JP2501738Y2 - Optical surface roughness measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a surface roughness measuring device, and more particularly, to an optical surface roughness measuring device for measuring surface roughness by utilizing light interference. It is a thing.

[Prior Art] The applicant of the present invention, as a kind of surface roughness measuring device, collects one of two types of linearly polarized light whose polarization planes are orthogonal to each other and different in frequency in a minute range on the surface of the object to be measured. A measurement beat signal is obtained by irradiating the other of the two types of linearly polarized light on a relatively wide range of the surface of the DUT in the form of a parallel beam, and causing the measurement light and the reference light reflected by the surface to interfere with each other. Has been proposed, and an optical surface roughness measuring device has been proposed which measures the surface roughness based on the phase change or frequency change of the measured beat signal corresponding to the unevenness of the surface (Practical application 1- No. 56385).

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 the object to be measured is relatively moved in a direction that intersects the optical axes of those beams, the measurement light corresponds to minute irregularities on the surface of the object to be measured. The optical path length can be changed, but the reference light is canceled out by averaging out the effects of minute irregularities.
There is no phase change or frequency change due to the unevenness of the surface. Then, the phase or frequency change of the measurement beat signal obtained by causing the measurement light and the reference light to interfere with each other is changed in accordance with the phase change or the frequency change of the measurement light. The surface roughness can be measured based on In other words, since the measurement light and the reference light are both radiated on the surface of the measured object, the effects of vibration and other disturbances when the measured object is moved relative to each other cancel each other out, and the phase change and frequency change of the measurement beat signal are canceled. Does not affect

FIG. 5 is a configuration diagram illustrating an example of the above-described optical surface roughness measuring device. The laser light source 30 is composed of, for example, a Zeeman laser that outputs laser light L including 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 LP and S-polarized light LS. Laser light source 30
The laser light L output from the non-polarizing beam splitter
The laser light that has been split into two by 32 and has passed through the non-polarizing beam splitter 32 is detected by the reference optical sensor 34, and the reference beat signal FB is output. P polarization above
When the frequencies of the LP and S-polarized light LS are fp and fs, respectively, the frequency fB of the reference beat signal FB is | fs−fp |.

On the other hand, the laser light L reflected by the non-polarizing beam splitter 32 is the beam expander 74 arranged coaxially.
The beam diameter is expanded by and converted into a circular parallel beam having a circular cross section, which is then incident on the bifocal lens 76. The bifocal lens 76 is composed of an optical glass and a birefringent material, and has a property that the refractive index differs depending on the direction of the plane of polarization of an incident light ray. Therefore, of the laser light L incident on the bifocal lens 76, P
Polarization LP becomes convergent light, S-polarization LS becomes parallel light and objective lens
It is incident on 44. The objective lens 44 is configured such that its front focus is located at the rear focus of the bifocal lens 76,
The P-polarized light LP incident as the convergent light is made into parallel light and is irradiated onto a relatively wide area of the surface 18 of the DUT 12, while the S-polarized light LS incident as the parallel light is the convergent light on the surface of the DUT 12. It is focused on one point at 18. The device under test 12 is driven by the drive device 58.
Is mounted on a moving table 60 which can be moved in a two-dimensional direction in the xy plane perpendicular to the optical axis of the objective lens 44 by the S-polarized light LS which is condensed on one point of the surface 18 thereof.
Is a Doppler shift Δfs generated corresponding to the minute unevenness of the surface 18 as the DUT 12 is moved by the moving table 60, and a Doppler shift Δfd due to vibration or other disturbance during the movement of the moving table 60. Then, the frequency of the reflected light becomes fs + Δfd + Δfs. On the other hand, the P-polarized light LP irradiated on the relatively wide area of the surface 18 in the state of the circular parallel beam is canceled out by the Doppler shift Δfd due to the disturbance because the influence of the minute unevenness of the surface 18 is averaged and canceled out. The frequency of the reflected light is fp + Δfd only when affected by. The S-polarized light LS is measurement light, and P
The polarized LP is the reference light.

The P-polarized light LP and the S-polarized light LS reflected by the surface 18 are made incident on the non-polarization beam splitter 32 by following the optical paths opposite to the incident paths, transmitted through the non-polarized beam splitter 32, received by the measurement optical sensor 62, and measured by the measurement beat. The signal FD is output. This measured beat signal FD corresponds to a beat due to the interference between the P-polarized LP and the S-polarized LS, and its frequency fD is | (fs + Δfd + Δ
fs) − (fp + Δfd) | = | fs−fp + Δfs |, and the Doppler shift Δfd due to the disturbance is canceled.

The measurement beat signal FD and the reference beat signal FB are supplied to the measurement circuit 64, and the frequency fD of the measurement beat signal FD is
(= | Fs-fp + Δfs |) to the frequency fB of the reference beat signal FB
By subtracting (= | fs−fp |), only the Doppler shift Δfs due to the unevenness of the surface 18 is taken out, and a signal representing this Doppler shift Δfs is supplied to the control circuit 66. The control circuit 66 is composed of, for example, a microcomputer, and while sequentially moving the moving table 60 in the xy direction by the driving device 58, based on the signal (Δfs) supplied from the measuring circuit 64 based on the following equation (1). The displacement Zs at each position is calculated, and the surface roughness of the entire surface 18 of the object to be measured 12 is three-dimensionally displayed on the display 68.

Zs = ∫ (λ / 2) Δfsdt (1) (λ: wavelength of laser) [Problem to be solved by the invention] However, in the above method, since there is only one objective lens 44, the measured object is left as it is. The measurement magnification could not be changed according to the surface roughness of the object 60. Therefore, adjustment of the device was time-consuming even when high-precision measurement was not required. In addition, in order to change the measurement magnification, the objective lens 44
When the lens is replaced, the focal length of the lens also changes if the measurement magnification changes, so the distance between the lens and the bifocal lens 76 must be finely adjusted each time the lens is replaced.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to facilitate replacement of an objective lens and use a bifocal lens when the surface roughness of an object to be measured is small. The purpose of this study is to make highly accurate measurements and to make simple measurements that do not require a bifocal lens and are easy to adjust if they are relatively large.

[Means for Solving the Problem] In order to achieve this object, the optical surface roughness measuring device of the present invention uses two types of linearly polarized light whose polarization planes are orthogonal to each other and whose frequencies are different from each other. In the optical surface roughness measuring device for detecting the reflected light from each of the two and measuring the surface roughness of the object to be measured based on the change of the beat frequency of the reflected light, a laser beam including the two types of linearly polarized light And a bifocal lens that makes one of the two types of linearly polarized light included in the laser light of the laser light source device parallel light and the other convergent light, and outputs one linearly polarized light Highly converging light on the surface of the member to be measured and irradiating the other linearly polarized light with parallel light, and with an irradiation diameter sufficiently larger than the irradiation diameter of the one linearly polarized light on the surface of the member to be measured. Precision optics and A simple optical system for condensing only one of the two types of linearly polarized light included in the laser light on the surface of the member to be measured,
The optical systems can be switched so that only one of the two types of optical systems can be used.

[Operation] In the optical surface roughness measuring device of the present invention having the above configuration, the laser light source device outputs laser light including two kinds of linearly polarized light whose polarization planes are orthogonal to each other and different in frequency, and When the surface roughness of the measured object is small, the optical system switching device switches to a high-precision optical system including a bifocal lens, and when the surface roughness is relatively large, a simple optical system not including a bifocal lens is switched to perform measurement.

When switching to a high-precision optical system including a bifocal lens, the bifocal lens converts two types of linearly polarized light included in the laser light from the laser light source device into parallel light and focused light on a common optical axis. At the same time, one of the two types of linearly polarized light is condensed as measurement light on the surface of the member to be measured, and the other linearly polarized light is parallel light and is The linearly polarized light is converged onto the condensing point with an irradiation diameter sufficiently larger than the irradiation diameter of the one linearly polarized light. In the measurement beat signal of the reflected light from the one or the other linearly polarized light measured member, the phase corresponding to the change in the relative height position between the condensing point of the one and the other linearly polarized light and the irradiation surface. A shift will occur. Therefore, the surface roughness of the member to be measured can be measured by detecting the frequency shift or the phase change in the measurement beat signal.

On the other hand, when switching to a simple optical system that does not include a bifocal lens, only one linearly polarized light component of the two types of linearly polarized light included in the laser light is condensed on the surface of the member to be measured. In the reflected light from the member to be measured, a phase shift corresponding to the change in the relative height position at the converging point occurs, and the surface roughness of the member to be measured can be measured.

[Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following first and second embodiments are the ones in which the present invention is applied to the conventional example of FIG. 5, and common portions are given the same reference numerals and detailed description thereof will be omitted.

1 and 2 are block diagrams for explaining the first embodiment of the present invention. In FIG. 1, the mirror 75, the bifocal lens 76 and the objective lens 44 are fixed to a uniaxial table 50 which is movable in the x direction. Also a polarizing beam splitter
40, the mirror 42, and the objective lens revolver 46 are also fixed to the same uniaxial table 50. Uniaxial table 50 Knob 52
By moving in the x direction, the optical system can be switched as shown in FIG. Here, the former optical system consisting of the mirror 75, the bifocal lens 76 and the objective lens 44 is a high precision optical system, and the latter optical system consisting of the polarization beam splitter 40, the mirror 42 and the objective lens revolver 46 is a simple optical system,
The uniaxial table 50 and the knob 52 are an optical system switching system.
A relatively high-magnification objective lens 44 is used as the high-precision optical system, and an objective lens 45 having a lower magnification than that is attached to the revolver 46 of the simple optical system. The principle of roughness measurement when switching to the high-precision optical system shown in FIG.

As shown in FIG. 2, when the uniaxial table 50 is used to switch to the simple optical system, the laser beam L from the beam expander 74 is polarized by the polarization beam splitter 40 into S-polarized light LS and P-polarized light.
It is divided into polarized light LP. The S-polarized light LS is reflected downward and is incident on the objective lens 45 mounted on the revolver 46, and is P-polarized light.
The LP passes through the polarization beam splitter 40 and is applied to the mirror 42. The S-polarized light LS that has entered the objective lens 45 is condensed as a convergent light on a point on the surface 18 of the DUT 12. Revolver
By rotating 46, the objective lens can be replaced and the measurement magnification can be changed. The reflected light from the surface 18 is moved by the moving table 60 and is caused by the Doppler shift Δfs corresponding to the minute unevenness of the surface 18.
And the Doppler shift Δfd due to vibrations and other disturbances when the moving table 60 moves, the frequency of the reflected light becomes fs + Δfd + Δfs. Further, the frequency of the reflected light from the mirror 42 remains unchanged at fp because the mirror 42 is fixed. The S-polarized light LS is measurement light and the P-polarized light LP is reference light. The reflected lights of the P-polarized light LP and the S-polarized light LS are combined by the polarization beam splitter 40 and received by the measurement optical sensor 62, and the measurement beat signal FD is output. This measurement beat signal FD corresponds to a beat due to the interference between the P polarized light LP and the S polarized light LS, and its frequency fD is | fs−fp + Δfd + Δf.
s |, which is affected by the Doppler shift Δfd due to disturbance, but in the simple optical system, the object to be measured, which has a relatively large roughness, is measured at a low magnification. The influence of disturbance can be ignored. The surface roughness of the surface 18 of the DUT 12 is calculated from the measurement beat signal FD received by the measurement optical sensor 62 in the same manner as in the conventional method, and displayed on the display 68.

3 and 4 are block diagrams for explaining the second embodiment of the present invention.

In FIG. 3, a high-precision optical system including a bifocal lens 76 and an objective lens 44, a polarization beam splitter 82, and a mirror 84.
And a simple optical system consisting of objective lens 45 is a revolver 80.
Attached to. By rotating the revolver 80, the high precision optical system and the simple optical system can be switched as shown in FIG. Here, the revolver 80 is an optical system switching system. The objective lens 44 of the high precision optical system has a relatively high magnification, and the objective lens 45 of the simple optical system has a lower magnification than that. The principle of roughness measurement when switching to the high-precision optical system shown in FIG. 3 is almost the same as the prior art and the first embodiment described above, but the bifocal lens 76 rotates 90 degrees around the optical axis. In the above-mentioned two examples, the S-polarized light LS is the measurement light and the P-polarized light LP is the reference light, so that the P-polarized light LP is the measurement light and the S-polarized light LS is the reference light in the present embodiment. Has become.

As shown in FIG. 4, when the revolver 80 switches to the simple optical system, the reflected laser light L from the mirror 75 is split by the polarization beam splitter 82 into S-polarized light LS and P-polarized light LP. The S-polarized LS is reflected and irradiated on the mirror 84,
The P-polarized light LP passes through the polarization beam splitter 82 and enters the objective lens 45. The P-polarized light LP incident on the objective lens 45 is condensed as a convergent light on one point on the surface 18 of the DUT 12.
The reflected light from the surface 18 is caused by the Doppler shift Δfs corresponding to the minute unevenness of the surface 18 as the DUT 12 is moved by the moving table 60 and the moving table 60.
The frequency of the reflected light is fp + Δfd + Δfs due to the Doppler shift Δfd due to vibrations and other disturbances during the movement. Further, the frequency of the reflected light from the mirror 42 remains unchanged at fs because the mirror 42 is fixed. Above P
The polarized light LP is the measurement light, and the S polarized light LS is the reference light. The P-polarized LP and S-polarized LS reflected lights are polarized beam splitter 82.
Is received by the measurement optical sensor 62, and the measurement beat signal FD is output. This measurement beat signal FD is P-polarized LP
The frequency fD is | fp−fs + Δfd + Δfs |, which is affected by the Doppler shift Δfd due to disturbance, but the simple optical system has relatively large roughness. Since the object to be measured is measured at a low magnification, the influence of disturbance can be ignored in comparison with the magnitude of surface roughness. From the measurement beat signal FD received by the measurement optical sensor 62, the surface roughness of the surface 18 of the DUT 12 is calculated in the same manner as in the conventional method, and displayed on the display 68.

Although the two embodiments of the present invention have 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 laser light source 30 is orthogonal 2
Although the frequency Zeeman laser was used, a laser light source of the type that forms a desired frequency difference between two linearly polarized lights by using a frequency shifter provided with an acousto-optic modulator or the like may be used. In this case, the reference beat signal FB can also be detected from the drive frequency signal of the acousto-optic modulator.

Further, in the above-described embodiment, the object to be measured 12 is moved in two directions by the moving table 60 driven in the x direction and the y direction. The surface roughness may be measured by moving in only one direction.

Further, for example, a microscope lens barrel is provided above the polarization beam splitter 40 so that the measurement state can be monitored, or an optical isolator is inserted between the laser light source 30 and the beam splitter 32. It can be implemented in a mode in which various changes and improvements are added based on the above.

[Advantages of Device] As is clear from the above description, according to the present invention, it is possible to switch between a high-precision optical system using a bifocal lens and a simple optical system not using a bifocal lens. Therefore, the objective lens can be easily replaced, and when the surface roughness of the DUT is small, high-precision measurement is performed using the bifocal lens, and when it is relatively large, it is easy without using the bifocal lens. Simple measurement can be performed with simple adjustment.

[Brief description of drawings]

1 to 4 show an embodiment in which the present invention is embodied, and FIGS. 1 and 2 show the construction of an optical surface roughness measuring apparatus according to the first embodiment of the present invention. FIGS. 3 and 4 are schematic diagrams for explaining the configuration of an optical surface roughness measuring apparatus according to a second embodiment of the present invention.
FIG. 1 is a configuration diagram illustrating an example of a conventional optical surface roughness measuring device. 30: Laser light source 32: Beam splitter 33: Polarizer 34: Reference optical sensor 74: Beam expander 75: Mirror 76: Dual focus lens 44: Objective lens 12: Object to be measured 18: Surface 60: Moving table 61: Polarizer 62: Optical sensor for measurement 40: Polarization beam splitter 46: Revolver 45: Objective lens 42: Mirror 50: Uniaxial table 52: Knob 64: Measurement circuit 66: Control circuit 68: Display 58: Drive device 80: Revolver 82 : Polarizing beam splitter 84: Mirror LP: P polarized light (linear polarized light) LS: S polarized light (linear polarized light)

Claims (1)

(57) [Scope of utility model registration request] 1. Reflected light from an object to be measured detects two kinds of linearly polarized light whose polarization planes are orthogonal to each other and different in frequency, and the object to be measured is based on a change in beat frequency of the reflected light. An optical surface roughness measuring device for measuring the surface roughness of a laser light source device for outputting a laser beam containing the two types of linearly polarized light, and two types of linearly polarized light included in the laser beam of the laser light source device. A bifocal lens having one of them as parallel light and the other as converging light is included, and one linearly polarized light is condensed on the surface of the member to be measured, and the other linearly polarized light is parallel light, and A high-precision optical system that irradiates the surface of the member to be measured with an irradiation diameter that is sufficiently larger than the irradiation diameter of the one linearly polarized light, and only one of the two types of linearly polarized light included in the laser light is measured. Collected on the surface of the member It is a simple optical system causes the two optical systems the optical surface roughness measuring apparatus characterized by capable of switching the optical system to be able to use only one of.