JPH0413907A - Measuring method of minute dimension - Google Patents

Abstract

PURPOSE:To measure a gap dimension with high precision by a method wherein a laser beam is applied with deflection and the position of an edge of a substance to be measured is detected from a shift of the position of a peak intensity in the intensity distribution of a reflected light in measurement of the dimension of a gap or the like of a magnetic head. CONSTITUTION:In measurement of the dimension of a gap or the like of a magnetic head, a laser beam 100 is applied to a substance 3 to be measured, through a light deflecting element 110. Deflection is made over an area including a dimension part 115 of the substance 3 to be measured. A reflected light 120 is detected by a beam profile detecting unit 5, and a reference peak intensity position Ps at the time when the laser light irradiates a position to be a reference of a base part 116 is detected by a first peak position detecting unit 6. By a second peak position detecting unit 7, a peak intensity position Pm at the time when the deflection is made toward the dimension part 115 is detected. Positions of deflection of the applied beam at which a shift Pm - Ps becomes the maximum and the minimum are detected by a maximum peak shift detecting unit 10, and a gap dimension is calculated from these positions of deflection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for optically measuring minute dimensions of submicrons smaller than 1 μm, such as the gap dimension of a magnetic head.

[Conventional technology]

With the recent advances in precision processing technology, workpieces have become smaller and their dimensions have reached the submicron range, smaller than 1 micron (μm), and the need for precise dimensional measurement of workpieces has increased. There is. For example, in magnetic heads,
With the improvement in recording density, the size of the gap portion has become approximately 0.3 μm, and dimensional control in gap formation has become important.

A typical conventional optical method for measuring minute dimensions is a half-width detection method using an image sensor.

FIG. 6 shows this half-width detection method.

FIG. 6(A) shows an example of the shape of the object to be measured 60 whose dimensions are measured, and 61 is a dimension part whose dimensions are measured;
Its dimension is G. Reference numeral 62 denotes a base material portion, which is present on both sides of the dimension portion 61. Note that when the object to be measured 60 is a magnetic head, the dimension portion 61 and the base material portion 62 are a gap made of glass, and the base material portion 62 is a magnetic material made of ferrite.

Further, the dimension portion 61 and the base material portion 62 have different reflectances,
The reflectance of the dimension portion 61 is rm, and the reflectance of the base material portion 62 is rl.
Let it be l. In the following explanation, r s ) r m
Assume that Further, it is assumed that the dimension portion 61 and the base material portion 62 are formed to be substantially coplanar in the height direction.

A waveform 66 in FIG. 6(b) is a video signal waveform obtained when the object to be measured 60 is irradiated with focused white light and the reflected light from the object to be measured 60 is detected by an image sensor. . The horizontal axis of the graph is the address of each pixel constituting the image sensor, and the vertical axis is the reflected light intensity. Since there is a difference in reflectance between the dimension portion 61 and the base material portion 62, a v-shaped reflected light intensity pattern as shown in the figure is shown.

A straight line 64 is a slice level for binarizing the waveform 66.

The waveform 65 shown in FIG. A value width P is calculated, and the half value width P is converted into a dimension G. In this way, the waveform 66 is binarized in order to detect the edges on both sides of the dimension portion 61, and the slice level for the binarization is generally set to a relative 50% intensity level.

[Problem to be solved by the invention]

The half-width detection method described above is based on a specific dimension G. (for example, 06 μm), 50
When binarizing with a slice level set to % level, the number of binarized pixels and the dimension G are in a proportional relationship, but the specific dimension G. If the size is smaller than that, the number of binarized pixels and the size will no longer be proportional, making it impossible to detect the edges of the object to be measured. In this case, it is necessary to perform binarization by changing the slice level value, but since the dimensions are unknown,
The value of the slice level to be set is also unknown, making accurate dimension measurement impossible.

Furthermore, as the dimensions become smaller, the changes in the falling and rising edges of the video signal waveform 66 shown in FIG. , the reliability of dimension measurements decreases.

The purpose of the present invention is to solve the conventional problems as described below.
It is an object of the present invention to provide a minute dimension measuring method that measures submicron dimensions with high precision by directly detecting the edges of a measured object.

[Failure to solve the problem]

In order to achieve the above object, the present invention is characterized in that minute dimensions are measured by the method shown below.

In a dimension measurement method in which a laser beam focused on a minute spot diameter is irradiated onto the surface of the object to be measured, the light is deflected, and the dimensions are measured by changes in the intensity of the reflected light from the object. The beam profile of the reflected light is detected in accordance with the deflection of the laser beam, and the peak intensity of the beam profile when the laser beam is irradiated onto a reference location on the surface of the object to be measured is determined within the detection coordinate system of the beam profile. Using this point as a reference, find the amount of shift of the peak intensity point of the beam profile at each deflection position of the laser beam, then find the deflection position of the laser beam that gives the maximum and minimum values of this shift amount, and calculate the deviation of both deflection positions. The dimensions of the object to be measured are obtained based on the difference between

Furthermore, the beam profile detection coordinate system is divided by a boundary passing through the peak intensity point of the beam profile obtained when the laser beam is irradiated to a reference location on the surface of the object to be measured, and the light intensity of the beam profile is Set up two detection areas that are equally divided and detected, find the difference in the light intensity detected in these two detection areas of the beam profile at each deflection position, and then calculate the maximum value and minimum orange value of this difference. The deflection position of the applied laser beam is determined, and the dimensions of the object to be measured are obtained based on the difference between both deflection positions.

[Effect]

The light intensity distribution of the laser beam has a Gaussian distribution, and has a light intensity distribution that is symmetrical with respect to the beam spreading direction with the peak intensity position as the center. When a laser beam having such a light intensity distribution is irradiated onto the surface of the object to be measured 600 as shown in FIG. There are two situations in which the edge of the object is irradiated. In the irradiation state at this time, the diameter of the irradiation beam is approximately 15 μm and the dimension of the dimension portion 61 is approximately 0.3 μm, so that the dimension portion 61 is irradiated with approximately 115 of the diameter of the irradiation beam. When the peak intensity of the irradiated laser beam is irradiated to each edge, the intensity of the reflected light is lower in one half area (the entire area is irradiated to the base material part 62) centering on the peak intensity position. is in the maximum state, and in the other half region (a state in which part of it is irradiated to the dimension portion 61 and the rest is irradiated to the base material portion 62), the intensity of the reflected light is in the minimum state. In this case, the beam profile of the entire reflected light becomes a profile in which the Gaussian distribution is modulated due to the unbalance of the intensity distribution in the two regions.

At this time, the peak intensity position of the reflected light beam profile shifts with respect to the peak intensity position of the reflected light beam profile in a state where the base material portion 62 is irradiated with the irradiated laser beam, and the amount of shift becomes the maximum. Therefore, by detecting the state in which the shift amount of the peak intensity position is maximum, the edge of the object to be measured 60 is detected, and the dimension can be calculated from the deflection control voltage that controls the deflection when the irradiation beam is deflected to the edge position. It can be calculated.

Furthermore, at the edge position, as a result of the reflected light intensity distribution being modulated by the shift of the peak intensity position, the peak intensity position is used as a reference for the reflected light when the base material portion 62 is irradiated with the irradiated laser beam. A difference occurs in the intensity of reflected light in regions on both sides of the center, and the intensity difference becomes maximum. By detecting this intensity difference, the object to be measured 6o
edge position can be detected.

Edge position detection using the above method is possible as long as there is a difference in reflectance between the base material part and the dimension part, and edge position detection is not affected even if the reflectance of both changes. .

〔Example〕

FIG. 1 shows a system block diagram explaining the operation of the first embodiment of the present invention.

Reference numeral 1 denotes a laser light source, which is composed of, for example, a He-Ne laser or a semiconductor laser, and emits a laser beam 100.

2 is an optical system, which includes a light deflection element 11o and a beam splitter.
112, an objective lens 114, and various other lenses and optical elements (not shown). Reference numeral 6 denotes an object to be measured whose dimensions are to be measured, and has a configuration as shown in FIG. 6(a), and is composed of a dimension part 115 (reflectance rm) and a base material part 116 (reflectance rg).

Here, the edges of the dimension portion 115 are 117 and 118, and the dimension between the edges is measured.

A deflection control driver 4 generates an electric signal for electrically controlling the deflection operation of the optical deflection element 110 and supplies it to the optical deflection element 110. This electric signal uses a ramp wave voltage signal in which the voltage changes linearly. Light deflection element 110
has high deflection stability, with minute steps (e.g. 0.0
05 μm), an acousto-optic deflection element is used. The laser beam deflected by the optical deflection element 110 passes through the beam splitter 112, is focused by the objective lens 114 to a minute spot diameter of about 1 μm, and is irradiated onto the object to be measured. deflected in the direction

The reflected light from the object to be measured 6 passes through the objective lens 114,
The course is changed by the beam splitter 112, and the reflected light 1
20.

5 is a beam profile detection unit that detects the beam profile of the reflected light 120. The beam profile of the reflected light 120 can be easily obtained by moving a slit having a minute width in the beam diameter direction and detecting the amount of light transmitted through the slit. This kind of detector is for example P
hoton.

It is commercially available from J++C, Inc. as the 13eam-SCan model 1180. Furthermore, the beam profile may be detected by a multi-segment image sensor.

Note that the beam profile is detected in synchronization with voltage changes in the deflection control voltage.

6 is a first peak position detection unit, and the laser beam is directed to the object to be measured 6.
The peak intensity position in the beam profile of the reflected light is detected when the reference position of the base member 116 is irradiated. The reference peak intensity position at this time is expressed as pS. Thus, the position in the beam profile refers to the position in the coordinate system in which the beam profile is detected.

Reference numeral 7 denotes a second peak position detection unit that detects the peak intensity position in the beam profile of the reflected light when the laser light is irradiated onto a region including the dimension portion 115 of the object to be measured. The peak intensity position detected at this time is assumed to be pm. The peak intensity position pm is detected in synchronization with each state of light deflection on the surface of the object to be measured. It changes accordingly. 8 is a peak shift detection section,
The peak intensity that is not detected by the second peak position detector 7 when the dimension portion 115 of the object to be measured 6 is deflected with respect to the reference peak intensity position P8 detected by the first peak position detector 6 Detect Schiff l-Pd at position pm.

Reference numeral 9 denotes a peak shift storage unit which stores the shift of the peak position in each deflection state detected by the peak shift detection unit 8).
The data of Pd is stored over one period of deflection.

10 is a maximum peak shift detection unit that detects the maximum (positive sign) and minimum value (negative sign) of the shift amount data of the peak position stored in the peak shift storage unit 9, and also detects the maximum and minimum values. Detect the deflection position of the irradiation beam when obtained. The deflection position at this time will be described later, but the intensity peak position of the laser light irradiated onto the object to be measured is at the edge 117, 1.
It is obtained when it matches 18. 11 is the dimension calculation section,
The dimensions are calculated from the deflection positions when the positive and negative maximum peak shift positions detected by the maximum peak shift detection unit 10 are obtained. Here, the deflection position when the peak intensity position of the reflected light beam profile causes the maximum shift is given by the deflection control voltage of -4 that drives the optical deflection element 110. Therefore, The voltage difference between the deflection control voltages when deflecting between two edges is converted into dimensions. At this time, the aforementioned deflection control voltage difference is measured for a sample with known dimensions, and the correlation formula between the amount of deflection and dimensions is calculated. It is necessary to obtain the following.The amount of deflection and the dimensions are in a proportional relationship.

FIG. 2 shows a state diagram of light deflection on the surface of the object to be measured.

20 represents the beam profile of the laser beam irradiated onto the object to be measured, which has a Gaussian intensity distribution.

202 is the maximum intensity part, with the 2 points on the left and right centering on the point 202.
The intensity distributions of the two regions 210 (L region) and 212 (R region) are symmetrical. A laser beam having such an intensity distribution is optically deflected in the direction from A to B in the figure. State S1 is a state in which the entire irradiated laser beam is irradiated to the base material part 116,
Use as reference position.

As the optical deflection progresses from the S1 state, the R region of the irradiation beam comes to irradiate the dimension portion 115, and in the state S2, the peak intensity 202 is irradiated to the edge 117. At this time, L
Although the entire area 210 is irradiated to the base material part 116, R
A part of the area 212 is a dimension part 115, and the rest is a basic part 116.
is irradiated. As the light deflection progresses further, a state is reached in which the peak intensity 202 is irradiated onto the center of the dimensional portion 115 in the S3 state. At this time, L area 210, R area 212
The irradiation conditions of are equal. In the S4 state, the edge 118 is irradiated with the peak intensity 202, and the positional relationship is opposite to that of the 82 state described above.

If the light deflection progresses further from state S4, state S5 is reached, and the entire irradiation beam 200 is irradiated onto the base member 116 again. The above state S1 to state S is one cycle of optical deflection, and the deflection step is, for example, the irradiation beam 200.
This is done with minute distance changes of 1/100 (approximately 0.01 μm) or less of the diameter of.

To measure dimension section 1150 dimension, edge 117.1
18, and for that purpose state S2 and state S4
Detect. In states 81 to S5, the irradiation beam 20
Since the reflection state of the object to be measured 3 with respect to 0 is different, a unique reflected light intensity profile is obtained in each state, and the edges 117 and 118 can be determined by analyzing this profile.

FIG. 3 explains the beam profile of the reflected light intensity and the state of shift of the peak intensity position.

Note that the S1 state...S state in the explanation of FIG. 3 refers to the state shown in FIG. 2.

In FIGS. 3(a), (b), (/→, the waveform 60 is the reflected light detected when the irradiation beam 200 is irradiated to the reference position (S+ state) of the base member 116 in FIG. The waveform 60 shows a Gaussian intensity distribution similar to that of the irradiation beam 200, and the position of the peak intensity 61 at that time is the reference peak intensity position PB.

The waveform 66 in FIG. 3(a) is the beam profile of the reflected light detected when the irradiation state is 82, and the position where the peak intensity 64 is obtained at that time is the peak intensity position Pm.
It is 2. In the S2 state, L of the irradiation beam 200
The reflection in the region 210 is the maximum, and the reflection in the R region 212 is the minimum (assuming that the reflectance is r s ) r m).

In this case, the intensity of the reflected light from the two left and right regions 210 and 212 is unbalanced, so the beam profile of the entire reflected light is modulated from a Gaussian intensity distribution. Therefore, the peak intensity position also shifts.

The peak intensity position pm of the reflected light is also shifted in the optical deflection states from the S1 state to the 82 state, but it is on the right side of the peak intensity position Pm2 mentioned above, and the positions ps and Pm2 are shifted.
The position is between.

The waveform 65 in FIG. 3(b) is the beam profile of the reflected light when the irradiation beam 200 is in the S3 state, and the position pm3 at which the peak intensity 66 is obtained is approximately equal to the reference position P. We are doing so.

In the S state, the reflected light intensities from the left and right regions 210 and 212 are both equal, and there is no imbalance in the difference in intensity between the two, so the beam profile 65 of one reflected light approaches a Gaussian distribution, and the peak intensity position pms shifts rarely occur. In the deflection states from state S2 to state S3, the peak intensity position pm is between the reference peak intensity position ps and the aforementioned peak intensity position prn2.

The waveform 67 in FIG. However, the position is in the opposite direction. This is because in the S2 state and the S state, regions opposite to each other centering on the peak intensity 202 of the irradiation beam 200 are irradiated onto the dimension portion 115 in FIG. 2. When the optical deflection state is from the 83 state to the S state, the peak intensity position pm exists on the right side of the reference position P.

As described above, the beam profile of the reflected light in each optical deflection state is detected, and the variation in the peak intensity position pm is detected and stored.

A waveform 69 in FIG. 3(a) illustrates the shift of the peak intensity position pm with respect to the reference peak intensity position P8 described above. The horizontal axis of the graph is the deflection control voltage that controls optical deflection, and the vertical axis is the peak shift amount.

The waveform 69 has a maximum part 690 and a minimum part 695, the maximum value at the maximum part 390 is obtained in the S2 state, and the minimum value (the maximum value in absolute value) at the minimum part 695 is obtained in the S4 state.

If the deflection control voltage when optically deflecting the irradiation beam 200 to the S2 and S4 states detected above is You can take it by converting it.

The above-mentioned change in the peak intensity position of the beam profile of the reflected light occurs due to the effect of trying to equalize the imbalance in the reflected light intensity distribution caused by the difference in reflectance, and the shift in the peak intensity position Pm In this case, the dimension portion 115 in FIG. 2 is large, and the base material portion 116 and the dimension portion 11
The larger the difference between the reflectances r8 and rm of 5, the larger the difference becomes.

In the case of the same dimensions, if the reflectances rs and rm change, the magnitude of the intensity of the beam profile of the reflected light and the shift amount of the peak position will change, especially in the S2 and S4 states, but the maximum value of the peak position shift will be Obtained in the same S2 and S4 states.

Therefore, according to the present invention, even if the reflectance of the object to be measured B changes, dimensions can be measured without being affected by the change in reflectance.

Next, a second embodiment of the present invention will be described.

FIG. 4 shows a system block diagram illustrating a second embodiment of the present invention.

Components 1 to 6 in FIG. 4 are the same as those in FIG. 1, so their explanations will be omitted.

Reference numeral 41 denotes a reflected light intensity detection unit, which detects the beam profile of the reflected light detected in each state of optical deflection as described in FIGS. 2 and 31, with the reference peak intensity position ps as the center, and the Reflected light intensity of area 1. ．． 1.
Detect. This reflected light intensity 1. ．． 1. changes according to the light deflection position.

Reference numeral 42 denotes an intensity difference detection unit that detects the difference between the reflected light intensities IL and IR detected in the two regions.

The intensity of this difference also changes according to the light deflection position.

Reference numeral 46 denotes a difference intensity storage unit that stores difference intensity data detected by the intensity difference detection unit 42 over one period of optical deflection. 44
is a maximum difference intensity detection unit which detects the maximum and minimum intensities of the difference intensity data and also detects the deflection control voltages VL, V when the light is deflected to that position.

45 is a dimension calculating section which converts the voltage difference V, -V between the deflection control voltages detected by the maximum difference intensity detecting section 44 into dimensions.

The second embodiment of the present invention shown above will be explained based on FIG. In the following description of this embodiment, S, state...S, state refers to the state shown in FIG. Figure 3 (a)
, (b), and (c), the intensity distribution of the reflected light beam profile 66.35.67 is detected by dividing it into two regions on the left and right sides of the reference position ps.

The reflected light intensity in the area to the left of the reference position P8 is IL,
The reflected light intensity in the area on the right side is 18, but generally the intensity is 1.1, which is the size of the dimension part 115 and the reflectance r8
, rm, the intensity difference is 1. -I. Detect. In the beam profiles of the S2 and S4 states shown in FIG. 3(a), 0→, the shift of the peak intensity position pm is maximum, so the intensity difference is 1. -I.

gives the maximum and minimum states. Further, in the beam profile in the Ss state shown in FIG. 3(b), since no shift occurs in the peak intensity position pm, the intensities 8 and 2 are equal, and the difference in intensity is 0.

Figure 5 shows the reflected light intensity over one period of optical deflection.■8,■
, and the change characteristics of the difference intensity.

The waveform 51 in Fig. 5 (a) is the intensity ■1, and the waveform 52 is the intensity ■
8, intensity IL, 1. An equal condition exists at point 56. This position is the S3 state.

The waveform 54 in FIG. 5(b) shows a difference intensity of 1. -I, and has a maximum part 55 and a minimum part 56. In the maximum portion 55, the difference intensity is maximum, and the deflection control voltage at that time is . This state is obtained in the S2 state. In the minimum portion 56, the difference intensity is the minimum (the absolute value is the maximum), and the deflection control voltage at that time is .

This state is obtained in the S4 state. As described above, the edge position of the object to be measured 6 can also be detected by determining the maximum and minimum positions of the intensity difference between the two regions. In this example, the reflected light intensity also depends on the reflectances rs and rm, but even if the reflectance changes, the positions where the intensity difference is maximum and minimum do not change, so it depends on the reflectance of the object to be measured 3. Dimensions can be measured without

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to detect only the maximum and minimum states of the fluctuation in the peak intensity position of the reflected light or the fluctuation in the difference in the intensity of the reflected light, depending on the fluctuation of the material of the object to be measured. It is possible to directly determine the edge position without having to do so, and the dimensions can be measured from the amount of light deflection between the edges.

The edge position can be determined by simple arithmetic processing, and the measurement quantity can be converted to a dimension by a simple proportional equation, so that the processing system can be configured with a simple software configuration.

[Brief explanation of drawings]

FIG. 1 is a system block diagram explaining the first embodiment of the present invention, FIG. 2 is a diagram explaining the state of optical deflection when detecting a beam profile according to the present invention, and FIG. 3 is a beam of reflected light. FIG. 4 is a system block diagram explaining the second embodiment of the present invention.
FIG. 5 is a diagram illustrating changes in reflected light intensity according to the second embodiment of the present invention, and FIG. 6 is a diagram illustrating a conventional method for measuring minute dimensions. 1... Laser light source, 3... Measured object, 5... Beam profile detection section, 6...
...First peak position detection unit, 7...Second peak position detection unit, 8...Peak shift detection unit, 9...Peak shift storage unit, 10 ...Maximum peak shift detection section, 11...
...Dimension calculation unit, 41...Reflected light intensity detection unit, 42...Intensity difference detection unit, 46...Difference intensity storage unit, 44... - Maximum difference intensity detection unit, 45...Dimension calculation unit, 110...Light deflection element, 114...Objective lens. Figure 6

Claims (2)

[Claims] (1) In a micro-dimensional measurement method in which a laser beam is irradiated onto the surface of an object to be measured while being deflected, and the dimensions of the object to be measured are measured from changes in the light intensity of reflected light, , detecting a beam profile of the reflected light, and within the detection coordinate system of the beam profile,
After determining the amount of shift of the peak intensity point of the beam profile at each deflection position based on the peak intensity point of the beam profile when the laser beam is irradiated onto a reference location on the surface of the object to be measured, the shift amount is determined. maximum value of quantity,
Find the deflection position of the laser beam that gives the minimum value,
A method for measuring minute dimensions, characterized in that the dimensions of the object to be measured are obtained based on the difference between both deflection positions. (2) In a micro-dimensional measurement method in which a laser beam is irradiated onto the surface of the object to be measured while being deflected, and the dimensions of the object to be measured are measured from changes in the light intensity of the reflected light, , detecting the beam profile of the reflected light, and within the detection coordinate system of the beam profile,
Two detection methods that are divided by a boundary passing through a peak intensity point of a beam profile obtained when the laser beam is irradiated onto a reference location on the surface of the object to be measured, and that the light intensity of the beam profile is equally divided and detected. Set the area,
After determining the difference in light intensity detected in the two detection areas of the beam profile at each deflection position, determining the deflection position of the laser beam that gives the maximum value and minimum value of the difference in light intensity, A method for measuring minute dimensions, characterized in that the dimensions of the object to be measured are obtained based on the difference in position.