JPH06273112A - Microscope interferometer - Google Patents

Abstract

PURPOSE:To observe a sharp interference fringe of high resolution, by letting a sample surface and a reference surface reflect lighting rays from a light source, and by observing the interference fringe formed by piling the wave fronts of both reflected rays through a microscopic optical system. CONSTITUTION:When a light source 3 provided within the housing 1a of an interferometer optical system 1 is lighting rays are emitted, the lighting rays are collimated by a collimator lens 11, the lighting rays are divided in two by a beam splitter 12, one is reflected on a sample surface 4, and the other on a reference surface 5. When the wave fronts of both reflected waves are piled each other in the beam splitter 12, and they are observed through a microscopic optical system 2, the information referring to the shape of the sample surface 4 can be recognized as interference fringe information. Hereupon, some of an infrared emitting diode, light emitting diode and laser diode of longitudinal multi-mode oscillation, capable of obtaining the lighting rays having a coherent distance of 3-30mum is used as the light source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microscopic interferometer in which a microscope and an interferometer are combined, and more particularly to improvement of a light source of the microscopic interferometer.

[0002]

2. Description of the Related Art A microscopic interferometer is used for finely inspecting and measuring the surface state of a sample surface, and for example, it measures the surface shape of a semiconductor wafer or a mask substrate or a magnetic disk. It is used to measure the film thickness of the film, and further to measure the shape of the magnetic head.

This microscopic interferometer is a combination of a microscope and an interferometer, and a so-called Michelson interferometer is preferably used as the interferometer. That is, the illumination light from the light source is made into a parallel light flux by the collimator lens and divided into two by the beam splitter, and one light flux is reflected on the sample surface. The other light flux is reflected by the reference surface, the reflected light from these sample surfaces is transmitted through the beam splitter, and the reflected light from the reference surface is reflected by the beam splitter, so that the wavefronts of both reflected light overlap. To do so.
The interference fringes can be observed by guiding this to a microscope equipped with an objective lens and an eyepiece and observing it with the naked eye or by imaging with an imaging means.

[0004]

By the way, in order to form the interference fringes by the interferometer, the illumination light from the light source is required to have a certain degree of coherence. A laser light source is well known as a light source that can obtain coherent light.
However, when a laser light source is used, a laser microscope must be used as a microscope for observing interference fringes, and this laser microscope has a complicated structure and is large in size as compared with an optical microscope. There is. Further, the laser beam has a long coherence length of several tens of centimeters, which causes speckle patterns, diffraction patterns, etc.
There is also a problem that noise in the interference fringes to be observed becomes large and the interference fringe image becomes difficult to see.

From the above points, a halogen lamp is usually used as a light source for a microscopic interferometer.
However, since the halogen lamp has a low coherence, the wavelength is selected through an interference filter so that the coherence is provided to some extent.
However, even if an interference filter is interposed, a coherence length of at most about 1 μm can be obtained.
The number of interference fringes appearing in the visual field is about 3 to 4, and when the change in shape on the sample surface is large, it cannot be substantially measured.

The present invention has been made in view of the above points, and an object of the present invention is to make it possible to observe clear and high-resolution interference fringes.

[0007]

In order to achieve the above-mentioned object, a microscopic interferometer of the present invention comprises a microscope optical system and an interferometer optical system, and illuminates illumination light from a light source on a sample surface and a reference surface. The surface shape of the sample surface is measured by observing the interference fringes generated by superimposing the wavefronts of the two reflected lights through a microscope optical system. The feature is that a structure having a distance of 3 to 30 μm is used.

[0008]

[Function] As the microscope optical system in the microscopic interferometer, a compact optical microscope having a simple structure is used. As the light source, a light source having a coherence distance that can obtain a sufficient number of interference fringes in the field of view for measuring the shape of the sample surface and does not generate noise such as a speckle pattern or a diffraction pattern is generated. To use. Here, the coherence length of a light source such as an infrared light emitting diode, a light emitting diode, and a laser diode of vertical multimode oscillation is 3 to 30 μm. Therefore, these light sources are preferably used. When the coherence length is 3 μm or less, the number of interference fringes obtained in the observation visual field is small, and when the unevenness on the sample surface is large, a resolution sufficient to analyze the surface shape cannot be obtained. . If the light from the light source has a coherence length of 3 μm or more,
The required number of interference fringes can be obtained, and the surface shape of the sample surface having considerably unevenness can be measured. However, when a light source having a coherence length of 30 μm or more is used, noise is generated in the interference fringe image, such as a speckle pattern of spots, even if the sample surface has an extremely small rough surface, and is difficult to see. However, the measurement accuracy deteriorates.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. First, FIG. 1 shows the overall configuration of an optical system of a microscopic interferometer. In the figure, 1 is an interferometer optical system, 2
Is a microscope optical system, and 3 is a light source. The Michelson interferometer shown below is preferably used as the interferometer optical system 1, but it goes without saying that other interferometers can be used. Thus, the interferometer optical system 1 includes the collimator lens 11 and the beam splitter 12, and the light source 3
The illumination light from is converted into a parallel light flux by the collimator lens 11, and the light flux is divided into two by the beam splitter 12. The light reflected by the reflecting surface 12 a of the beam splitter 12 is reflected by the sample surface 4. The light transmitted through the reflecting surface 12 a of the beam splitter 12 is reflected on the reference surface 5. The reflected light from the sample surface 4 is transmitted through the reflecting surface 12a of the beam splitter 12, and the reflected light from the reference surface 5 is reflected by the reflecting surface 12a, so that the wavefronts of the two reflected lights overlap each other. Then, the two wavefronts that interfere with each other are guided to the microscope optical system 2 including the objective lens 21 and the eyepiece lens 22, and when an observer makes an eyepiece to the eyepiece lens 22 or an image is taken by an image pickup means such as a television camera. , Sample surface 4
The interference fringes according to the surface shape of No. 1 are observed, and the observation can be performed at a magnification corresponding to the magnification of the microscope optical system 2.

Here, in the microscopic interferometer, the interferometer optical system 1
The interference fringe information obtained by observing the interference fringe information is magnified and observed by the microscope optical system 2 so as to have a predetermined magnification, and the spot diameter of the illumination light does not need to be so large. However, sample surface 4
The number of interference fringes required to analyze the shape of
Moreover, it is necessary to prevent the observation image from becoming difficult to see due to speckle patterns, diffraction patterns, and the like. From the above points, as the light source 3, one that can obtain illumination light having a coherence length of 3 to 30 μm, that is, an infrared light emitting diode, a light emitting diode, or a laser diode of longitudinal multimode oscillation is used. Even a laser diode in which the longitudinal mode oscillates in a single mode is not preferable because the coherence length is too large. From the viewpoint of output power, an infrared light emitting diode that emits near infrared light is most preferable. These light sources are essentially point sources,
By arranging the collimator lens 11 at a position distant from the collimator lens 11 to some extent, the light is incident on the collimator lens 11 in a divergent state, so that a required spot diameter can be obtained.

The interferometer optical system 1 and the microscope optical system 2 are housed in casings 1a and 2a, respectively. The casing 1a of the interferometer optical system 1 is detachably connected to the casing 2a of the microscope optical system 2. There is. Microscope optical system 2
In the casing 2a of the above, in addition to each part constituting the optical system,
The light source 3 is built in.

The present embodiment has the above construction, and the operation of this microscopic interferometer will be described below. When the light source 3 provided in the casing 1a of the interferometer optical system 1 is turned on and the illumination light is emitted, the illumination light is collimated by the collimator lens 11, and the beam splitter 12
The illumination light is divided into two by the beam splitter 12 and a part of the light is reflected by the sample surface 4 and another part is reflected by the reference surface 5.
In the optical system of the microscope 2
When observed with, information about the surface shape of the sample surface 4 can be recognized as interference fringe information.

Here, as the light source 3, any one of an infrared light emitting diode, a light emitting diode, and a laser diode of longitudinal multimode oscillation, which can obtain illumination light having a coherence length of 3 to 30 μm, is used. When observed with the optical system 3, a maximum of about 100 interference fringes are observed within the field of view, and interference fringe information sufficiently representing the surface shape of the sample surface 4 is obtained. Moreover, in the range of the coherence distance, the speckle pattern, the diffraction pattern, or the like does not occur in the interference fringe image, and thus the observed interference fringe image becomes clear, which is advantageous in performing image analysis and the like.

Here, the light source 3 is a casing 1a.
One type can be fixedly installed inside,
As shown in FIGS. 2 and 3, a plurality of types of light sources having different wavelengths or the like may be replaceable. In the figure, reference numeral 30 denotes a support plate, and the support plate 3
Two types of light sources 3a and 3b are attached to 0.
One light source 3a is an infrared light emitting diode, and the other light source 3a
Reference numeral b is a laser diode of longitudinal multimode oscillation. In addition, the support plate 30 is provided with an external light source mounting portion 31 between the light sources 3a and 3b. The mounting portion 31 is formed of a tubular member having a through hole 31a for inserting a light guide or the like therein.
To project outward from an opening 32 formed in the casing 1a. A cap 33 is detachably attached to the tip of the mounting portion 31, and by removing the cap 33, a light guide, which is a light guide unit connected to a light source device including a halogen lamp, a xenon lamp, or the like, can be connected. Like

The switching of the light source is performed by sliding the support plate 30, and for this purpose, the casing 1a is provided with guide rails 34 for vertically guiding the support plate 30 in the up-down direction. Then, in order to position the mounting portion 31 to which the light sources 3a, 3b and the external light source are connected to a position facing the optical path from the collimator lens 11, a leaf spring 35 for positioning is provided in the opening 32 of the casing 1a. Has been. The leaf spring 35 is formed with three curved portions, and the mounting portion 31 is engaged with any one of the curved portions to be positioned.

With this structure, if the support plate 30 is moved appropriately according to the sample to be measured, the light source 3
Since a, 3b or an external light source selectively faces the optical path, it becomes possible to select a light source having characteristics such as an optimum wavelength according to the sample to be measured.

[0017]

As described above, according to the present invention, since the light source of the microscopic interferometer has a coherence length of 3 to 30 μm, the interference fringes observed through the microscope optical system can be eliminated. The required number can be obtained, and the surface shape can be accurately measured even on a sample surface with considerably large unevenness, and there is no noise in the interference fringe image such as a speckle pattern or a diffraction pattern. , The surface shape of the sample surface can be measured with extremely high accuracy.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a microscopic interferometer showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a light source switching mechanism.

FIG. 3 is a diagram viewed from the X direction in FIG.

[Explanation of symbols]

 1 Interferometer Optical System 1a Housing 2 Microscope Optical System 3, 3a, 3b Light Source 4 Sample Surface 5 Reference Surface 11 Collimator Lens 12 Beam Splitter 21 Objective Lens 22 Eyepiece 30 Support Plate 31 Attachment Part 34 Guide Rail 35 Leaf Spring

Claims (5)

[Claims] 1. A microscope optical system and an interferometer optical system are provided,
The surface shape of the sample surface can be measured by reflecting the illumination light from the light source on the sample surface and the reference surface and observing the interference fringes generated by superimposing the wavefronts of both reflected lights through the microscope optical system. In what to do, as the light source,
A microscopic interferometer characterized in that a structure having a coherence length of 3 to 30 μm is used. 2. The microscopic interferometer according to claim 1, wherein the light source is any one of an infrared light emitting diode, a light emitting diode, and a laser diode of longitudinal multimode oscillation. 3. The microscopic interferometer according to claim 1, wherein the light source is built in a housing of the interferometer optical system. 4. The microscopic interferometer according to claim 3, wherein a plurality of light sources having different wavelengths are provided in a replaceable manner in the housing of the interferometer optical system. 5. The housing of the interferometer optics includes 1
4. The microscopic interferometer according to claim 3, wherein a plurality of internal light sources and external light sources are replaceable.