JPH04328409A - Surface roughness meter - Google Patents

Abstract

PURPOSE:To measure accurate roughness by providing a constitution wherein fluctuations are canceled even if there are fluctuations in the direction perpendicular to the optical axis and in the moving direction when the surface to be detected of a material to be detected for a surface roughness meter using a differential-type laser-interference length measuring machine in moved. CONSTITUTION:There are length measuring luminous flux and reference luminous flux which are emitted in parallel from an interference prism 1. The length measuring luminous flux enters a main condenser lens 2. The luminous flux is converged on a surface to be dected 5 and reflected from the surface 5. The luminous flux passes through the lens 2 again and becomes the luminuous flux which is in parallel with the length measuring flux. The luminous flux is returned to the interference prism 1. Meanwhile, the reference luminous flux is converged through a reference luminous flux condenser lens. The image is formed in a position in front of the focal point of the main condenser lens 2, and the luminous flux is reflected. The luminous flux enters the main condenser lens 2 at an incident angle theta. The parallel luminous flux is formed in that direction and reflected from the surface to be detected 5. The parallel luminous flux is made to enter with a main luminous flux lens at a reflecting angle theta and outputted. The luminous flux is reflected from a second reflecting mirror or prism 6 so as to enter into a second reference luminous flux condenser lens 7. The parallel luminous flux is formed and returend into the interference prism 1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface roughness meter that uses a differential laser interferometric length measuring device to reduce errors caused by movement of an object to be inspected during movement or scanning.

0002

2. Description of the Related Art In an interference prism 1 of a differential laser interferometric length meter, as shown in FIG. After converging the light and focusing it on the surface 5 to be measured and reflecting it from the surface 5, it passes through the length measuring beam condenser lens 2 again to create a beam parallel to the other beam. By folding it back as a reflective surface,
The surface roughness of the test surface 5 can be measured. The important thing at this time is
The convergent light of the length measurement light measures the displacement of the test surface 5 in a very narrow range of the test surface 5, and the parallel light beam of the reference light measures the displacement of the test surface 5 in a relatively wide range. By doing so, straightness errors such as lateral wobbling when moving/scanning the test surface 5 or when moving/scanning the interference prism 1 relative to the test surface are made difficult to detect as common mode displacement. , to improve the detection S/N of surface roughness components in minute areas.

0003

[Problems to be Solved by the Invention] However, in the conventional means, since the convergent light beam and the parallel light beam serving as its reference light beam were not coaxial, it was necessary to change the angle between the optical axis of the convergent light beam and the parallel light beam as shown in FIG. When θ is assumed, a common mode error of S·(1−cos θ) is superimposed on the detected length measurement signal S, and surface roughness information with sufficient accuracy is not necessarily obtained. Conventionally, in order to reduce this error as much as possible, it was important to make θ small, but for example, even if it was about 10 degrees, (1-cos θ) was 1.5%.
This amount of system error was unavoidable.

[0004] The present invention makes the convergent light beam and the parallel light beam of the differential laser interferometric length measuring device coaxial, and completely converts the straightness error caused by movement and scanning into a common mode for both, canceling it out, thereby reducing systematic errors. Moreover, the objective is to enable inexpensive surface roughness measurement.

[0005]

[Means for Solving the Problem] This object is achieved by either of the following technical means a or b.

(a) A length measurement light beam and a reference light beam are provided which are emitted in parallel from an interference prism of a differential laser interferometer,
The length measurement light flux is made into a convergent light flux through the main condenser lens, the convergence point is reflected on the test surface, and the returned light flux is made into a parallel light flux by passing through the main condenser lens, and the other reference light flux is A first reference beam condenser lens is used to condense the light to the front focal position of the main condenser lens, and a first reflecting mirror or prism is used to match the light beam with the principal ray of the convergent beam, and the main The beam is made incident on a condensing lens, is reflected as a parallel beam by the surface to be inspected, and then passed through the main condensing lens and converted into a convergent beam.The direction of the convergence point is changed by a second reflecting mirror or a prism, and the above-mentioned A surface roughness meter characterized in that a second reference beam condenser lens similar to the first reference beam condenser lens returns the beam to a parallel beam and makes it parallel to other parallel beams.

(b) The surface roughness meter according to item (a), characterized in that the first and second reflecting mirrors or prisms are arranged closer to the interference prism than the main condensing lens indicating the front focal position.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be explained with reference to FIG. 1 showing an optical system.

In the parallel reference beam and measurement beam emitted from the interference prism 1, the reference beam passes through the first reference beam condenser lens 3 and becomes a convergent beam, and the optical axis is adjusted by the first reflecting mirror or prism 4. can be tilted by θ. Since the focal point of this convergent light beam is the front focus of the next main condenser lens 2, the reference light beam becomes a parallel light beam after passing through the main condenser lens 2 and reaches the test surface 5 at an incident angle θ. The returning light beam from the surface to be inspected 5 enters as a parallel light beam, and becomes convergent light by passing through the main condenser lens 2. Thereafter, the direction of the optical axis is changed by a second reflecting mirror or prism 6, and the beam passes through a second reference beam condenser lens 7 having the same performance as the first reference beam condenser lens 3, and becomes a parallel beam, which forms an interference prism. 1.

On the other hand, the length measurement light flux becomes a parallel light flux from the interference prism 1 to the main condenser lens 2, and after passing through the main condenser lens 2, it becomes a convergent light and is reflected at a position where the position of the test surface 5 is the focal point. Fold back. At this time, the angle of incidence and reflection of the length measurement optical axis is θ,
It becomes coaxial with the reference beam mentioned above. Folded main condenser lens 2
The light beam that passes through becomes a parallel light beam and enters the interference prism 1.

In the example shown in FIG. 1, the above-mentioned path is passed twice, and the displacement information of the condensing portion of the surface to be inspected 5 can be measured with high sensitivity based on the detection signal. To obtain 2D or 3D information,
This can be obtained by moving and scanning the condensing point of the light beam on the surface to be inspected 5, but at this time, if the straightness of the moving/scanning mechanism is poor and there is lateral wobbling, The lateral vibration in the direction perpendicular to the test surface 5 cannot be completely converted into a common mode using the conventional method, and is superimposed on the detection signal as an error. In the present invention, since the length measurement and reference light beams are coaxial, displacement components perpendicular to the test surface 5 due to lateral shaking are applied equally, and are completely canceled by the differential optical arrangement.

The differential interference prism 1 of the laser interferometric length measuring device does not need to be the one shown in FIG. 1; even if a conventional one is used, exactly the same effect can be obtained using the configuration of the present invention.

[0013]

Effects of the Invention According to the present invention, a differential laser interferometer is used to move or scan an object in a direction perpendicular to the optical axis of the lens, thereby preventing lateral vibration in the optical axis direction. Even if there is wobbling in the direction of movement, accurate roughness measurements can now be stably obtained without being affected by such wobbling.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an optical system according to an embodiment of the present invention. FIG. 2 is a diagram showing the optical system of a conventional roughness meter.

[Explanation of symbols]

1...Interference prism
2... Main condensing lens 3... First reference beam condensing lens 4... First reflecting mirror or prism 5... Test surface
6...Second reflecting mirror or prism 7...Second reference beam condensing lens

Claims (2)

[Claims] [Claim 1] A length measurement light beam and a reference light beam are provided which are emitted in parallel from an interference prism of a differential laser interferometric length measurement meter, and the length measurement light beam is made into a convergent light beam through a main condensing lens, and its convergence point is on the surface to be measured. The returned light flux is made into a parallel light flux by passing through the main condenser lens, and the other reference light flux is brought to the front focal position of the main condenser lens using the first reference light condenser lens. The light beam is condensed and made to coincide with the chief ray of the convergent light beam using a first reflecting mirror or prism, and is made to enter the main condenser lens, and after being reflected and returned by the test surface as a parallel light beam, After passing through the optical lens and being converted into a convergent beam, the direction of the converging point is changed by a second reflecting mirror or prism, and the convergence point is changed into a parallel beam by a second reference beam condensing lens similar to the first reference beam condensing lens. A surface roughness meter characterized in that the beam is returned to the beam and made parallel to other parallel beams. 2. The surface roughness meter according to claim 1, wherein the first and second reflecting mirrors or prisms are arranged closer to the interference prism than the main condenser lens indicating the front focal position.