JPS6236502A - Microcsope for measuring minute displacement - Google Patents

Abstract

PURPOSE:To make it possible to conduct measurement while observing a point of measurement, by providing an optical system for displacement measurement and an optical system for observation and by making coaxial the optical axes of the parts of the two optical systems including objective lenses. CONSTITUTION:A light from an illuminating system for observation comprising a lamp 35a and lenses 35b and 35c enters a beam splitter 34 and then enters a beam splitter 36 together with a laser beam. The laser beam and the illuminating light which are made to get into an optical axis of observation by the beam splitter 36 pass through a beam splitting plane 36a and a 1/4 wavelength plate 37 and enters an objective lens 38 of an a focal design system. The illuminating light is made to illuminate the whole of a visual field by the objective lens 38, while the laser beam projects a minute spot for displacement measurement onto a sample 39. The reflected light of the illuminating light from the sample goes in the reverse course and forms an image on the plane of a field stop of an eyepiece 42.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a micro-displacement measuring microscope for measuring surface roughness, micro-displacement (vertical change), etc. of a workpiece.

Recently, micro-displacement measuring microscopes have been used as non-contact optical measuring instruments to measure surface roughness and micro-displacements of workpieces. Those that apply a focus detection method are attracting attention as they have the potential for miniaturization, and these include those that apply a critical angle method, an astigmatism method, etc.

First, as an example of a method using the critical angle method, there is a method shown in FIG. 6, for example. This means that the infrared laser beam from the laser diode 1 is transmitted through the collimator lens 2. Polarizing beam splitter 3. λ/4 tentative 4. The reflected light is projected onto the sample 6 through the objective lens 5. λ/4 plate 4
．． Polarizing beam splitter 3. The beam passes through the beam splinter 7 and enters the critical angle prism 8 or 9.
Or the light reflected by 9 is transmitted to two photodiodes 10 respectively.
．． 11 or 12.13 (see FIG. 7). When the measurement surface of the sample 6 is at the focal point of the objective lens 5, the light reflected from the measurement surface becomes a parallel beam of light by the objective lens 5 and enters the critical angle prism 8 or 9. If the Hfi field angle prism 8 is set so that all the light is totally reflected, each of the two photodiodes 10.11 or 12.13 receives the same amount of light as shown in FIG. 7(b). reach.

In addition, when the measurement surface is located closer to the objective lens 5 than the focal position, the reflected light becomes a diverging light after passing through the objective lens 5 and enters the critical angle prism L8 or 9, but at this time, the incident angle is different on both sides of the optical axis. Since the light on the side that does not satisfy the total reflection condition (1) exits the prism 8 or 9, and the light on the side that satisfies the total reflection condition is totally reflected, as shown in Fig. 7 (a
), only a small amount of light U7 does not reach the fumate diode 10 or 12, and the photodiode 11 or 1
Enough light reaches 3. If the measurement surface is located farther from the objective lens 5 than the focal position, the above will be reversed, and as shown in FIG. 7(C), sufficient light will reach the photodiode 10 or 12 and the photo diode 11
Or only a small amount of light reaches 13. Therefore, by moving and scanning the sample 6 while reading the output difference between the two photodiodes 10.11 or 12.13, it is possible to measure the surface roughness, minute displacement, etc. of the measurement surface.

Further, as an example using the J-point aberration method, there is one shown in FIG. 8, for example. 1, the laser light from the laser light source 14 passes through the spatial filter 15 and enters the polarizing beam splitter 16, and then the λ/4 temporary 17. Objective lens 1
The reflected light is projected onto the sample 1119 through the objective lens 18.8. λ, /4+ffl? , W optical beam splitter 16. The light flux passes through the beam splitter 20 and enters the cylindrical lens 21 or 22, and is condensed by the nolindrical lens 21 or 22 so as to produce 119 points of aberration.
26°27.28 (see FIG. 9). Since this optical system has astigmatism, the laser beam tA14
When a point image from the sample 19 is incident on the measurement surface of the sample 19, the shape of the point image formed on the detector 24 after being reflected by the measurement surface is before and after the focal point as shown in FIG. 9(a).

! b1. (The image changes as shown in C1. The image is detected by photodiodes 25, 26, 27, and 28, and the calculation (
By moving and scanning the sample 19 while performing V2S + Vz'+) (V26+ Vzs) and reading the value, it is possible to measure the surface roughness, minute displacement, etc. of the measurement surface. However, Vi is the output of detector i.

However, in all of the above-mentioned 8-microscopes for measuring minute displacements, the diameter of the measurement spot on the measurement surface is very small, 1 to 2 μm, so there is a problem that the position being measured cannot be accurately determined. In particular, it is necessary to position measurement points on the micron order for Ic wafers that have a narrow structure, but this has not been possible. In addition, even if an abnormal signal is generated due to scratches, dust, etc. on the measurement point, there is a problem in that it is impossible to determine whether it is really caused by scratches, dust, etc.

The present invention addresses the above-mentioned problems and is a micro-displacement measuring microscope that allows you to accurately determine the position being measured and to check whether there are scratches, dust, etc. on the measurement point. We aim to provide the following.

Mutual = 1 The micro displacement measuring microscope according to the present invention is equipped with a displacement measuring optical system and an observation optical system, and the optical axes of the parts including the objective lenses of both optical systems are made coaxial, so that measurement can be performed while observing the measurement point. At the same time, the presence or absence of scratches, dirt, etc. on the measurement points can be visually confirmed.

Hereinafter, the present invention will be described in detail based on one embodiment shown in FIGS. 1 to 4. FIG. 1 shows an optical system when the critical angle method is used, and 31 is a laser light source that outputs a linearly polarized laser, and the beam diameter of the laser light is expanded by a beam expander 32 and becomes parallel light, which enters the ζ beam splitter 34. On the other hand, the lamp 35a,
Light from the observation illumination system composed of lenses 35b and 35c also enters the beam splitter 2, and enters the beam splitter 36 as one with the laser light. The laser beam and illumination light that entered the observation optical axis by the beam splitter 36 are transferred to a polarized beam splitting surface 36a and a quarter-wave plate 37.
and enters an infinite design objective lens (for example, 50x, depth of focus 1μ) 38. Note that when the laser beam passes through the quarter-wave plate 37, the linearly polarized light is converted into circularly polarized light. Further, the illumination light illuminates the entire field of view through the objective lens 38, and the laser light projects a minute spot for displacement measurement onto the sample 39.

The sample reflected light of the illumination light passes through the opposite path, namely the objective lens 38 .
1/4 wavelength plate 37. It passes through a beam splitter 36 and an imaging lens 40 . The prism 41 forms an image on the field stop surface of the eyepiece lens 42 . The sample reflected light of the laser beam is focused by the objective lens 38 and passes through the 1/4 wavelength plate 37, thereby becoming linearly polarized light whose vibration plane has been rotated by 90 degrees from the time of incidence, and enters the polarized beam split surface 36a. The laser beam is on this surface 36
a, the observation illumination light passes through a cant filter (bandpass filter) 43, is split by a beam splitter 44, enters a critical angle prism 45 or 46, is reflected near the critical angle, and is transmitted to a two-split light receiving element 47 or 48, respectively. to go into. Although some illumination light passes through the observation illumination light cut filter 43, it does not pose a problem for measurement. The principle of displacement measurement thereafter is the same as that when using the conventional critical angle method described above.

With this configuration, not only can the flare of the displacement measurement light source be minimized and the laser beam be effectively used for displacement measurement, but also it is possible to prevent the laser beam from directly entering the observation system. Further, the extinction ratio of the polarized beam splitting surface 36a is set so that some laser light enters the observation system. Therefore, a laser spot whose light is extremely dimmed can be seen in the observation field, and it is possible to accurately correlate the displacement measurement position and observe it. If the amount of light is small, it can be adjusted by slightly shifting the polarization of the laser beam. For this purpose, if it is a linearly polarized laser, it is sufficient to rotate the laser light source 31, or a polarizing plate is placed between the laser light source 31 and the beam splinter 34, and this is rotated to generate the observation light. The light intensity ratio of the laser beams may be adjusted.

Furthermore, by using a non-polarized laser and inserting a laser light source light filter 49 into the observation optical system, it is possible to make a laser spot with extremely dimmed light visible in the observation field.

Further, the light source for displacement measurement may be a laser light source such as He-Ne, or any point light source other than a laser light source as long as it has high brightness. In either case, the measurement light may not become visible light, but as shown in the second circle, the light emitted from the displacement measurement light source 50 is placed in a visible light source at a position conjugate with the linear light rA50. (lamp, LED, etc.) By configuring the light from 51 to be combined with the beam splitter 52 and replacing this part with the laser beam tA31 and beam splinter 32 shown in FIG. 1, the displacement measurement position can be confirmed. It is also possible to make it possible. Furthermore, the positional relationship between the optical axis of the laser and observation illumination light and the optical axis for displacement measurement in the beam splitter 36 can be reversed.

In the above embodiment, the objective lens 38 is of an infinitely designed type, but it is also possible to use an objective lens of an infinitely designed type. In this case, by placing an aperture 33 between the beam expander 32 and the beam brick 34 and projecting the aperture image onto the measurement point using the objective lens, the diameter of the laser beam () which determines the measurement range can be determined by its unit area. It is possible to change the amount of light that hits the device while keeping it constant, which is convenient for performing minute displacement measurements while checking the measurement point range.

In addition, the critical angle prism 45.46 and the light receiving element 47.48
are set in pairs for the purpose of canceling out the influence of interference light due to the edge of sample 39, noise, etc., but if there is no such problem, the critical angle of - In principle, this is possible with a prism and a light receiving element.

FIG. 3 shows a block diagram of the signal processing system of the above embodiment, in which the photoelectric signals output from each of the two-split light receiving elements 54 and 55 are transmitted through the differential circuit r! Differences between the three signals are determined by B56 and B57, and these are further added by an adder circuit 58 and output as a displacement output. Also, in general, try gi 43
Since the reflectance of 9 is not constant, the displacement output is also corrected using the sum signal of the four light receiving elements.

In addition, large vertical displacement of the surface of the sample 39 (Fig. 4) and stage 59 that occurs when the sample 39 is scanned in the lateral direction.
(Fig. 1), the measurement point is often blurred and cannot be seen due to vertical movement, but when the sample 39 is scanned at a constant speed, the displacement measurement system detects a large displacement as a low-frequency signal and converts it into a small displacement. are detected as high-frequency signals, so by controlling the stage vertical servo circuit 61 and driving the stage vertical movement motor 62 using the signals obtained through the high-frequency cut circuit 6° as shown in FIG. Measurement points can be made visible at all times. This can also be done by moving the objective lens 38 up and down. In addition, this method has a highly sensitive displacement detection system that can detect minute irregularities on the sample 39, but the dynamic range in which linearity can be ensured is narrow, so it can be used in cases where large displacements are outside the dynamic range. By correcting this, it becomes possible to measure small displacements within the dynamic range (see Fig. 4). In addition, in FIG. 3, if the displacement signal is directly input to the servo circuit 61 to function as an autofocus mechanism, the sample position can be easily set at the center of the dynamic range of the displacement measurement system.

Figure 5 shows the optical system when using the astigmatism method as another embodiment, and the laser illumination system, observation illumination, and observation system are the same as in the above embodiment, so their explanation will be omitted. . The difference is in the displacement measurement system, in which the laser beam reflected by the sample 39 and returned is reflected by the polarized beam splitting surface 36a, passes through the imaging lens 63 and the observation light cut filter 43, and is split into two by the beam splitter 44. The light is divided into two parts and imaged into a spot on a four-division optical axis element 66 or 67 via cylindrical lenses 64 and 65, respectively.

Displacement measurement is then performed using the same principle as in the example using the conventional astigmatism method described above. Here, the reason why we used two cylindrical lenses and two quadrant light-receiving elements is to cancel out the tilt of the sample, the influence of interference light, noise, etc., as in the case of the critical angle method. Needless to say, if there is no problem, it is possible in principle to do it one by one. Other signal processing systems and peripheral usage techniques are exactly the same as those mentioned above.

1 Atsushi Atsushi: As mentioned above, the micro-displacement measuring microscope according to the present invention is equipped with a displacement measuring optical system and an observation optical system, and the optical axes of the parts including the objective lenses of both optical systems are made coaxial. This has the important practical advantage of not only being able to accurately determine the location of the measurement point, but also being able to confirm whether there are scratches, dirt, etc. on the measurement point.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an optical system of an embodiment of a micro displacement measuring microscope according to the present invention, Fig. 2 is a diagram showing a modification of the displacement measuring light source section of the above embodiment, Figure 5 shows the optical system of another embodiment, Figure 6 shows the optical system of a conventional example. , FIG. 7 is a diagram showing the light receiving state on the photodiode of the above-mentioned conventional example, FIG. 8 is a diagram showing another conventional example, and FIG. 9 is a diagram showing the light receiving state on the photodiode of the above-mentioned other conventional example. It is a diagram. 3I...Laser light source, 32...Beam exvanter, 33...Aperture, 34...Beam splitter, 35...Illumination system for observation, 36...Beam splitter , 36a...Polarized beam split surface, 3
7...1/4 wavelength plate, 38...Objective lens, 3
9... Sample, 40... Imaging lens, 41...
・Prism, 42... Eyepiece, 43... Observation illumination light cut filter, 44... Beam splitter, 45° 46... Critical angle prism, 47.4
8...Two-split light receiving element, 49...Laser beam attenuation filter, 50,...Light source for displacement measurement, 51...
・Visible light source, 52...Beam brick, 54.5
5.90. Two-split light receiving element, 56.57...Differential circuit, 58.0.・Addition circuit, 59...Stage, 6
0...High frequency power circuit, 61.08. Stage vertical servo circuit, 62... Stage vertical movement motor,
63... Imaging lens, 64.65... Cylindrical lens, 66.67... Quadrant light receiving element. Figure 5 2'6 Figure 6 ~ [== Toni Takou, Figure i7

Claims (3)

[Claims] (1) A minute displacement measuring microscope comprising a displacement measuring optical system and an observation optical system, with the optical axes of the parts including the objective lenses of both optical systems being coaxial. (2) The minute displacement measuring microscope according to claim (1), wherein the light source for displacement measurement is a visible light source. (3) The minute displacement measuring microscope according to claim (1), characterized in that the displacement measuring light source is composed of an invisible light source and a visible light source, and the emission optical axes of both light sources are made coincident in the middle.