JPH0458884B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field The present invention relates to a measuring method in a distance measuring device using an annular light beam.

(2) Prior Art Conventionally, there is a Japanese Patent Application No. 59-242490 filed by the present applicant regarding an optical distance measuring device. The distance measuring device proposed here is shown in FIG. In the figure, 1 is a laser light source, 2 is a collimator lens, 3 is a first conical mirror, 4 is a second conical mirror, 5 is a variable focal length lens, 6 is a polarizing beam splitter, and 7
is a 1/4 wavelength plate, 8 is a condenser lens, 9 is an object to be measured,
10 is a focus detection means, and 11 is a processing device.

The laser beam emitted from the laser light source 1 is turned into a flat beam by a collimator lens 2, and then passes through a first conical mirror 3 and a second conical mirror 4 into an annular beam with a dark center (hereinafter referred to as a ring beam). ). This ring beam passes through a variable focal length lens 5 and a polarizing beam splitter 6, converts linearly polarized light into circularly polarized light, and then projects it onto an object to be measured 9 via a condenser lens 8. The ring beam reflected on the top surface of the object to be measured 9 passes through a condensing lens 8 and is converted from circular polarization by a quarter-wave plate 7 into linearly polarized light perpendicular to the incident light, and then reflected by a polarizing beam splitter 6. It is deflected and projected onto the focus detection means 10.

FIG. 2 shows the light receiving surface of the focus detection means 10, in which annular ring sensors 12 and 13 form concentric circles.

The ring beam projected onto the focus detection means 10 changes its beam diameter according to the positional relationship between the focal position of the ring beam and the object to be measured 9, so that the focal position of the ring beam is on the upper surface of the object to be measured 9. If the beam diameter and the diameter of the ring sensors 12 and 13 are set so that the outputs obtained from each of the ring sensors 12 and 13 are equal when the Changes can be detected by the difference in output between ring sensors 12 and 13. Incidentally, as shown in FIG. 3, a focus signal (usually a ring sensor 12,
13, which is normalized by the output sum), maintains a good linear relationship within a predetermined measurement range.

Therefore, when performing measurements using such a device, it is necessary to know the approximate location of the object to be measured in advance, or
The object to be measured itself must be placed within a predetermined measurement range, making it impossible to shorten the measurement time and making automation difficult. Furthermore, since the focal position of the ring beam with the best detection sensitivity is not known during measurement, it is virtually impossible to measure under the best conditions, and the measurement accuracy is not sufficiently reliable.

(3) Summary of the Invention In view of the above-mentioned conventional drawbacks, an object of the present invention is to provide a distance measuring method that can automate and speed up measurement.

In order to achieve the above-mentioned object, the distance measuring method according to the present invention sequentially changes the focusing position of the measurement light beam focused at one point in the optical axis direction to a plurality of positions in the optical axis direction, and reflects it on the surface to be measured. a first step of detecting the measured light beam with a focus detection means having two sensor sections arranged in a direction in which the measurement light beam is displaced according to the position of the surface to be measured in the optical axis direction; a second process of obtaining two light focusing positions before and after the polarity of the focusing signal obtained as a function of the difference based on the respective outputs of the two sensor sections of the focus detection means changes; and from the two light focusing positions; a third step of selecting a light focusing position having the surface to be measured within a measurement range in which the position of the surface to be measured and the focusing signal have a substantially linear relationship; The method is characterized in that the distance from the focusing signal obtained at the optical position to the surface to be measured is measured.

Preferably, the measurement light beam is a ring beam, and the focus detection means usually includes two inner and outer beams.
It has a ring sensor divided into two parts, and uses the difference in output between the outside and inside of the ring sensor, or a value obtained by normalizing the output difference by the sum of the outputs of the outside and inside of the ring sensor, as a focusing signal. An output from the inside of the ring sensor when the polarity of the focusing signal changes with a change in the focusing position of the ring beam, and an output from the outside of the ring sensor before the polarity of the focusing signal changes. or,
The output from the outside of the ring sensor when the polarity of the focus signal changes is compared with the output from the inside of the ring sensor before the polarity of the focus signal changes, and the one with the larger output is focused. The distance to the surface to be measured can be measured by the signal.

If the measurement is performed according to the above method, the optimum light focusing position can be automatically detected and the distance to the surface to be measured can be measured at the light focusing position.

The basic principle of the distance measuring method according to the present invention will be explained below.

FIG. 4 is a diagram illustrating the basic principle of the present invention, and the same members as in FIG. 1 are designated by the same numbers. In addition, 14 is a ring beam condensed by the condensing lens 8, P ₁ , P ₂ ,
P ₃ is each focusing position of the ring beam 14 when the focal length of the optical system is changed, and A ₁ , A ₂ , A ₃ is the measurement range at each focusing position P ₁ , P ₂ , P _{3 .} show.

In the device as shown in FIG.
The position and focus signal have a good linear relationship. Therefore, using a variable focal length lens, etc., the focusing position is set to P ₁ ,
P ₂ , P ₃ ..., and the measurement range is changed to A ₁ , P 3 ...
By shifting A ₂ , A ₃ ..., the object to be measured 9
The ring beam 14 can be focused on a focusing position that has a measurement range that can detect the position of the ring beam.

For example, a ring sensor 12 as shown in FIG.
If the outputs from 13 are D ₁ and D ₂ respectively, the focusing signal is the value F which is the difference signal D ₂ - D ₁ normalized by the intensity signal D ₂ + D ₁ , that is, F = D ₂ - D ₁ /D ₂ +D ₁ ...(1) It can be expressed as: At this time, when the condensing position of the ring beam 14 is sequentially changed from the condensing lens 8 side as shown in _FIG. When the beam is between the condenser lens 8 and the object to be measured 9 as shown in ₂ , the beam diameter is expanded and enters the condenser lens 8, and becomes converged light by the condenser lens 8, so the ring sensor 1
2 and 13 are projected with a smaller diameter than when in focus. Therefore, the value of the focus signal F becomes F<0 from equation (1). Next, when the condensing position is on the opposite side of the object to be measured 9 from the condensing lens 8, as shown in _P3 , the beam diameter becomes smaller and enters the condensing lens 8, and the condensing lens 8 converts the beam into a diverging beam. Therefore, the beam is projected onto the ring sensors 12 and 13 with a larger diameter than when in focus. Therefore, the value of the focus signal F is F>0 from equation (1). That is, by sequentially changing the focusing position of the ring beam 14 and determining the polarity of the focusing signal F, it is possible to determine the polarity of the focusing signal F by sequentially changing the focusing position of the ring beam 14. Since the polarity changes between two adjacent light focusing positions, at least one of the two light focusing positions becomes the optimum light focusing position for measurement.

In the above description, the condensing position is sequentially changed from the condenser lens 8 side, but it may be sequentially changed from the side opposite to the condenser lens 8 via the object to be measured 9. Further, it is preferable that the measurement ranges determined by the amount of change in the light focusing position are continuous, with each light focusing position being the center, and it is of course possible for adjacent measurement ranges to partially overlap. Furthermore, although the above explanation uses a standardized value as the focus signal, it is simply the difference signal D ₂ −
Of course, D ₁ may be used as the focusing signal, and the value of D ₁ −D ₂ may be used as the difference signal. However, when using the value of D ₁ - _{D 2} as the difference signal, the linear relationship between the object to be measured and the focusing signal will be a straight line sloping upward to the left, contrary to what is shown in Fig. The manner in which the focusing signal changes is also reversed.

Hereinafter, the present invention will be explained in detail with reference to Examples.

(4) Embodiment FIG. 5 shows a flowchart of the distance measuring method according to the present invention.

Figures 1 and 2 show an apparatus for measuring the distance to a surface to be measured by applying the distance measuring method shown in this example.
Consider the device shown in the figure. Here, it is assumed that the focal length variable lens 5 can change the focusing position in steps of distance N, and the focusing position on the focusing lens 8 side is of the two focusing positions closest to the surface to be measured. Inside 12 and outside 1 of the ring-shaped sensor in
The outputs of 3 are respectively D' ₁ and D' ₂ , and the outputs of the ring sensor 1 at the focal position opposite to the condenser lens 8 are
2. Let the outputs of the outside 13 be D ₁ and D ₂ respectively. Furthermore, the focusing signal is expressed as F=D ₂ -D ₁ /D ₂ +D ₁ as described above.

First, the ring beam is focused at the focal length closest to the condenser lens 8, and detection of the focus signal F is started. The focal length is increased by +N by the variable focal length lens 5 until F>0, that is, the focal position of the ring beam is on the opposite side of the surface to be measured from the condensing lens 8, and each time the focus signal is Determine the polarity of F,
The output signal _D1 of the ring sensor 12 at the light focusing position when F>0 is stored.

Next, return to the position -N away from the focusing position when F>0 (closer to the focusing lens by N), that is, the focusing position closest to the surface to be measured and on the side of the focusing lens 8. The ring beam is focused, and the output signal D' ₂ of the ring sensor 13 at this time is stored.

Here, the stored output signals D ₁ and D' ₂ are compared in magnitude, and if D ₁ ≦ D' ₂ , it is determined from the in-focus signal F and focal length at the current focusing position where F < 0. The resulting distance to the surface to be measured is taken as the measured value. Also D ₁
>D′ ₂ , the ring beam is again focused at a position +N away from the current focusing position where F<0, and the focus signal F at this focusing position and the focal length obtained from the focal length are The distance to the measurement surface is taken as the measured value.
Note that this comparison of D ₁ and D' ₂ is based on the measurement range that is closer to the surface to be measured and centered on the focal point of the two focal points via the surface to be measured. This is done in order to detect the optimum light focusing position that includes the surface to be measured (see Fig. 3).

FIG. 6 shows another flow chart of the distance measuring method according to the present invention. As the apparatus to which this method is applied, the apparatus shown in FIGS.
No. 13 output signals D ₁ , D ₂ , D' ₁ , D' ₂ , focus signal F, etc. are all handled as in the previous embodiment.

First, the apparatus is started and a focus signal F from the ring sensors 12 and 13 at an arbitrary light focusing position is detected. Here, the polarity of F is detected to determine whether the current focusing position of the ring beam is on the condensing lens 8 side or on the opposite side when viewed from the surface to be measured.

When the focus signal F>0, the condensing position of the ring beam is on the opposite side of the condenser lens 8 when viewed from the surface to be measured, so the condensing position is changed by -N from the current position, and the condensing position is gradually focused. Bring it closer to the optical lens 8. At this time, the polarity of the focusing signal F is determined for each focusing position. F>0
If so, repeat this determination and obtain the output signal of the ring sensor 13 at the condensing position when F<0.
Remember D′ ₂ . Next, the ring beam is again focused at a focusing position that is +N away from the current position where F<0, and the output signal D ₁ of the ring sensor 12 at this focusing position is stored. Stored output signal D′ ₂ ,
The magnitude of D ₁ is compared, and if D ₁ ≧D′ ₂ , the measured value obtained from the focus signal F and the focal length at this focusing position is taken as the distance to the surface to be measured. Also, if D' ₂ > D ₁ , the ring beam is focused at a position -N away from the current position where F < 0, and the measurement obtained from the focusing signal F and focal length at this focusing position is Let the value be the distance to the surface to be measured.

Next, the polarity of the focusing signal F immediately after the device is activated is F<
In the case of 0, the condensing position of the ring beam is on the condensing lens 8 side when viewed from the surface to be measured, so it is + from the current position.
The condensing position is changed by N, and the condensing lens 8 is gradually
keep away from At this time, the focus signal F for each focus position
Determine the polarity of

If F<0, this determination is repeated, and the output signal _D1 of the ring sensor 12 at the condensing position when F>0 is stored. Next, the ring beam is again focused at a focusing position that is −N away from the current position where F>0, and the ring sensor 1 at this focusing position is
3, the output signal D' ₂ is stored. The stored output signals D ₁ and D′ ₂ are compared in magnitude, and if D′ ₂ ≧D ₁ , the measurement value obtained from the focal signal F and focal length at this condensing position is used as the distance to the surface to be measured. Distance. or,
If D ₁ >D' ₂ , the ring beam is focused at a position +N away from the current position, and the measured value obtained from the focusing signal F and focal length at this focusing position is calculated as the distance to the surface to be measured. shall be.

If the focus signal F becomes F=0 during the measurement, the surface to be measured exists at the condensing position of the ring beam, and this means that the position of the surface to be measured has been detected immediately.

In addition, if there is an overlapping part in each measurement range that is continuously obtained according to the change in the focusing position for each distance N, and the surface to be measured exists in the overlapping part, which of the focusing positions with each measurement range is located? The distance to the surface to be measured may be detected using the focusing signal F.

Measurement using the above method is automatically controlled by a microcomputer built into the processing device 11 of the apparatus shown in FIG. 1, for example, so high-speed processing is possible and measurement results can be obtained immediately. I can do things.

In the above two embodiments, the two light focusing positions closest to the surface to be measured are detected, and the output of the ring sensor is
After detecting the optimal focusing position by comparing D ₁ and D′ ₂ , the distance from the focusing signal F to the surface to be measured is measured. After memorizing the measured values and detecting the optimal focusing position, the stored focusing signal F corresponding to that position is
Alternatively, there is also a method of calling the measured value. Therefore,
Various applications other than the above-mentioned embodiments are possible as long as they do not depart from the spirit of the present invention.

Furthermore, although this embodiment has described a method for measuring the distance to the surface to be measured, it can also be applied to, for example, a gap measuring device that measures the distance between a mask and a wafer in a semiconductor device. By measuring each distance and taking the difference, you can measure the distance between them.

(5) Effects of the Invention As explained above, the distance measuring method according to the present invention can automatically detect the optimum light focusing position during measurement, and can detect the optimum light focusing position at high speed to This is a measurement method that can measure the distance to.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of an optical distance measuring device.
FIG. 2 is a diagram showing a ring-shaped sensor. FIG. 3 is a diagram showing the relationship between the focus signal and the measured position. FIG. 4 is a diagram explaining the basic principle of the distance measuring method according to the present invention. Fifth
FIG. 6 is a flowchart showing an example of the distance measuring method according to the present invention. 1... Laser light source, 2... Collimator lens,
3...First conical mirror, 4...Second conical mirror, 5...Variable focal length lens, 6...Polarizing beam splitter, 7...1/4 wavelength plate, 8...
Condensing lens, 9...Object to be measured, 10...Focus detection means, 11...Processing device, 12, 13...Ring sensor, _A1 , _A2 , _A3 ...Measurement range, _P1 , _P2 ,
P ₃ ……Focusing position.

Claims (1)

[Scope of Claims] 1. Sequentially changing the convergence position of the measurement light beam condensed at one point in the optical axis direction to a plurality of positions in the optical axis direction, and directing the measurement light beam reflected from the surface to be measured to the measurement object. a first step of detecting with a focus detection means having two sensor sections arranged in a direction in which the measurement light beam is displaced according to the position of the surface in the optical axis direction, and the two sensor sections of the focus detection means; A second process of obtaining two light focusing positions before and after the polarity of the focusing signal obtained as a function of the difference based on each output of a third step of selecting a focusing position having the surface to be measured within a measurement range having a substantially linear relationship with the focusing signal; A distance measurement method characterized by measuring the distance to a surface to be measured. 2. The measurement light beam is annular, and the focus detection means has an annular sensor divided into an inner and an outer part as the two sensor parts, and the output of the outer and inner parts of the annular sensor is The difference or the value obtained by normalizing the output difference by the sum of the outputs of the outside and inside of the annular sensor is the focus signal, and the output of the inside of the annular sensor when the polarity of the focus signal changes. , the focus signal is compared with the output from the outside of the annular sensor before the polarity changes, and the distance from the focus signal with the larger output to the surface to be measured is measured. A distance measuring method according to claim 1. 3. The measurement light beam is annular, and the focus detection means has an annular sensor divided into two, an inner and an outer part, as the two sensor parts, and an outer and an inner part of the annular sensor. The output difference or the value obtained by normalizing the output difference by the sum of the outputs of the outside and inside of the annular sensor is the focus signal, and the output of the outside of the annular sensor when the polarity of the focus signal changes. and an output from the inner side of the annular sensor before the polarity of the focusing signal changes, and the distance from the focusing signal with the larger output to the surface to be measured is measured. A distance measuring method according to claim 1.