JPH044167Y2 - - Google Patents

Description

[Detailed explanation of the invention] a. Purpose of the invention (industrial application field) The micro-shape measuring instrument according to the invention is used for various high-precision measurements such as measuring the surface roughness of mirror-finished metal surfaces. Ru.

(Prior art) In order to perform various precision shape measurements such as the surface roughness of metal surfaces, optical lever type or electric type fine shape measuring instruments, or devices with relatively low precision such as micrometers and dial gauges are used. It is used.

Among these, an electric micro-shape measuring device will be explained. As shown in Fig. 1, the electric micro-shape measuring device has an iron core 3 fixed in the middle of a stylus 2 that moves up and down following the irregularities of the surface to be measured 1, and a structure surrounding the iron core 3. The coil 4 constitutes a differential transformer, and when the stylus 2 supported by a pair of upper and lower springs 5, 5 parallel to each other rises and falls according to the unevenness of the surface to be measured 1, the output of the coil 4 changes. The voltage changes in proportion to the amount of displacement of the stylus 2. Therefore, the uneven shape of the surface to be measured 1 can be known from this voltage change. 6 is a spring for adjusting measurement pressure.

Such conventional micro-shape measuring instruments move the stylus while keeping it in contact with the surface of the object to be measured during measurement, thereby damaging the surface of the object to be measured. For this reason, various types of optical micro-shape measuring instruments using laser light are known that can measure the shape of a surface to be measured without bringing a probe such as a stylus into contact with the surface to be measured. Next, the principle of this optical micro-shape measuring instrument will be briefly explained.

2 to 4 show a first example of the principle of an optical micro-shape measuring device. This principle is described in Proceedings of the 1986 Precision Machinery Society Autumn Conference Academic Lectures, Nos. 391-392.
Page 1 and pages 1 to 2 of Kikaiken News No. 9, 1983, published by the Institute of Mechanical Technology, Agency of Industrial Science and Technology. The laser beam sent out from the laser diode 7 passes through the collimator lens 8 shown in FIG.
polarizing beam splitter 9, quarter wavelength plate 10,
is projected onto the surface to be measured 1 through the objective lens 11,
Furthermore, this laser beam is reflected by this surface to be measured 1 and passes through the objective lens 11 and the quarter wavelength plate 10 again.
It is reflected by the polarizing beam splitter 9 and sent to the half mirror 12. The laser beam reflected by this half mirror 12 is projected onto a first critical angle prism 13 at a critical angle, and is then transmitted to the first and second photodiodes 1.
The laser beam transmitted through the half mirror 12 is projected onto the second critical angle prism 15 at a critical angle, and is similarly sent to the first and second photodiodes 14 and 16. When the distance between the objective lens 11 fixed to the measurement head and the surface to be measured 1 changes,
The incident angle of the laser beam that enters the first and second critical angle prisms 13 and 15 after being reflected from this surface to be measured changes, and as a result, the light that reaches the first and second photodiodes 14 and 16 Since the strength of the photodiode changes, the unevenness of the surface to be measured can be determined by detecting the change in the output difference between the first and second photodiodes 14 and 16. Part 3 showing the principle of critical angle prism
To further explain with reference to the figure, when the surface to be measured is at position B, the laser beam reflected from the surface to be measured enters the first and second photodiodes 14 and 16 along the path shown by the solid line in the figure. Both photodiodes output the same magnitude (potential difference 0). When the surface to be measured approaches position A, the reflected laser beam passes through the critical angle prism 13, along the path shown by the chain line in the figure.
Enter 15. In this state, a portion of the laser light is transmitted through the prism without being reflected, so that the first and second photodiodes 14, 1
The laser beam entering the photodiode 6 becomes weaker, but the degree of this weakening is greater in the first photodiode 14 than in the second photodiode 16, so there is a difference in the outputs of both diodes 14 and 16. On the other hand, when the surface to be measured moves away to position C, the reflected laser light enters the critical angle prisms 13 and 15 along the path shown by the broken line in the same figure, and the potential difference opposite to that at position A described above becomes first, second photodiode 14,
Occurs between 16 and 16. Since there is a relationship as shown in FIG. 4 between the amount of displacement of the surface to be measured and the output potential difference V, the minute shape of the surface to be measured can be determined from this potential difference V. The reason why two critical angle prisms, first and second, and two sets of first and second photodiodes 14 and 16 are provided in FIG. 2 is based on the inclination of the surface to be measured 1. This is to cancel errors.

Further, FIG. 5 shows another principle of the optical micro-shape measuring device. This principle is called the astigmatism method, and is published in the Proceedings of the 1981 Spring Conference of the Japan Society of Precision Machinery Engineers.
It is described on pages 393-394, and when the light beam is focused by a semicircular cylindrical lens 19,
Using the fact that the cross section of the light flux changes continuously into a straight line, a vertically elongated ellipse, a circle, and a horizontally elongated ellipse depending on the distance from this lens, the cross-sectional change of the light flux is determined using a four-part photodiode. The minute shape of the surface to be measured is measured based on this cross-sectional change.

Other principles of measuring instruments that use laser light include those described in the Proceedings of the 1981 Spring Conference of the Japan Society of Precision Machinery Engineers, pages 523 to 526, and the Proceedings of the Academic Conference of the Japan Society of Precision Machinery Autumn Conference, pages 413 to 526 of the same year. These include those listed on page 414. A fine shape measuring device manufactured based on either principle can measure the fine shape of a surface to be measured without bringing a contactor or the like into contact with the surface to be measured.

(Problems to be Solved by the Invention) However, in the conventional optical micro-shape measuring instrument as described above, the following disadvantages occur.

That is, the cross-sectional shape of the beam of laser light projected from the laser diode 7 to irradiate the surface to be measured is not circular but elliptical as shown in FIG.
The intensity of light in such a light beam having an elliptical cross section has a Gaussian distribution in which it is strong in the center and gradually becomes weaker toward the periphery. That is, A-A in FIG.
The short axis direction shown by the line has a sharp intensity distribution as shown in FIG. 7, and the long axis direction also shown by the line B-B has a relatively gentle distribution as shown in FIG.

By the way, when projecting a laser beam onto a surface to be measured, it is preferable that the cross section of the laser beam is not elliptical but circular. For this reason, in the past, a laser diode 7 was used to convert the flared laser beam into a parallel beam.
The size of the collimator lens 8, which is installed immediately after the laser beam, is designed to allow only the central circular part of the laser beam with an elliptical cross section to pass through, as shown by the oblique lattice in Figure 6, and is sent to the rear of the collimator lens 8. The cross section of the light beam is made to be circular. When a part of the light beam with an elliptical cross section is extracted by the collimator lens 8 in this way, the intensity distribution of the light in the direction of line B-B in FIG. 6 becomes as shown by the diagonal lattice in FIG. 8. A non-Gaussian distribution is formed in which the light intensity rapidly decreases at both ends. However, even in this case, the intensity distribution of light in the direction of line A--A in FIG. 6 becomes a Gaussian distribution as shown in FIG. 7.

A light beam having such an intensity distribution is narrowed down by the objective lens 11 to reduce its diameter and irradiate the surface to be measured 1. However, when the intensity distribution is a non-Gaussian distribution as shown by the oblique lattice in FIG. , objective lens 1
Due to the diffraction of light that occurs when passing through the light beam 1, the cross section of the light beam changes as shown in FIG. That is, in addition to the original circular portion 17, crescent-shaped interference portions 18, 18 are generated in the cross section of the light beam. The intensity of the light from the interference portions 18, 18 is weaker than the intensity of the light from the circular portion 17, as shown in FIG. The presence of these substances may adversely affect the measurement results.

It is an object of the present invention to provide a micro-shape measuring instrument in which measurement is not adversely affected by the presence of such interference parts.

b. Structure of the invention The micro-shape measuring device of the invention converts the cross-sectional shape of the laser beam from an ellipse to a circle between the laser diode 7 that projects the laser beam and the objective lens 11, and furthermore, the micro-shape measuring instrument of the present invention converts the cross-sectional shape of the laser beam from an ellipse to a circular shape. By providing a filter such that the intensity distribution is Gaussian in any direction of the cross section, interference parts 18, 18 as shown in FIG. I try not to exist.

In this way, the filter that converts the cross-sectional shape of the beam of the laser beam from an ellipse to a circle and at the same time makes the intensity distribution of the light in the cross-sectional direction into a Gaussian distribution is the 11th filter.
Use something like the one shown in the diagram. In FIG. 11, the portion indicated by the diagonal lattice is an opaque portion that does not transmit any light, and a circular portion 21 that transmits light is provided at the center of this opaque portion 20. Furthermore, inside this circular part 21, there is a semi-transparent part 2 shown by diagonal lines that allows only a portion of the light to pass through, and a transparent part 2 shown by white lines that allows 100% or close to the light to pass through.
3 are provided. The transparent portion 23 is provided across the diameter of the circular portion, and the semi-transparent portions 22 shown with diagonal lines are provided on both sides of the transparent portion 23. The rate at which the semi-transmissive portion 22 transmits the laser beam (transmittance) is not uniform throughout the hatched portion, and the opaque portion 2 indicated by the diagonal grid
The transmittance is continuously changed so that the closer it is to 0, the lower the transmittance is, and conversely, the closer it is to the transparent portion 23 shown in white, the higher the transmittance is. Furthermore, transparent part 2
3 also does not have 100% transmittance throughout, but the transmittance of the part near the semi-transparent part 22 is slightly lower,
The laser beam is transmitted in all directions of the circular portion 21 in a Gaussian distribution.

When projecting a laser beam with an elliptical cross section toward such a filter, the short axis of the laser beam and the direction of the transparent portion 23 of the filter should match, as shown by the chain line a in FIG. and project it. When a laser beam is thus projected toward the filter configured as described above, the cross-sectional shape of the laser beam becomes a circle matching the circular portion 21 at the center of the filter. Furthermore, due to the presence of the semi-transparent part 22 provided inside the circular part 21, the laser beam that passes through this circular part 21 has a circular cross section, and the light intensity distribution of the laser beam sent to the rear of the filter is determined in either direction of the cross section. Even in this case, the luminous flux has a Gaussian distribution shape as shown in FIG. 7, in which the central part is high and the luminous flux is low toward the periphery.

Therefore, even when the beam of the laser beam after passing through the filter is focused by the objective lens 11 and projected onto the surface to be measured 1, a portion of the beam of the laser beam will have interference parts 18, 18 as shown in FIG. This does not occur, and the presence of the interfering parts 18, 18 does not cause errors in the measured values.

Note that the filter may be provided between the laser diode 7 and the collimator lens 8 or between the collimator lens 8 and the objective lens 11. In addition, in the illustrated example, the diameter of the circular portion 21 that transmits light at the center of the filter is equal to the short axis of the ellipse in the cross section of the laser beam, so the white transparent portion 23 extending in the short axis direction is The light should be 100% over the entire length of the circular part 21.
When the diameter of the ellipse is smaller than the minor axis of the ellipse, the transmittance of both ends of the transparent portion is made to gradually decrease.

c. Effects of the invention Since the micro-shape measuring instrument of the present invention is constructed as described above, no interference occurs in the laser beam that irradiates the surface to be measured, and minute irregularities on the surface to be measured are not affected by interference. Accurate measurements can be taken without any interference.

[Brief explanation of the drawing]

Fig. 1 is a schematic vertical side view showing an example of a contact type micro-shape measuring device, Fig. 2 is a schematic side view showing a first example of the principle of an optical micro-shape measuring device, and Fig. 3 is a critical angle A schematic side view showing the principle of a prism, Fig. 4 is a diagram showing the relationship between the potential difference and displacement generated by a critical angle prism, and Fig. 5 is a schematic side view showing a second example of the principle of an optical micro-shape measuring instrument. 6 is a diagram showing a cross section of a light beam projected from a laser diode, and FIG. 7 is a diagram showing a light intensity distribution of this light beam in the short axis direction.
Figure 8 is a diagram showing the light intensity distribution in the major axis direction, Figure 9 is a cross-sectional view showing the light flux due to interference occurring in the major axis direction, and Figure 10 is a diagram showing the light intensity distribution in the major axis direction. FIG. 11 is a plan view of a filter to be incorporated into the micro-shape measuring instrument of the present invention. 1... Surface to be measured, 2... Stylus, 3... Iron core, 4
... Coil, 5, 6 ... Spring, 7 ... Laser diode, 8 ... Collimator lens, 9 ... Polarizing beam splitter, 10 ... Quarter wavelength plate, 11
...Objective lens, 12...Half mirror, 13...
...first critical angle prism, 14...first photodiode, 15...second critical angle prism, 1
6... Second photodiode, 17... Circular part, 18... Interference part, 19... Cylindrical lens, 20... Non-transparent part, 21... Circular part, 22... Semi-transparent part, 23... Transparent part.

Claims (1)

[Scope of utility model registration request] It consists of a light projecting means and a light receiving means, and the light projecting means is
The laser light emitted by the laser diode 7 is passed sequentially through a collimator lens 8, a polarizing beam splitter 9, a quarter wavelength plate 10, and an objective lens 11, and the objective lens 11 is applied to the measurement surface 1 of the object placed on the sample stage. The light receiving means reflects the light from the surface to be measured, and includes an objective lens 11 and a quarter wavelength plate 1.
The laser beam passing through 0 is reflected by the polarizing beam splitter 9 and is incident on the critical angle prisms 13 and 15 at a critical angle, so that the laser beam is perpendicular to the optical axis of the laser beam exiting from the critical angle prism and the incident light is changed from parallel to diffused. / Two photodiodes 1 in the direction in which the ratio of the amount of light incident on each changes as it shifts to converge.
4 and 16 arranged adjacent to each other, there is a circular part 21 into which light with a Gaussian distribution in the short axis direction of the elliptical laser beam emitted from the laser diode 7 is inserted, and light that deviates from this circular part 21. The circular part 21 has a transmissive part 23 with high transmittance in the short axis direction of the elliptical laser beam passing through the center, and a semi-transparent part 22 with low transmittance in the long axis direction peripheral part. In addition, the laser diode 7 is provided with a filter that gradually increases the transmittance from the periphery toward the center and makes the transmitted light have a Gaussian distribution in all directions of the circular portion 21.
and an objective lens 11.