JP2008268121A - Optical interference type measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical interference type measuring device capable of measuring the height difference between two points, in a non-contact manner. <P>SOLUTION: This device is provided with a light source 114 for emitting an irradiation light; a first half mirror 41 for splitting the irradiation light to first reference light and first inspection light; a first optical element 31 for forming a first interference fringe, by making the first reference light and the first inspection light irradiate on a first measurement point 91 and advancing to a first measurement light optical length interfere with each other; a second half mirror 42 for dividing the irradiation light to second reference light and second inspection light; a second optical element 32 forming a second interference fringe, by making the second reference light and the second inspection light irradiated to a second measurement point 92 and advancing to a second measurement optical path length interfere with each other, an interference fringe detecting element 153 for detecting combined interference fringe of the first interference fringe and the second interference fringe; an extraction module 310 for extracting an interference fringe component varying, according to the optical path difference between the first measurement optical path length and the second measurement optical path length from the combined interference fringe; and a calculation module 330 for calculating the height difference between the first measurement point 91 and the second measurement point 92 from the interference fringe component. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to measurement technology, and more particularly to an optical interference measurement device.

When manufacturing a semiconductor device, it is desired to accurately measure the height of a step formed by etching on a silicon substrate, the thickness of a metal wiring formed on the silicon substrate, and the like. Conventionally, when measuring the height of a step, a stylus type step gauge has been used. However, if the stylus of the stylus profilometer touches the silicon substrate, the silicon substrate may be scratched or soiled. Also, if a foreign object adheres to the tip of the stylus, the step height cannot be measured accurately. An apparatus that can measure the height of the step is a scanning atomic force microscope (AFM) (see, for example, Patent Document 1). However, although AFM can measure at the nanometer level, it is difficult to measure the height of a step of submicron or more. In addition, since the scanning range of AFM is narrow, the height difference between two distant points cannot be measured accurately.
JP 2004-12466 A

  An object of the present invention is to provide an optical interference measuring device capable of measuring a height difference between two points without contact.

  The features of the present invention are (a) a light source that emits irradiation light, (b) a first semi-transparent mirror that divides the irradiation light into first reference light and first inspection light, and (c) first reference light and first A first optical element that interferes with the first inspection light that has been irradiated to the measurement point and has traveled the first measurement optical path length to form a first interference fringe; and (d) the irradiation light is a second reference light and a second inspection. The second semi-transparent mirror that divides the light, and (e) the second reference light and the second inspection light that has been irradiated to the second measurement point and traveled the second measurement optical path length interfere with each other to form a second interference fringe. A second optical element; (f) an interference fringe detecting element for detecting a synthetic interference fringe of the first interference fringe and the second interference fringe; and (g) a first measurement optical path length and a second measurement optical path length from the synthetic interference fringe. An extraction module that extracts an interference fringe component that fluctuates according to the optical path difference between the first measurement point and a calculation module that calculates a height difference between the first measurement point and the second measurement point from the interference fringe component. Interferometric measuring device And summary that is.

  According to the present invention, it is possible to provide an optical interference measurement device capable of measuring a height difference between two points without contact.

  Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic. Therefore, specific dimensions and the like should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(First embodiment)
As shown in FIG. 1, the optical interference measurement apparatus according to the first embodiment includes a light source 114 that emits irradiation light, a first semi-transparent mirror 41 that divides the irradiation light into first reference light and first inspection light, First optical element 31 for irradiating the first reference light and the first inspection light that has been irradiated to the first measurement point 91 of the object to be measured 190 and traveled the first measurement optical path length to form a first interference fringe, irradiation Second semi-transparent mirror 42 that divides the light into second reference light and second inspection light, second inspection light that is irradiated to the second reference light and the second measurement point 92 of the measurement object 190 and advances the second measurement optical path length A second optical element 32 that interferes with light to form a second interference fringe and an interference fringe detection element 153 that detects a combined interference fringe of the first interference fringe and the second interference fringe are provided. The optical interference measurement apparatus further includes a central processing unit (CPU) 300. The CPU 300 includes an extraction module 310 that extracts an interference fringe component that varies according to the optical path difference between the first measurement optical path length and the second measurement optical path length from the combined interference fringe, and a first measurement point 91 based on the interference fringe component. A calculation module 330 that calculates the height difference of the second measurement point 92 is provided. Note that the first measurement surface 291 including the first measurement point 91 and the second measurement surface 292 including the second measurement point 92 are parallel to each other.

As the light source 114, a multi-wavelength light source such as a xenon lamp, a light emitting diode, a super luminescent diode, or a multimode laser diode capable of supporting a continuous spectrum from the ultraviolet region to the infrared region (185 nm to 2,000 nm) can be used. . The irradiation light intensity S ₀ (λ) that is the light intensity of the irradiation light is expressed by, for example, the following formula (1). :
S ₀ (λ) = D × exp {-(λ-λ _CS / Δλ _S ) ² }… (1)
In Equation (1), D represents a constant, λ _CS represents the irradiation light center wavelength of the irradiation light emitted from the light source 114, and Δλ _S represents the emission bandwidth of the light source 114.

A common optical waveguide 29 such as an optical fiber that propagates the irradiation light is connected to the light source 114. The spectroscope 3 is connected to the common optical waveguide 29. As shown in FIG. 2, the spectroscope 3 scans the wavelength λ of the wavelength component through which the irradiation light can be transmitted according to time t. The spectroscope 3 has, for example, a Fabry-Perot resonance structure shown in FIG. In this case, the spectroscope 3 has a casing 14 in which a cavity is provided. An input-side internal housing 13 is inserted into the housing 14 from the outside toward the internal cavity. The input side inner casing 13 connects the common optical waveguide 29 and the ferrule 192. An input-side semi-transparent mirror 125 is disposed on the end face of the ferrule 192. The output-side internal housing 12 is inserted into the housing 14 at a position facing the input-side internal housing 13 from the outside to the inside. The output-side inner housing 12 connects the common optical waveguide 30 and the ferrule 191. An output-side semi-transparent mirror 124 is disposed on the end face of the ferrule 191. When pressure or the like is applied to the casing 14, the casing 14 is bent, and the interval L _O between the input-side semi-transparent mirror 125 and the output-side semi-transparent mirror 124 changes.

A part of the irradiation light propagated toward the spectroscope 3 in the common optical waveguide 29 is reflected by the input-side semi-transparent mirror 125, and the other is transmitted through the input-side semi-transparent mirror 125. Part of the irradiation light that has passed through the input-side semi-transparent mirror 125 is reflected by the surface of the output-side semi-transparent mirror 124, and part of it passes through the output-side semi-transparent mirror 124. The reflected irradiation light travels in the direction of the input-side semi-transparent mirror 125 and is reflected again toward the output-side semi-transparent mirror 124 on the surface of the input-side semi-transparent mirror 125. At this time, when the phase of the wavelength component that travels from the output-side semi-transparent mirror 124 to the input-side semi-transparent mirror 125 and the wavelength component that travels from the input-side semi-transparent mirror 125 to the output-side semi-transparent 124 direction in the irradiation light, The light intensity of the wavelength component is not attenuated. However, if the phase of the wavelength component that travels in the direction from the output-side semi-transparent mirror 124 to the input-side semi-transparent mirror 125 and the wavelength component that travels from the input-side semi-transparent mirror 125 to the output-side semi-transparent mirror 124 in the irradiating light is not aligned, The light intensity of the component is attenuated. Therefore, it is possible to select the wavelength of the irradiation light transmitted through the spectroscope 3 by changing the distance L _O between the input-side semi-transparent mirror 125 and the output-side semi-transparent mirror 124. When the wavelength resolution of the spectrometer 3 is Δλ _R , the frequency resolution Δν of the spectrometer 3 is given by the following equation (2).

Δν = cΔλ _R / λ _CS ² (2)
In equation (2), c represents the speed of light. The coherence length L _C of the irradiation light is given by the following equation (3).
L _C = c / Δν (3)
As shown in FIG. 1, the spectroscope 3 is connected to a common optical waveguide 30 such as an optical fiber that propagates the irradiation light transmitted through the spectroscope 3. The common optical waveguide 30 is connected to a splitter 21 that divides the irradiated light in two directions. For the splitter 21, an optical fiber coupler (optical fiber beam splitter), a half mirror, a thin film waveguide branching device, or the like can be used. A first optical element 31 and a second optical element 32, which are optical waveguides such as optical fibers, are connected to the splitter 21, respectively. The first optical element 31 and the second optical element 32 propagate the irradiation light. Here, the optical path length L _R2 of the second optical element 32 is longer than the optical path length L _R1 of the first optical element 31 by the detour optical path length L _F given by the following equation (4), which is longer than half of the coherence length L _C. .

L _F >> (L _C / 2) ... (4)
The end surface of the first optical element 31 is disposed so as to face the first measurement point 91 of the first measurement surface 291. As shown in FIG. 4, the first optical element 31 has a core 130a made of quartz (SiO ₂ ) or the like and a clad 131a. Due to the refractive index difference between quartz and air, the end surface of the first optical element 31 functions as the first semi-transparent mirror 41. Part of the irradiation light is reflected as the first reference light by the first semi-transparent mirror 41, and the other part of the irradiation light passes through the first semi-transmission mirror 41 as the first inspection light. The first half mirror 41 is arranged at a first measurement distance L _T1 in a direction perpendicular to the first measuring surface 291 shown in FIG. The optical axis of the first inspection light emitted from the first semi-transparent mirror 41 is perpendicular to the first measurement surface 291. The first inspection light is reflected at the first measurement point 91 and returns to the first semi-transparent mirror 41. The first inspection light therefore, between the first half mirror 41 and the first measuring point 91, the first measurement path given by the following equation (6) is a length of two times the first measured distance L _T1 the length F ₁ advance. As shown in the following equations (5) and (6), the first measurement distance L _T1 is set to be shorter than half of the coherence length L _C , and the first measurement optical path length F ₁ is less than the coherence length L _C Is set to be shorter. :
2L _T1 <L _C (5)
F ₁ = 2L _T1 (6)
Part of the first inspection light that has returned to the first semi-transparent mirror 41 passes through the first semi-transparent mirror 41, enters the first optical element 31, and travels toward the splitter 21. In addition, a portion of the first inspection light that has returned to the first semi-transparent mirror 41 is reflected by the first semi-transparent mirror 41 and travels toward the first measurement point 91 again. At this time, the phase of the wavelength component of the first inspection light traveling from the first measurement point 91 to the first semi-transparent mirror 41 and the wavelength component of the first inspection light traveling from the first semi-transmission mirror 41 to the first measurement point 91 Are equal, the light intensity of the wavelength component is not attenuated. However, the phase of the wavelength component of the first inspection light traveling from the first measurement point 91 to the first semi-transmission mirror 41 and the wavelength component of the first inspection light traveling from the first semi-transmission mirror 41 to the first measurement point 91 are If not, the light intensity of the wavelength component is attenuated. Accordingly, in the first inspection light, the light intensity in the wavelength band in which the phases are not uniform is attenuated when the multiple reflection between the first semi-transparent mirror 41 and the first measurement point 91 is performed.

As shown in the above equation (5), the first measurement optical path length F ₁ is shorter than the coherence length L _C. By the optical path difference corresponding to the first measuring optical path length F ₁ Therefore, the first reference light reflected by the first half mirror 41, a first test which is incident on the first optical element 31 again and is reflected by the first measuring point 91 Interferes with light. The first light intensity ratio R _S1 , which is the ratio of the interference intensity of the first reference light and the first inspection light traveling in the first optical element 31 toward the splitter 21 with respect to the light intensity of the irradiation light, is expressed as (7 ). :
R _S1 = {R _1Ra + η _a R _2Ra -2 (η _a R _1Ra R _2Ra ) ^1/2 cos2φ _a } / {1 + η _a R _1Ra R _2Ra -2 (η _a R _1Ra R _2Ra ) ^1/2 cos2φ _a }… (7)
Here, R _1Ra represents the reflectance of the first semi- _transparent mirror 41, and R _2Ra represents the reflectance of the first measurement surface 291. η _a represents the optical loss between the first semi-transparent mirror 41 and the first measurement point 91, and is given by the following equation (8). Φ _a represents _a phase and is given by the following equation (9). In equation (8), q represents the beam diameter of the irradiation light. :
η _a = 1 / {1 + (λ × F ₁ ) / (2πq ² )} ² … (8)
φ _a = πF ₁ / λ (9)
In the following, for simplification, the first light intensity ratio R _S1 is given by the following equation (10), where A is a constant representing the coherence between the first semi-transparent mirror 41 and the first measurement point 91.

R _S1 = 1 + A cos {2π × F ₁ / λ} (10)
The first reference light and the first inspection light are propagated by the first optical element 31 and divided in two directions by the splitter 21. Further, the first reference light and the first inspection light are propagated through the common optical waveguide 33.

The end surface of the second optical element 32 is disposed so as to face the second measurement point 92. The second optical element 32 also has a core and a clad. The end surface of the second optical element 32 functions as the second half mirror 42. Part of the irradiation light is reflected as second reference light by the second semi-transparent mirror 42, and the other part of the irradiation light passes through the second semi-transmission mirror 42 as second inspection light. The second half mirror 42 is disposed at a second measurement distance L _T2 in a direction perpendicular to the second measuring surface 292. In the direction perpendicular to the first measurement surface 291, the height at which the second semi-transparent mirror 42 is arranged is the same as the height at which the first semi-transparent 41 is arranged. The optical axis of the second inspection light emitted from the second semi-transparent mirror 42 is perpendicular to the second measurement surface 292. The second inspection light is reflected at the second measurement point 92 and returns to the second half mirror 42. The second inspection light therefore, between the second half mirror 42 and the second measurement point 92, the length of the double is below (12) the second measuring optical path is given by the equation of the second measuring distance L _T2 the length F ₂ advance. As shown in the following equations (11) and (12), the second measurement distance L _T2 is set to be shorter than half of the coherence length L _C , and the second measurement optical path length F ₂ is calculated from the coherence length L _C Is set to be shorter. :
_{2L T2 <L C ... (11} )
F ₂ = 2L _T2 (12)
By the optical path difference corresponding to the second measuring optical path length F _2, the second reference light reflected by the second half mirror 42, a second inspection light incident on the second optical element 32 again and is reflected by the second measurement point 92 Interfere with. A second light intensity ratio R _S2 , which is a ratio of the interference intensity of the second reference light and the second inspection light traveling in the second optical element 32 toward the splitter 21 with respect to the light intensity of the irradiation light, is expressed by the following (13 ). :
R _S2 = {R _1Rb + η _b R _2Rb -2 (η _b R _1Rb R _2Rb ) ^1/2 _{cos2φ b} } / {1 + η _b R _1Rb R _2Rb -2 (η _b R _1Rb R _2Rb ) ^1/2 cos2φ _b }… (13)
Here, R _1Rb represents the _reflectance of the second semi-transparent mirror 42, and R _2Rb represents the reflectance of the second measurement surface 292. η _b represents the optical loss between the second semi-transparent mirror 42 and the second measurement point 92, and is given by the following equation (14). Φ _b represents a phase and is given by the following equation (15). :
η _b = 1 / {1 + (λ × F ₂ ) / (2πq ² )} ² … (14)
φ _b = πF ₂ / λ (15)
In the following, for simplification, the second light intensity ratio R _S2 is given by the following equation (16), where B is a constant representing the coherence between the second semi-transparent mirror 42 and the second measurement point 92.

R _S2 = 1 + B cos {2π × F ₂ / λ} (16)
The second reference light and the second inspection light are propagated by the second optical element 32 shown in FIG. Further, the second reference light and the second inspection light are propagated through the common optical waveguide 33. Therefore, the common optical waveguide 33 propagates the first reference light, the first inspection light, the second reference light, and the second inspection light. Here, the optical path length L _R2 of the second optical element 32 is longer than the optical path length L _R1 of the first optical element 31 by the detour optical path length L _F given by the equation (4). The optical path of the light reciprocating the first optical element 31 Accordingly, the optical path difference between the optical path of the light reciprocating the second optical element 32 is twice or more bypass optical path length L _F. For this reason, the optical path difference is longer than the coherence length L _C , so that the first reference light and the second reference light do not interfere with each other.

The optical path length L _R1 of the first optical element 31 and the sum of the first measurement optical path length F ₁ , the optical path length L _R2 of the second optical element 32 and the sum of the second measurement optical path length F ₂ and The absolute value of the difference is set to be longer than the coherence length L _C as shown in the following equation (17). Therefore, the first inspection light and the second inspection light do not interfere.

| 2L _R1 + F _1- (2L _R2 + F ₂ ) | ≫ L _C … (17)
The absolute value of the difference between twice the optical path length L _R1 of the first optical element 31 and the sum of the first measurement optical path length F ₁ and twice the optical path length L _R2 of the second optical element 32 is (18 ) Is set to be longer than the coherence length L _C as shown in the equation. Therefore, the first inspection light and the second reference light do not interfere.

_{| 2L R1 + F 1 - 2L} R2 | »L C ... (18)
The absolute value of the difference between twice the optical path length L _R1 of the first optical element 31 and twice the optical path length L _R2 of the second optical element 32 and the sum of the second measurement optical path length F ₂ is (19 ) Is set to be longer than the coherence length L _C as shown in the equation. Therefore, the first reference light and the second inspection light do not interfere.

| 2L _R1- (2L _R2 + F ₂ ) | ≫ L _C … (19)
An interference fringe detection element 153 that receives the first reference light, the first inspection light, the second reference light, and the second inspection light is connected to the common optical waveguide 33. As the interference fringe detecting element 153, a CCD image sensor or the like can be used. Here, the first inspection light intensity S ₁ (λ), which is the light intensity of the first interference light formed by the first reference light and the first inspection light received by the interference fringe detection element 153, is given by the following equation (20). It is done.

S ₁ (λ) = (1/4) × S ₀ (λ) × T _L1 (λ) × R _S1 … (20)
In equation (20), 1/4 relating to the irradiation light intensity S ₀ (λ) indicates a loss of light intensity due to the irradiation light passing through the splitter 21 a total of two times. T _L1 (λ) is the common optical waveguide 29, the common optical waveguide 30, the first optical element 31, and the common optical waveguide through which the irradiation light, the first reference light, and the first inspection light pass until they reach the interference fringe detection element 153. The transmittance of 33 mag is shown.

Further, the second inspection light intensity S ₂ (λ) that is the light intensity of the second interference light formed by the second reference light and the second inspection light received by the interference fringe detection element 153 is given by the following equation (21).

S ₂ (λ) = (1/4) × S ₀ (λ) × T _L2 (λ) × R _S2 … (21)
In Equation (21), T _L2 (λ) is the common optical waveguide 29, the common optical waveguide 30, and the first optical element through which the irradiation light, the second reference light, and the second inspection light reach the interference fringe detection element 153. 31 shows the transmittance of the common optical waveguide 33 and the like. From the equations (20) and (21), the output light intensity S _OUT (λ) that is the light intensity of the combined interference fringe of the first interference fringe and the second interference fringe is given by the following equation (22). FIG. 5 shows an example of the spectrum of the output light intensity S _OUT (λ) when the center wavelength λ _CS is 880 nm, the wavelength resolution Δλ _R is 3.6 nm, the bypass optical path length L _F is 7.2 m, and the coherence length L _C is 200 μm. is there.

S _OUT (λ) = S ₁ (λ) + S ₂ (λ)
= (1/4) × S ₀ (λ) × {T _L1 (λ) × R _S1 + T _L2 (λ) × R _S2 }
= (1/4) × S ₀ (λ) [{T _L1 (λ) + T _L2 (λ)} + T _L1 (λ) × A cos {2π × F ₁ / λ}
+ T _L2 (λ) × B cos {2π × F ₂ / λ}]… (22)
If the variables α and β given by the following equations (23) and (24) are defined, the output light intensity S _OUT (λ) given by the equation (22) is transformed into the following equation (25).

α = T _L1 (λ) × A (23)
β = T _L2 (λ) × B… (24)
S _OUT (λ) = (1/4) × S ₀ (λ) [{T _L1 (λ) + T _L2 (λ)} +
2αcos {(π / λ) (F _1- F ₂ )} cos {(π / λ) (F ₁ + F ₂ )}
+ (β-α) cos {(2π / λ) × F ₂ }]
= (1/4) × S ₀ (λ) [{T _L1 (λ) + T _L2 (λ)} +
2αcos {(π / λ) (F _1- F ₂ )} cos {(π / λ) (F ₁ + F ₂ )}
+ (β-α) cos {(2π / λ) × F ₂ }]… (25)
The second term cos {(π / λ) (F ₁ − F ₂ )} appears as a low frequency component of the spectrum of the output light intensity S _OUT (λ). As shown in FIG. 6, the low-frequency component is expressed by an envelope of the spectrum of the output light intensity S _OUT (λ). Here, the maximum point or minimum point of the low frequency component appears every 2π period. Therefore the n as an integer of 2 or more, the wavelength giving the n-th maximum point and lambda _n, and the wavelength giving the n-1 th maximum point and lambda _n-1, the following (26) is established.

(π / λ _n ) (F _1- F ₂ )-(π / λ _n-1 ) (F _1- F ₂ ) = 2π… (26)
From the equation (26), the interval between the maximum points of the low frequency component of the output light intensity S _OUT (λ) or the peak interval P which is the interval between the minimum points is given by the following equation (27).

P = 1 / λ _n -1 / λ _n-1
= 2 / (F ₁ -F ₂ )… (27)
If the positions of the first semi-transparent mirror 41 and the second semi-transparent mirror 42 are fixed, the first half point depends only on the height difference (L _T1 -L _T2 ) between the first measurement point 91 and the second measurement point 92. Optical path difference between measurement optical path length and second measurement optical path length (F _1- F ₂ ) varies, and as a result, the peak interval P of the low-frequency component of the synthetic interference fringe varies. Note that the fluctuation in the peak interval P of the low frequency component is not affected by the difference between the light intensity of the first inspection light and the light intensity of the second inspection light.

The interference fringe detection element 153 shown in FIG. 1 transmits the output light intensity S _OUT (λ) of the combined interference fringe to the CPU 300. The correction module 306 of the CPU 300 always receives the output light intensity S _OUT (λ) of the combined interference fringes. The correction module 306 corrects the output light intensity S _OUT (λ) of the combined interference fringe by the moving average method. Here, the “moving average method” will be described. When the spectrum of the output light intensity S _OUT (λ) is obtained as shown in FIG. 6, the correction module 306 shown in FIG. 1 performs the low-frequency component cos {(π / λ) (F _1- F ₂ )} is defined as a section having a width of at least one period and less than one period of the spectral distribution of the irradiation light intensity S ₀ (λ). Further, the correction module 306 calculates the average value of the output light intensity S _OUT (λ) in the defined section and plots it at the center of the section. Next, the correction module 306 moves the section in the wavelength direction, calculates the average value of the output light intensity S _OUT (λ) in the moved section, and plots it at the center of the section. Thereafter, the correction module 306 moving average shown in FIG. 7 is a collection of moving the repeated calculation of the average value of the output light intensity S _OUT (λ), the mean value of the calculated output light intensity S _OUT (lambda) of the section Calculate the line.

The spectral distribution of the output light intensity S _OUT (λ) illustrated in FIG. 6 includes the spectral distribution of the irradiated light intensity S ₀ (λ), the low-frequency component cos {(π / λ) (F _1- F ₂ )} spectral distribution, high-frequency component cos {(π / λ) (F ₁ + F ₂ )} included in the second term of equation (25), and third term of equation (25) The spectral distribution of the given reflected light component (β-α) cos {(2π / λ) × F ₂ } is superimposed. Where the low frequency component cos {(π / λ) (F ₁ − F ₂ )} period or more and shorter than the period of the spectral distribution of the irradiation light intensity S ₀ (λ), and calculating the moving average line of the output light intensity S _OUT (λ), the low frequency component cos {(π / λ) (F _1- F ₂ )}, high-frequency component cos {(π / λ) (F ₁ + F ₂ )}, and reflected light component (β-α) cos {(2π / λ) × F ₂ } The spectral distribution is averaged. Therefore, the moving average line shown in FIG. 7 reflects only the spectral distribution of the irradiation light intensity S ₀ (λ).

As shown in the following equation (28), the correction module 306 shown in FIG. 1 divides the output light intensity S _OUT (λ) by the irradiation light intensity S ₀ (λ) approximated by the moving average line to obtain the output light intensity. The spectrum distribution of the irradiation light intensity S ₀ (λ) is removed from the spectrum distribution of S _OUT (λ), and the spectrum distribution of the corrected output light intensity S _{OUT_C} (λ) shown in FIG. 8 is calculated.

S _{OUT_C} (λ) = S _OUT (λ) / S ₀ (λ)
= (1/4) [{T _L1 (λ) + T _L2 (λ)} +
2αcos {(π / λ) (F _1- F ₂ )} cos {(π / λ) (F ₁ + F ₂ )}
+ (β-α) cos {(2π / λ) × F ₂ }]… (28)
Here, the relationship among the light frequency ν, the light velocity c, and the wavelength λ is given by the following equation (29).

ν = c / λ (29)
The conversion module 307 shown in FIG. 1 uses the expression (29) to convert the expression (28), which is a function of the wavelength λ, into a function of the frequency ν shown in FIG. The corrected output light intensity S _{OUT — C} (ν) expressed as a function of the frequency ν is given by the following equation (30).

S _{OUT_C} (ν) = (1/4) [{T _L1 (c / ν) + T _L2 (c / ν)} +
2αcos {(πν / c) (F _1- F ₂ )} cos {(πν / c) (F ₁ + F ₂ )}
+ (β-α) cos {(2πν / c) × F ₂ }]… (30)
When the frequency that gives the nth local maximum point of the low frequency component of the output light intensity S _{OUT_C} (ν) given by equation (30) is ν _n and the wavelength that gives the n-1st local point is ν _n-1. The following equation (31) is established.

(πν _n / c) (F _1- F ₂ )-(πν _n-1 / c) (F _1- F ₂ ) = 2π… (31)
From the equation (31), the peak interval P of the low frequency component of the output light intensity S _{OUT — C} (ν) is given by the following equation (32).

P = (ν _n -ν _n-1 ) / c
= 2 / (F ₁ -F ₂ )… (32)
Therefore, the peak interval P of the low frequency component of the output light intensity S _{OUT — C} (ν) also varies depending on only the height difference (L _T1 − L _T2 ) between the first measurement point 91 and the second measurement point 92. For example, FIG. 10 shows the output light intensity S _{OUT_C} (ν) when the height difference (L _T1 -L _T2 ) between the first measurement point 91 and the second measurement point 92 is 0 μm, 4.56 μm, 7.89 μm, 11.04 μm. Is the spectrum. As the height difference (L _T1 −L _T2 ) decreases, the peak interval P of the low frequency component of the combined interference fringes increases. The extraction module 310 shown in FIG. 1 extracts the peak interval P of the low frequency component from the output light intensity S _{OUT — C} (ν). The calculation module 330 uses, for example, the relationship between the height difference (L _T1 -L _T2 ) of two measurement points acquired in advance shown in FIG. 11 and the peak interval P of the low frequency component to extract the frequency shown in FIG. A difference in height between the first measurement point 91 and the second measurement point 92 (L _T1 −L _T2 ) is calculated from the peak interval P of the low frequency component extracted by the module 310.

A data storage device 200 is connected to the CPU 300. The data storage device 200 includes an interference fringe component storage module 201, a relation storage module 202, and a result storage module 203. The interference fringe component storage module 201 stores the peak interval P of the low frequency component of the combined interference fringe extracted by the extraction module 310. The relationship storage module 202 stores the relationship between the height difference (L _T1 −L _T2 ) between two measurement points acquired in advance and the peak interval P of the low frequency component. The result storage module 203 stores the height difference (L _T1 −L _T2 ) between the first measurement point 91 and the second measurement point 92 calculated by the calculation module 330.

  In the optical interference measurement apparatus described above, each of the common optical waveguides 29, 30, 33, the first optical element 31, and the second optical element 32 includes a single mode optical fiber, a graded index optical fiber, and a step index. Type optical fiber or the like can be used. As shown in FIG. 12, a lens 45 may be disposed between the first semi-transparent mirror 41 and the first measurement point 91, and a lens 46 may be disposed between the second semi-transparent mirror 42 and the second measurement point 92. . The lenses 45 and 46 may be a condensing lens that collects light or a collimating lens that converts light into parallel light. The surfaces of the lenses 45 and 46 may be anti-reflection coated.

  Next, the optical interference measurement method according to the first embodiment will be described with reference to FIG.

(a) In step S101, the light source 114 shown in FIG. 1 emits irradiation light having a spectrum of irradiation light intensity S ₀ (λ) given by equation (1). The irradiation light is propagated to the spectroscope 3 through the common optical waveguide 29. In step S102, the spectrometer 3 selectively transmits the wavelength component of the irradiation light according to the time t as shown in FIG. The irradiation light transmitted through the spectroscope 3 shown in FIG. 1 is propagated to the splitter 21 through the common optical waveguide 30. In step S103, the irradiation light is split by the splitter 21 in two directions, ie, the first optical element 31 and the second optical element 32. Irradiation light divided toward the first optical element 31 by the splitter 21 is propagated to the first semi-transparent mirror 41 by the first optical element 31. Irradiation light split toward the second optical element 32 by the splitter 21, propagated in the optical path length L bypass optical path length than _R1 L _F only long second optical element 32 of the first optical element 31 to the second half mirror 42 Is done.

(b) In step S201, a part of the irradiation light propagated by the first optical element 31 is reflected by the first semi-transparent mirror 41 as the first reference light, and a part of the first semi-transparent 41 is passed through the first inspection light. As transparent. In step S202, the first inspection light travels toward the first measurement point 91 and is reflected by the first measurement point 91. The first inspection light reflected at the first measurement point 91 is transmitted again through the first semi-transparent mirror 41 and enters the first optical element 31. When the first half mirror 41 reciprocates between the first measuring point 91, first inspection light advances a first measuring optical path length F _1. In step S203, the first reference light reflected by the first half mirror 41 interferes with the first first inspection light advanced measurement optical path length F _1. Thereafter, the first reference light and the first inspection light are propagated through the first optical element 31 and the splitter 21 to the interference fringe detection element 153 through the common optical waveguide 33.

(c) In step S301, the irradiation light propagated by the second optical element 32 is partly reflected by the second semi-transparent mirror 42 as the second reference light, and part of the second semi-transparent mirror 42 passes through the second inspection light. As transparent. In step S302, the second inspection light travels toward the second measurement point 92 and is reflected at the second measurement point 92. The second inspection light reflected at the second measurement point 92 passes through the second semi-transparent mirror 42 again and enters the second optical element 32. When the second half mirror 42 reciprocates between the second measurement point 92, the second inspection light advances a second measurement optical path length F _2.

(d) In step S303, the second reference light reflected by the second half mirror 42 interferes with the second inspection light advanced to the second measuring optical path length F _2. Thereafter, the second reference light and the second inspection light are propagated to the interference fringe detection element 153 through the second optical element 32 and the splitter 21 through the common optical waveguide 33. Note that the progress of steps S301 to S303 is parallel to the progress of steps S201 to S203. Further, Step S103, Step S201 to Step S203, and Step S301 to Step S303 are continuously performed for each wavelength component of the irradiation light that is selectively transmitted according to time t in Step S102.

(e) In step S401, the interference fringe detection element 153 detects the first interference fringe by the first inspection light and the first reference light and the combined interference fringe of the second interference fringe by the second inspection light and the second reference light. . The interference fringe detecting element 153 transmits the output light intensity S _OUT (λ) given by the above equation (25) of the combined interference fringe to the CPU 300. In step S402, the correction module 306 of the CPU 300 receives the output light intensity S _OUT (λ) of the combined interference fringe. Next, the correction module 306 calculates a moving average line of the spectrum distribution of the output light intensity S _OUT (λ). After that, the correction module 306 divides the spectral distribution of the output light intensity S _OUT (λ) by the spectral distribution of the irradiation light intensity S ₀ (λ) approximated by the moving average line, and corrects the corrected output given by Equation (28). The light intensity S _{OUT_C} (λ) is calculated. The correction module 306 transmits the output light intensity S _{OUT — C} (λ) to the conversion module 307.

(f) In step S403, the conversion module 307 receives the output light intensity S _{OUT — C} (λ) given by equation (28). Next, the conversion module 307 converts equation (28), which is a function of wavelength λ, into equation (30), which is a function of frequency ν. The conversion module 307 transmits the output light intensity S _{OUT — C} (ν) given by the equation (30) to the extraction module 310. In step S404, the extraction module 310 receives the output light intensity S _{OUT — C} (ν). Next, the extraction module 310 extracts the peak interval P of the low frequency component included in the spectrum of the output light intensity S _{OUT — C} (ν). The extraction module 310 stores the extracted value of the peak interval P of the low frequency component in the interference fringe component storage module 201.

(g) In step S405, the calculation module 330, for example, shows the relationship between the height difference (L _T1 -L _T2 ) between two measurement points acquired in advance shown in FIG. 11 and the peak interval P of the low frequency component. Read from the relationship storage module 202 shown in FIG. Next, the calculation module 330 approximates the relationship between the height difference (L _T1 −L _T2 ) and the peak interval P using an approximate expression of the height difference (L _T1 −L _T2 ) with the interval as a variable. Thereafter, the calculation module 330 reads the value of the peak interval P of the low frequency component extracted by the extraction module 310 from the interference fringe component storage module 201. The calculation module 330 substitutes the value of the peak interval P into the approximate expression, and calculates the height difference (L _T1 −L _T2 ) between the first measurement point 91 and the second measurement point 92. Finally, the calculation module 330 saves the calculated height difference (L _T1 −L _T2 ) in the result storage module 203 and ends the optical interference measurement method according to the first embodiment.

  Conventionally, there has been a confocal level gauge that measures the height of a step without contact. The confocal step meter changes the position of the lens so that the reflected light intensity is constant when scanning the vicinity of the step with light. The confocal level difference meter detects a variation amount of the lens position with a displacement sensor, and calculates a step height based on the displacement amount. However, the resolution of the height that can be measured with the confocal step meter is not high because it depends on the displacement sensor. Furthermore, the spatial resolution is limited to the wavelength order due to the diffraction limit of light. Further, when calculating the height of the step, the confocal level difference meter calculates the confocal positions of the upper surface and the lower surface of the step, and calculates the difference between the confocal positions. Accordingly, there is a problem that it takes a long time to scan and the measurement resolution is less than half of the position resolution of the variable focus lens.

In contrast, the optical interference measurement apparatus according to the first embodiment has an optical path difference between the first measurement optical path length and the second measurement optical path length (F ₁ − The difference in height between F ₂₎ first measuring point 91 and the second measuring point 92 on the basis of (L _T1 - L _T2) for calculating the difference in height (L _T1 - is shorter than the wavelength L _T2) In some cases, it can be measured. The equation (4), (17) to (19) as long as it satisfies the equation, even if the optical path length L _R2 of the optical path length L _R1 of the first optical element 31 second optical element 32 is changed, the height The measurement result of the difference (L _T1 -L _T2 ) is not affected. Therefore, even if the first measurement point 91 and the second measurement point 92 are separated from each other, it is possible to accurately measure the height difference (L _T1 −L _T2 ).

(First modification of the first embodiment)
Cos {(π / λ) (F ₁ − Paying attention to F ₂ )}, the first period G _{1 at} an arbitrary first wavelength λ ₁ of the low frequency component of the spectrum of the output light intensity S _OUT (λ) is given by the following equation (33), The second period G ₂ of the low frequency component at the second wavelength λ ₂ different from the wavelength λ ₁ is given by the following equation (34). The difference between the first period G ₁ and the second period G ₂ is given by the following equation (35). Furthermore, from equation (35), the difference between the first measurement optical path length F ₁ and the second measurement optical path length F ₂ (F ₁ − F ₂ ) is given by the following equation (36).

G ₁ = (F _1- F ₂ ) / (2 × λ ₁ )… (33)
G ₂ = (F _1- F ₂ ) / (2 × λ ₂ )… (34)
G ₁ -G ₂ = (F _1- F ₂ ) × {(1 / (2 × λ ₁ ))-(1 / (2 × λ ₂ ))}… (35)
F _1- F ₂ = (G ₁ -G ₂ ) / {(1 / (2 × λ ₁ ))-(1 / (2 × λ ₂ ))}… (36)
From the above equations (6), (12), and (36), the height difference (L _T1 -L _T2 ) between the first measurement point 91 and the second measurement point 92 is given by the following equation (37): .

L _T1 -L _T2 = (G ₁ -G ₂ ) / {(1 / λ ₁ )-(1 / λ ₂ )}… (37)
Here, the difference (G ₁ -G ₂ ) between the first period G ₁ and the second period G ₂ is the interference of the low frequency component between the first wavelength λ ₁ and the second wavelength λ ₂ Represents the number of stripes. Therefore, if the number of interference fringes due to the low frequency component of the spectrum of the output light intensity S _OUT (λ) between the first wavelength λ ₁ and the second wavelength λ ₂ is known, the above equation (37) gives the first The difference in height (L _T1 −L _T2 ) between the measurement point 91 and the second measurement point 92 can be calculated.

In the first modification that applies the principle described above, the extraction module 310 shown in FIG. 1 uses the spectrum data of the output light intensity S _OUT (λ) of the combined interference fringes to obtain an arbitrary first wavelength λ ₁ and the _first wavelength λ ₁ . Extract the maximum point of the low frequency component between the _two wavelengths λ ₂ . The extraction module 310 calculates the envelope of the spectrum of the output light intensity S _OUT (λ) of the combined interference fringe, and the maximum point of the envelope between any first wavelength λ ₁ and second wavelength λ ₂ May be extracted.

The calculation module 330 counts the number of extracted maximum points. Further, the calculation module 330 substitutes the value of the _first wavelength λ ₁ , the value of the second wavelength λ ₂ , and the number of extracted maximum points into the above equation (37), and the first measurement point 91 and the second measurement point The height difference (L _T1 -L _T2 ) of the measurement point 92 is calculated. In the first modification, the interference fringe component storage module 201 stores the value of the _first wavelength λ ₁ , the value of the second wavelength λ ₂ , and the maximum point extracted by the extraction module 310. The relationship storage module 202 stores the above equation (37).

  Next, an optical interference measurement method according to a first modification of the first embodiment will be described with reference to FIG.

(a) Steps S101 to S103, Steps S201 to S203, Steps S301 to S303, Step S401, and Step S402 are performed in the same manner as in the first embodiment. Step S403 is omitted. Next, in step S404, the extraction module 310 shown in FIG. 1 performs the maximum point of the low frequency component of the spectrum of the output light intensity S _OUT (λ) between the arbitrary first wavelength λ ₁ and the second wavelength λ _2. Are extracted as interference fringe components that vary according to the optical path difference between the first measurement optical path length F ₁ and the second measurement optical path length F ₂ . The extraction module 310 stores the extracted value of the _first wavelength λ ₁ , the value of the second wavelength λ ₂ , and the maximum point of the low frequency component in the interference fringe component storage module 201.

(b) In step S405, the calculation module 330 uses the interference fringe component storage module 201 to calculate the value of the _first wavelength λ ₁ , the value of the second wavelength λ ₂ , and the maximum point of the low frequency component extracted by the extraction module 310. Read from and count the number of local maxima. In addition, the calculation module 330 reads the expression (37) from the relation storage module. Next, the calculation module 330 substitutes the value of the _first wavelength λ ₁ , the value of the second wavelength λ ₂ , and the number of local maximum points into the equation (37), so that the first measurement point 91 and the second measurement point The height difference (L _T1 −L _T2 ) of the point 92 is calculated, and the optical interference measurement method according to the first modification of the first embodiment is completed.

Even with the optical interference measurement apparatus and the optical interference measurement method according to the first modification of the first embodiment described above, the difference in height between the first measurement point 91 and the second measurement point 92 can be achieved with high accuracy. (L _T1 -L _T2 ) can be measured. It should be noted that the extraction module 310 determines the number of minimum points of the low frequency component of the spectrum of the output light intensity S _OUT (λ) between the arbitrary first wavelength λ ₁ and the second wavelength λ ₂ or the output light intensity S. The number of minimum points in the envelope of the spectrum of _OUT (λ) may be extracted as an interference fringe component that varies depending on the optical path difference between the first measurement optical path length F ₁ and the second measurement optical path length F ₂ .

(Second modification of the first embodiment)
As shown in FIG. 14, the optical interference measurement apparatus according to the second modification includes a rail 170 that sets the arrangement position of the end face of the second optical element 32. The end surface of the second optical element 32 moves along the rail 170. In the vertical direction of the first measurement surface 291, the height of the position where the rail 170 is arranged is the same everywhere. Therefore, the end surface of the second optical element 32 moves in parallel to the first measurement surface 291. Other components of the optical interference measurement apparatus shown in FIG. 14 are the same as those in FIG. According to the optical interference measurement apparatus according to the second modification, measuring the plurality of height differences (L _T1 -L _T2 ) while moving the end surface of the second optical element 32 along the rail 170. Is possible. Therefore, it is possible to measure the in-plane distribution of height with reference to the first measurement point 91.

(Second embodiment)
In the optical interference measurement apparatus shown in FIG. 1, a common optical waveguide 29, a spectroscope 3, and a common optical waveguide 30 are arranged between a light source 114 and a splitter 21. On the other hand, in the optical interference measurement apparatus according to the second embodiment, only the common optical waveguide 34 is disposed between the light source 114 and the splitter 21 as shown in FIG. However, the common optical waveguide 35 and the spectrometer 3 are arranged between the splitter 21 and the interference fringe detection element 153. For example, as shown in FIG. 16, the spectroscope 3 includes a lens 53 and a diffraction grating. The lens 53 makes the first inspection light, the first reference light, the second inspection light, and the second reference light irradiated from the end of the common optical waveguide 35 into parallel light. The diffraction grating 54 reflects the first inspection light, the first reference light, the second inspection light, and the second reference light toward the interference fringe detection element 153. Here, the diffraction grating 54 reflects the wavelength components of the first inspection light, the first reference light, the second inspection light, and the second reference light in different directions for each wavelength. Therefore, different wavelength components are incident on each of the plurality of pixels of the interference fringe detection element 153. The other components of the optical interference measurement apparatus according to the second embodiment are the same as those in FIG. 1 or FIG.

  Next, the optical interference measurement method according to the second embodiment will be described with reference to FIG.

(a) In step S 111, the light source 114 shown in FIG. 15 emits irradiation light having a spectrum of irradiation light intensity S ₀ (λ), and the irradiation light is propagated to the splitter 21 through the common optical waveguide 34. Thereafter, step S113, step S211, step S212, step S311 and step S312 are performed in the same manner as step S103, step S201, step S202, step S301 and step S302 in FIG. 13, respectively.

  (b) In step S213 in FIG. 17, the first reference light and the first inspection light that interfere with each other propagate through the first optical element 31 and the splitter 21 shown in FIG. Is done. In step S313, the second reference light and the second inspection light that interfere with each other are propagated to the spectroscope 3 through the second optical element 32 and the splitter 21 through the common optical waveguide 35.

  (c) In step S410, the spectroscope 3 reflects the wavelength components of the first reference light, the first inspection light, the second reference light, and the second inspection light to the interference fringe detection element 153. Thereafter, steps S411 to S415 in FIG. 17 are performed in the same manner as steps S401 to S405 in FIG. 13, and then the optical interference measurement method according to the second embodiment is terminated.

  According to the optical interference measurement device and the optical interference measurement method according to the second embodiment described above, the spectroscope 3 can be disposed near the CPU 300. Therefore, the transmission wavelength of the spectrometer 3 can be easily set.

(Third embodiment)
Unlike the optical interference measurement apparatus shown in FIG. 15, the optical interference measurement apparatus according to the third embodiment includes a modulation drive circuit 115 shown in FIG. As shown in FIG. 19, the modulation drive circuit 115 supplies a drive current that varies with time t to the light source 114 shown in FIG. By supplying a drive current that varies according to time t, the light source 114 such as a semiconductor laser resonator changes the wavelength of irradiation light according to time t as shown in FIG. Since the light source 114 changes the wavelength of irradiation light, the optical interference measurement apparatus shown in FIG. 18 does not require a spectroscope, and the common optical waveguide 35 is directly connected to the interference fringe detection element 153. The other components of the optical interference measurement apparatus shown in FIG. 18 are the same as those of the optical interference measurement apparatus shown in FIG.

  Next, an optical interference measurement method according to the third embodiment will be described with reference to FIG.

  In step S101, the modulation drive circuit 115 shown in FIG. 18 supplies the light source 114 with a drive current that varies according to time t. The light source 114 supplied with the drive current emits irradiation light whose wavelength changes with time t. The irradiation light is propagated to the splitter 21 through the common optical waveguide 34. After step S103, step S201, step S202, step S301, and step S302 are performed in the same manner as in FIG. 13, the first reference light and the first inspection light that interfere with each other in step S203 in FIG. The light is propagated to the interference fringe detecting element 153 through the common optical waveguide 35 via the element 31 and the splitter 21. In step S303, the second reference light and the second inspection light that interfere with each other are propagated to the interference fringe detection element 153 through the second optical element 32 and the splitter 21 through the common optical waveguide 35. Then, after steps S401 to S405 are performed in the same manner as in FIG. 13, the optical interference measurement method according to the third embodiment is terminated.

According to the optical interference measurement device and the optical interference measurement method according to the third embodiment described above, the light intensity loss of the irradiation light by the spectroscope is eliminated. Therefore, it is possible to prevent the output light intensity S _OUT (λ) from being reduced. Note that the modulation drive circuit 115 may vary the drive current in a sawtooth shape according to the time t.

(Fourth embodiment)
Unlike the optical interference measurement device shown in FIG. 18, the optical interference measurement device according to the fourth embodiment has a common optical waveguide 34a connected to the light source 114 as shown in FIG. 21, and a splitter connected to the common optical waveguide 34a. 20 is connected. An irradiation optical waveguide 80a and a common optical waveguide 34b are connected to the splitter 20. A wavelength filter 85 is connected to the irradiation optical waveguide 80a. The wavelength filter 85 selectively transmits a part of the wavelength components of the irradiation light propagated through the irradiation optical waveguide 80a. As the wavelength filter 85, a multilayer interference filter, a Fabry-Perot filter, a fiber Bragg grating, or the like can be used. The wavelength filter 85 is connected to an irradiation optical waveguide 80b that propagates the irradiation light transmitted through the wavelength filter 85. An irradiation light receiving element 154 that receives irradiation light is connected to the irradiation optical waveguide 80b. Since the wavelength filter 85 is disposed, the irradiation light receiving element 154 emits the irradiation light with the strongest light intensity when the wavelength of the irradiation light emitted from the light source 114 coincides with the center of the transmission wavelength band of the wavelength filter 85. Receive light. Hereinafter, the drive current when the wavelength of the irradiation light coincides with the center of the transmission wavelength band is referred to as a set drive current.

  When a semiconductor laser resonator or the like is used as the light source 114, the wavelength of irradiation light may change due to a change in ambient temperature even if the drive current is managed by the modulation drive circuit 115. When the light source 114 has a Fabry-Perot structure, mode hopping (wavelength jump) may occur due to a temperature change as shown in FIG. When a surface emitting laser (VCSEL) light source is used as the light source 114, the wavelength of the irradiation light changes almost in proportion to the drive current. However, if the ambient temperature changes, the wavelength of the irradiated light may change as shown in FIG. 23 even if the drive current is the same.

  Therefore, a feedback circuit 116 is connected to the modulation driving circuit 115 and the irradiation light receiving element 154 shown in FIG. The feedback circuit 116 monitors the drive current supplied to the light source 114 by the modulation drive circuit 115 and the light intensity of the irradiation light received by the irradiation light receiving element 154. Further, as shown in FIG. 24, the feedback circuit 116 stores the center wavelength of the transmission wavelength band in the initial state and the set drive current. Here, as shown in FIG. 25, when the driving current when the irradiation light receiving element 154 receives the irradiation light of the center wavelength becomes weaker than the setting driving current due to the temperature change, the feedback circuit 116 uses the modulation driving circuit 115 as the light source 114. Is set so that the light source 114 emits irradiation light in the same wavelength range as the initial state. Further, when the driving current when the irradiation light receiving element 154 receives the irradiation light having the center wavelength is increased from the setting driving current due to the temperature change, the feedback circuit 116 scans the driving current supplied to the light source 114 by the modulation driving circuit 115. Is set so that the light source 114 emits irradiation light in the same wavelength range as the initial state.

  The other components of the optical interference measurement apparatus shown in FIG. 21 are the same as those in FIG. Next, the optical interference measurement method according to the fourth embodiment will be described with reference to FIG.

  (a) In step S51, the modulation drive circuit 115 shown in FIG. 21 supplies drive current to the light source 114 in the scanning range determined by the initial setting. The feedback circuit 116 monitors the drive current. In step S52, the light source 114 emits irradiation light having a wavelength corresponding to the drive current. The irradiation light propagates through the common optical waveguide 34a, and is split by the splitter 20 in the direction of the irradiation optical waveguide 80a and the direction of the common optical waveguide 34b. The irradiation light divided in the direction of the irradiation optical waveguide 80a is propagated to the wavelength filter 85 through the irradiation optical waveguide 80a.

  (b) In step S53, the wavelength component of the irradiation light in the band equal to the transmission wavelength band of the wavelength filter 85 is transmitted through the wavelength filter 85. The irradiation light transmitted through the wavelength filter 85 is propagated through the irradiation optical waveguide 80b and received by the irradiation light receiving element 154 in step S54. The irradiation light receiving element 154 transmits the light intensity of the received irradiation light to the feedback circuit 116. In step S55, the feedback circuit 116 monitors whether or not the light intensity of the irradiation light received by the irradiation light receiving element 154 is maximum at the set drive current. If the set drive current is not the maximum, the process proceeds to step S56. If the set drive current is the maximum, the process proceeds to step S60.

(c) When the light intensity of the irradiation light received by the irradiation light receiving element 154 is maximum at a driving current weaker than the set driving current, the feedback circuit 116 scans the driving current of the modulation driving circuit 115 in step S56. Shift the range in the negative direction. When the light intensity of the irradiating light received by the irradiating light receiving element 154 is maximized at a driving current stronger than the set driving current, the feedback circuit 116 shifts the scanning current scanning range of the modulation driving circuit 115 in the plus direction. Let In step S60, the height difference (L _T1 -L _T2 ) between the first measurement point 91 and the second measurement point 92 is measured in the same manner as in the optical interference measurement method according to the third embodiment, and the fourth measurement is performed. The optical interference measurement method according to the embodiment is completed.

When the wavelength of the irradiation light is modulated in accordance with the temperature change, an error occurs when calculating the height difference (L _T1 −L _T2 ) between the first measurement point 91 and the second measurement point 92 from the above equation (25). On the other hand, according to the optical interference measurement device and the optical interference measurement method according to the fourth embodiment, the feedback circuit 116 prevents the wavelength modulation of the irradiation light accompanying the temperature change. Therefore, the height difference (L _T1 −L _T2 ) between the first measurement point 91 and the second measurement point 92 can be calculated with high accuracy.

(Fifth embodiment)
In the first embodiment, as shown in FIG. 1, the difference in height between the first measurement surface 291 and the second measurement surface 292 of the measurement object 190 having a step was obtained. On the other hand, as shown in FIG. 27, it is also possible to measure the film thickness of the film to be measured 390 arranged in close contact with the flat surface of the object to be measured 290. In this case, the first semi-transparent mirror 41 is disposed at a first measurement distance _LT 1 in the direction perpendicular to the first measurement surface 391 that is the surface of the film to be measured 390. The first inspection light transmitted through the first semi-transmissive mirror 41 is reflected at the first measurement point 491 on the first measurement surface 391 and returns to the first semi-transmissive mirror 41. The second semi-transparent mirror 42 is disposed at a second measurement distance _LT2 in the direction perpendicular to the second measurement surface 292 that is the surface of the object 290 to be measured. The second inspection light transmitted through the second semi-transmissive mirror 42 is reflected at the second measurement point 492 on the second measurement surface 392 and returns to the second semi-transmissive mirror 42. Other components shown in FIG. 27 are the same as those in FIG.

FIG. 28 shows the output light intensity S _{OUT_C} (ν) when the height difference (L _T1 -L _T2 ) between the first measurement point 491 and the second measurement point 492 corresponding to the film thickness of the measured film 390 is 100 μm. Is the spectrum. Fig. 29 shows the spectrum of output light intensity S _{OUT_C} (ν) when the height difference (L _T1 -L _T2 ) is 80μm, and Fig. 30 shows the height difference (L _T1 -L _T2 ) when the height difference (L _T1 -L _T2 ) is _60μm . a spectrum of the output light intensity S _{OUT_C} (ν), FIG. 31 is the difference in height - a spectrum of (L _T1 L _T2) output light intensity when of 40μm S _{OUT_C} (ν). As shown in FIG. 32, the peak interval P of the low frequency component of the synthetic interference fringes becomes wider as the film to be measured 390 becomes thinner. Therefore, the low frequency component extracted by the extraction module 310 shown in FIG. 27 using the relationship between the height difference (L _T1 -L _T2 ) of two measurement points acquired in advance and the peak interval P of the low frequency component. From the peak interval P, the calculation module 330 calculates the film thickness (L _T1 -L _T2 ) of the film 390 to be measured. Needless to say, the film thickness of the film to be measured 390 can also be measured by the optical interference measuring apparatus shown in FIGS. 12, 14, 15, 18, and 21.

  Conventionally, there has been a capacitance method as a method for measuring the thickness of a thin film. According to the capacitance method, the thin film is sandwiched between electrodes, the capacitance of the thin film is measured, and the film thickness of the thin film is calculated using the measured capacitance and the known dielectric constant of the thin film. However, since the capacitance method needs to sandwich the thin film between the electrodes, there is a risk of damaging the thin film, and there is a problem that the film thickness cannot be calculated if the dielectric constant of the thin film is not known. In addition, there is a problem that it is easily affected by electromagnetic noise when measuring capacitance. On the other hand, according to the fifth embodiment, even if the dielectric constant of the film to be measured 390 is unknown, the film thickness of the film to be measured 390 can be measured with high accuracy without contact.

(Modification of the fifth embodiment)
When the material of the measured film 390 shown in FIG. 27 is made of glass, quartz, sapphire, etc., and the measured film 390 is transparent, a part of the first inspection light is reflected on the first measurement surface 391, and the other A part of the light enters the film to be measured 390 and is reflected by the surface of the object to be measured 290. If twice the thickness of the measured film 390 is shorter than the coherence length L _C, first inspection light reflected by the surface of the object 290 is incident on the measured film 390 is reflected by the measurement layer 390 surface Interferes with the first inspection light. In this case, the reflectance R _2Ra of the first measurement surface 391 included in the first light intensity ratio R _S1 given by the equation (7) with respect to the light intensity of the irradiation light is given by the following equation (38). :
R _2Ra = {R _3Ra + η _M R _4Ra -2 (η _M R _3Ra R _4Ra ) ^1/2 _{cos2φ M} } / {1 + η _M R _3Ra R _4Ra -2 (η _M R _3Ra R _4Ra ) ^1/2 cos2φ _M } (38)
Here, R _3Ra represents the reflectance of the surface of the film to be measured 390, and R _4Ra represents the reflectance of the back surface of the film to be measured 390. η _M represents the optical loss between the front and back surfaces of the film 390 to be measured, and is given by the following equation (39). Φ _M represents a phase and is given by the following equation (40). :
η _M = 1 / {1 + (λ × 2M) / (2πq ² )} ² … (39)
φ _M = 2πM / λ (40)
In this case, H is a constant, and the first light intensity ratio R _S1 is simplified by the following equation (41).

R _S1 = 1 + (1 + H × cos4Mπ / λ) cos {2π × F ₁ / λ}… (41)
Therefore, the frequency that gives the maximum point of the envelope of the low frequency component of the output light intensity S _{OUT — C} (ν) is modulated by (H × cos 4 Mπ / λ) included in the equation (41). However, the frequency giving the local minimum is not modulated by (H × cos4Mπ / λ). Therefore, when the film to be measured 390 is transparent, the extraction module 310 may extract the interval between the minimum points of the low frequency component envelope of the output light intensity S _{OUT — C} (ν) as the peak interval P of the low frequency component.

  Conventionally, as a method for measuring the film thickness of a transparent thin film, there has been a method for spectroscopically obtaining the film thickness of a thin film by causing interference between reflected light from the surface of the thin film and reflected light from the back surface. However, the spectroscopic method has a problem that the thickness of the thin film cannot be calculated when the refractive index of the thin film is not known. In addition, since the refractive index of the thin film varies depending on the doping amount of the impurity to the thin film and the distortion of the thin film, it is necessary to measure the refractive index of the thin film one by one before measuring the film thickness. In contrast, according to the modification of the fifth embodiment, even when the refractive index of the transparent film 390 to be measured is unknown, the film thickness of the film 390 to be measured can be measured without contact and with high accuracy. It becomes possible.

(Other embodiments)
Although the present invention has been described by the embodiments as described above, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques should be apparent to those skilled in the art. For example, in the optical interference measurement apparatus shown in FIG. 33, the first antireflection film 61 is disposed on the end surface of the first optical element 31 as shown in FIG. Therefore, the irradiation light propagated by the first optical element 31 is not reflected by the end face of the first optical element 31, but is emitted toward the first measurement surface 291. A second antireflection film 62 is disposed on the end face of the second optical element 32 shown in FIG. Further, a semi-transparent substrate 140 is disposed between the first antireflection film 61 and the second antireflection film 62 and the measurement object 190. A semi-transparent mirror substrate 140 surface 151 of the vertical distance between the first measuring surface 291 and the first measurement distance L _T1, and the surface 151 of the semi-transparent mirror substrate 140 in the vertical direction distance between the second measuring surface 292 The second measurement distance L _{T2 is} assumed. Note that the height of the position where the surface 151 of the semi-transparent substrate 140 is arranged in the direction perpendicular to the first measurement surface 291 is the same everywhere.

  The surface 150 facing the first antireflection film 61 and the second antireflection film 62 of the semi-transparent substrate 140 is subjected to antireflection treatment. On the other hand, the surface 151 of the semi-transparent substrate 140 that faces the object to be measured 190 is not subjected to antireflection treatment. Accordingly, a part of the illumination light emitted from the first optical element 31 is reflected as the first reference light on the surface 151 of the semi-transparent substrate 140, and the other part is transmitted through the semi-transparent substrate 140 as the first inspection light. Therefore, the portion of the surface 151 of the semi-transparent substrate 140 that reflects the first reference light functions as the first semi-transparent 141. A part of the illumination light emitted from the second optical element 32 is reflected as the second reference light on the surface 151 of the semi-transparent substrate 140, and the other part is transmitted through the semi-transparent substrate 140 as the second inspection light. Therefore, the portion of the surface 151 of the semi-transparent substrate 140 that reflects the second reference light functions as the second semi-transparent 142.

The first inspection light transmitted through the semi-transparent substrate 140 is reflected at the first measurement point 91 and returns to the semi-transparent substrate 140. The first inspection light therefore, between the semi-transparent mirror substrate 140 and the first measurement point 91, the first measuring optical path length given by the above equation (6) is a length of two times the first measured distance L _T1 Continue on F ₁ . The second inspection light transmitted through the semi-transparent substrate 140 is reflected at the second measurement point 92 and returns to the semi-transparent substrate 140. The second inspection light therefore, between the semi-transparent mirror substrate 140 and the second measurement point 92, the second measuring optical path length given by equation (12) is a length of 2 times the second measured distance L _T2 Continue on F ₂ . The other components of the optical interference measuring apparatus shown in FIG. 33 are the same as those in FIG. A lens may be disposed between the first antireflection film 61 and the semi-transparent substrate 140 and between the second antireflection film 62 and the semi-transparent substrate 140, respectively.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

It is the 1st schematic diagram of the optical interference type measuring device concerning a 1st embodiment of the present invention. It is a graph which shows the selection wavelength for every time by the spectrometer which concerns on the 1st Embodiment of this invention. It is a schematic diagram which shows the spectrometer which concerns on the 1st Embodiment of this invention. It is a schematic diagram which shows the 1st optical element which concerns on the 1st Embodiment of this invention. It is a 1st spectrum of the synthetic | combination interference fringe which concerns on the 1st Embodiment of this invention. It is a 2nd spectrum of the synthetic | combination interference fringe which concerns on the 1st Embodiment of this invention. It is a graph which shows the moving average line which concerns on the 1st Embodiment of this invention. It is a 1st example of the spectrum of the corrected synthetic | combination interference fringe which concerns on the 1st Embodiment of this invention. It is a 2nd example of the spectrum of the corrected synthetic | combination interference fringe which concerns on the 1st Embodiment of this invention. It is a 3rd example of the spectrum of the corrected synthetic | combination interference fringe which concerns on the 1st Embodiment of this invention. It is a graph which shows the relationship between the height difference which concerns on the 1st Embodiment of this invention, and a peak space | interval. It is a 2nd schematic diagram of the optical interference type measuring device which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the optical interference type measuring method which concerns on the 1st Embodiment of this invention. It is a schematic diagram of the optical interference type measuring apparatus which concerns on the 2nd modification of the 1st Embodiment of this invention. It is a schematic diagram of the optical interference type measuring apparatus which concerns on the 2nd Embodiment of this invention. It is a schematic diagram which shows the spectrometer which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the optical interference type measuring method which concerns on the 2nd Embodiment of this invention. It is a schematic diagram of the optical interference type measuring apparatus which concerns on the 3rd Embodiment of this invention. It is a graph which shows the drive current for every time by the modulation drive circuit which concerns on the 3rd Embodiment of this invention. It is a flowchart which shows the optical interference type measuring method which concerns on the 3rd Embodiment of this invention. It is a schematic diagram of the optical interference type measuring device which concerns on the 4th Embodiment of this invention. It is a 1st graph which shows the temperature dependence of the wavelength of the irradiation light which concerns on the 4th Embodiment of this invention. It is a 2nd graph which shows the temperature dependence of the wavelength of the irradiation light which concerns on the 4th Embodiment of this invention. It is a 1st graph which shows the relationship between the wavelength of the irradiation light which concerns on the 4th Embodiment of this invention, and a drive current. It is a 2nd graph which shows the relationship between the wavelength of the irradiation light which concerns on the 4th Embodiment of this invention, and a drive current. It is a flowchart which shows the optical interference type measuring method which concerns on the 4th Embodiment of this invention. It is a schematic diagram of the optical interference type measuring device which concerns on the 5th Embodiment of this invention. It is a 1st example of the spectrum of the corrected synthetic | combination interference fringe which concerns on the 5th Embodiment of this invention. It is a 2nd example of the spectrum of the corrected synthetic | combination interference fringe which concerns on the 5th Embodiment of this invention. It is a 3rd example of the spectrum of the corrected synthetic | combination interference fringe which concerns on the 5th Embodiment of this invention. It is a 4th example of the spectrum of the corrected synthetic | combination interference fringe which concerns on the 5th Embodiment of this invention. It is a graph which shows the relationship between the film thickness which concerns on the 5th Embodiment of this invention, and a peak space | interval. It is a schematic diagram of the optical interference type measuring apparatus which concerns on other embodiment of this invention. It is a schematic diagram which shows the 1st optical element and 1st antireflection film which concern on other embodiment of this invention.

Explanation of symbols

3 Spectrometer
12… Output side internal housing
13… Input side internal housing
14 ... Case
20, 21 ... Splitter
29, 30, 33, 34, 34a, 34b, 35… Common optical waveguide
31 ... First optical element
32 ... Second optical element
41 ... First semi-transparent mirror
42… Second semi-transparent mirror
45, 46, 53… Lens
54 ... Diffraction grating
61. First antireflection film
62… Second antireflection film
80a, 80b ... Irradiation optical waveguide
85… Wavelength filter
91… First measurement point
92… Second measurement point
114 ... Light source
115: Modulation drive circuit
116 ... Feedback circuit
124 ... Output side translucent mirror
125 ... Input side translucent mirror
130a ... Core
131a ... clad
140… Semi-transparent substrate
141… First semi-transparent mirror
142 ... Second semi-transparent mirror
150, 151 ... face
153 ... Interference fringe detector
154 ... Irradiation light receiving element
170 ... Rail
190 ... DUT
191, 192 ... Ferrule
200 ... Data storage device
201 ... Interference fringe component storage module
202 ... Relational memory module
203 ... Result storage module
290 ... DUT
291… First measurement surface
292… Second measuring surface
300 ... CPU
306 ... Correction module
307 ... Conversion module
310 ... Extraction module
330 ... Calculation module
390 ... film to be measured
391… First measurement surface
392… Second measuring surface
491 ... 1st measurement point
492 ... Second measurement point

Claims (10)

A light source that emits irradiation light;
A first semi-transparent mirror that divides the irradiation light into first reference light and first inspection light;
A first optical element that forms a first interference fringe between the first reference light and the first inspection light that has been irradiated to the first measurement point and traveled the first measurement optical path length;
A second semi-transparent mirror that divides the irradiation light into second reference light and second inspection light;
A second optical element that forms a second interference fringe between the second reference light and the second inspection light that has been irradiated to the second measurement point and traveled the second measurement optical path length;
An interference fringe detecting element for detecting a combined interference fringe of the first interference fringe and the second interference fringe;
An extraction module that extracts an interference fringe component that varies according to an optical path difference between the first measurement optical path length and the second measurement optical path length from the combined interference fringe;
An optical interference measurement apparatus comprising: a calculation module that calculates a difference in height between the first measurement point and the second measurement point from the interference fringe component.   2. The optical interference according to claim 1, wherein the first semi-transparent mirror is disposed at a first measurement distance shorter than a half of a coherence length of the irradiation light with respect to the first measurement point. Type measuring device.   The second semi-transparent mirror is disposed at a second measurement distance shorter than half of the coherence length of the irradiation light with respect to the second measurement point. Optical interference type measuring device.   The first optical element and the second optical element are interference between the first inspection light and the second inspection light, interference between the first inspection light and the second reference light, the first reference light and the second 4. The optical interference measurement apparatus according to claim 1, wherein interference with inspection light and interference between the first reference light and the second reference light are prevented. 5.   5. The optical interference measurement apparatus according to claim 1, wherein the extraction module calculates an envelope of a spectrum of the combined interference fringe.   The optical interference measurement apparatus according to claim 5, wherein the extraction module extracts an interval between extreme points of the envelope.   The optical interference measurement apparatus according to claim 1, further comprising a spectrometer that selectively transmits a wavelength component of the irradiation light.   7. A spectroscope that selectively transmits the wavelength components of the first inspection light, the first reference light, the second inspection light, and the second reference light, respectively. The optical interference type measuring apparatus according to any one of the above.   The optical interference measurement apparatus according to claim 1, wherein the light source changes a wavelength of the irradiation light.   The optical interference measurement apparatus according to claim 1, further comprising a correction module that removes the spectrum distribution of the irradiation light from the spectrum distribution of the combined interference fringes.

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