JP2012154765A - Optical measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high accuracy optical measurement device by suppressing the influence of a variety of noise components included in a phase shift image in a height measurement device using an interference fringe by a phase shift method.SOLUTION: A relation between the height of the measuring plane of a measuring object and the phase of the part in which the brightness of each point in an interference fringe image varies by the light having a plurality of different wavelengths according to the height of the measuring plane is mathematically formulated into a predetermined computing equation. The combination of the height of the measuring plane of the measuring object and the phase of the part in which the brightness of each point in an interference fringe image varies by the light having a plurality of different wavelengths according to the height of the measuring plane is calculated based on the mathematically formulated predetermined computing equation. The phase information obtained by the calculation is reflected to a phase code conversion table. Then, the height of the measuring plane of the measuring object can be measured.

Description

  The present invention is an optical measurement that uses monochromatic light with different wavelengths to measure the height of, for example, semiconductor wafers, liquid crystal displays, glass substrates, surface textures of machine parts, step surfaces of minute objects such as metal films, etc. It relates to the configuration of the apparatus.

  Now, for example, FIG. 5 shows an example of the configuration of an optical measuring device for measuring the height of a stepped surface or the like of such a conventional minute object. This optical measuring device includes first, second, and third light generating means L1, L2, and L3 that generate a plurality of light beams having different wavelengths (for example, R, G, and B), First, second, and third narrowband filters F1, F2, and F3 for branching and selecting light of each wavelength from the third light generating means for each wavelength, and the first, second, and third The light branched through the narrow-band filters F1, F2, and F3 are merged in a predetermined direction, and the two lights, the irradiation light to the measurement surface of the measurement object W and the reference light to the reference mirror MR The first, second, third, and fourth beam splitters B1, B2, B3, and B4 that irradiate the light separately, the reference mirror RM that forms the reference light, and the reference mirror RM are rotated in both the left and right directions. Rotation driving means D, measurement object W, and measurement object W are finely moved by a predetermined amount in the optical axis direction. It incorporates a nanostage ST that moves slightly to change the optical path length, and a narrow band filter for selecting and shooting an interference image by light of each wavelength whose optical path length has been changed by the nanostage ST for each wavelength. An imaging means (camera) CAM such as a CCD is provided.

  The R, G, and B wavelengths emitted from the first, second, and third light generating means L1, L2, and L3 are the first, second, and third narrowband filters F1, After being accurately branched for each wavelength via F2 and F3, the light beams are first reflected by the first, second, and third beam splitters B1, B2, and B3 toward the fourth beam splitter B4, respectively. The beam splitter B4 portion irradiates the measurement object W by being divided into two lights, that is, irradiation light to the measurement object W and reference light to the reference mirror RM.

  Then, the reflected light from the measurement object W and the reflected light from the reference mirror RM are input again to the imaging unit CAM while forming an interference image again at the fourth beam splitter B4 part, and the wavelength thereof. By capturing the interference image of the child, an interference image for each wavelength is observed.

  That is, when the above-mentioned nanometer stage ST is slightly moved in the optical axis direction in units of several nanometers, and the optical path length is changed for each desired predetermined distance (ΔL), the measurement object installed on the nanometer stage ST Since the optical path length between the reflected light from the measurement surface of the object W and the reference light is different and the interference state is changed, the brightness of the formed interference image changes in a sine wave shape. This is because if the difference in optical path length changes by one wavelength of the first, second, and third light generating means L1, L2, and L3, the brightness of the image changes by one period of each wavelength. It can be recorded as.

  Now, for example, as a unit of movement (ΔL) when the nanometer stage ST is moved by a predetermined distance in the optical axis direction, a unit wavelength that is a divisor of the wavelength of light (for example, 5 nm, 10 nm, etc. if the wavelength is 660 nm) ) Is selected, and the change in brightness of light of each wavelength is obtained for each unit amount (unit wavelength ΔL), the phase of brightness change for each unit amount (unit wavelength ΔL) is recorded as shown in FIG. Can do.

  In addition, when a sample having a stepped surface is used as the measurement object W as shown in FIG. 7, the difference in the optical path length differs depending on the location according to the unevenness of the surface of the measurement object W, so the brightness in the interference image The distribution of change differs for each pixel, and the difference in brightness for each pixel corresponds to the brightness change amount for each unit amount (unit wavelength ΔL) when the nanometer stage ST is moved in the optical axis direction. To do.

  That is, as shown in FIG. 6, if the phase of the brightness change for each unit amount (unit wavelength ΔL) is obtained and recorded in advance, the brightness change for each pixel in the interference image can be expressed as “one cycle unit”. The ratio of the number of measurements per unit quantity relative to the quantity (unit wavelength ΔL) ”is derived, and the relative height H between the pixels is obtained by integrating the“ ratio of the number of measurements ”and the“ unit quantity (unit wavelength ΔL) ”. be able to.

  By the way, as can be seen from FIG. 6, since the sine wave-like brightness change is restored in one period of the wavelength, only the light source of one wavelength is expressed as an interference fringe only up to a height at which the difference in optical path length is equivalent to one wavelength. Can not. Further, as can be seen from the configuration of the measuring apparatus shown in FIG. 5, the difference in optical path length occurs between round trips of the distance from the fourth beam splitter B4 to the measurement object W, so that the difference in optical path length is one wavelength. The minute height, that is, the height H that can be measured at one wavelength is half the wavelength of the light source (λ / 2).

  Thus, the height H that can be measured with a light source of one wavelength is limited to half the wavelength of the light source (λ / 2), and which part of the measuring object W protrudes with only one interference image. Alternatively, it is impossible to determine whether it is recessed, and only the relative height between the pixels can be determined.

  Therefore, in the measurement apparatus of FIG. 5, a plurality of light sources having different wavelengths are used, and the phase is shifted as shown in FIG. In this way, since the period of the brightness change due to the difference in the optical path length depends on each wavelength, when observing several periods of interference fringes within the coherent distance, half of each light source wavelength (λ / 2) The brightness change repeated in step) is repeated with a slight shift depending on the wavelength.

  That is, as shown in FIG. 9, even if one wavelength ends one cycle and returns to the origin, the other wavelengths are still in the middle of change. It is possible to record the brightness change and the phase shift amount at a distance much longer than the measurement distance in the case of the wavelength.

  For example, as shown in FIG. 10, the deviation of the brightness change of the interference fringes of each wavelength appearing within the coherent distance is regarded as a combination of brightness for each unit amount (unit wavelength ΔL), and the light source (wavelength) 1 And the light source (wavelength) 2 brightness change combination as a phase code conversion table, the brightness change of each wavelength can be divided with a resolution finer than λ / 2, and any light source This means that measurement at a distance larger than one wavelength is possible.

  For example, as shown in FIG. 10, when the light source 1 is evaluated in five levels 0-4 for the light source 1 and four levels 0-3 for the light source 2, the number of combinations is 20 as shown in FIG. It becomes a kind. This means that the distance that can be measured increases by four times for the light source 1 and five times for the light source 2 compared to the height that can be measured at a single wavelength.

  If these two wavelengths are used to list values until the same combination of brightness changes appears again, for example, a phase code conversion table as shown in FIG. 11 is obtained. 11 is created in the case of two wavelengths as an example for the sake of simplicity, but a three-dimensional structure is obtained by using the light of the three wavelengths in FIG. 5 described above.

  In order to perform height measurement using such a phase code conversion table, the unit quantity (unit wavelength ΔL) is set in the direction of the optical axis by using the measurement apparatus of FIG. 5 described above. The interference fringe image of the measuring object W having the step as shown in FIG. 7 described above is captured while moving each time to change the brightness of the interference fringes, or the reference mirror RM of the measurement apparatus of FIG. By deliberately tilting and capturing an interference fringe image in which the brightness of the interference fringes is changed by providing a difference in the optical path length of the reflected light between the reference mirror RM and the measurement object W, for each pixel position If a combination of phases of interference fringes of a plurality of wavelengths is obtained and the phase code conversion table of each wavelength is referred to using them as parameters, the desired height H can be calculated (Patent Documents 1 and 2). See).

Japanese Patent Application No. 2009-028723 (Details and drawings of application filed on Feb. 10, 2009) Japanese Patent Application No. 2007-219054 (details and drawings of application filed on August 24, 2007)

  However, in the case of the conventional measuring apparatus as described above, since image data must be prepared in advance as described above, noise (for example, vibration, thermal noise of the camera, etc.) is included at the time of image acquisition. There is a problem.

  That is, in order to create the phase code conversion table shown in FIG. 11, a plurality of phase shift images or the reference mirror RM is intentionally tilted as described above, and the reflected light from the reference mirror RM and the measurement object W is reflected. Although it is necessary to prepare an interference fringe image in which the brightness of the interference fringe is changed by providing a difference in the optical path, various noise components are included for the following reasons.

  For example, when creating a phase code conversion table from combinations of brightness variations of interference fringes at a plurality of wavelengths, the nanometer stage ST is moved for each unit amount (unit wavelength ΔL), and the brightness obtained at that time is obtained. The code table was created by making the combination of changes corresponding to the shift amount (= height = unit wavelength × number of measurements). In that case, positional deviation due to hysteresis of the nanometer stage ST and vibration at the time of driving the nanometer stage ST Such noise components are included in the image information.

  In addition, thermal noise and shot noise peculiar to an imaging camera such as a CCD are randomly generated during acquisition of a plurality of images, so that there may be a difference in phase information between images.

  Another problem is that the wavelength of the measurement light is not a good numerical value.

  For example, the light source wavelength for generating interference fringes rarely has a good value such as 450 nm and 600 nm, tends to be a fraction such as 453 nm and 667 nm, and is inherently affected by other optical components. It may deviate from the assumed wavelength range. Therefore, even if the nanometer stage ST can be moved for each unit amount (unit wavelength ΔL), the brightness change due to the phase shift due to the vertical movement of the nanometer stage ST in FIG. A code table cannot be created by dividing a physical unit amount (for example, a common divisor such as 5 nm or 10 nm for 450 nm and 600 nm), and the axial direction data of the code table is inconsistent with the light source wavelength. It becomes impossible to arrange the height information regularly.

  Furthermore, in order to make it easy to divide by a physical unit quantity such as wavelength [nm], even if an approximate quantity is set, for example, 453 nm → 450 nm, 607 nm → 605 nm, the height data between codes is not effective. As matching occurs and the error is accumulated due to the influence of mismatch between codes as the height of the measurement object increases, for example, correction work as shown in Patent Document 2 is separately performed. Need to accompany it.

  The present invention has been made in order to solve such a problem, and each point in the image of the interference fringe image by the light of a plurality of different wavelengths according to the height of the step surface and the height of the step surface. The relationship between the phase of the part where the brightness changes is expressed numerically, and the brightness of each point in the image of the interference fringe image due to the light of a plurality of different wavelengths according to the height of the step surface and the like is determined. By combining the phase of the changing part with the phase division method that reflects the phase information obtained by the calculation based on the formula, the height of the minute object can be obtained without causing the above problems. It is an object of the present invention to provide an optical measuring device capable of accurately measuring the above.

  In order to achieve the same object, the present invention is configured with the following problem solving means.

(1) Invention of Claim 1 The problem-solving means of the present invention includes a light generating means for generating a plurality of lights having different wavelengths, and a light emitted from the light generating means is branched into the light having a plurality of wavelengths. Interference fringe generating means for generating interference fringes corresponding to the differences in the optical path lengths after passing through separate optical paths having different optical path lengths, and imaging for picking up the interference fringes generated by the interference fringe generating means Means, image analysis means for analyzing the relationship between the brightness change and the phase for each wavelength of the light from the interference fringe image obtained by the imaging means, and interference fringes according to the height of the measurement surface of the measurement object The phase of the portion where the brightness of each point in the image changes is obtained for each of a plurality of different wavelengths of the light, and is obtained by the phase code conversion table combining the height and phase of the measurement surface and the image analysis means. Parameter with phase information An optical measurement apparatus comprising a height calculating means for obtaining the height of the measurement surface of the measurement object by referring to the phase code conversion table, the measurement surface of the measurement object The relationship between the height of the light and the phase of the portion where the brightness of each point in the interference fringe image due to a plurality of different wavelengths of light according to the height of the measurement surface changes is formulated into a predetermined arithmetic expression, and The combination of the height of the measurement surface of the object to be measured and the phase of the portion where the brightness of each point in the interference fringe image changes due to the light of the plurality of different wavelengths according to the height of the measurement surface The height of the measurement surface of the measurement object is measured by calculating based on the predetermined calculation formula and reflecting the phase information obtained by this calculation in the phase code conversion table. Yes.

  In the above configuration, as in the prior art, the phase code conversion table is based on an image obtained by using a unit amount representing a combination of brightness change and phase as a unit amount when the nanometer stage ST is moved in the optical axis direction. The phase of the portion in which the brightness of each point in the interference fringe image changes due to the light of a plurality of different wavelengths according to the height of the measurement surface of the measurement object and the height of the measurement surface. And the brightness of each point in the interference fringe image due to the light of the plurality of different wavelengths according to the height of the measurement surface of the measurement object and the height of the measurement surface. The combination with the phase of the portion whose length changes is calculated based on a predetermined arithmetic expression expressed in the same formula, and the phase information obtained by this calculation is reflected in the phase code conversion table, thereby the measurement object. Measure the height of the measurement surface It is way.

  Therefore, if the center wavelength of the light source is acquired as data in advance by a spectroscope or the like, it can be obtained by interference of light from a plurality of light sources having different wavelengths within a range where height measurement can be obtained by calculation. The relationship (combination) between the phase change and the height of the interference fringes can be recorded as a code conversion table. Therefore, the position is shifted by the nanometer stage for shifting the phase, and the vibration is generated when driving the nanometer stage. Problems caused by noise or noise peculiar to imaging cameras such as CCDs, data mismatch in the phase code conversion table due to misalignment of center wavelengths of multiple light sources, or separate correction work corresponding to misalignment of center wavelengths of multiple light sources Can be eliminated.

  In the conventional method, as described above, by deliberately tilting the plurality of phase-shifted images or the reference mirror RM, a difference is made in the optical path of the reflected light between the reference mirror RM and the measurement object W, and the brightness of the interference fringes Since various noise components are included in the created phase code conversion table while preparing a plurality of interference fringe images with different values, interference images with light of multiple wavelengths (R, G, B) are included. Even if it is converted into height data, the calculation result is inaccurate as shown in the image of FIG. 3 described later.

  On the other hand, according to the present invention, the height of the step surface and the phase of the portion where the brightness of each point in the image of the interference fringe image due to the light of a plurality of different wavelengths according to the height of the step surface changes. The relationship is accurately reflected, and the surface shape can be expressed with high accuracy as shown in FIG.

(2) Invention of Claim 2 The problem solving means of the present invention corresponds to the change in brightness of light at each point in the interference image based on a predetermined arithmetic expression in the configuration of the problem solving means of the invention of Claim 1 above. The calculation of the phase information is characterized in that the center wavelength of each light from the preliminary light generating means is acquired and set as data, and is calculated based on the center wavelength of the acquired light. .

  In the case of such a configuration, as described above, if the center wavelength of the light from the generating means, which is a light source, is acquired as data in advance, for example, by a spectroscope, the height measurement can be obtained by calculation. The relationship (combination) between the phase change (shift amount) and height of interference fringes obtained by interference of light from a plurality of light sources having different wavelengths can be accurately recorded as a phase code conversion table. Phase code conversion table data due to position shift due to nanometer stage to shift phase, noise due to vibration when driving nanometer stage, noise peculiar to imaging cameras such as CCD, and center wavelength shift of multiple light sources It is possible to solve problems caused by inconsistency or separate correction work corresponding to the center wavelength shift of the plurality of light sources. Kill.

  As a result, according to the present invention, the above-described problems of the conventional optical measuring device can be solved almost certainly.

Phase shift amounts and interference fringe colors in the process of creating a phase code conversion table of an optical measuring device such as the height of a minute object using interference images of light (RGB) of a plurality of wavelengths according to an embodiment of the present invention It is a figure which shows the relationship with a period (figure which normalized the data height of FIG. 9 mentioned later). Wavelength 1 code and wavelength 2 code in the process of creating a phase code conversion table of an optical measurement device such as the height of a minute object using interference images of light (RGB) of a plurality of wavelengths according to an embodiment of the present invention FIG. 5 is a diagram (a diagram illustrating an order of storing height data). In the figure, 0 to 7 represent the order in which the arrangement of the indexes for storing the height data obtained from the combination of the interference fringe brightness change phases changes according to the combination of phases. This is an image in which the height of a measurement object is calculated from a conventional interference image using a plurality of wavelengths of light (RGB) and the height data is expressed in gray scale. In the height conversion from the phase combination obtained from the interference image, the phase code conversion table before improvement created in the conventional example (wavelength base) is used. In addition, the same interference image by the light (RGB) of a some wavelength is used as FIG. It is the image which calculated the height of the measuring object from the interference image by the light (RGB) of a plurality of wavelengths concerning an embodiment of the invention in this application, and expressed height data in gray scale. In the height conversion from the phase combination obtained from the interference image, the improved phase code conversion table created in the present invention (phase base) is used, and the improvement improvement effect is shown. In addition, the same interference image by the light (RGB) of a some wavelength is used as FIG. It is a figure which shows the structure (common) of the optical measuring device using the interference image of the light based on the prior art which this invention presupposes. It is explanatory drawing which shows the brightness change (sine wave-like change) of the measurement image by the change of the interference state of the reflected light from a measurement target object and the reference light with respect to the change of the optical path length in the same apparatus. It is explanatory drawing which shows that the difference of the height of a measurement object can be measured from phase difference (DELTA) (theta) corresponding to the brightness change (sine wave-like change) of the measurement image in the same apparatus. It is a sine waveform figure which shows the relationship between the phase shift amount of the light of each wavelength in the same apparatus, and the brightness of an interference fringe. Explanatory diagram showing that measurement of wavelength or more can be performed by combining multiple laser beams, because the brightness change due to the optical path length variation of multiple laser beams in the same device is determined by the wavelength of the laser beam (phase shift amount and interference fringes) FIG. 4 is a diagram showing a relationship with a period of each color. Description of an encoding method in the case where the optical path length is moved for each ΔL in the same apparatus, and the phase θ of the sine wave of the brightness change is coded for each ΔL, and the length of one wavelength or more is measured by the combination of the codes. FIG. It is a figure which shows the structure of the phase code-height conversion table which converts the phase code into height in the same apparatus.

  Next, the form for implementing this invention is demonstrated in detail with reference to FIGS.

  First, FIG. 1 is a diagram showing the relationship between the phase shift amount (height) and the period of each color of interference fringes in the process of creating the phase code conversion table of the optical measuring device according to the embodiment of the present invention (in FIG. 9 described above). (The figure which normalized the data height for every light source).

  FIG. 2 is a diagram showing the relationship between the wavelength 1 code and the wavelength 2 code in the phase code conversion table creation process of the optical measurement apparatus of the present embodiment (a diagram showing the order in which the height data is stored). It is.

  In the figure, 0 to 7 represent the order in which the arrangement of the indexes for storing the height data obtained from the combination of the interference fringe brightness change phases changes according to the combination of phases.

  In addition, FIG. 3 employs a conventional wavelength division phase code conversion table to calculate the height of the measurement object from interference images of light (RGB) of a plurality of wavelengths, and the same height data is converted to gray scale. FIG.

  Further, FIG. 4 calculates the height of the measurement object from the interference image by the light (RGB) of a plurality of wavelengths according to the embodiment of the present invention, which employs the phase code conversion table of the phase division method, It is a measurement surface image figure which expressed thickness data in gray scale.

  FIG. 5 is a diagram showing a configuration (common) of an optical measurement apparatus using an optical interference image according to the above-described conventional example on which the present invention is based.

  In the case of this embodiment, it is exactly the same as the conventional example in that the apparatus configuration of FIG. 5 described above is used, but the unit amount representing the combination of the brightness change and the phase is changed to the nanometer stage ST as the conventional example. Rather than creating a phase code conversion table based on an image acquired as a unit amount when moving in the axial direction, the first, second, and third light generating means L1 to L3 that are the preliminary light sources are used. The center wavelength of light is acquired as data, and based on the acquired center wavelength of each light source, the equations (1) to (5) 5) Based on the unit amount (unit phase θ) included therein, the phase information of the brightness (brightness) change of the interference fringes is calculated, and this phase information is reflected in the phase code conversion table of FIG. It is characterized by that.

  That is, in this embodiment, first, changes in the brightness of the interference fringes (luminance) by the light sources (R, G, B) of the three wavelengths of the first, second, and third light generating means L1 to L3 in FIG. The formula corresponding to (change) is set to the above (1) to (5), and a code table is created by the following procedures [1] to [5].

  Among these formulas (1) to (5), formula (1) represents a range in which height measurement is possible, and formulas (2) to (4) represent the above-described first, second, and third. This is a height (phase shift amount) calculation formula corresponding to the wavelengths of the RGB light sources of the light generating means L1 to L3, and shows the relationship between the height H appearing as a stripe and the phase θ. Furthermore, since the height of the measurement surface such as the stepped surface of the measurement object W should be the same regardless of the wavelengths of R, G, and B, the equation (5) should be equal to the above ( It shows that the difference in height for each wavelength of R, G and B calculated in 2) to (4) is minimized (theoretically zero).

  [1] First, the central wavelength (λ) and the full width at half maximum (Δλ) of the three types of light source wavelengths of R, G, and B are obtained, and the center wavelength of each light source R, G, and B is calculated based on the above formula (1). The measurable range (measurement range L) of the unit amount (unit phase θ) is calculated.

  Then, all combinations of variables i, j, and k in equations (2) to (4) are obtained. This represents a combination of the unit phases θ when the phase difference exceeds one wavelength, and the height of the light source wavelength according to the height H of the measurement object W exceeds the height even when the phase change exceeds one wavelength. This corresponds to checking the combination of indexes such that the data fits in the phase code conversion table of FIG.

  [2] Subsequently, for each combination of the variables i, j, and k obtained previously, the unit amount (unit phase) in the arithmetic expressions (2) to (4) corresponding to the wavelengths of the R, G, and B light sources. θ ... The unit is [rad], which corresponds to the index of the phase code conversion table in FIG.

  These formulas (2) to (4) indicate that the combination of unit quantities is a combination of unit phases θ when the phase difference is one wavelength or less, and interference fringes due to multiple R, G, and B light sources. This is equivalent to creating an index in which all combinations of phases fall within the phase code conversion table of FIG. 11 as the amount of change within one wavelength.

  For example, when the phase code conversion table of FIG. 11 is created by dividing one cycle (360 [rad]) of brightness (brightness) change of interference fringes by each wavelength in units of phase 5 [rad], it corresponds to each wavelength. 72 [pieces] (= 360 [rad] ÷ 5 [rad]). For example, if light sources having two wavelengths are used, the phase combination in that case is 72 × 72 = There are 5,184 ways.

  [3] Therefore, the combination of unit phases θ calculated in advance is substituted into the above formulas (2) to (4), and the combination of variables i, j, k indicating the order (number) in the cycle is changed Then, the heights HR, HG, and HB corresponding to the R, G, and B wavelengths are calculated (however, the variables i, j, and k are selected from the measurement range range of Equation (1)).

  Here, HR, HG, and HB are heights (phase shift amounts) calculated from three different wavelengths of R, G, and B, λ is each of the three wavelengths of the R, G, and B light sources, and θ is the same. The phase amount of the change in brightness (luminance value) of the interference fringes obtained from each wavelength λ is represented, and i, j, and k represent constant terms (0, 1, 2, 3,...) Including zero.

  [4] Subsequently, based on the above formula (5), a combination that minimizes the difference in height HR, HG, HB corresponding to each wavelength of R, G, B is obtained.

  This represents a combination of unit phases θi, θj, and θk when the phase difference exceeds one wavelength, and R, G, and B light source wavelengths corresponding to the height H of the step surface of the measuring object W are shown. Even when the phase change exceeds one wavelength, this corresponds to checking an index combination in which the height data fits in the phase code conversion table of FIG.

  [5] Then, the average values of the heights HR, HG, HB when the differences in the heights HR, HG, HB are the smallest are obtained and stored in the corresponding index.

  In this way, when the detection height H is stored according to the combination of phases of the interference fringe brightness change, the phase code value shifts from 0 to 1 as shown in FIG. If it changes by one wavelength, it jumps from 1 to 2, then moves from 2 to 3, then if wavelength 2 changes by one wavelength, it jumps from 3 to 4 and then moves from 4 to 5 Is repeated up to the applicable range (within the range of the measurement range L).

  In the case of such a configuration, for example, if the center wavelengths of the light sources having the three wavelengths R, G, and B are acquired in advance by a spectroscope or the like, a height measurement range that can be obtained by calculation (measurement range L ), The relationship (combination) between the phase change and height of interference fringes obtained by interference of light from R, G, and B light sources having different wavelengths can be accurately recorded as a code conversion table. Therefore, the position shift by the conventional nanometer stage for shifting the phase, the noise due to the vibration when driving the nanometer stage, the noise peculiar to the imaging camera such as CCD, and the phase code conversion table by the shift of the center wavelength of the plurality of light sources It is possible to solve problems caused by data inconsistency or separate correction work corresponding to the center wavelength shift of the plurality of light sources.

  First, FIG. 3 shows a step surface of a predetermined measurement object W using a phase code conversion table created by the conventional wavelength division method described above (a step in the vertical direction on a line portion of 1/3 from the bottom in the vertical direction. A measurement image when the height in the horizontal direction is measured, and FIG. 4 shows a similar measurement object W using the phase code conversion table created by the phase division method of the present embodiment. The measurement image figure when measuring the height in the left-right direction of a level | step difference surface (the step part of an up-down direction exists in the line part 1/3 from the up-down direction) is shown.

  As is apparent from the comparison of the image data in FIGS. 3 and 4, in the case of the measurement image in FIG. 3, the contrast of the height change of the step surface in which the height H gradually increases from the left to the right (the lower one). It is not always clear, but the image is distorted in the center despite the fact that the height gradually increases from the left side to the right side. The waveform diagram (chart) on the lower side showing the change in height is also distorted and is not accurate image data.

  On the other hand, in the case of FIG. 4, the change in contrast according to the change in height in the left-right direction is also clear, and a waveform diagram showing the change in height in the left-right direction on the lower side is also shown. The right-side waveform diagrams representing the stepped portions are also shown approximately accurately. Therefore, according to the above-described optical measurement apparatus of the present embodiment, it can be understood that highly accurate measurement can be performed without being affected by noise components as in the prior art.

  In the above case, in FIG. 3 and FIG. 4, a substantially central portion in the vertical direction of the drawing is selected as the measurement target surface.

  L1, L2 and L3 are first, second and third light generating means, B1 to B4 are first to fourth beam splitters, CAM is an imaging means, F1 to F3 are narrow band filters, and RM is a reference light mirror. , ST is a nanometer stage, and W is a measurement object.

Claims (2)

  Light generating means for generating light of a plurality of different wavelengths, and the light emitted from the light generating means is branched into light of the plurality of wavelengths, passed through separate optical paths with different optical path lengths, and then superimposed again From the interference fringe generating means for generating the interference fringes according to the difference in the optical path length, the imaging means for imaging the interference fringes generated by the interference fringe generating means, and the interference fringe image obtained by the imaging means, the light Image analysis means for analyzing the relationship between the change in brightness and the phase for each wavelength of the wavelength, and the phase of the portion where the brightness of each point in the interference fringe image changes according to the height of the measurement surface of the measurement object The phase code conversion table obtained by combining the height and phase of the measurement surface and the phase information obtained by the image analysis means as parameters, obtained for each of a plurality of different wavelengths of light, and referring to the phase code conversion table Further, an optical measurement device comprising a height calculation means for obtaining the height of the measurement surface of the measurement object, according to the height of the measurement surface of the measurement object and the height of the measurement surface The relationship between the phase of the portion where the brightness of each point in the interference fringe image with a plurality of different wavelengths of light changes to a predetermined arithmetic expression, and the same measurement surface as the measurement surface height of the measurement object. The combination of the phase of the portion where the brightness of each point in the interference fringe image due to the light of the plurality of different wavelengths according to the height of the light is changed is calculated based on a predetermined calculation formula expressed in the same formula, An optical measurement apparatus characterized in that the height of the measurement surface of the measurement object is measured by reflecting the phase information obtained by calculation in the phase code conversion table.   The calculation of the phase information corresponding to the brightness change of the light at each point in the interference image based on the predetermined calculation formula is obtained by acquiring the center wavelength of each light from the preliminary light generating means as data and placing it. 2. The optical measuring device according to claim 1, wherein the calculation is based on the center wavelength of the light.

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