JPH0742084Y2 - Surface shape measuring instrument - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a surface shape measuring instrument for measuring the surface shape of an object.

<Prior Art> As an example of such a surface shape measuring instrument, an apparatus including a continuous white light source having a wide emission spectrum width, a measuring interferometer section, a spectral diffraction grating, a photodiode array, and an arithmetic processing section. There is. In this device, the interference signal from the interferometer unit for measurement with respect to the wide spectrum from the white light source is dispersed by the diffraction grating, detected by the photodiode array, and calculated by the calculation processing unit, which enables absolute measurement. I am trying.

<Problems to be Solved by the Invention> However, the surface profile measuring instrument as described above has the following problems in order to correct the gain characteristic of the spectrum.

-Since it is necessary to measure the power spectrum of the input light for each wavelength and calculate the cross-correlation, the measurement time and calculation time become long, and high-speed measurement is difficult.

-Because the power spectrum of the input light is measured serially, relatively fast noise components such as vibration and fluctuations in the air refractive index cannot be canceled, making high-precision measurement difficult.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a surface profile measuring instrument capable of high-speed and high-accuracy measurement and capable of measuring an absolute value.

<Means for Solving the Problems> The structure of the present invention for solving the above problems is a surface shape measuring instrument that measures the surface shape of an object by utilizing the interference of light, and has a wide spectral line width of white. A light source that emits light,
A wavelength tunable light source unit including a spectroscopic acousto-optic element on which light emitted from the light source is incident, and a pinhole into which the first-order diffracted light and the second-order diffracted light diffracted by the acousto-optic element are incident, and the pinhole. Measuring interferometer section on which the first-order diffracted light that has passed through is incident, a first detecting section that receives the measuring interfering light from the measuring interferometer section, and second-order diffracted light that has passed through the pinhole. And a divider for taking a ratio of the output signal from the second detector and the interference signal from the first detector, and the object receiving the output of the divider. An interference phase measuring device for measuring an interference phase and a shape corresponding to the surface shape of the white light having a wide spectral line width from the light source is dispersed by the acousto-optic device,
The first-order diffracted light is used as a measuring interference light, the second-order diffracted light is used as a power monitor, and the ratio of the two is used by the divider to remove the influence of the intensity change. Is.

<Operation> According to the present invention, an acousto-optic device is used as a spectroscope,
By using the first-order diffracted light as the measurement light and the second-order diffracted light as the power monitor, the power fluctuation can be corrected in real time.

<Example> Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the surface profile measuring instrument of the present invention. In FIG. 1, reference numeral 1 denotes a wavelength variable light source unit, and its configuration is a light source 11 (for example, LED, SLD, xenon lamp, halogen lamp, etc.) that emits white light with a wide spectral line width, and driving of this light source 11. Section 12, fiber 13 for obtaining spatial coherence, acousto-optic element 14 for spectroscopy, drive section 15 that can drive this acousto-optic element 14 and change its drive frequency, and acousto-optic A pinhole 16 through which the light diffracted by the element 14 passes.
Reference numeral 2 denotes a Michelson-type measuring interferometer unit, which includes a half mirror 21 that splits the first-order diffracted light that has passed through the pinhole 16 into two, a reference-light mirror 22, and a collector for collecting the measurement light. It is composed of an optical lens 23, a measurement symmetry 24, and a stage 25 for moving the measurement object 24. 3 is a photodiode for receiving the measurement interference light from the measurement interferometer unit 2 (hereinafter, simply referred to as PD), 4 is a PD for receiving the second-order diffracted light that has passed through the pinhole 16, and 5 is a PD 3 or 4 A divider for taking the ratio of the output signals, and 6 is an interference phase measuring instrument for receiving the output of the divider 5 and measuring the interference phase and shape corresponding to the measurement symmetry 24.

In such a configuration, the device of the present invention is basically
This is an absolute surface profile measuring instrument that uses the FM modulation method. It measures the change of the interference phase when the light source frequency is continuously changed, and is expressed by the following formula: L = (Δθ / 2π) (c / Δf ) However, c: High speed Δθ: Interference phase Δf: Frequency L is calculated from the distance L, and the stage where the measurement symmetry 24 is installed
The surface shape of the measurement symmetry 24 is obtained by scanning 25.

The light emitted from the light source 11 is incident on the fiber 13 in order to obtain spatial coherence, and is guided to the acousto-optic element 14 for spectroscopy. This acousto-optic element 14 is driven by the drive unit 15,
The drive frequency can be changed. The first-order diffracted light diffracted by the acousto-optic element 14 is guided to the measuring interferometer unit 2 through the pinhole 16. The second-order diffracted light diffracted by the acousto-optic element 14 is received by the PD 4 as a power monitor through the pinhole 16. The light incident on the measuring interferometer unit 2 is split into two by the half mirror 21. The reference light is reflected by the reference light mirror 22, passes through the half mirror 21, and enters the PD 3. The measurement light is condensed on the measurement symmetry 24 on the stage 25 by the condenser lens 23, and the reflected light is reflected by the half mirror 21 through the same path and is incident on PD3, and interferes with the reference light on PD3. The interference signal obtained by PD3 and the output signal of PD4 are made incident on the divider 5, the ratio between them is taken out, the influence of power fluctuation is eliminated, and the interference corresponding to the symmetry 24 is measured by the interference phase measuring device 6. Phase and shape are measured.

Here, the feature of the present invention is that a wavelength tunable light source unit 1 including a light source 11 that emits white light with a wide spectral line width, an acousto-optic device 14 for spectroscopy, and a pinhole 16, and the power of the wavelength tunable light source unit 1 is used. The point is that the influence of fluctuations can be corrected. The function and operation will be described below with reference to the drawings.

Regarding the wavelength tunable light source unit 1, in the wavelength tunable light source unit 1, the diffraction angle of the acousto-optic element 14 changes depending on the wavelength λ of the incident light and the frequency fa of the ultrasonic wave. Therefore, when white light with a wide spectral line width as shown in FIG. 2 (a) is incident on the acousto-optic element 14, the diffraction angle varies depending on the wavelength. Different spectral outputs of are obtained. If you cut out a part of this output with pinhole 16 and use it,
Light having a desired wavelength is obtained. The spectral line width is determined by the diameter of the pinhole 16. Next, if the frequency of the ultrasonic wave of the drive unit 15 that drives the acousto-optic device 14 is changed, the diffraction angle changes as shown in FIG. 2C, and the wavelength of the selected light changes. Therefore, by changing the frequency of the ultrasonic waves of the drive unit 15, the wavelength of light can be continuously and electrically changed over a wide range.

Correction of the influence of power fluctuation Since the spectral intensity of white light is not constant as shown in Fig. 2 (a), the amplitude of the obtained FM interference wave is shown in Fig. 3 (a).
As shown in, it is difficult to measure the phase accurately due to the modulation. On the other hand, the influence of the power fluctuation is corrected by using the second-order diffracted light shown in FIG. 3B as a monitor of the intensity of emitted light and taking the ratio with the interference light. (FIG. 3 (c)) In this way, the wavelength variable light source unit 1 can electrically and continuously change the wavelength of light over a wide range, and an acousto-optical element is used as a spectroscope. By using the first-order diffracted light as the measurement light and the second-order diffracted light as the power monitor, it is possible to correct the power fluctuation in real time, so that high-speed and highly accurate measurement can be performed.

FIG. 4 is a block diagram showing another embodiment of the surface profile measuring instrument of the present invention. Note that in FIG. 4, the same elements as those in FIG. In FIG. 4, 26 is a polarization beam splitter, 27 and 28 are quarter-wave plates, and 7 is a polarizing plate. This embodiment uses the polarization of light and is a polarization interference method that effectively uses the power of light. The white light with a wide spectral line width emitted from the light source is separated by the polarization beam splitter 26 in each polarization direction, one of which is reflected by the reference light mirror 22 and the other of which is reflected by the measurement symmetry object 24 and the polarization beam splitter. Returning to 26,
Since both optical paths pass through the quarter-wave plates 27 and 28 twice, the polarized light is converted and all incident on the acousto-optic element 14, so that the power is used more effectively than the device in FIG. It will be.

In addition, by using a PD array or CCD camera instead of PD3 that detects the intensity of coherent light, two-dimensional information can be captured, so stage 25 is not required, and mechanical moving parts are eliminated. Can enable measurement.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, since the light source composed of the acousto-optic device and the white light is used, the light of a wide range of several hundreds of nanometers is used. The wavelength can be changed continuously, enabling highly accurate absolute measurement. Further, since it can be electrically changed, it is possible to realize a surface shape measuring instrument having effects such as high-speed measurement.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the surface shape measuring instrument of the present invention, FIG. 2 is a diagram showing the spectral characteristics of a light source and the output of an acousto-optic device used in the apparatus of FIG. 1, and FIG. FIG. 4 is a diagram showing a correcting operation for the influence of fluctuation, and FIG. 4 is a diagram showing another embodiment of the surface profile measuring instrument of the present invention. 1 ... Wavelength variable light source section, 2 ... Measurement interferometer section, 3, 4 ...
… Detector, 5 …… Divider, 6 …… Interference phase measurer, 11…
… A light source that emits white light with a wide spectral line, 12 ……
Driving part of light source 11, 13 ... Fiber, 14 ... Acousto-optic element for spectroscopy, 15 ... Driving part of acousto-optic element 16, 16 ... Pinhole, 21 ... Half mirror, 22 ... Reference light mirror ,twenty three
...... Condensing lens, 24 …… Measurement symmetry, 25 …… Stage.

Claims (1)

[Scope of utility model registration request] 1. A surface shape measuring instrument for measuring the surface shape of an object by utilizing the interference of light, comprising a light source for emitting white light having a wide spectral line width, and light emitted from this light source. An acousto-optic element for spectroscopy,
1st-order diffracted light and 2 diffracted by this acousto-optic element
A variable wavelength light source unit including a pinhole into which the secondary diffracted light enters, a measuring interferometer unit into which the first-order diffracted light passing through the pinhole enters, and the measuring interference light from the measuring interferometer unit are received. First to do
Detection unit, a second detection unit that receives the second-order diffracted light that has passed through the pinhole, and a ratio of the output signal from the second detection unit and the interference signal from the first detection unit. A divider and an interference phase measuring device that receives an output of the divider and measures an interference phase and a shape corresponding to the surface shape of the object, and obtains white light with a wide spectral line width from the light source. The light is split by an acousto-optic device, and the first-order diffracted light is measured as interference light
The surface shape measuring instrument is characterized in that the second-order diffracted light is used as a power monitor and the ratio of the two is taken by the divider to eliminate the influence of the intensity change.