JPH0452401B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a device for measuring minute distances between objects,
In particular, the present invention relates to a micro-gap measuring device suitable for measuring micro-gap measurements at high speed and with high precision, such as measuring the flying height of a magnetic disk head or measuring film thickness in a semiconductor manufacturing process.

[Background of the invention]

Conventional technology for measuring the flying height of magnetic disk heads and film thickness in semiconductor manufacturing processes involves irradiating light with a wavelength with a narrow spectral width, finding the peaks and valleys of the intensity pattern distribution of the resulting interference fringes, and then determining the wavelength. Absolute measurements of the gap were made by changing the gap and repeating the same measurements.

However, the prior art has the following drawbacks.

It takes time to change the wavelength.

It takes time to detect the peaks and valleys of the interference fringe intensity pattern.

The amount of gap that is truly desired to be measured needs to be extrapolated from the peaks and troughs of the interference fringe intensity, so accurate measurement cannot be performed.

These points will be explained in more detail with reference to the drawings.

FIGS. 1, 2a, 2b, c, and d show a conventional technique for measuring minute gaps, and show a case in which it is applied to measuring the flying height of a magnetic disk head.

As shown in FIG. 1, the irradiation light 13 having a narrow spectrum width is irradiated by a beam splitter 14 onto the surface where the minute gap G is formed. The light reflected by the magnetic head 11 of the magnetic disk head and the glass disk 12 becomes interference light, passes through the lens 16, and enters the image pickup device 17. Since interference fringes are formed in this imaging device 17, if the x-coordinate is taken on the air bearing surface on the magnetic head 11 as shown in FIG. 2a, the interference intensity along the x-axis is as shown in FIG. 2b, It changes like c. That is, FIG. 2b shows the interference intensity when the wavelength λ is _λ1 , and when the wavelength λ is changed from _λ1 to _λ2 , the interference intensity changes as shown in FIG. 2c. By finding the positions where the interference intensity is maximum and minimum for each, the minute gap G is found as shown in FIG. 2c.

Note that 101 and 102 in FIGS. 1 and 2A indicate the parts to be measured, and 1 and 2 in FIGS. _2B and _2C indicate the interference intensity of reflected light.

However, in this prior art, only the * mark in FIG. 2b and the x mark in FIG. There is no choice but to extrapolate the gap data.
However, this extrapolated value has the disadvantage that it cannot be accurately determined unless the surface shape of the magnetic head 11 is accurately known, and also has the disadvantage that it cannot be measured at high speed.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a micro-distance measuring device capable of measuring micro-distances at a plurality of locations at high speed and with high precision, in order to solve the problems of the prior art.

[Summary of the invention]

In order to achieve the above object, the present invention includes a multi-wavelength coherent light source, a multi-wavelength coherent light source that separates the multi-wavelength light beam emitted from the multi-wavelength coherent light source into a plurality of light beams, and focuses each separated light beam on a minute spot. micro-spot irradiation means for irradiating a plurality of different positions of the part to be measured forming a micro-gap between two opposing surfaces; a wavelength separation means for separating into each wavelength component a plurality of interference lights generated by the reflected light; and two wavelength separation means that are in substantially image forming relationship with the measurement target part and forming the measurement target part at each of the plurality of positions. four or more light blocking means for blocking reflected light from surfaces other than the surface and passing the interference light for each wavelength for each of the plurality of interference lights separated by the wavelength separation means; and passing through each of the light blocking means. four or more interference light intensity detection means for separately detecting the interference light intensity component for each wavelength as an interference light intensity signal for each of the plurality of interference lights; For each of the interference light intensity signals detected for each wavelength in correspondence with the light, a common minute interval amount is calculated from the relationship between the pre-calculated interfering light intensity of each wavelength and the candidate value. a micro-interval calculation means for calculating micro-intervals at a plurality of different positions of the part to be measured; Due to the relationship between the values, it is possible to measure minute intervals at multiple locations with high precision at high speed and by blocking reflected light from surfaces other than the two surfaces forming the part to be measured. This is a minute interval measuring device.

[Embodiments of the invention]

First, we will explain the principle of the present invention in Figures 3 and 4.
This will be explained based on the diagram.

The principles of the present invention are illustrated by the multi-wavelength coherent light source 18, the spot forming means 19, the spot irradiating means 19, the beam splitter 21 as the spot irradiating means, the mirror 25, the wavelength selective beam splitters 26 to 28, and the interference beam splitter 21. It comprises filters 29-32, lenses 33-36, slits 37-40, light intensity detectors 41-44 as interference intensity detection means, and a calculation circuit 45 as calculation execution means.

According to this principle, the fine gap between the front surface of the magnetic head 11 and the back surface of the glass disk 12 as the flying height of the magnetic disk head including the magnetic head 11 and the glass disk 12 is 1
The measured portion 101 is measured at a certain location.

The multi-wavelength coherent light source 18 is adapted to simultaneously emit coherent light having a large number of wavelength components.

The spot forming means 19 is adapted to focus the multi-wavelength light emitted from the multi-wavelength coherent light source 18 onto a minute spot 20.

The beam splitter 21 is configured to irradiate a multi-wavelength minute spot 20 onto a part to be measured 101 between the magnetic head 11 and the glass disk 12, which is an object having a minute gap.

The mirror 25 is connected to the surface of the magnetic head 11;
Reflected light 2 from the back and front surfaces of the glass disk 12
2, 23, 24 as a wavelength selection beam splitter 26
~28 is designed to be reflected.

the wavelength selective beam splitters 26 to 28;
Interference filters 29-32 and lenses 33-36
The slits 37 to 40 constitute wavelength separation means for separating the interference light reflected from the two surfaces forming the minute gap into each wavelength component. The wavelength selection beam splitters 26 to 28 separate the interference light beams 22 and 23 reflected from the front surface of the magnetic head 11 and the back surface of the glass disk 12, which are two surfaces forming a minute gap, into respective wavelength components. It's becoming like that. The interference filters 29 to 32 extract only pure wavelength components from each separated beam. The lenses 33 to 36 are designed to focus light of each wavelength. The slits 37 to 40 are arranged so as to selectively take out only the interference light of the light reflected from the front surface of the magnetic head 11 and the back surface of the glass disk 12, and to block the reflected light from the surface of the glass disk 12. There is.

The light intensity detectors 41 to 44 are configured to detect interference intensities from light of each wavelength component almost simultaneously.

The calculation circuit 45 includes light intensity detectors 41 to 44.
The micro gap is calculated based on the interference intensity signal as a result of detection.

Next, the operation according to the principle of the present invention will be explained.

The light having a large number of wavelength components emitted from the multi-wavelength coherent light source 18 is transmitted to the micro spot forming means 1.
9, a minute spot 2 with a diameter of several tens to hundreds of microns
0, and this minute spot 20 is irradiated onto the part to be measured 101 between the magnetic head 11 and the glass disk 12 via the beam splinter 21.

The surface of the magnetic head 11 and the glass disk 1
Since the gap between the back surfaces of the magnetic heads 2 and 2 is a minute gap of about 0.2 to 2 μm, the reflected light 22 from the magnetic head 11
and reflected light 23 from the back surface of the glass disk 12.
travel along the same optical path and interference occurs. Since the incident light on the measured part 101 has an incident angle of about several tens to ten degrees with respect to the glass disk 12, the reflected light 24 from the surface of the glass disk 12
As shown enlarged in FIG. 4, the reflected light 2
2 and 23.

The interference light between the reflected light 22 from the front surface of the magnetic head 11 and the reflected light 23 from the back surface of the glass disk 12 and the reflected light 24 from the front surface of the glass disk 12 are transmitted by a mirror 25 to wavelength selective beam splitters 26 to 26. The wavelength selective beam splitters 26 to 28 separate each wavelength component of the multi-wavelength coherent light, and from this separated light, interference filters 29 to 32 further separate each wavelength component into pure wavelength components. is extracted, and the light of each wavelength component is focused by lenses 33 to 36, and passed through slit 37.
40, only the interference light of the light reflected from the front surface of the magnetic head 11 and the back surface of the glass disk 12 is extracted, and the reflected light from the surface of the glass disk 12 is blocked.

The light transmitted through each of the slits 37 to 40 is sent to light intensity detectors 41 to 44, where the interference intensity is detected, and an interference intensity signal as a result of the detection is sent to a calculation circuit 45.

The calculation circuit 45 has calculated gap candidate values for each wavelength intensity in advance, and calculates the minute gap amount from these calculated values in a very short time.

As a result, the surface of the magnetic head 11 and the glass disk 1 are combined as the flying height of the magnetic disk head.
Regarding the minute gap between the back surfaces of 2, the part to be measured 101
It is possible to measure minute gaps at high speed and with high accuracy.

Next, an embodiment of the present invention will be described based on FIG. 5.

The embodiment shown in this figure includes a multi-wavelength simultaneous emission laser 46 as a multi-wavelength coherent light source, a beam expanding optical system 47, a condensing lens 48 as a minute spot forming means, a multi-beam generator 50, and a lens 53. , 54, beam splitter 55 as spot irradiation means, lens 58, mirror 59, wavelength selective beam splitters 60-62, lenses 63-
66, interference filters 67-70, slits 71-
74. Light intensity detector 7 as interference intensity detection means
5 to 78, and a calculation circuit 79 as a calculation execution means.

In this embodiment, the magnetic head 1
1 and a glass disk 12, and the fine gap between the front surface of the magnetic head 11 and the back surface of the glass disk 12 is measured at two locations to be measured 101 and 102. ing.

Further, the surface of the glass disk 12 is coated with antireflection coating to eliminate the influence of specularly reflected light from the surface of the glass disk 12.

The multi-wavelength simultaneous oscillation laser 46 is capable of simultaneously emitting multi-wavelength laser beams.

The beam expanding optical system 47 is configured to expand the multi-wavelength laser beam to a set diameter.

The condensing lens 48 is adapted to focus the multi-wavelength laser beam onto a minute spot 49.

The multi-beam generator 50 has a prism or the like, and divides the micro spot 49 into a number of beams corresponding to the number of parts to be measured, that is, two beams 51 and 52 in this second embodiment. It is configured to obtain.

The lens 53 forms each beam into parallel multi-beams, and the other lens 54 forms each beam into parallel multi-beams.

The beam splitter 55 is arranged so as to reflect each beam onto the parts to be measured 101 and 102 and condense the beams.

The lens 58 forms interference beams 56 and 57 of the light reflected from the parts to be measured 101 and 102 in parallel, respectively, and sends them to a mirror 59, and the mirror 59 reflects each interference beam to wavelength selection beam splitters 60 to 62. It's becoming like that.

the wavelength selective beam splitters 60 to 62;
Lenses 63-66 and interference filters 67-70
and the slits 71 to 74 constitute wavelength separation means that separates the interference light of the light reflected from the two surfaces forming the minute gap into each wavelength component. The wavelength selective beam splitters 60 to 62 are configured to separate each interference light into each wavelength component. The lenses 63-66 are arranged so as to focus the light separated into each wavelength component onto the openings of the slits 71-74. The interference filters 67 to 70 are adapted to extract only pure wavelength components from the light separated for each wavelength component. The slits 71 to 74 are connected to the interference filter 6.
The light intensity detectors 75 to 78 are installed so that the light of each wavelength component extracted from the detectors 7 to 70 is transmitted through the light intensity detectors 75 to 78.

The light intensity detectors 75 to 78 are connected to the part to be measured 10.
Detection elements 75 correspond to 1 and 102, respectively.
1,752 sets, 761,762 sets, 771,
There are a set of 772 and a set of 781 and 782, and the interference intensity of each wavelength component of the reflected light from the parts to be measured 101 and 102 can be detected almost simultaneously.

The calculation circuit 79 includes detection elements 751 and 752.
The set 761,762, the set 771,772,
Based on the interference intensity signal as a detection result sent from the set of 781 and 782, the part to be measured 10
The micro gap amount of 1,102 is calculated.

Next, the operation of this embodiment will be explained.

The multi-wavelength laser beam oscillated by the multi-wavelength simultaneous oscillation laser 46 is expanded into a beam with a set width by the beam expansion optical system 47, and then passed through the condenser lens 4.
8 to focus on a minute spot 49.

The minute spot 48 focused by the condensing lens 48 is divided into two beams 51 and 52 by a multi-beam generator 50 corresponding to the parts to be measured 101 and 102 in this embodiment.
1 and 52 are formed into parallel beams by a lens 53, and then the two beams are formed by a lens 54.
The beams are formed parallel to each other and sent to the beam splitter 55.

The two beams are reflected by the beam splitter 55, and are focused and irradiated onto the parts to be measured 101 and 102.

Interfering light beams 56 and 57 of the beams reflected by the respective measurement target parts 101 and 102 are transmitted through the beam splitter 55 and the lens 58, reflected by the mirror 59, and each wavelength-selective beam splitter 60 to 62 It is separated into each wavelength component, and then the lens 6
The light is focused onto the openings of the slits 71 to 74 by the slits 71 to 74, and only the pure wavelength components are extracted by the interference filters 67 to 70.
~74 is transmitted.

The light transmitted through each of the slits 71 to 74 is detected by a set of detection elements 751, 752, a set of detection elements 761, 762, and a set of detection elements 771, 772 of light intensity detectors 75 to 78 that detect the interference intensity of each part to be measured 101, 102. and the sets 781 and 782, and the interference intensity is detected almost simultaneously by these eight detection elements,
The interference intensity signal is sent to calculation circuit 79.

As shown in FIGS. 2b and d and 2c and d, the calculation circuit 79 has previously calculated a plurality of candidate values for arbitrary interference intensity for each wavelength, and this calculated value ( From the interval (candidate value), a common infinitesimal interval value for the input interference intensity signals for each wavelength can be found in an extremely short time.

In this embodiment, multiple parts to be measured can be measured simultaneously at high speed and with high precision.

In this embodiment, as described above, the surface of the glass disk 12 is coated with anti-reflection coating to eliminate the influence of specularly reflected light from the surface of the glass disk 12. In this case, the angle of incidence on the glass disk 12 is set to several degrees, and the glass disk 12 is
The reflected light from the surface may be removed.

Further, in the above embodiment, the light intensity detector as the interference intensity detection means is configured to be able to detect one after another at a time interval, and the calculation circuit as the calculation execution means detects minute gaps from the inspection results moment by moment. If the amount can be calculated, it is possible to measure dynamic changes in the microgap.

Furthermore, in the case of measuring very high-speed changes, the data may be temporarily stored in the memory of the calculation circuit, and calculations may be performed after data collection.

Further, in the present invention, a spot position changing means may be provided to selectively measure any measurement location.

Both the first and second embodiments can be applied not only to measuring the flying height of the illustrated magnetic disk head, but also to general micro gap measurements such as film thickness measurements in semiconductor manufacturing processes.

According to the embodiment, the following effects are achieved in comparison with the prior art.

(1) Since the emitted light from the multi-wavelength coherent light source is focused only on the part to be measured, the detection signal is much smaller than when irradiating with a large beam diameter to cover the entire object with minute gaps. becomes larger.

For example, when measuring the flying height of a magnetic disk head, the gap between the magnetic head and the glass disk surface is about 0.2 to 2 .mu.m, and since the disk is tilted, the gap varies depending on the location. Therefore, to perform accurate measurements, it is necessary to measure gaps in an area of about 50 μm. Now, assuming that the approximate size of the magnetic head is 4 mm, the ratio of the reflected light intensity from the part to be measured is 13000 when the entire magnetic head is irradiated and when a 50 μm diameter area is concentratedly irradiated.
becomes. Considering the reflectance of the object forming the microgap and the loss of the optical system, about 0.5% of the amount of light emitted at each wavelength from the light source is received. If the amount of light at each wavelength is, for example, 10 mw, the received light intensity in the present invention will be as large as 50 μw. On the other hand, the total uniform irradiation method in the conventional technology is 4nw,
It is extremely difficult to perform detection with a good signal-to-noise ratio with such a weak amount of light. In contrast, in the present invention, the absolute measurement of interference intensity is carried out over 100 times.
There is an effect that can be measured by the signal-to-noise ratio.

(2) As mentioned above, in the conventional technology, the position of the darkest or brightest part of the interference fringes is determined, and the gap at the measured part is determined by extrapolating from the gap amount at this position. Unless the surface shape of the object is known, the amount of gap cannot be determined accurately. On the other hand, in the present invention, since the part to be measured is directly measured, the accuracy is very accurate at 0.005 μm or less.

(3) Since the present invention obtains interference intensity data at a small number of locations, each measurement data can be obtained simultaneously, and an accurate minute gap amount at the time of detection can be obtained. In comparison, conventional methods for extracting interference images require tens of milliseconds to extract image information.
It is not possible to obtain instantaneous information, and the values are averaged over time. Therefore, when trying to measure dynamic gap changes, it is not only very difficult to shorten the measurement period of dynamic changes, but also because it is impossible to calculate in a short time, it is necessary to save a large amount of data once. However, it is necessary to process this for a long time. In contrast, in the present invention, a small number of data can be processed in parallel and can be processed in a short period of time, making it possible to accurately measure high-speed changes in minute gaps.

〔Effect of the invention〕

As explained above, according to the present invention, reflected light from three or more surfaces can be obtained, for example, a large interference light intensity signal with very high sensitivity can be obtained at multiple locations from minute intervals inside a transparent object. As a result, it is possible to measure minute intervals at a plurality of locations at high speed and with high accuracy.

[Brief explanation of drawings]

Figures 1, 2 a, b, c, and d are diagrams showing the conventional method for measuring minute gaps, Figure 3 is a block diagram showing the principle of the present invention, and Figure 4 is the part to be measured in Figure 3. FIG. 5 is a block diagram showing an embodiment of an apparatus for carrying out the method of the present invention. 11...Magnetic head as an object having a minute gap to be measured, 12...Glass disk, 1
01, 102... Part to be measured, 18... Multi-wavelength coherent light source, 19... Spot forming means, 20...
Micro spot, 21...Beam splitter as spot irradiation means, 22-23...Reflected light, 2
6-28... Wavelength selective beam splitter constituting the wavelength separation means, 29-32... Interference filter, 33-36... Same lens, 37-40... Same slit, 41-44... Interference intensity detection. Light intensity detector as means, 45... Calculation circuit as calculation execution means, 46... Multi-wavelength simultaneous oscillation laser as multi-wavelength coherent light source, 47... Beam expanding optical system, 48... Spot forming means A condensing lens as a means for forming a plurality of microspots, 49, 50, a multi-beam generator as a means for forming a plurality of microspots, 53, 54, a beam as a microspot, 53, 54, a plurality of microspots. Lens for guiding a minute spot, 55...Beam splitter as spot irradiation means, 56, 57...Reflected light from the measured part, 60-62...Wavelength selective beam splitter constituting wavelength separation means, 63-66 ...Same lens, 67-70 ...Same interference filter, 71-74
. . . same slit, 75 to 78 . . . light intensity detector as interference intensity detection means, 79 . . . calculation circuit as calculation execution means.

Claims (1)

[Claims] 1 A multi-wavelength coherent light source, a multi-wavelength light beam emitted from this multi-wavelength coherent light source, is separated into a plurality of light beams, each separated light beam is focused on a minute spot, and the light beam is focused between two opposing surfaces. A minute spot irradiation means for irradiating a plurality of different positions of a part to be measured forming a minute interval, and a plurality of interference lights generated by reflected light from two surfaces at each of a plurality of different positions of the part to be measured. a wavelength separation means that separates each wavelength component; and a wavelength separation means that is substantially in an image forming relationship with the part to be measured and blocks reflected light from surfaces other than the two surfaces forming the part to be measured at each of the plurality of positions. , four or more light shielding means for passing the interference light of each wavelength for each of the plurality of interference lights separated by the wavelength separation means, and for each wavelength of each of the plurality of interference lights that have passed through each of the light shielding means. Four or more interference light intensity detection means for separately detecting the interference light intensity components of the interference light intensity components as interference light intensity signals, and each of the interference light intensity detection means detects each wavelength in correspondence with a plurality of interference lights. For each of the interference light intensity signals to be measured, a common minute interval amount is calculated from the relationship between the pre-calculated interfering light intensity for each wavelength and the candidate value. 1. A micro-distance measuring device comprising: micro-distance calculation means for calculating micro-distances at positions.