JP3461566B2 - Interferometer for measuring cone shape - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conical measuring interferometer capable of accurately measuring the shape of a conical surface of an object to be measured such as a conical lens.

[0002]

2. Description of the Related Art Conventionally, the shape of a conical object such as a conical lens is measured by contacting the conical lens with a Newton plate and visually observing interference fringes, or It was done by applying a stylus.

[0003]

However, when the Newton plate is used, the Newton plate has a planar shape and therefore only partially contacts the conical shape. It could only be predicted by combining the measurement results.

Further, when a stylus is applied, the measurement accuracy is low, and it has been difficult to obtain sufficient accuracy when measuring a conical lens or the like.

Therefore, an object of the present invention is to provide a conical shape measuring interferometer capable of measuring the shape of the conical surface of an object having a conical surface with high accuracy.

[0006]

In order to achieve the above object, the invention according to claim 1 provides a light supply means for supplying measurement light of a certain wavelength and a light from the light supply means in parallel. A collimator lens, a reflecting film, and a flat reference plate having a concentric circular diffraction grating at equal intervals formed on one surface, and reflects a part of the light from the collimator lens. Along with the reference plate that diffracts the light of other parts and makes it incident perpendicularly on the conical surface of the DUT, and diffracts the light reflected by this surface again, it is placed between the light supply means and the reference plate, and A semi-transparent mirror that reflects the light reflected by the film and the light reflected by the surface of the DUT and diffracted by the diffraction grating,
And a light receiving section for receiving the two lights reflected by the semitransparent mirror.

Further, the invention according to claim 2 is characterized in that the light supplying means for supplying the parallel light for measuring a constant wavelength and the parallel light are
A semi-transparent mirror that is formed by transmitting a part of the light and reflecting the other part to separate the light into two parts, and a flat reference plate on one surface of which diffraction gratings with equal intervals and concentric circles are formed. It is separated by a semi-transparent mirror and a reference plate that diffracts one of the two light beams separated by the mirror and makes it vertically incident on the conical surface of the DUT, and diffracts the light reflected by this surface again. Further, the flat mirror that reflects the other of the two lights and the light receiving unit that receives the light from the reference plate and the light from the flat mirror, which are combined again by the semitransparent mirror, are provided.

Further, in claim 1 or 2, the light supply means may include a wavelength tunable laser light source.

[0009]

In the present invention, the light reflected by the conical surface whose optical path is bent by the diffraction grating and the light reflected by the reference plane interfere with each other to form interference fringes. Therefore, the shape of the conical surface can be measured with high accuracy by observing the interference fringes.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the same reference numerals are used for the same or corresponding parts in the drawings.

FIG. 1 is a diagram showing the structure of a Fizeau-type conical interferometer for measuring a cone shape according to the present invention. In FIG. 1, a laser beam for measurement having a constant wavelength supplied from a laser light source 1 passes through a diver jar lens 2 and a semitransparent mirror 3 and then is collimated by a collimator lens 4 to form a flat reference plate. Up to 5. A reflection film 6 made of chrome or the like is formed on the surface of the reference plate 5 opposite to the collimator lens 4, and a part of the light from the collimator lens 4 is reflected by the reflection film 6. The reflected light is converged by the collimator lens 4, reflected by the semitransparent mirror 3 to have its optical path bent, further imaged by the imaging lens 7, and received by the television camera 8.

On the other hand, the reflection film 6 is engraved with concentric circular diffraction gratings at equal intervals by electron beam drawing or the like, and a part of the light traveling from the collimator lens 4 toward the reference plate 5 is diffracted by the diffraction grating. . The diffracted light has its optical path bent in the direction of the central axis of the concentric diffraction grating, and has the conical shape of the conical lens 9 which is the object to be measured and is arranged on the side opposite to the collimator lens 4 with respect to the reference plate 5. Incident perpendicular to the surface. The object to be measured may be something other than a conical lens as long as it has a conical surface. The light that is incident perpendicularly to the surface of the conical lens 9 is reflected by that surface and returns to the reference plate 5 through the original optical path. Then, the optical path is bent again by the diffraction grating to make the light flux parallel, and the light is received by the television camera 8 through the same optical path as the light reflected by the reflective film 6.

The laser light source 1 and the diver jar lens 2 constitute a light supplying means, and the television camera 8 constitutes a light receiving portion.

Between the two lights received by the television camera 8, that is, the light reflected by the reflective film 6 and the light reflected by the surface of the conical lens 9, the surface of the reflective film 6 on the conical lens 9 side and the conical surface. There is an optical path difference depending on the distance between the lens 9 and the conical surface. Therefore, as long as the surface shape of the surface of the reference plate 5 on which the reflective film 6 is formed is highly accurate, the interference fringes of the two lights observed by the television camera 8 are conical surfaces of the conical lens 9. It represents the shape of.
This interference fringe is displayed on the monitor 10 connected to the television camera 8, and the conical surface of the conical lens 9 can be measured with high accuracy from the displayed interference fringe.

Although the light receiving unit is the television camera 8, a screen (not shown) arranged behind the imaging lens 7 may be used as the light receiving unit. In this case,
By observing the interference fringes projected on the screen with the naked eye, the conical surface of the conical lens 9 is measured with high accuracy.

Next, the details of the diffraction grating formed on the reflection film 6 will be described with reference to FIG. FIG. 2 (a) is a diagram showing the relationship between the reference plate 5 and the conical lens 9, and FIG. 2 (b)
FIG. 3A is a side view of (a) and is a view of the reflective film 6 seen from the front. First, all the lights that are incident perpendicularly on the conical surface of the conical lens 9 are bent at the same diffraction angle θ, so that the interval d between the concentric circles is constant. Also, the conical lens 9 to be measured
Assuming that the apex angle of α is α, there is a relation of θ = (π−α) / 2 (1) between α and θ from FIG. If this θ is used, the concentric circle interval d is determined as follows: d = λ / sin θ (2) where λ is the wavelength of the laser light of the laser light source 1. For example, in order to measure an object to be measured having an apex angle α = 120 ° with a laser beam having a wavelength λ = 632.8 nm, the distance d between the diffraction gratings is about 0.7 μm. Also, using a diffraction grating with a spacing d = 1 μm, the wavelength λ = 63
The apex angle α of the object to be measured which can be measured by the 2.8 nm laser beam is about 101.5 °.

Concentric diffraction gratings are drawn on the reflection film 6 by the electron beam drawing method at the intervals d thus obtained. The diffraction grating may be formed by etching. Further, as can be seen from FIG. 2, it is not necessary to form a diffraction grating in the center of the reflective film 6.

In this embodiment, the diffraction grating spacing d
Since the apex angle α of the cone is determined when is determined, only the measurement object having the same apex angle α can be measured. Therefore, if the wavelength of the laser light supplied from the laser light source 1 is made variable, it is possible to measure the objects to be measured having various apex angles with one reference plate 5. For example, if the distance between the diffraction gratings is d = 1 μm and the wavelength of the laser light of the laser light source 1 is variable between λ ₁ = 690 nm and λ ₂ = 825 nm, the movable range of θ can be calculated from equation (2). Therefore, the range of the apex angle α measurable by the equation (1) is α ₁ = 9
2.7 ° to α ₂ = 68.8 ° is obtained. That is, in this case, the shape of a conical surface having an apex angle of 68.8 ° to 92.7 ° can be measured.

Although the Fizeau type interferometer has been described in the above embodiment, a Michelson type or a Twyman-Green type interferometer may be used.

FIG. 3 is a diagram showing the configuration of a conical shape measuring interferometer using a Michelson type interferometer. The laser light supplied from the laser light source 1 has its light flux expanded by the lens 11 and is converted into parallel light by the collimator lens 12. Part of this parallel light is transmitted through the semitransparent mirror 13, passes through the diffraction grating as in the case of FIG.
It is reflected by the conical surface of, and is reflected by the semitransparent mirror 13 to reach the television camera 8. On the other hand, the light reflected by the semitransparent mirror 13 is reflected by the plane mirror 14, passes through the semitransparent mirror 13, and reaches the television camera 8. The laser light source 1, the lens 11 and the collimator lens 12 constitute a light supply means. Then, the two lights incident on the TV camera 8 are
Since interference fringes are formed as in the case of FIG. 3, the shape of the conical surface of the conical lens 9 can be measured with high accuracy.

In the case of FIG. 1 using a Fizeau interferometer, it is preferable to form the reflection film 6 on the surface of the reference plate 5 on the side of the conical lens 9 among the two surfaces. This is because if the light path inside the reference plate 5 is common to the light reflected by the reflection film 6 and the light reflected by the object to be measured, the surface of the reference plate 5 on which the reflection film 6 is not formed is highly accurate. This is because it does not need to be processed.
On the other hand, in the case of FIG. 3 using the Michelson type interferometer, the surface of the reference plate 5 on which the reflection film 6 is not formed needs to be processed with high accuracy. This is because the light passing through the reference plate 5 is only one of the two interfering lights, and therefore the thickness of the reference plate 5 directly affects the measurement accuracy.

Further, although the light source is the laser light source in the above embodiments, it may be a monochromatic light source.

[0023]

As described above, according to the present invention, the light reflected by the conical surface whose optical path is bent by the diffraction grating and the light reflected by the reference plane interfere with each other to form an interference fringe. Therefore, it is possible to obtain a conical shape measuring interferometer capable of measuring the surface shape of the object to be measured having a conical surface with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a Fizeau-type conical measuring interferometer configured according to the present invention.

FIG. 2A is a view showing a relationship between a reference plate and a conical lens which is an object to be measured, and FIG. 2B is a side view of FIG. 2A, which is a front view of a reflection film.

FIG. 3 is a diagram showing a configuration of a Michelson-type conical interferometer for measuring a cone shape, which is configured according to the present invention.

[Explanation of symbols]

1 ... Laser light source, 2 ... Diver jar lens, 3 ... Semi-transparent mirror, 4 ... Collimator lens, 5 ... Reference plate, 6 ... Reflective film, 9 ... Cone lens, 11 ... Lens, 12 ... Collimator lens, 13 ... Semi-transparent mirror.

Claims (3)

(57) [Claims] 1. A light supply means for supplying measurement light having a constant wavelength, a collimator lens for collimating the light from the light supply means, a reflection film, and a diffraction grating having equal intervals and concentric circles. Is a flat reference plate formed on the surface of, and while reflecting a part of the light from the collimator lens,
A reference plate for diffracting the light of the other part to make it perpendicularly incident on the conical surface of the DUT, and diffracting the light reflected by this surface again, and arranged between the light supply means and the reference plate, A semi-transparent mirror that reflects the light reflected by the reflection film and the light that is reflected by the surface of the object to be measured and diffracted by the diffraction grating; and a light-receiving unit that receives the two lights reflected by the semi-transparent mirror,
A conical interferometer for measuring a conical surface of an object to be measured by the interference of two lights received by the light receiving section. 2. A light supply means for supplying parallel light for measuring a constant wavelength, and a semitransparent mirror for separating the parallel light into two by transmitting a part of the parallel light and reflecting the other part. A flat reference plate having equidistant and concentric circular diffraction gratings formed on one surface thereof, and diffracts one of the two lights separated by the semitransparent mirror to form a conical shape of an object to be measured. A reference plate for making the light incident perpendicularly on the surface of the light and diffracting the light reflected by this surface again; a plane mirror for reflecting the other of the two lights separated by the semitransparent mirror; A light receiving section for receiving light from the reference plate and light from the plane mirror,
A conical interferometer for measuring a conical surface of an object to be measured by the interference of two lights received by the light receiving section. 3. The conical shape measuring interferometer according to claim 1, wherein the light supply unit includes a variable wavelength laser light source.