JPH0875433A - Surface form measuring device - Google Patents

Abstract

PURPOSE: To provide a compact surface form measuring device capable of measuring a surface form accurately and sensitively. CONSTITUTION: A laser beam of which oscillating frequency and luminous intensity are modulated at a specified frequency is introduced into a detector main body 11 through an optical fiber 16, and divided into two directions by a beam splitter 36. One is applied to a reference mirror 37, and the other is collected by an objective lens 45 supported on a variable mechanism and applied as an optical probe to a surface to be measured. The beam reflected from the surface to be measured returns through an optical path, and a part of it bent at a beam splitter 41 and received by a photo diode 48 to become the deviated focal signal of the objective lens 45. Also a variable mechanism control circuit 15 controls the position of the objective lens 45 so as to secure the state of a focusing point on the surfaces to be measured. Then, objective beam moved straightforward through a beam splitter 41 is superposed on the reference beam in the beam splitter 36. Thus, an interference signal of heterodyne interference produced between the both is photoelectrically transduced by a photo diode 38 so as to measure the surface form of an object to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact type surface profile measuring apparatus for irradiating an object to be measured with a laser beam to measure the surface profile and surface roughness.

[0002]

2. Description of the Related Art There are two types of conventional optical roughness gauge pickups, one of which is called an astigmatism method or a critical angle method, which collects a light beam and irradiates an object to be measured at a focal position. The amount of deviation of the focus position caused by the unevenness of the measurement surface is detected. The other one is called the focus servo system, and when focusing the light beam and irradiating it to the object to be measured, the objective lens is adjusted according to the unevenness of the measurement surface so that the focus of the light beam irradiates the measurement surface. Is moved up and down, and a control signal for moving up and down or an output signal of a differential transformer synchronized with this objective lens is used as a detection signal.

[0003]

The optical pickup based on the astigmatism method or the critical angle method described above has the advantage that high sensitivity and high speed measurement can be performed, but on the other hand, the linear range of the detection element is narrow and the measurement range is small. There is a drawback that it is limited to about ± 1 μm. On the other hand, the focus servo type pickup can measure a wide range of about ± 400 μm, but it is not suitable for high-speed and high-resolution measurement because it drives the objective lens according to the unevenness of the measurement surface. There are drawbacks.

The present invention has been made in view of the above circumstances, and has the feature of having both of the above in combination, with high accuracy,
It is an object of the present invention to provide a surface profile measuring device capable of high sensitivity and wide range measurement.

[0005]

In order to achieve the above object, the present invention provides a laser light source section for generating a frequency-modulated laser beam, and an objective lens for irradiating a part of the laser beam onto an object to be measured. System, a lens driving mechanism for moving the objective lens system far and near with respect to a surface to be measured, a laser beam introduced from the laser light source unit is split, and one of the split laser beams is transmitted through the objective lens system. A Michelson-type interference optical system for irradiating the measurement surface to obtain reflected light, irradiating the other laser beam to the reference reflecting mirror to obtain reflected light, and causing both reflected light to interfere, and the objective lens system A part of the reflected light from the surface to be measured is taken in to detect the defocus of the objective lens system on the surface to be measured, and the objective on the surface to be measured based on the defocus detected by the detecting means. Les Lens drive control circuit that drives and controls the lens drive mechanism so that the focal point of the lens system is in focus, and receives interference light due to heterodyne interference that occurs in the Michelson type interference optical system, and converts the received optical interference signal into an electrical signal. It is characterized by comprising a photoelectric conversion unit and a control unit for calculating the displacement amount of the shape of the object to be measured based on the detection signal of the photoelectric conversion unit and controlling the frequency modulation of the laser light source.

[0006]

According to the present invention, a part of the frequency-modulated laser beam is condensed by the objective lens system as an optical probe and is irradiated to the object to be measured at the focal point position. When the focal point is deviated due to the unevenness of the surface to be measured, the objective lens system is vertically controlled according to the unevenness, so that the laser beam is always applied to the object to be measured in a focused state. Even if the objective lens system is moved, there is no change in the optical path length to the object to be measured and it does not directly affect the measured value, so that it is possible to measure a wide range in the uneven direction.

Since the amount of displacement is detected by utilizing the Doppler frequency shift of the heterodyne interference in the optical interferometer which guides a part of the reflected light on the surface to be measured of the laser beam, the influence of electrical noise is exerted. In addition to being difficult to receive, the detection light is electrically converted and processed, so that sensitivity calibration is not required, and high precision and high sensitivity measurement can be performed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the surface profile measuring apparatus according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows an embodiment of a surface profile measuring apparatus according to the present invention. This surface profile measuring apparatus comprises a laser light source section 10 for generating a laser beam, a roughness detector main body section 11, and a laser light source. And a control unit 14 for calculating the surface shape displacement of the object to be measured W based on the signal from the detector, and the laser light source unit 10 and the detector body 11 are detachably attached to both ends of the optical connector 16A, Connected by an optical fiber 16 with 16B. The optical fiber 16 is composed of a single mode fiber.

The detector body 11 and the control unit 14 are connected by an electric cable 20, and a detection signal from the detector is sent to the control unit 14. On the other hand, the laser light source unit 10 includes the control unit 1
4 and the electric cable 21 are connected. As shown in FIG. 1, the laser light source unit 10 in this embodiment includes a laser diode 24, a Peltier element 25, a collimator lens 26, an optical isolator 27, and an objective lens 28.

The laser diode 24 of the light emission source is provided with a Peltier element (heating and / or cooling element) 25 and a temperature sensor (not shown), and is controlled by a temperature controller of the control unit 14 described later so as to maintain a constant temperature. To be done. On the other hand, the laser diode 24 receives a frequency modulation current from the control unit 14 described later via the electric cable 21, and emits the frequency-modulated laser light.

The modulated laser light is collimated by a collimator lens 26, passes through an optical isolator 27 that prevents reflected light, and is condensed by an objective lens 28.
It is incident on the optical fiber 16. The modulated laser light is
It is guided to the detector main body 11 via this optical fiber 16. Next, the configuration of the detector body will be described. An opening 13 is formed on the lower surface of the main body case 12, and a part of the laser light is applied to the object to be measured W through the opening as a light probe as described later.

The laser light guided to the detector main body 11 is collimated by a collimator lens 35, and its optical axis L
The beam splitter 36 above ₁ splits the beam into two different directions. That is, one laser beam is bent to the optical axis L ₂ orthogonal to the optical axis L ₁ and irradiated on the reference mirror 37, and the other laser beam goes straight on the optical axis L ₁ and passes through the beam splitter 41 to change the optical path. It is bent to the optical axis L ₃ by the mirror 42, and through the objective lens 45, the opening 1
The object to be measured W is irradiated from 3.

Light reflected by the reference mirror 37 (reference light)
Returns to the beam splitter 36 and is superimposed on the object light described later, and the reference mirror 37 is sandwiched by the beam splitter 36.
The light is received by the photodiode 38 arranged so as to confront it. On the other hand, the light reflected by the object to be measured W (object light) is
The incident optical path is returned in the opposite direction, and the beam is split by the beam splitter 41 into two different directions. One of them is moved straight along the optical axis L ₁ and the optical path is bent by the beam splitter 36, is superimposed on the reference light, and is received by the photodiode 38. The distance between the detector body and the surface to be measured is measured based on this interference signal. On the other hand, the beam splitter 41
A part of the object light bent to the optical axis L ₄ by means of the cylindrical lens 46 passes through a four-division photodiode 48.
The light is received by and photoelectrically converted. Based on this signal, the defocus of the objective lens 45 on the measured surface is detected.

The optical path conversion mirror 42 is not essential in the construction of the detector body, and the optical axes L ₁ and L ₃ may be arranged coaxially. The photodiode 38 is a detachable connector 5 attached to the main body case 12 via an electric cable 51.
3 and the electric cable 20 is connected to the connector 53.
It is connected to the detector main body 11 via the connector and is also connected to the control unit 14 via the detachable connector 54.
This is because the detection signal photoelectrically converted by the photodiode 38 is taken out to the outside of the main body case so that it can be easily connected to the control unit 14 described later.

The objective lens 45 is variably supported by a linear motor (not shown) and its drive mechanism, and minimizes the focal shift of the objective lens 45 on the surface to be measured based on the signal from the four-division photodiode 48. ,
The drive is controlled by a control circuit 15 that controls the linear motor. The lens drive control circuit 15 includes the detector body 11
May be incorporated in the control unit 14 or may be incorporated in the control unit 14 described later.

When incorporated in the control unit, the four-division photodiode 48 and the drive mechanism (linear motor) for the objective lens 45 are connected to a detachable connector 53 by an electric cable (not shown), and the control unit 14 is connected via the electric cable 20. Connected with. On the other hand, in addition to the lens drive control circuit 15, the control unit 14 mainly includes a sawtooth wave or triangular wave generator 55, a temperature controller 51, a bandpass filter 57, a waveform shaper 58, 5 as shown in FIG.
9, frequency multiplication circuits 60 and 61, a gate circuit 62, and an up / down counter 63.

The principle of measurement in the surface profile measuring apparatus configured as described above will be described using a sawtooth wave modulation current. FIG. 2 shows a block diagram of the control unit. The sawtooth wave or triangular wave generator 55 outputs a sawtooth wave modulation current Sa (FIG. 3A) having a period T _S (frequency f _s , angular frequency ω _s ) to the laser diode (light source unit) and the waveform shaper 58. To do. The sawtooth wave or triangular wave generator 55 outputs a sawtooth wave modulation current Sa having a modulation width smaller than that of the bias current as shown in FIG.

The laser diode has a sawtooth wave modulation current Sa.
The oscillation frequency and the emission intensity are modulated by. The laser diode is provided with a heating and / or cooling element (Peltier element) 25 and a temperature sensor, and the temperature controller 56 heats and / or cools the temperature detected by the temperature sensor to a constant value. The element (Peltier element) 25 is controlled. This suppresses the wavelength change due to the temperature change of the laser diode and improves the measurement accuracy.

The modulated laser beam output from the laser diode 24 is focused on the tip of the optical fiber 16 via the collimator lens 26, the optical isolator 27, and the objective lens 28, and is guided to the detector body 11 through the optical fiber 16. Get burned. It should be noted that the laser light source unit 10 and the detector body 11 have optical connectors 16A and 1A, both ends of which are detachable.
Since it is optically connected by the optical fiber 16 having 6B, it is easy to attach and detach the connection.

The laser beam incident on the detector body 11 is
The collimator lens 35 collimates the light into parallel beams and splits the beam.
The optical axis L₁Light orthogonal to
Axis L ₂And irradiate the reference mirror 37, etc.
Is the optical axis L₁And go straight through the beam splitter 41,
The optical axis L with the optical path changing mirror 42₃The objective is bent into
The object W to be measured is irradiated via the lens 45.

Laser light reflected from the object to be measured W (object light)
Goes back in the same optical path, and a part thereof is bent by the beam splitter 41 to the optical axis L ₄ . A part of the object light whose optical path is changed to the optical axis L ₄ is a cylindrical lens 46.
Then, the light is received by the four-division photodiode 48 and photoelectrically converted. This signal is sent to the lens drive control circuit 15 via an electric cable (not shown) and serves as a signal for calculating the focus shift of the objective lens 45 on the surface to be measured.

On the other hand, the object light traveling straight through the beam splitter 41 has its optical path bent by the beam splitter 36, is superimposed on the above-mentioned reference light, is received by the photodiode 38, and is photoelectrically converted. This signal is sent to the control unit 14 via the electric cables 51 and 20. The control unit 14 processes the interference signal and calculates the surface shape of the measured object W.

When the shape of the surface of the object to be measured W changes, a deviation occurs between the surface to be measured and the focal position of the objective lens 45. The deviation is a cylindrical lens that guides a part of the reflected light from the surface to be measured. It is reflected in the light collection of 46. The cylindrical lens 46 has the property of collecting light with astigmatism, and its image is detected by the four-division photodiode 48. The light receiving surface of the four-divided photodiode 48 is vertically and horizontally divided into four, and outputs four electric signals corresponding to the light amount of the laser beam incident on each divided surface to the control unit of the lens drive control circuit 15. The lens drive control circuit 15 control unit determines the focus deviation direction from the difference between the levels of the electric signals corresponding to the upper and lower split surfaces and the levels of the electrical signals corresponding to the left and right split surfaces, out of the four input electrical signals. The shift amount is calculated, and a control signal for driving the linear motor is output in a direction that minimizes the shift amount.

The variable mechanism of the objective lens 45 drives the objective lens 45 up and down based on this control signal. As a result, the objective lens 45 is controlled to move up and down by following the concave-convex direction of the surface to be measured, and as a result, the laser beam is always applied to the surface to be measured in a focused state. Even if the objective lens 45 is moved, the optical path length to the object to be measured does not change, and the movement of the lens does not directly affect the surface shape measurement value of the object to be measured, which will be described later.

The laser light radiated to the surface to be measured in the focused state is reflected by the surface to be measured, returns in the reverse path of the incident light, and a part thereof is superposed on the reference light by the beam splitter 36.
There is a time delay between the object light and the reference light corresponding to the distance between the detector body and the surface to be measured, and the frequencies of the two are different.
Therefore, heterodyne interference occurs between the reference light and the object light.

This interference signal is detected by the photodiode 38. The frequency and phase of the signal Se (FIG. 3C) detected by the photodiode 38 are proportional to the optical path distance difference D between the reference mirror and the surface to be measured. The level of the signal Se is affected by the change in the emission intensity due to the frequency modulation of the laser diode 24 and the reflectance of the surface to be measured. According to the present invention, the influence of the change in the emission intensity of the laser diode 24 is removed from the signal detected by the photodiode 38 based on the following principle.

First, the modulation of the oscillation frequency of the laser diode and the modulation of the emission intensity will be described. When a sawtooth wave modulation current Sa (t) having a period T _s and a modulation width Δi as shown in FIG. 3A is input to the laser diode, the oscillation angular frequency ω (t) and the emission intensity I (t of the laser diode are input. ) Is also modulated in a sawtooth shape (see FIGS. 3B and 3C).

Here, one modulation period (-T _s / 2≤t≤T)
_s / 2), the sawtooth wave modulation current Sa (t) is given by the following expression: Sa (t) = i ₀ + Δi · t / T _s = i ₀ + α _i · t (1) ω (t) and emission intensity I (t)
Is the following equation: ω (t) = ω ₀ + Δω · t / T _s = ω ₀ + k _wi · α _i · t (2) I (t) = I ₀ + ΔI · t / T _s = I ₀ + k _Ii・ It can be written as α _i · t (3).

However, the definitions of i ₀ , ω ₀ , Δi, Δω, and ΔI are shown in FIG. Further, α _i = Δi / T _s (current modulation rate) k _wi = Δω / Δi (modulation constant of oscillation angular frequency) k _Ii = ΔI / Δi (modulation constant of emission intensity)

Next, the interference signal detected by the photodiode 38 will be described. Beam splitter 36
The emission intensity of the laser diode 24 reaching
And However, η is a constant determined by the coupling rate of the laser light to the optical fiber 16. If the intensity of the reflected light (reference light) of the reference mirror 37 is I _r (t) and the reflected light (object light) of the surface to be measured is I ₀ (t), then I _r (t), I ₀
(t) is expressed by the following equation: I _r (t) = β _r · ηI (t) (4) I ₀ (t) = β ₀ · ηI (t) (5) However, β _r and β ₀ are reflection coefficients.

The reference light and the object light undergo heterodyne interference, and the interference signal Se detected by the photodiode 38 is detected.
(t) is given by the following equation. Se (t) = K · ηI (t) × _{[β r + β 0 +2 (β} r β 0) 1/2 cos (ω b t + φ b) ] ... (6) where, K is the photoelectric conversion of the photodiode 38 , Ω _b ,
φ _b is the angular frequency and phase of the beat signal, and is expressed by the following equation, ω _b = 2Δω / T _S τ (7) φ _b = ω ₀ τ (8) In Expressions (7) and (8), τ is the time delay between the reference light and the object light, as shown in FIG.

Since I (t) in equation (6) can be expressed by equation (3), if (k _Ii ·
α _i · t) is smaller than I _0, and the following equation is given: I ₀ >> | k _Ii · α _i · t _max | = k _Ii · α _i · T _s / 2 = k _Ii (Δi / T _s ) If (T _s / 2) = k _Ii · Δi / 2 = ΔI / 2 (9) is satisfied, (k _Ii · α _i · t) can be ignored. Then, in this case, the above equation (6) is expressed by the following equation: Se (t) ≈K · ηI ₀ [β _r + β ₀ +2 (β _r β ₀ ) ^1/2 cos (ω _b t + φ _b )] ... (10) is obtained, and by cutting the DC component (β _r + β ₀ ), the following equation (11) can be obtained.

[0033] Se (t) = A · cos (ω b t + φ b) ... (11) However, in order to satisfy the above expression (9) may be as follows. (1) Increase I ₀ . (2) Reduce Δi. (3) _Reduce k _Ii .

The above (1) and (2) increase the bias current i ₀ in the modulation current Sa (t) shown in the equation (1),
This means reducing the modulation width Δi. Also, k _{Ii in} (3) cannot be changed freely due to the inherent characteristics of the laser diode, but k _Ii is small and
Select a laser diode with a large _wi and use it.

In the present embodiment, as described above, the sawtooth wave or triangle wave generator 55 has the sawtooth wave modulation current S whose modulation width is smaller than that of the bias current as shown in FIG. 3 (A).
As a result, the interference signal Se detected by the photodiode 38 is so small that the change in the emission intensity due to the frequency modulation of the laser diode 24 is negligible as shown in FIG. 3 (C).

Now, referring to FIG. 2, the photodiode 38
The interference signal Se detected by is output to the bandpass filter 57. The bandpass filter 57 has a center frequency f _s and a bandwidth Δν (for example, f _s / 10), extracts the component of f _s from the input signal Se, and shapes the extracted signal Sf (FIG. 3D). Output to the container 59.
The waveform shaper 59 converts the input signal Sf into a rectangular wave signal Sg (FIG. 3 (E)), and the frequency multiplication circuit 61 outputs this signal Sg.
The frequency g is a preset magnification m (m = 2 in FIG. 3)
So that the signal becomes a pulse signal.
Sg ′ is output to the input G ₁ of the gate circuit 62 (see FIG. 3).
(See (G) and (H)).

On the other hand, the waveform shaper 58 converts the sawtooth wave modulation current Sa inputted from the sawtooth wave or triangle wave generator 55 into a rectangular wave signal Sb (FIG. 3 (B)), and the frequency multiplication circuit 60 uses this. The frequency of the signal Sb is multiplied by the frequency multiplication circuit 61.
Multiplied by the same multiplication factor, and the multiplied signal (pulse signal)
Sb ′ is output to the input G ₂ of the gate circuit 62 (see FIG. 3).
(See (F)).

The gate circuit 62, the input G ₁ 'and enter G ₂ of the pulse signal Sb' pulse signal Sg create a new pulse signal by the frequency difference, and outputs the up input U or down input D of the up-down counter 63 . Therefore, the up / down counter 63 integrates the frequency difference between the pulse signal Sb ′ and the pulse signal Sg ′. By the way, when the DUT is stopped, the frequency of the pulse signal Sg ′ output from the frequency multiplication circuit 61 is the reference pulse signal Sb ′ output from the frequency multiplication circuit 60.
, And the count value of the up / down counter 60 does not change, but when the DUT moves, the signal Sg output from the waveform shaper 59 due to the Doppler frequency shift (the pulse output from the frequency multiplication circuit 61) Signal S
The frequency of g ') changes.

That is, when the object to be measured moves away, the frequency of the pulse signal Sg 'increases (see FIG. 3).
(Refer to (G)), when the measured object moves in the direction of,
The frequency of the pulse signal Sg 'becomes smaller (see FIG. 3 (H)). Therefore, the difference between the pulse numbers of the pulse signal Sb ′ and the pulse signal Sg ′ corresponds to the moving speed and moving direction of the measured object, and the integrated value of the difference between the pulse numbers corresponds to the moving amount of the measured object. Thus, the moving distance of the measured object can be measured based on the amount of increase or decrease in the count value of the up / down counter 63 when the measured object is moved from a certain position to another position.

The modulation current waveform is not limited to the sawtooth wave, but a triangular wave may be used. When a triangular wave is used, the doubled sensitivity can be obtained by inverting the phase of the folded portion and adding it to the first half portion. The application example of FIG. 6 uses a contact-type detector body 71 instead of the detector body 11 of the embodiment of FIG. 1, and the same or similar members in the embodiment of FIG. Numbered,
The description is omitted.

The detector main body shown in FIG.
An opening 73 is formed on the lower surface of 2, and a probe 75 that is vertically movable via a leaf spring 74 is arranged in the opening 73. A reflecting mirror 76 is fixed on the line of motion of the probe. The reflecting mirror formed on the probe may be a separate mirror fixed as described above, or may be directly mirror-finished on the probe to form a mirror.

The laser light guided to the detector main body 71 is collimated by the collimator lens 35, and its optical axis L
The beam splitter 36 above ₁ splits the beam into two different directions. Then, one of the laser beams is bent by the optical path changing mirror 42 to the optical axis L ₅ , is irradiated on the reflecting mirror 76, and the other laser beam is arranged on the optical axis L ₂ which is orthogonal to the optical axis L _1. The optical system is arranged so that the laser beam is irradiated on. Further, the photodiode 38 is arranged on the optical axis L ₂ so as to face the reference mirror 37 with the beam splitter 36 interposed therebetween.

The optical path changing mirror 42 is not essential in the construction of the detector body, and the optical axis L ₁ and the optical axis L ₅ may be arranged coaxially. The probe 75 in contact with the surface of the object to be measured W
However, the reflecting mirror 76 that is movable in the uneven direction of the object to be measured and is provided on the line of motion of the probe 75 reflects the motion of the probe without error. Between the laser beam (object light) reflected by the reflecting mirror 76 and the laser beam (reference light) reflected by the reference mirror 37, the reflecting mirror 7
There is a time delay corresponding to the movement distance of 6, and the frequencies of both are different. Therefore, heterodyne interference occurs between the object light and the reference light. The light is received by the photodiode 38,
The process of measuring the surface shape of the object to be measured in the control unit 14 based on this photoelectrically converted interference signal is the same as in the embodiment of FIG.

If the above-mentioned detector main body 71 is used, it can be mounted compatible with the non-contact type detector main body 11 of the embodiment of FIG. 1, and the same control unit (including the light source unit) is used. Both non-contact and contact type detectors can be selectively used. It is also possible to use an optical fiber composed of a single mode fiber instead of the electric cable 20 of the embodiment of FIG. 1, and in this case, the light receiving part of the detector main body is for optical path conversion instead of the photodiode 38 of FIG. It is composed of a reflecting mirror and an objective lens, a photoelectric conversion element is provided in the control section instead of the photodiode 38, and the detector main body and the control section are connected by an optical fiber which is detachable by an optical connector.

In the surface profile measuring apparatus configured as described above, the laser light reflected by the reference mirror 37 (reference light) and the laser light reflected by the surface to be measured (object light) are beam splitter 36. Are superposed by each other, and heterodyne interference occurs in both. The above process is similar to that described in the embodiment of FIG. The detection light due to this interference has its optical path bent by the reflection mirror for optical path conversion having the above-described configuration, is condensed by the condensing lens, and enters the end face of the optical fiber composed of the single mode fiber. Incidentally, the optical path changing reflecting mirror is not essential in the configuration.

The detection light sent to the control unit via the optical fiber is photoelectrically converted and processed by the control unit. The principle of measurement in the controller is similar to that of the embodiment shown in FIGS. In the embodiment of FIG. 1, the detection light is converted into an electric signal in the detector body and sent to the control unit via the electric cable, but in the above-mentioned embodiment, the detection light is controlled via the optical fiber. Since it is sent to the control section and photoelectrically converted in the control section, it is more resistant to electrical noise than the embodiment of FIG. 1, and there is no problem of frequency response delay due to the electric cable, which is advantageous in high-speed response. Is.

In the embodiment shown in FIG. 1 and the application shown in FIG. 6, the laser light source section and the control section have been described as being independent of each other. However, as shown by the imaginary lines in FIGS. It may be integrated with the control unit. Further, as a scanning method at the time of measurement, the detector body 11 may be fixed and the object to be measured W may be moved, or conversely, the object to be measured W may be scanned.
Alternatively, the detector main body may be fixed and the main body of the detector may be moved for scanning.

In the embodiment according to the present invention, since the polarization of the laser beam is not used, unlike the interferometer using the polarization, the polarizing element, the polarization beam splitter, etc. are not required, and the optical system is simplified. There is. Further, the detector body and the light source unit and the control unit can be easily attached to and detached from each other, and the entire apparatus can be made compact with a simple optical system.

[0049]

As described above, according to the surface profile measuring apparatus of the present invention, the laser beam as the optical stylus is always irradiated on the surface to be measured in a focused state and a part of the reflected light is introduced. The surface shape of the object to be measured is optically measured by the optical interferometer. Therefore, in spite of being a non-contact type, it is possible to perform a wide range measurement in the direction of surface irregularities, and it is also possible to perform a highly sensitive and highly accurate measurement.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the overall configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing an embodiment of a control unit in the shape measuring apparatus according to the present invention shown in FIG.

3 (A) to 3 (H) are signal waveform diagrams output from the respective units of FIG. 3 when a sawtooth wave modulation current is used.

4A to 4C are waveform diagrams showing a modulation current of a sawtooth wave input to a laser diode, an oscillation angular frequency of the laser diode and an emission intensity generated by the modulation current, respectively.

FIG. 5 is a waveform diagram showing changes in oscillation angular frequency and emission intensity of object light and reference light when a sawtooth wave modulation current is used.

FIG. 6 is a schematic view of a main part showing an application example of the present invention.

[Explanation of symbols]

 10 ... Laser light source 11 ... Detector main body 12 ... Main body case 14 ... Control part 15 ... Lens variable mechanism control circuit 16 ... Optical fiber 20 ... Electric cable 36, 41 ... Beam splitter 37 ... Reference mirror 38 ... Photodiode 45 ... Objective lens 46 ... Cylindrical lens 48 ... Quadrant photodiode 53, 54 ... Connector

Claims (1)

[Claims] 1. A laser light source section for generating a frequency-modulated laser beam, an objective lens system for irradiating a part of the laser beam onto an object to be measured, and the objective lens system to a distance from a surface to be measured. A lens driving mechanism for moving, dividing the laser beam introduced from the laser light source unit,
One of the divided laser beams is applied to the surface to be measured through the objective lens system to obtain reflected light, and the other laser beam is applied to the reference reflecting mirror to obtain reflected light. A Michelson type interference optical system for causing interference, a detection means for capturing a part of the reflected light from the surface to be measured through the objective lens system, and detecting a defocus of the objective lens system on the surface to be measured; A lens drive control circuit that drives and controls a lens drive mechanism so that the objective lens system is focused on the surface to be measured based on the defocus detected by the means; and interference light due to heterodyne interference generated in the Michelson type interference optical system. And a photoelectric conversion unit that converts the received optical interference signal into an electric signal, and calculates the displacement of the shape of the DUT based on the detection signal of the photoelectric conversion unit, and the laser A surface shape measuring apparatus comprising: a control unit that controls frequency modulation of a light source.