JP2527877B2 - Two-dimensional deformation detection device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-dimensional deformation detecting device for detecting two-dimensional deformation of an object to be measured by using optical heterodyne interferometry.

[0002]

2. Description of the Related Art Conventionally, the following optical interferometers have been used to measure this type of two-dimensional deformation.

First, there is the device shown in FIG.

The laser light emitted from the excitation laser 1 is intermittently applied to the back surface of the DUT 3 placed in the high temperature furnace 2. Therefore, the DUT 3 is rapidly heated, and ultrasonic waves are generated by the thermal stress generated at this time. This ultrasonic wave is detected as a surface displacement by a Michelson interferometer arranged on the opposite side of the DUT 3. The Michelson interferometer comprises an interference laser 4, a half mirror 5, a reference mirror 6 and a photoelectric detector 7. Laser for interference 4
The laser light emitted from becomes the measurement light and the reference light,
The measurement light is applied to the DUT 3, and the reflected light interferes with the reference light. This interference light is converted into an electric signal by the photoelectric detector 7 and observed by the digital oscilloscope 8. By this observation, a predetermined physical property value such as the elastic modulus of the surface of the DUT 3 is measured.

Second, there is the device shown in FIG.

The light from the interference laser (He-Ne laser) 11 is guided to the interference objective lens 13 by the single mode optical fiber 12. This light is emitted from the beam splitter 14
As a result, the surface of the DUT 16 on the stage 15 is irradiated, and the reflected light and the reference light from the reference mirror 17 interfere with each other. On the other hand, pumping laser (Ar laser) 18
Light is interrupted by a chopper 19 made of a rotating disk having holes, and guided to a microscope 21 by a multimode optical fiber 20. The guided light is reflected by the dichroic mirror 22 and focused on the surface of the DUT 16 by the interference objective lens 13. After passing through the dichroic mirror 22, the light from the interferometer is photoelectrically converted by the photoelectric detector 23, and the photothermal vibration displacement of the surface of the DUT 16 is measured.
From this photothermal vibration displacement, the thermal properties, light absorption properties, etc. of the DUT 16 are detected.

Third, there is the device shown in FIG.

This device is a device for performing more accurate measurement by using the optical heterodyne interferometry. The beam expander 32 expands the diameter of the laser light of frequency f ₀ and makes it enter the half mirror 33. One of the laser lights incident on the half mirror 33 becomes reference light, passes through the frequency shifter 34, and is reflected by the reference mirror 35, and its frequency is f.
_It is shifted to ₀ + 2Δf. Further, the other laser light becomes measurement light and is irradiated on the DUT 36. These laser lights are combined again by the half mirror 33, and an interference image is formed on the observation surface by the condenser lens 37. This interference image is observed when the measurement photoelectric detector 38 and the reference photoelectric detector 39 are scanned under the observation surface and each signal is captured by the phase meter 40. Then, by comparing with the signal at the reference point, the measurement can be performed with an accuracy of about λ / 100.

[0009]

However, in each of the above-mentioned first and second conventional devices, a beam-shaped laser beam is emitted from the laser source, so that the point-like light beam is emitted to the sample to be measured. Is being irradiated. Therefore,
Only the deformation of a certain point part of the measured sample is measured. In order to measure the deformation of an object in a two-dimensional area having a certain range, it is necessary to irradiate a sample to be measured with laser and scan a photodetector for detecting this laser light. Therefore, a scanning system is required for the device, and it takes time to measure the two-dimensional deformation.

Further, in the above-mentioned third conventional device,
Since the diameter of the laser light output from the laser light source is widened, it is not necessary to scan the laser light as described above.
However, it is necessary to scan the photoelectric detector that detects the laser light below the observation surface where the interference image is formed. Therefore, also in the third device, mechanical scanning is required, and the measurement takes time.

Further, in each of the above-mentioned conventional devices, there is a problem that the deformation measurement can be performed only on a sample such as a semiconductor wafer that reflects light.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and a laser light source for irradiating a laser beam on a measured object to cause displacement on the surface of the measured object, First heterodyne interference means for converting the first two-dimensional optical phase information about the surface of the object to be measured into a first two-dimensional optical phase information signal, and a predetermined time converted by the first heterodyne interference means A part of the first two-dimensional optical phase information signal on the surface of the object to be measured having a specific carrier frequency is used as a reference second two-dimensional optical signal having a predetermined temporal carrier frequency. A second heterodyne interfering means for converting into a phase information signal and a first heterodyne interfering means for converting the first and second two-dimensional signals from the first and second optical heterodyne interfering means into two-dimensional binarized optical information, respectively. First and second binarizing means, and first and second binarizing means Arithmetic means for giving a two-dimensional logical product optical signal between the two-dimensional binary optical information from the quantizing means, and integrating means for integrating the two-dimensional logical product optical signal output from the arithmetic means. The two-dimensional deformation detection device is configured by including.

When the object to be measured is a light scattering object, a light non-absorbing medium and a light reflecting object are provided behind the surface to be measured.

[0014]

Function: The displacement generated on the surface of the object to be measured is the first and second
Of the first and second two on the predetermined temporal carrier frequency of
It is detected as the phase difference of the dimensional signal.

Further, by providing the light non-absorbing medium and the light reflecting object behind the surface to be measured, the surface displacement of the light scattering object is efficiently propagated to the reflecting object via the light non-absorbing medium.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the entire two-dimensional deformation detecting apparatus according to an embodiment of the present invention.

The two-dimensional deformation detecting apparatus according to the present embodiment comprises the first and second optical heterodyne interference means 51, 52 and the first optical heterodyne interference means 51, 52.
And a second threshold value element 53, 54, a beam splitter 55, an optical logical product calculating means 56, a two-dimensional integrating element 57 and a laser light source 58.

The laser light source 58 comprises an exciting laser 59 and a condenser lens 60, and irradiates the object 61 to be measured with laser light to cause displacement on the surface of the object 61. The first optical heterodyne interfering means 51 converts the first two-dimensional optical phase information about the measured surface of the measured object 61 into a first two-dimensional signal having a predetermined temporal carrier frequency. To do. The second optical heterodyne interference means 52 converts the reference second two-dimensional optical phase information into a second two-dimensional signal having a predetermined temporal carrier frequency. First and second
Of the threshold elements 53 and 54 convert the first and second two-dimensional signals from the first and second optical heterodyne interference means 51 and 52 into two-dimensional binarized optical information, respectively. The optical logical operation element 56 includes the first and second threshold elements 5
The two-dimensional binarized optical information from 3, 54 is taken in via the beam splitter 55, and a two-dimensional logical product optical signal between the respective binarized optical information is generated. The two-dimensional integration element 57 is
The two-dimensional logical product optical signal output from the optical logical operation element 56 is integrated.

The object 61 to be measured is usually a reflecting object such as a semiconductor wafer whose surface to be measured is mirror-polished, but it may be a non-specular light-scattering object as well as a reflecting object. However, in this case, as shown in FIG. 2, a light non-absorbing medium 69 and a light reflecting object 70 such as a mirror are provided behind the surface to be measured of the non-mirror-like scattering object 68, and further, the light reflecting object 70. Is covered with glass 71. In this way, the surface displacement of the scattering object 68 is efficiently reflected by the reflecting object by adopting a configuration in which the measured surface of the scattering object 68, which is the object to be measured, and the reflecting object 70 are attached via the non-absorbing medium 69. ,
This reflected light can be used as the measurement light.

The excitation laser 59 shown in FIG. 1 is a CO ₂ laser. When this CO ₂ laser is controlled by the drive controller, the excitation laser 59
Is a laser beam with a wavelength of 10.6 μm and an output of 3 W at 5 kHz
It oscillates intermittently in the cycle of z. The oscillated laser light is expanded to a beam diameter of about φ20 by a condenser lens 60 having a focal length f100, and is radiated to the DUT 61. The object 61 to be measured generates heat by this laser light irradiation, and the surface to be measured repeatedly expands and contracts to generate ultrasonic waves. This expansion / contraction causes photothermal vibration displacement on the surface to be measured,
By measuring the spatial distribution of this photothermal vibration displacement, that is, the two-dimensional deformation, it becomes possible to detect the fine structure and defects under the surface to be measured. For example, this two-dimensional deformation is shown in FIG. FIG. 9A shows a state before the laser beam L is irradiated on the DUT 61. FIG. 3B shows a state in which the back surface of the object 61 to be measured is irradiated with the laser light L, and the surface to be measured of the laser light L undergoes photothermal vibration displacement and is curved. From the spatial distribution of this photothermal vibration displacement, it is confirmed that no defect exists inside the DUT 61. Further, FIG. 7C shows the surface to be measured when a defect exists inside the object 61 to be measured. Non-uniformity appears in the propagation of heat and ultrasonic waves generated on the back surface of the sample due to the irradiation of the laser beam L to the surface of the sample, and a dent corresponding to the defect occurs on the surface to be measured.

The first optical heterodyne interference means 51 of FIG.
For this, the conventional optical heterodyne interferometer shown in FIG. 8 can be used. A He-Ne laser having a wavelength of 632.8 nm and an output of 1 mW is used as the interference laser 62 of the optical interferometer. The beam-shaped laser light emitted from the interference laser 62 is converted into parallel light by the spatial filter 63 and the collimator lens 64 having the focal length f300. A part of the converted parallel light is a half mirror 65.
Is reflected by the reference mirror 66 of the interferometer. In front of the reference mirror 66, an acousto-optic modulator (AOM: AOM: AFM) whose frequency changes by Δf by applying a voltage.
acousto optical modulator) 67 is provided.
When the laser light is reflected from the half mirror 65 and returns to the original state, a frequency change of 2Δf occurs in the laser light, and the light having the changed frequency becomes the reference light. In addition, part of the parallel light from the collimator lens 64 is partially reflected by the half mirror 6.
5 is transmitted as it is, and the DUT 61 is irradiated with the measurement light. That is, two types of laser light having different frequencies are used for measurement, and the device according to this embodiment is a device to which a so-called optical heterodyne interferometer is applied.

Here, the principle of the heterodyne interferometry for converting the two-dimensional optical phase information into a two-dimensional signal will be briefly described below. Consider on the arbitrary x-axis of the observation plane.

The two-dimensional optical phase information of the surface to be measured of the object to be measured 61 is projected on the surface of the threshold element 53, and the object to be measured at time t at an arbitrary point x on the projected surface. The measurement light from 61 and the reference light from the reference mirror 66 are expressed as follows, respectively.

U _r (t) = u _r · exp {i [2π (f ₀ + 2Δf) t + φ _r ]} U ₀ (x, t) = u ₀ (x) · exp {i [2πf ₀ t + φ ₀ (x )]} Here, U _r and φ _r represent the amplitude and phase of the reference light, respectively. Further, U ₀ (x) and φ ₀ (x) represent the amplitude and phase of the measurement light, respectively. Therefore, the intensity of the light detected at the point x is given by the following equation.

I (x, t) = | U _r (t) + U ₀ (x, t) | ² = u _r ² + u ₀ (x) ² + 2u _r · u ₀ (x) cos [4πΔft + φ _r −φ ₀ (x)] As can be seen from this equation, the intensity of the detection light changes sinusoidally at the frequency 2Δf of the difference between the measurement light and the reference light, and the phase φ _r −φ ₀ (x) is the same for both laser lights. Optical phase difference between them (optical path length difference in wavelength units). That is, the optical phase difference between the two laser beams can be converted into the phase difference between the intensity-modulated temporal carriers.

The above description relates to the conversion of the phase difference along the x-axis, but in the y-axis direction having the direction perpendicular to the x-axis in the observation plane, the intensity modulation from the optical phase difference is performed by the same principle. Can be converted into a phase difference of. As a result, the two-dimensional optical phase information can be converted into a two-dimensional signal having a predetermined temporal carrier frequency.

The first two-dimensional signal IN1 output from the first optical heterodyne interfering means 51 is the half mirror 7.
2 to the threshold element 53. Focusing on a certain point on the surface of the threshold element 53, the first two-dimensional signal IN1 has a temporal light intensity as shown in FIG. 4 due to the flow of interference fringes due to the AOM 67. It changes like a sine wave. The two-dimensional signal IN1 is binarized at a predetermined light intensity value by passing through a threshold element 53 formed of, for example, a nonlinear etalon gate array,
It is converted into three-dimensional binarized optical information TH1. Therefore, the signal waveform changes from a sine waveform to a rectangular waveform.

On the other hand, the second optical heterodyne interference means 52
The information of one point of the two-dimensional signal IN1 output from the first optical heterodyne interference means 51 is two-dimensionally uniformly expanded, and this is output as a second two-dimensional signal, that is, a reference signal. To do. It should be noted that the same reference signal is generated by using the output of another interferometer instead of the output of the first interfering means 51. The light output partially reflected by the half mirror 72 is taken in through a hole formed in the aperture 73, and the beam diameter is expanded by the spatial filter 74.
The laser light whose beam diameter has been expanded is further converted into parallel light by the collimator lens 75. This parallel light is the second two-dimensional signal IN2 that serves as a reference signal, and is projected on the threshold element 54 through the optical path defined by the total reflection mirrors 76 and 77. In this two-dimensional signal IN2, since the information of one point of the interference fringes flowing with time is taken out from the first interference means 51, the light intensity is shown in FIG. The sinusoidal waveform shown in Fig. 3 is obtained, and exactly the same information is generated on the element plane. This two-dimensional signal IN2 passes through a threshold element 54 composed of a non-linear etalon gate array, etc.
It is binarized and converted into the second two-dimensional binarized optical information TH2 having the rectangular waveform shown in FIG.

The two-dimensional binarized optical information TH1 and TH2 emitted from the threshold elements 53 and 54 are combined by the cum beam splitter 55 and are incident on the optical logical operation element 56. The optical logical operation element 56 is composed of a non-linear etalon gate array or the like, and the two-dimensional binarized optical information TH1,
The optical logical product (signal light AND) at each point of TH2 is taken to generate a two-dimensional logical light signal and output it to the integrating element 57. This signal light AND is, for example, as shown in FIG. The integrating element 57 is composed of a two-dimensional CCD array or the like and integrates the two-dimensional logical light signal. That is, the two-dimensional logical product optical signal emitted from the logical operation element 56 is flattened at each point, and the output of the first interference unit 51 and the second
The phase difference of the optical phase information output from the interference means 52 is detected as a charge distribution corresponding to these phase differences. This charge distribution is shown in the signal INT shown in FIG. 4, for example.
That is, this charge distribution corresponds to the unevenness distribution on the surface of the DUT 61.

Regarding the measurement accuracy of this uneven distribution measurement,
If it is estimated that detection is possible even if one set of interference fringes is divided into 100, it is possible to measure up to about λ / 100, that is, an accuracy of several nm.

As described above, according to the two-dimensional deformation detecting apparatus of the present embodiment, the displacement generated on the surface of the DUT 61 is the first and second predetermined temporal carrier frequencies. And the phase difference of the second two-dimensional signal. Therefore, the surface displacement of the DUT 61 can be two-dimensionally measured in a non-contact and non-invasive manner. By providing the light non-absorbing medium 69 and the light reflecting object 70 behind the surface to be measured, the surface displacement of the light scattering object is efficiently propagated to the reflecting object 70 via the light non absorbing medium 69. For this reason,
According to the apparatus of this embodiment, the two-dimensional deformation of the sample surface can be measured even if the DUT 61 is a light scattering object.

In the above description of the embodiment, the DUT 6
Although the CO ₂ laser was used as the excitation laser 59 for irradiating the laser beam on the _first laser beam, it is not necessary to limit to this CO ₂ laser, and a laser using external modulation of a Q-switch Nd: YAG laser or a high-power semiconductor laser, that is, a high Any laser with high output or peak power may be used. In addition, the threshold element 53,
As the 54 and the logical operation element 56, a two-dimensional optical bistable element using, for example, a spatial light modulator (MSLM), a liquid crystal spatial light modulator (LCLV) or the like can be used in addition to the nonlinear etalon gate array. Needless to say, various two-dimensional photodetectors other than the CCD array can be used as the integrating element 57. In each of these cases, the same effect as that of the above-described embodiment can be obtained.

Further, the excitation laser light with which the DUT 61 is irradiated may be irradiated from the reflection side constituting the interferometer, and the same effect as that of the above-mentioned embodiment can be obtained.

Next, a two-dimensional deformation detecting device according to another embodiment of the present invention will be described.

FIG. 5 is a block diagram showing the outline of this apparatus. The same or corresponding parts as in FIG. 1 are designated by the same reference numerals and the description thereof is omitted. In the figure, the first
The description of the optical heterodyne interference means 51 and the laser light source 58 is omitted.

The structure of the optical system which is provided with the first interference means and the second interference means and binarizes and integrates the two-dimensional signal and the reference signal is the same as that of the above-mentioned embodiment. However, there are the following configuration differences. That is, the hologram 80 is provided on the detection side of the interferometer. When the detection light in a state where the excitation laser is not applied to the DUT 61 is recorded in the hologram 80 and the excitation laser is applied, moire fringes are observed on the hologram 80. When the frequency of the reference light is changed by the AOM 67, moire fringes flow, and when there is a defect inside the DUT 61, a change appears in the way the moiré fringes flow. This change is optically detected as an internal defect of the DUT 61.

According to each of the above-mentioned embodiments, there is provided a device for two-dimensionally detecting and evaluating internal information such as physical properties and defects of an object and surface information in a non-contact and non-invasive manner.

[0038]

As described above, according to the present invention, the displacement generated on the surface of the object to be measured has the first and second predetermined temporal carrier frequencies. It is detected as a phase difference between two-dimensional signals. Therefore, by processing the first and second two-dimensional signals from the optical heterodyne interference means in parallel and obtaining the phase difference between the first and second two-dimensional signals, the two-dimensional surface of the DUT is measured. The deformation is detected in a non-contact, non-invasive manner, with high accuracy and at high speed.

By providing the light non-absorbing medium and the light reflecting object behind the surface to be measured, the surface displacement of the light scattering object is efficiently propagated to the reflecting object via the light non-absorbing medium. Therefore, it is possible to detect the two-dimensional deformation of the light scattering object.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of a two-dimensional deformation detection device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram for attaching the light scattering object to an interferometer when the light scattering object is an object to be measured.

FIG. 3 is a diagram showing an example of a surface displacement of an object to be measured before and after irradiation with an excitation laser.

FIG. 4 is a diagram showing a signal waveform in each part of the apparatus according to the present embodiment.

FIG. 5 is a schematic diagram showing a two-dimensional deformation detection device using a hologram according to another embodiment of the present invention.

FIG. 6 is a configuration diagram of a first conventional two-dimensional deformation detection device that detects a surface displacement and measures a physical property value of an object.

FIG. 7 is a configuration diagram of a second conventional two-dimensional deformation detection device that measures photothermal vibration displacement to measure thermal properties, light absorption, and the like of an object.

FIG. 8 is a third conventional example using an optical heterodyne interferometer.
It is a block diagram of a dimensional deformation detection apparatus.

[Explanation of symbols]

51, 52 ... First and second optical heterodyne interference means, 5
3, 54 ... First and second threshold elements, 55 ... Beam splitter, 56 ... Optical logic operation element, 57 ... Integrating element, 5
8 ... Laser light source, 59 ... Excitation laser, 60 ... Focusing lens, 61 ... Object to be measured, 62 ... Interference laser, 63 ... Spatial filter, 64 ... Collimating lens, 65 ... Half mirror, 66 ... Reference mirror, 67 ... Acousto-optic modulator (AOM).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Hara 1 126-1, Nomachi, Hamamatsu, Shizuoka Prefecture, Hamamatsu Photonics Co., Ltd. (56) References JP-A-62-69110 (JP, A)

Claims (2)

(57) [Claims] 1. A laser light source for irradiating a measured object with a laser beam to generate a displacement on the surface of the measured object, and first two-dimensional optical phase information on the surface of the measured object.
To convert the light into a first two-dimensional optical phase information signal
Rhodyne interfering means and a predetermined one converted by the first heterodyne interfering means
Of the surface of the DUT on the time carrier frequency of
A part of the first two-dimensional optical phase information signal is set to the predetermined value.
Second two-dimensional reference that is based on the number of parallel transport laps in time
Second heterodyne interferometer for converting to optical phase information signal
And first and second binarizing means for converting the first and second two-dimensional signals from the first and second optical heterodyne interfering means into two-dimensional binarized optical information, respectively. And the first
And a computing means for providing a two-dimensional AND optical signal between the two-dimensional binary optical information from the second binarizing means, and the two-dimensional logical product output from the computing means. A two-dimensional deformation detecting device comprising: an integrating means for integrating an optical signal. 2. The two-dimensional deformation detecting device according to claim 1, wherein when the object to be measured is a light scattering object, a non-light absorbing medium and a light reflecting object are provided behind the surface to be measured .