JP4634884B2 - Surface texture measuring device - Google Patents

Description

    The present invention relates to a surface texture measuring apparatus for measuring the surface texture of a measurement object.

While projecting light from the light source onto the object to be measured to obtain measurement light, the reference light from the reference mirror interferes with the measurement light, and the object to be measured is moved relatively to change the light intensity of the interference light. For example, Patent Document 1 discloses a shape measuring apparatus that measures the surface properties of an object to be measured by obtaining the value for each pixel. In such an apparatus, a drive mechanism for relatively moving the object to be measured and a mechanism (encoder or the like) for measuring the drive amount are indispensable, and there is a problem that the system cannot be complicated.
JP 2001-66122 A

  The present invention provides a surface texture measuring apparatus that does not require relative movement of an object to be measured by a mechanical drive mechanism, thereby simplifying the system and not being affected by mechanical scanning accuracy or scale accuracy. The purpose is to do.

  In order to achieve the above object, the surface texture measuring apparatus according to the present invention outputs incident light having a constant wavelength width centered on the center wavelength, and the center wavelength is variable within a predetermined variable wavelength range. The incident light is separated into a variable light source, object light directed to the measurement object, and reference light directed to the reference surface, and the object light and the reference light reflected by the measurement object and the reference surface are combined. In the case where the center wavelength changes within the variable wavelength range inserted into one of the optical path of the object light or the optical path of the reference light, and a beam splitter that is combined light, an imaging unit that receives the combined light An optical path length changing optical member that gives a change of an optical path length of the object light path or the optical path of the reference light beyond a predetermined measurement range; and the center that guides the combined light to the imaging unit. An imaging optical system in which the in-focus position of the combined light is invariable regardless of a change in length; a wavelength control unit that controls the variable wavelength light source to change the central wavelength; and an imaging unit A measurement unit that measures the height of the part on the measurement object corresponding to the specific light receiving position based on the center wavelength when the light intensity of the combined light at the specific light receiving position becomes maximum. It is characterized by that.

  According to the present invention, a surface texture measuring device that does not require relative movement of the object to be measured by a mechanical drive mechanism, thereby simplifying the system and not being affected by mechanical scanning accuracy or scale accuracy. Can be provided.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the surface texture measuring apparatus 1 according to this embodiment includes a wavelength variable light source 11, a collimator lens 12, a beam splitter 13, a parallel plane plate 14, a reference mirror RP, and an imaging optical system. 15, a CCD image pickup device 16, a computer 20, and a wavelength control unit 21, and configures a Twiman Green interferometer that performs measurement by measuring interference fringes on the surface property of the measurement target W.

As shown in FIG. 2, the wavelength tunable light source 11 is a low-coherence light source that emits light having a center wavelength λc as a peak and a spectral distribution with a constant wavelength width Δλ. Therefore, in this surface texture measuring apparatus, when the optical path difference between the reference optical path and the object optical path is set to a certain distance lc = λc ² / Δλ or less, interference fringes are observed by the CCD imaging device 16. The wavelength tunable light source 11 is configured to change the center wavelength λc in the range of λmin to λmax in response to a control signal from the wavelength control unit 21. The computer 20 is in charge of controlling the wavelength control unit 21 and the like in addition to analyzing the interference fringe signal obtained by the CCD image pickup device 16 to measure the shape of the measurement object W.

The collimator lens 12 converts the light from the wavelength variable light source 11 into a parallel light beam. The beam splitter 13 divides the parallel light beam into reference light directed to the reference mirror RP and object light directed to the measurement target W, and combines the reference light and the object light reflected by the reference mirror RP and the measurement target W. It has the function to do. The beam splitter 13 may be a half mirror as shown in FIG. 1 or a prism type. The plane parallel plate 14 is made of a highly dispersed material such as F2 glass, and its refractive index n varies greatly depending on the wavelength of light passing therethrough. When the center wavelength λc changes in the range of λmin to λmax, the optical path length of the reference light is changed beyond the measurement range of the surface property measuring apparatus 1. FIG. 3 shows an example of a change in the light intensity of the combined light due to the light (measurement light) from a certain point on the measurement object W and the reference light with respect to the change in the center wavelength λc. When the center wavelength λc changes and the optical path length difference between the reference optical path and the object optical path is zero, the light intensity of the interference light is maximized. The height h can be determined. The interference fringes can be observed in the range of ± lc = λc ² / Δλ from the position where the optical path length difference is zero.

  The imaging optical system 15 employs an optical system from which chromatic aberration is removed so that the imaging position does not change due to the change in the center wavelength λc. As a preferred example, a double-sided telecentric optical system as shown in FIG. 4 can be adopted so that the image formation state and size of the interference fringes on the CCD image sensor 16 do not change depending on the position of the measurement object W. .

  This double telecentric optical system includes a first imaging lens 151, a diaphragm 152, and a second imaging lens 153. The stop 152 is disposed so as to coincide with the image-side focal position of the first imaging lens 151 and coincide with the object-side focal position of the second imaging lens 153, thereby forming a bilateral telecentric optical system. Furthermore, the first imaging lens 151 and the second imaging lens 153 are similar with respect to the stop 152, and the first imaging lens 151 and the second imaging lens 153 are respectively for the front focus and the rear focus. The structure is achromatic. Accordingly, the light incident on the first imaging lens 151 in parallel to the optical axis A from the measurement object W side enters the second imaging lens 153 through the aperture of the diaphragm 152 and is parallel to the optical axis A. Light exits from the second imaging lens 153 and reaches the imaging surface of the CCD image sensor 16.

  When the size of the central wavelength λc changes, for example, as λ1 and λ2, the object-side focal point of the first imaging lens 151 also changes its position as Fλ1 and Fλ2 shown in FIG. The distance from the position is Xλ1, Xλ2), and the image-side focal point of the second imaging lens 153 is also changed to F ″ λ1, F ″ λ2 (the distance from the imaging surface of the CCD image sensor 16 is X ″ λ1, X "Λ2). The position of the principal point of the first imaging lens 151 also changes (distances f1λ1, f2λ2 from the diaphragm 152), and the position of the principal point of the second imaging lens 153 also changes (distances f2λ1, f2λ2 from the diaphragm 152). . However, since the both-side telecentric optical system is configured, the CCD image pickup device 16 has substantially the same size regardless of the movement of the focal position due to the change of the wavelength λc and the position (height) of the measurement object 16. An interference fringe image can be observed.

  Next, the operation of the thus-configured surface texture measuring device will be described with reference to FIG. When the center wavelength λc of the light emitted from the wavelength tunable light source gradually increases in the range of λmin to λmax, the optical path length of the reference optical path is gradually shortened by the action of the plane parallel plate 14, and when it becomes λmax, The length is shorter by 2 × t × (nmin−nmax) than in the case of λmin. Where t is the thickness of the plane parallel plate 14, and nmax and nmin are the refractive indices of the plane parallel plate 14 when the center wavelengths λ are λmax and λmin, respectively.

  At points A (height hA) and B (height hB <hA) having different heights h on the measurement object W, different wavelengths λA and λB (λB <λA) are obtained as shown in FIGS. ), The optical path length of the reference light coincides with the optical path length of the object light, and the magnitude of the interference signal becomes maximum. By specifying the size of the center wavelength λc when the interference signal reaches the maximum value, the height of each point on the measurement object W can be calculated. Thereby, the surface property of the measuring object W can be measured.

  Although the embodiments of the invention have been described above, the present invention is not limited to these embodiments, and various modifications and additions can be made without departing from the spirit of the invention. For example, in the above-described embodiment, an example in which the plane-parallel plate 14 is inserted in the optical path of the reference light has been described, but it may be inserted in the optical path of the object light. Further, a plane parallel plate may be inserted in both the optical path of the reference light and the optical path of the object light, and the thickness or material thereof may be different. In short, the center wavelength λc of the emitted light from the wavelength tunable light source 11 has changed. In this case, it is only necessary that the optical path length difference between the reference optical path and the object optical path can be changed over a predetermined measurement range.

The whole structure of the surface property measuring apparatus 1 of embodiment of this invention is shown. An example of the spectral distribution of the light emitted from the wavelength variable light source 11 is shown. An example of the change in the light intensity of the combined light due to the light (measurement light) from a certain point on the measurement object W and the reference light when the center wavelength λc of the light emitted from the wavelength tunable light source 11 is changed. It is shown. A specific configuration of the imaging optical system 15 is shown. The effect | action of the surface texture measuring apparatus 1 of this Embodiment is shown. The effect | action of the surface texture measuring apparatus 1 of this Embodiment is shown. The effect | action of the surface texture measuring apparatus 1 of this Embodiment is shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Variable wavelength light source, 12 ... Collimator lens, 13 ... Beam splitter, 14 ... Parallel plane plate, RP ... Reference mirror, 15 ... Imaging optical system, 16 ... CCD image sensor, 20... Computer, 21... Wavelength control unit 21, 151, 153.

Claims (4)

A wavelength tunable light source that outputs incident light having a constant wavelength width centered on the center wavelength and whose center wavelength is variable within a predetermined variable wavelength range;
The incident light is separated into object light directed to the measurement object and reference light directed to the reference surface, and the object light and the reference light reflected by the measurement object and the reference surface, respectively, are combined to obtain a combined light. A beam splitter,
An imaging unit for imaging an interference fringe image by the combined light;
When the central wavelength is inserted in either the optical path of the object light or the reference light and changes in the variable wavelength range, a predetermined measurement is performed on the optical path length of the optical path of the object light or the optical path of the reference light. An optical path length changing optical member that gives a change over the range;
An imaging optical system configured to guide the combined light to the imaging unit and to make the in-focus position of the combined light unchanged regardless of the change in the center wavelength;
Wavelength control means for controlling the wavelength tunable light source to change the center wavelength;
Measurement for measuring the height of the part on the measurement object corresponding to the specific light receiving position based on the center wavelength when the light intensity of the combined light at the specific light receiving position on the imaging unit becomes maximum And a surface texture measuring device.   The surface texture measuring apparatus according to claim 1, wherein the imaging optical system is a double-sided telecentric optical system.   The surface texture measuring apparatus according to claim 1, wherein the optical path length changing optical member is a plane parallel plate.   2. The surface property measuring apparatus according to claim 1, wherein the wavelength tunable light source emits light having a predetermined spectral spread with a center wavelength as a peak.

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