JP6853572B2 - Three-dimensional shape measurement method using a scanning white interference microscope - Google Patents

Description

The present invention relates to a method of performing three-dimensional shape measurement 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 obtained interference signal into height information, and performs various calculations from the obtained interference signal to obtain the surface shape. Judge height, step, film thickness, surface roughness, similar material / dissimilar material, etc.

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

For example, in Patent Document 1, imaging is performed by OCT (optical coherence tomography), but when the detection is saturated, saturated artifacts are generated, so that 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 larger than the Nyquist interval, and data within the sample point interval is interpolated to obtain height information.

Special Table 2015-523578 Japanese Unexamined Patent Publication No. 2009-047527

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

The second problem is the S / N ratio (signal-to-noise ratio) of the sensor. Generally, in a sensor that detects light, the S / N ratio increases exponentially as the incident light intensity increases. In other words, the ratio of noise to the signal decreases exponentially as the incident light intensity increases. Therefore, there is a demand to increase the amount of light from 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 interference microscope, in which an interference signal corresponding to the irradiation light from a light source irradiating a measurement object is acquired by using a sensor to obtain an interference signal. Among them, the irradiation for acquiring a negative interference signal whose signal strength is smaller than the baseline corresponding to the offset value of the signal strength and measuring the height information of the measurement object based on the signal strength of the negative interference signal. Set the measured light amount, which is the light amount of light.

According to the present invention, even if the light amount of the light source is increased and the output value of the sensor reaches the maximum value, that is, it is saturated, the measurement target (sample) is measured with a high light amount by using the component of the negative interference signal. ) Surface shape can be measured. Therefore, it is possible to easily grasp the shape of the surface of a measurement object having 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 the 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 measurement results of a positive interference signal and a negative interference signal with respect to the light amount set value of the light source. 6 (a) to 6 (e) are graphs of interference signals at the representative points shown in FIGS. 5 (a) to 5 (e). FIG. 7 is a graph showing an example of square detection, which is one of the examples used to obtain the envelope of the interference signal waveform. 8 (a) to 8 (e) are graphs showing waveforms for obtaining envelopes after applying square-law detection to the graphs of FIGS. 6 (a) to 6 (e). FIG. 9 is a conceptual diagram showing how the envelope of the interference signal waveform when the light amount setting value of the light source is changed changes with respect to the output value of the sensor. FIG. 10 is a graph in which the measured results of FIG. 5 are explained again based on the interpretation of FIG. 11A and 11B are diagrams showing a method for setting the measured light amount in one embodiment, FIG. 11A shows a flowchart of the method, and FIG. 11B shows the baseline while reaching the output saturation value of the sensor. , The conceptual diagram of the interference signal in the state where the signal strength of the negative interference signal is not the maximum value is shown, and (c) shows the signal strength of the negative interference signal when the baseline reaches the output saturation value of the sensor. The conceptual diagram of the interference signal in the state of the maximum value is shown. FIG. 12 is a flowchart showing a method for setting the measured light amount in another embodiment, and is a flowchart of a three-dimensional shape measuring 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 method of setting a light amount at which the signal intensity of at least a part of the baseline of the interference signal becomes equal to the output saturation value of the sensor as the measured light amount, and FIG. 14A is a flowchart of an example. , (B) is a conceptual diagram showing the corresponding step of (a) on the interference signal. FIG. 15 shows another example of the method of setting the amount of light at which the signal intensity of at least a part of the baseline of the interference signal becomes equal to the output saturation value of the sensor as the amount of measured light, and FIG. 15A shows an example of this example. It is a flowchart, (b) is a conceptual diagram which showed the corresponding step of (a) on an interference signal. FIG. 16 shows still another example of a method of setting the amount of light 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 amount of measured light, and FIG. 16A shows this example. (B) is a conceptual diagram showing the corresponding step of (a) on an interference signal.

Hereinafter, preferred embodiments of the three-dimensional shape measuring method using the scanning white interference microscope according to the present invention will be described in detail with reference to FIGS. 1 to 11.

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 target) 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-luminous flux interference objective lens (objective lens) 14, a sensor (detector) 15, and a piezo actuator 16.

As shown by the arrow A, the irradiation light (white light) emitted from the light source 11 passes through the filter (for example, wavelength filter, polarizing filter, etc.) 12 and then is guided to the diluminous flux interference objective lens 14 by the beam splitter 13. Arrow B). The irradiation light is a beam splitter in the two-luminous flux interference objective lens 14, and the first irradiation light toward the measurement target (including the sample S itself and the substance inside the sample S) side and the second irradiation light toward the reference mirror side (not shown). It is divided into two parts of the irradiation light. A measurement signal 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 and the optical distance from the beam splitter to the reference mirror become equal. Is observable in the form of interference signals of two irradiation lights, 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 the reference mirror (not shown) is fixed, by sweeping with the piezo actuator 16 (movement of arrow C), the distance from the object to be measured is increased. The distance is changing. 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 biluminal interference objective lens 14 in the height direction along the arrow C, and measures the object to be measured (including the sample D and the substance inside the sample D). Is scanned in the height direction (z direction), and the surface properties (unevenness, etc.) of the object to be measured are observed.

FIG. 2 is a log-log 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 general, the larger the amount of light incident on the sensor, the smaller the proportion of noise generated from the sensor 15 according to the power function (since the graph is a logarithmic display, it decreases linearly). From the characteristics of this sensor 15, it can be seen that the noise ratio becomes smaller when the incident light amount, that is, the output signal intensity is as large as possible, and the measurement can be performed under the condition of good S / N ratio (right side of the graph). The sensor 15 is a device capable of capturing light, and in a broad sense, includes an image sensor, a camera, and the like, and is not particularly limited.

FIG. 3 shows a general interference signal observed by a scanning white interference microscope 100, that is, an interference signal obtained when an object to be measured is irradiated with irradiation light (white light) from a light source 11 with a predetermined amount of light I. It is a graph which shows. The horizontal axis corresponds to the z position (height position), which is the position of the object to be measured in the sample S. Here, the horizontal axis corresponds to the optical path difference (OPD: Optical Path Difference) Δp, and the optical path length difference Δp is the optical distance from the beam splitter in the two-beam interference objective lens 14 described above to the object to be measured. 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 object to be measured exists at this position.

The signal intensity S (I) observed by the sensor 15 of the scanning white interference microscope 100 is the reference light intensity I ₁ and the reflected light from the object to be measured at a certain incident light intensity I as shown by the following equation (1). It consists of an offset term (first and second terms) of intensity I _{2 and a third term which is an interference signal.} Δp in the third term is the above-mentioned optical path length difference. As shown in FIG. 3, the offset term is an offset value of the signal strength given as a standard with respect to the signal strength 0 of the interference signal, regardless of the existence of the object to be measured.

The third term, which is the interference term of the equation (1), corresponds to the interference signal shown by the solid line in FIG. Generally, the _{portion above the offset terms of I 1} and I ₂ is called a positive interference signal that interferes positively, and the portion below the offset term is called a negative interference signal that interferes negatively. In the positive interference signal portion, the interference signal becomes bright, and in the negative interference signal portion, the interference signal becomes dark, and interference fringes in which light and dark patterns are repeated are formed. This interference fringe corresponds to the unevenness which is the height information (height position) of the object to be measured.

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

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

In FIG. 3, the offset terms (I ₁ + I _{2 ) of I 1} and I ₂ correspond to the baseline B (I) and are given by the following equation (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 is. It is a negative interference signal.

It should be noted that since the equation (1) represents a physical phenomenon, it is measured by the sensor 15 after the interference phenomenon actually occurs. Therefore, even if the _{offset term by 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, a portion below 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 strength of the equation (3) is detected by the sensor 15. Will be done.

Here, when the amount of light I of the irradiation light of the light source 11 _{is increased, the ascending speed of the baseline B, which is the offset term of I 1} and I ₂ , (the change in B (I) with respect to the change in I, and B. (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, if the ascending speed of the magnitude of the interference signal of the third term in the equation (1) is larger than the ascending speed of the offset term represented by the above equation (5). As the amount of light I of the light source 11 increases, the interference signal also increases, which is preferable in terms of measurement. However, in reality it cannot happen. This is because, as shown in the following equation (6), the offset term B (I) is always equal to or greater than the maximum value of the third term when viewed from the relationship between the additive and geometric mean, and is obtained by differentiating the equation (6). This is because, as shown in the equation (7), the ascending speed of the offset term is always equal to or higher than the ascending speed of the third term.

As shown in FIG. 2, from the viewpoint of the S / N ratio, it is premised that the larger the amount of light emitted from the light source is, the more preferable it is. However, an increase in the amount of light naturally leads to an increase in the baseline, which is an offset term. According to the above equations (5) to (7), the rate of increase of the baseline is larger than the rate of increase of the interference signal important for measurement, and the interference signal is easily generated by the sensor 15 due to the increase in the amount of light. It has been generally thought that the saturation value of the output is reached, making it difficult to detect accurate intensity.

In view of these circumstances, a concept indicating the sharpness of interference fringes, which is generally called visibility V, is used to select an interference signal that is preferable for measuring height information. That is, the visibility V is a quantity representing the contrast between the light and dark of the interference fringes, and is considered to be synonymous with the contrast and the transfer function MTF (Modulated Transfer Function).

Visibility V is expressed by the following equation (8), and it is generally considered that an interference signal having a large visibility V is preferable for measurement. In the equation (8), I _max is the maximum observed interference signal intensity and I _min is the minimum observed interference signal intensity, respectively, as shown in FIG. 3, as absolute values based on the signal intensity 0 of the sensor 15. The strength of. That is, the visibility V is the ratio of the difference between the maximum observed interference signal intensity and the minimum observed interference signal intensity to the sum of the two.

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 irradiation light of the light source 11 fluctuates along the horizontal axis. The amount of change in visibility with respect to the amount of change in the amount of light on the horizontal axis is dV / dI, and _{corresponds to the slopes γ A} (= 0.33) and γ _B (= 0.13) drawn in FIG. The two slopes correspond to two different measurement objects. FIG. 4 shows a change in visibility in a positive interference signal, and the slope γ (+) becomes the following equation (9) and takes a value of 0 ≦ γ ≦ 1. On the other hand, in the case of the ratio with the negative interference speed, if it is defined as γ (−), it becomes the equation (10), and the value of -1 ≦ γ ≦ 0 is taken.

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

Conventionally, as shown in FIG. 4, attention has been paid to a change in visibility in a positive interference signal, and the amount of light corresponding to the value with the best visibility has been considered to be the optimum amount of light for the light source 11. In Figure 4, the first measurement object having a first slope (first visibility sensitivity) gamma _A is most visibility increases with the amount of light L _1. On the other hand, the second measurement object having a second slope (second visibility sensitivity) gamma _B is most visibility increases with the amount of light L _3. The first measurement object and the second measurement object differ in physical properties such as reflectance (including surface shape, inclination angle, etc.), and the first inclination (first visibility sensitivity) and the second. The slope (second visibility sensitivity) is different.

That is, according to the conventional general idea, the light intensity L ₁ for the first measurement object and the light intensity L ₃ for the second measurement object are the optimum light intensity setting values for the irradiation light, respectively. That is, _{in the range where the slopes γ A} and γ _B are established, the equation (9) is established, and the visibility increases as the amount of light increases. However, when the light _{intensity is larger than the light intensity L 1} and the light intensity L ₃ (on the right side of the graph), the visibility is reduced because the saturation value of the output of the sensor 15 is exceeded, and the output of the light source 11 is the light intensity L ₁ and the light intensity. The conventional way of thinking is that it can be suppressed to _{L 3 or less.} Under this state, for example, the upper envelope shown by the dotted line in FIG. 3, that is, the envelope of the positive interference signal is fitted by a predetermined method (for example, the model function of the sample point of the positive interference signal obtained by sampling). ), And the height information is obtained from the peak.

However, it should be considered that the amount of light that can obtain the maximum signal strength is the optimum amount of light. Therefore, the inventor paid attention to the change of the negative interference signal, particularly the change of the negative interference signal with respect to the change of the amount of light, unlike the conventional way of thinking. This is because it is also possible to acquire the peak of the envelope from a negative interference signal, as in the lower envelope shown by the alternate long and short dash line in FIG. FIG. 5 is a graph plotting the intensity of the positive interference signal and the intensity of the negative interference signal with respect to the set value of the amount of light of the light source 11. In order to make it easier to understand the phenomenon, the light source 11 is selected so that the amount of output light changes linearly. From this figure, as the light intensity setting is increased, the intensity of the positive interference signal reaches its peak, and then the intensity of the negative interference signal reaches the smallest value (negative peak). The object to be measured with the slope γ _A is the part represented by the representative points (c) and (d).

FIG. 6 is a graph of interference signals at the representative points shown by (a) to (e) of the light amount setting values of the light source for the measurement object _{of γ A = 0.33 in FIG.} 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 also increases. At this time, it should be noted that the condition of the equation (7) is satisfied. Then, when the light intensity setting value is further increased, as shown in FIG. 6C, the positive interference signal reaches the maximum output value of the sensor, that is, the saturation value (upper limit in the graph). Then, when the light intensity setting value is further increased, the baseline reaches the saturation value of the sensor as shown in FIG. 6D. Then, as the light intensity setting value is further increased, even the negative interference signal reaches the saturation value, and the magnitude of the interference signal gradually observed as shown in FIG. 6E becomes smaller.

In such an event, the equation (7) is established, that is, the rate of increase in the magnitude of the interference signal in the third term of the equation (1) is offset by the equation (5) under an increase in the amount of light. Derived from the term, that is, below the rate of rise of the baseline. Except when γ = 1 (when the ratio of the numerator and denominator in equation (9) is the same, that is, when the interference signal intensity increases equally as the average luminance value increases), increasing the light intensity setting value causes interference. The magnitude of the signal finally becomes smaller as shown in FIG. 6 (e). In addition, in FIG. 6 (d), the positive interference signal is 0, and originally, even in FIG. 5 (d), the part of the positive interference signal (the symbol of the white diamond shape ◇) must theoretically be 0. However, due to a measurement error, a predetermined value is output.

FIG. 7 shows an example of square-law detection, which is one of the methods for obtaining an envelope. Note that the maximum peak positions of the envelopes of the positive and negative interference signals (magnitude ₄ I _{1 I 2} ) originally consist of the third term of equation (1) and therefore match. To do. By using square detection, it is possible to utilize twice as much data as a combination of positive and negative interference signals.

8 (a) to 8 (e) are the results of applying the generation of envelopes by square detection as shown in FIG. 7 to the waveforms of FIGS. 6 (a) to 6 (e). In particular, it is possible to generate an envelope even when a part of the interference signal is saturated as shown in FIGS. 8 (d) and 8 (e). In this case, the original was only a negative interference signal, but by using square detection, it is possible to compare the positive interference signals shown in FIGS. 8A to 8C by absolute values. However, although the square detection is taken as an example of the method for obtaining the envelope, any method may be used without limitation.

FIG. 9 shows the change in the envelope of the interference signal when the light amount set value of the light source 11 is increased. Although the observer can observe the interference signal only through the sensor 15, even if the output value of the sensor 15 is saturated and the observer cannot observe the interference signal, the interference phenomenon as a physical phenomenon actually occurs. That is, FIGS. 9 (d) and 9 (e) show the expected interference signal even at the saturation value or higher of the sensor 15.

As shown in FIGS. 9A and 9B, when the light intensity setting value of the light source 11 is small, the output value of the sensor 15 is not saturated, so that the observed positive interference signal intensity and negative interference signal are observed. The 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 strength of the positive interference signal (positive interference signal strength) becomes maximum. Become. As for the signal intensity of the observed positive interference signal, the saturation value −B is observed. On the other hand, at this time, since the negative interference signal has not reached the saturation value yet, the signal strength of the negative interference signal (negative interference signal strength) is observed at S (−) −B.

When the light intensity setting value of the light source 11 is further increased, the baseline reaches the saturation value and the signal intensity of the observed positive interference signal becomes 0, as shown in FIG. 9D. Then, when the baseline reaches the saturation value, the signal strength of the negative interference signal becomes maximum. Since the baseline has reached the saturation value, the signal strength of the S (−)-saturation value is observed.

As the light intensity setting value of the light source 11 is further increased, as shown in FIG. 9 (e), the maximum value S (-)-saturation value of the signal intensity of the negative interference signal gradually decreases, and the light intensity further decreases. If the set value is increased, it will eventually reach 0 as in the case of a positive interference signal.

FIG. 10 is a graph obtained by analyzing the relationship between the change in the amount of light of the light source 11 and the change in the signal intensity of the interference signal based on the concept of FIG. 9 with respect to the graph of FIG. The white diamond (◇), which is a positive interference signal of the measurement object of 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 strength increases (see arrow A). Then, when the signal intensity of the positive interference signal reaches the saturation value of the sensor 15, the light amount setting value is L1 (see FIG. 4). Since the positive interference signal has already reached the saturation value of the sensor 15 at a light intensity 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 is reduced (see arrow B).

On the other hand, the signal strength of the negative interference signal increases for a while even 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 strength of the negative interference signal reaches the maximum value, it can be considered that the baseline strength reaches the saturation value.

The same conclusion can be obtained for the object to be measured with the second inclination (second visibility sensitivity) γ _B (= 0.13), and the amount of light L3 at which the signal intensity of the positive interference signal reaches its peak (see FIG. 4). 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 intensity of the light source 11 is the optimum value of the light intensity when the visibility is maximum or before the interference signal is saturated, that is, before the positive interference signal reaches the maximum value. It was generally set (see FIG. 4).

However, in order to obtain the three-dimensional shape of the object to be measured, it is sufficient to obtain the maximum value of the envelope as shown in FIG. 3, that is, the peak of the envelope, and even if a part of the positive interference signal is saturated. However, it is possible to find the envelope. That is, it is possible to obtain the peak position of the envelope only from the negative interference signal, and even from a part of the negative interference signal, it is possible to obtain the peak position of the envelope (for example, FIG. 8E). reference). In particular, it is possible to acquire at least the envelope of a negative interference signal and set the measured light amount based on at least the peak of the envelope after the square detection obtained by the square detection of the envelope. In this case, as long as there is no problem, the envelope of the saturated positive interference signal may be acquired, and the measured light amount may be set together with the envelope of the negative interference signal. Further, the envelope of the positive interference signal and the envelope of the negative interference signal may be combined for square detection.

The present invention concludes that the amount of light at which the signal intensity takes the maximum value is the optimum amount of light for acquiring height information for a negative interference signal that is estimated to have the maximum magnitude of the interference signal rather than visibility. Derived. In this document, this optimum amount of light to be set is called "measured light amount" in order to measure the height information of the object to be measured.

FIG. 11A is a flowchart for setting the measured light amount according to the embodiment of the present invention. The operator operates the computer 30 of the scanning white interference microscope 100, scans (scans) in the height direction, and focuses on a predetermined observation position (predetermined height position) of the measurement object. The light beam interference objective lens 14 is moved. Then, a mode for increasing the amount of irradiation light of the light source 11 is set at a predetermined observation position, and the amount of light 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. (Step S2), if not reached (see FIGS. 9 (a) and 9 (b)), the process returns to step S1 and the increase in the amount of light is continued (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), and if not, 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 the observation region which is the current height position and the region (in the xy plane) of the measurement object currently being observed. Within (for example, 14 fields of view of the two-luminous flux interference objective lens), it is determined that the light amount is the optimum light amount for measuring the height information of the object to be measured, and the light amount is set as the measurement light amount of the irradiation light. (Step S5). This state is the state shown in FIG. 9D, and the signal strength 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.

Further, the computer 30 also determines whether or not the negative interference signal (envelope) has reached the maximum value (for example, whether the peak of the envelope has reached the maximum value) (step S6), and if it has not reached the maximum value. Return to step S1 and continue increasing the amount of light (step S6; No). When the negative interference signal (envelope) has reached the maximum value (step S6; Yes), the computer 30 sets the amount of light in the interference signal as the measured amount of 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 and the time when the peak of the negative interference signal reaches the maximum value are the same in all observation regions. Therefore, the process of FIG. 11 ends in step S4. However, the baseline signal strength is generally not a constant value as shown in FIG. 3, but fluctuates in an arbitrary direction in the measurement object, for example, in the xy plane. In FIGS. 11 (b) and 11 (c), as a premise for determining step S6, the signal strength of the baseline is not a straight line as shown in FIG. 3, but the horizontal axis is an arbitrary direction in the xy plane, and this direction. Indicates a state in which the signal strength of the baseline fluctuates (takes a baseline curve). In this case, the baseline signal strength of each pixel fluctuates within the observation region.

FIG. 11B shows a conceptual diagram of an interference signal in a state where the baseline reaches the output saturation value of the sensor but the signal strength of the negative interference signal (envelope) is not maximized (step S6). No). Here, the signal strength of the baseline fluctuates in an arbitrary direction in the measurement object, and the signal strength of at least a 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 amount in this state may be set as the measured light amount without further increasing the light amount. 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 (envelope) is the maximum value. The conceptual diagram of the interference signal in the state of is shown (step S7). This means that the optimum amount of light is obtained in the pixel of interest. In this state, all of the positive interference signals having a signal strength higher than that of the baseline of the interference signals exceed the output saturation value of the sensor 15, so that the positive interference signals are not detected by the sensor 15. In this respect, it is the same as FIGS. 9 (d) and 9 (e).

In the above processing, the computer 30 acquires a negative interference signal having a signal strength smaller than the baseline corresponding to the offset value of the signal strength of the interference signal, and based on the signal strength of the negative interference signal, the object to be measured. The measured light amount, which is the amount of irradiation light for measuring the height information of the computer, is set. More specifically, the computer 30 acquires the envelope of the negative interference signal as described above, and sets the measured light amount 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 strength of at least a part of the baseline of the first measurement object is the sensor 15. When the output saturation value is reached, the first measured light intensity is set. On the other hand, for the second measurement object having the second visibility sensitivity, when the signal strength of at least a part of the baseline of the second measurement object reaches the output saturation value of the sensor 15. , Set a second measured light amount different from the first measured light amount. In this way, it is possible to set the optimum measurement light amount for each material (which may be two or more types) having different visibility.

FIG. 12 is a flowchart for determining the optimum amount of light according to another embodiment of the present invention, and shows a three-dimensional shape measurement method by multiple scanning. Multiple scan is to acquire information (height information) of all pixels in an image corresponding to an observation area or a predetermined number or more of pixels in the image by one scan (scanning) in the height direction (z direction). Instead, pixel information is acquired only partially in the image corresponding to the observation area for each scan. Multiple scanning is a concept of acquiring information on 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 (scans) in the height direction, and focuses on a predetermined observation position (predetermined height position) of the measurement object. The light beam interference objective lens 14 is moved. Then, a mode for increasing the amount of irradiation light of the light source 11 is set at a predetermined observation position, and the amount of light 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), and if not, 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 to the measured 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), and if the light amount reaches the maximum output value (step S14; Yes), the process ends. On the other hand, when the amount of light does not reach the maximum output value (step S14; No), the computer 30 determines whether or not the scanning white interference microscope 100 is set to the mode for performing multiple scans (step S15). If the mode for performing multiple scans is not set (step S15; No), the process ends.

On the other hand, when the mode is set to perform multiple scans (step S15; Yes), the computer 30 determines whether or not the number of scans already performed has reached the specified number of multiple scans specified in advance. (Step S16). Further, the computer 30 also determines in parallel whether or not the pixel whose height information has been acquired in the scan already performed has reached the acquisition rate of the pixel specified in advance (step S17). When the number of scans already performed has not reached the specified number of multiple scans (step S16; No), or the pixel whose height information has been acquired in the scan already performed has reached the acquisition rate of the specified pixel. If not (step S17; No), the pixel whose height information is obtained from the interference signal obtained by the measured light amount in step S13 is removed from the measurement target (step S18), and the other remaining pixels are again removed. The process from step S11 is started. In step S11 and subsequent steps, 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 amount of measured light is set.

On the other hand, when the number of scans already performed has reached the specified number of multiple scans (step S16; Yes), or the pixels for which height information has been acquired in the scans already performed have the acquisition rate of the specified number of pixels. If it has been reached (step S17; Yes), the process ends in any case.

FIG. 13 is a conceptual diagram showing the processing 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). This indicates a state in which the signal strength of the baseline fluctuates in this direction. (1) and (2) show the processing of steps S11 and S12 of FIG. 12, and (3) is a part of the images corresponding to the observation area of the xy plane in steps S13 to S17 of FIG. It shows that the height information is obtained only for the pixels. (4) shows the process of step S18 of FIG. 12, and (5) and (6) indicate that the process of steps S11 and S12 of FIG. 12 is performed again.

FIG. 14 shows an 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 becomes equal to the output saturation value of the sensor as the measured light amount. FIG. 14A is a flowchart of the present method, and FIG. 14B is a conceptual diagram showing the corresponding step of FIG. 14A on an interference signal. In advance, the operator operates the scanning white interference microscope 100 to acquire a predetermined height position (z position) where interference fringes are observed, that is, a peak of the interference signal (step S21). The operator operates the scanning white light interference microscope 100, at an upper position away at intervals of more than corresponding coherence length L _C of the half-width of a positive or negative of the interference signal from the position L (L> L _C) Acquire the baseline (step S22). At this position, the waveform of the interference fringes cannot be observed, so only the baseline can be acquired.

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

FIG. 15 shows another example of a method of setting the amount of light 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 amount of measured light. FIG. 15A is a flowchart of the present method, and FIG. 15B is a conceptual diagram showing the corresponding step of FIG. 15A on an interference signal. In advance, the operator operates the scanning white interference microscope 100 to acquire a predetermined height position (z position) where interference fringes are observed, that is, a peak position of an 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 removes the positive interference signal and the negative interference signal from the interference signal in the height direction to obtain the baseline (step S33). Then, it is determined whether or not the intensity of this baseline has reached the output saturation value of the sensor 15 (step S34). If the baseline signal strength has not reached the output saturation value of the sensor 15 (step S34; No), the amount of light is increased (step S35), and the processes after step S32 are performed again. When the signal strength of the baseline has reached the output saturation value of the sensor 15 (step S34; Yes), an interference signal is obtained in a state where the baseline has reached the output saturation value of the sensor 15 (step S36). .. As a result, the amount of light at which the signal intensity of at least a part of the baseline becomes equal to the output saturation value of the sensor 15 is set as the measured light amount.

FIG. 16 shows still another example of a method of setting the amount of light 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 amount of measured light. 16 (a) is a flowchart of the present method, and FIG. 16 (b) is a conceptual diagram showing the corresponding step of FIG. 16 (a) on an interference signal. In advance, the operator operates the scanning white interference microscope 100 to observe 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. ) Acquires the peak position of the interference signal (step S41).

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

In the three-dimensional shape measurement method using the scanning white interference microscope of the present invention, the computer 30, particularly the arithmetic unit of the computer 30, reads the programs stored in various storage devices and executes each step of the method. .. In other words, this program acts to force the computer to perform the 3D shape measurement method.

According to the present invention, it is possible to obtain the envelope even if a part of the interference signal is saturated, and it is possible to obtain the maximum value peak. Therefore, the shape of the surface of the object to be measured can be measured.

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

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

The present invention is not limited to the above-described embodiment, and can be appropriately modified, improved, and the like. In addition, the material, shape, size, numerical value, form, number, arrangement location, etc. of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.

According to the present invention, in the three-dimensional shape measuring method using a scanning white interference microscope, it is possible to measure an appropriate surface shape even for a measurement object having a small reflectance, that is, a dark object.

10 Device body 11 Light source (white light source)
12 filters (including wavelength filter)
13 Beam splitter 14 Two-luminous flux interference objective lens (objective lens)
15 Sensor 16 Piezo actuator 20 Stage 30 Computer 100 Scanning white interference microscope D Sample (including object to be measured)

Claims (11)

This is a three-dimensional shape measurement method using a scanning white interference microscope.
Using a sensor, acquire an interference signal corresponding to the irradiation light from the light source that irradiates the object to be measured.
Of the interference signals, a negative interference signal whose signal strength is smaller than the baseline corresponding to the offset value of the signal strength is acquired.
When the peak of the envelope of the signal intensity of the negative interference signal reaches the maximum value, the amount of light in the interference signal is the amount of light of the irradiation light for measuring the height information of the object to be measured. Set as the amount of light,
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 1.
Of the interference signals, at least a part of the positive interference signal having a signal strength 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 2.
At least the envelope of the negative interference signal is acquired, and at least a partially saturated envelope of the positive interference signal is acquired, and the measured light amount is set based on the two envelopes.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 2.
At least the envelope of the negative interference signal is acquired, and at least the measured light amount is set based on the peak of the envelope after the square detection obtained by the square detection of the envelope.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 1.
The signal strength of the baseline fluctuates in any direction within the measurement object,
The measured light amount is set when the signal intensity of at least a part of the baseline reaches the output saturation value of the sensor.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 5.
Of the interference signals, all of the positive interference signals having a signal strength higher than the baseline exceed the output saturation value of the sensor, so that the positive interference signal is not detected by the sensor.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 5.
When there are a plurality of measurement objects, the plurality of measurement objects each have a unique visibility sensitivity, and each measurement of the plurality of measurement objects is performed under the unique visibility sensitivity. Set the amount of light,
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 1.
From the image corresponding to the observation area of the measurement target, the pixel from which the height information is obtained is removed from the measurement target from the interference signal obtained by the measurement light amount.
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 amount of measured light is set.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 1.
A baseline is obtained at an upper position separated from the peak of the interference signal at intervals 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 measured light amount.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 2.
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 the 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 measured light amount.
Three-dimensional shape measurement method. The three-dimensional shape measuring method according to claim 2.
The positive interference signal and the negative interference signal are removed from the interference signal in the predetermined in-plane direction of the measurement object to obtain the 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 measured light amount.
Three-dimensional shape measurement method.

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