JPH06241720A - Measuring method for displacement quantity and displacement meter - Google Patents

Abstract

PURPOSE:To measure displacement quantity absolutely and optically, even when an objective surface for measurement is very small by providing an auto matic focusing mechanism which focuses on the basis of light reflected from the objective surface for measurement. CONSTITUTION:A displacement meter comprises a moving drive mechanism 3 for moving a sensor unit 1 in directions to and away form an object for measurement 2, a move quantity detector 4 for detecting a move quantity of the sensor unit 1 and a numeric calculation/control system 5. Light L from a light source 13, via an objective lens 16, is converged and thus irradiates objective measurement surfaces 61a, 62a. An automatic focusing mechanism is constituted of a mirror 14 having a knife-edge and a light detector 18, and thus focusing is made on the basis of light L reflected from the objective surfaces 61a, 62a along light paths. That is, the lens 16 is moved in directions to and from the objective surfaces 61a, 62a by the drive mechanism 3 and the control system 5, so that the quantity of move is taken as a displacement quantity concerning a reference surface 2a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement amount measuring method and a displacement meter for measuring a displacement amount of a surface to be measured with respect to a reference surface.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional displacement meter includes a laser light source 102 for irradiating a surface 101 to be measured with a laser beam L in an oblique direction, and a surface 101 to be measured in an oblique direction. It is composed of a photodetector 104 on which the reflected laser light L is incident via the objective lens 103. The photodetector 104 is provided with a large number of light receiving elements, and specifically, the same number of light receiving elements are arranged on the left and right sides with the light receiving element provided at the center in the longitudinal direction as a base point.

In actual displacement measurement, first, the reference plane 101a is determined, and the photodetector 104 is positioned as follows. That is, the laser light source 1 with respect to the reference surface 101a
02, the optical axis of the reflected light L reflected by the reference surface 101a coincides with the light receiving element at the center of the photodetector 104, and the optical axis and the received light are received. The photodetector 104 is positioned so that it is perpendicular to the plane. At this time, the longitudinal direction of the photodetector 104 (arrangement direction of the light receiving elements) has a positional relationship inclined by a predetermined angle with respect to the reference plane 101a.

Then, the actual displacement measurement is started,
In this displacement measurement, how much the measured surface 101b is displaced with respect to the reference surface 101a is measured by the amount of movement of the photodetector 104. For example,
When the surface to be measured 101b is located above the reference surface 101a, the light emitted from the laser light source 102 is reflected at a position above the reference surface 101a. The light L passes through the optical path above the center line of the objective lens 103, and as a result, forms an image on the light receiving element located obliquely below the central light receiving element.

From this state, the objective lens 103 and the photodetector 104 are kept until the optical axis of the reflected light L and the center line of the objective lens 103 coincide with each other while maintaining the positional relationship between the objective lens 103 and the photodetector 104. Move diagonally upward. That is, the objective lens 103 and the photodetector 104 are moved to a position where the reflected light L is incident on the central light receiving element. Since the amount of movement at this time corresponds to the amount of displacement of the surface to be measured 101b with respect to the reference surface 101a, the displacement of the surface to be measured 101b is displayed by displaying the amount of movement through, for example, a display means. You can know the quantity.

[0006]

However, in the above conventional displacement measurement, the laser beam L is applied to the surface 1 to be measured.
01 is irradiated from an oblique direction, and the measured surface 10
Since the displacement of 1 is measured, for example, when measuring the depth of a small hole or the like formed in the reference surface 101a, the following inconvenience occurs. That is, as shown in FIG. 5, even when the laser light L is applied to the bottom portion 102a of the hole 102, the laser light L is blocked by the upper edge portion of the hole 102, and the laser light L is on the side wall of the hole. Irregularly reflected at 102b, or even if the laser light L is reflected by the bottom portion 102 of the hole 102.
The photodetector 104 of the reflected light L even if the light is irradiated to a.
The incident that the incident light is blocked by the opposite side wall 102b of the hole 102 occurs, and it becomes impossible to measure the depth of the hole 102.

This is also the case when the surface roughness of an object is optically measured, for example, when the arrangement pitch of wiring patterns formed on a substrate is measured. As described above, in the conventional displacement measurement, the measurement cannot be performed when the surface to be measured is extremely narrow, such as the bottom of the concave portion of the uneven surface, the bottom of the hole, and the bottom of the wiring pattern. There was a problem.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce the uneven surface, particularly the bottom of a recess, the bottom of a hole, and the bottom of a wiring pattern. It is an object of the present invention to provide a displacement amount measuring method capable of reliably optically measuring the displacement amount even when the surface to be measured is extremely narrow.

Another aspect of the present invention is that even when the surface to be measured is extremely narrow, such as the bottom of a concave portion of an uneven surface, the bottom of a hole, and the bottom of a wiring pattern, its displacement is ensured. An object of the present invention is to provide a displacement meter capable of optically measuring a quantity.

[0010]

The present invention provides a displacement measuring method for optically measuring the amount of displacement of a surface to be measured (such as the bottom 61a of the hole 61 and the upper surface 62a of the protrusion 62) with respect to the reference surface 2a. , The objective lens 16 receives the light L from the light source 13.
To be measured and converged through (61a, 62a, etc.)
To the subject surface (61a, 62a, etc.) and performs focusing based on the light L reflected along the forward optical path (mirror 1 with knife edge).
4, the photodetector 18, the movement driving mechanism 3 and the control system 5) are used to move the objective lens 16 to the measurement target surface so that the distance between the objective lens 16 and the measurement target surface (61a, 62a, etc.) becomes constant. (61a, 62a, etc.) is moved in the direction of contact and separation, and the amount of movement is measured (61a, 62a).
And the like) relative to the reference surface 2a.

In another invention, the surface to be measured (hole 61
Reference surface 2 of the bottom portion 61a of the
In a displacement meter that optically measures the amount of displacement with respect to a,
The light source 13 and the objective lens 16 that converges the light L from the light source 13 and irradiates it on the surface to be measured (61a, 62a, etc.).
And the optical system 12 that is movable in the direction toward and away from the surface to be measured (61a, 62a, etc.) and the light emitted from the light source 13 of the optical system 12 causes the surface to be measured ( 61a, 62a, etc.), so that the distance between the objective lens 16 and the surface to be measured (61a, 62a, etc.) becomes constant based on the reflected light L reflected along the forward light path.
Automatic focusing mechanism (mirror 14 with knife edge, photodetector 18, movement driving mechanism 3) for moving the optical system 12 in the direction of contact with and away from the surface to be measured (61a, 62a, etc.).
And a control system 5) and a movement amount detection means 4 for detecting the movement amount of the optical system 12.

[0012]

In the displacement measuring method according to the present invention, first, the light L from the light source 13 is converged through the objective lens 16 and applied to the surface to be measured (61a, 62a, etc.).
Then, an automatic focusing mechanism (a mirror 1 with a knife edge) that performs focusing based on the light L reflected from the surface to be measured (61a, 62a, etc.) along the forward optical path.
4, the photodetector 18, the movement driving mechanism 3 and the control system 5) are used to move the objective lens 16 to the measurement target surface (until the distance between the objective lens 16 and the measurement target surface (61a, 62a, etc.) becomes constant. 61a, 62a, etc.) in the contacting / separating direction, and the amount of movement is taken as the amount of displacement of the measurement target surface (61a, 62a, etc.) with respect to the reference surface 2a.

In this case, the surfaces to be measured (61a, 62a)
Since the light L reflected by the surface of the object to be measured is along the outgoing light path, the surface to be measured (61) such as the bottom of the concave part of the uneven surface, the bottom of the hole, the bottom of the wiring pattern, etc.
Even if (a, 62a, etc.) is very narrow, the displacement can be reliably measured optically.

Next, in a displacement meter according to another invention,
First, the light L from the light source 13 in the optical system 12 is applied to the surface to be measured (61a, 62a, etc.). Then, the automatic focusing mechanism (the mirror 14 with the knife edge, the photodetector 18, the movement driving mechanism 3 and the control system 5), based on the light L reflected by the surface to be measured (61a, 62a, etc.), The objective lens 16 and the surface to be measured (61a, 62a
The optical system 12 is moved in the contacting / separating direction with respect to the surface to be measured (61a, 62a, etc.) until the distance to the object surface (61a, 62a, etc.) becomes constant. At this time, the amount of movement of the optical system 12 is detected by the movement amount detecting means 4. Then, the movement amount detected by the movement amount detecting means 4 is the surface to be measured (6
The displacement amount (1a, 62a, etc.) is displayed through, for example, the known display means 55.

In this case, the surfaces to be measured (61a, 62a)
Since the light L reflected by the surface of the object to be measured is along the outgoing light path, the surface to be measured (61) such as the bottom of the concave part of the uneven surface, the bottom of the hole, the bottom of the wiring pattern, etc.
Even if (a, 62a, etc.) is very narrow, the displacement can be reliably measured optically.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the displacement amount measuring method according to the present invention is embodied as a displacement gauge (hereinafter, simply referred to as a displacement gauge according to an embodiment) will be described below with reference to FIGS.

The displacement meter according to this embodiment, as shown in FIG. 1, includes a sensor unit 1 and a sensor unit 1.
Drive mechanism 3 for moving the object 2 to and from the object 2 to be measured, a movement amount detector 4 for detecting the movement amount of the sensor unit 3, and a control system 5 for electrically controlling numerical calculation and various circuits. Have and.

The sensor unit 1 has a housing 11 in which a knife-edge type optical system 12 is incorporated. This optical system 12 includes at least a laser diode 13, a knife edge 14 with a mirror, a lens 15, and an objective lens 1.
6, a mirror 17, and a photodetector 18. Among these optical components, a knife edge 14 with a mirror, a lens 15 and an objective lens 16 are sequentially arranged on an emission optical path of a laser diode 13, and a mirror 17
Are arranged on the optical path through which the reflected light separated by the knife edge 14 with a mirror passes and at a position where the reflected light is guided to the photodetector 18 side.

Further, the sensor unit 1 is positioned so that the optical axis of the laser light L emitted from the laser diode 13 and the surface of the DUT 2 are in a vertical relationship. The photodetectors 18 are, in this example, two isolated from each other.
It is composed of two photodiodes (not shown in FIG. 1). Further, the objective lens 16 is a holder 19 which is detachably attached to the housing 11 of the sensor unit 1.
It is built in and can be replaced as needed.

Further, the housing 11 of the sensor unit 1
On the side surface, a rack 21 with which a drive gear 33 of the moving drive mechanism 3 described later is meshed is provided. This rack 21
Is provided so that the arrangement direction of a large number of gear teeth extends along the up-down direction of the housing 11. Therefore, the rotation of the drive gear 33 causes the sensor unit 1 to move in the vertical direction.

In addition, a tongue piece 22 having a plate shape, for example, which projects in the lateral direction, is provided in the lower portion of the housing 11 of the sensor unit 1. The tip of the contactor 41 of the movement amount detector 4 described later is always in contact with the upper surface of the tongue piece 22.

The moving drive mechanism 3 includes a fixed plate 3 extending vertically.
1 is provided with a motor 32 that is a drive source, and a reduction mechanism that reduces the rotational force of the motor 32 and transmits it to the drive gear 33. This reduction mechanism is composed of, for example, a belt transmission mechanism and a gear train. In FIG. 1, the transmission of the rotational force of the motor 32 by this reduction mechanism is shown only by the arrow.

Further, the movement amount detector 4 is attached to the fixed plate 31 of the movement drive mechanism 3 at a lower portion thereof. The movement amount detector 4 is provided with a contactor 41 slidable in the vertical direction.
Is always urged downward by a spring (not shown) mounted inside the detector housing 42. In addition, a sliding piece (not shown) that contacts a resistor (not shown) is fixed to the center of the contactor 41 in the longitudinal direction.

Therefore, the movement amount detector 4 is composed of the contactor 4
1. A variable resistor including a sliding piece and a resistor, in which the contactor 41 slides up and down with the vertical movement of the sensor unit (that is, the vertical movement of the tongue in contact with the tip). Thus, the length of the resistor is equivalently changed, its electric resistance is changed, and the voltage signal dropped according to the resistance change is output. This voltage signal is converted into a digital signal in the movement amount detector 4 and output to the outside.

The control system 5 performs calculation based on various input signals and controls the various circuits based on the calculation, and the photodetector 18 in the optical system 12 in the sensor unit 1. Detection signal from (S
a, Sb) is converted into digital detection data (Da, Db) and supplied to the computer 51, and the digital movement amount data Dc input from the movement amount detector 4 is converted into the computer 51. Based on the read signal Sr from the
Digital input / output circuit (hereinafter simply referred to as I / O
Circuit 53), a motor drive circuit 54 that supplies a drive current i to the motor 32 of the movement drive mechanism 3 based on a drive signal Sd from the computer 51, and the computer 51.
And a display 55 for displaying the display data Dd from No. 1 as numbers or line images.

Next, the operation of the displacement meter according to this embodiment will be described. Before that, the operation principle of the optical system 12 will be described with reference to FIGS.

The laser light L emitted from the laser diode 13 has a semi-circular spot shape by the mirror 14 with a knife edge, and the lens 15 and the objective lens 1
An image is formed on the DUT 2 through 6. By the way, the laser light L reflected by the DUT 2 returns to the objective lens 16 and the lens 15 in reverse, is reflected by the mirror 14 with knife edge, is further reflected by the mirror 17 and is incident on the photodetector 18. To do.

This photodetector 18 is, as shown in FIG.
It is composed of two photodiodes (first photodiode PA and second photodiode PB) divided from each other, and these photodiodes PA and P
As shown in FIG. 2B, B is arranged when the surface 2a of the DUT 2 exists at the focal length f of the objective lens 16, that is, when the surface 2a of the DUT 2 is just the focus point (hereinafter, simply The positions of the two photodiodes PA and PB are aligned so that the reflected light L forms an image at the midpoint between the two photodiodes PA and PB when they coincide with each other.

With this arrangement, the object to be measured 2
When the surface 2a of the laser beam moves away from the JF point, the semi-circular spot of the reflected light L moves toward the first photodiode PA as shown in FIG. 2C, and as shown in the characteristic diagram of FIG. 3A. , The detection signal Sa at the first photodiode PA
The level will increase. The waveform of this detection signal Sa is such that the surface 2a of the DUT 2 gradually moves away from the JF point,
The first photodiode PA has a waveform that approximates a Gaussian distribution with the level peak at the position where the semicircular spot completely enters the light-receiving surface of the first photodiode PA.

On the other hand, when the surface 2a of the object 2 to be measured approaches the objective lens 16 side from the point J · F, as shown in FIG. 2A, the semi-circular spot of the reflected light L, this time, becomes the second spot. It moves toward the photodiode PB, and the level of the detection signal Sb in the second photodiode PB increases as shown in the characteristic diagram of FIG. 3A. The waveform of this detection signal Sb shows that the surface 2a of the DUT 2 is from the point JF to the objective lens 1
It has a waveform that approximates a Gaussian distribution with the level peak at the position where the semicircular spot completely enters the light receiving surface of the second photodiode PB as it gradually approaches the 6th side.

The detection signals Sa and Sb shown in FIG.
When the difference (Sa-Sb) is taken, as shown in FIG. 3B,
The waveform is almost S-shaped, and the middle point (zero point) is JF.
Corresponds to the point. The S-shaped waveform has a characteristic that the vicinity of the zero point is close to a straight line, and in this displacement meter, the straight line portion is used as a displacement measurement region. Therefore, the difference (Sa-Sb) between the detection signals is almost proportional to the amount of deviation between the surface 2a of the DUT 2 and the JF point. In the actual displacement measurement, if the computer 51 performs calibration,
Linearity is not an issue.

However, since the output levels of the detection signals Sa and Sb change depending on the light reflectance of the sample (object to be measured 2) and the light amount variation of the laser diode 13, the above linear region is used as it is as the displacement measurement region. Then, the measurement error becomes large. Therefore, in this embodiment, FIG.
By taking the sum (Sa + Sb) of the detection signals Sa and Sb shown in (see FIG. 3C) and calculating (Sa−Sb) / (Sa + Sb), the above fluctuation is corrected and a highly accurate displacement is read. I have to.

Specifically, the overall operation of the above displacement meter will be described. First, a plane (reference plane) serving as a reference for displacement measurement is determined, and reference alignment processing (calibration) is performed. For example, in the surface 2a of the object to be measured 2, a reference surface (referred to as 2a for convenience) is determined in advance, and displacement measurement is performed on the reference surface 2a. In this measurement, first, for example, a stage (not shown) on which a sample (measurement object 2) is placed is moved in the lateral direction, and the objective lens 16 is moved.
The reference surface 2a should be located immediately below the. This stage is pre-positioned so that the surface 2a of the sample 2 placed on the upper surface of the stage comes to a position substantially close to points J and F of the optical system 12 in the sensor unit 1.

In the initial stage, the movement amount detector 4
The upper and lower positions of the sensor unit 1 are determined so that the intermediate value is output from. This is, for example, a computer 5
I / O from the movement amount detector 4 in the program ROM 1
The drive signal Sd is supplied to the motor drive circuit 54 until the movement amount data Dc input via the circuit 53 becomes an intermediate value.
This can be achieved by a method of registering a program for outputting and setting such that the program is started at the same time the power is turned on.

Thereafter, the reference surface 2a of the sample 2 is J · F.
The distance from the point is measured. this is,
When the reflected light L from the reference surface 2a is incident on the first and second photodiodes PA and PB, these first and second photodiodes PA and PB are incident.
Is measured by the detection signals Sa and Sb from the photodiodes PA and PB, respectively. That is, in this example, the detection signals Sa and Sb from the first and second photodiodes PA and PB are converted into digital detection data Da and Db by the A / D converter 52, respectively, and then the computer 51 at the next stage. Is supplied to. The computer 51 performs an operation on the supplied detection data Da and Db based on the operation program transferred from the program ROM to the operation RAM. This calculated value D is the following formula 1
It is represented by.

[0036]

## EQU1 ## D = (Da-Db) / (Da + Db)

Here, for example, when D> 0, the reference surface 2a is J
When the position is far from the point F, for example, the drive signal + Sd in the forward direction is output to the motor drive circuit 54. When the drive signal + Sd in the forward direction is supplied from the computer 51, the motor drive circuit 54 supplies the drive current + i in the forward direction to the motor 32 to rotate the motor 32 in the forward direction. With the forward rotation of the motor 32, the drive gear 33
By the rotation-linear motion conversion between the rack 21 and the rack 21, the sensor unit 1 itself moves so as to approach the reference surface 2a. This movement is performed until D = 0, that is, the reference surface 2a coincides with the point J · F.

Then, when the reference plane 2a coincides with the point J · F, the computer 51 outputs the read signal Sr to the I / O circuit 53 to open the gate of the I / O circuit 53, and at the present time, I The movement amount data Dc input to the / O circuit 53 is read, and this data Dc is registered as a reference data in the data area of the RAM. At this stage,
Reference alignment processing (calibration) in displacement meters
Is completed.

Then, the displacement of the actual surface to be measured is measured. The surface to be measured is, for example, the bottom of the hole 61 provided in the sample 2, the unevenness formed on the surface of the sample 2, or the wiring pattern.

Here, for example, the case of measuring the displacement (depth) of the bottom 61a of the hole 61 formed in the reference surface 2a will be described. The stage (not shown) on which the sample 2 is mounted is moved. Then, the hole 61 to be measured is positioned immediately below the sensor unit 1 on which the reference matching process is completed. At this time, the laser light L emitted from the laser diode 13 is applied to the bottom portion 61a of the hole 61, and the light (reflected light) L reflected by the bottom portion 61a of the hole 61.
Enters the optical system 12 along the outgoing light path. The reflected light L that has entered the optical system 12 enters the photodetector 18 via the mirror 14 with knife edge and the mirror 17.

With the incidence of the reflected light L, the photodetectors (first and second photodiodes PA and PB) output detection signals Sa and Sb, respectively, and the computer 51 outputs the detection data Da and Db. Is entered.
The computer 51 uses the input detection data Da and D
The calculation of b is performed based on the calculation formula shown in the above mathematical expression 1. In this case, since the bottom portion 61a of the hole 61 is located below the reference surface 2a, a value in the + direction (D>
0).

The computer 51 supplies a positive drive signal + Sd to the motor drive circuit 54 to rotate the motor 32 in the forward direction, as in the case of the reference adjustment process. With the forward rotation of the motor 32, the sensor unit 1 itself moves downward, that is, in the direction toward the hole 61. This movement is performed until D = 0.

Then, when the bottom portion 61a of the hole 61 coincides with the point J · F, the computer 51 outputs the read signal Sr to the I / O circuit 53 to open the gate of the I / O circuit 53, and at the present time. At, the movement amount data Dc input to the I / O circuit 53 is read. After that, the computer 51 calculates the difference between the read data Dc and the reference data registered in the data area of the RAM,
Further, displacement conversion and unit conversion are performed on the difference data to calculate the actual displacement amount. After that, the computer 51 supplies the displacement amount calculated as described above as the displacement data (display data) Dd to the display device 55 connected to the outside.

The display 55 converts the displacement data Dd from the computer 51 into character data (numerical data in this case), and displays the characters on a display surface composed of, for example, a liquid crystal display. The operator can confirm the depth of the hole 61 by reading the number displayed on the display 55.

Next, a case of measuring the displacement (height) of the convex portion 62 formed on the reference surface 2a will be explained. The stage on which the sample 2 is placed is moved to perform the reference adjustment process. Immediately below the finished sensor unit 1, the convex portion 62 to be measured is positioned. At this time, the laser light L emitted from the laser diode 13 is applied to the convex portion 62, and the light (reflected light) L reflected by the upper surface 62a of the convex portion 62 is incident on the optical system 12 along the forward optical path. To do. The reflected light L incident on the optical system 12 passes through the mirror 14 with knife edge and the mirror 17, and the photodetector 1
It is incident on 8.

With the incidence of the reflected light L, the photodetectors (first and second photodiodes PA and PB) output detection signals Sa and Sb, respectively, and the computer 51 outputs detection data Da and Db. Is entered.
The computer 51 uses the input detection data Da and D
The calculation of b is performed based on the calculation formula shown in the above mathematical expression 1. In this case, since the upper surface 62a of the convex portion 62 is located above the reference surface 2a, a value in the-direction (D <
0).

The computer 51 supplies a negative drive signal -Sd to the motor drive circuit 54 to rotate the motor 32 in the reverse direction, as in the case of the reference adjusting process. With the reverse rotation of the motor 32, the sensor unit 1 itself moves upward, that is, in the direction away from the convex portion 62. This movement is performed until D = 0.

Then, when the upper surface 62a of the convex portion 62 coincides with the point J · F, the computer 51 causes the I / O circuit 53
A read signal Sr is output to open the gate of the I / O circuit 53 to read the movement amount data Dc currently input to the I / O circuit 53. After that, the computer 51 calculates the difference between the read data Dc and the reference data registered in the data area of the RAM, and further performs displacement conversion and unit conversion on the difference data to obtain the actual displacement. Figure out the amount. After that, the computer 51 supplies the displacement amount calculated as described above as the displacement data Dd to the display device 55 connected to the outside. The operator can check the height of the convex portion 62 by reading the number displayed on the display 55.

In the above example, the case where the depth of the hole 61 and the height of the convex portion 62 are measured has been described. However, in addition, the unevenness formed on the surface of the sample and the step of the wiring pattern are measured by the same method as described above. Can be measured at. The surface to be measured may be appropriately plotted and measured like the hole 61 or the convex portion 62, but the surface to be measured may be scanned by the sensor unit 1 (or the stage). By continuously moving detection data Da and Db and simultaneously reading the movement amount data Dc from the I / O circuit 53 in real time to measure the surface state (roughness, etc.) of the surface to be measured. You can also do it.

In this case, by supplying the clock signal synchronized with the scanning timing to the display 55, the change of the displacement data Dd sequentially sent from the computer 51 is image-processed along the time axis of the clock signal, You may make it display the change of the displacement data Dd as a line image. When displayed as a line image, the surface condition of the surface to be measured can be confirmed at a glance.

As described above, according to the displacement meter of this embodiment, the light L reflected by the surface to be measured (the bottom 61a of the hole 61, the upper surface 62a of the protrusion 62, etc.) follows the forward optical path. Therefore, even if the surface to be measured is very narrow, such as the bottom of a concave or concave surface, the bottom of a hole, or the bottom of a wiring pattern, the displacement can be reliably measured optically. be able to.

Further, the displacement of a sample having a relatively small reflectance (the surface of water, glass, etc.) can be measured with high accuracy, and by exchanging the objective lens 16,
The resolution of the measurement position and the resolution of the displacement data can be appropriately selected.

In the above embodiment, the knife edge method is used as the optical system 12, but in addition, the difference (Sa-Sb) between the detection signals Sa and Sb is the difference between the surface 2a of the object 2 to be measured and the JF point. A method such as an astigmatism method may be used as long as it has a characteristic of drawing an S-shaped waveform with respect to the shift amount.

[0054]

As described above, according to the displacement amount measuring method of the present invention, in the displacement amount measuring method for optically measuring the displacement amount of the surface to be measured with respect to the reference plane, the light from the light source is used. Is converged through an objective lens to irradiate the object surface to be measured, and an automatic focusing mechanism for performing focusing based on the light reflected from the object surface to be measured along the forward optical path The objective lens is moved in the contact direction with respect to the surface to be measured so that the distance to the surface to be measured is constant, and the amount of movement is the amount of displacement of the surface to be measured with respect to the reference surface. I decided to do so,
Even if the surface to be measured is extremely narrow, such as the bottom of a concave portion of a surface having irregularities, the bottom of a hole, or the bottom of a wiring pattern, the displacement can be reliably measured optically.

According to another aspect of the present invention, in the displacement meter for optically measuring the displacement amount of the surface to be measured with respect to the reference surface, the light source and the light from the light source are converged to measure the above-mentioned measured object. An optical system having an objective lens for irradiating a target surface, and capable of moving in a contact direction with respect to the measured target surface, and by light emission from the light source of the optical system,
Based on the reflected light reflected along the forward optical path on the measured surface, the optical system with respect to the measured surface so that the distance between the objective lens and the measured surface is constant. Since the automatic focusing mechanism for moving in the contact and separation direction and the movement amount detecting means for detecting the movement amount of the optical system are provided, especially the bottom of the concave portion of the uneven surface, the bottom of the hole,
Also, even when the surface to be measured is very narrow, such as the bottom of the wiring pattern, the displacement can be reliably measured optically.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment (hereinafter simply referred to as a displacement meter according to an embodiment) in which a displacement amount measuring method according to the present invention is embodied as a displacement meter.

FIG. 2 is an explanatory diagram showing an operating principle of an optical system (knife edge method) used in the displacement meter according to the present embodiment, that is, an image formation state of reflected light. The image forming state when the optical system is closer to the objective lens side than the just focus point (hereinafter, simply referred to as JF point) is shown, and FIG. 9B shows that the surface of the measured object coincides with the JF point. FIG. 6C shows the image formation state when the surface of the object to be measured is away from the JF point.

FIG. 3 is a characteristic diagram showing the output characteristics of the first and second photodiodes constituting the photodetector, and FIG. 3A shows the first and second output characteristics with respect to the amount of deviation between the surface of the DUT and the point J · F. The output waveform distribution of the second photodiode is shown in FIG.
And the waveform distribution when the difference between the outputs of the second photodiode is taken, and FIG. C shows the waveform distribution when the sum of the outputs of the first and second photodiodes is taken.

FIG. 4 is a configuration diagram showing a principle of displacement measurement according to a conventional example.

FIG. 5 is an explanatory diagram showing disadvantages of displacement measurement according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sensor unit 2 Object to be measured 2a Surface (reference surface) 3 Movement drive mechanism 4 Movement amount detector 5 Control system 12 Optical system 13 Laser diode 14 Mirror with knife edge 15 Lens 16 Objective lens 17 Mirror 18 Photodetector 21 Rack 22 Tongue 32 Motor 33 Drive gear 41 Contact 51 Computer 52 A / D converter 53 Digital input / output circuit 54 Motor drive circuit 55 Display PA First photodiode PB Second photodiode

Claims (2)

[Claims] 1. A displacement amount measuring method for optically measuring a displacement amount of a measurement target surface with respect to a reference surface, wherein light from a light source is converged through an objective lens to irradiate the measurement target surface. By the automatic focusing mechanism for focusing on the light reflected from the surface to be measured along the forward optical path, the objective lens is adjusted so that the distance between the objective lens and the surface to be measured becomes constant. Is moved toward and away from the surface to be measured, and the amount of movement is used as the amount of displacement of the surface to be measured with respect to the reference plane. 2. A displacement meter for optically measuring a displacement amount of a surface to be measured with respect to a reference surface, comprising a light source and an objective lens for converging light from the light source and irradiating the surface to be measured. Further, the optical system that is movable in the direction of contact with and away from the surface to be measured and the light emitted from the light source of the optical system are reflected on the surface to be measured along the forward optical path. An automatic focusing mechanism that moves the optical system in the contact and separation directions with respect to the surface to be measured so that the distance between the objective lens and the surface to be measured becomes constant based on the reflected light; A displacement amount detecting means for detecting the amount of movement of the displacement meter.