JPH05133725A - Surface shape measuring device - Google Patents

Abstract

PURPOSE:To provide a surface shape measuring device, which can make surface measuring over a wide measuring range for surface unevenness on an object to be measured in the height direction. CONSTITUTION:A surface shape measuring device is equipped with an interferential light projecting means to project a moving interferential fringes due to two-waveform light onto an object 4 to be measured, a light sensing means 2 to observe this projected moving interferential fringe at an angle different from the projection angle, and a phase measuring means 3 to measure the phase of the change in photo-intensity at different measuring points on the object sensed by the photo-sensing means 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the surface shape of an object.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional shape measuring method using a light cutting method.
Shown in. A fan-shaped light is projected from the projector 5 to the DUT 4,
The reflected light is observed by the light receiver 6 from an angle different from the projection angle. The image obtained here is shown in the figure, and the positions above and below the bright line due to the reflected light in the image represent the unevenness of the measured object.
With this method, since only the unevenness information of the portion irradiated by the fan-shaped light can be obtained, in order to obtain the unevenness information of the surface of the measured object,
It is necessary to scan the fan-shaped light from one end to the other end of the object to be measured, and to capture all the corresponding images.

As shown in FIG. 8, the light receiver 6 includes a lens 60.
And a photodetector 61. The measurement range in the height direction is
Limited by lens 60 and photodetector 61, range B to C. Therefore, when the object to be measured for measuring the minute irregularities on the surface is tilted, it is impossible to measure the entire surface. Further, when the measurement range from B to C is expanded without changing the position resolution of the photodetector 61, the uneven resolution to be measured deteriorates.

Further, as a conventional shape measuring method by interference, there is a configuration shown in FIG. In the shape measurement by this interference,
It is characterized in that surface irregularity information can be obtained at one time and the measurement range in the height direction is wide. Since the wavelength of the laser 15 used for interferometry is around 1 μm, the unevenness of the measured object is 0.
Interference fringes will appear at about 5 μm. At this time, if the difference in the unevenness of the DUT 4 between the adjacent pixels of the photodetector 8 exceeds 0.5 μm, the interference fringes cannot be measured and the surface unevenness cannot be measured.

[0005]

As described above, in the shape measurement by the light section method, the surface cannot be measured at once and the measurement range in the height direction is narrow. Also, the measurement by interference cannot be performed when the measured object has a step of 0.5 μm or more. Therefore, it is an object of the present invention to provide a surface shape measuring apparatus that has a wide measurement range of unevenness in the height direction of an object to be measured and can measure a surface.

[0006]

In order to achieve the above object, the present invention provides an interference projection means for projecting moving interference fringes of two-wavelength light onto an object to be measured 4 as shown in FIG. 1 (a). 1, light detection means 2 for observing the moving interference fringes projected on the DUT 4 from an angle different from the projection angle, and changes in the light intensity of each point of the DUT detected by this light detection means 2. Phase measuring means 3 for measuring the phase of is provided.

[0007]

In the above structure, the moving interference fringe C is projected from the interference light projecting means 1 onto the object to be measured. The interference fringes move by one fringe in the cycle of the difference between the two light waves (hereinafter referred to as the heterodyne cycle). Image 1 (b) observed by the light detection means 2 is
With an image similar to that of multiple fan-shaped light projected by the light cutting method,
This interference fringe moves in a heterodyne period. Focusing on one point in the image, the intensity change at that point becomes a sine wave with a heterodyne period. Since the projection angle and the reception angle are different, the unevenness on the surface of the object to be measured can be detected as the phase of the intensity change at each point in the image.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic configuration of the surface profile measuring apparatus of the present invention is shown in FIG.
First, a method for obtaining the unevenness of the object to be measured from the change in the light intensity of the observed image will be described with reference to FIG. 2 showing the spatial light intensity distribution of the moving interference fringes projected by the interference light projecting means 1. Show. The thick line in FIG. 2 indicates the interference fringe.

The optical axis of the light detecting means 2 is parallel to the z axis.
This does not lose generality either. The light wave B1 is projected at an angular frequency ω ₁ with an inclination of θ _{1 with} respect to the z axis. The light wave B2 is projected at an angular frequency ω ₂ with an inclination of θ _{2 with} respect to the z axis. Since ω ₂ −ω ₁ << ω ₁ , the wavelengths of B ₁ and B 2 are both represented by λ. Light wave B
Assuming that the light intensities of 1 and B2 are a ₁ and a ₂ , the electric field is E _B1 (x, y, z, t) = a ₁ exp i {ω ₁ t + φ ₁ (x, y, z)} EB2 ( x, y, z, t) = a ₂ exp i {ω ₂ t + φ ₂ (x, y, z)} (1) Becomes The light intensity of the interference fringe due to B1 and B2 is I (x, y, z, t) = | E _B1 + E _B2 | ² = | E _B1 | ² + | E _B1 | ² + 2a ₁ a ₂ cos {(ω ₂ −ω ₁ ) t + (φ ₂ −φ ₁ )} (2) That is, the phase of the light intensity at the x, y, and z points is ψ = φ ₂ −φ ₁ Given in.

Since the optical axis of the light detecting means 2 is parallel to the z axis, it is possible to obtain the reflected light intensity change at the x and y points regardless of the z coordinate of the object to be measured. That is, in order to obtain the heights of the coordinates x and y on the surface of the object to be measured, the phase of the change in the light intensity at that point can be obtained and the z coordinate can be obtained from equation (3). Further, as can be seen from the equation (3), the phase of the light intensity and the z value have a linear relationship.

Further, since the measuring range in the height direction is a portion where the moving interference fringes and the light flux of the light detecting means intersect, if the moving interference fringes are widely generated in the z direction, the measurement can be performed correspondingly.

FIG. 3 shows a concrete configuration example of the interference light projecting means 1. The two-wavelength laser 10 generates coherent two-wavelength light waves whose polarization planes differ by 90 °. The beam expander 11 expands the beam diameter, and the polarization beam splitter
Only one light wave B1 is reflected by 12. The other transmitted light wave B2 is made to intersect with the light wave B1 at a minute angle by the mirror 13. This angle is determined by the measurement resolution and equation (3).
To set the required angle. Since the intersecting light waves have different polarization planes, interference fringes are generated by the polarizing plate 14.

Another example of the structure of the interference light projecting means 1 is shown in FIG.
Shown in. In this example, the laser 15 may be single wavelength. The laser light is divided into two by the beam splitter 16, and the frequency of the light wave is changed by the optical frequency shifter 17. Here, the frequency difference between the optical frequency shifters 17A and 17B becomes the heterodyne frequency. These light waves are expanded by the beam expander 11 and are intersected at a minute angle by the mirror 13 and the beam splitter 16 to generate interference fringes.

The structure of the interference projecting means shown in FIG. 3 is characterized in that the number of parts can be reduced, and the structure of the interference means shown in FIG. 4 can be miniaturized by using a semiconductor laser for the laser and the frequency of the optical frequency shifter. By selecting, there is a great deal of freedom in setting the heterodyne frequency.

FIG. 5 shows an example of a specific configuration of the light detecting means 2 and the phase detecting means 3. In the light detecting means 2, the lens 20
Thus, the reflected light of the DUT 4 is collected on the photoelectric detector 21.
Although a large number of photoelectric detectors 21 need to be arranged in order to obtain an image, only two photoelectric detectors 21 are shown here for the purpose of explaining the principle. The photoelectric detectors 21A and 21B are the A.D. The change in the reflected light intensity at the B portion is detected, and the signals SA and S are detected.
B is generated. The signals SA and AB include height information of the portions A and B of the device under test as phase information. Therefore,
In the phase measuring means 3, the zero voltage detectors 30A and 30B detect the phase by starting / stopping the counter 32 at the timing when each signal voltage changes from negative to positive. Thereby, the height difference between the A portion and the B portion can be measured.

The light detecting means 2 and the phase detecting means 3 are also provided.
FIG. 6 shows another specific example of the configuration. In this case, the reflected light of the DUT 4 is captured by the CCD image detector 22.
Since the CCD image detector cannot detect continuous intensity changes, for example, images are captured four times in one period of heterodyne. The intensities of the x and y points of these four images are A ₀ (x, y), A ₁ (x, y), A ₂ (x, y), A
_{If 3} (x, y), the phase of points x and y is Therefore, the data calculator 34 can measure the above-mentioned phase and measure the unevenness of the object to be measured.

FIG. 5 of the light detecting means 2 and the phase detecting means 3.
With this configuration, since the signal of the photoelectric detector 21 is processed in real time to obtain the phase, high-speed measurement can be performed. Further, according to the configuration of FIG. 6, since the output of the CCD image detector 22 is serial, only one A / D converter and one data calculator 34 is needed, and the hardware is simple.

[0018]

According to the present invention, by projecting the moving interference fringes onto the object to be measured, the unevenness can be measured by obtaining the phase of the intensity change of the reflected light at each point of the object to be measured. The required surface can be measured. Moreover, if the moving interference fringes are generated widely in the height direction, a wider measurement range can be obtained.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a surface profile measuring apparatus of the present invention and an image observed by a light measuring means 1.

FIG. 2 is a side view of a moving interference fringe according to the present invention.

FIG. 3 is a specific configuration example of the interference light projecting means 1 according to the present invention.
(1).

FIG. 4 is a specific configuration example of the interference light projecting means 1 according to the present invention.
(2).

FIG. 5 is a specific configuration example (1) of the light detecting means 2 and the phase measuring means 3 according to the present invention.

FIG. 6 is a specific configuration example (2) of the light detecting means 2 and the phase measuring means 3 according to the present invention.

FIG. 7 is a diagram showing a conventional shape measuring method by a light section method.

FIG. 8 is a diagram showing the principle of a light cutting method.

FIG. 9 is a diagram showing a conventional shape measuring method by interference.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Interference projection means, 2 ... Photodetection means 3 ... Phase measurement means, 4 ... DUT, 10 ... 2 wavelength laser, 11 ... Beam expander, 12 ... Polarization beam splitter, 13 ... Mirror, 14 ... Polarization wave , 15 ...
Single wavelength laser, 16 ... Beam splitter, 17 ... Optical frequency shifter, 18 ... Aperture, 20 ... Lens, 21 ...
Photoelectric detector, 22 ... CCD image detector, 30 ... Zero voltage detector, 31 ... Pulse generator, 32 ... Counter,
33 ... A / D converter, 34 ... Data calculator,
B1, B2 ... light wave, C ... moving interference fringe.

Claims (1)

[Claims] 1. An interference light projecting means for projecting moving interference fringes of two-wavelength light onto an object to be measured, and light detection for observing the moving interference fringes projected onto the object to be measured from an angle different from a projection angle. Means and phase measuring means for measuring the phase of the change in the light intensity of each point of the measured object detected by the light detecting means, and measuring each unevenness by the phase of the change of the light intensity of each point of the measured object A surface shape measuring device characterized by: