JP4357361B2 - A micro height measurement device using low coherence interferometry - Google Patents

Description

  The present invention relates to a measurement apparatus that measures a minute height of a measurement object using an interference optical system, and more particularly to a minute height measurement apparatus that uses a low coherence interferometry.

  With the recent miniaturization of electronic devices, the shapes and sizes of electronic components and materials incorporated therein are diversified and miniaturized. In addition, devices represented by MEMS (Micro Electro Mechanical Systems) have a micron-order concavo-convex structure and a nanometer-order fine surface shape. Under these circumstances, it is necessary to precisely perform surface shapes having a height difference of submicron to several hundred microns with measurement accuracy on the order of nanometers.

  For the measurement of the height of such a fine surface shape, a high precision interference method using an interference optical system is generally used. One example of this high-accuracy interference method is phase shift interferometry. However, when measuring the height of a long range by phase shift interferometry, discontinuous folding may occur in the measurement result. In this case, it is assumed that the surface of the object to be measured changes continuously. It is necessary to perform the phase connection (unwrapping) process used. However, when there is a large step in the surface shape, the above continuity assumption does not hold, so measurement becomes difficult. Another high-precision interference method that avoids this is a low-coherence interference method.

  FIG. 8 is an explanatory diagram showing a configuration example of a conventional interferometer using a low coherence interference optical system. As shown in FIG. 8, in the conventional measuring apparatus, light having a short interference fringe distance (low coherence light) from the light source unit 101 is measured on the stage 102 and the reference surface in the interference lens 104. Are simultaneously irradiated. Then, the interference fringes of the interference light due to the both reflected lights reflected on the surface of the measurement object 103 and the reference surface of the interference lens 104 are observed by the imaging unit 105 including a CCD (Charge Coupled Device) camera or the like. The interference fringes are sampled by moving the stage 102 minutely in the height direction (z direction) of the measurement target 103, but because of the low coherence light, the optical path difference between the reflected light from the measurement target 103 and the reference surface is small. The stripes with zero amplitude have the largest amplitude and become brighter. In the illustrated example, the measurement object 103 is moved in the height direction by driving the stage 102, but the interference lens 104 may be moved.

  FIG. 9 is an explanatory diagram showing the measurement principle of the conventional low coherence interferometry. That is, the measurement of the minute height of the measurement object 103 is performed by measuring the position of the stage 102 where the optical path difference is zero (generally interference) from an interferogram obtained by moving the measurement object 103 in the vertical direction at a certain sample point interval. This is performed by detecting each point in the interference fringe image (the peak position where the intensity is maximum) (see, for example, Patent Document 1).

  That is, by calculating the moving distance of the stage 102 and the interval between the two interferograms where the interference intensity is maximized by the movement (such as the distance calculated from the number of pixels), the interval between the two interferograms to be measured is calculated. It can be seen that there is a height corresponding to the moving distance of the stage 102.

  10 and 11 are explanatory diagrams showing a method for detecting the peak position of the interferogram. FIG. 11A shows a sample point sequence created in the actual measurement, the horizontal axis thereof represents the position of the measurement target 103, and the vertical axis represents the interference light intensity. FIG. 11B shows a distribution of a feature amount, which will be described later, calculated at the time of the main measurement. The horizontal axis represents the position of the measurement target 103, and the vertical axis represents the feature amount.

  That is, in the measurement of the surface shape of the measurement target 103, first, as shown in FIG. 10, each measurement target 103 or the interference lens 104 is moved at regular intervals (sample point intervals) in the height direction of the measurement target 103. Image interference fringes. Then, as shown in FIG. 11A, a sample point sequence using the interference light intensity obtained at this time as a parameter is created.

  Subsequently, the peak position of the interferogram is obtained from this sample point sequence. In order to accurately obtain the peak position, a sample point interval equal to or smaller than the Nyquist interval determined by the spectral characteristics of the light source is required. When using visible light, the sample point interval is generally several tens of nanometers.

  In order to obtain the peak position from these sample point sequences, in general, a feature amount that reflects the peak position of the obtained sample point sequence is calculated. As this feature amount, for example, as shown in FIG. 11B, an absolute value of a difference in interference intensity between adjacent sample points is used. In the figure, an approximate curve (least square approximation) obtained from the feature amount is shown. By obtaining the peak position (arrow in the figure) of this approximate curve for each point in the image, the surface shape of the measuring object 103 can be obtained with high accuracy. In the illustrated example, as a result of obtaining the peak position from the interferogram in which the height of the measuring object 103 is located at 0 μm, the peak position of the approximate curve is located at approximately the 0 μm position.

In this way, using low coherence interferometry, a short range of white light coherence distance (several μm) is used, and a long range of object heights with sub-micron to hundreds of micron height differences can be measured at the nanometer level. It can be measured with high accuracy.
US Pat. No. 5,133,601

  However, in order to accurately determine the peak position of the interferogram obtained by low coherence interferometry, it is necessary to capture a plurality of interference fringe images at sample point intervals that are less than or equal to the Nyquist interval determined by the spectral characteristics of the light source. A problem arises when the sample point interval is set beyond the Nyquist interval.

  FIG. 12 is an explanatory diagram showing a problem when the sample point interval is widened by the conventional measurement method described above. FIG. 12A shows a sample point sequence created in the measurement in this case, the horizontal axis represents the position of the measurement object 103, and the vertical axis represents the interference light intensity. FIG. 12B shows a distribution of a feature amount, which will be described later, calculated at the time of measurement in this case. The horizontal axis represents the position of the measurement target 103 and the vertical axis represents the feature amount.

  That is, as shown in FIG. 12 (A), when the sample point interval is set beyond the Nyquist interval, the peak position which should originally be 0 μm is shifted as shown by the arrow in FIG. 12 (B). It can be seen that the accuracy is greatly reduced.

  As described above, in order to accurately measure the height of a measurement object having a long range height with the conventional measurement method, it is necessary to capture an interference fringe image according to the sample point interval determined from the spectral characteristics of the light source. There is. For this reason, the number of interference fringe images to be captured increases and the imaging time becomes longer, the memory capacity necessary for storing sampling data increases, and the calculation time required for measurement increases, resulting in an increase in calculation cost. There was a problem.

  The present invention has been made in view of such points, and provides a measurement method and a measurement apparatus that can accurately measure the height of a measurement object having a long range height using low coherence interferometry, In particular, it is an object of the present invention to reduce the memory cost and calculation time required at the time of measurement so as to reduce the calculation cost.

  In the present invention, in order to solve the above problem, as shown in FIG. 1, a light source unit 1 capable of irradiating low-coherence light having a preset center wavelength, and irradiation light from the light source unit 1 are measured 7. The interference optical system 2 that reflects the object surface and the reference surface of the reference object 6 and interferes both reflected light, the stage 10 that movably supports at least one of the measurement object 7 and the reference object 6, and the stage 10 , The position adjustment mechanism 3 that can adjust the distance between the object surface and the reference surface, the imaging unit 4 that captures and acquires the interference fringe images of both reflected lights, and the interference fringes acquired by the imaging unit 4 There is provided a minute height measuring apparatus including an arithmetic control unit 5 that measures the height of an object surface using an image. The arithmetic control unit 5 includes interference light intensity measurement means, feature amount calculation means, sampling means, and height calculation means.

The interference light intensity measuring means sets a point of interest on the object surface and its neighboring points in the interference fringe image picked up by the imaging unit, and measures the interference light intensity at the point of interest and the neighboring points, respectively.
The feature amount calculating means calculates the absolute value of the difference between the two interference light intensities caused by the difference in height between the attention point and the neighboring point, and the absolute value of the difference between the two interference light intensities at the attention point when the stage 10 is moved by the height difference. This is calculated as a feature amount.

The sampling means samples the distribution of the feature amount sequentially calculated by moving the stage 10 by a predetermined sampling point interval by the position adjusting mechanism 3.
The height calculation means calculates the height of the measurement object 7 by detecting the peak position of the feature quantity from the distribution of the feature quantity and detecting the position of the stage 10 at which the feature quantity is the peak position.

  According to such a minute height measuring method, a point of interest and a neighboring point are set in the interference fringe image, and the interference light intensity at the point of interest and the neighboring point is measured. The absolute value of the difference between the two interference light intensities caused by the height difference is regarded as the absolute value of the difference between the two interference light intensities at the point of interest when the stage 10 is moved by the difference in height, and the feature amount is calculated.

  In the minute height measurement apparatus of the present invention, the absolute value of the difference between the two interference light intensities caused by the difference in height between the attention point and the neighboring point is the difference between the two interference light intensity differences at the attention point when the stage is moved in the height difference. Since it is regarded as an absolute value, there is no need to measure the interference light intensity by moving the stage to a position corresponding to a neighboring point for this attention point.

  For this reason, the number of stage movements can be reduced, and the calculation time can be shortened. Further, in order to measure the interference light intensity between the attention point and its neighboring points, it is easy to detect the position where the interference light intensity changes sharply, that is, the peak position of the interference light intensity. As a result, even when the measurement is performed by moving the stage and widening the sampling point interval when sampling, the height of the measurement object, and thus the surface shape can be measured with high accuracy. Furthermore, by widening the sampling point interval in this way, the number of samplings can be reduced, and the measurement speed can be increased by reducing the calculation cost such as the required memory and calculation time during measurement.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration example of a minute height measuring apparatus according to an embodiment of the present invention.
This minute height measuring apparatus includes a light source unit 1, an interference optical system 2, a position adjustment mechanism 3, an imaging unit 4, and a calculation control unit 5, and is configured as a phase shift interferometer.

The light source unit 1 is capable of irradiating light having a center wavelength and a short interference fringe distance (low coherence light). In this example, a white light source is used.
The interference optical system 2 includes a half mirror for branching an optical path and an interference lens 6 (reference object) having a reference surface. The interference optical system 2 once divides the irradiation light from the light source unit 1 and reflects it on each of the object surface of the measuring object 7 and the reference surface of the interference lens 6, and causes both reflected light beams that have returned to interfere with each other.

  The position adjusting mechanism 3 moves the reference surface along the optical axis direction, and moves the object surface of the measuring object 7 in the optical axis direction and the direction perpendicular to the optical axis, or in the height direction. A stage driver 9 for tilting is provided. The piezo driver 8 drives the piezo stage 10 on which the interference lens 6 is mounted according to a command from the arithmetic control unit 5. This piezo stage 10 incorporates a piezo element. The stage driver 9 drives the moving stage 11 on which the measurement object 7 is placed according to a command from the arithmetic control unit 5. By driving the moving stage 11, the position of interest of the measuring object 7 is placed in the field of view of the imaging unit 4.

The imaging unit 4 includes a two-dimensional imaging device such as a CCD camera and captures the interference fringe image of the both reflected lights.
The arithmetic control unit 5 is composed of a computer centered on a CPU (Central Processing Unit), executes arithmetic processing associated with processing functions to be described later, and sends control command signals to the piezo driver 8, the stage driver 9, and other actuators. Is output. The arithmetic control unit 5 includes a storage device such as a memory for accumulating image data picked up by the image pickup unit 4, a display device for appropriately outputting the calculation result to the screen, and the like.

  In the micro-height measuring apparatus configured as described above, the low coherence light emitted from the light source unit 1 is simultaneously irradiated onto the object surface of the measurement target 7 and the reference surface in the interference lens 6. Then, both reflected lights reflected by the object surface and the reference surface are merged to form an interference fringe image on the imaging surface of the imaging unit 4. The arithmetic control unit 5 captures and analyzes the interference fringe image captured by the imaging unit 4 as a digital image. The interference fringes are sampled by moving the moving stage 11 in the height direction of the measuring object 7, and the fringes when the optical path difference between the reflected light from the object surface and the reference surface is zero have the largest amplitude. Bigger and brighter.

In the above, an example of a so-called phase shift interferometer has been shown, but a mirrow interferometer or other phase shift interferometer may be used.
Next, the minute height measuring method of the present embodiment will be described.

  First, the measuring object 7 is set on the moving stage 11 from a handler or the like (not shown). When the calculation control unit 5 determines that the measurement object 7 is installed on the moving stage 11 based on the output of a sensor (not shown), the calculation control unit 5 drives the moving stage in the horizontal direction, the height direction, or the tilt direction via the stage driver 9. The measurement object 7 is moved to a predetermined position to prepare for measurement.

  Then, low-coherence light is emitted from the light source unit 1, and is irradiated onto the measurement object 7 through the interference lens 6. At this time, the reflected light reflected by the reference surface of the interference lens 6 and the object surface of the measurement object 7 interferes according to the relative distance between the reference surface and the object surface, and the interference fringes are imaged by the imaging unit 4. The The interference lens 6 can be moved up and down by a small amount by a piezo stage 10 via a piezo driver 8 and has a range in which the optical path difference is zero in the attention area of the measurement object 7 at the stage of measurement preparation. Positioning in the height direction is performed in advance so that it can be included.

  When the above measurement preparation is completed, a signal indicating that is input to the arithmetic control unit 5. In response to this, the arithmetic control unit 5 moves the piezo stage 10 to a predetermined initial position, captures the interference fringe image picked up by the image pickup unit 4 as a digital image, and stores it in an internal memory.

  Subsequently, the arithmetic control unit 5 moves the piezo stage 10 by a preset sample point interval and captures the interference fringe image again. The arithmetic control unit 5 repeats this operation, and when a plurality of interference fringe images are obtained by moving a predetermined distance, the surface height of the measurement object 7 is calculated according to the measurement principle described later.

  When the calculation of the surface height of a certain area of the measurement object 7 is completed, the arithmetic control unit 5 moves the piezo stage 10 and the moving stage 11 as appropriate, and moves the measurement point to the next measurement point on the measurement object 7. . The calculation control unit 5 appropriately outputs the calculation result to the display device during the measurement process.

Next, the measurement principle of the measurement process executed by the arithmetic control unit 5 will be described. FIG. 2 is an explanatory diagram showing the measurement principle of the minute height.
In the present embodiment, when an interferogram of each point on the surface of the measurement target is obtained, the point of interest and its neighboring points are set in the same interference fringe image as shown in FIG. This neighboring point can be set, for example, at a position several pixels away from the point of interest. Assuming that the surface shape of the measurement target is the same quality having a constant change in the vicinity of this point of interest, the absolute value of the difference between the interference light intensity at this point of interest and the interference light intensity at the nearby point is defined as the feature amount. To do.

  That is, in the conventional example shown in FIG. 9, a point of interest on the surface of the measurement target is set, the measurement target is moved perpendicularly to the optical path, and the absolute value of the difference in the interference light intensity at that point of interest is high as the feature quantity. Therefore, it was necessary to move the measurement object for each sampling of the interference light intensity. On the other hand, in the present invention, as shown in FIG. 2, sampling is performed for two points, that is, a point of interest and a neighboring point at a certain sampling position, and the interference light intensity measured at the neighboring point at that time is measured as an In the pherogram, the calculation proceeds with the interference light intensity of the unmeasured part corresponding to the phase of the neighboring point. Assuming that the surface condition of the measurement target is homogeneous as described above, the shapes of the two interferograms obtained at two adjacent points on the surface of the measurement target are ideally the same. For this reason, it is used that the difference in the interference light intensity between neighboring points due to the slight difference in height of the surface of the measurement object is the same as the difference in the interference light intensity in the vertical direction when the height difference is regarded as the sample point interval. It is a thing.

  If the above-described operation is repeated at an interval in the height direction of the measurement target, a sample point sequence using the difference in interference intensity between the attention point and the neighboring points as a parameter can be obtained. In this case, since the sample point interval of the sample point sequence is equal to or less than the Nyquist interval, two sample points can be obtained by one image pickup, so that the image pickup time can be almost halved. As a result, even if the measurement target has a long range height, the height can be measured accurately, and the memory capacity and calculation time required for measurement can be reduced to reduce the calculation cost. it can.

  In the above, the absolute value of the difference between the interference light intensity at the attention point and the interference light intensity at the neighboring point is used as the feature amount, but the interference light intensity between the attention point and the neighboring point in the same interference fringe image is used. Visibility (visibility and contrast) that can be calculated may be used as the feature amount. In this case, one visibility can be calculated from the interference light intensity of the attention point and at least two neighboring points.

FIG. 3 is an explanatory diagram showing an example of calculation when there are three measurement points at each sampling position.
In this example, the number of measurement points is increased by one more from the calculation example shown in FIG. 2, and two neighboring points with equal intervals (the same number of pixels) are set on both sides of the target point of measurement. The difference between the interference light intensity of each and the interference light intensity of each of the neighboring points is calculated. Then, the larger absolute value of the difference between the two interference light intensities is set as the feature amount.

  That is, as shown in FIG. 3, a light intensity difference A that is a difference between the interference light intensity at the point of interest by the interferogram in the center of the figure and the interference light intensity at the first neighboring point by the interferogram on the left side of the figure, A light intensity difference B, which is the difference between the interference light intensity at the point of interest and the interference light intensity at the second neighboring point according to the interferogram on the right side of the figure, is calculated, and the larger light intensity difference A is used as the feature amount. However, it is assumed that the height difference a between the attention point and the first neighboring point and the height difference b between the attention point and the second neighboring point are substantially the same. Here, the reason that only the larger one of the two light intensity differences is used as the feature amount is that the purpose is to obtain the peak position of the feature amount, so that only the larger information needs to be known.

  FIG. 4 is an explanatory diagram illustrating a simulation result obtained by calculating a feature amount with respect to an imaging height position of a measurement target. (A) is a graph showing the result of calculation by setting three measurement points at each imaging height position as shown in FIG. 3, and (B) shows each imaging height as a comparative example as shown in FIG. It is a graph showing the result calculated by the conventional method which sets one measurement point in the position. In both graphs, the horizontal axis represents the position of the measurement target, the vertical axis represents the feature amount, and the simulation result is shown when the position of zero optical path difference is set to a position of about 4 μm in height. In the figure, in addition to the feature quantity for each actual sampling point interval indicated by the corner points, the value (waveform) of the feature quantity when the sampling point interval is extremely small is also shown as a reference.

According to this simulation result, in the comparative example (conventional method) of FIG. 4B, a false peak position may appear as shown in FIG. 4 depending on the imaging interval, that is, the sampling point interval.
On the other hand, in the present method shown in FIG. 4B, since the shape of the graph is almost unimodal, the peak position can be detected without much influence from the sample point interval.

  FIG. 5 is an explanatory diagram illustrating a detection example of the peak position of the feature amount when the sample point interval is widened by the measurement method described above. (A) represents the sample point sequence created in the measurement in this case, the horizontal axis represents the position of the measuring object 7, and the vertical axis represents the interference light intensity. (B) represents a distribution of a feature amount, which will be described later, calculated at the time of measurement in this case, the horizontal axis represents the position of the measurement object 7, and the vertical axis represents the feature amount.

  According to FIG. 5 (B), even when the sample point interval is set beyond the Nyquist interval, the peak position of zero optical path difference (0 μm in the figure) is shown accurately, and even if the sample point interval is increased, It can be seen that the height can be obtained with high accuracy by using a slight difference in height between the point of interest and the neighboring points. This is considered to be due to the following reasons.

  That is, as shown in FIG. 4B, when the absolute value of the difference between adjacent sample points is used as a feature amount, the position where the difference in interference light intensity between adjacent sample points greatly fluctuates many times. Therefore, the feature amount is likely to fluctuate greatly. For this reason, if the sampling point interval is large, it is difficult to sample a portion having a large feature amount, and the peak position of the feature amount may be detected erroneously.

  On the other hand, as shown in FIG. 4A, when the smaller absolute value of the difference between the two interference light intensities is ignored as the feature amount, the difference in the interference light intensity between adjacent sample points is large. Since the probability of passing through the fluctuating position is reduced, the fluctuation of the feature amount is reduced. For this reason, the graph is close to a single peak, and even if the sampling point interval is large, it becomes easy to sample a portion having a large feature amount, and it is possible to prevent or suppress erroneous detection of the peak position of the feature amount. For the above reasons, the measurement accuracy is improved by this method.

  In the low coherence interference optical system shown above, it is advantageous from the simulation results of the applicants that the measurement accuracy is advantageous if the height difference shown in FIG. 3 is within a certain range with respect to the light source wavelength. found.

  FIG. 6 is an explanatory diagram showing the relationship between the setting of the height difference shown in FIG. 3 and the measurement accuracy. Here, the V value calculated | required by following formula (1) is defined about A part which is the vertex vicinity of the graph of FIG. 4 (A), and it was simulated how this V value changes with a height difference. FIG. 6 is a graph showing the simulation results, where the horizontal axis represents the height difference and the vertical axis represents the V value. At this time, the center wavelength of the light source was about 580 nm, and the height differences a and b of adjacent neighboring points were made substantially the same as shown in FIG.

V = (Max−Min) / (Max + Min) (1)
Here, Max is the value of the peak portion of the waveform representing the feature amount shown in the graph of FIG. 4A, and Min is the value of the valley portion adjacent to this Max. From the above equation (1), 0 <V <1, and the V value decreases as the graph of FIG. That is, the smaller the V value, the smaller the variation in the feature value, and the more accurate the detection of the peak value of the feature value.

  According to FIG. 6, it can be seen that the V value takes a minimum value when the height difference is about 75 nm. That is, when the height difference is about 1/8 of the center wavelength of the light source, the V value is minimum, and when it is 1/9 to 1/7 of the center wavelength (especially 10% around 1/8 of the center wavelength). It was found that particularly good measurement accuracy can be obtained.

  Since it has been found that it is advantageous in terms of measurement accuracy to maintain the height difference to about 1/8 of the light source wavelength in this way, the distance between the point of interest and the neighboring point may be selected to be the above height difference, The measuring object 7 may be tilted so that the height difference between the attention point and the neighboring points is appropriate.

FIG. 7 is an explanatory diagram illustrating a calculation example in the case where there is no height difference between the attention point and the neighboring points of the measurement object 7.
That is, when there is no height difference in the direction connecting the attention point and the neighboring points, the measurement object 7 is necessary in the direction perpendicular to the surface without intentionally creating a height difference by tilting the measurement object 7 or the like. It is also possible to repeat the operation of taking the data by moving the difference in height and moving it by the sampling point interval.

Alternatively, although not shown, data may be obtained while compensating for a portion where there is no difference in height between the attention point and the neighboring points by performing the measurement twice or more by changing the inclination of the object by the method of FIG.
As described above, according to the present method, the height of the measurement object can be obtained with high accuracy using the principle of the low coherence interferometry while increasing the speed even if the sampling point interval is increased.

  As described above, according to the micro height measurement apparatus of the present invention, when measuring a measurement object having a long range height, the measurement cost is reduced by suppressing the calculation cost such as memory required for measurement and calculation time. Therefore, even when the measurement is performed with a wide sampling point interval, the height of the measurement object, and thus the surface shape, can be measured with high accuracy.

  In addition, although each processing function which the arithmetic control part 5 mentioned above performs is implement | achieved by the computer, the program which described the processing content of each function is provided in that case. By executing the program on a computer, the above processing functions are realized on the computer. The program describing the processing contents can be recorded on a computer-readable recording medium. Examples of the computer-readable recording medium include a magnetic recording device, an optical disk, a magneto-optical recording medium, and a semiconductor memory. Examples of the magnetic recording device include a hard disk device (HDD), a flexible disk (FD), and a magnetic tape. Examples of the optical disc include a DVD (Digital Versatile Disc), a DVD-RAM (Random Access Memory), a CD-ROM (Compact Disc Read Only Memory), and a CD-R (Recordable) / RW (ReWritable). Magneto-optical recording media include MO (Magneto-Optical disk).

  When distributing the program, for example, a portable recording medium such as a DVD or a CD-ROM in which the program is recorded is sold. It is also possible to store the program in a storage device of a server computer and transfer the program from the server computer to another computer via a network.

  The computer that executes the program stores, for example, the program recorded on the portable recording medium or the program transferred from the server computer in its own storage device. Then, the computer reads the program from its own storage device and executes processing according to the program. The computer can also read the program directly from the portable recording medium and execute processing according to the program. In addition, each time the program is transferred from the server computer, the computer can sequentially execute processing according to the received program.

It is a figure which shows the structural example of the micro height measuring apparatus of embodiment of this invention. It is explanatory drawing showing the measurement principle of micro height. It is explanatory drawing showing the example of a calculation at the time of making three measurement points in each sampling position. It is explanatory drawing showing the simulation result which computed the feature-value with respect to the imaging height position of a measuring object. It is explanatory drawing showing the example of a detection of the peak position of the feature-value at the time of extending a sample point space | interval. It is explanatory drawing showing the relationship between the setting of a height difference shown in FIG. 3, and a measurement precision. It is explanatory drawing which shows the example of a calculation when there is no height difference at all between the attention point of a measuring object, and a nearby point. It is explanatory drawing showing the structural example of the conventional interferometer using a low coherence interference optical system. It is explanatory drawing showing the measurement principle of the conventional low coherence interferometry. It is explanatory drawing which shows the detection method of the peak position of an interferogram. It is explanatory drawing which shows the detection method of the peak position of an interferogram. It is explanatory drawing showing the problem at the time of extending the sample point space | interval with the conventional measuring method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source part 2 Interference optical system 3 Position adjustment mechanism 4 Imaging part 5 Operation control part 6 Interference lens 7 Measurement object 8 Piezo driver 9 Stage driver 10 Piezo stage 11 Moving stage

Claims (5)

A light source unit capable of irradiating a low-coherence light having a preset center wavelength, and irradiating light from the light source unit is reflected on each of the object surface to be measured and the reference surface of the reference object, and the both reflected lights interfere with each other. An interference optical system, a stage that movably supports at least one of the measurement object and the reference object, and a position adjustment mechanism that can adjust a distance between the object surface and the reference surface by driving the stage; A micro height provided with an imaging unit that captures and acquires the interference fringe image of both reflected lights, and an arithmetic control unit that measures the height of the object surface using the interference fringe image acquired by the imaging unit In the measuring device,
The arithmetic control unit is
Interference light intensity measuring means for setting an attention point and its neighboring points on the object surface to the interference fringe image imaged by the imaging unit, and measuring the interference light intensity at the attention point and the neighboring points, respectively;
The absolute value of the difference between the two interference light intensities caused by the difference in height between the attention point and the neighboring point is regarded as the absolute value of the difference between the two interference light intensities at the attention point when the stage is moved by the difference in height. , A feature amount calculating means for calculating this as a feature amount;
Sampling means for sampling the distribution of the feature values sequentially calculated by moving the stage by a predetermined sampling point interval by the position adjusting mechanism;
A height calculating means for calculating a height of the measurement object by detecting a peak position of the feature quantity from the distribution of the feature quantity, and detecting a position of the stage at which the feature quantity becomes a peak position;
A minute height measuring device characterized by comprising:   2. The minute height measuring apparatus according to claim 1, wherein the interference light intensity measuring unit sets the attention point and the neighboring point in the same interference fringe image at each moving position of the stage. The interference light intensity measuring means sets at least two points near the point of interest at each moving position of the stage,
The feature amount calculating means is configured to obtain only the largest absolute value of the difference in interference light intensity between the attention point and each neighboring point, or the visibility obtained from the interference intensity between the attention point and each neighboring point, Calculating as a feature value,
The micro height measuring apparatus according to claim 2.   The interference light intensity measurement unit sets the attention point and each neighboring point in the interference fringe image so that a difference in height between the attention point and each neighboring point is constant. Item 4. A micro height measurement apparatus according to Item 3. The interference light intensity measuring means moves the stage in the height difference height direction by the position adjusting mechanism, acquires at least three interference fringe images picked up by the image pickup unit, and includes in each interference fringe image. Measure the interference light intensity with one of the measurement points at the same position as the attention point and the other as the neighboring point,
The feature quantity calculating means only selects the one having the largest absolute value of the difference in interference light intensity between the attention point adjacent to the height direction and each neighboring point, or the interference intensity between the attention point and each neighboring point. Calculating the visibility obtained from the feature amount,
The micro height measuring apparatus according to claim 1.