JP2018173338A - Three-dimensional shape measuring method using scanning white interference microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-dimensional shape measuring method using scanning white interference microscope capable of carrying out proper measurement of an object to be measured by ensuring the amount of light of interference signals by using negative interference signals.SOLUTION: The three-dimensional shape measuring method using a scanning white interference microscope includes the steps of: acquiring an interference signal corresponding to irradiation light from a light source irradiated to an object to be measured using a sensor; acquiring a negative interference signal the signal strength of which is smaller than a base line equivalent to an offset value of the signal strength from the interference signals; and setting a measurement amount of light which is the amount of light of irradiation light for measuring a piece of height information of the object to be measured based on the signal strength of the negative interference signal.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a method for measuring a three-dimensional shape by interference measurement using a white light source.

  A scanning white interference microscope is a device that performs three-dimensional measurement by irradiating a sample with white light and converting the resulting interference signal into height information. Judgment of height, step, film thickness, surface roughness, same / different materials, etc.

  In 3D measurement using a scanning white-light interference microscope, conventionally, in order not to lose the information of the interference signal measured by the sensor, the light intensity of the light source is set so that the interference signal intensity does not exceed the output saturation value of the sensor. Has been adjusted.

  For example, in Patent Document 1, imaging by OCT (optical coherence tomography) is performed. However, when detection is saturated, saturation artifacts are generated, so the power of the light source is reduced and rescanning is performed. Measures have been taken. In Patent Document 2, data is acquired at a sample point interval equal to or greater than the Nyquist interval, and the height information is obtained by interpolating data within the sample point interval.

Special table 2015-523578 gazette JP 2009-047527 A

  The conventional three-dimensional shape measurement using a scanning white interference microscope has the following two problems regarding the setting of the light amount of the light source. The first problem is the saturation of the output of the sensor that detects light. That is, depending on the characteristics of the measurement object, the contrast of the interference fringes to be measured may be small, that is, the visibility may not be good. In this case, in order to increase the interference signal intensity, it is desirable to increase the light amount of the light source as much as possible. However, when the amount of light from the light source is increased, the intensity of incident light that enters the sensor that detects light also increases. Then, the output value of the sensor increases corresponding to the intensity of the incident light, the output value easily reaches the output saturation value of the sensor, and the output of the sensor is easily saturated. For example, such a problem is likely to occur when the reflectance of the measurement object is small and the reflected light intensity is low.

  The second problem is related to the S / N ratio (signal to noise ratio) of the sensor. In general, in a sensor that detects light, the S / N ratio increases in a power function as the incident light intensity increases. In other words, the ratio of noise to signal decreases as a power function as the incident light intensity increases. Therefore, there is a demand for increasing the light quantity of the light source to increase the S / N ratio as much as possible, that is, to reduce the noise ratio.

  The present invention provides a three-dimensional shape measurement method using a scanning white interference microscope that can realize more appropriate measurement.

  The present invention is a three-dimensional shape measurement method using a scanning white-light interference microscope, which uses a sensor to acquire an interference signal corresponding to irradiation light from a light source irradiated to a measurement object, Among them, the irradiation for obtaining a negative interference signal whose signal intensity is smaller than the baseline corresponding to the offset value of the signal intensity and measuring the height information of the measurement object based on the signal intensity of the negative interference signal Sets the measurement light quantity that is the light quantity.

  According to the present invention, even when the light amount of the light source is increased and the output value of the sensor reaches the maximum value, that is, saturated, the measurement object (sample) can be obtained with a high light amount by using the negative interference signal component. ) Surface shape can be measured. Therefore, it is possible to easily grasp the shape of the surface of a measurement object with poor visibility.

FIG. 1 is an overall configuration diagram of a scanning white interference microscope according to an embodiment of the present invention. FIG. 2 is a diagram depicting an N / S curve with respect to a sensor signal. FIG. 3 is a graph of a general interference signal observed by a scanning white interference microscope. FIG. 4 is a graph showing the observation result of the visibility of the interference signal when the light amount setting value of the light source is changed. FIG. 5 is a graph showing an example of the measurement result of the positive interference signal and the negative interference signal with respect to the light amount setting value of the light source. 6A to 6E are graphs of interference signals at the representative points indicated by (a) to (e) in FIG. FIG. 7 is a graph showing an example of square detection, which is one of the examples used for obtaining the envelope of the interference signal waveform. FIGS. 8A to 8E are graphs showing waveforms for obtaining an envelope after applying square detection to the graphs of FIGS. 6A to 6E. FIG. 9 is a conceptual diagram showing how the envelope of the interference signal waveform changes with respect to the output value of the sensor when the light amount setting value of the light source is changed. FIG. 10 is a graph illustrating the measured results of FIG. 5 again based on the interpretation of FIG. FIG. 11 is a diagram illustrating a method for setting the measurement light quantity in one embodiment, (a) shows a flowchart of the method, and (b) shows that the baseline reaches the output saturation value of the sensor. The conceptual diagram of the interference signal in the state where the signal intensity of the negative interference signal does not reach the maximum value is shown, and (c) shows that the baseline reaches the output saturation value of the sensor and the signal intensity of the negative interference signal is The conceptual diagram of the interference signal of the state which has become the maximum value is shown. FIG. 12 is a flowchart showing a method for setting the measurement light quantity in another embodiment, and is a flowchart of a three-dimensional shape measurement method by multiple scanning. FIG. 13 is a conceptual diagram showing processing according to the flowchart of FIG. FIG. 14 shows an example of a technique for setting a light amount at which a signal intensity of at least a part of the baseline of the interference signal is equal to the output saturation value of the sensor as a measured light amount, and (a) is an example flowchart. (B) is the conceptual diagram which showed the applicable step of (a) on the interference signal. FIG. 15 shows another example of a method of setting a light amount at which the signal intensity of at least a part of the baseline of the interference signal is equal to the output saturation value of the sensor as a measured light amount. It is a flowchart and (b) is the conceptual diagram which showed the applicable step of (a) on the interference signal. FIG. 16 shows still another example of a method for setting, as a measurement light amount, a light amount at which the signal intensity of at least a part of the baseline of the interference signal is equal to the output saturation value of the sensor. (B) is a conceptual diagram showing the corresponding step of (a) on the interference signal.

  Hereinafter, a preferred embodiment of a three-dimensional shape measurement method using a scanning white interference microscope according to the present invention will be described in detail with reference to FIGS.

  FIG. 1 is an overall configuration diagram of a scanning white interference microscope according to an embodiment of the present invention. The scanning white interference microscope 100 includes an apparatus main body 10, a stage 20 on which a sample S (measurement object) to be measured is placed, and a computer (processor) 30 that processes the obtained data. The apparatus main body 10 includes a light source (white light source) 11, a filter 12, a beam splitter 13, a two-beam interference objective lens (objective lens) 14, a sensor (detector) 15, and a piezo actuator 16.

  Irradiated light (white light) emitted from the light source 11 as shown by an arrow A passes through a filter (for example, a wavelength filter, a polarizing filter) 12 and then is guided to a two-beam interference objective lens 14 by a beam splitter 13 ( Arrow B). The irradiation light is a beam splitter in the two-beam interference objective lens 14, and the first irradiation light toward the measurement target (including the sample S itself and the substance therein) and the second toward the reference mirror (not shown). Are divided into two. When the optical distance from the beam splitter to the measurement object in the two-beam interference objective lens 14 arranged to face the measurement object is equal to the optical distance from the beam splitter to the reference mirror, the measurement signal Can be observed in the form of interference signals of the two irradiation lights, and the sensor 15 images the interference signals as interference fringes (interference patterns), and the interference signals are held and stored in the computer 30. Further, in the embodiment of FIG. 1, since the distance from the beam splitter 13 to a reference mirror (not shown) is fixed, by sweeping using the piezo actuator 16 (movement of arrow C), The distance is changed. Since the scanning white interference microscope 100 uses a light source having a short coherence length (for example, the coherence length is 1 μm or less), the position where the interference signal is obtained is the z position (height position) where the measurement object exists. The operator operates the computer 30 of the scanning white interference microscope 100, moves the two-beam interference objective lens 14 in the height direction along the arrow C, and the measurement object (including the sample D and the substance therein). Is scanned in the height direction (z direction), and the surface properties (such as irregularities) of the measurement object are observed.

  FIG. 2 is a characteristic diagram showing the N / S ratio, which is the ratio of noise to the output signal intensity, of the sensor 15 that acquires the interference signal corresponding to the irradiation light, in logarithmic terms. In general, as the amount of light incident on the sensor increases, the proportion of noise generated from the sensor 15 decreases according to the power function (the graph is linearly lowered because it is a logarithmic display). It can be seen from the characteristics of the sensor 15 that the ratio of noise is smaller when the incident light amount, that is, the output signal intensity is as large as possible, and that measurement can be performed under a good S / N ratio (right side of the graph). The sensor 15 is a device that can capture light, and includes an image sensor, a camera, and the like in a broad sense and is not particularly limited.

  FIG. 3 shows a general interference signal observed by the scanning white interference microscope 100, that is, an interference signal obtained when the measurement object is irradiated with irradiation light (white light) from the light source 11 with a predetermined light amount I. It is a graph which shows. The horizontal axis corresponds to the z position (height position) that is the position of the measurement object in the sample S. Here, the horizontal axis corresponds to an optical path difference (OPD) Δp, but the optical path length difference Δp is the optical distance from the beam splitter in the two-beam interference objective lens 14 to the measurement object, and This corresponds to the difference in optical distance from the beam splitter to the reference mirror. The interference signal has a peak value at the position where the optical path length difference Δp = 0, and the measurement object exists at this position.

The signal intensity S (I) observed by the sensor 15 of the scanning white interference microscope 100 is the reflected light from the reference light intensity I ₁ and the measurement object as shown by the following formula (1) at a certain incident light quantity I. It consists of an offset term (first term and second term) of intensity I ₂ and a third term that is an interference signal. Δp in the third term is the optical path length difference described above. As shown in FIG. 3, the offset term is a signal strength offset value that is given as a standard with respect to the signal strength 0 of the interference signal regardless of the presence of the measurement target.

The third term, which is the interference term in Equation (1), corresponds to the interference signal indicated by the solid line in FIG. Generally, the upper part of the offset terms of I ₁ and I ₂ is called a positive interference signal that interferes positively, and the lower part of the offset term is called a negative interference signal that interferes negatively. In the portion of the positive interference signal, the interference signal becomes bright, and in the portion of the negative interference signal, the interference signal becomes dark, and an interference fringe in which the light / dark pattern is repeated is formed. This interference fringe corresponds to the unevenness which is the height information (height position) of the measurement object.

  In equation (1), the maximum value S (+) of the positive interference signal is obtained when cos (Δp) = 1, and is obtained from the following equation (2).

  On the other hand, the maximum value S (−) of the negative interference signal in equation (1) is when cos (Δp) = − 1, and is obtained from the following equation (3).

In FIG. 3, the offset term (I ₁ + I ₂ ) of I ₁ and I ₂ corresponds to the baseline B (I), and is expressed by the following formula (4). The portion located above the baseline B (I) and having a higher signal strength than the baseline is a positive interference signal, and the portion located below the baseline B (I) and having a lower signal strength than the baseline Negative interference signal.

Note that since equation (1) represents a physical phenomenon, it is measured by the sensor 15 after an actual interference phenomenon has occurred. Therefore, even if the offset term due to I ₁ and I ₂ , that is, the baseline B (I) of the equation (4) exceeds the saturation value of the output of the sensor 15, that is, the output saturation value (maximum output value) of the sensor 15. However, the lower part of the baseline B (I), that is, a negative interference signal smaller than the baseline B (I) can be detected by the sensor 15, and at this time, the signal intensity of the expression (3) is detected by the sensor 15. Is done.

Here, when the light quantity I of the light emitted from the light source 11 is increased, the rising speed of the baseline B, which is an offset term of I ₁ and I ₂ (the change in B (I) with respect to the change in I, B The differentiation of (I) by I is expressed by the following equation (5).

  When the amount of light I of the light source 11 is increased, in equation (1), if the rate of increase in the magnitude of the interference signal in the third term is greater than the rate of increase in the offset term expressed in equation (5) above. As the light quantity I of the light source 11 is increased, the interference signal is increased, which is preferable in measurement. In reality, however, it cannot happen. This is because the offset term B (I) is always greater than or equal to the maximum value of the third term as seen from the relationship of additive / geometric mean as in the following equation (6), and is obtained by differentiating the equation (6). This is because the rising speed of the offset term is always equal to or higher than the rising speed of the third term, as shown in Equation (7).

  As shown in FIG. 2, from the viewpoint of the S / N ratio, there is a premise that the larger the amount of light emitted from the light source, the better. However, the increase in the amount of light naturally increases the baseline as an offset term. According to the above equations (5) to (7), the increase rate of the baseline is larger than the increase rate of the interference signal important for measurement, and the interference signal can be easily detected by the increase in the amount of light. It has generally been thought that the saturation value of the output is reached, making it difficult to detect the correct intensity.

  In view of such circumstances, in order to select an interference signal preferable for measuring height information, a concept indicating visibility of interference fringes generally called visibility V is used. That is, the visibility V is an amount representing the contrast of the interference fringes, and is considered synonymous with contrast and transfer function MTF (Modulated Transfer Function).

Visibility V is expressed by the following equation (8). In general, an interference signal having a large visibility V is considered preferable for measurement. In Expression (8), I _max is the maximum observed interference signal intensity, and I _min is the minimum observed interference signal intensity. As shown in FIG. 3, each of the absolute values is based on the signal intensity 0 of the sensor 15 as a reference. Of strength. That is, visibility V is the ratio of the difference between the maximum observed interference signal strength and the minimum observed interference signal strength.

FIG. 4 is a graph showing the observation result of the visibility of the positive interference signal when the light amount setting value of the irradiation light of the light source 11 is changed. The amount of light emitted from the light source 11 varies along the horizontal axis. The change in visibility with respect to the change in the amount of light on the horizontal axis is dV / dI, which corresponds to the slopes γ _A (= 0.33) and γ _B (= 0.13) drawn in FIG. The two inclinations correspond to two different measurement objects. FIG. 4 shows a change in visibility in a positive interference signal. The slope γ (+) is expressed by the following equation (9), and takes a value of 0 ≦ γ ≦ 1. On the other hand, in the case of the ratio to the negative interference speed, if it is defined as γ (−), it becomes Equation (10) and takes a value of −1 ≦ γ ≦ 0.

  Note that the slope γ indicates the degree of change in visibility with respect to the change in the amount of irradiation light, and can also be referred to as the sensitivity of visibility to the change in the amount of light. In this document, γ is also referred to as “visibility sensitivity”. The measurement object has a unique visibility sensitivity depending on its type.

Conventionally, as shown in FIG. 4, focusing on the change in visibility in a positive interference signal, the light amount corresponding to the best value of this visibility has been considered as the optimum light amount of the light source 11. In FIG. 4, the first measurement object having the first inclination (first visibility sensitivity) γ _A has the highest visibility at the light amount L ₁ . On the other hand, the second measurement object having the second inclination (second visibility sensitivity) γ _B has the highest visibility at the light amount L ₃ . The first measurement object and the second measurement object have different physical properties such as reflectance (including surface shape and inclination angle), and the first inclination (first visibility sensitivity) and the second Have different slopes (second visibility sensitivity).

That is, according to the conventional general idea, the light quantity L ₁ for the first measurement object and the light quantity L ₃ for the second measurement object are optimum light quantity setting values of the irradiation light. That is, in the range where the gradients γ _A and γ _B are established, the equation (9) is established, and the visibility increases as the amount of light increases. However, the light intensity larger than the light quantity L ₁ and the light quantity L ₃ (on the right side of the graph) exceeds the saturation value of the output of the sensor 15, so the visibility is reduced, and the output of the light source 11 is the light quantity L ₁ , the light quantity. The conventional way of thinking is to be suppressed to L ₃ or less. Under this condition, for example, the upper envelope indicated by the dotted line in FIG. 3, that is, the envelope of the positive interference signal is fitted by a predetermined method (for example, fitting by a model function of the sample point of the positive interference signal obtained by sampling) ) To obtain height information from the peak.

However, it should be considered that the amount of light with which the highest signal intensity is originally obtained is the optimum amount of light. Therefore, the inventor paid attention to a negative interference signal, particularly, a change in the negative interference signal with respect to a change in the amount of light, unlike the conventional way of thinking. This is because the peak of the envelope can also be acquired from the negative interference signal, as in the lower envelope indicated by the one-dot chain line in FIG. FIG. 5 is a graph in which the intensity of the positive interference signal and the intensity of the negative interference signal are plotted against the set value of the light amount of the light source 11. In order to make it easier to grasp the phenomenon, the light source 11 is selected so that the amount of light output changes linearly. From this figure, as the light intensity setting is increased, after the intensity of the positive interference signal reaches a peak, the intensity of the negative interference signal reaches the minimum value (negative peak). The measurement object having the inclination γ _A is a portion represented by representative points (c) and (d).

FIG. 6 is a graph of interference signals at representative points indicated by (a) to (e) among the light amount setting values of the light source for the measurement target with γ _A = 0.33 in FIG. 5. In FIG. 6A showing the case where the light amount setting value of the light source is small, the baseline is low and the interference signal is small, but as the light amount setting value is increased, the baseline rises as shown in FIG. 6B. At the same time, the interference signal increases. Note that at this time, the condition of equation (7) is satisfied. When the light amount set value is further increased, the positive interference signal reaches the maximum output value of the sensor, that is, the saturation value (upper limit in the graph) as shown in FIG. 6C. When the light amount setting value is further increased, the baseline reaches the saturation value of the sensor as shown in FIG. As the light amount setting value is further increased, even the negative interference signal reaches the saturation value, and the magnitude of the interference signal that is gradually observed decreases as shown in FIG.

  Such an event is caused by the fact that the expression (7) is satisfied, that is, the increase rate of the interference signal of the third term of the expression (1) is increased by the offset of the expression (5) under the increase of the light amount. It is derived from the term, that is, the rate of increase of the baseline or less. In cases other than γ = 1 (when the ratio between the numerator and the denominator in equation (9) is the same, that is, when the average luminance value is increased and the interference signal intensity is also increased), increasing the light amount set value increases the interference. The magnitude of the signal finally decreases as shown in FIG. In FIG. 6 (d), the positive interference signal is 0. Originally, in FIG. 5 (d), the portion of the positive interference signal (the symbol of white diamond ◇) must not be 0 theoretically. However, due to measurement errors, a predetermined value is output.

FIG. 7 shows an example of square detection, which is one of the methods for obtaining the envelope. Note that the maximum peak positions (sizes of 4I ₁ I ₂ ) of the envelopes of the positive interference signal and the negative interference signal are originally composed of the third term of the equation (1), and therefore coincide with each other. To do. By using the square detection, it is possible to use twice as much data including the positive interference signal and the negative interference signal.

  FIGS. 8A to 8E show results of applying envelope generation by square detection as shown in FIG. 7 to the waveforms of FIGS. 6A to 6E. In particular, it is possible to generate an envelope even in a state in which a part of the interference signal is saturated as shown in FIGS. 8D and 8E. In this case, only the negative interference signal was originally used, but by using square detection, the positive interference signal in FIGS. 8A to 8C can be compared with the absolute value. However, here, square detection is used as an example of a method for obtaining an envelope, but this is not a limitation, and any method may be used.

  FIG. 9 shows changes in the envelope of the interference signal when the light amount setting value of the light source 11 is increased. Although the observer can observe the interference signal only through the sensor 15, the interference phenomenon as a physical phenomenon actually occurs even if the output value of the sensor 15 is saturated and the observer cannot observe the interference signal. That is, FIG. 9D and FIG. 9E show an interference signal that is expected even when the saturation value of the sensor 15 is exceeded.

  As shown in FIGS. 9A and 9B, when the light amount setting value of the light source 11 is small, the output value of the sensor 15 is not saturated. Therefore, the observed positive interference signal intensity and negative interference signal are not saturated. Intensities are represented by S (+)-B and S (-)-B, respectively. Then, as shown in FIG. 9C, when the maximum value of the positive interference signal reaches the saturation value of the output value of the sensor 15, the signal intensity of the positive interference signal (positive interference signal intensity) is maximum. Become. A saturation value −B is observed as the signal intensity of the observed positive interference signal. On the other hand, since the negative interference signal has not yet reached the saturation value at this time, the signal strength of the negative interference signal (negative interference signal strength) is observed at S (−) − B.

  When the light amount setting value of the light source 11 is further increased, as shown in FIG. 9D, the baseline reaches a saturation value, and the signal intensity of the observed positive interference signal becomes zero. When the baseline reaches the saturation value, the signal intensity of the negative interference signal is maximized. Since the baseline has reached a saturation value, a signal strength of S (−) − saturation value is observed.

  As the light amount setting value of the light source 11 is further increased, the maximum value S (−) − saturation value of the signal intensity of the negative interference signal gradually decreases as shown in FIG. If the set value is increased, it will eventually reach 0 like the positive interference signal.

FIG. 10 is a graph obtained by analyzing the relationship between the change in the light amount of the light source 11 and the change in the signal intensity of the interference signal based on the concept of FIG. _A white diamond (◇), which is a positive interference signal of the measurement object having the first inclination (first visibility sensitivity) γ _A (= 0.33), is set to the light amount setting value of the light source 11 on the low light amount side. On the other hand, the interference signal intensity increases (see arrow A). The light intensity setting value when the signal intensity of the positive interference signal reaches the saturation value of the sensor 15 is L1 (see FIG. 4). Since the positive interference signal has already reached the saturation value of the sensor 15 for the light quantity of L1 or more, the signal intensity does not increase, and the baseline rises as shown in FIGS. 9 (d) and 9 (e). Nevertheless, the signal strength decreases (see arrow B).

On the other hand, the signal strength of the negative interference signal increases for a while after the signal strength of the positive interference signal reaches the saturation value at L1. Signal strength of negative interference signal when the maximum value, when the light quantity setting value is L2, the light quantity is the minute large [Delta] L _A. The magnitude of the negative of the interference signal in the light quantity L2, from the magnitude of the positive interference signal in the light quantity L1, increased by the amount of [Delta] I _A. That is, the optimum light quantity set value rather than L1, a correspondingly larger by L2 of [Delta] L _A than that. When the signal intensity of the negative interference signal reaches the maximum value, it can be considered that the baseline intensity reaches the saturation value.

A similar conclusion is obtained for the measurement object having the second slope (second visibility sensitivity) γ _B (= 0.13), and the light intensity L3 (see FIG. 4) at which the signal intensity of the positive interference signal takes a peak. in [Delta] L _B is larger by the amount of light L4 than), the signal intensity of the negative of the interference signal is peaked, the signal intensity of the interference signal in the light amount L4 is increased by the amount of [Delta] I _B than the signal intensity of the interference signal in the light quantity L3 .

  As described above, conventionally, the optimum value of the light amount of the light source 11 is the optimum light amount when the visibility is maximized or when the interference signal is not saturated, that is, before the positive interference signal reaches the maximum value. It was common to set (see FIG. 4).

  However, in order to obtain the three-dimensional shape of the measurement object, it is only necessary to obtain the maximum value of the envelope as shown in FIG. 3, that is, the peak of the envelope, even if a part of the positive interference signal is saturated. However, it is possible to obtain the envelope. That is, it is possible to determine the peak position of the envelope only with a negative interference signal, and even to determine the peak of the envelope from a part of the negative interference signal (for example, FIG. 8 (e)). reference). In particular, at least an envelope of a negative interference signal can be acquired, and at the same time, the amount of light to be measured can be set based on at least a new envelope peak after square detection obtained by square detection of the envelope. In this case, a saturated positive interference signal envelope may be acquired as long as there is no problem, and the measurement light quantity may be set together with the negative interference signal envelope. Alternatively, square detection may be performed by combining the envelope of the positive interference signal and the envelope of the negative interference signal.

  The present invention concludes that the light intensity at which the signal intensity takes the maximum value for the negative interference signal that is estimated to be the maximum, not the visibility, is the optimal light quantity for obtaining height information. Derived. In this document, this optimum light amount to be set in order to measure the height information of the measurement object is referred to as “measurement light amount”.

  FIG. 11A is a flowchart for setting the measurement light quantity according to an embodiment of the present invention. The operator operates the computer 30 of the scanning white interference microscope 100, scans in the height direction, and focuses on a predetermined observation position (predetermined height position) of the measurement object. The beam interference objective lens 14 is moved. And the mode which increases the light quantity of the irradiation light of the light source 11 in a predetermined observation position is set, and a light quantity is increased (step S1). While monitoring the interference signal acquired by the sensor 15, the computer 30 determines whether or not the maximum value of the positive interference signal (for example, the peak of the envelope) has reached the output saturation value (maximum output value) of the sensor 15. However (step S2), if not reached (see FIGS. 9A and 9B), the process returns to step S1 to continue the increase in the amount of light (step S2; No). When it is determined that the maximum value of the positive interference signal has reached the saturation value (step S2; Yes), the computer 30 acquires the maximum value of the positive interference signal (step S3; see FIG. 9C).

  Next, the computer 30 determines whether or not the baseline of the interference signal has reached the output saturation value of the sensor (step S4). If not, the computer 30 returns to step S1 and continues to increase the amount of light (step S4). No). When the baseline has reached the output saturation value (step S4; Yes), the computer 30 is an observation region that is the current height position and the region (in the xy plane) of the measurement object currently being observed. In (for example, 14 fields of view of the two-beam interference objective lens), it is determined that the light quantity is the optimum light quantity for measuring the height information of the measurement object, and the light quantity is set as the measurement light quantity of the irradiation light. (Step S5). This state is the state of FIG. 9D, and the signal intensity of at least a part (all in FIG. 9D) of the positive interference signals among the interference signals exceeds the output saturation value of the sensor 15. At least a part of the positive interference signal (all in FIG. 9D) is saturated.

  Furthermore, the computer 30 also determines whether or not the negative interference signal (the envelope) has reached the maximum value (for example, whether or not the peak of the envelope is the maximum value) (step S6). Returning to step S1, the light quantity continues to increase (step S6; No). If the negative interference signal (envelope) has reached the maximum value (step S6; Yes), the computer 30 sets the light amount in the interference signal as the measured light amount of the irradiation light (step S5).

  Here, if the signal strength of the baseline is a straight line as shown in FIG. 3, the time when the baseline reaches the output saturation value is the same as the time when the peak of the negative interference signal reaches the maximum value in any observation region. Therefore, the process in FIG. 11 ends in step S4. However, the baseline signal intensity is generally not a constant value as shown in FIG. 3, and varies in an arbitrary direction in the measurement object, for example, in the xy plane. 11B and 11C, on the premise that the determination in step S6 is performed, the signal strength of the baseline is not a straight line as in FIG. 3, and the horizontal axis is an arbitrary direction in the xy plane. Shows a state in which the signal strength of the baseline fluctuates (takes a baseline curve). In this case, the baseline signal intensity of each pixel varies within the observation region.

  FIG. 11B shows a conceptual diagram of the interference signal in a state where the signal intensity of the negative interference signal (the envelope thereof) is not maximized while the baseline reaches the output saturation value of the sensor (step S6). No). Here, the signal strength of the baseline fluctuates in an arbitrary direction within the measurement object, and the signal strength of at least part of the baseline has reached the output saturation value of the sensor 15. This state corresponds to No in step S6, but the light quantity in this state may be set as the measurement light quantity without further increasing the light quantity. However, from this state, by increasing the amount of light, the signal intensity can be increased without further saturating the negative interference signal. FIG. 11C shows a state in which the amount of light is increased from FIG. 11B, the baseline reaches the output saturation value of the sensor 15, and the signal intensity of the negative interference signal (the envelope thereof) is the maximum value. The conceptual diagram of the interference signal of the state which has become is shown (step S7). This means that an optimum light amount is obtained in the pixel of interest. In this state, among the interference signals, all of the positive interference signals whose signal strength is higher than the baseline exceeds the output saturation value of the sensor 15, so that the positive interference signal is not detected by the sensor 15. This point is the same as FIGS. 9D and 9E.

  In the above processing, the computer 30 acquires a negative interference signal whose signal strength is smaller than the baseline corresponding to the offset value of the signal strength of the interference signal, and based on the signal strength of this negative interference signal, the measurement object A measurement light amount that is a light amount of irradiation light for measuring the height information is set. More specifically, the computer 30 acquires the envelope of the negative interference signal as described above, and sets the measurement light quantity based on the peak of the envelope.

  As described with reference to FIG. 4, for the first measurement object having the first visibility sensitivity, the signal intensity of at least a part of the baseline of the first measurement object is the sensor 15. In a state where the output saturation value is reached, the first measurement light quantity is set. On the other hand, for the second measurement object having the second visibility sensitivity, in a state where the signal intensity of at least a part of the baseline of the second measurement object reaches the output saturation value of the sensor 15. A second measurement light amount different from the first measurement light amount is set. In this way, it is possible to set an optimum measurement light amount for each material (which may be two or more types) having different visibility.

  FIG. 12 is a flowchart for determining an optimum light amount according to another embodiment of the present invention, and shows a three-dimensional shape measurement method using multiple scanning. Multiple scan refers to obtaining information (height information) of all pixels in an image corresponding to an observation area or a predetermined number of pixels or more in one height direction (z direction) scan (scan). Instead, for each scan, pixel information is acquired only partially from the image corresponding to the observation region. Multiple scan is a concept of acquiring information of pixels of a predetermined ratio or more in this image by repeating such processing.

  The operator operates the computer 30 of the scanning white interference microscope 100, scans in the height direction, and focuses on a predetermined observation position (predetermined height position) of the measurement object. The beam interference objective lens 14 is moved. And the mode which increases the light quantity of the irradiation light of the light source 11 in a predetermined observation position is set, and a light quantity is increased (step S11). Next, the computer 30 determines whether or not the baseline of the interference signal has reached the output saturation value of the sensor (step S12). If not, the computer 30 returns to step S11 and continues to increase the amount of light (step S12). No). When the baseline has reached the output saturation value (step S12; Yes), the computer 30 sets the light amount as the measurement light amount and measures the interference signal (step S13).

  Next, the computer 30 determines whether or not the light amount of the light source has reached the maximum output value (step S14). If the light amount has reached the maximum output value (step S14; Yes), the process is terminated. On the other hand, when the light quantity has not reached the maximum output value (step S14; No), the computer 30 determines whether or not the scanning white interference microscope 100 is set to a mode for performing multiple scanning (step S15). If the mode is not set to perform multiple scanning (step S15; No), the process is terminated.

  On the other hand, when the mode is set to perform the multiple scan (step S15; Yes), the computer 30 determines whether or not the number of scans that have already been performed has reached the designated number of multiple scans designated in advance. (Step S16). The computer 30 also determines in parallel whether or not the pixels for which height information has already been acquired in a scan that has already been performed have reached a pre-designated pixel acquisition rate (step S17). If the number of scans that have already been performed has not reached the designated number of multiple scans (step S16; No), or the pixels for which height information has already been acquired in the scans that have already been performed have reached the designated pixel acquisition rate. If not (step S17; No), the pixel whose height information is obtained from the interference signal obtained with the measurement light quantity in step S13 is removed from the measurement target (step S18), and the remaining pixels are again determined. The process from step S11 is started. After step S11, the amount of irradiation light is increased so that the baseline of the interference signal of the remaining pixels reaches the output saturation value of the sensor, and a new measurement light amount is set.

  On the other hand, when the number of scans that have already been performed has reached the designated number of multiple scans (step S16; Yes), or pixels that have already acquired height information in a scan that has already been performed have an acquisition rate of the specified number of pixels. If it has been reached (step S17; Yes), the process is terminated in any case.

  FIG. 13 is a conceptual diagram showing the process according to the flowchart of FIG. 12, and the horizontal axis is an arbitrary direction in the xy plane in the measurement object, as in FIGS. 11 (b) and 11 (c). In this direction, the baseline signal intensity varies. (1) and (2) show the processing of steps S11 and S12 in FIG. 12, and (3) shows a part of the image corresponding to the observation area on the xy plane in steps S13 to S17 in FIG. It shows that height information is obtained only for pixels. (4) shows the process in step S18 in FIG. 12, and (5) and (6) show that the processes in steps S11 and S12 in FIG. 12 are performed again.

FIG. 14 shows an example of a technique for setting a light amount at which the signal intensity of at least a part of the baseline of the interference signal is equal to the output saturation value of the sensor as the measured light amount. FIG. 14A is a flowchart of this method, and FIG. 14B is a conceptual diagram showing the corresponding steps of FIG. 14A on the interference signal. The operator operates the scanning white interference microscope 100 in advance to obtain a predetermined height position (z position) where interference fringes are observed, that is, the peak of the interference signal (step S21). The operator operates the scanning white interference microscope 100 and at an upper position separated from this position by an interval L (L> L _C ) equal to or greater than the coherence length L _C corresponding to the half-value width of the positive or negative interference signal. A baseline is acquired (step S22). At this position, only the baseline can be acquired because the interference fringe waveform cannot be observed.

Here, the intensity of the baseline is increased to the output saturation value of the sensor 15 by increasing the light amount of the light source 11 (step S23). Thereafter, by returning the focus to the original height position in step S21 (step S24), an interference fringe waveform in a state where the baseline reaches the output saturation value of the sensor 15 can be obtained (step S25). As a result, the amount of irradiation light at which at least part of the signal intensity of the baseline is equal to the output saturation value of the sensor 15 is set as the measurement light amount. According to this method, since it always moves upward during scanning, there is no useless movement and the measurement time can be shortened.

  FIG. 15 shows another example of a technique for setting a light amount at which the signal intensity of at least a part of the baseline of the interference signal is equal to the output saturation value of the sensor as the measured light amount. FIG. 15A is a flowchart of this method, and FIG. 15B is a conceptual diagram showing the corresponding steps of FIG. 15A on the interference signal. The operator operates the scanning white interference microscope 100 in advance to obtain a predetermined height position (z position) where the interference fringes are observed, that is, the peak position of the interference signal (step S31). Then, scanning is performed to obtain an interference signal in the height direction (z direction) indicating the signal strength in the height direction (step S32).

  Next, the computer 30 obtains a baseline by removing the positive interference signal and the negative interference signal from the interference signal in the height direction (step S33). Then, it is determined whether or not the baseline intensity has reached the output saturation value of the sensor 15 (step S34). When the baseline signal intensity does not reach the output saturation value of the sensor 15 (step S34; No), the light amount is increased (step S35), and the processing after step S32 is performed again. When the baseline signal strength has reached the output saturation value of the sensor 15 (step S34; Yes), an interference signal in a state where the baseline has reached the output saturation value of the sensor 15 is obtained (step S36). . As a result, the amount of light at which at least part of the signal intensity of the baseline is equal to the output saturation value of the sensor 15 is set as the measured amount of light.

  FIG. 16 shows still another example of a method for setting, as a measurement light amount, a light amount at which the signal intensity of at least a part of the baseline of the interference signal is equal to the output saturation value of the sensor. FIG. 16A is a flowchart of this method, and FIG. 16B is a conceptual diagram showing the corresponding steps of FIG. 16A on the interference signal. An operator operates the scanning white interference microscope 100 in advance, and a predetermined in-plane direction position (xy in-plane position) where interference fringes are observed, that is, an in-plane direction (xy direction) indicating signal intensity in the in-plane direction. ) Is acquired (step S41).

  Next, the computer 30 removes the positive interference signal and the negative interference signal from the interference signal in the in-plane direction, and obtains a baseline in the in-plane direction (step S42). Then, it is determined whether or not the baseline signal intensity has reached the output saturation value of the sensor 15 (step S43). When the baseline signal intensity does not reach the output saturation value of the sensor 15 (step S43; No), the light amount is increased (step S44), and the processing after step S42 is performed again. When the intensity of the baseline has reached the output saturation value of the sensor 15 (step S43; Yes), an interference signal in a state where the baseline has reached the output saturation value of the sensor 15 is obtained (step S45). As a result, the amount of light at which at least part of the signal intensity of the baseline is equal to the output saturation value of the sensor 15 is set as the measured amount of light.

  In the three-dimensional shape measurement method using the scanning white interference microscope of the present invention, the computer 30, particularly the arithmetic unit included in the computer 30, reads the program stored in various storage devices and executes each step of the method. . In other words, this program acts to cause a computer to execute a three-dimensional shape measurement method.

  According to the present invention, the envelope can be obtained even when a part of the interference signal is saturated, and the maximum value peak can be obtained. Therefore, the shape of the surface of the measurement object can be measured.

  In particular, according to the present invention, it is possible to obtain the peak of the envelope by using the component of the interference signal that has negatively interfered even in a situation where half of the interference signal has reached saturation, and The shape can be measured.

  Further, according to the present invention, it is possible to obtain an envelope from an interference signal that has negatively interfered and obtain a maximum value peak even in a situation where more than half of the interference signal is saturated.

  In addition, this invention is not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably. In addition, the material, shape, dimension, numerical value, form, number, arrangement location, and the like of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.

  ADVANTAGE OF THE INVENTION According to this invention, in the three-dimensional shape measurement method using a scanning white interference microscope, it is possible to measure an appropriate surface shape even on a measurement object with a low reflectance, that is, a dark object.

10 Device body 11 Light source (white light source)
12 filters (including wavelength filters)
13 Beam splitter 14 Two-beam interference objective lens (objective lens)
15 Sensor 16 Piezo Actuator 20 Stage 30 Computer 100 Scanning White Interference Microscope D Sample (Including Measurement Object)

Claims (12)

A three-dimensional shape measurement method using a scanning white interference microscope,
Using the sensor, acquire the interference signal corresponding to the irradiation light from the light source irradiated to the measurement object,
Among the interference signals, obtain a negative interference signal having a signal strength smaller than the baseline corresponding to the offset value of the signal strength,
Based on the signal intensity of the negative interference signal, a measurement light amount that is a light amount of the irradiation light for measuring the height information of the measurement object is set.
Three-dimensional shape measurement method. The three-dimensional shape measurement method according to claim 1,
Obtaining an envelope of the negative interference signal;
Set the measurement light quantity based on the peak of the envelope,
Three-dimensional shape measurement method. The three-dimensional shape measurement method according to claim 1,
Among the interference signals, at least a part of the positive interference signal whose signal intensity is higher than the baseline exceeds the output saturation value of the sensor, so that at least a part of the positive interference signal is saturated. ,
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 3,
Obtaining at least an envelope of the negative interference signal, obtaining an envelope of the positive interference signal at least partially saturated, and setting the measurement light quantity based on the two envelopes;
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 3,
Obtaining at least the envelope of the negative interference signal and setting the measured light quantity based on at least the peak of the envelope after square detection obtained by square detection of the envelope;
Three-dimensional shape measurement method. The three-dimensional shape measurement method according to claim 1,
Baseline signal strength varies in any direction within the measurement object,
In a state where the signal intensity of at least a part of the baseline has reached the output saturation value of the sensor, the measurement light quantity is set.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 6,
Among the interference signals, all of the positive interference signals whose signal intensity is larger than the baseline exceeds the output saturation value of the sensor, so that no positive interference signal is detected by the sensor.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 6,
In the case where there are a plurality of measurement objects, each of the plurality of measurement objects has a unique visibility sensitivity, and each of the plurality of measurement objects is measured under the unique visibility sensitivity. Set the light intensity,
Three-dimensional shape measurement method. The three-dimensional shape measurement method according to claim 1,
Of the image corresponding to the observation area of the measurement object, from the interference signal obtained with the measurement light quantity, the pixel from which the height information was obtained is removed from the measurement object,
Increase the amount of irradiation light so that the baseline of the interference signal of the remaining pixels reaches the output saturation value of the sensor, and set a new measurement light amount.
Three-dimensional shape measurement method. The three-dimensional shape measurement method according to claim 1,
A baseline is obtained at an upper position separated from the peak of the interference signal by an interval equal to or greater than the coherence length,
The amount of irradiation light at which the signal intensity of at least a part of the baseline is equal to the output saturation value of the sensor is set as the measurement light amount.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 3,
From the interference signal in the height direction of the measurement object, the positive interference signal and the negative interference signal are removed to obtain a baseline in the height direction,
The amount of irradiation light at which the signal intensity of at least a part of the baseline is equal to the output saturation value of the sensor is set as the measurement light amount.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 3,
From the interference signal in the predetermined in-plane direction of the measurement object, to remove the positive interference signal and the negative interference signal, to obtain a baseline in the in-plane direction,
The amount of irradiation light at which the signal intensity of at least a part of the baseline is equal to the output saturation value of the sensor is set as the measurement light amount.
Three-dimensional shape measurement method.