′ outputs the time reset to 0 each time the index signal Index is input therein, and the time output circuit 74 ′ The time when the detection signal is input is output.

  When detecting the time by changing the rotation angle, the thickness and refractive index of the measurement light are known as disclosed in Japanese Patent Application Laid-Open No. 2013-221811 described in Patent Document 2 in the prior art document. After passing through the reference light transmitting body, the measurement object OB may be irradiated, and the distance D may be obtained from the thickness of the reference light transmitting body, the refractive index, and the time at the peak. In this case, the light reception signal output from the amplifier circuit 71 has three peaks for one change in optical path length. A detection circuit 72 ′ and a time output circuit 74 ″ for detecting peaks corresponding to the front and back surfaces of the reference light transmitting body are provided separately from the detection circuit 72 and the time output circuit 74 ′. Since the generation time of the peak corresponding to is substantially constant, the output destination of the received light signal is switched between the detection circuit 72 and the detection circuit 72 ′ based on the signal output from the time measurement circuit 73 ′, and the timing designation circuit 76. Is set when the output destination of the received light signal is the detection circuit 72. According to this, even if there is rotational jitter in the rotation of the spindle motor 44, the measurement is accurately performed. be able to.

(Second Embodiment)
Although the said 1st Embodiment is a form when this invention is applied to a surface profile measuring apparatus, this invention is applicable also to a translucent object thickness measuring apparatus. Hereinafter, a translucent object thickness measuring apparatus to which the present invention is applied will be described as a second embodiment of the present invention. It should be noted that the same parts as those in the first embodiment are the same as those in the first embodiment, and a description thereof will be omitted. The overall configuration diagram of the translucent object thickness measuring apparatus is the same as that shown in FIG. The description about the measurement unit 10, the optical head 20, the optical path length variable device 40, the stage driving device 50, and the computer device 90 is the same as that in the first embodiment.

  The configuration of the data processing device 70 is the same as that of the first embodiment, but the distance calculation circuit 75, the timing designation circuit 76, and the level setting circuit 78 are as follows. When the command from the controller 91 is input, the distance calculation circuit 75 executes a program similar to the program of the flow shown in FIG. 4 except for the following points. It is Dfb and Dbb that put 0 in S202. This is because there are two distances D, the distance to the front surface of the measurement object OB and the distance to the back surface. It is the data of the rotation angles P1, P2, P3, and P4 that determines whether or not the input has been made in S204. This is because the peak of the received light signal occurs on the front and back surfaces of the measurement object OB.

  In S214, the distance Df to the surface of the measurement object OB, the thickness t of the measurement object OB, and the distance Df to the back surface of the measurement object OB are calculated, and only the thickness t of the measurement object OB is calculated by the controller 91. Output to. For the distance Df to the surface of the measurement object OB, the peak rotation angle Pf corresponding to the surface of the measurement object OB is obtained from the rotation angles P1 and P2, and the optical path length change amount at the rotation angle Pf is multiplied by 1/2. Ask. The thickness t of the measurement object OB is obtained by calculating the peak rotation angle Pb corresponding to the surface of the measurement object OB from the rotation angles P3 and P4, and the optical path length change amount at the rotation angle Pf and the optical path length change amount at the rotation angle Pb. Is obtained by multiplying the difference by 1/2 and dividing by the refractive index of the measurement object OB. The distance Db to the back surface of the measurement object OB is obtained by multiplying the optical path length change amount at the rotation angle Pb by 1/2.

  In S216, it is determined whether the latest distance Df and the stored distance Dfb do not exceed the allowable value, and whether the stored distance Db and the latest distance Db do not exceed the allowable value, If any exceeds the allowable value, “Yes” is determined and the process goes to S218. In S218, the drive signal intensity corresponding to the distance Df and the distance Db is output to the signal generation circuit 26. In S220, the latest distance Df is entered in Dfb, and the latest distance Db is entered in Dbb. The reason why the two distances Df and Db are necessary in the present embodiment is that the change of the focal position of the measurement light is in the range of the vicinity position above the surface of the measurement object OB and the vicinity position below the back surface of the measurement object OB. To do.

  In S222 and S224, it is determined whether the rotation angles P3 and P4 are not larger than the upper limit value and smaller than the lower limit value. This is because the peak intensity of the light reception signal corresponding to the back surface of the measurement object OB is smaller than the peak intensity of the light reception signal corresponding to the surface of the measurement object OB, and thus the light reception signal corresponding to the back surface of the measurement object OB. This is because the detection level is set with respect to the peak intensity. In S226, the rotation angle Pm that follows the rotation angle P4 is output at a rotation angle that is the same optical path length change amount as the optical path length change amount at an intermediate rotation angle between the rotation angles P1 and P4. This is because the start timing of the period for detecting the peak intensity of the received light signal is made after the peak of the received light signal corresponding to the surface of the measurement object OB is generated. Other than this, the second embodiment is the same as the first embodiment.

  Next, the timing designating circuit 76 stores the rotation angles (A1, A2), (B1, B2), (C1, C2), (D1, D2) shown in FIG. When the angle Pm is input, the rotation angle group to which the rotation angle Pm belongs is selected from the stored rotation angle groups (A1, A2), (B1, B2), (C1, C2), (D1, D2). A start signal is output to the peak hold circuit 77 at the rotation angle Pm, and an end signal is output at the rotation angle after the selected rotation angle group. Visually, if the distance calculation circuit 75 detects a point indicated by a black dot in FIG. 8A as two peak timings and determines that the detection level is not appropriate, the amount of change in optical path length is the same, and The coming rotation angle Pm is output to the timing designation circuit 76, and the timing designation circuit 76 outputs a start signal and an end signal to the peak hold circuit so as to detect the peak signal intensity generated between the rotation angle Pm and B2.

  Further, when the rotation angle Pn is input from the distance calculation circuit 75, the timing designating circuit 76, as in the first embodiment, sets the rotation angle groups (A1, A2), (B1, B2), (C1, C2), ( A start signal and an end signal are output at the next set of rotation angles among D1, D2). In this case, the peak hold circuit 77 detects the signal intensity of the peak corresponding to the surface of the measurement object OB.

  Next, the level setting circuit 78 performs the following processing in addition to performing the same processing as in the first embodiment. The level setting circuit 78 stores the input peak signal intensity and the output signal intensity (detection level) until the next signal intensity is output, and the input peak signal intensity is equal to the previously input signal intensity. When the difference is within the set minute range, the ratio set in advance to the difference between the signal intensity (detection level) output last time and the ground level (smaller than the ratio in the first embodiment) And the signal strength obtained by adding the ground level is output. Thus, when the detection level is larger than the peak signal intensity corresponding to the back surface of the measurement object OB and the peak hold circuit 77 detects the peak signal intensity corresponding to the surface of the measurement object OB, the detection level is reset. By repeating the setting, the detection level decreases, and the detection level can be set based on the peak signal intensity corresponding to the back surface of the measurement object OB.

  The signal generating circuit 26 receives the index signal Index and the pulse train signals φA and φB from the encoder 44a, converts the peak value data of the signal stored as digital data into the memory in the circuit into an analog signal, and outputs the analog signal. The same as in the first embodiment. The difference is that the first embodiment inputs one drive signal strength from the distance calculation circuit 75, whereas the second embodiment inputs two drive signal strengths, and the two input This is the point of creating peak value data using data in which only the intensity within the set range is stored from the drive signal. Visually, when the distance calculation circuit 75 detects the optical path lengths (distance Df × 2 and distance Db × 2) of two peak points indicated by black dots in FIG. 8A, the distance calculation circuit 75 generates a signal. Two drive signal intensities indicated by black dots in FIG. 8B are output to the circuit 26. The signal generation circuit 26 generates data corresponding to the thick line in FIG. 8B in which the maximum and minimum values are set above and below the two drive signal intensities, and thereafter this data is output.

  The program executed by the controller 91 is only partially different from the program in the first embodiment. The program flow diagram shown in FIG. 5 determines whether four detection signals have been input within a preset short time instead of determining whether a detection signal has been input in S114. This is because the detection level set in the detection circuit 72 is larger than the peak signal intensity corresponding to the back surface of the measurement object OB, but smaller than the peak corresponding to the front surface of the measurement object OB, so that even when measurement is impossible. This is because a detection signal may be input. Similarly, in S302 of the program flowchart shown in FIG. 6, it is determined whether four detection signals have been input within a preset short time. Moreover, in S308 of the flowchart of the program shown in FIG. 6, it is determined whether the thickness t of the measurement object OB has been input. Other than this, the second embodiment is the same as the first embodiment.

  As can be understood from the above description, also in the second embodiment in which the present invention is applied to a translucent object thickness measuring apparatus by optical coherence tomography, the same effect as in the first embodiment can be obtained. Also in the second embodiment, the same modifications as in the first embodiment are possible. That is, the timing at which the peak occurs can be detected by the elapsed time after the index signal is input from the encoder 44a instead of the rotation angle. In addition, a reference translucent body is provided between the objective lens 24 and the measurement object OB, and a measured value can be obtained by detecting a peak timing in the reference translucent body and a peak timing in the measurement object OB.

  As described above, the first embodiment and the second embodiment, which are a case where the present invention is applied to a surface profile measuring apparatus and a case where the present invention is applied to a translucent object thickness measuring apparatus, have been described. The present invention is not limited to the first embodiment and the second embodiment, and various modifications can be made without departing from the object of the present invention.

  In the first embodiment and the second embodiment, as the optical path length varying device 40, a device in which the triangular reflector 42 is arranged on the disc-like plate 41 and the disc-like plate 41 is rotated is used. As long as the optical path length can be changed at high speed and the focal position of the measurement light can be changed in synchronization with the change in the optical path length, any optical path length variable device may be used. For example, an optical path length variable device that reciprocates the reflector in the linear direction at high speed may be used.

  In the first and second embodiments, the detection level set in the detection circuit 72 is reset when the difference between the detected two intersection timings is not within the allowable range. However, if the reflectance for each measurement object OB is substantially constant and the reflectance in the measurement object OB is substantially constant, the detection level set in the detection circuit 72 may be fixed. Good.

  In the first embodiment and the second embodiment, the range in which the focus position of the measurement light changes from the peak generation timing of the received light signal is the minute range above and below the measurement object OB, or the measurement target. The range was from the vicinity position above the surface of the object OB to the vicinity position below the back surface. However, if the thickness of each measurement object OB is substantially constant, the range in which the focus position of the measurement light changes from the beginning may be limited as in the first and second embodiments. .

  In the first embodiment and the second embodiment, the optical path length of the reference light is changed by the optical path length varying device 40. However, the optical path length of the reference light is made constant and the optical path length of the measurement light is changed. May be.

  In the first embodiment and the second embodiment, the focus position of the measurement light is changed by changing the relay lens 22 in the optical axis direction of the measurement light. However, the objective lens 24 changes the focus position at high speed. If the mechanism can be changed, the objective lens 24 may be changed in the optical axis direction of the measurement light.

  In the first and second embodiments, four triangular reflectors 42 are arranged on the disk-shaped plate 41 so that four data can be obtained by one rotation of the disk plate 41. However, the number of triangular reflectors 42 arranged on the disk plate 41 may be changed as appropriate in consideration of the measurement speed and the cost of the apparatus. However, when seven or more are arranged, another triangular reflector 42 blocks the laser light applied to a certain triangular reflector 42, so the number of triangular reflectors 42 is preferably six or less.

  In the first embodiment and the second embodiment, the optical path length change amount is changed from the small side to the large side by rotating the disk plate 41 of the optical path length varying device 40 clockwise. Even if the disk plate 41 is rotated counterclockwise to change the optical path length change amount from the large side to the small side, the optical path length change amount curves shown in FIGS. If the drive signal intensity of the relay lens 22 is generated so as to match this, the present invention can be implemented without any problem.

DESCRIPTION OF SYMBOLS 10 ... Measuring part, 11 ... Laser light source, 14 ... Optical coupler, 15 ... Light receiving sensor, 16, 17, 31, 32 ... Optical fiber, 20 ... Optical head, 26 ... Signal preparation circuit, 40 ... Optical path length variable device, 41 ... Disc-shaped plate, 42 ... Triangular reflector, 44 ... Spindle motor, 47 ... Spindle motor control circuit, 50 ... Stage drive device, 51 ... Stage, 52 ... X direction feed motor, 53 ... Y direction feed motor, 62 ... X Direction feed motor control circuit, 63 ... Y direction feed motor control circuit, 64 ... X direction position detection circuit, 65 ... Y direction position detection circuit, 70 ... Data processing device, 72 ... Detection circuit, 73 ... Rotation angle detection circuit, 74 Rotation angle output circuit 75 Distance calculation circuit 76 Timing designation circuit 77 Peak hold circuit 78 Level setting circuit 90 Computer device, 91 ... controller, 92 ... input apparatus, 93 ... display unit, OB ... measurement object

In order to achieve the above object, the present invention is characterized in that, in an apparatus for measuring a surface profile of an object to be measured by optical coherence tomography, a measurement light objective lens is used in synchronization with a change in optical path length by an optical path length variable device. Focus position changing means for changing the focus position of the measurement light in the optical axis direction of the measurement light so that the optical path length of the measurement light at the focus position is equal to the optical path length of the reference light, and light reception corresponding to the intensity of the interference light A means for detecting the target peak timing corresponding to the surface of the measurement object having a peak signal intensity as a change in the optical path length by the optical path length variable device or an elapsed time from the predetermined timing, and a light reception signal at the target peak timing The detection level smaller than the intensity is set, two detection timings at which the received light signals cross the detection level are detected, and the detected two In that a peak timing detection means for detecting the target peak timing from the difference timing.

According to this, in synchronization with the change in the optical path length, the focal position of the measurement light is adjusted so that the optical path length of the measurement light at the focal position by the objective lens of the measurement light is equal to the optical path length of the reference light. Since it changes in the optical axis direction, the measurement light is focused on the surface of the measurement object when the optical path lengths of the measurement light and the reference light are equal on the surface of the measurement object regardless of the position of the measurement object surface. Therefore, the peak intensity of the interference light, that is, the peak intensity of the received light signal is substantially constant. Therefore, if a detection level smaller than the peak intensity is appropriately set and two crossing timings at which the received light signal crosses the detection level are detected, the target peak timing corresponding to the surface of the measurement object can be accurately obtained from this. . Since the target peak timing is obtained from the two intersection timing data, the data processing can be completed in a short time, and the measurement can be performed at high speed.

Claims (8)

An optical path length variable device that emits incident laser light through a set optical path and changes the optical path length of the optical path;
A low-coherence laser beam is branched into measurement light and reference light, and the measurement light is irradiated and reflected on the measurement object via an objective lens, and then the measurement light and the reference light are combined to interfere. An optical system that guides the interference light to a light receiver that outputs a received light signal having an intensity corresponding to the amount of received light, and passes either the measurement light or the reference light through the optical path length variable device Optical system,
A focal position changing means for changing the focal position of the measurement light by the objective lens in the optical axis direction of the measurement light in synchronization with the change of the optical path length by the optical path length variable device;
Moving means for moving the measurement object relative to the measurement light applied to the measurement object while detecting a movement position;
At each moving position by the moving means, the target peak timing corresponding to the surface of the object to be measured at which the intensity of the light reception signal output from the light receiver reaches a peak is changed by the optical path length changing device, or predetermined A means for detecting an elapsed time from the timing, wherein a detection level smaller than the intensity of the light reception signal at the target peak timing is set, and two intersection timings at which the light reception signal intersects the detection level are detected, and the detection Peak timing detecting means for detecting the target peak timing from the two intersecting timings,
A surface profile measurement apparatus comprising: a calculation unit that calculates a surface profile of the measurement object using the target peak timing at each moving position detected by the peak timing detection unit. In the surface profile measuring device according to claim 1,
Peak signal intensity detection means for detecting the intensity of the received light signal at the target peak timing,
The peak timing detection means resets the detection level based on the signal intensity detected by the peak signal intensity detection means when the difference between the detected two intersection timings is not within a preset allowable range. Surface profile measuring device. In the surface profile measuring device according to claim 1 or 2,
The focus position changing unit sets a start timing and an end timing to start changing the focus position of the measurement light based on the target peak timing detected by the peak timing detection unit, and after the setting, the peak timing When the difference between the latest target peak timing detected by the detection means and the target peak timing at the time of setting the start timing and end timing is not within an allowable value, the start timing and end based on the latest target peak timing A surface profile measuring apparatus characterized by resetting the timing. In the surface profile measuring device according to claim 1 to 3,
Before the measurement light is incident on the objective lens, the relay lens is provided with the measurement light incident and emitted;
The focus position changing means is means for driving one of the relay lenses in the optical axis direction of the measuring light. An optical path length variable device that emits incident laser light through a set optical path and changes the optical path length of the optical path;
A low-coherence laser beam is branched into measurement light and reference light, and the measurement light and the reference light are reflected by irradiating the measurement object, which is a translucent object, through an objective lens. Are combined to form interference light, and the interference light is guided to a light receiver that outputs a light reception signal having an intensity corresponding to the amount of received light, and either one of the measurement light or the reference light is used as the optical path. An optical system via a variable length device;
A focal position changing means for changing the focal position of the measurement light by the objective lens in the optical axis direction of the measurement light in synchronization with the change of the optical path length by the optical path length variable device;
Moving means for moving the measurement object relative to the measurement light applied to the measurement object while detecting a movement position;
At each movement position by the moving means, the first target peak timing corresponding to the surface of the measurement object at which the intensity of the light reception signal output from the light receiver peaks, and the first corresponding to the back surface of the measurement object. 2 is a means for detecting the target peak timing as an optical path length change by the optical path length varying device or an elapsed time from a predetermined timing, and has a detection level smaller than the intensity of the received light signal at the second target peak timing. The first two crossing timings and the second two crossing timings that are set and the light reception signal crosses the detection level are detected, and the first target peak timing is detected from the detected first two crossing timings. And detecting the second target peak timing from the detected second two intersection timings And the timing detection means,
Translucent object thickness measurement comprising calculation means for calculating the thickness of the measurement object using the first and second target peak timings at the respective movement positions detected by the peak timing detection means. apparatus. In the translucent object thickness measuring apparatus of Claim 5,
Peak signal intensity detecting means for detecting the intensity of the received light signal at the second target peak timing;
The peak timing detection means resets the detection level based on the signal intensity detected by the peak signal intensity detection means when the difference between the detected second two intersection timings is not within a preset allowable range. A translucent object thickness measuring apparatus characterized by the above. In the translucent object thickness measuring apparatus of Claim 5 or Claim 6,
The focal position changing means sets a start timing for starting the change of the focal position of the measurement light based on the first target peak timing detected by the peak timing detecting means, and the peak timing detecting means detects An end timing for ending the change of the focus position of the measurement light is set based on the second target peak timing, and the latest first target peak timing and the start timing detected by the peak timing detection means after the setting is set. The difference between the first target peak timing at the time of setting or the difference between the latest second target peak timing detected by the peak timing detecting means and the second target peak timing at the time of setting the end timing is allowed When not within the value, based on the latest first and second target peak timings. Te, the start timing and end timing and wherein the reset light-transmitting body thickness measuring device. In the translucent object thickness measuring apparatus of Claim 5 thru | or 7,
Before the measurement light is incident on the objective lens, the relay lens is provided with the measurement light incident and emitted;
The translucent object thickness measuring device, wherein the focal position changing means is means for driving one of the relay lenses in the optical axis direction of the measuring light.