JP5289383B2 - Shape measuring device and shape measuring method - Google Patents

Shape measuring device and shape measuring method Download PDF

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JP5289383B2
JP5289383B2 JP2010122330A JP2010122330A JP5289383B2 JP 5289383 B2 JP5289383 B2 JP 5289383B2 JP 2010122330 A JP2010122330 A JP 2010122330A JP 2010122330 A JP2010122330 A JP 2010122330A JP 5289383 B2 JP5289383 B2 JP 5289383B2
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object
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intensity
phase shift
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JP2011013212A (en
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英毅 松岡
和彦 田原
卓哉 厚見
将人 甘中
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株式会社コベルコ科研
株式会社神戸製鋼所
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  The present invention relates to a shape measuring method and a shape measuring apparatus for measuring the surface shape of an object to be measured using an interferometer.

A non-contact type shape measuring apparatus using an interferometer is widely used for measuring the shape of an object to be measured such as a semiconductor wafer. This is to obtain the surface shape of the object to be measured, that is, the distribution of the surface height (or the distribution of the surface position) from the intensity of the interference light in which the reference light having the same wavelength and the object light are superimposed. is there. Here, light obtained by reflecting one of the two light beams reflected on the surface of the object to be measured is object light, and the other light beam is reflected on a reference surface serving as a reference to the object to be measured. The light that is not irradiated is the reference light.
More specifically, in the measurement of the surface shape of an object to be measured by an interferometer, an object reflected by a number of measurement sites on the surface of the object to be measured by an interferometer arranged opposite to the surface of the object to be measured. The intensity of the interference light obtained by causing the light to interfere with the reference light is detected. At this time, the intensity of a plurality of types of interference light in which the phase difference between the object light and the reference light is shifted by a predetermined amount, for example, by changing the optical path length of the reference light for each measurement site is detected. Then, for each measurement site, a phase difference between the object light and the reference light at the measurement site is calculated from the obtained intensities of the plurality of types of interference light, and phase connection processing based on phase difference data for each of the plurality of measurement sites Is done. The phase data for each measurement site obtained by this phase connection process can be converted into a dimension value of the surface height based on the wavelength of the object light. For this reason, the distribution information of the phase data obtained by the phase connection process is equivalent to the distribution information of the surface height of the object to be measured, that is, the shape information. The phase connection process is referred to as an unwrap process.
Thus, since the surface shape of the object to be measured can be measured in a non-contact manner, the surface shape can be measured without causing scratches or the like on the surface of the object to be measured, unlike the case of measuring with a stylus shape meter.

Patent Document 1 discloses details of the phase connection process.
Patent Document 1 discloses a technique for measuring a change in characteristics of a fluid contained in a cell by detecting a change in phase of interference light in which the object light passed through the cell and other reference light are superimposed. It is shown. At that time, the phase data is sampled at a predetermined period. Further, with respect to the phase data sampled at a certain time point, the phase data at a certain time point is an integer multiple of 2π so that the phase difference falls within the range of −π to + π with reference to the phase data at the previous time point. A phase connection process for shifting the phase by an amount is performed.
Similarly, in phase connection processing in shape measurement, one phase correction processing of two phase data obtained at two adjacent measurement points is performed. The correction process is a process of correcting one phase of two adjacent measurement points by an integral multiple of 2π so that the phase difference based on the other phase is within the range of −π to + π. . This phase connection process is based on the premise that the difference in surface height between two adjacent measurement points does not exceed a quarter wavelength of object light.

Patent Document 2 discloses a two-dimensional information acquisition apparatus that obtains three interference lights by the following method.
That is, in the apparatus disclosed in Patent Document 2, parallel light obtained by enlarging laser light is irradiated on the reference surface and the surface to be measured, and sensing light (non-interfering light) having the reference light and the object light as orthogonal polarization components is emitted. can get. Further, the sensing light is branched into three, and the polarization components having different polarization angles are extracted from the three branched lights by the three polarizing plates P1 to P3, so that the phase difference of each component of the reference light and the object light is 90 °. Three interference lights shifted by one can be obtained. As described above, the phase shift of the reference light and the object light is optically performed using a plurality of polarizing plates having different polarization components to be extracted, so that the plurality of interference lights subjected to the phase shift can be simultaneously performed. can get. Then, the phase difference between the reference light and the object light can be calculated from the intensity of the plurality of interference lights, and the surface height distribution of the object to be measured can be calculated from the phase difference distribution.
The technique disclosed in Patent Document 2 is a technique in which phase shift is optically performed using a polarizing plate in shape measurement by a phase shift method using a homodyne interferometer.
According to the technique disclosed in Patent Document 2, the measurement is faster than the shape measurement by a general phase shift method in which the phase difference between the reference light and the object light is changed by sequentially moving the position of the reference surface mechanically. Is possible.

JP 2000-292351 A JP-A-2-287107

However, the shape measurement method disclosed in Patent Document 2 has a problem that a measurement error due to the following reason may occur.
Hereinafter, in the shape measuring method disclosed in Patent Document 2, four light and signal paths from the optical path of sensing light (non-interfering light) branched into four to the output line of the interference light intensity detector This is called a channel. Of the four channels, one channel for which the phase difference between the object light and the reference light is calculated is referred to as a reference channel, and the other three channels are referred to as non-reference channels.
The intensity of the interference light obtained by the interferometer is determined by the intensity of the object light, the intensity of the reference light, and the phase difference between the object light and the reference light. Therefore, in the homodyne interferometer shown in Patent Document 2, simultaneous equations including four relational expressions of the intensity of each of the object light, the reference light, and the interference light that are established for each channel and the phase difference are established.
Further, when the homodyne interferometer disclosed in Patent Document 2 is used without going through a special calibration process, the intensity of the object light and the intensity of the reference light in each channel do not always match. Similarly, the intensity of the object light between the channels and the intensity of the reference light between the channels do not necessarily match. Further, a phase shift amount assumed in advance (for example, −90 °, + 90 °, + 180 °) between the phase difference of the interference light of the reference channel and each of the phase differences of the interference light of the three non-reference channels. ), An unknown error that differs for each non-reference channel is added.
Therefore, when the homodyne interferometer disclosed in Patent Document 2 is used without going through a special calibration process, the simultaneous equations include 12 unknown parameters including the phase difference to be measured. become.
For example, even if the non-interfering light P2 of the reference channel is subjected to phase shifts of −90 °, + 90 °, and + 180 ° to the three non-interfering lights P1, P3, and P4 of the non-reference channel, respectively. , The actual phase differences of the three non-reference channel interference lights with respect to the reference channel interference light include individual errors ε1, ε3, ε4, respectively (−90 ° + ε1), (+ 90 ° + ε3), (+ 180 °). + Ε4). Such a phase shift error is a non-negligible error when it is desired to measure the surface shape of the object to be measured with high accuracy.
Further, it is not practical to reduce the errors ε1, ε3, and ε4 to a negligible level because the device is complicated and expensive, and the calibration work of the device is complicated.
Accordingly, the present invention has been made in view of the above circumstances, and its object is to optically perform phase shift using a plurality of polarizing plates in shape measurement by a phase shift method using an interferometer. It is an object of the present invention to provide a shape measuring method and a shape measuring device capable of easily obtaining a measurement result that is not affected by a phase shift error that occurs in some cases.

The shape measuring method according to the first invention for achieving the above object is as follows:
A non-interfering light branching optical system for branching incoherent light, which includes object light reflected by an object placed at a predetermined measurement position and other reference light as polarization components, into four parts;
A phase shift optical system that generates different phase differences between the polarization component of the reference light and the polarization component of the object light in each of the four branched lights of the non-interfering light;
Four polarizing plates for extracting interference light between the reference light and the object light from each of the four branched lights of the non-interference light that have passed through the phase shift optical system;
A light intensity detecting means for detecting the intensity of each of the light passing through the four polarizing plates;
Light intensity correction means for independently correcting each of the four light intensities obtained by the light intensity detection means;
A shape measuring method for measuring the surface shape of an object to be measured using an interferometer equipped with
Detection intensity of the reference light when the object light is blocked in a state where the optical path lengths of the object light and the reference light are kept constant under the first arrangement state where the calibration object is arranged at the measurement position. And a polarizing plate holding angle adjustment step of adjusting the holding angle of the polarizing plate so that the detected intensity of the object light when the reference light is blocked matches.
After the polarizing plate holding angle adjusting step, the four interference light beams obtained by the light intensity correcting means by giving a time-series fluctuation to the optical path length of the object light or the reference light under the first arrangement state. A gain setting step of setting a correction gain for the light intensity correction means so that the amplitudes of the time-series changes of the respective intensities coincide with each other;
After the gain setting step, the intensity of each of the four interference lights obtained by the light intensity correction means by giving a time-series fluctuation to the optical path length of the object light or the reference light under the first arrangement state A phase shift error calculating step for calculating an error of the phase shift by the phase shift optical system based on the information;
Based on the intensity of the interference light obtained by the light intensity correction means and the calculation result of the phase shift error calculation step under the second arrangement state where the object to be measured is arranged at the measurement position. A phase difference calculating step of calculating a phase difference between the object light and the reference light with respect to a measurement object;
It is a shape measuring method characterized by comprising.
The calibration object may be the object to be measured or any other object.

An example of more specific contents of the phase shift optical system and the phase difference calculation step in the first invention is as follows.
For example, the phase-shifting optical system calculates the phase difference between the three non-interfering lights that are the sources of the non-reference interference light with respect to the one non-interfering light that is the source of the reference interference light. 90 ° (−π / 2), + 90 ° (+ π / 2), and + 180 ° (+ π).
The phase difference calculating step includes the reference interference light intensity I2 ′ obtained by the measurement interference light intensity detection step and the three non-reference interference light intensities I1 ′, I3 ′, and I4 ′. By applying the phase shift errors ε1, ε3, ε4 for each of the three non-reference interference lights obtained in the phase shift error calculating step to the following equation (A1), This is a step of calculating a phase difference φ between the object light and the reference light.

Hereinafter, the four light and signal paths from the optical path of the non-interfering light that is made by being branched into four by the non-interfering light branching optical system to the output line of the light intensity detecting means are referred to as channels. Of the four channels, one channel for which the phase difference between the object light and the reference light is calculated is referred to as a reference channel, and the other three channels are referred to as non-reference channels.
Also in the interferometer used in the present invention, as in the homodyne interferometer disclosed in Patent Document 2, there are four relational expressions for the intensity of each of the object light, reference light, and interference light established for each channel and the phase difference. Including simultaneous equations.
Similarly to the homodyne interferometer disclosed in Patent Document 2, when the interferometer used in the present invention is used without going through a special calibration process, the simultaneous equations include the phase difference to be measured. Including 12 unknown parameters will be included.
In such an interferometer, the intensity of the object light and the intensity of the reference light in each of the four channels coincide with each other by the polarizing plate holding angle adjusting step (b1). Further, the interference light intensities I1 ′ to I4 ′ corrected (linearly corrected) by the light intensity correcting means in the gain setting step match the object light intensity and the reference light intensity among the four channels. It is a measured value that can be regarded as being.
Therefore, as will be described later, the interference light intensities I1 ′ to I4 ′ of each of the four corrected channels obtained by the light intensity correction means and the channels corresponding to the object light and reference light intensities are common. Is a simultaneous equation consisting of four equations, including the unknown phase difference φ to be calculated, and three unknown phase shift amount errors ε1, ε3, ε4 that differ for each non-reference channel. To establish. Then, in the phase shift error calculation step, by applying the corrected interference light intensity I1 ′ to I4 ′ of each of the four channels to an equation derived by removing the one variable from the simultaneous equations. , Phase shift errors ε1, ε3, ε4 in each of the non-reference channels can be calculated.
As a result, in the phase difference calculation step, the phase difference φ that is not affected by the errors ε1, ε3, and ε4 of the phase shift amount can be calculated. In addition, the above process may be performed once before measuring the shape of the object to be measured, and the contents of the execution are simple.

Moreover, the shape measuring method according to the second invention for achieving the above object is as follows:
A non-interfering light branching optical system for branching incoherent light, which includes object light reflected by an object placed at a predetermined measurement position and other reference light as polarization components, into four parts;
A phase shift optical system that generates different phase differences between the polarization component of the reference light and the polarization component of the object light in each of the four branched lights of the non-interfering light;
Four polarizing plates for extracting interference light between the reference light and the object light from each of the four branched lights of the non-interference light that has passed through the phase shift optical system;
A light intensity detecting means for detecting the intensity of each of the light passing through the four polarizing plates;
Light intensity correction means for independently correcting each of the four light intensities obtained by the light intensity detection means;
A shape measuring method for measuring the surface shape of an object to be measured using an interferometer equipped with
Under the first arrangement state in which the calibration object is arranged at the measurement position, only the reference light is blocked while the optical path length of the object light is kept constant. A gain setting step for setting a correction gain for the light intensity correction means so that the intensities of the object lights coincide;
After the gain setting step, the four reference lights obtained by the light intensity correction means by blocking only the object light while keeping the optical path length of the reference light constant under the first arrangement state. An offset correction value setting step for setting the intensity of the light as an offset correction value of the light intensity correction means;
After the offset correction value setting step, each of the four interference lights obtained by the light intensity correction means by giving a time-series variation to the optical path length of the object light or the reference light under the first arrangement state. A phase shift error calculating step for calculating an error of the phase shift by the phase shift optical system based on the intensity information;
Based on the intensity of the interference light obtained by the light intensity correction means and the calculation result of the phase shift error calculation step under the second arrangement state where the object to be measured is arranged at the measurement position. A phase difference calculating step of calculating a phase difference between the object light and the reference light with respect to a measurement object;
It is a shape measuring method characterized by comprising.

An example of more specific contents of the phase shift optical system and the phase difference calculation step in the second invention is as follows.
For example, with respect to one non-interfering light that is the source of the reference interference light, the phase shift optical system calculates a phase difference between the three non-interfering lights that are the source of the non-reference interference light by −90 The angle is set to ° (−π / 2), + 90 ° (+ π / 2), and + 180 ° (+ π).
The phase difference calculation step includes the reference interference light intensity I2 ″ obtained by the measurement interference light intensity detection step and the three non-reference interference light intensities I1 ″, I3 ″, I4 ″. The phase shift errors ε1, ε3, ε4 and the offset correction values arl, ar2, set in the offset correction value setting step for each of the three non-reference interference lights obtained in the phase shift error calculation step This is a step of calculating a phase difference φ between the object light and the reference light for the object to be measured by applying a r3 and ar4 to the following equation (A2).

In the interferometer used in the present invention, the component of the intensity of the object light in the intensity of the interference light corrected by the light intensity correction means in the linear correction gain setting step is consistent among the four channels. It will be in a state that can be considered. Further, the reference light intensities arl to arl in each channel are known by the offset correction value setting step, and the interference light intensity corrected by the light intensity correction means is an offset component corresponding to the reference light intensity. Will be the measurement value removed.
Therefore, as will be described later, the interference light intensity I1 "to I4" of each of the four corrected channels obtained by the light intensity correction means, and one variable common to each channel corresponding to the object light intensity, , Unknown phase difference φ to be calculated, errors ε1, ε3, ε4 of three unknown phase shift amounts that differ for each non-reference channel, and each channel that has been known by the offset correction value setting step Simultaneous equations composed of four equations including the reference light intensities arl to arl are established. Then, in the phase shift error calculating step, by applying the corrected interference light intensity I1 "to I4" of each of the four channels to an expression derived by removing the one variable from the simultaneous equations. , Phase shift errors ε1, ε3, ε4 in each of the non-reference channels can be calculated.
As a result, in the phase difference calculation step, the phase difference φ that is not affected by the errors ε1, ε3, and ε4 of the phase shift amount can be calculated. In addition, each step may be performed once before measuring the shape of the object to be measured, and the execution content is simple.

Further, the present invention for achieving the above object can also be understood as a shape measuring device that realizes the shape measuring method of each of the first invention and the second invention.
That is, a phase shift optical system that generates a different phase difference between the polarization component of the reference light and the polarization component of the object light in each of the four branched lights of the non-interference light,
Four polarizing plates for extracting interference light between the reference light and the object light from each of the four branched lights of the non-interference light that have passed through the phase shift optical system;
A light intensity detecting means for detecting the intensity of each of the light passing through the four polarizing plates;
Light intensity correction means for independently correcting each of the four light intensities obtained by the light intensity detection means;
Polarizing plate holding means for holding the polarizing plate in a variable angle;
Light blocking means for blocking each of the object light and the reference light;
Under the first arrangement state in which a calibration object is arranged at the measurement position, four light intensity correction means obtainable when the optical path length of the object light or the reference light is given in time series. A gain setting means for setting a correction gain for the light intensity correction means so as to match the amplitudes of time-series changes in the intensity of the interference light;
Based on intensity information of each of the four interference lights obtained by the light intensity correction means when a time-series variation is given to the optical path length of the object light or the reference light under the first arrangement state. Phase shift error calculating means for calculating an error of phase shift by the phase shift optical system,
Based on the intensity of the interference light obtained by the light intensity correction unit and the calculation result of the phase shift error calculation unit under the second arrangement state in which the object to be measured is arranged at the measurement position. Phase difference calculating means for calculating a phase difference between the object light and the reference light with respect to a measurement object;
It is a shape measuring apparatus characterized by comprising.
If the shape measuring apparatus according to the first invention described above is used, the shape measuring method according to the first invention can be easily realized.

The shape measuring device according to the second invention is
A shape measuring device for measuring the surface shape of an object to be measured by optical interferometry,
A non-interfering light branching optical system for branching incoherent light, which includes object light reflected by an object placed at a predetermined measurement position and other reference light as polarization components, into four parts;
A phase shift optical system that generates different phase differences between the polarization component of the reference light and the polarization component of the object light in each of the four branched lights of the non-interfering light;
Four polarizing plates for extracting interference light between the reference light and the object light from each of the four branched lights of the non-interference light that have passed through the phase shift optical system;
A light intensity detecting means for detecting the intensity of each of the light passing through the four polarizing plates;
Light blocking means for blocking each of the object light and the reference light;
Light intensity correction means for independently correcting each of the four light intensities obtained by the light intensity detection means;
Under the first arrangement state in which the calibration object is arranged at the measurement position, the light intensity is maintained when the optical path length of the object light is kept constant and the reference light is blocked by the light blocking means. A gain setting means for setting a correction gain for the light intensity correction means so that the intensities of the four object lights obtained by the correction means match;
The four reference lights obtained by the light intensity correcting means when the optical path length of the reference light is kept constant under the first arrangement state and the object light is blocked by the light blocking means. Offset correction value setting means for setting the intensity as an offset correction value of the light intensity correction means;
Based on intensity information of each of the four interference lights obtained by the light intensity correction means when a time-series variation is given to the optical path length of the object light or the reference light under the first arrangement state. Phase shift error calculating means for calculating an error of phase shift by the phase shift optical system,
Based on the intensity of the interference light obtained by the light intensity correction unit and the calculation result of the phase shift error calculation unit under the second arrangement state in which the object to be measured is arranged at the measurement position. Phase difference calculating means for calculating a phase difference between the object light and the reference light with respect to a measurement object;
It is a shape measuring apparatus characterized by comprising.
If the shape measuring apparatus according to the second invention described above is used, the shape measuring method according to the second invention can be easily realized.

  According to the present invention, in the shape measurement by the phase shift method using an interferometer, the measurement result which is not affected by the phase shift error generated when the phase shift is optically performed using a plurality of polarizing plates can be simplified. Can be obtained.

The schematic block diagram of the shape measuring apparatus X which concerns on embodiment of this invention. The block diagram of the interference light measurement part Y with which the shape measuring apparatus X is provided. The schematic diagram showing an example of distribution of the measurement point of the surface of the to-be-measured object in the shape measuring apparatus X. FIG. The flowchart showing the procedure of the shape measuring method which concerns on 1st Example performed using the shape measuring apparatus X. FIG. The flowchart showing the procedure of the shape measuring method which concerns on 2nd Example performed using the shape measuring apparatus X. FIG. The figure showing an example of the Lissajous waveform based on the measured value of the interference light by the shape measuring apparatus X. Explanatory drawing of the relationship between the Lissajous waveform of two measured values, and a phase difference.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

Hereinafter, the shape measuring apparatus X according to the embodiment of the present invention will be described with reference to the configuration diagram shown in FIG.
The shape measuring device X is a device that measures the thickness distribution of the device under test 1 by measuring the heights of the front and back surfaces of the thin plate-like device under test 1 such as a semiconductor wafer and calculating the difference.
As shown in FIG. 1, the shape measurement apparatus X includes an interference light measurement unit Y including two optical interferometers 20 that are homodyne interferometers, and a movable support device Z. The interference light measurement unit Y includes two phase difference calculation computers 4 and one shape calculation computer 5 in addition to the two optical interferometers 20.
In the shape measuring device X, the DUT 1 is supported by the movable support device Z.
Hereinafter, for the sake of convenience, one surface (the upper surface in FIGS. 1 and 2) of the DUT 1 will be referred to as the A surface, and the other surface in the relationship between the A surface and the front and back surfaces will be referred to as the B surface. Further, the thickness measurement site on the A surface of the DUT 1 is referred to as an A surface measurement point 1a, and the thickness measurement site on the B surface opposite to the A surface measurement point 1a is referred to as a B surface measurement point 1b.
One optical interferometer a20 is arranged on the A surface side of the device under test 1 and the other optical interferometer b20 is arranged on the B surface side of the device under test 1.
The phase difference calculator 4 and the shape calculator 5 are each provided with a CPU, a memory, a signal input / output interface, etc., and when the CPU executes a predetermined program, various calculations are performed through the signal input / output interface. Transmission / reception of signals to / from an external device, recording of data in the memory, and the like are executed.

The two optical interferometers 20 respectively irradiate beam light to a reference surface serving as a reference and measurement points 1a and 1b on the front and back surfaces of the object 1 to be measured, and reference light and object light that are reflected light. Is a homodyne interferometer that outputs intensity signals Sg1 to Sg4 of interference light superimposed.
Further, the phase difference calculation computer 4 executes a process of calculating the phase difference φ between the reference light and the object light based on the intensity signals Sg1 to Sg4 of the interference light output from the optical interferometer 20. To do. Details thereof will be described later. Hereinafter, for the sake of convenience, when the phase difference φ calculated for each of the A plane side and the B plane side is distinguished, they are referred to as a phase difference φa and a phase difference φb, respectively.
Further, the shape calculation required computer 5 is based on the distribution of the difference (φa−φb) between the phase differences φa and φb calculated for the plurality of A-side measurement points 1a and B-side measurement points 1b. A process for calculating the thickness distribution of the DUT 1 is executed.
Hereinafter, the detail of each component with which the shape measuring apparatus X is provided is demonstrated.

The movable support device Z is a device that supports the device under test 1 between the object light emitting portions from the two optical interferometers 20 and moves the support position in a two-dimensional direction. That is, the movable support device Z is a device that changes the relative position of the DUT 1 in the two-dimensional direction with respect to the two optical interferometers 20. In the example shown in FIG. 1, the movable support device Z moves the device under test 1 in the horizontal direction.
As shown in FIG. 1, the movable support device Z includes a rotation shaft 41, a support portion 44 connected to the rotation shaft 41, a rotation drive portion 42, a linear movement mechanism 43, and a movement control device 7.
A disk-shaped object to be measured 1 such as a semiconductor wafer is supported at three points by the support portions 44 arranged at three locations on the circumference at the edge portion. These three support portions 44 are connected to the rotating shaft 41 extending toward the center of the circumference.
Further, the rotating shaft 41 is driven to rotate by the rotation driving unit 42 such as a servo motor. As a result, the DUT 1 rotates with its center portion as the center of rotation.
The linear movement mechanism 43 moves the rotating shaft 41 and the rotation driving unit 42 in a direction parallel to the front and back surfaces of the device under test 1, that is, in a direction orthogonal to the thickness direction of the device under test 1. A straight line is moved within a predetermined movement range. That is, the linear moving mechanism 43 moves the disk-shaped object 1 to be measured along the radial direction thereof.
The movement control device 7 is a device that controls the movement of the rotation driving unit 42 and the linear movement mechanism 43. Further, the movement control device 7 detects the irradiation position of the object light on the device under test 1, that is, the position of the measurement points 1 a and 1 b that change as needed, and transmits the detection result to the third computer 5. . The detection of the positions of the measurement points 1a and 1b is detected based on, for example, the history of operation commands for the rotation drive unit 42 and the linear movement mechanism 43, that is, the movement history of the device under test 1. Alternatively, it is also conceivable that the positions of the measurement points 1a and 1b are detected by detection results of position detection sensors (not shown) provided in the rotation driving unit 42 and the linear movement mechanism 43, respectively.

Then, the shape measuring apparatus X uses the rotation of the device under test 1 by the rotation driving unit 42 and the movement of the device under test 1 in the linear direction by the linear movement mechanism 43 in combination. The phase differences φa and φb at a plurality of measurement points 1a and 1b are measured while sequentially changing the positions of the measurement points 1a and 1b in FIG.
For example, the movement control device 7 continuously rotates and linearly moves the device under test 1 at a constant speed, or at a constant cycle or whenever the positions of the measurement points 1a and 1b become predetermined positions. Then, a data acquisition command is transmitted to the shape calculation computer 5. Then, the shape calculation computer 5 requests the phase difference calculation computer 4 to calculate the phase differences φa and φb in response to reception of the data acquisition command, and acquires the calculation results. Further, the shape calculation computer 5 calculates the thickness distribution of the DUT 1 from the distribution of the differences in the phase differences φa and φb at the plurality of measurement points 1a and 1b.
FIG. 3 is a schematic diagram illustrating an example of the distribution of the measurement points 1 a and 1 b at a plurality of locations on the surface of the DUT 1 in the shape measuring apparatus X.
When the phase differences φa and φb are sequentially measured while rotating and linearly moving the device under test 1, the positions of the measurement points 1a and 1b are determined as shown by the broken lines in FIG. It changes sequentially along the spiral trajectory R on the surface. The plurality of measurement points 1a, 1b and the corresponding phase differences φa, φb are identified by, for example, measurement point numbers (1, 2, 3,...) Assigned according to the measurement order. FIG. 3 shows the trajectories of the measurement points 1a and 1b from the (K-1) th to the (K + 2) th measurement number.
As described above, in the shape measuring apparatus X, the object light from each of the two optical interferometers 20 is scanned along one scanning line R on the device under test 1.

Next, the interference light measurement unit Y including the two optical interferometers 20 will be described with reference to the configuration diagram shown in FIG.
As shown in FIG. 2, the interference light measurement unit Y includes a laser light source 2, a polarization beam splitter 3, a plurality of mirrors 11, and two optical interferences provided respectively on the A surface side and the B surface side. And a phase difference calculator 4 and the shape calculator 5.

The laser light source 2 is a light source that emits beam light P0. The beam light P0 is single wavelength light, and its frequency is not particularly limited. For example, when the beam light P0 of visible light is employed, the frequency ω of the beam light P0 may be about 5 × 10 8 MHz (wavelength λ≈0.6 μm).
The polarization beam splitter 3 splits the beam light P0 emitted from the laser light source 2 into two branches. Then, each beam light Pi which is a branched light obtained by the polarization beam splitter 3 is transmitted by the mirror 11 in the direction of the A surface measurement point 1a and the direction of the B surface measurement point 1b of the object 1 to be measured. Led to.
In addition, as an optical device for guiding the beam light Pi to each of the A-surface measurement point 1a and the B-surface measurement point 1b, an optical fiber or the like can be considered in addition to a mirror.
The beam light Pi guided to the A surface side and the B surface side of the DUT 1 is input to each of the two optical interferometers 20.

The optical interferometer 20 is a homodyne interferometer, and the beam light Pi guided to the front and back surfaces of the object 1 to be measured is used as a reference surface and a front and back surfaces of the object 1 to be measured. The intensity of the interference light of the reference light Pr and the object light Ps reflected at the measurement points 1a and 1b opposite to each other is detected.
As shown in FIG. 2, the two optical interferometers 20 have exactly the same configuration except that the measurement target surface of the DUT 1 is different.
As shown in FIG. 2, the optical interferometer 20 includes a half-wave plate 31, a polarizing beam splitter 21, two quarter-wave plates 22 and 23, a reference plate 24, and condenser lenses 32 and 3. Two non-polarizing beam splitters 251, 252, and 253, two quarter-wave plates 261 and 263, half-wave plates 264, four polarizers 271, 272, 273, and 274, four photodetectors 281 , 282, 283 and 284, four amplifiers 63 are provided.
Further, the interferometer 20 includes four polarizing plate holding mechanisms 61, two light blocking mechanisms 62, and four amplifiers 63.

The half-wave plate 31 is an optical element that adjusts the polarization plane of the beam light Pi guided near the surface of the DUT 1 by the mirror 11.
The polarization beam splitter 21 splits the beam light Pi, the polarization plane of which has been adjusted by the half-wave plate 31, into two beam lights whose polarization directions are orthogonal to each other. The reference surface is irradiated and the other branched light beam is irradiated to the measurement points 1a and 1b. The reference surface is the surface of the reference plate 24 held at a predetermined position.
The reference light Pr, which is the reflected light of the light beam incident on the reference surface, returns to the polarization beam splitter 21 in a state where the incident light beam and the optical axis coincide.
The quarter-wave plate 23 is disposed in the optical path of the beam light between the polarizing beam splitter 21 and the reference surface. The reference light Pr having a polarization direction rotated by 90 ° with respect to the original light beam after reciprocating through the quarter-wave plate 23 passes through the polarization beam splitter 21.

On the other hand, the object light Ps, which is the reflected light of the beam light incident on the measurement points 1a and 1b, returns to the polarization beam splitter 21 in a state where the incident beam light and the optical axis coincide.
The quarter-wave plate 22 is disposed in the optical path of the beam light between the polarizing beam splitter 21 and the measurement points 1a and 1b. The object light Ps whose polarization direction is rotated by 90 ° with respect to the original light beam after reciprocating through the quarter-wave plate 22 is aligned with the reference light Pr by the polarization beam splitter 21. Reflect in the direction. As a result, non-interfering light Px is obtained in which the reference light Pr and the object light Ps are included as polarization components orthogonal to each other.
As described above, the polarization beam splitter 21 and the two quarter-wave plates 22 and 23 divide the beam light Pi into two parts to each of the reference plane and the measurement points 1a and 1b. It is an optical system that obtains the incoherent light Px that is irradiated and is included as polarized light components in which the reference light Pr and the object light Ps are orthogonal to each other. These are hereinafter referred to as non-interfering light acquisition optical systems.

Further, between the quarter-wave plate 22 and the measurement points 1a and 1b, the condenser lens 32 having the measurement points 1a and 1b as focal points is disposed. That is, the condensing lens 32 is arranged in the optical path of the object light Ps which is the beam light and the reflected light between the non-interference light acquisition optical system and the measurement points 1a and 1b.
Thereby, even if there is a slight difference in the surface angle for each of the measurement points 1a and 1b, the optical axis shift of the object light can be suppressed by the action of the condenser lens 32. As a result, it is possible to suppress a decrease in the amount of received light of the object light Ps and a decrease in interference efficiency due to a shift in the optical axis of the object light Ps due to a difference in surface angle between the measurement points 1a and 1b.
Moreover, the irradiation spot of the beam light with respect to the measurement points 1a and 1b can be reduced. By spatially scanning the beam light on the surface of the device under test 1, the spatial resolution for measuring the thickness distribution in the two-dimensional direction along the surface of the device under test 1 can be further increased.

Further, the three non-polarized beam splitters 251, 252, and 253 are configured so that the non-interfering light Px obtained by the non-interfering light acquisition optical system is divided into four non-interfering lights P1, P2, This is an optical system that branches into P3 and P4. Hereinafter, the three non-polarized beam splitters 251, 252, and 253 are referred to as non-interfering light branching optical systems.
That is, the beam splitter 251 performs the first two-stage branching of the original non-interfering light Px. Further, the remaining beam splitters 252 and 253 perform the second branching on each of the branched lights by the non-interfering light Px.

The two quarter-wave plates 261 and 263 and the one-half wavelength plate 264 are the four non-interfering lights P1 to P4 obtained by the optical system for splitting the non-interfering light. This is a birefringent element that changes the phase difference of orthogonal polarization components for the three non-interfering lights P1, P3, and P4. Here, the quarter-wave plate 261 shifts the phase difference of orthogonal polarization components in the non-interfering light P1 by −π / 2 (−90 °). The quarter-wave plate 263 shifts the phase difference of orthogonal polarization components in the non-interfering light P3 by + π / 2 (+ 90 °). The half-wave plate 264 shifts the phase difference of orthogonal polarization components in the branched light P4 by π (+ 180 °). Note that no phase shift is performed on the branched light P2.
That is, the three wave plates 261, 263, and 264 are used for the remaining three non-interfering lights P1, P3, and P4 based on the second non-interfering light P2 among the four non-interfering lights P1 to P4. Changes in −π / 2 (−90 °), + π / 2 (+ 90 °), and π (+ 180 °) are given to the phase difference between the polarization component of the reference light Pr and the polarization component of the object light Ps.
In this way, the three wave plates 261, 263, and 264 give different changes to the phase difference between the component of the reference light Pr and the component of the object light Ps, respectively, and thereby each of the four non-interfering lights P1 to P4. The phase shift optical system generates a different phase difference between the polarization component of the reference light Pr and the polarization component of the object light Ps.

The four polarizing plates 271 to 274 change the polarization directions of the reference light Pr and the object light Ps from the four non-interfering lights P1 to P4 that have passed through the phase shift optical systems 261, 263, and 264, respectively. This is an interference light extraction optical system that extracts interference light Q1 to Q4 between the reference light Pr and the object light Ps by extracting polarization components having a common reference angle. The angle of the extracted polarization component is either + 45 ° or −45 ° based on the polarization direction of the reference light Pr and the object light Ps.
Here, the angle of the polarization component that each of the four polarizing plates 271 to 274 passes is unified to be either + 45 ° or −45 ° based on the polarization direction of the reference light Pr and the object light Ps. It is desirable that
The four photodetectors 281 to 284 detect the intensity of each of the four interference lights Q1 to Q4 extracted by the interference light extraction optical system and output the detection signals Sig1 to Sig4. It is an example of a means.
Further, the four amplifiers 63 independently amplify the detection signals of the four photodetectors 281 to 284, and output the amplified detection signals to the phase difference calculation computer 4. That is, the amplifier 63 applies linear correction to each of the four light intensity signals obtained by the photodetectors 281 to 284 in accordance with amplification gains set individually. It is an example of a means. The amplification gain is a linear correction gain.
Further, as will be described later, the four light intensity signals Sig1 to Sig4 output from the amplifier 63 are individually offset-corrected by the phase difference calculator 4 for the four light intensity signals Sig1 to Sig4. In some cases, offset correction may be added by adding values. In this case, an example of the light intensity correction unit in which the four amplifiers 63 and the phase difference calculation computer 4 independently perform linear correction and offset correction on each of the four light intensities obtained by the photodetectors 281 to 284. It becomes.

The four polarizing plate holding mechanisms 61 hold each of the four polarizing plates 271 to 274 in a variable manner. More specifically, the polarizing plate holding mechanism 61 holds the polarizing plates 271 to 274 so as to be orthogonal to the optical axes of the non-interfering lights P1 to P4, and uses the optical axis as a rotation center. Each of the polarizing plates 271 to 274 is rotatably held.
The polarizing plate holding mechanism 61 includes a manual holding angle adjusting mechanism, or an automatic holding angle adjusting mechanism that changes the holding angles of the polarizing plates 271 to 274 in accordance with a control command from a predetermined controller. The thing with is considered.
For example, the manual holding angle adjusting mechanism may be one that changes the holding angle of the polarizing plates 271 to 274 in accordance with an adjusting operation for a screw or the like by an operator. Further, the automatic holding angle adjusting mechanism may include a driving source such as a piezo element that changes the holding angle of the polarizing plates 271 to 274 in accordance with a control command from a predetermined controller. Further, the controller can be realized by the phase calculation computer 4 or the shape calculation computer 5.

  The two light blocking mechanisms 62 are an example of a light blocking unit that individually blocks the object light Ps and the reference light Pr. The light blocking mechanism 62 includes, for example, a light blocking member that blocks light, and a moving mechanism that moves the light blocking member to a position on the optical path of the object light Ps or the reference light Pr and a position retracted from the optical path. I have. The moving mechanism may be a manual moving mechanism that moves in response to an operator's operation, or an automatic moving mechanism that automatically moves in response to a control command from a predetermined controller. Further, the controller can be realized by the phase calculation computer 4 or the shape calculation computer 5.

  Hereinafter, the non-interfering light Px is branched into four by the non-interfering light branching optical systems 251 to 253 to reach the output lines of the photodetectors 281 to 284 from the optical paths of the non-interfering lights P1 to P4. The four light and signal paths are called channels. Of the four channels, the channel of the second interference light Q2 to be calculated for the phase difference φ between the object light Ps and the reference light Pr is a reference channel, and the other three channels are non-reference channels. Called.

When the optical interferometer 20 does not consider the phase shift amount errors caused by the quarter-wave plates 261 and 263 and the half-wave plate 264, the intensity as1 to as4 of the object light Ps of each channel, Four relational expressions are included among the intensities arl to ar4 of the reference light Ps in each channel, the intensities I01 to I04 of the interference lights Q1 to Q4 in each channel, and the phase difference φ between the object light Ps and the reference light Pr. The following equation (B1) which is a simultaneous equation is established. I01 to I04 correspond to detection values of the photodetectors 281 to 284 before being amplified by the amplifier 63.
In the equation (B1), when all the intensities as1 to as4 of the object light Ps in each channel and the intensities arl to ar4 of the reference light Ps in each channel are equal, the equation (B1) B2) can be transformed.
If the equation (B2) is actually established, the phase difference φ can be calculated with high accuracy from the intensities I01 to I04 of the interference lights Q1 to Q4 of the respective channels detected by the photodetectors 281 to 284. .

However, in actuality, the phase shift amount by the quarter-wave plates 261 and 263 and the half-wave plate 264 in the non-reference channel includes individual phase shift errors ε 1, ε 3, ε4 is included. Considering the phase shift errors ε1, ε3, and ε4, the following equation (B1 ′) is established instead of the equation (B1).
That is, when the optical interferometer 20 is used without going through a special calibration step, the above-mentioned position is calculated based on the equation (B1 ′) including 12 unknown parameters including the phase difference φ to be measured. The phase difference φ must be calculated. Then, the phase difference φ must be calculated under many assumptions and approximations, and the accuracy of the calculated phase difference φ is lowered.
Therefore, in the shape measurement using the shape measuring device X, the shape of the device under test 1 is measured after a relatively simple device calibration process for obtaining the highly accurate phase difference φ.

Hereinafter, the shape measuring method according to the first embodiment executed using the shape measuring apparatus X will be described with reference to the flowchart shown in FIG. Note that S11, S12, S13,... Shown below represent identification codes of respective steps in the shape measurement.
As shown below, in the shape measuring method according to the first embodiment using the shape measuring device X, first, a device calibration step (S11 to S14) for obtaining the phase difference φ with high accuracy is performed. Then, the shape measurement process (S15-S19) about the said to-be-measured object 1 is performed.
In the apparatus calibration step, first, a predetermined calibration object is placed and held at the measurement position (S11). A measurement position in the shape measuring apparatus X is a space between the two optical interferometers 20. The calibration object may be the object to be measured 1 that is the object of the first shape measurement, or may be an object prepared elsewhere.
The calibration object is arranged at the measurement position by, for example, operating the calibration object with the movable support device Z by an operator's operation or a transport device having a manipulator for transporting the device under test 1. It is done by letting it support.
Hereinafter, a state in which the calibration object is arranged at the measurement position is referred to as a first arrangement state.

Next, in the state where the optical path lengths of the object light Ps and the reference light Pr are kept constant under the first arrangement state, the following polarizing plate holding angle adjustment step is executed (S12). Here, the state where the optical path lengths of the object light Ps and the reference light Pr are held constant is a state where the reference plate 24 and the calibration object are held so as not to vibrate. In this state, it goes without saying that the positions of other optical devices that affect the optical path lengths of the object light Ps and the reference light Pr are also fixed.
In the polarizing plate holding angle adjusting step, for each of the four photodetectors 281 to 284, the detected intensity of the reference light Pr when the object light Ps is blocked and the object light when the reference light Pr is blocked. In this step, the holding angles of the four polarizing plates 271 to 274 are adjusted so that the detected intensity of Ps matches.
The object light Ps and the reference light Pr are blocked by the two light blocking mechanisms 62. The holding angles of the four polarizing plates 271 to 274 are adjusted through the holding angle adjusting mechanism 61.
In the following description, the difference between the detected intensity of the reference light Pr when the object light Ps is blocked and the detected intensity of the object light Ps when the reference light Pr is blocked is referred to as an intensity difference between two lights. Called.
By executing the polarizing plate holding angle adjusting step in step S12, as1 = ar1, as2 = ar2, as3 = ar3, and as4 = ar4 in the above-described equation (B1 ′). In this case, I1 to I4 in the equation (B1 ′) are values of output signals of the amplifier 63 of the four channels after the polarizing plate holding angle adjusting step.

For example, the phase difference calculation computer 4 can calculate the intensity difference between the two lights based on the detected intensity of each of the four photodetectors 281 to 284, and the intensity difference between the two lights can be approximated to 0 or 0. A command for changing the holding angle of the polarizing plates 271 to 274 is output to the four automatic holding angle adjusting mechanisms 61 so as to obtain a value of about.
Alternatively, the phase difference calculation computer 4 sequentially calculates the intensity difference between the two lights for each of the four photodetectors 281 to 284 and displays the calculation result on a predetermined display device. Then, while the operator confirms the displayed intensity difference between the two lights, the four manual holding angle adjusting mechanisms are adjusted so that the intensity difference between the two lights becomes 0 or a value that can be approximated to zero. 61 is adjusted to change the holding angle of the polarizing plates 271 to 274.
In step 12, the phase difference calculation computer 4 compares, for example, two values of the output signal of the amplifier 63 set to the amplification gain of 0 dB (1 time) to be compared in the polarizing plate holding angle adjustment step. May be used as the detected intensity.
In the polarizing plate holding angle adjusting step, the detected intensity of the reference light Pr when the object light Ps is blocked matches the detected intensity of the object light Ps when the reference light Pr is blocked. It is only necessary to make a relative comparison as to whether or not the absolute values of both detection intensities are large. Therefore, even when the amplification gain set in the amplifier 63 is not 0 dB, the detection intensity of the two lights compared in the polarizing plate holding angle adjustment step is the detection signal of the photodetectors 281 to 284. The value of the signal after being amplified by the amplifier 63 may be used.

Further, after execution of the polarizing plate holding angle adjusting step, the optical path length of the object light Ps or the reference light Pr under the first arrangement state is greater than the wavelength λ of the object light Ps and the reference light Pr. The linear correction gain setting step shown below is executed (S13).
In the linear correction gain setting step (S13), the amplification gain for the amplifier 63 is adjusted so that the amplitudes of the time series changes of the intensities I1 to I4 of the four interference lights Q1 to Q4 obtained by the amplifier 63 coincide with each other. That is, it is a step of setting a gain for linear correction.
As a method for giving the fluctuation of the amplitude of the wavelength λ or more to the optical path length of the object light Ps or the reference light Pr, for example, the calibration object or the reference plate 24 is vibrated with an amplitude of (λ / 2) or more. Can be considered. Further, as a method of vibrating the calibration object or the reference plate 24, for example, a method of applying an impact to the calibration object having elasticity, a calibration object or a support portion of the reference plate 24 is used. It is conceivable to give vibration by a predetermined driving source. However, if the amplitude of vibration of the calibration object or the reference plate 24 is too large, the light amount of the object light Ps or the reference light Pr varies depending on the inclination. Therefore, the amplitude of vibration of the calibration object or the reference plate 24 needs to be suppressed to about 5 μm or less.

In the linear correction gain setting step (S13), for example, the phase difference calculation computer 4 stores time series changes in the value of the output signal of the amplifier 63 in each of the four channels under the first arrangement state. The amplitude is calculated while recording. Further, the phase difference calculation computer 4 automatically sets the amplification gain for each of the four amplifiers 63 so that the difference in amplitude between the four channels can be approximated to 0 or 0.
Alternatively, the phase difference calculation computer 4 calculates the amplitude while recording the time series change in the value of the output signal of the amplifier 63 for each of the four channels in the memory, and displays the calculation result on a predetermined display device. . Then, the operator confirms the amplitudes of the four displayed channels, and manually adjusts the amplification gains for each of the four amplifiers 63 so that the difference between the amplitudes can be approximated to 0 or 0. Set.
By executing the polarizing plate holding angle adjusting step (S12) and the linear correction gain setting step (S13), in the above-described equation (B1 ′), as1 = ar1 = as2 = ar2 = as3 = ar3 = as4 = ar4 It becomes.
Accordingly, when the values of the output signals of the amplifiers 63 of the four channels after the polarizing plate holding angle adjusting step and the linear correction gain setting step are executed are I1 ′, I2 ′, I3 ′, and I4 ′, respectively. The following equation (C1) is established. In Equation (C1), k is a constant (k = 2 × ar1).
Here, the predetermined variable φ ′ is defined by the following equation (C2).
When the expression (C1) is established, the following expression (C3) derived from the expression (C1) is established.
Then, the following equation (C4) is obtained by deriving an inverse function for obtaining the phase difference φ from the equation (C3).
That is, the measured values of the interference lights Q1 to Q4, which are the output values of the amplifier 63 in each of the four channels, after the polarizing plate holding angle adjusting step (S12) and the linear correction gain setting step (S13) are executed. Are I1 ′, I2 ′, I3 ′, and I4 ′, the equations (C2) and (C4) are established.

Further, after the execution of the linear correction gain setting step (S13), the phase difference calculation computer 4 calculates phase shift errors ε1, ε3, ε4 by the phase shift optical systems 261, 263, 264 to obtain a predetermined value. A phase shift error calculating step to be stored in the memory is executed (S14).
In the linear correction gain setting step (S13), with the amplification gain of the amplifier 63 set so that the amplitude of each channel is equal, the amplifier 63 of each of the four channels under the first arrangement state. A time-series change in the value of the output signal is recorded in the memory.
In the phase shift error calculating step (S14), first, the phase difference calculation computer 4 has the four channels of interference light Q1 to Q1 obtained through the amplifier 63 after the amplification gain adjustment obtained in step S13. The information of the Lissajous waveform based on the time series change of the detected intensity of Q4 is calculated.
The Lissajous waveform to be processed in step S14 includes the time series change of the intensity I2 ′ of the interference light Q2 of the reference channel and the intensity I1 ′, I3 ′ of the interference light Q1, Q3 of the two non-reference channels. It is a Lissajous waveform representing the relationship between each time series change and the relationship between the time series changes of the intensities I3 ′ and I4 ′ of the interference lights Q3 and Q4 of the non-reference channel.
FIG. 6 shows an example of the Lissajous waveform observed in step S14.
As shown in FIG. 6, the Lissajous waveform g1 based on the intensity I2 ′ and the intensity I1 ′ is changed to the Lissajous waveform g3 based on the intensity I2 ′ and the intensity I3 ′, and the intensity I3 ′ and the intensity I4 ′. The base Lissajous waveform g4 has an elliptical shape.
However, when the phase shift error ε1 = 0, the Lissajous waveform g1 is circular. Similarly, when the phase shift error ε3 = 0, the Lissajous waveform g3 is circular. Further, when the difference between the phase shift errors ε3 and ε4 is 0 (ε4−ε3 = 0), the Lissajous waveform g4 is circular.

FIG. 7 is an explanatory diagram of a relationship between a Lissajous waveform of two measured values and a phase difference.
In a Lissajous waveform with the measured value in the X-axis direction as Ix and the measured value in the Y-axis direction as Iy, the width in the Y-axis direction of the Lissajous waveform is Wb, and the X-axis coordinates of the center position (Ixo, Iyo) of the Lissajous waveform The width in the Y-axis direction at Ixo is defined as Wa. Then, the difference Δφ between the phase of the measurement value Ix and the phase of the measurement value Iy is sin −1 (Wa / Wb).
Therefore, in step S14, the phase difference calculator 4 (Wa1, Wb1), (Wa3, Wb3) and (Wa4, Wb4) are the widths (Wa, Wb) for the Lissajous waveforms g1, g3, g4, respectively. ) Calculate each.
Further, the phase difference calculator 4 calculates the phase shift errors ε1, ε3, ε4 in each channel where phase shifts of −π / 2, + π / 2, and + π are performed as follows: ε1 = sin −1 (Wa1 / Wb1 ) + (Π / 2), ε3 = sin −1 (Wa3 / Wb3) − (π / 2), ε4 = sin −1 (Wa4 / Wb4) − (π / 2) The calculation result is stored in the memory.
By executing the apparatus calibration steps (S11 to S14) described above, the above equations (C2) and (C4) are established, and the phase shift errors ε1, ε3, ε4 in the equation (C4) are satisfied. Are all known.
Accordingly, if the intensities I1 ′, I2 ′, I3 ′, and I4 ′ of the four channels of the interference light Q1 to Q4 are measured for the DUT 1 after the apparatus calibration process (S11 to S14) is performed, the measurement is performed. By applying the values I1 ′, I2 ′, I3 ′, I4 ′ and the phase shift errors ε1, ε3, ε4 to the equation (A1) consisting of the equations (C2) and (C4), The phase difference φ between the object light Ps and the reference light Pr can be calculated. The phase difference φ is obtained by removing the phase shift errors ε1, ε3, and ε4.

Then, after the above-described apparatus calibration process (S11 to S14) is performed, the shape measurement process (S15 to S19) for the device under test 1 is performed.
In the shape measuring step, first, similarly to step S11, the device under test 1 is arranged and held at the measurement position, and the movable support device Z moves the support position of the device under test 2 in the two-dimensional direction. Start (S15). When the calibration object placed at the measurement position in step S1 is the device under test 1, the step of replacing the calibration object with the device under test 1 that is the first object to be measured. Is skipped.
Hereinafter, the state in which the DUT 1 is arranged at the measurement position is referred to as a second arrangement state.

Next, the phase difference calculation computer 4 detects and detects the intensities I1 ′ to I4 ′ of the interference light beams Q1 to Q4 of the four channels obtained by the amplifier 63 under the second arrangement state. A measurement interference light intensity detection step of recording the result in a predetermined memory is executed (S16).
Further, the phase difference calculation computer 4 has the intensities I1 ′ to I4 ′ of the four interference lights Q1 to Q4 obtained in the measurement interference light intensity detection step (S16) and the phase shift error calculation step ( The phase shift errors ε1, ε3, ε4 for each of the three interference light beams of the non-reference channel obtained in S14) are applied to the equation (A1) consisting of the equations (C2) and (C4). Thus, a phase difference calculating step for calculating the phase difference φ between the object light Ps and the reference light Pr is executed (S17). The phase difference φ calculated in step S17 is transmitted to the shape calculation computer 5.
Then, the phase difference calculation computer 4 repeats the processes of steps S16 and S17 for all scheduled measurement points 1a and 1b in the DUT 1. For example, the shape calculation computer 5 determines whether or not the measurement for all the measurement points 1a and 1b is completed (S18).
And when the measurement process (S16, S17) about all the measurement points 1a and 1b is complete | finished, the said shape calculation computer 5 will be the said each of the A surface side and B surface side obtained about all the measurement points 1a and 1b. Based on the distribution of the difference (φa−φb) between the phase differences φa and φb at the measurement points 1a and 1b, a shape calculation process for calculating the thickness distribution of the DUT 1 is executed (S19).
Further, when the shape measuring step (S15 to S19) is executed by replacing the DUT 1, the device calibration step (S15 to S19) is performed before the second and subsequent shape measuring steps (S15 to S19). S11-S14) need not be executed.
Phase shift errors ε1, ε3, ε4 that occur when the phase shift is optically performed using the plurality of polarizing plates 261, 263, 264 by the shape measuring method according to the first embodiment shown in FIG. It is possible to easily obtain the measurement result φ that is not affected by the above.

Hereinafter, the shape measuring method according to the second embodiment executed using the shape measuring apparatus X will be described with reference to the flowchart shown in FIG. Note that S21, S22, S23,... Shown below represent identification codes of respective steps in the shape measurement.
As shown below, also in the shape measuring method according to the second embodiment using the shape measuring device X, first, a device calibration step (S21 to S24) for obtaining the phase difference φ with high accuracy is performed. Then, the shape measuring step (S25 to S29) for the DUT 1 is executed.
In the shape measurement method according to the second embodiment, as will be described later, the four amplifiers 63 and the phase difference calculation computer 4 are independent of each of the four light intensity signals obtained by the photodetectors 281 to 284. Thus, it functions as light intensity correction means for applying linear correction based on the amplification gain and offset correction based on the offset correction value.
In the apparatus calibration step, first, as in step S11, the calibration object is placed and held at the measurement position (S21). As a result, the first arrangement state is obtained.

Next, the linear correction gain setting step shown below is executed in a state where the optical path lengths of the object light Ps and the reference light Pr are kept constant under the first arrangement state (S22).
In the linear correction gain setting step (S22), only the reference light Pr is blocked and the four object lights Ps obtained by the four amplifiers 63 have the same intensity so that the four amplifiers 63 have the same intensity. It is a step of setting the amplification gain which is a linear correction gain. The reference light Pr is blocked through the light blocking mechanism 62 on the reference light Pr side.
In the linear correction gain setting step (S22), for example, when the phase difference calculation computer 4 is in the state where the reference light Pr is blocked under the first arrangement state, the amplifier 63 for each of the four channels. The amplification gains are automatically set for each of the four amplifiers 63 so that the difference between them is 0 or close to zero.
Alternatively, the phase difference calculation computer 4 calculates the difference in the value of the output signal of the amplifier 63 for each of the four channels and displays the calculation result on a predetermined display device. Then, the operator confirms the difference in the output signal value of the amplifier 63 for each of the four displayed channels, and each of the four amplifiers 63 so that the difference is 0 or approximate to zero. The amplification gain is set manually.
By executing the linear correction gain setting step (S22), the values of the output signals of the respective channels by the amplifier 63 after the amplification gain adjustment are set to I1 ′, I2 ′, I3 ′, and I4 ′, as described above ( In the equation (B1 ′), the following equation (D1) is established with as1 = as2 = as3 = as4 = as.

Next, after the linear correction gain setting step (S22) is executed, an offset correction value setting step shown below is executed under the first arrangement state (S23).
In the offset correction value setting step (S23), only the object light Ps is blocked while the optical path length of the reference light Pr is kept constant, and the intensities arl ~ of the four reference lights Pr obtained by the amplifier 63 are obtained. In this step, ar4 is set as the offset correction value in the phase difference calculator 4. Here, the phase difference calculation computer 4 performs offset correction for subtracting the intensities arl to arl4 from the output values of the four amplifiers 63. The offsets ar1 to ar4, which are offset correction values, are stored in the memory of the phase difference calculator 4.
By performing the linear correction gain setting step (S22) and the offset correction value setting step (S23), the interference light of each channel subjected to linear correction and offset correction by the amplifier 63 and the phase difference calculator 4 Assuming that the measured intensity values of Q1 to Q4 are I1 ", I2", I3 ", and I4", the offset correction values arl to arl4 are subtracted from the left and right sides of the four formulas in the formula (D1). (D2) is established.
Here, the predetermined variable Z is defined by the following equation (D3).
When the expression (D2) is established, the following expression (D4) derived from the expression (D2) is established.
Then, the following equation (D5) is obtained by deriving an inverse function for obtaining the phase difference φ from the equation (D4).
That is, after the linear correction gain setting step (S22) and the offset correction value setting step (S23) are executed, linear correction and offset correction obtained by the amplifier 63 and the phase difference calculation computer 4 of each of four channels. Assuming that the measured values of the interference lights Q1 to Q4 after that are I1 ″, I2 ″, I3 ″, and I4 ″, the equations (D3) and (D5) are established.

Further, after the execution of the offset correction value setting step (S23), the phase difference calculation computer 4 calculates phase shift errors ε1, ε3, ε4 by the phase shift optical systems 261, 263, 264 to obtain predetermined values. A phase shift error calculating step to be stored in the memory is executed (S24).
In the phase shift error calculation step (S24), the phase difference calculation computer 4 executes the following processes.
First, similarly to step S13, the phase difference calculation computer 4 adds the object light Ps and the reference light Pr to the optical path length of the object light Ps or the reference light Pr under the first arrangement state. A time series change in intensity of each of the four interfering lights Q1 to Q4 after correction obtained by linear correction of the amplifier 63 and offset correction of the phase difference calculation computer 4 while giving fluctuations in amplitude of the wavelength λ or more, The data is stored in the memory of the phase difference calculator 4.
Further, the phase difference calculation computer 4 performs the time series of the intensities of the interference light Q2 of the reference channel and the interference light Q1, Q3, and Q4 of the three non-reference channels stored in the memory, as in step S14. The information of the Lissajous waveform obtained from the change is calculated. Thus, the widths (Wa1, Wb2), (Wa3, Wb3), (Wa4, Wb4) are calculated for each of the three Lissajous waveforms corresponding to the measured values of the three non-reference channels.
Further, the phase difference calculator 4 calculates the errors ε1, ε3, ε4 of the phase shift in each channel where phase shifts of −π / 2, + π / 2 and + π2 are performed, as follows: ε1 = sin −1 (Wa / Wb ) + (Π / 2), ε3 = sin −1 (Wa / Wb) − (π / 2), ε4 = [sin −1 (Wa / Wb) + ε3] − (π / 2) The calculation result is stored in the memory.
By executing the apparatus calibration steps (S21 to S24) described above, the above equations (D3) and (D5) are established, and errors ε1, ε3, ε4 of the phase shift in the equation (D5) are established. Are all known.
Therefore, after executing the apparatus calibration process (S21 to S24), if the intensities I1 ", I2", I3 "and I4" of the four channels of the interference light Q1 to Q4 are measured for the device under test 1, the measurement is performed. The values I1 ″, I2 ″, I3 ″, I4 ″, the phase shift errors ε1, ε3, ε4 and the intensities arl to arl of the reference light Pr that are the offset correction values are expressed by the equation (D3) and The phase difference φ between the object beam Ps and the reference beam Pr can be calculated by applying the equation (A2) including the equation (D5). The phase difference φ is obtained by removing the phase shift errors ε1, ε3, and ε4.

Then, after the above-described apparatus calibration process (S21 to S24) is performed, the shape measurement process (S25 to S29) for the device under test 1 is performed.
In the shape measuring step, first, similarly to step S15, the device under test 1 is placed and held at the measurement position, and the movable support device Z moves the support position of the device under test 2 in the two-dimensional direction. Start (S25). As a result, the second arrangement state is obtained.
When the calibration object placed at the measurement position in step S1 is the device under test 1, the step of replacing the calibration object with the device under test 1 that is the first object to be measured. Is skipped.

Next, the phase difference calculation computer 4 has four channels of interference light Q1 to Q4 obtained by linear correction of the amplifier 63 and offset correction of the phase difference calculation computer 4 under the second arrangement state, respectively. A measurement interference light intensity detection step of detecting the intensities I1 "to I4" and recording the detection results in a predetermined memory is executed (S26).
Further, the phase difference calculator 4 calculates the corrected intensities I1 "to I" of the four interference lights Q1 to Q4 obtained in the measurement interference light intensity detection step (S26) and the phase shift error. The phase shift errors ε1, ε3, ε4 and the offset correction values arl to ar4 for each of the three interference light beams of the non-reference channel obtained in the calculation step (S24) are expressed by the equations (D3) and (D3). A phase difference calculating step of calculating the phase difference φ between the object light Ps and the reference light Pr is executed by applying the expression (A2) consisting of the expression D5) (S27). The phase difference φ calculated in step S27 is transmitted to the shape calculation computer 5.
Then, the phase difference calculation computer 4 repeats the processes of steps S26 and S27 for all scheduled measurement points 1a and 1b in the device under test 1. For example, the shape calculation computer 5 determines whether or not the measurement for all the measurement points 1a and 1b has been completed (S28).
Then, when the measurement processing (S26, S27) for all the measurement points 1a, 1b is completed, the shape calculation computer 5 performs each of the A side and B side obtained for all the measurement points 1a, 1b. Based on the distribution of the difference (φa−φb) between the phase differences φa and φb at the measurement points 1a and 1b, a shape calculation process for calculating the thickness distribution of the DUT 1 is executed (S29).
Also in the shape measuring method according to the second embodiment, the apparatus calibration steps S21 to S24 may be performed once before measuring the shape of one or a plurality of the objects to be measured 1.
Also by the shape measuring method according to the second embodiment of FIG. 5 described above, phase shift errors ε1, ε3, which are generated when the phase shift is optically performed using the plurality of polarizing plates 261, 263, 264, The measurement result φ that is not affected by ε4 can be easily obtained.

In the embodiment described above, the shape measuring apparatus X provided with two optical interferometers 20 is shown. However, one of the objects to be measured 1 is measured by the shape measuring apparatus provided with one optical interferometer 20. It is also conceivable to measure the surface shape (height distribution) of the surface.
It is also conceivable that the offset correction function of the light intensity is provided in the amplifier 63 instead of the phase difference calculator 4.

  The present invention is applicable to a shape measuring method for measuring the surface shape of an object to be measured using a homodyne interferometer.

X: shape measuring device Y according to an embodiment of the present invention: interference light measuring unit Z: movable support device 1: object to be measured 1a, 1b: measurement point 2: laser light source 3: polarization beam splitter 4: phase difference calculation computer 5 : Shape calculator 7: movement control device 11: mirror 20: optical interferometer 21: polarization beam splitter 22, 23: quarter wave plate 24: reference plate 31: half wave plate 32: condenser lens 61 : Polarizing plate holding mechanism 62: Light blocking mechanism 63: Amplifiers 251 and 252: Non-polarizing beam splitters 261 and 263: Quarter wavelength plate 264: Half wavelength plates 271 to 274: Polarizing plates 281 to 284: Photodetectors P0, Pi: Beam light Px, P1-P4: Non-interference light Q1-Q4: Interference light

Claims (9)

  1. A non-interfering light branching optical system for branching incoherent light, which includes object light reflected by an object placed at a predetermined measurement position and other reference light as polarization components, into four parts;
    A phase shift optical system that generates different phase differences between the polarization component of the reference light and the polarization component of the object light in each of the four branched lights of the non-interfering light;
    Four polarizing plates for extracting interference light between the reference light and the object light from each of the four branched lights of the non-interference light that have passed through the phase shift optical system;
    A light intensity detecting means for detecting the intensity of each of the light passing through the four polarizing plates;
    Light intensity correction means for independently correcting each of the four light intensities obtained by the light intensity detection means;
    A shape measuring method for measuring the surface shape of an object to be measured using an interferometer equipped with
    Detection intensity of the reference light when the object light is blocked in a state where the optical path lengths of the object light and the reference light are kept constant under the first arrangement state where the calibration object is arranged at the measurement position. And a polarizing plate holding angle adjustment step of adjusting the holding angle of the polarizing plate so that the detected intensity of the object light when the reference light is blocked matches.
    After the polarizing plate holding angle adjusting step, the four interference light beams obtained by the light intensity correcting means by giving a time-series fluctuation to the optical path length of the object light or the reference light under the first arrangement state. A gain setting step of setting a correction gain for the light intensity correction means so that the amplitudes of the time-series changes of the respective intensities coincide with each other;
    After the gain setting step, the intensity of each of the four interference lights obtained by the light intensity correction means by giving a time-series fluctuation to the optical path length of the object light or the reference light under the first arrangement state A phase shift error calculating step for calculating an error of the phase shift by the phase shift optical system based on the information;
    Based on the intensity of the interference light obtained by the light intensity correction means and the calculation result of the phase shift error calculation step under the second arrangement state where the object to be measured is arranged at the measurement position. A phase difference calculating step of calculating a phase difference between the object light and the reference light with respect to a measurement object;
    A shape measuring method comprising:
  2. The phase shift optical system sets the phase difference of the three non-interfering lights that are the sources of the non-reference interference light to -90 ° with respect to one non-interfering light that is the source of the reference interference lights, + 90 ° and + 180 °,
    In the phase difference calculating step, the reference interference light intensity I2 ′ obtained by the measurement interference light intensity detection step and the three non-reference interference light intensities I1 ′, I3 ′, I4 ′ and the phase Applying the phase shift errors ε1, ε3, and ε4 for each of the three non-reference interference lights obtained by the shift error calculation step to the following equation (A1), the object for the object to be measured: The shape measuring method according to claim 1, which is a step of calculating a phase difference φ between light and the reference light.
  3. A non-interfering light branching optical system for branching incoherent light, which includes object light reflected by an object placed at a predetermined measurement position and other reference light as polarization components, into four parts;
    A phase shift optical system that generates different phase differences between the polarization component of the reference light and the polarization component of the object light in each of the four branched lights of the non-interfering light;
    Four polarizing plates for extracting interference light between the reference light and the object light from each of the four branched lights of the non-interference light that has passed through the phase shift optical system;
    A light intensity detecting means for detecting the intensity of each of the light passing through the four polarizing plates;
    Light intensity correction means for independently correcting each of the four light intensities obtained by the light intensity detection means;
    A shape measuring method for measuring the surface shape of an object to be measured using an interferometer equipped with
    Under the first arrangement state in which the calibration object is arranged at the measurement position, only the reference light is blocked while the optical path length of the object light is kept constant. A gain setting step for setting a correction gain for the light intensity correction means so that the intensities of the object lights coincide;
    After the gain setting step, the four reference lights obtained by the light intensity correction means by blocking only the object light while keeping the optical path length of the reference light constant under the first arrangement state. An offset correction value setting step for setting the intensity of the light as an offset correction value of the light intensity correction means;
    After the offset correction value setting step, each of the four interference lights obtained by the light intensity correction means by giving a time-series variation to the optical path length of the object light or the reference light under the first arrangement state. A phase shift error calculating step for calculating an error of the phase shift by the phase shift optical system based on the intensity information;
    Based on the intensity of the interference light obtained by the light intensity correction means and the calculation result of the phase shift error calculation step under the second arrangement state where the object to be measured is arranged at the measurement position. A phase difference calculating step of calculating a phase difference between the object light and the reference light with respect to a measurement object;
    A shape measuring method comprising:
  4. The phase shift optical system sets the phase difference of the three non-interfering lights that are the sources of the non-reference interference light to -90 ° with respect to one non-interfering light that is the source of the reference interference lights, + 90 ° and + 180 °,
    In the phase difference calculating step, the reference interference light intensity I2 ″ and the three non-reference interference light intensities I1 ″, I3 ″, I4 ″ obtained by the measurement interference light intensity detection step and the phase Applying the phase shift errors ε1, ε3, and ε4 for each of the three non-reference interference lights obtained by the shift error calculation step to the following equation (A2), the object for the object to be measured: The shape measuring method according to claim 3, which is a step of calculating a phase difference φ between light and the reference light.
  5. A shape measuring device for measuring the surface shape of an object to be measured by optical interferometry,
    A non-interfering light branching optical system for branching incoherent light, which includes object light reflected by an object placed at a predetermined measurement position and other reference light as polarization components, into four parts;
    A phase shift optical system that generates different phase differences between the polarization component of the reference light and the polarization component of the object light in each of the four branched lights of the non-interfering light;
    Four polarizing plates for extracting interference light between the reference light and the object light from each of the four branched lights of the non-interference light that have passed through the phase shift optical system;
    A light intensity detecting means for detecting the intensity of each of the light passing through the four polarizing plates;
    Light intensity correction means for independently correcting each of the four light intensities obtained by the light intensity detection means;
    Polarizing plate holding means for holding the polarizing plate in a variable angle;
    Light blocking means for blocking each of the object light and the reference light;
    Under the first arrangement state in which a calibration object is arranged at the measurement position, four light intensity correction means obtainable when the optical path length of the object light or the reference light is given in time series. A gain setting means for setting a correction gain for the light intensity correction means so as to match the amplitudes of time-series changes in the intensity of the interference light;
    Based on intensity information of each of the four interference lights obtained by the light intensity correction means when a time-series variation is given to the optical path length of the object light or the reference light under the first arrangement state. Phase shift error calculating means for calculating an error of phase shift by the phase shift optical system,
    Based on the intensity of the interference light obtained by the light intensity correction unit and the calculation result of the phase shift error calculation unit under the second arrangement state in which the object to be measured is arranged at the measurement position. Phase difference calculating means for calculating a phase difference between the object light and the reference light with respect to a measurement object;
    A shape measuring apparatus comprising:
  6. The phase shift optical system sets the phase difference of the three non-interfering lights that are the sources of the non-reference interference light to -90 ° with respect to one non-interfering light that is the source of the reference interference lights, + 90 ° and + 180 °,
    The phase difference calculating means includes the phase shift for each of the reference interference light intensity I2 ′ and the three non-reference interference light intensities I1 ′, I3 ′, I4 ′ and the three non-reference interference lights. The shape according to claim 5, wherein the phase difference φ between the object light and the reference light with respect to the object to be measured is calculated by applying the errors ε1, ε3, ε4 to the following equation (A1): measuring device.
  7.   Under the first arrangement state, the object light is blocked by the light blocking means for the detection intensity of each of the four light intensity detection means in a state where the optical path lengths of the object light and the reference light are kept constant. Polarized light that adjusts each holding angle of the polarizing plate by the polarizing plate holding means so that the detected intensity of the reference light coincides with the detected intensity of the object light when the reference light is blocked by the light blocking means The shape measuring apparatus according to claim 5, further comprising a plate holding angle adjusting unit.
  8. A shape measuring device for measuring the surface shape of an object to be measured by optical interferometry,
    A non-interfering light branching optical system for branching incoherent light, which includes object light reflected by an object placed at a predetermined measurement position and other reference light as polarization components, into four parts;
    A phase shift optical system that generates different phase differences between the polarization component of the reference light and the polarization component of the object light in each of the four branched lights of the non-interfering light;
    Four polarizing plates for extracting interference light between the reference light and the object light from each of the four branched lights of the non-interference light that have passed through the phase shift optical system;
    A light intensity detecting means for detecting the intensity of each of the light passing through the four polarizing plates;
    Light blocking means for blocking each of the object light and the reference light;
    Light intensity correction means for independently correcting each of the four light intensities obtained by the light intensity detection means;
    Under the first arrangement state in which the calibration object is arranged at the measurement position, the light intensity is maintained when the optical path length of the object light is kept constant and the reference light is blocked by the light blocking means. A gain setting means for setting a correction gain for the light intensity correction means so that the intensities of the four object lights obtained by the correction means match;
    The four reference lights obtained by the light intensity correcting means when the optical path length of the reference light is kept constant under the first arrangement state and the object light is blocked by the light blocking means. Offset correction value setting means for setting the intensity as an offset correction value of the light intensity correction means;
    Based on intensity information of each of the four interference lights obtained by the light intensity correction means when a time-series variation is given to the optical path length of the object light or the reference light under the first arrangement state. Phase shift error calculating means for calculating an error of phase shift by the phase shift optical system,
    Based on the intensity of the interference light obtained by the light intensity correction unit and the calculation result of the phase shift error calculation unit under the second arrangement state in which the object to be measured is arranged at the measurement position. Phase difference calculating means for calculating a phase difference between the object light and the reference light with respect to a measurement object;
    A shape measuring apparatus comprising:
  9. The phase shift optical system sets the phase difference of the three non-interfering lights that are the sources of the non-reference interference light to -90 ° with respect to one non-interfering light that is the source of the reference interference lights, + 90 ° and + 180 °,
    The phase difference calculating means is configured to detect the phase shift for each of the reference interference light intensity I2 ″ and the three non-reference interference light intensity I1 ″, I3 ″, I4 ″ and the three non-reference interference lights. The shape according to claim 8, wherein the phase difference φ between the object light and the reference light with respect to the object to be measured is calculated by applying the errors ε1, ε3, and ε4 to the following equation (A1). measuring device.
JP2010122330A 2009-06-05 2010-05-28 Shape measuring device and shape measuring method Active JP5289383B2 (en)

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