JP4326356B2 - Phase correction value measurement method - Google Patents

Description

  The present invention relates to a method for measuring a phase correction value, and more particularly to an improvement in a method for measuring a phase correction value for a dimension measurement value by optical interference measurement.

Conventionally, an end measure is used as a reference for length. The edge scale is a standard that represents a specified dimension by the distance between the surfaces of both ends, and a typical example is a block gauge.
This block gauge has extremely high dimensional accuracy, and its measurement surface is easily adhered (ringing) to the measurement surface of another block gauge. And a required dimension is obtained by sticking several block gauges. On the other hand, since this block gauge is used in such a way that the measurement surface always comes into contact with other measurement surfaces, it is easy to cause scratches and wear, and there is a secular change of the material, and a periodic inspection is necessary.
In order to calibrate the dimension between the opposing end faces of the block gauge with high accuracy, a light wave interference measuring apparatus is used (see Patent Document 1). Furthermore, in the non-contact optical interference measuring apparatus described in Patent Documents 2 and 3, light is irradiated from between both end faces of the block gauge, and the dimensions are measured using interference fringes by reflected light from the respective end faces. It is possible to perform non-contact measurement without having to block the block gauge to the base plate.

  As described above, the block gauge is premised on a usage method involving physical contact, ringing, and the like. Therefore, when measuring the dimension between the end faces, the dimension is measured using the outermost part (particularly excluding the protruding part) of the respective roughness curves on both end faces as the measurement position. However, in the light wave interference measurement, this position does not become the measurement position due to the two problems of the problem of surface roughness and the problem of phase change upon reflection of light due to the optical properties of the material.

  As shown in FIG. 6, the end surface of the block gauge is microscopically uneven. When the dimension is measured by bringing the contact element into contact with the end face, as shown in FIG. 6A, the contact element touches the highest uneven part, and the dimension is measured using that part as the measurement position. However, when the measurement is performed by the light wave interferometry, as shown in FIG. 6B, the measurement is performed using the reflected light from the uppermost part of the roughness curve or the reflected light from the lowermost part. Cannot be identified. Therefore, the dimension with the measurement position as the middle between the uppermost part and the lowermost part (arithmetic mean roughness of the roughness curve) is measured. Therefore, as long as the measurement end face has roughness, it cannot be measured at the outermost surface, and the measurement is shorter than the dimension due to mechanical contact. In other words, if correction is not performed, the position which is always submerged from the surface to be measured is measured, so that the measurement is shorter than the actual measurement. Also, the greater the surface roughness, the greater the influence of sinking. The phase change due to this influence is called a shape correction value.

Even if the measurement surface is an ideal surface without roughness, there is a problem of phase change of light due to the optical properties of the material. The phase change during reflection of vertically incident light can be ignored in the case of a material having a small imaginary part (absorption coefficient) of the complex refractive index. However, in the case of a material having a large absorption coefficient such as metal, the phase change at the time of reflection is an amount that cannot be ignored. That is, as shown in FIG. 6C, a delay in the phase of the light occurs at the time of reflection, so that the measurement result is similar to the state in which the measurement is performed in the middle part that is submerged from the actual surface. For this reason, even if the measurement surface is an ideal surface with no surface roughness, the measurement is made shorter than the actual dimension. The amount of phase change due to this influence is called an optical correction value.
In actual measurement, it is necessary to consider the shape correction value and the optical correction value at the same time, and the sum of the shape correction value and the optical correction value is referred to as a phase correction value. By adding this phase correction value to the measurement result by the light wave interference measurement, the mechanical dimension between the end faces described above (the dimension between the outermost portions of the roughness curves on both end faces) can be obtained.

As a method for obtaining this phase correction value, a conventional auxiliary gauge method will be described. In the auxiliary gauge method, the correction value is obtained by utilizing two characteristics that glass made of quartz or the like has almost no phase change due to optical constants and that the surface roughness can be negligibly small. is there. First, as shown in FIG. 7A, measurement is performed by ringing the same material. In other words, the light wave in a state where the block gauge (GB) of the material whose phase correction value is to be measured is ringed to the block gauge (GB) or the base plate (BP) of the same material to cancel the phase change at the time of reflection on each measurement surface. Perform interference measurements. When the dimension L _A obtained by this measurement is the dimension L _{GB of the} block gauge, the thickness d _W of the ringing layer, and the phase correction value C,
L _A = L _GB −C + d _W + C = L _GB + d _W
It is represented by

Next, as shown in FIG. 7B, measurement is performed by ringing a block gauge (GB) of glass such as quartz or a base plate (BP) into a block gauge (GB) of a material whose correction value is to be measured. Glass such as quartz is finished with a very small surface roughness, and has a small absorption coefficient and a phase change due to an optical constant that can be ignored. Therefore, there is almost no phase change on the base plate surface. L _B obtained by this measurement, using a phase correction value C of the block gauge,
L _B = L _GB + d _w −C
It is expressed. From the equations of L _A and L _B, the phase correction value C is
C ₌ L B -L _A
Is required.

JP-A-6-341809 JP-A-8-271216 JP 2003-194523 A

  However, the above-described conventional method has an advantage that a special device other than the device for measuring the size of the block gauge is not necessary, but has a problem that ringing is involved in the measurement. Ringing requires skill in the work itself and is very difficult to perform with good reproducibility. In the above conventional method, it is assumed that the thickness of the ringing layer when ringing on the base plate made of the same material as the target block gauge is equal to the thickness of the ringing layer when ringing on a base plate such as quartz glass. is there. However, it is very difficult to perform ringing with good reproducibility because the ringing force is different between the same material and different materials, and it is not as expected. That is, the deviation from the premise appears as a systematic error as it is.

Also, it is assumed that the surface roughness and optical characteristics of the two materials are equal when measuring the close contact between the same materials, and the phase changes that occur in each of them are completely offset. However, in reality, there is a problem that the two states are not exactly the same, so they are not as expected. A deviation from the premise at this time also becomes a systematic error.
As another conventional method, there is a method of performing measurement by stacking block gauges on a base plate such as glass. However, since this method also uses ringing, the same problem as described above occurs.
Further, as a conventional method that does not use ringing, there is a method of directly measuring the surface roughness and the optical constant. However, in this method, the above-mentioned shape correction value must be obtained by measuring the complex refractive index with a roughness measuring machine and the optical correction value with an ellipsometer, and a separate measuring device is required for measuring each. There is a problem of becoming.

It is necessary to add a phase correction value to the size value of the edge gauge such as a block gauge obtained by the light wave interference measurement and correct it to a correct value. Therefore, in order to further reduce the uncertainty of dimension measurement, the uncertainty of the phase correction value must also be reduced. At present, the phase correction value is measured by a light wave interferometer using ringing. However, as can be seen from the above reason, it is difficult to obtain a stable phase correction value due to variations in the ringing layer.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for measuring a phase correction value in light wave interference measurement simply and with high accuracy.

In the phase correction value measuring method of the present invention, light is divided into two coherent light beams, one is used as reference light, the other is used as measurement light, the measurement light is irradiated onto the measurement object, and the reflected light and reference light are used. In the phase correction value measurement method for obtaining the phase change amount at the time of reflection of the measurement light in the light wave interference measurement for measuring the dimension between the opposite end faces of the measurement object based on the interference,
Preparing a measurement object whose phase change C _X is unknown and a reference object whose phase change C _S is known;
Irradiate measurement light to both opposite end surfaces of the measurement object to be dimensioned, interference between the reflected light from one end surface of the measurement object and the reference light, and the other of the measurement object Using a non-contact optical interference measuring apparatus that measures the optical dimension of the measurement object based on the interference between the reflected light from the end surface and the reference light, the optical dimension L _{IX of the} object to be measured and the reference Determining an optical dimension difference ΔL _I (ΔL _I = L _{I X} −L _{I S} ) which is a difference from the optical dimension L _IS of the object;
A contact-type length measuring device that contacts a contact surface with an end surface of a measurement object to be dimensioned and measures a mechanical dimension between opposing end surfaces of the measurement object based on a contact position of the contact device. And obtaining a mechanical dimension difference ΔL (ΔL = L _X −L _S ) , which is a difference between the mechanical dimension L _{X of the} object to be measured and the mechanical dimension L _S of the reference object, by contact-type comparative measurement When,
Said optical dimensional difference [Delta] L _I, the mechanical dimensions difference [Delta] L, and the phase change amount C _X the following equation of the object to be measured from the phase variation amount C _S of the reference object,
_{C X = C S + ΔL /} 2 -ΔL I / 2
And a step of obtaining by the following.
Here, in the description of the optical dimensional difference ΔL _I (ΔL _I = L _IX −L _IS ), the formula in parentheses defines the meaning of the sign (ΔL _I ) before the parentheses . Therefore, the process for obtaining the optical size difference [Delta] L _I, limited to the method of calculating the individual values L _IX, the L _IS were measured indirectly optically dimensional differences [Delta] L _I taking the difference in parentheses not, it may be a method of measuring only the optical size difference [Delta] L _I.

In the above-described phase correction value measuring method, the non-contact light wave interference measuring apparatus divides the light irradiated from the light irradiating means having a predetermined beam diameter and wavelength, and the light irradiated from the light irradiating means into two light beams. A first observation for observing the light splitting means, the first interference means and the second interference means having an optical axis coinciding with the measurement axis of the measurement object, and the interference fringes of the first interference means and the second interference means, respectively. Means and second observation means,
One of the two light beams divided by the light splitting unit is incident on the first interference unit, a part of the light beam becomes the first reference light, and the rest of the beam is measured by the first interference unit. Reflected in the measuring axis direction,
The other light beam of the two light beams split by the light splitting unit is incident on the second interference unit, a part of the beam becomes second reference light, and the rest of the beam is measured by the second interference unit. Reflected in the measuring axis direction,
A part of the light reflected from the first interference means in the measuring axis direction of the measurement object is reflected at one end of the measurement object, returns to the first interference means, and overlaps with the first reference light. 1 measurement interference light, the remainder passes by the side of the measurement object, enters the second interference means, and is superimposed on the second reference light to become the second reference interference light,
A part of the light reflected from the second interference means in the measuring axis direction of the measurement object is reflected on the other end surface of the measurement object, returns to the second interference means, and is superimposed on the second reference light. It becomes the second measurement interference light, the remainder passes by the side of the measurement object, enters the first interference part, is superposed on the first reference light and becomes the first reference interference light,
The first observation unit observes the first reference interference light and the first measurement interference light formed by the first interference unit as a first reference interference fringe and a first measurement interference fringe, respectively.
The second observation unit observes the second reference interference light and the second measurement interference light formed by the second interference unit as a second reference interference pattern and a second measurement interference pattern, respectively.
The measurement object based on a phase difference between the first reference interference fringe and the first measurement interference fringe, a phase difference between the second reference interference fringe and the second measurement interference fringe, and a preliminary value of the measurement object It is an apparatus for measuring the optical dimension of an object, and it is preferable that an optical dimension difference between the object to be measured and the reference object is obtained by measurement using the apparatus.

In the phase correction value measuring method, the contact-type comparative measurement uses a jig including a contactor that is in contact with an end face to be measured and a mirror surface that is installed on a non-contact side of the contactor. , The contactors are brought into contact with the opposite end surfaces of the measurement object, and the mirror surface is installed so as to be parallel to the end surface of the measurement object,
Irradiating measurement light to both end surfaces of the measurement object to which the mirror surface is attached, and interference light between reflected light from the mirror surface of one end surface of the measurement object and reference light that is coherent with the reflected light, and The optical dimension between the mirror surfaces is measured based on the reflected light from the mirror surface of the other end surface of the object to be measured and the interference light of the reference light that is coherent with the reflected light, and from the optical dimension between the mirror surfaces. It is preferable to measure a mechanical dimension difference between the object to be measured and the reference object by using a length measuring device for obtaining a mechanical dimension of the object to be measured.
In the phase correction value measuring method, the reference object is formed of a material having a complex refractive index that does not substantially cause a phase change due to an optical constant, and the surface roughness of the surface irradiated with the measurement light of the reference object Is preferably smaller than the wavelength of light used for measurement.

  According to the phase correction value measuring method of the present invention, the phase correction value is obtained from the optical dimensional difference by the non-contact optical interference measurement and the mechanical dimensional difference by the contact-type comparative measurement. The necessary work is unnecessary, and the phase correction value can be measured easily, efficiently and with high accuracy. As a result, the accuracy of the phase correction value can be improved, and the uncertainty of calibration of the edge scale can be reduced.

Hereinafter, preferred embodiments of the present invention will be described.
A phase correction value measurement method according to an embodiment of the present invention includes a step of preparing a measurement object such as a protractor whose phase correction value is unknown and a reference object whose phase correction value is known; A step of measuring an optical dimension difference between an optical dimension and an optical dimension of the reference object by non-contact optical interference measurement, and a mechanical dimension difference between the object to be measured and the reference object and a contact type comparative measurement. And a step of performing. Then, the phase correction value of the object to be measured is calculated based on the measured optical dimensional difference and mechanical dimensional difference.
In the present embodiment, a light wave interference measuring apparatus for measuring an optical dimensional difference is one that measures light in a non-contact manner by irradiating light from both end faces to be measured (see FIG. 3). For example, the apparatuses described in Patent Documents 2 and 3 can be used.

In the present embodiment, as a measurement object and a reference object, a block gauge X (measurement object) of a material whose phase correction value is to be measured and a reference block gauge S (reference object) having the same nominal size are prepared. As shown in FIG. 1, optical dimension measurement is performed by non-contact optical interference measurement. If the optical interference measurement result of the block gauge X at this time is L _IX and the phase change generated on one side of the measurement surface is C _X , the mechanical dimension L _X between the end surfaces of the block gauge _X is
L _X = L _IX + 2C _X (Formula 1)
It becomes. Here, in the non-contact type light wave interference measurement, since the measurement light is reflected on both surfaces of the measurement object, twice the phase change on one side becomes the phase correction value.

Similarly, the reference gauge block S is an optical dimension L _IS, when the phase variation generated in the measurement surface side and C _S, the mechanical dimensions L _S between the end faces,
L _S = L _IS + 2C _S (Formula 2)
It becomes.
Next, as shown in FIG. 2, the measured block gauge and the reference block gauge are compared and measured using a contact-type length measuring device. The dimension difference ΔL between the end faces measured in this way is ΔL = L _X −L _S (Equation 3)
It becomes. In the contact-type comparative measuring instrument, the contact is brought into contact with the end face of the block gauge and the measurement is performed. Therefore, the measured dimension is obtained with the uppermost portion of the roughness curve of the end face as the measurement position. In addition, since the machine dimensional difference is obtained by comparative measurement by comparison with a reference object, a highly accurate value with little error can be obtained.

Therefore, if (Equation 1) and (Equation 2) are substituted into (Equation 3),
ΔL = L _IX -L _IS + 2C _X -2C _S
Solving this for _CX ,
C _X = C _S + ( _LIS− L _IX + ΔL) / 2 (Formula 4)
It becomes. Thereby, if the phase change C _S of the reference block gauge S is known, the phase change C _X generated on one side of the measurement surface of the block gauge _X is obtained by (Equation 4), and this is the phase correction value. That is, when the dimension is measured by the light wave interference measuring instrument, the actual dimension value can be obtained by adding twice the phase change _{CX to} the optical dimension value. Further, when measured by contact-type light wave interference measurement, the measurement light is irradiated only on one surface of the block gauge, so that the actual dimensions can be obtained by adding the above-described phase change _CX. .

  In this way, a reference object with a known phase correction value is prepared, and the dimensional difference is obtained by comparison measurement with the reference object. Therefore, it is possible to obtain the phase correction value with very high accuracy. Since the optical dimensions are measured by close-contact optical interference measurement, ringing is not necessary, and high-accuracy measurement can be easily performed. That is, the present invention enables highly accurate phase correction value measurement by using both measurement results of contact-type comparative measurement and non-contact-type light wave interference measurement.

Further, when measuring the optical dimensional difference, the measurement object and the reference object may be measured separately, or the measurement object and the reference object may be arranged in parallel and simultaneously measured.
Further, it is preferable to use a material having a complex refractive index that does not cause a phase change at the time of reflection due to an optical constant as a reference object. That is, it is only necessary that the imaginary part (absorption coefficient) of the complex refractive index of the material is substantially 0 (to the extent that the measurement accuracy required at that time can be ignored). Specifically, it depends on how much measurement accuracy is required, but it is sufficient if the imaginary part of the complex refractive index is 0.1 or less, more preferably 0.04 or less.

Furthermore, as the surface roughness, it is preferable to use the surface roughness processed so as to be smaller than the wavelength of light used for measurement. That is, the surface roughness may be equal to or less than the standard corresponding to the required measurement accuracy. Specifically, although it depends on the required measurement accuracy, if the maximum peak height Rp of the roughness curve is approximately 10 nm or less, and more preferably less than the first half of an order of magnitude, the shape correction can be performed even with high accuracy measurement. The value can be regarded as 0.
As a material satisfying these conditions, for example, there are optical glass materials such as synthetic quartz and borosilicate glass. When these materials as a reference object S is the phase correction value C _S can be regarded as zero.

The above is the outline of the phase correction value measurement method of the present embodiment. Next, individual dimensional difference measurement steps will be described. FIG. 2 is a schematic configuration diagram of an embodiment of a contact-type comparative measuring instrument.
2 has a configuration in which displacement gauges 212 and 214 are supported on both measurement surface sides of the measurement object. That is, the device under test (block gauge (GB) for measuring the phase correction value) and the reference object (reference block gauge (GB)) are placed on the support base 218 with the length measurement axis vertical. The displacement meter 212 which is supported by the support post 216 is installed on the upper measurement surface of the measurement object, the displacement meter 214 is placed under the support base 21 8 is installed in the lower measurement surface of the measurement object The Contact 222 of the displacement gauge 214, through a hole in the support table 21 8 side, and to be able to contact the front end to the lower measurement surface of the measurement object. Further, the contact 220 of the displacement meter 212 can come into contact with the upper measurement surface of the measurement object. Information on the displacement amounts from the two displacement meters 212 and 214 is sent to the comparator 224, and a mechanical dimensional difference between the two measurement objects can be obtained.

The dimensional difference is measured as follows. First, placed by the measurement axis in the vertical direction on the hole in the reference GB support base 21 8 surface. Next, the contacts 220 and 222 of the displacement meters 212 and 214 are brought into contact with the upper and lower end surfaces of the reference GB with a predetermined measuring force, and the values of the respective displacement meters at this time are set as the origins. Then on the hole in the GB measuring the phase correction value to the support table 21 eight surfaces, placed in a measurement axis in the vertical direction. Then, the contacts 220 and 222 of the displacement meters 212 and 214 are brought into contact with the upper and lower end surfaces of the GB to be measured. The displacement amounts of the displacement meters 212 and 214 are sent to the comparator 224, and the displacement amount from the previously set origin is measured. A mechanical dimensional difference between the reference GB and the GB to be measured is obtained from the displacement amounts of the displacement meters 212 and 214 thus obtained. Further, the measuring force applied to the measurement object by the above-described contact must be sufficiently small so that the deformation of the measurement object can be ignored. The magnitude of the measurement force may be determined in consideration of the material of the measurement object.

In this way, the contact-type comparative measuring device has a contact portion in direct contact with the surface of the object to be measured and the diameter of the contact is sufficiently larger than the surface roughness of the object to be measured. Measurement with the measurement position can be easily realized. In general, a comparative measuring instrument can perform highly accurate measurement by narrowing the measurement range to a narrow range. Therefore, if only the reproducibility of the measurement is limited, a higher reproducibility can be obtained than the light wave interference measurement by ringing, and therefore, a highly accurate comparative measurement can be easily performed.
In laboratories and calibration rooms that own optical wave interference measuring devices, a contact-type measuring device is required as a device for performing preliminary measurement with accuracy within a half of the wavelength of the measuring light in advance. Therefore, it is not a device that requires special preparation.
In FIG. 2, a comparative measuring instrument using a two-point measuring method using two displacement meters has been described, but a comparative measuring instrument using a one-point measuring method having only one displacement meter may be used.

  Next, the non-contact light wave interference measuring apparatus will be described. FIG. 3 is a schematic configuration diagram of an embodiment of the optical interference measurement apparatus. 3 includes a light irradiation unit 312, a first half mirror 314 (light division unit) that divides the emitted light, and a second half mirror 316 (a light separation unit) that is spaced apart by a predetermined distance. First interference means) and third half mirror 318 (second interference means), first reference mirror 320 (first interference means) and second reference mirror 322 corresponding to the second and third half mirrors 316 and 318, respectively. Second interference means), a first screen 324 (first observation means), and a second screen 326 (second observation means). The second half mirror 316 and the third half mirror 318 are arranged so that the optical axis of the measurement light connecting them coincides with the measurement axis of the measurement object 328. In addition, the first screen 324 and the second screen 326 are respectively installed at the subsequent stage of the second and third half mirrors 316 and 318, and interference fringes are formed here. The light irradiation means 312 includes a light source 330, a collimator lens 332, a reflecting mirror 334, and the like, and irradiates laser light having a predetermined beam diameter and wavelength. Since the laser light needs to be reflected by the end face of the object 328 to be measured and to pass through the side of the object to be measured, the beam diameter of the laser light needs to have a certain size. For this reason, it is desirable that the beam diameter is larger than the cross-sectional area of the measurement object.

Further, the set of the first reference mirror 320 and the second half mirror 316 and the set of the second reference mirror 322 and the third half mirror 318 function as interference means for causing the measurement light and the reference light to interfere with each other. The first half mirror 314, the second half mirror 316, and the third half mirror 318 constitute an annular interferometer.
The laser light emitted from the light irradiation means 312 is divided into two light fluxes by the first half mirror 314 and directed to the second half mirror 316 and the third half mirror 318, respectively. The light incident on the second half mirror 316 is divided into light that is reflected in the length measuring axis direction and light that passes through the second half mirror 316 and travels toward the first reference mirror 320. The light directed to the first reference mirror 320 is reflected there, returns to the second half mirror 316, and this light becomes the first reference light. Further, part of the light traveling in the direction of the measuring axis is reflected by the left end surface 328a of the measurement object 328 in the drawing and returns to the second half mirror 316, and the rest passes by the measurement object 328 and passes through the third half mirror. Head to 318.

Similarly, of the two light beams divided by the first half mirror 314, the light incident on the third half mirror 318 is transmitted through the third half mirror 318 and the second reference mirror 322 through the third half mirror 318 and the light reflected in the measurement axis direction. It is divided into the light which goes to. The light directed to the second reference mirror 322 is reflected there, returns to the third half mirror 318, and becomes the second reference light. Further, a part of the light traveling in the length measuring axis direction is reflected by the right end surface 328b of the measurement object 328 in the drawing and returns to the third half mirror 318, and the rest passes through the measurement object 328 and passes through the second half mirror. Head to 316.
In the second half mirror 316, the light that has traveled the optical path as described above interferes with the first reference light coming from the first reference mirror 320 and the light that has passed by the side of the measurement object 328, so that the first reference The light becomes interference light, and the light reflected by the left end surface 328a of the measurement object 328 interferes with the first reference light to become the first measurement interference light. These interference lights travel to the first screen 324, where they are observed as interference fringes, and the phase difference between the first reference interference fringes and the first measurement interference fringes is read.

Similarly, in the third half mirror 318, the light that has passed by the side of the measurement object 328 interferes with the second reference light from the second reference mirror 322 to become the second reference interference light, and the measurement object 328 is obtained. The light reflected by the right end surface 328b of the second reference mirror 322 interferes with the second reference light from the second reference mirror 322 to become second measurement interference light. These interference lights are observed as the second reference interference fringe and the second measurement interference fringe on the second screen 326, respectively, and the phase difference between the reference interference fringe and the measurement interference fringe is read.
As described above, the phase difference between the first reference interference fringe and the first measurement interference fringe observed on the first screen 324 and the second screen 36, respectively, and the positions of the second reference interference fringe and the second measurement interference fringe. Based on the phase difference and the preliminary value of the measurement object, the optical dimension L _B of the measurement object is measured.

FIG. 5A is an explanatory diagram of the calculation of the phase difference from the interference fringes. GB in the figure schematically shows the end face of the measurement object, and the portion surrounded by a circle in the figure schematically shows the measurement light beam. From average values of phases Φ _A and Φ _C obtained from reference interference fringes (not shown) at both sides of the measurement object and measurement interference fringes (not shown) at points on the end face of the measurement object by calculating the difference between the obtained phase [Phi _B, it is possible to obtain the phase difference between the reference interference fringe and the measured interference fringe.

Calculation of the dimension from the phase difference of the interference fringes obtained above will be described with reference to FIG. From the first half mirror 314 to the second half mirror 316, further reflected by the left end in the drawing surface 328a of the workpiece 328, the optical path length of the optical path and _{L 1} back to the second half mirror 316 again. Further, from the first half mirror 314 toward the third half mirror 318, where the optical path length to be reflected to enter the second half mirror 316 through the side of the object to be measured 328 and L _2. Similarly, the optical path length L ₃ is an optical path length that travels to the first half mirror 314, the third half mirror 318, the right end surface 328 b of the DUT 42, and the third half mirror 318. The optical path length L ₄ is an optical path length from the first half mirror 314 to the second half mirror 316, reflected there, passing through the side of the measured object 328, and entering the third half mirror 318.

Then dimension _{L B} of the measurement object by using the above-mentioned optical path length _{L 1, L 2, L 3} , L 4 is represented by the following formula.
L _B = 1/2 {(L ₄ −L ₃ ) + (L ₂ −L ₁ )} (Formula 5)
The above optical path lengths L ₁ , L ₂ , L ₃ , and L ₄ are expressed as follows using the wavelength λ of the laser light used for measurement.
L _i = λ (N _i + ε _i ) (i = 1 to 4) (Expression 6)
Here, N _i is the integer part of the quotient when the optical path length L _i is divided by the wavelength λ, and ε _i is the fractional part (phase) of the quotient. Substituting (Equation 6) into (Equation 5), L _B = λ / 2 {(N ₄ −N ₃ ) + (N ₂ −N ₁ ) + (ε ₄ −ε ₃ ) + (ε ₂ −ε ₁ ) }
= Λ / 2 {N + (ε ₄ −ε ₃ ) + (ε ₂ −ε ₁ )} (Expression 7)
It becomes. However, N = (N ₄ −N ₃ ) + (N ₂ −N ₁ ).
(Ε ₂ −ε ₁ ) in the above equation is the phase difference between the first reference interference fringe and the first measurement interference fringe observed on the first screen 324, and (ε ₄ −ε ₃ ) is the second screen 326. Is the phase difference between the second reference interference fringe and the second measurement interference fringe observed in FIG. The wavelength λ are known, the dimension L _B of the measurement object from using N calculated from the pre-value and the wavelength λ of the measurement object (7) is determined.

A first reading unit 336 is provided at the subsequent stage of the first screen 326. The first reading unit 336 reads the phase difference (ε ₂ −ε ₁ ) between the first reference interference fringe and the first measurement interference fringe observed on the first screen, and the reading result is stored in the measurement data of the computer 340. Stored in the unit 344. Similarly, a second reading unit 338 is provided at the subsequent stage of the second screen 326 to read the phase difference between the second reference interference fringe and the second measurement interference fringe observed on the second screen 326. The read result is similarly stored in the measurement data storage unit 344. Then, the optical means of the measurement object is calculated from the phase difference information by the computing means 342 of the computer 340. In addition, the computer 340 includes a calculation information storage unit 346, and preliminarily stores information on a preliminary value of a measurement object such as a block gauge, a program for calculating a dimension from a phase difference, and the like.

Using the non-contact light wave measuring apparatus configured as described above, the above-described measurement is performed on an object whose phase correction value is unknown, and its optical dimension is measured. Similarly, the same measurement is performed on a reference object whose phase correction value is known, and the optical dimension is measured. And from each measurement result, the optical dimensional difference of a to-be-measured object and a reference | standard thing is calculated | required.
Also, when measuring the optical dimensions, the optical dimension of the object to be measured and the optical dimension of the reference object may be measured separately in order, or the object to be measured and the reference object are arranged in parallel and measured simultaneously. May be performed. That is, the object to be measured and the reference object are arranged in parallel so that the light from the second half mirror 316 and the third half mirror 318 is irradiated to both the end faces of the object to be measured and both end faces of the reference object. Install. Further, the object to be measured and the reference object are arranged apart so that light can pass between the object to be measured and the reference object. With reference to FIG. 5B, calculation of the phase difference when arranged in parallel will be described. The two squares in the figure schematically show the end face of the object to be measured (GB1 in the figure) and the end face of the reference object (GB2), and the circle schematically shows the portion of the measurement light beam. The calculation of the phase difference from the interference fringes (not shown) may be performed in the same manner as in the case where there is one measurement object (in the case of FIG. 5A). That is, the phase difference between the reference interference fringe and the measurement interference fringe in GB1 is obtained by the difference between the average value of the phases Φ _A and Φ _C at the points on both sides of GB1 and the phase Φ _B at the point on the end face of GB1. . The phase [Phi _C in terms of both sides of the GB2 in the same _manner, the difference between the phase [Phi _D at the end face of the mean and GB2 of [Phi _E, obtains the phase difference of the interference fringes in GB2. The optical dimensions of GB1 and GB2 can be obtained from these phase differences, and the optical dimension difference between GB1 and GB2 is calculated from them.

FIG. 4 shows another embodiment of the contact type comparative measurement. FIG. 4 shows contacts 412 and 414 brought into contact with the end face to be measured, mirror surfaces 416 and 418 installed on the non-contact side of the contacts 412 and 414, and a support part 420 for fixing the contacts 412 and 414. The jig | tool 410 provided with these is shown. Using the jig 410, the contacts 412 and 414 are brought into contact with the opposing end surfaces of the measurement object with a predetermined contact force and fixed. The mirror surfaces 416 and 418 provided on the contacts 412 and 414 are installed such that their reflection surfaces are parallel to the end surface of the measurement object. The material constituting the mirror surface is a material whose phase correction value is known or a material whose phase correction value is almost zero.
Using such a jig 410, the mechanical dimension of the measurement object can be measured using the non-contact optical interference measuring apparatus as described in FIG.

  That is, the jig 410 is attached to an object to be measured whose phase correction value is unknown and a reference object whose phase correction value is known. The dimension between the mirror surfaces is measured by the non-contact light wave interference device with respect to the object to be measured and the reference object to which the jig is attached. That is, the mirror surfaces 416 and 418 attached to the non-contact side of the contacts 412 and 414 become measurement surfaces on which measurement light irradiated by the non-contact light wave measuring device is incident. Since mirror surfaces with known phase correction values are used, the distance between the mirror surfaces can be accurately obtained. Therefore, the mechanical dimension of the measurement object sandwiched between the contacts is measured using the measurement result of the dimension between the mirror surfaces. By taking the difference between the mechanical dimension of the object to be measured thus obtained and the mechanical dimension of the reference object, the mechanical dimension difference can be obtained.

Illustration of non-contact optical interference measurement Explanatory drawing of one embodiment of a contact type comparative measuring instrument Schematic configuration diagram of an embodiment of a non-contact light wave measuring device Schematic configuration diagram of an embodiment of a light wave interference measurement jig for contact measurement Explanatory drawing of calculation of phase difference between reference interference fringe and measurement interference fringe Explanatory diagram of phase change during reflection due to surface roughness and optical constants Explanatory drawing of conventional phase correction value measurement method

Explanation of symbols

210 Contact-type comparative measuring device 310 Non-contact light wave interference measuring device 410 Light wave interference measuring jig

Claims (4)

The light is divided into two coherent light beams, one is the reference light, the other is the measurement light, the measurement light is irradiated to the measurement object, and the measurement object is opposed to each other based on the interference between the reflected light and the reference light In the phase correction value measurement method for obtaining the phase change amount at the time of reflection of the measurement light in the light wave interference measurement for measuring the dimension between the end faces,
Preparing a measurement object whose phase change C _X is unknown and a reference object whose phase change C _S is known;
Irradiate measurement light to both opposite end surfaces of the measurement object to be dimensioned, interference between the reflected light from one end surface of the measurement object and the reference light, and the other of the measurement object Using a non-contact optical interference measuring apparatus that measures the optical dimension of the measurement object based on the interference between the reflected light from the end surface and the reference light, the optical dimension L _{IX of the} object to be measured and the reference Determining an optical dimension difference ΔL _I (ΔL _I = L _{I X} −L _{I S} ) which is a difference from the optical dimension L _IS of the object;
A contact-type length measuring device that contacts a contact surface with an end surface of a measurement object to be dimensioned and measures a mechanical dimension between opposing end surfaces of the measurement object based on a contact position of the contact device. And obtaining a mechanical dimension difference ΔL (ΔL = L _X −L _S ) , which is a difference between the mechanical dimension L _{X of the} object to be measured and the mechanical dimension L _S of the reference object, by contact-type comparative measurement When,
Said optical dimensional difference [Delta] L _I, the mechanical dimensions difference [Delta] L, and the phase change amount C _X the following equation of the object to be measured from the phase variation amount C _S of the reference object,
_{C X = C S + ΔL /} 2 -ΔL I / 2
The process sought by
A phase correction value measuring method comprising: In the phase correction value measuring method according to claim 1,
The non-contact light wave interference measuring apparatus includes a light irradiating unit that irradiates light having a predetermined beam diameter and wavelength, a light dividing unit that divides light emitted from the light irradiating unit into two light beams, and a measurement object. First interference means and second interference means having optical axes that coincide with the measurement axis, and first observation means and second observation means for observing interference fringes of the first interference means and the second interference means, respectively. Prepared,
One of the two light beams divided by the light splitting unit is incident on the first interference unit, a part of the light beam becomes the first reference light, and the rest of the beam is measured by the first interference unit. Reflected in the measuring axis direction,
The other light beam of the two light beams split by the light splitting unit is incident on the second interference unit, a part of the beam becomes second reference light, and the rest of the beam is measured by the second interference unit. Reflected in the measuring axis direction,
A part of the light reflected from the first interference means in the measuring axis direction of the measurement object is reflected at one end of the measurement object, returns to the first interference means, and overlaps with the first reference light. 1 measurement interference light, the remainder passes by the side of the measurement object, enters the second interference means, and is superimposed on the second reference light to become the second reference interference light,
A part of the light reflected from the second interference means in the measuring axis direction of the measurement object is reflected on the other end surface of the measurement object, returns to the second interference means, and is superimposed on the second reference light. It becomes the second measurement interference light, the remainder passes by the side of the measurement object, enters the first interference part, is superposed on the first reference light and becomes the first reference interference light,
The first observation unit observes the first reference interference light and the first measurement interference light formed by the first interference unit as a first reference interference fringe and a first measurement interference fringe, respectively.
The second observation unit observes the second reference interference light and the second measurement interference light formed by the second interference unit as a second reference interference pattern and a second measurement interference pattern, respectively.
The measurement object based on a phase difference between the first reference interference fringe and the first measurement interference fringe, a phase difference between the second reference interference fringe and the second measurement interference fringe, and a preliminary value of the measurement object An apparatus for measuring an optical dimension of an object, wherein a difference in optical dimension between the object to be measured and the reference object is obtained by measurement using the apparatus. In the phase correction value measuring method according to claim 1 or 2,
The contact-type comparative measurement uses a jig provided with a contactor to be brought into contact with an end surface to be measured and a mirror surface placed on the non-contact side of the contactor, and the contact-type comparative measurement is performed on the opposite end surfaces of the measurement object. Contact each contact, set the mirror surface parallel to the end surface of the measurement object,
Irradiating measurement light to both end surfaces of the measurement object to which the mirror surface is attached, and interference light between reflected light from the mirror surface of one end surface of the measurement object and reference light that is coherent with the reflected light, and The optical dimension between the mirror surfaces is measured based on the reflected light from the mirror surface of the other end surface of the object to be measured and the interference light of the reference light that is coherent with the reflected light, and from the optical dimension between the mirror surfaces. A phase correction value measuring method, comprising: measuring a mechanical dimension difference between the object to be measured and the reference object using a length measuring device that obtains a mechanical dimension of the object to be measured. In the phase correction value measuring method according to claims 1 to 3,
The reference object is formed of a material having a complex refractive index that does not substantially cause a phase change due to an optical constant, and the surface roughness of the surface irradiated with the measurement light of the reference object is smaller than the wavelength of light used for measurement. A method of measuring a phase correction value.

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