JPH044166Y2 - - 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. When the stylus 2, which is supported by an upper and lower pair of parallel springs 5 and 5, 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 the half mirror 12 is sent to the first and second photodiodes 14 and 16 through the first critical angle prism 13, and the laser beam transmitted through the half mirror 12 is transmitted to the second critical angle prism 13. 15 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 is reflected from the surface to be measured and enters the first and second critical angle prisms 13 and 15 changes. changes, and as a result, the intensity of the light reaching the first and second photodiodes 14 and 16 changes, so if a change in the output difference between the first and second photodiodes 14 and 16 is detected, the You can see the unevenness of the measurement surface. To further explain the principle of the critical angle prism with reference to Figure 3,
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 light enters the critical angle prisms 13 and 15 through a path as shown by the chain line in the figure. In this state, a portion of the laser light passes through the prism without being reflected, so the laser light entering the first and second photodiodes 14 and 16 becomes weaker, but the degree of this weakening is is larger 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 figure, and the potential difference opposite to that at position A described above becomes first, occurs between the second photodiodes 14,16. 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 fine shape of the surface to be measured can be determined from this potential difference V. In addition, in FIG. 2, two critical angle prisms, first and second, are prepared, and first and second photodiodes 14, 1
The reason why two sets of 6 are provided is to cancel errors caused by the inclination of the surface 1 to be measured.

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. Furthermore, the collimator lens 8
Since the laser light passing through is only a part of the laser light projected from the laser diode 7, the intensity of the laser light projected onto the surface to be measured 1 becomes weaker, and the reflectance of the surface to be measured 1 decreases. If it is low, it will be difficult to make accurate measurements.

It is an object of the present invention to provide a micro-shape measuring instrument that does not adversely affect measurement due to the presence of such interference portions and can effectively utilize the laser light projected from the laser diode.

b. Structure of the invention The micro-shape measuring device of the invention has a device between a laser diode that projects a laser beam and an objective lens that narrows down the laser beam to project it onto a surface to be measured.
By providing an optical path that converts the cross section of the laser beam into a circular one, an interference portion 18 as shown in FIG.
18 does not exist.

The optical path that converts the cross section of the light beam from an ellipse to a circular shape in this way is constructed by a cylindrical lens, a prism, or a combination of the two, and the light beam of the laser beam is directed in the long axis direction of the elliptical cross section. By compressing or stretching in the minor axis direction, the cross-sectional shape of the beam of this laser beam is converted into a circular shape.

First, a case where the optical path for cross-sectional shape conversion is constructed by a cylindrical lens will be explained with reference to FIG. 11. The optical path formed by this cylindrical lens includes a concave cylindrical lens 20 and a convex cylindrical lens 21 arranged in series. When converting the cross-sectional shape of a light beam from an ellipse to a circle using this optical path, the short axis direction can be stretched or the long axis direction can be compressed, but first, the case of stretching the short axis direction will be explained. When a light beam having an elliptical cross section is stretched in the short axis direction, the light beam having an elliptical cross section is projected from the side of the cylindrical lens 20 having a concave lens shape. At this time, the long axis direction of the ellipse and the arrangement direction of the cylindrical lenses are made to coincide. In this way, the light beam projected from the side of the concave cylindrical lens 20 passes through this lens 20, so that
It is spread out in the direction of the minor diameter. Since the long axis direction of the ellipse is not diffused and passes through the cylindrical lens 20 in the diffused or parallel state projected from the laser diode, the light beam after passing through the cylindrical lens 20 has a circular cross section at a certain distance behind. Become. The cross-sectional shape of the light beam becomes an elliptical shape behind the certain distance, with the long axis facing in a direction perpendicular to that in front of the certain distance. Therefore, a convex cylindrical lens 21 is arranged parallel to the concave cylindrical lens 20 at the certain distance position where the cross-sectional shape of the light beam is exactly circular, and the angle at which the light beam is diffused after passing through the concave cylindrical lens 20 is adjusted. It is configured so that the diffusion angle of the light flux, which is increased in only one direction, is made to be the same in all directions. Therefore, the cross section of the light beam after passing through the convex cylindrical lens 21 is circular in any part. In the micro-shape measuring instrument shown in FIG. 2, this light beam with a circular cross section is converted into a parallel light beam through a collimator lens 8, and then projected onto a polarizing beam splitter 9.
The light is further focused by an objective lens 11 and then projected onto the surface to be measured 1. A pair of cylindrical lenses 20, 21
The beam of laser light whose cross section has been converted into a circular shape by passing through the The result is a Gaussian distribution as shown in the figure. Therefore, when this light beam is condensed by the objective lens 11, interference parts 18, 18 as shown in FIG. 9 will not occur due to diffraction.

In the above description, an example has been described in which the cross-sectional shape of the light beam is converted into a circular shape by stretching it in the short axis direction, but it is also possible to convert the cross section into a circular shape by compressing the cross section in the long axis direction using a similar configuration. That is, when compressing the cross section in the long axis direction, a light beam having an elliptical cross section is projected from the side of the cylindrical lens 21 having a convex lens shape to converge the light beam in the long axis direction. A concave cylindrical lens 21 is arranged to obtain a light beam having a circular cross section.

Further, the cross-sectional shape of the light beam can be converted from an ellipse to a circle by using a prism, in addition to the above-mentioned cylindrical lens. That is, as shown in FIGS. 12 and 13, by passing a light beam having an elliptical cross section through a triangular prism 22, the light beam having an elliptical cross section is stretched in the short axis direction or compressed in the long axis direction, so that the cross section of the light beam becomes circular. can do. By passing through one prism,
Although the direction of the optical axis changes, this does not cause any particular inconvenience when it is incorporated into a fine shape measuring instrument, and the direction of the optical axis can be easily maintained as it is by combining two prisms.

Furthermore, by combining a prism and a cylindrical lens, it is also possible to configure an optical path that turns a light beam with an elliptical cross section into a light beam with a circular cross section.

No matter which way the optical path is configured, the entire beam of light with an elliptical cross section projected from the laser diode is used to illuminate the surface to be measured 1, and before passing through the objective lens, the light beam with a circular cross section is Since the light beam has a Gaussian intensity distribution in any direction, the intensity of the laser beam after passing through the objective lens is sufficiently strong, and there is no interference as shown in FIG. 9.

c. Effects of the invention Since the micro-shape measuring device of the present invention is configured as described above, it is possible to accurately measure minute irregularities on the surface to be measured without being affected by interference, and the laser beam projected onto the surface to be measured can be used. Since the intensity of the light is high, it becomes possible to measure surfaces to be measured with lower reflectance than before.

[Brief explanation of drawings]

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 the first example of the principle of an optical micro-shape measuring device, and Fig. 3 is a critical angle Figure 4 is a schematic side view showing the principle of a prism, Figure 4 is a diagram showing the relationship between the potential difference and displacement generated by a critical angle prism, and Figure 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. Figure 11 is a perspective view showing the optical path for cross-sectional shape conversion using a cylindrical lens;
Figure 12 is a perspective view of the optical path using a prism,
Figure 3 is also a plan view. 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 portion, 18... Interference portion, 19, 20, 21... Cylindrical lens, 22... Prism.

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 that has passed through 0 is reflected by the polarizing boom 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 coming out of 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.
In a micro-shape measuring instrument in which cylindrical lenses 19, 20,
21 and a prism 22 to make the cross section of the elliptical laser beam emitted by the laser diode 7 circular so that the intensity distribution of the light is Gaussian in either direction. A fine shape measuring instrument characterized by being provided in front of a beam splitter 9.