JP5199141B2 - Shape measuring device - Google Patents

Description

  The present invention relates to a shape measuring apparatus that measures the thickness of an object to be measured such as a semiconductor wafer in a non-contact manner by an optical interference method.

  In the shape measurement of a thin semiconductor wafer (an example of an object to be measured, hereinafter referred to as a wafer), a non-contact type shape measuring apparatus using an interferometer has become widespread. This is because measurement light that is reflected light that reflects one of the light beams branched into two on the surface of the object to be measured, and reference light that is reflected light that reflects the other light beam on a predetermined reference surface, and The surface shape (surface height distribution) of the object to be measured is obtained from the interference image formed by the interference light. As a result, the surface shape of the wafer can be measured in a non-contact manner, so that the surface shape can be measured without causing scratches or the like on the wafer surface as in the case of measuring with a stylus type shape meter. In the measurement of the shape of the wafer, it is necessary to measure the shape over the entire surface thereof, and therefore generally the measurement is performed with the edge portion around the wafer supported (usually, three points are supported).

By the way, when a thin plate-like object to be measured such as a wafer (for example, a thickness of less than 1 mm) is supported only by its edge portion, the wafer vibrates due to slight wind pressure, vibration of other machines, or the like. This vibration is a vibration having a non-negligible amplitude in wafer shape measurement that requires very high measurement accuracy (for example, an error of 20 nm or less). In order to prevent such wafer vibration, Patent Document 1 discloses a method of suppressing wafer vibration by disposing a transparent rigid body close to the wafer. However, this method has a problem that interference light may be disturbed by inserting a transparent rigid body into the optical path.
In Patent Document 2, two types of measurement light having slightly different frequencies are branched into two and guided to the heterodyne interferometers on the front and back surfaces of the object to be measured. A shape measuring device for measuring the thickness of an object to be measured by reversing the relationship is shown.
According to the technique disclosed in Patent Document 2, by taking the difference between the detection signals of the front and back heterodyne interferometers, the influence of the displacement of the object to be measured caused by vibration is eliminated, and the influence of the vibration of the object to be measured is not affected. Highly accurate thickness measurement is possible.
Further, in Patent Document 2, two kinds of branched light beams of measurement light immediately before entering the front and back heterodyne interferometers are caused to interfere, and the intensity signal of the interference light is used as a reference signal for the detection signal of the heterodyne interferometer. Is shown about. As a result, it is possible to eliminate measurement errors caused by phase fluctuations of the two types of measurement light that occur in the optical path from the light source to the two heterodyne interferometers.

JP 2002-5640 A JP 2008-180708 A

However, even with the technique disclosed in Patent Document 2, when the phase fluctuations of the two types of measurement light generated in the optical path from the light source to the two heterodyne interferometers are high-speed, the phase detection circuit changes the speed of the change. I can't follow it enough. For example, when two types of measurement light are transmitted from the light source to two heterodyne interferometers using an optical fiber, the optical fiber may vibrate at high speed depending on the surrounding environment, and the phase of the two types of measurement light may fluctuate at high speed. is there. Then, in the technique disclosed in Patent Document 2, the processing for eliminating the phase fluctuation of the two types of measurement light using the reference signal does not function sufficiently. As described above, even the technique disclosed in Patent Document 2 has a problem in that a measurement error caused by phase fluctuations of two types of measurement light may not be sufficiently eliminated.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is not to be affected by the vibration of the object to be measured and the vibration of the transmission medium of the measurement light from the light source to the interferometer. An object of the present invention is to provide a shape measuring apparatus that can easily and accurately measure the thickness of a measurement object.

In order to achieve the above object, a shape measuring apparatus according to the present invention is a measuring apparatus used for scanning the front and back surfaces of a measured object and measuring the thickness distribution of the measured object in a non-contact manner. The components shown in (1) to (11) are provided.
(1) First light branching means for bifurcating basic light emitted from a predetermined light source.
(2) A light guiding means for guiding each of the branched lights by the first light branching means in the respective directions of the measurement parts facing each other on the front and back surfaces of the object to be measured.
(3) Second light branching means for further branching each branched light of the basic light guided in the direction of the measurement site on each of the front and back sides of the object to be measured.
(4) Light modulation means for performing frequency modulation on one or both of the branched lights by the second light branching means on the front and back of the object to be measured to generate two measurement lights having different frequencies.
(5) On each of the front and back sides of the object to be measured, one of the measurement light beams is irradiated onto the measurement site, and the object beam that is the one measurement beam reflected by the measurement site and the reference beam that is the other measurement beam Two heterodyne interferometers that interfere with each other.
(6) Third optical branching means for bifurcating each of the two measurement lights into main light input to the heterodyne interferometer and other auxiliary light on each of the front and back sides of the object to be measured.
(7) Sub-light interference means for causing the two sub-lights branched by the third light branch means to interfere with each other on the front and back sides of the object to be measured.
(8) The measurement optical system including the second optical branching unit, the optical modulation unit, the heterodyne interferometer, the third optical branching unit, and the auxiliary optical interference unit is integrated on each side of the object to be measured. Measuring optical system holding means for holding.
(9) Measuring light intensity detecting means for receiving each interference light obtained by the two heterodyne interferometers and outputting an intensity signal thereof.
(10) Reference light intensity detection means for receiving the interference light obtained by the auxiliary light interference means and outputting the intensity signal on each of the front and back sides of the object to be measured.
(11) The phase difference between the two beat signals by phase detection of the two beat signals composed of the output signal of the measurement light intensity detection means and the output signal of the reference light intensity detection means on the front and back sides of the object to be measured. Means for detecting phase information.

In the shape measuring apparatus according to the present invention, the phase of the detection signal (beat signal) of the measurement light intensity detecting means corresponding to each of the front and back heterodyne interferometers is determined according to the principle of a known heterodyne interferometer. It is determined according to the height of the measurement part opposite to the front and back of the object.
The phase difference between the two beat signals detected by the phase information detection means for each of the measurement sites on the front and back sides of the object to be measured is the distance from the heterodyne interferometer to the measurement site, that is, the measurement site. Represents the height of. Therefore, the measured value of the thickness of the object to be measured can be obtained from the difference between the detection results of the phase information detecting means for the front and back of the object to be measured.
Further, in the shape measuring apparatus according to the present invention, after the branched light based on the one basic light emitted from the light source is guided to the vicinity of the measurement site on each of the front and back surfaces of the object to be measured, the light The light is converted into two types of measurement light input to the heterodyne interferometer by the modulation means. Therefore, in the optical path of the branched light from the light source to the heterodyne interferometers on the front and back, two types of phase fluctuations of the measurement light cannot occur.
Further, the measurement optical system for transmitting two kinds of measurement light generated by the light modulation means is integrally held on the front and back of the object to be measured. Therefore, the phase fluctuation of the two types of measurement light that can occur in the measurement optical system is suppressed to a very small level.
Further, the measured value of the thickness of the measurement object obtained as described above is a measurement value in which the displacement component due to the vibration of the measurement object is canceled on both the front and back sides of the measurement object. Therefore, the shape measuring apparatus according to the present invention can measure the thickness of the measurement object without being affected by the vibration of the measurement object.
In the measurement optical system, even if some phase fluctuations occur in the two types of measurement light, the phase fluctuations occur approximately equally in each of the two beat signals. For this reason, even if some phase fluctuation occurs in the two types of measurement light, the phase fluctuation is hardly reflected in the phase difference between the two beat signals.
Therefore, the shape measuring apparatus according to the present invention can measure the shape with very high accuracy.

Further, in the shape measuring apparatus according to the present invention, the measurement optical system holding means is a rigid body having a plate-like holding portion that shares and holds the measurement optical system on each of the front and back sides, and the plate-like holding portion includes It is suitable if a through-hole through which light propagating through the measurement optical system passes is formed. In this case, the measurement optical system holding means holds the measurement optical system in a three-dimensional manner across both sides of the plate-like holding unit.
Thereby, the plate-like holding portion for holding the measurement optical system can be made small, and the small plate-like holding portion can ensure sufficient rigidity even when a relatively thin and lightweight member is employed. Therefore, the measurement optical system holding means having a small and very simple structure can prevent the occurrence of a phase shift of the two types of measurement light due to deformation (deflection) of the plate-like holding part. For example, the plate-like holding portion may be a member reinforced by fixing its edge to another member.
By the way, in order to make the apparatus compact, a signal transmission path from the measurement light intensity detection means to the phase detection means, a signal transmission path from the reference light intensity detection means to the phase detection means, If they are placed close to each other, unnecessary radiation of electromagnetic waves generated from the transmission path of one beat signal becomes noise with respect to the other beat signal, thereby degrading measurement accuracy.
Therefore, it is more preferable that the shape measuring apparatus according to the present invention further includes the constituent element shown in the following (12).
(12) Arranged between a signal transmission path from the measurement light intensity detection means to the phase information detection means and a signal transmission path from the reference light intensity detection means to the phase information detection means. Metal shield plate.
Thereby, the deterioration of the measurement accuracy due to the unnecessary radiation can be prevented.

  According to the shape measuring apparatus according to the present invention, the thickness of the object to be measured can be easily and accurately measured without being affected by the vibration of the object to be measured and the vibration of the transmission medium of the measurement light from the light source to the interferometer. .

The block diagram of the shape measuring apparatus X which concerns on embodiment of this invention. The schematic block diagram of an example of the measurement optical unit Z with which the shape measuring apparatus X is provided. The schematic diagram showing an example of the thickness distribution measuring method of the to-be-measured object using the shape measuring apparatus X. FIG. The schematic diagram showing an example of the locus | trajectory of the measurement site | part in the case of measuring the thickness distribution of a to-be-measured object using the shape measuring apparatus X. FIG. The graph showing an example of the time-sequential change of the measured value of the conventional shape measuring apparatus. The graph showing an example of the time-sequential change of the measured value of the shape measuring apparatus X.

  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 measuring device used to measure the thickness of a thin plate-like object 1 such as a semiconductor wafer without contact.
As shown in FIG. 1, the shape measuring device X includes a light source unit Y, two measuring optical units Z disposed opposite to the front and back surfaces of the DUT 1, and 2 provided for each measuring optical unit Z. Two phase detection circuits W and a computer 6 are provided.
Hereinafter, for the sake of convenience, one surface (the upper surface in FIG. 1) of the DUT 1 is referred to as the A surface, and the other surface having the front and back relationship is referred to as the B surface. Further, the surface portion on the A surface side at the measurement position of the thickness of the DUT 1 is referred to as an A surface measurement site 1a, and the surface portion of the B surface facing the A surface measurement region 1a is referred to as a B surface measurement region 1b. Further, the measurement optical unit Z disposed to face the A surface is referred to as an A surface side measurement optical unit aZ, and the measurement optical unit Z disposed to face the B surface is referred to as a B surface side measurement optical unit bZ. Further, the phase detection circuit W provided for the A-plane side measurement optical unit aZ is used as the A-plane-side phase detection circuit aW, and the phase detection circuit W provided for the B-plane measurement optical unit bZ is used as the B-plane. This is referred to as a side phase detection circuit bW.
Although not shown in FIG. 1, the shape measuring apparatus X supports a peripheral portion of the object to be measured 1 (for example, three-point support), and the support portion in a two-dimensional direction (measured object). A moving mechanism for moving the object to be measured 1 in a two-dimensional direction by moving the object 1 in a two-dimensional direction parallel to both measurement surfaces of the object 1. Then, the shape measuring apparatus X obtains measurement values while changing the positions of the A-surface measurement site 1a and the B-surface measurement site 1b in the measurement object 1 by moving the device 1 by the moving mechanism. .

The light source unit Y includes a single-wavelength laser light source 2 that emits beam light P0 that is predetermined coherent light, an isolator 2x, a non-polarized beam splitter 3, two wavelength plates 2y, and two optical fiber connections. And a terminal 11.
The single wavelength laser light source 2 is a laser light source that outputs a single wavelength laser beam having a frequency ω0. For example, as the short-wavelength laser light source 2, a helium neon laser that outputs laser light having a wavelength of 633 nm may be employed. Hereinafter, for the sake of convenience, the light emitted from the short-wavelength laser light source 2 is referred to as basic light P0.
The beam splitter 3 is an example of the first light branching unit that splits the basic light P0 emitted from the single wavelength laser light source 2 into two.

Further, the shape measuring apparatus X has an input-side optical fiber a10 that guides each of the branched lights from the beam splitter 3 in the directions of the A-side measurement site 1a and the B-side measurement site 1b of the DUT 1, respectively. , B10. More specifically, one of the optical fibers a10 guides one of the branched lights to the A-side measurement optical unit aZ that is disposed to face the A-side of the DUT 1. The other optical fiber b10 guides the other of the branched lights to the B-side measurement optical unit bZ arranged to face the B-side of the DUT 1.
The optical fibers a10 and b10 are single mode optical fibers. Thereby, the polarization plane of the branched light transmitted through the optical fibers a10 and b10 is kept constant so as not to be disturbed in the middle.
Note that light guiding means such as a mirror may be provided instead of the optical fibers a10 and b10. However, in this case, it takes time to adjust the optical path of the branched light of the basic light P0.

The optical fiber connection terminal 11 is a terminal to which one end of each of the optical fibers a10 and b10 is connected.
The wave plate 2y is disposed between the beam splitter 3 and the light inlets of the optical fibers a10 and b10, and the polarization plane (polarized wave) of the branched light input to the optical fibers a10 and b10. Direction).
The isolator 2x is disposed between the single-wavelength laser light source 2 and the beam splitter 3, and reflected light from the beam splitter 3, entrances of the optical fibers a10 and b10, and the like. It is an optical element which prevents returning to (1). The isolator 2x can prevent the reflected light from returning to the single wavelength laser light source 2 and the light emitted from the single wavelength laser light source 2 from becoming unstable.

As shown in FIG. 1, the measurement optical unit Z includes an optical fiber connection terminal 12 on the input side, a non-polarized beam splitter 13 on the primary side, two acoustooptic elements 15 and 16, and heterodyne interference. A total of 20, a reference interferometer 30, and two optical fiber connection terminals 26 and 36 on the output side are provided.
The optical fiber connection terminal 12 is a terminal to which one end of the optical fibers a10 and b10 connected to the light source unit Y is connected. The branched light of the basic light P0 in the light source unit Y is introduced into the measurement optical unit Z through the optical fiber connection terminal 12.

The beam splitter 13 further splits the branched light of the basic light P0 guided in the direction of the measurement sites 1a and 1b on the front and back surfaces of the device under test 1 by the optical fibers a10 and b10, respectively. It is an example of the optical branching means.
The acousto-optic elements 15 and 16 are light that generates two measurement lights P1 and P2 having different frequencies by frequency-modulating each of the branched lights by the beam splitter 13 on the front and back sides of the device under test 1, respectively. It is an example of a modulation | alteration means.
For example, it is conceivable that one of the two acoustooptic elements 15 and 16 has a modulation frequency of 80 MHz and the other modulation frequency is about 81 MHz.
The two types of measurement lights P1 and P2 are single wavelength beam lights, respectively. The frequencies (ω, ω + Δω) of the measurement lights P1 and P2 are not particularly limited. For example, the frequency difference Δω between the two light beams is about several tens of kHz to several megaHz.

Further, the heterodyne interferometer 20 irradiates the measurement site 1a or 1b with one measurement beam P1 on each of the front and back sides of the object 1 to be measured, and the object beam that is the measurement beam P1 reflected at the measurement site. And an interferometer that interferes with the reference light that is the other measurement light P2. One heterodyne interferometer 20 is provided for each of the two measurement optical units Z.
As shown in FIG. 1, the heterodyne interferometer 20 includes a polarizing beam splitter 21, a quarter-wave plate 22, a non-polarizing beam splitter 24, and a polarizing plate 25.
The polarization beam splitter 21 passes one measurement light P1 in the direction of the measurement site 1a or 1b and reflects the object light that is the measurement light P1 reflected by the measurement site 1a or 1b in a predetermined direction. To do.
The quarter-wave plate 22 is disposed between the polarization beam splitter 21 and the measurement site 1a or 1b. Due to the presence of the quarter-wave plate 22, the polarization state of the measurement light P1 (P-polarized light or S-polarized light) from the polarization beam splitter 21 toward the measurement site 1a or 1b, and the measurement site 1a or 1b The state of polarization of the object light, which is the measurement light P <b> 1 that is reflected by and reflected on the polarization beam splitter 21, is switched.
The measurement optical unit Z also includes a condensing lens 23 that is disposed opposite to the surface of the device under test 1. The condensing lens 23 condenses the measurement light P1 on the measurement site 1a or 1b and makes the object light reflected by the measurement site 1a or 1b enter the polarization beam splitter 21 along the optical axis of the forward path. Let
The beam splitter 24 aligns the optical axes of the object light that is the reflected light of the one measurement light P1 at the measurement site 1a or 1b and the reference light that is the other measurement light P2 in the same direction. The optical element to guide.
Further, the polarizing plate 25 receives the object light and the reference light whose optical axes coincide with each other by the beam splitter 24, and extracts the polarization components in the same direction, thereby interference between the object light and the reference light. It is an optical element that outputs light Ps.
Hereinafter, the interference light Ps of the object light and the reference light obtained by the heterodyne interferometer 20 is referred to as measurement interference light Ps.
The heterodyne interferometer 20 is also provided with a deflecting element such as a mirror for redirecting one or both of the two measurement beams P1 and P2 as necessary.

In addition, the reference interferometer 30 converts the two measurement lights P1 and P2 into the main light input to the heterodyne interferometer 20 and the other auxiliary light on the front and back sides of the device under test 1, respectively. It is an interferometer that causes the two auxiliary lights to interfere while branching.
As shown in FIG. 1, the reference interferometer 30 includes three non-polarized beam splitters 31, 32, and 34 and a polarizing plate 35.
The beam splitters 31 and 32 split the two measurement lights P1 and P2 into the main light input to the heterodyne interferometer 20 and the other auxiliary light on the front and back sides of the object to be measured, respectively. 3 is an example of a third optical branching unit.
The beam splitter 34 is an optical element that matches the optical axes of the two sub-lights that are branched lights of the two measurement lights P1 and P2 by the beam splitters 31 and 32 and guides them in the same direction.
The polarizing plate 35 receives the two sub-lights whose optical axes coincide with each other by the beam splitter 34, and outputs the interference light Pr of the two sub-lights by extracting the polarization components in the same direction. It is an element.
The beam splitter 34 and the polarizing plate 35 are an example of a secondary light interference unit that causes the secondary light to interfere with each other on the front and back of the DUT 1.
Hereinafter, the two interference lights Pr of the secondary light obtained by the reference interferometer 30 will be referred to as reference interference lights Pr.
Note that the reference interferometer 30 is also provided with an optical element such as a mirror for changing the optical path of one or both of the two sub-lights as necessary. The reference interferometer 30 shown in FIG. 1 includes a mirror 33 that redirects the branched light of the measurement light P2.

One optical fiber connection terminal 26 on the output side is a terminal to which one end of an optical fiber a27 or b27 for transmitting the measurement interference light Ps to a measurement photodetector b28 described later is connected. One optical fiber a27 transmits the measurement interference light Ps on the A surface side of the DUT 1, and the other optical fiber b27 is on the B surface side of the DUT 1. The measurement interference light Ps is transmitted.
The other optical fiber connection terminal 36 on the output side is a terminal to which one end of an optical fiber a37 or b37 for transmitting the reference interference light Pr to a reference photodetector b38 to be described later is connected. One optical fiber a37 transmits the reference interference light Pr on the A surface side of the DUT 1, and the other optical fiber b37 is provided on the B surface side of the DUT 1. The reference interference light Pr is transmitted.
Since the measurement interference light Ps and the reference interference light Pr do not need to hold a wavefront in the transmission path, the optical fibers a27, a37, b27, and b37 on the output side are general multimode optical fibers. Is adopted. Here, single-mode optical fibers may be employed as the optical fibers a27, a37, b27, and b37.
In general, a multi-mode optical fiber has a fiber core diameter larger than that of a single-mode optical fiber, can easily adjust the optical axis of propagating light, and can propagate a larger amount of light. Therefore, it is preferable to use a multimode optical fiber as the optical fibers a27, a37, b27, and b37 on the output side from the viewpoint of optical axis adjustment and the superiority of the amount of propagating light.

As shown in FIG. 1, the phase detection circuit W includes a measurement photodetector 28, a reference photodetector 38, amplifiers 29 and 39 for signal amplification of the measurement system and the reference system, and a phase detector. 4 and a shield plate 8.
The measurement photodetector 28 is a photoelectric conversion element that receives the measurement interference light Ps obtained by the heterodyne interferometer 20 and outputs the intensity signal Sig1 or Sig2. The intensity signal Sig1 is a signal obtained on the A plane side of the device under test 1, and the intensity signal Sig2 is a signal obtained on the B surface side of the device under test 1.
Hereinafter, the intensity signals Sig1 and Sig2 are referred to as measurement beat signals Sig1 and Sig2.
The reference photodetector 38 is a photoelectric conversion element that receives the reference interference light Pr obtained by the reference interferometer 30 and outputs the intensity signal Ref1 or Ref2. The intensity signal Ref1 is a signal obtained on the A surface side of the device under test 1, and the intensity signal Ref2 is a signal obtained on the B surface side of the device under test 1.
Hereinafter, the intensity signals Ref1 and Ref2 are referred to as reference beat signals Ref1 and Ref2.

The phase detector 4 includes the measurement beat signal Sig1 or Sig2 that is an output signal of the measurement photodetector 28 and the reference beat signal Ref1 or Ref2 that is an output signal of the reference photodetector 38. The electronic component detects the phase difference ΔΦ1 or ΔΦ2 between the two beat signals by performing phase detection of the two beat signals. That is, the phase detector 4 in the phase A side phase detection circuit aW detects a phase difference ΔΦ1 between the measurement beat signal Sig1 and the reference beat signal Ref1. In addition, the phase detector 4 in the B-side phase detection circuit bW detects a phase difference ΔΦ2 between the measurement beat signal Sig2 and the reference beat signal Ref2.
The difference (ΔΦ1−ΔΦ2) of the phase difference between the two beat signals obtained for each of the front and back surfaces of the device under test 1 is a measurement value representing the thickness of the device under test 1.
The two phase detectors 4 on the A plane side and the B plane side simultaneously perform phase detection of the two beat signals in synchronization with the synchronization signal output from the computer 6. Thereby, the difference (ΔΦ1−ΔΦ2) of the phase difference between the two beat signals represents the thickness of the device under test 1 without being affected by the vibration of the device under test 1.
For example, a lock-in amplifier or the like can be used as the phase detector 4.
The phase detector 4 is an example of the phase information detecting means.

The shield plate 8 includes a signal transmission path from the measurement photodetector 28 to the phase detector 4 and a signal transmission path from the reference photodetector 38 to the phase detector 4. It is a metal plate arranged between them.
If the measurement photodetector 28, the reference photodetector 38, and the phase detector 4 are arranged close to each other in order to make the apparatus compact, unnecessary radiation of electromagnetic waves generated from one beat signal transmission path is generated. The other beat signal interferes with noise and degrades measurement accuracy. In order to realize sub-nanometer order shape measurement accuracy, it is necessary to suppress the noise component of mutual interference due to unnecessary radiation to less than 0.5% of the signal component.
Due to the presence of the shield plate 8, it is possible to prevent the measurement accuracy from deteriorating due to the unnecessary radiation.
Further, in order to suppress mutual interference due to the unnecessary radiation, it is desirable that the interval between the transmission paths of the two beat signals is about 20 mm or more.

Further, the calculator 6 calculates a measured value of the thickness of the DUT 1 according to the difference (ΔΦ1−ΔΦ2) of the phase difference between the two beat signals obtained for the front and back sides of the DUT 1. A thickness calculation process is executed.
Specifically, the calculator 6 calculates the measured value Ds of the thickness of the DUT 1 by substituting the phase differences ΔΦ1 and ΔΦ2 of the two beat signals into the following equation (d1).
Ds = (ΔΦ1-ΔΦ2) × (λ / 2) / (2π) (d1)
In the equation (d1), λ is the wavelength of the measurement light P1. The equation (d1) is an equation based on an approximation that the wavelength of the measurement light P2 is equal to the wavelength of the measurement light P1. Further, the equation (d1) is obtained when the relationship between which one of the two measurement beams P1 and P2 is the object beam or the reference beam is the same in the measurement optical unit Z on the A side and the B side, that is, This is an expression in the case where the relationship between the frequency of the object light and the frequency of the reference light is the same on the A plane side and the B plane side.
On the other hand, in the measurement optical unit Z on the A surface side and the B surface side, when the conditions regarding which of the two measurement beams P1 and P2 are the object beam or the reference beam are reversed, that is, on the A plane side and The equation for calculating the measured value Ds of the thickness of the DUT 1 when the relationship between the frequency of the object light and the frequency of the reference light is opposite on the B side is the following equation (d2).
Ds = (ΔΦ1 + ΔΦ2) × (λ / 2) / (2π) (d2)

Next, a specific example of the structure of the measurement optical unit Z will be described with reference to FIG. FIG. 2 is a schematic configuration diagram of an example of the measurement optical unit Z. FIG. 2 shows a side view (a) of the measurement optical unit Z. In FIG. 2, the same components as those shown in FIG. 1 are denoted by the same reference numerals.
Various optical elements included in the measurement optical unit are integrally held by a predetermined optical system holder 70 on each of the front and back sides of the DUT 1.
FIG. 2B is a side view of the optical system holder 70 viewed from a direction different from 90 ° with respect to the viewing direction of the side view of FIG.
Hereinafter, the devices included in the measurement optical unit, that is, the optical fiber connection terminals 12, 26, 36, the beam splitter 13, the acoustooptic elements 15, 16, the heterodyne interferometer 20, and the reference interferometer 30, And the condenser lens 23 are collectively referred to as a measurement optical system.
The optical system holder 70 is a rigid body having a plate-like holding part 71 that shares and holds part or all of the measurement optical system on each of the front and back sides. The plate-like holding portion 71 is formed with a through hole 71h through which the light beam propagating through the measurement optical system passes. For example, the plate-shaped holding unit 71 holds the remaining optical elements other than the condenser lens 23 in the measurement optical system.
As shown in FIG. 2, the optical system holder 70 holds the measurement optical system three-dimensionally on both sides of the plate-like holding portion 71. Thereby, the plate-like holding portion 71 holding the measurement optical system can be made small, and the small plate-like holding portion 71 can ensure sufficient rigidity even if a relatively thin and lightweight member is adopted. Therefore, the optical system holder 70 having a small and very simple structure can prevent occurrence of a phase shift between the two types of the measurement light beams P1 and P2 due to the deformation (deflection) of the plate-like holding portion 71. .
For example, the optical system holder 70 has a size of about 150 mm × 90 mm × 100 mm and can integrally hold the measurement optical system.
In FIG. 2A, the description of the support member that fixes the measurement optical system to the plate-like holding portion 71 is omitted.

Further, the plate-like holding portion 71 is a member reinforced by fixing its edge to another member.
In the example shown in FIG. 2, the plate-like holding portion 71 is a rectangular plate material, and the three side edges thereof are fixed to three reinforcing plates 72 to 74 that are connected in a bent shape, thereby reinforcing the plate-like holding portion 71. Has been.
Further, in the example shown in FIG. 2, a through hole 74 h that passes in the direction of the DUT 1 is also formed in one of the reinforcing plates 74, and the through hole 74 h is an optical path of the measurement light P <b> 1. ing. The condensing lens 23 is held on the reinforcing plate 74.
The optical system holder 70 is made of a metal member such as stainless steel, iron, or aluminum.

Next, a mechanism for scanning the surface of the DUT 1 with the shape measuring device X will be described with reference to FIG.
As shown in FIG. 3, the shape measuring apparatus X includes a movable support device 40 that movably supports the device under test 1.
The shape measuring apparatus X can measure the thickness of a specific part of the device under test 1 with high accuracy and high speed without being affected by the vibration of the device under test 1.
Then, the shape measuring apparatus X supports the device under test 1 at its center, end, or the like, and places the device under test 1 in a plane perpendicular to its thickness direction (on the front and back surfaces of the device under test 1). A movable support device 40 is provided which scans the object to be measured 1 while moving in a parallel plane.

The movable support device 40 shown in FIG. 3 is configured so that the disk-shaped object 1 such as a semiconductor wafer 3 is supported by support portions 44 arranged at three locations on the circumference at the edge (edge portion). Point support. These three support portions 44 are connected to a rotation shaft 41 extending toward the center of the circumference.
Further, the support shaft 41 is rotationally driven by a rotational drive unit 42 such as a servo motor. As a result, the DUT 1 is rotated with its center portion as the center of rotation.
Further, the support shaft 41 and the rotation drive unit 42 are linearly moved within a predetermined movement range in a direction parallel to the front and back surfaces of the DUT 1 (direction perpendicular to the thickness direction) by the linear movement mechanism 43. Is done. That is, the linear movement mechanism 43 moves the device under test 1 along its radial direction.
Further, the flexible support device 40 including the support shaft 41, the rotation drive unit 42, and the linear movement mechanism 43 includes the irradiation position of the measurement light P1 by the heterodyne interferometer 20 on the A plane side and the B The object to be measured 1 is supported between the irradiation position of the measurement light P1 by the heterodyne interferometer 20 on the surface side.

Then, by using both the rotation of the device under test 1 by the rotation drive unit 42 and the movement of the device under test 1 in the linear direction by the linear movement mechanism 43, the measurement site 1a of the device under test 1 is measured. , 1b, the thickness is measured by the shape measuring device X while the position is sequentially changed.
For example, while continuously rotating and linearly moving the object to be measured 1 at a constant speed, the computer 6 is configured so that the measurement point 1a, 1b becomes a predetermined position every time the measurement point 1a, 1b becomes a predetermined position. Data of the phase differences ΔΦ1 and ΔΦ2 on the A plane side and the B plane side are acquired from the phase detector 4. Further, the calculator 6 calculates the thickness Ds of the DUT 1 by substituting these two phase differences ΔΦ1 and ΔΦ2 into the equation (c1).
FIG. 4 is a schematic diagram showing an example of the distribution of the measurement sites 1a and 1b in the DUT 1.
When the phase of the interference light is sequentially detected while rotating and linearly moving the device under test 1, the positions of the measurement sites 1 a and 1 b are spirals on the surface of the device under test 1 as shown in FIG. 4. It changes sequentially along a line (wave line).
Then, if the thickness measurement is sequentially performed by moving the holding position of the DUT 1 in the two-dimensional direction by the movable support device 40 and the measurement data is stored in a predetermined storage unit, the DUT 1 Thickness distribution data is obtained.
Here, when the disk-shaped object to be measured 1 is thin, if the object to be measured 1 is supported in part as shown in FIG. Vibrate. However, even if the device under test 1 vibrates in this way, the shape measuring apparatus X can measure the thickness distribution of the device under test 1 with high accuracy without being affected by the vibration.
In addition, the mechanism for positioning the device under test 1 in a plane parallel to the surface thereof crosses the support portion of the device under test 1 such as a so-called XY plotter in addition to the mechanism shown in FIG. It may be a mechanism that moves along two straight lines.

FIG. 5 is a graph showing an example of the time series change of the measurement value of the conventional shape measuring apparatus, and FIG. 6 is a graph showing an example of the time series change of the measurement value of the shape measuring apparatus X. Here, in the conventional shape measuring apparatus, the reference interferometers 30 on the A-side and B-side are respectively sent from the position of the light source to the two measuring beams P1, P2 having slightly different frequencies by using an optical fiber. And a device for measuring the thickness of the DUT 1 by transmitting to the position of the heterodyne interferometer 20. In the conventional shape measuring apparatus and the shape measuring apparatus X, the two optical beams P1 and P2 or the branched light of the basic light P0 are transmitted from the position of the light source to both surfaces of the object 1 to be measured. On the other hand, no measures are taken to prevent vibration.
As shown in FIG. 5, in the conventional shape measuring apparatus, the measured value of the thickness largely fluctuates due to noise such as vibration of the transmission path of the two measuring beams P1 and P2.
On the other hand, the shape measuring apparatus X can obtain a stable thickness measurement value even though no signal prevention measures are taken for the optical fibers a10 and b10.
Therefore, according to the shape measuring apparatus X, it is not affected by the vibration of the device under test 1 and the vibration of the transmission medium of the branched light of the basic light P0 from the single wavelength laser light source 2 to the measurement optical unit Z. In addition, the thickness of the DUT 1 can be easily measured with high accuracy.

  The present invention is applicable to a shape measuring apparatus for an object to be measured such as a semiconductor wafer.

X: shape measuring apparatus Y according to an embodiment of the present invention Y: light source unit Z: measurement optical unit W: phase detection circuit 1: measured object 1a, 1b: measurement site 2: single wavelength laser light source 3: beam splitter 4: phase Detector 6: Computers 11, 12, 26, 36: Optical fiber connection terminals 15, 16: Acousto-optic element 20: Heterodyne interferometer 30: Interferometer for reference 40: Movable support devices a10, b10: Optical fiber a27 on the input side , B27, a37, b37: output side optical fiber P0: backbone light P1, P2: measurement light

Claims (3)

A shape measuring device used for scanning the front and back surfaces of a measured object to measure the thickness distribution of the measured object in a non-contact manner,
First light branching means for branching the basic light emitted from a predetermined light source;
A light guiding means for guiding each of the branched lights by the first light branching means in the respective directions of the measurement parts opposite to the front and back surfaces of the object to be measured;
Second light branching means for further branching the branched light of the basic light guided in the direction of the measurement site on each of the front and back sides of the object to be measured;
Light modulating means for performing frequency modulation on one or both of the branched lights by the second light branching means on each of the front and back sides of the object to be measured to generate two measurement lights having different frequencies,
In each of the front and back sides of the object to be measured, one measurement light is irradiated onto the measurement site, and the object light that is one measurement light reflected from the measurement site interferes with the reference light that is the other measurement light. Two heterodyne interferometers to be
Third optical branching means for bifurcating each of the two measurement lights into main light input to the heterodyne interferometer and other auxiliary light on each of the front and back sides of the object to be measured;
Sub-light interference means for causing the two sub-lights branched by the third light branch means to interfere with each other on the front and back sides of the object to be measured;
Measurement optical systems including the second optical branching unit, the optical modulation unit, the heterodyne interferometer, the third optical branching unit, and the auxiliary optical interference unit are integrally held on the front and back sides of the object to be measured. Measuring optical system holding means;
A measuring light intensity detecting means for receiving interference light obtained by the two heterodyne interferometers and outputting an intensity signal thereof;
A reference light intensity detecting means for receiving interference light obtained by the auxiliary light interference means and outputting an intensity signal on each of the front and back sides of the object to be measured;
The phase difference between the two beat signals is detected by phase detection of two beat signals composed of the output signal of the measurement light intensity detection means and the output signal of the reference light intensity detection means on the front and back sides of the object to be measured. Phase information detection means;
A shape measuring apparatus comprising:   The measurement optical system holding means is a rigid body having a plate-like holding portion that shares and holds the measurement optical system on each of the front and back sides, and allows light propagating through the measurement optical system to pass through the plate-like holding portion. The shape measuring apparatus according to claim 1, wherein a through hole is formed.   Metal made between a signal transmission path from the measurement light intensity detection means to the phase information detection means and a signal transmission path from the reference light intensity detection means to the phase information detection means The shape measuring apparatus according to claim 1, comprising a shield plate.

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