JP2514577Y2 - Optical surface roughness measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement of an optical surface roughness measuring device that measures surface roughness by utilizing interference of light.

2. Description of the Related Art One type of surface roughness measuring device collects one of two types of linearly polarized light whose polarization planes are orthogonal to each other and has different frequencies in a minute range on the surface of the object to be measured. Irradiate the other side of the DUT in a relatively wide area on the surface of the object to be measured in the form of a parallel beam, and the measurement light and the reference light reflected on the surface interfere with each other to extract the measurement beat signal, and There is known an optical surface roughness measuring device which measures a surface roughness based on a phase change or a frequency change of a corresponding measurement beat signal. For example, Japanese Patent Application Laid-Open No. 1-20
The optical surface roughness measuring device according to Japanese Patent Application No. 3914, Japanese Patent Application No. 63-95788 and Japanese Patent Application No. 1-56385 is one example.

In such an optical surface roughness measuring device, one of two types of linearly polarized light is condensed as a measurement light in a minute range on the surface of the object to be measured, and the other is used as a reference light in the state of a parallel beam to form a surface of the object to be measured. Since it is irradiated in a relatively wide range of, the measurement light is moved relative to the direction in which it intersects the optical axis of those beams, and the measurement light corresponds to the minute irregularities on the surface of the measurement object. Although the optical path length is changed and the phase and frequency are changed accordingly, the reference light does not undergo phase change or frequency change due to the unevenness of the surface because the influence of the minute unevenness is averaged out and cancelled. The phase and frequency of the measurement beam signal obtained by causing the measurement light and the reference light to interfere with each other can be changed in accordance with the phase change and the frequency change of the measurement light, but the object to be measured is relatively moved. Since the influences of vibrations and other external disturbances upon canceling each other cancel each other out, the surface roughness can be measured based on this phase change and frequency change.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-described conventional apparatus, since the objective lens is fixed, it is difficult to perform measurement at a measurement magnification according to the surface roughness of the object to be measured. Although it is possible to replace the objective lens with another one with a different focal length in order to change the measurement magnification, it is necessary to replace the objective lens so that the measurement light is focused in a minute range on the surface of the object to be measured. Every time, the complicated work of finely adjusting the distance between the objective lens and the bifocal lens was required.

The present invention has been made in view of such circumstances, and its purpose is to provide an optical surface roughness measuring device capable of easily selecting a desired measurement magnification according to the surface roughness of the object to be measured. To provide.

Means for Solving the Problems The gist of the present invention for achieving the above-mentioned object is to provide two types of linearly polarized light having an objective lens positioned in an optical path and having mutually orthogonal polarization planes and different frequencies. Irradiate the surface of the DUT through the lens respectively, detect the reflected light from the DUT through the objective lens respectively, and determine the surface roughness of the DUT based on the change of the beat frequency of the reflected light. An optical surface roughness measuring device of a measuring type, comprising: (a) a plurality of bifocal lenses for converging one of the two types of linearly polarized light and making the other parallel light. (B) A plurality of types of objective lenses having different focal lengths, and (c) the rear focus of the dual focus lens and the front focus of the objective lens match, and the focus position of the objective lens is the same on the object side. location and A plurality of lens holding members respectively holding a plurality of pairs of bifocal lenses and objective lenses, and (d) a lens holding member corresponding to a desired measurement magnification among the plurality of lens holding members, A positioning device for selectively positioning the objective lens held by the lens holding member so as to be positioned in the optical path.

By doing this, the back focus of the bifocal lens and the front focus of the objective lens match, and the focal positions of the plurality of types of objective lenses having different focal lengths are the same position on the measured object side, The plurality of pairs of bifocal lenses and the objective lens are respectively held by the plurality of lens holding members, and the positioning device allows the lens holding member corresponding to a desired measurement magnification among the plurality of lens holding members to be
The objective lens held by the lens holding member is selectively positioned so as to be positioned in the optical path.

Therefore, each time the objective lens is replaced with another objective lens having a different focal length in order to change the measurement magnification, it is necessary to finely adjust the distance between the objective lens, the bifocal lens and the DUT. Since the desired objective lens can be easily positioned in the optical path by the positioning device according to the surface roughness of the object to be measured, the measurement magnification can be selected by a simple operation.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view of an optical surface roughness measuring device according to an embodiment of the present invention, and FIG. 2 shows an optical system of the device. In the figure, the object to be measured 12 is placed on the moving table 10. The moving table 10 is driven in the x direction and the y direction by a driving device 14 including a pulse motor or a servo motor, and the object to be measured 12 is moved in a desired direction in the xy plane. After being moved, two types of linearly polarized light described later, that is, P polarized light L _P and S polarized light, are moved on the surface 18 of the DUT 12.
L _S is to be scanned.

The laser light source 30 is, for example, two types of linearly polarized light whose polarization planes are orthogonal to each other and whose frequencies are slightly different, that is, P-polarized light.
It is composed of a Zeeman laser that outputs a laser beam L including L _P and S-polarized L _S. The laser light L output from the laser light source 30 is split by the non-polarizing beam splitter 32. First, the laser light L transmitted through the non-polarizing beam splitter 32 passes through the first polarization element 36 and the reference optical sensor 34.
And the reference beat signal F _B is output. If the frequencies of the P-polarized light L _P and the S-polarized light L _S are f _p and f _s , respectively,
Frequency f _B of the reference beat signal F _B is | f _s -f _p | become.

The laser beam L reflected by the non-polarizing beam splitter 32, that is, the P-polarized light L _P and the S-polarized light L _S, has a beam diameter expanded by a beam expander 44 constituted by convex lenses 40 and 42 arranged coaxially. After being converted into a circular parallel beam having a circular cross section, the beam is redirected by the mirror 46 and incident on the bifocal lens 50. The bifocal lens 50 includes a first lens 52 formed in a convex shape with, for example, optical glass, and a second lens 54 formed in a concave shape with a uniaxial crystal birefringent material such as calcite or quartz. It is configured by combining. The birefringent material has a property that the refractive index varies depending on the angle between the optical axis and the plane of polarization of the incident light, and the refractive index of the S polarized light L _S in the second lens 54 made of the birefringent material. Is larger than the refractive index of P-polarized light L _P , and the optical axis of the second lens 54 thereof is parallel to the plane of polarization of S-polarized light L _S or P-polarized light L _P.
50 are arranged. Depending on whether the birefringent material is a positive uniaxial crystal or a negative uniaxial crystal, the optical axis is parallel to the polarization plane of the S-polarized light L _S or the P-polarized light L _P
Is determined to be parallel to the plane of polarization.

In the bifocal lens 50 configured as above, the beam diameter is greatly expanded by the beam expander 44.
The polarized light L _S or the P polarized light L _P is condensed together in the first lens 52, but in the second lens 54, the S polarized light L _S is relatively diffused into parallel rays, while the P polarized light L S _P is slightly diffused and focused on the optical axis.

The front focus of the objective lens 56 is the above-mentioned bifocal lens 50.
It is located at a position that matches the rear focal point. For this reason,
The P-polarized light L _P condensed by the bifocal lens 50 is
The S-polarized light L _S converted into a circular parallel beam by the double focus lens 50 is converted into a circular parallel beam by the objective lens 56 and irradiated on a relatively wide area of the surface 18 of the DUT 12. The light is focused on the surface 18 of the DUT 12 by 56 at a point within the irradiation range of the P-polarized light L _P.

S-polarized light L _S and P-polarized light L _P reflected by the DUT 12
Is returned to the non-polarizing beam splitter 32 through the same optical path as the outward path, and is transmitted therethrough to be received by the measuring optical sensor 62 through the second polarizing element 60. The polarization axes of the second polarizing element 60 and the first polarizing element 36 are 45
The first polarizing element, which is arranged in a tilted state.
The 36 and the second polarizing element 60 adjust the ratio of the two types of light constituting the reference beat light or the measurement beat light,
The rotation position around the axis can be changed.

Here, the S-polarized light L _S focused on one point on the surface 18 has a Doppler shift Δf _s generated corresponding to minute irregularities on the surface 18 as the DUT 12 is moved by the moving table 10, The frequency of the reflected light is f _s + Δf _d + Δf _s due to the Doppler shift Δf _d due to vibrations and other disturbances when the moving table 10 moves. On the other hand, the P-polarized light L _P irradiated onto the comparatively wide area of the surface 18 in the state of the circular parallel beam is canceled out by the Doppler shift due to the disturbance because the influence of the fine irregularities on the surface 18 is averaged and canceled out. only affected by Delta] f _d, the frequency of the reflected light f _p +
Δf _d . The S-polarized light L _S is measurement light, and the P-polarized light L _P is reference light.

Measurement beat signal F _D received by the measurement optical sensor 62
Corresponds to howling due to interference between the P-polarized light L _P and the S-polarized light L _S, and its frequency f _D is | (f _s + Δf _d + Δf _s ) − (f _p +
Δf _d ) | = | f _s −f _p + Δf _s |, and the Doppler shift Δf _d due to the disturbance is offset.

The measurement beat signal F _D and the reference beat signal F _B are supplied to the measurement circuit 64, and the frequency f of the measurement beat signal F _D is
By subtracting the frequency f _B (= | f _s −f _p |) of the reference beat signal F _B from _D (= | f _s −f _p + Δf _s |), only the Doppler shift Δf _s due to the unevenness of the surface 18 is obtained. A signal representing the Doppler shift Δf _s taken out is supplied to the control circuit 66. The control circuit 66 is composed of, for example, a microcomputer, and controls the drive table 14 to move the moving table 10 to the X-axis.
Based on the signal (Δf _s ) supplied from the measurement circuit 64, the displacement of each position based on the following equation (1) while sequentially moving in the −Y direction.
Z _S is calculated, and the surface roughness of the entire surface 18 of the DUT 12 is three-dimensionally displayed on the display 68.

That is, the DUT 12 on the moving table 10 is a control circuit.
As the 66 is moved in the xy plane in the two-dimensional direction, the S-polarized light L _S focused on one point on the surface 18 is caused by the Doppler shift Δf _s corresponding to the minute irregularities on the surface 18.
And the Doppler shift Δf _d due to vibrations and other disturbances during the movement of the moving table 10, while the P-polarized light radiated onto a relatively wide range of the surface 18 in the state of parallel beams.
In L _P , the influence of minute irregularities on the surface 18 is averaged and canceled out as a whole, so the Doppler shift Δ
It only receives f _d . Therefore, in the measurement circuit 64, based on the measurement beam signal F _D and the reference beat signal F _B obtained by causing the reflected lights to interfere with each other, the surface roughness over the entire surface 18 of the DUT 12 is measured. Formula (1) Are sequentially measured and displayed three-dimensionally on the display 68.
In the measurement circuit 64, in the unevenness of λ / 2 unit or more, by counting the beat number C _I of the measurement beat signal F _D and the beat number D _B of the reference bead signal F _B respectively, the following equation ( The displacement amount ΔZ _S1 in the z direction is calculated from 2).

Further, for unevenness of λ / 2 unit or less, the phase difference between the measurement beat signal F _D and the reference beat signal F _B is detected by a clock counter that counts clock signals of about 100 MHz, and with a resolution of about λ / 2000. A small displacement ΔZ _S2 in the z direction at the focal point S ₁ is measured. That is, the Doppler shift Δf _s is expressed by the following equation (3) from the basic equation of the Doppler effect.

Δf _s = (2 / λ) · (ΔZ _S2 / Δt) (3) By integrating this equation (3), the small displacement ΔZ _S2 in the z direction at the focal point S ₁ can be calculated by the following equation (4) ), The small displacement ΔZ _S2 is calculated according to the equation (4).

Then, the amount of irregularities, that is, the surface roughness is obtained by adding the displacement amount ΔZ _{S1 in the} z direction and the minute displacement ΔZ _S2 .

In the optical surface roughness measuring device configured as described above, the bifocal lens 50 and the objective lens 56, in order to change to a desired measurement magnification according to the surface state of the DUT 12, the magnification, that is, It can be easily replaced with another bifocal lens 70 and an objective lens 72 having different focal lengths, or a bifocal lens 74 and an objective lens 76 having different focal lengths. That is, the bifocal lens 50 and the objective lens 56 are in the cylindrical first lens holding member 78, the bifocal lens 70 and the objective lens 72 are in the second lens holding member 80, and the bifocal lens 74 and the objective lens 76. Are held by the third lens holding member 82, and the first lens holding member 78, the second lens holding member 80, and the third lens holding member 82 are fixed to the revolver 84. First of the above three
Lens holding member 78, second lens holding member 80, and third
The lens holding member 82 has a central axis line which is the same as that of the mirror 46.
Is fixed to the revolver 84 so as to be located on one conical surface having the optical path from the to the surface 18 of the object to be measured 12 as a generatrix, and the revolver 84 is provided around the central axis of the conical surface by an axis not shown. It is rotatably installed. Further, the revolver 84 is provided with a detent device (not shown), and the three first lens holding members 78, the second lens holding member 80, and the third lens holding member 82 have central axes from the mirror 46. Each of them is selectively positioned so as to coincide with the optical path to the surface 18 of the DUT 12. The bifocal lens 50 and the objective lens 5
6, the bifocal lens 70 and the objective lens 72, and the bifocal lens 74 and the objective lens 76 have the same focal position when positioned in the optical path from the mirror 46 to the surface 18 of the DUT 12. So that the focal point is located on the object to be measured 12 regardless of which objective lens is switched, the position is preset in the first lens holding member 78, the second lens holding member 80, and the third lens holding member 82, respectively. Has been done.

Therefore, according to the present embodiment, the surface 18 of the DUT 12 is
Revolver that functions as a positioning device according to the roughness of the
By manually rotating 84, one of the three first lens holding members 78, the second lens holding member 80, and the third lens holding member 82 that corresponds to a desired measurement magnification is selectively mirrored. Since the desired objective lens can be selected by locating it in the optical path from 46 to the surface 18 of the DUT 12, it is possible to replace the lens and to adjust the distance between the objective lens and the bifocal lens and the DUT. No adjustment work is required, and the measurement magnification can be selected with a simple operation.

Although one embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be implemented in other modes.

For example, in the above-described embodiment, the three lens holding members 7
Although 8, 80 and 82 are provided on the revolver 84, two or four or more lens holding members may be provided.

Further, in the above-described embodiment, the lens holding member corresponding to the desired measurement magnification is selected by rotating the revolver 84 by manual operation, but it may be automatically rotated by the actuator.

Although not illustrated one by one, the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the configuration of an optical surface roughness measuring device according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the optical system of the embodiment of FIG. 1 in detail. 12: Object to be measured, 18: Surface 30: Laser light source, 50, 70, 74: Bifocal lens 56, 72, 76: Objective lens 78: First lens holding member 80: Second lens holding member 82: Third Lens holding member 84: Revolver (positioning device)

Claims (1)

(57) [Scope of utility model registration request] 1. An objective lens located in an optical path, wherein two types of linearly polarized light whose polarization planes are orthogonal to each other and different in frequency are applied to the surface of the object to be measured through the objective lens, respectively, and the object to be measured is irradiated from the object to be measured. Of the reflected light of each type through the objective lens, and measuring the surface roughness of the object to be measured based on the change in the beat frequency of the reflected light. A plurality of bifocal lenses for condensing one of the linearly polarized light beams and making the other into a parallel light beam, a plurality of types of objective lenses having different focal lengths, a back focus of the bifocal lens, and A plurality of lens holding members that respectively hold a plurality of pairs of bifocal lenses and objective lenses so that the front focal points of the objective lenses coincide with each other and the focal positions of the objective lenses are the same on the object side. A positioning device that selectively positions a lens holding member corresponding to a desired measurement magnification among the plurality of lens holding members so that the objective lens held by the lens holding member is located in the optical path. An optical surface roughness measuring device comprising: