Patent Publication Number: US-2022214275-A1

Title: Measurement apparatus and measurement method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Japanese Patent Application No. 2019-77371 filed on Apr. 15, 2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a measurement apparatus and a measurement method. 
     BACKGROUND 
     A method to measure the state of adhesion between layers by measuring the reflection or transmission of terahertz waves in a sample with a plurality of layers is known. For example, see patent literature (PTL) 1. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 5684819 B2 
     SUMMARY 
     Technical Problem 
     Improvement in the measurement accuracy of the state of adhesion between layers is desired. 
     It is an aim of the present disclosure to provide a measurement apparatus and a measurement method that can improve the measurement accuracy of the state of adhesion between layers. 
     Solution to Problem 
     A measurement apparatus according to an embodiment includes a generator configured to cause an electromagnetic wave to be incident on a sample; a receiver configured to receive an electromagnetic wave reflected by the sample; and a controller configured to control the generator and the receiver. The sample includes a first layer on which the electromagnetic wave is incident and a second layer stacked on the first layer, the controller is configured to detect whether the third layer is present between the first layer and the second layer based on the electromagnetic wave incident on the sample from the generator and the electromagnetic wave received by the receiver, and the generator is configured to cause the electromagnetic wave to be incident at an angle such that the electromagnetic wave is totally reflected between the first layer and the third layer and/or between the first layer and the second layer. In this way, an evanescent wave (near-field light) localized in the region of approximately the wavelength of the electromagnetic wave enables detection of the third layer, located near the interface between the first and second layers, with a depth resolution equal to or less than the wavelength of the electromagnetic wave. The measurement accuracy of the state of adhesion between layers can thereby be improved. 
     The measurement apparatus according to an embodiment may further include a displacer configured to displace at least one of the first layer and the second layer in a direction away from the other. In this way, the measurement apparatus can judge whether the sample is in a full contact state or a tightly adhered state. The measurement accuracy of the state of adhesion between layers can thereby be improved. 
     In the measurement apparatus according to an embodiment, the displacer may be configured to vibrate at least one of the first layer and the second layer. In this way, the measurement apparatus can judge, with a simple configuration, whether the sample is in a full contact state or a tightly adhered state. The measurement accuracy of the state of adhesion between layers can thereby be improved. 
     In the measurement apparatus according to an embodiment, the displacer may be configured to apply a force to at least one of the first layer and the second layer in a direction away from the other. In this way, the accuracy of determining whether the sample is in a full contact state or a tightly adhered state improves. The measurement accuracy of the state of adhesion between layers can thereby be improved. 
     In the measurement apparatus according to an embodiment, the controller may be configured to calculate the area over which the first layer and the third layer are in contact based on the electromagnetic wave incident on the sample from the generator and the electromagnetic wave received by the receiver. In this way, the detection accuracy of the third layer can be improved. The measurement accuracy of the state of adhesion between layers can thereby be improved. 
     In the measurement apparatus according to an embodiment, the controller may be configured to calculate the thickness of the third layer based on the electromagnetic wave incident on the sample from the generator and the electromagnetic wave received by the receiver. In this way, the detection accuracy of the third layer can be improved. The measurement accuracy of the state of adhesion between layers can thereby be improved. 
     In the measurement apparatus according to an embodiment, the controller may be configured to simultaneously calculate the area over which the first layer and the third layer are in contact and the thickness of the third layer based on the electromagnetic wave incident on the sample from the generator and the electromagnetic wave received by the receiver. In this way, the time required to detect the third layer may be reduced. 
     The measurement apparatus according to an embodiment may further include at least one of an incidence angle adjuster located between the generator and the first layer and an exit angle adjuster located between the receiver and the first layer. When the measurement apparatus includes the incidence angle adjuster, a simple configuration enables the angle of incidence on the first layer to satisfy the total reflection condition more easily. When the measurement apparatus includes the exit angle adjuster, loss of the electromagnetic wave can be reduced. 
     A measurement method according to an embodiment includes causing an electromagnetic wave to be incident on a sample including a first layer and a second layer that are stacked, the electromagnetic wave being incident on the first layer; receiving an electromagnetic wave reflected by the sample; and detecting whether the third layer is present between the first layer and the second layer based on the electromagnetic wave that is caused to be incident on the sample and the electromagnetic wave that is received. The causing of the electromagnetic wave to be incident includes causing the electromagnetic wave to be incident on the first layer at an angle such that the electromagnetic wave is totally reflected between the first layer and the third layer and/or between the first layer and the second layer. In this way, an evanescent wave (near-field light) localized in the region of approximately the wavelength of the electromagnetic wave enables detection to a depth equal to or less than the wavelength of the electromagnetic wave, i.e. detection of the state near the interface between the first and second layers with a depth resolution equal to or less than the wavelength. The measurement accuracy of the state of adhesion between layers can thereby be improved. 
     Advantageous Effect 
     According to the present disclosure, a measurement apparatus and a measurement method that can improve the measurement accuracy of the state of adhesion between layers are provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a block diagram illustrating an example configuration of a measurement apparatus according to an embodiment; 
         FIG. 2  is a cross-sectional diagram illustrating an example configuration of a measurement apparatus according to an embodiment; 
         FIG. 3  is a cross-sectional diagram illustrating total reflection between first and second layers; 
         FIG. 4  is a graph illustrating an example of the absorption spectrum of a sample; 
         FIG. 5  is a cross-sectional diagram illustrating total reflection between first and third layers; 
         FIG. 6  is a graph illustrating an example of the absorption spectrum of the first layer; 
         FIG. 7  is a cross-sectional diagram illustrating an example of a configuration in which an electromagnetic wave beam is totally reflected across second and third layers that are aligned in the in-plane direction of a sample; 
         FIG. 8  is a graph illustrating an example of the total reflection absorption spectrum measured by the configuration example in  FIG. 7 ; 
         FIG. 9  is a cross-sectional diagram illustrating an example of a configuration in which an evanescent field seeps across third and second layers that are aligned in the depth direction of a sample; 
         FIG. 10  is a graph illustrating an example of the total reflection absorption spectrum measured by the configuration example in  FIG. 9 ; 
         FIG. 11  is a plan view illustrating an example of scanning a sample in the in-plane direction; 
         FIG. 12  is a flowchart illustrating example procedures of a measurement method according to an embodiment; 
         FIG. 13  is a flowchart illustrating an example of procedures for detecting the third layer; 
         FIG. 14  is a graph illustrating an example of the total reflection absorption spectrum measured when a displacer displaces the first layer; 
         FIG. 15  is a flowchart illustrating an example of procedures for detecting the third layer while displacing the first layer; and 
         FIG. 16  is a cross-sectional diagram illustrating an example of electromagnetic wave progression when the refractive index of the first layer is smaller than the refractive index of the second layer. 
     
    
    
     DETAILED DESCRIPTION 
     Comparative Example 
     Various methods can be considered for measuring samples. As a comparative example, the amount of functional groups contained a sample can be measured by infrared light (IR), for example. However, IR is easily absorbed by materials. It is therefore easy to use IR to measure the surface or near-surface of a sample, but not the interior of a sample. IR is thus difficult to use for measuring the state of adhesion between a plurality of layers contained in a sample. 
     As a comparative example, X-rays, ultrasound, or laser ultrasound can be used to measure the voids present inside a sample. The use of X-rays, however, entails a risk of exposure and also requires large equipment. Ultrasound or laser ultrasound has the problem of depth resolution being on the order of several hundred micrometers, depending on the measurement conditions. Considering how the adhesive strength between a plurality of layers contained in a sample can be reduced by voids on the order of several micrometers, X-rays, ultrasound, or laser ultrasound, which only have a low depth resolution, are difficult to use for measuring the state of adhesion between layers. 
     As a comparative example, the thickness of each layer in a sample containing a base material and an adhesive layer can be measured by analyzing the time waveform of the terahertz wave reflection. However, when the pulse width of the terahertz wave is approximately 1 picosecond (psec), it is impossible to discern whether the reflected wave is reflected at the surface of the base material or at the adhesive interface unless the distance between each layer is a hundred and several tens of micrometers or more. In other words, the depth resolution of the reflected wave is low. Considering how the adhesive strength between a plurality of layers contained in a sample can be reduced by voids on the order of several micrometers, a method based on analysis of the time waveform of the reflection of terahertz waves, which only has a low depth resolution, is difficult to use for measuring the state of adhesion between layers. 
     As described above, problems arise in the possible comparative examples for measuring samples, such as the depth resolution of the measurement being on the order of 100 μm or more, or safety being at risk. To measure the state of adhesion between layers with high accuracy, measurement of the sample with high depth resolution is required. The ability to measure safely is also required. 
     Therefore, the present disclosure describes a measurement apparatus  1  (see  FIG. 1 ) and a measurement method that can measure the state of adhesion between layers with high accuracy and without increasing safety-related risks. 
     Embodiments 
     As illustrated in  FIGS. 1 and 2 , a measurement apparatus  1  according to an embodiment of the present disclosure includes a controller  10 , a generator  20 , and a receiver  30 . In the measurement apparatus  1 , the generator  20  generates electromagnetic waves, and the electromagnetic waves are incident on a sample  50 . The electromagnetic waves are reflected by the sample  50  and are incident on the receiver  30 . The measurement apparatus  1  receives the electromagnetic waves reflected by the sample  50  with the receiver  30  and detects the intensity of the electromagnetic waves. The measurement apparatus  1  measures information regarding the sample  50  based on the intensity of the electromagnetic waves generated by the generator  20  and the intensity of the electromagnetic waves received by the receiver  30 . 
     The generator  20  may generate terahertz waves as electromagnetic waves. Terahertz waves are electromagnetic waves having a frequency between 0.1 THz and 10 THz. The generator  20  may generate millimeter waves as electromagnetic waves. Millimeter waves are electromagnetic waves having a wavelength between 1 mm and 10 mm. Terahertz waves or millimeter waves penetrate into the sample  50  more easily than IR. The terahertz waves or millimeter waves that penetrate into the sample  50  contain information regarding the absorption spectrum of the material contained in the sample  50 . Terahertz or millimeter waves do not pose the same exposure risk as X-rays. The generator  20  is also referred to as a generation device. 
     The receiver  30  may receive the electromagnetic waves reflected by the sample  50  and detect the intensity of the electromagnetic waves. In other words, the measurement apparatus  1  may analyze the sample  50  based on the intensity of the totally reflected electromagnetic waves. The measurement apparatus  1  may analyze the sample  50  using, for example, attenuated total reflection (ATR). ATR enables the measurement apparatus  1  to analyze information in a region from the surface where an electromagnetic wave is totally reflected to a depth shorter than the wavelength. In other words, the measurement apparatus  1  can analyze the information in the sample  50  in a depth region shorter than the wavelength, i.e., near the interface. If the electromagnetic wave is a terahertz wave, the information in the depth direction of the sample  50  can be analyzed on the order of several micrometers to several hundred micrometers. If the electromagnetic wave is a millimeter wave, the information in the depth direction of the sample  50  can be analyzed on the order of several hundred micrometers to several millimeters. The receiver  30  is also referred to as a reception device. 
     The measurement apparatus  1  may further include a displacer  40 . The displacer  40  displaces at least a portion of the sample  50 , as described below. The displacer  40  may, for example, be configured to apply an external force, such as a tensile force, to the sample  50 . The displacer  40  may, for example, be configured to apply vibration to the sample  50 . The measurement apparatus  1  may analyze information on the sample  50  while at least a portion of the sample  50  is deformed by the displacer  40 . 
     The controller  10  acquires information from the components of the measurement apparatus  1  and controls the components. The controller  10  may include a processor such as a central processing unit (CPU). The controller  10  may implement the various functions of the measurement apparatus  1  by executing a predetermined program. 
     The measurement apparatus  1  may further include a memory  12 . The memory  12  may store various information used for operations of the measurement apparatus  1 , programs for implementing the functions of the measurement apparatus  1 , and the like. The memory  12  may function as a working memory of the controller  10 . The memory  12  may, for example, be a semiconductor memory. The memory  12  may be included in the controller  10 . 
     The measurement apparatus  1  may further include a user interface (UI)  14 . The UI  14  may include an input device, such as a mouse or other pointing device, physical keys, or a touch panel, that accepts operation input from a user. The UI  14  may include a display device, such as a display or a light emitting element, that displays information to report to the user. The UI  14  may include a sound device, such as a speaker, that outputs audio for reporting information to the user. The UI  14  is not limited to the above examples and may include various other devices. 
     The measurement apparatus  1  may include a housing  2  that holds the generator  20  and the receiver  30 . The measurement apparatus  1  may include tires  3  to enable movement over the surface of the sample  50 . The tires  3  may be replaced by another moving means. The moving means may, for example, be configured by a combination of a guide rail and a servo motor or a linear motor. The moving means is not limited to these examples and may be replaced by various other means. The measurement apparatus  1  may further include an incidence angle adjuster  22  located between the generator  20  and the sample  50 . The measurement apparatus  1  may further include an exit angle adjuster  32  located between the receiver  30  and the sample  50 . 
     The sample  50  includes a first layer  51 , a second layer  52 , and a substrate  55 . The first layer  51 , the second layer  52 , and the substrate  55  are stacked. The first layer  51  is also referred to as the base material. The second layer  52  adheres the first layer  51  (base material) and the substrate  55 . The second layer  52  is also referred to as the adhesive layer. The first layer  51  and the substrate  55  may be formed from various materials, including but not limited to glass. The second layer  52  may be formed from various materials, including but not limited to an adhesive made of resin or the like. 
     The first layer  51  and the second layer  52  are at least partially in contact. A void may be present, however, in a part of the area between the first layer  51  and the second layer  52 . The void is represented as the third layer  53 . The void can easily form when the adhesive strength between the first layer  51  and the second layer  52  is low. Put another way, the presence of a void between the first layer  51  and the second layer  52  decreases the adhesive strength between the first layer  51  and the second layer  52 . The refractive index of the first layer  51  is represented as n1. The refractive index of the second layer  52  is represented as n2. The refractive index of the third layer  53  is represented as n3. The refractive index of the air filling the void may be considered to be 1. Therefore, the refractive index (n3) of the third layer  53  will be considered to be 1. In the present embodiment, it is assumed that the refractive index (n1) of the first layer  51  is greater than the refractive index (n2) of the second layer  52 . In other words, it is assumed that the relationship n1&gt;n2 holds. The third layer may be a substance other than air, such as water, oil, or any other substance. 
     The electromagnetic wave incident on the sample  50  from the generator  20  is referred to as an incident electromagnetic wave  61 . The incident electromagnetic wave  61  is incident on the first layer  51 . The angle of incidence of the incident electromagnetic wave  61  is expressed as the angle between the normal direction of the surface of the first layer  51  and the travel direction of the incident electromagnetic wave  61 . The incident electromagnetic wave  61  incident on the first layer  51  is reflected at the surface of the second layer  52  or the surface of the third layer  53 . The electromagnetic wave reflected at the surface of the second layer  52  or the surface of the third layer  53  is referred to as a reflected electromagnetic wave  63 . The reflected electromagnetic wave  63  exits from the first layer  51  towards the receiver  30 . 
     When n1&gt;n2 holds, electromagnetic waves are incident from the first layer  51  on the second layer  52  at an angle greater than the critical angle, resulting in total reflection at the interface between the first layer  51  and the second layer  52 . The critical angle representing the total reflection condition when electromagnetic waves are incident from the first layer  51  on the second layer  52  is represented by θ C12 . The relationship sin θ C12 =n2/n1 holds between the refractive index of the first layer  51  and second layer  52  and the critical angle. 
     The incidence angle adjuster  22  adjusts the angle of incidence of the incident electromagnetic wave  61  so that the angle of incidence satisfies the total reflection condition. The refractive index of the incidence angle adjuster  22  may be made larger than the refractive index of the first layer  51 . By doing so, the angle between the travel direction of the electromagnetic wave incident on the first layer  51  from the incidence angle adjuster  22  and the normal direction of the first layer  51  becomes larger than the angle between the travel direction of the electromagnetic wave in the incidence angle adjuster  22  and the normal direction of the first layer  51 . Consequently, the angle of incidence of the incident electromagnetic wave  61  from the first layer  51  to the second layer  52  or the third layer  53  tends to become larger than the angle of incidence from the incidence angle adjuster  22  on the first layer  51 . The incidence angle adjuster  22  may have a hemispherical surface as the incident surface on the side where the electromagnetic waves are incident from the generator  20 . By the electromagnetic waves being incident perpendicularly or substantially perpendicularly to the hemispherical incident surface, the loss due to reflection of the electromagnetic waves at the incident surface can be reduced. Furthermore, by enabling electromagnetic waves traveling in various directions to be incident perpendicularly or substantially perpendicularly to the hemispherical incident surface, the measurement apparatus  1  can easily control the angle of incidence of the incident electromagnetic wave  61  from the first layer  51  to the second layer  52  or the third layer  53  over a wide range. Consequently, with a simple configuration, the angle of incidence of the incident electromagnetic wave  61  on the first layer  51  can easily satisfy the total reflection condition at the interface with the second layer  52  or the third layer  53 . 
     The exit angle adjuster  32  adjusts the travel direction of the reflected electromagnetic wave  63  so that the reflected electromagnetic wave  63  can propagate to the receiver  30 . The refractive index of the exit angle adjuster  32  may be made larger than the refractive index of the first layer  51 . By doing so, the travel direction of the reflected electromagnetic wave  63  traveling from the first layer  51  to the exit angle adjuster  32  approaches the normal direction of the first layer  51 . It thereby becomes easier for the receiver  30  to receive the reflected electromagnetic wave  63 . The exit angle adjuster  32  may have a hemispherical shape on the side that emits the electromagnetic wave towards the receiver  30 . In this way, regardless of the direction in which the reflected electromagnetic wave  63  travels, the reflected electromagnetic wave  63  can be received by the receiver  30 , and the exit angle of the electromagnetic wave emitted from the surface of the exit angle adjuster  32  can be reduced. Consequently, the loss of electromagnetic waves at the surface of the exit angle adjuster  32  can be reduced. 
     In the measurement apparatus  1 , the space between the surface of the first layer  51  and the incidence angle adjuster  22  and exit angle adjuster  32  may be filled with a liquid having a higher refractive index than that of air. This makes it easier for electromagnetic waves to enter the first layer  51  from the incidence angle adjuster  22  and to exit from the first layer  51  to the exit angle adjuster  32 . The liquid may include water, for example, or a liquid with a high refractive index. In the measurement apparatus  1 , the space between the surface of the first layer  51  and the generator  20  and receiver  30  may be filled with a liquid having a higher refractive index than that of air. In this way, the measurement apparatus  1  can easily adjust the angle of incidence without including the incidence angle adjuster  22  and the exit angle adjuster  32 . 
     As illustrated in  FIG. 3 , when an electromagnetic wave is totally reflected at the surface of the second layer  52 , the electromagnetic wave seeps out from the surface of the second layer  52  as an evanescent wave  62  in a predetermined range of depth. The predetermined depth to which the evanescent wave  62  seeps is also referred to as the seeping depth. The incident electromagnetic wave  61  is converted into the reflected electromagnetic wave  63  through the state of the evanescent wave  62 . The intensity of the evanescent wave  62  decays exponentially with depth from the surface of the second layer  52 . The seeping depth of the evanescent wave  62  may be the depth at which the intensity of the evanescent wave  62  becomes an inverse multiple of the natural logarithm. When the natural logarithm is represented by e, the seeping depth may be the depth at which the intensity of the evanescent wave  62  becomes a multiple of 1/e. 
     Electromagnetic waves are attenuated by their interaction with matter. In other words, electromagnetic waves are absorbed by matter. The absorption rate of an electromagnetic wave depends on the frequency of the electromagnetic wave. The relationship between the frequency and the absorption rate of the electromagnetic wave at each frequency is expressed as an absorption spectrum. The absorption spectrum is determined based on physical property parameters such as the composition or density of the material that absorbs the electromagnetic wave, or the bonding state of the atoms or molecules in the material. 
     The incident electromagnetic wave  61  and the reflected electromagnetic wave  63  are absorbed by the first layer  51  based on the absorption spectrum of the first layer  51 . The absorption rate of the electromagnetic wave in the first layer  51  increases with the distance over which the electromagnetic wave propagates through the first layer  51 . As the angle of incidence of the electromagnetic wave is greater, the distance over which the electromagnetic wave propagates through the first layer  51  is greater. Consequently, the absorption rate included in the absorption spectrum of the first layer  51  increases. 
     The evanescent wave  62  is absorbed by the second layer  52  based on the absorption spectrum of the second layer  52 . When the electromagnetic wave is totally reflected at the second layer  52 , the absorption spectrum of the second layer  52  is also referred to as the total reflection absorption spectrum of the second layer  52 . The difference between the spectrum of the electromagnetic wave incident on the sample  50  from the generator  20  and the spectrum of the electromagnetic wave received by the receiver  30  corresponds to the absorption spectrum of the sample  50 . The absorption spectrum of the sample  50  includes the absorption spectrum of the first layer  51  and the total reflection absorption spectrum of the second layer  52 . 
     An example of the absorption spectrum in the sample  50  is illustrated as a graph in  FIG. 4 . In the graph of  FIG. 4 , the horizontal axis represents the frequency of the electromagnetic wave. The vertical axis represents the absorption rate of the electromagnetic wave at each frequency. The absorption spectrum of the sample  50  is represented by a solid line. The absorption spectrum of the first layer  51  is represented by a dashed line. The total reflection absorption spectrum of the second layer  52  is represented by a dashed dotted line. The absorption spectrum of the first layer  51  has a peak at a first frequency, represented by ν1. The total reflection absorption spectrum of the second layer  52  has a peak at a second frequency, represented by ν2. The absorption spectrum of the sample  50  has peaks at ν1 and ν2. 
     The absorption spectrum of the sample  50  can be expressed as the sum of the absorption spectrum of the first layer  51  and the total reflection absorption spectrum of the second layer  52 . The absorption rate of each frequency in the sample  50  can be expressed as the sum of the absorption rate of each frequency in the first layer  51  and the absorption rate of each frequency in the second layer  52 . If the absorption spectrum of the first layer  51  is known, the measurement apparatus  1  can calculate the total reflection absorption spectrum of the second layer  52  as the difference between the measured absorption spectrum of the sample  50  and the absorption spectrum of the first layer  51 . The absorption spectrum of the first layer  51  is also referred to as a reference spectrum. The measurement apparatus  1  may acquire the reference spectrum in advance from a material database or the like. The measurement apparatus  1  may acquire the absorption spectrum obtained by total reflection of the electromagnetic wave at the interface between the first layer  51  and the air as the reference spectrum. The measurement apparatus  1  may correct the reference spectrum based on the angle of incidence of the electromagnetic wave. The measurement apparatus  1  may acquire the reference spectrum for each angle of incidence of the electromagnetic wave. The measurement apparatus  1  may store the angle of incidence of the electromagnetic wave and the reference spectrum corresponding to that angle of incidence in the memory  12  as a table. The reference spectrum may be corrected in accordance with the thickness of the first layer  51 . 
     When the third layer  53  is present between the first layer  51  and the second layer  52 , electromagnetic waves may be incident from the first layer  51  on the third layer  53 . The electromagnetic waves are totally reflected at the interface between the first layer  51  and the third layer  53  by being incident from the first layer  51  on the third layer  53  at an angle greater than the critical angle. The critical angle representing the total reflection condition when electromagnetic waves are incident from the first layer  51  on the third layer  53  is represented by θ C13 . The relationship sin θ C13 =1/n1 holds between the refractive index of the first layer  51  and the critical angle. 
     As illustrated in  FIG. 5 , when an electromagnetic wave is totally reflected at the surface of the third layer  53 , the electromagnetic wave seeps out from the surface of the third layer  53  as an evanescent wave  62  in a predetermined range of depth. The evanescent wave  62  is absorbed by the third layer  53  based on the unique absorption spectrum of the third layer  53 . When the third layer  53  is a void, the absorption of electromagnetic waves in the third layer  53  is negligibly small compared to the absorption of electromagnetic waves in the first layer  51  and second layer  52 . Therefore, when electromagnetic waves are totally reflected at the surface of the third layer  53 , the absorption spectrum of the sample  50  is represented only by the absorption spectrum of the first layer  51 , as illustrated in  FIG. 6 . The horizontal and vertical axes of the graph in  FIG. 6  are the same as the horizontal and vertical axes of the graph in  FIG. 4 . 
     When the spectrum illustrated in the graph of  FIG. 4  is obtained as the absorption spectrum of the sample  50 , the measurement apparatus  1  may judge that the electromagnetic wave was totally reflected by the second layer  52 . When the spectrum illustrated in the graph of  FIG. 6  is obtained as the absorption spectrum of the sample  50 , the measurement apparatus  1  may judge that the electromagnetic wave was totally reflected by the third layer  53 . In other words, the measurement apparatus  1  can judge whether the third layer  53  is present in the portion where the electromagnetic wave is totally reflected based on the measurement result of the absorption spectrum of the sample  50 . 
     The measurement apparatus  1  may calculate the absorption rate for each frequency included in the predetermined range and calculate the absorption spectrum of the sample  50  as the measurement result. The measurement apparatus  1  may calculate the absorption rate of a predetermined frequency as the measurement result. For example, the measurement apparatus  1  may calculate the absorption rate of the second frequency represented by ν2 as the measurement result. The measurement apparatus  1  may judge whether the third layer  53  is present based on the absorption rate of the predetermined frequency. 
     As described above, the measurement apparatus  1  according to the present embodiment judges whether the third layer  53  is present based on the reflection absorption spectrum identified by the absorption rate of the evanescent wave  62  in the second layer  52 . With this approach, the presence of the third layer  53  is detected in a depth region of approximately the seeping depth of the evanescent wave  62 , i.e., deeper than the wavelength of the electromagnetic wave. The measurement accuracy of the state of adhesion between the first layer  51  and the second layer  52  thereby improves. In addition, since the refractive index of the first layer  51  is larger than the refractive index of the second layer  52 , the incident electromagnetic wave  61  is totally reflected regardless of whether the third layer  53  is present. This increases the intensity of the reflected electromagnetic wave  63 . Consequently, the measurement apparatus  1  can calculate the reflection absorption spectrum with high accuracy and can also detect the presence of the third layer  53  with high accuracy. 
     &lt;Calculation of Area and Thickness of Void&gt; 
     The electromagnetic wave that the measurement apparatus  1  causes to be incident on the sample  50  has a predetermined spread. The electromagnetic wave with a predetermined spread is represented as an electromagnetic wave beam  60 , as illustrated in  FIG. 7 . The electromagnetic wave beam  60  is incident on the sample  50 , is totally reflected inside, and is emitted from the sample  50 . When the electromagnetic wave beam  60  is incident on the second layer  52  or the third layer  53  and is totally reflected, an evanescent field  64  is produced on the surface of the second layer  52  or the third layer  53 . The surface of the first layer  51  and the surface of the second layer  52  are assumed to be parallel. In this case, the area of the region where the evanescent field  64  is produced is equivalent to the incident area and the emission area of the electromagnetic wave beam  60  at the surface of the first layer  51 . 
     The absorption spectrum of the electromagnetic wave beam  60  in the sample  50  is determined based on the ratio of electromagnetic waves that are totally reflected at the second layer  52  to electromagnetic waves that are totally reflected at the third layer  53 . For example, if the evanescent field  64  extends across the second layer  52  and the third layer  53 , as illustrated in  FIG. 7 , the absorption spectrum of the electromagnetic wave beam  60  is determined based on the ratio between the respective areas of the evanescent field  64  extending across the second layer  52  and the third layer  53 . The respective areas of the evanescent field  64  extending across the second layer  52  and the third layer  53  are represented as A1 and A2. The sum of A1 and A2 corresponds to the area over which the electromagnetic wave beam  60  spreads. For example, the absorption rate of an electromagnetic wave with a frequency of ν2 when the evanescent field  64  extends across the second layer  52  and the third layer  53  is A1/(A1+A2) times the absorption rate when the evanescent field  64  only extends over the second layer  52 . The case of the evanescent field  64  only extending over the second layer  52  is referred to as ref. The case of the evanescent field  64  extending across the second layer  52  and the third layer  53  is referred to as case 1. In other words, the absorption rate in case 1 for an electromagnetic wave with frequency ν2 is A1/(A1+A2) times the absorption rate of ref. 
     The absorption rate in case 1 is A1/(A1+A2) times the absorption rate of ref not only for electromagnetic waves whose frequency is ν2, but also for electromagnetic waves of other frequencies. As illustrated in  FIG. 8 , the total reflection absorption spectrum for case 1 can be expressed as the spectrum yielded by transforming the total reflection absorption spectrum for ref by a multiple of A1/(A1+A2) in the vertical axis direction. The horizontal and vertical axes of the graph in  FIG. 8  are the same as the horizontal and vertical axes of the graph in  FIG. 4 . The total reflection absorption spectrum for ref is the same spectrum as the total reflection absorption spectrum of the second layer  52  illustrated in  FIG. 4 . 
     The absorption spectrum of the electromagnetic wave beam  60  is determined based on the ratio between A1 and A2. In other words, the measurement apparatus  1  can calculate the ratio between A1 and A2 based on the measurement result of the absorption spectrum of the electromagnetic wave beam  60 . The measurement apparatus  1  can thereby not only detect whether the third layer  53  is present between the first layer  51  and the second layer  52 , but can also calculate the area over which the third layer  53  spreads with high accuracy. If A1 is 0, the measurement apparatus  1  may calculate the area over which the electromagnetic wave beam  60  spreads as the area over which the third layer  53  spreads. The area over which the third layer  53  spreads corresponds to the area over which the first layer  51  and the third layer  53  are in contact. 
     As illustrated in  FIG. 9 , when the thickness of the third layer  53  is smaller than the seeping depth of the evanescent wave  62 , the absorption spectrum of the electromagnetic wave is affected by the absorption due to the second layer  52 . For example, the seeping depth of the evanescent wave  62  of an electromagnetic wave whose frequency is ν2 is represented by D. The thickness of the third layer  53  is represented by D1. If D is greater than D1, the evanescent wave  62  seeps into the second layer  52 . When the evanescent wave  62  seeps into the second layer  52 , the seeping depth is represented by D2, which is calculated as the difference between D and D1. 
     The intensity of the evanescent wave  62  decreases exponentially with depth from the surface of the third layer  53 . The higher the frequency of the electromagnetic wave is, the more the intensity of the evanescent wave  62  tends to decrease. The more the intensity of the evanescent wave  62  tends to decrease, the smaller the seeping depth of the evanescent wave  62  becomes. The seeping depth of the evanescent wave  62  can be expressed as a function of the frequency of the electromagnetic wave. Since the seeping depth is a function of frequency, the seeping depth of the evanescent wave  62  into the second layer  52  varies depending on the frequency of the electromagnetic wave. In some cases, the evanescent wave  62  may not seep into the second layer  52 . 
     The absorption rate of the electromagnetic wave is determined based on the depth at which the evanescent wave  62  seeps into the second layer  52 . The total reflection absorption spectrum for the case of the evanescent wave  62  seeping across the third layer  53  and the second layer  52  that are aligned in the depth direction corresponds to the absorption rate of the total reflection absorption spectrum of the second layer  52 , changed by a predetermined multiplication factor for each frequency. The case of the evanescent wave  62  seeping across the third layer  53  and the second layer  52  that are aligned in the depth direction is referred to as case 2.  FIG. 10  illustrates the total reflection absorption spectrum for case 2. The horizontal and vertical axes of the graph in  FIG. 8  are the same as the horizontal and vertical axes of the graph in  FIG. 4 . The total reflection absorption spectra for ref and case 1 are the same spectra as the total reflection absorption spectra for ref and case 1 illustrated in  FIG. 8 . 
     The graph in  FIG. 10  is normalized so that the absorption rates of electromagnetic waves whose frequency is ν2 match between case 1 and case 2. At frequencies higher than ν2, the absorption rate of case 2 is smaller than the absorption rate of case 1 due to the smaller seeping depth of the evanescent wave  62 . On the other hand, at frequencies lower than ν2, the absorption rate of case 2 is greater than the absorption rate of case 1 due to the greater seeping depth of the evanescent wave  62 . The multiplication factor with respect to the absorption rate of ref at each frequency differs between case 1 and case 2. The measurement apparatus  1  can calculate the thickness of the third layer  53  and the area of the third layer  53  based on the multiplication factor, with respect to the absorption rate of ref, of the absorption rate at each frequency. The measurement apparatus  1  may simultaneously calculate the thickness of the third layer  53  and the area of the third layer  53  based on one total reflection absorption spectrum. As described above, the change in the absorption rate corresponding to the magnitude of the area of the third layer  53  is not frequency dependent. The change in the absorption rate corresponding to the thickness of the third layer  53  is frequency dependent. By considering whether there is frequency dependence, the area and thickness of the third layer  53  can be calculated simultaneously in a predetermined measurement area on which the electromagnetic wave beam  60  is incident. The time required to detect the third layer  53  can be reduced as a result of the area and thickness of the third layer  53  being calculated simultaneously. Furthermore, in a predetermined measurement area, the third layer  53  has different thicknesses on a microscopic level. The measurement apparatus  1  may calculate the average value of the thickness of the third layer  53  within the predetermined measurement area. 
     By calculating the area or thickness of the third layer  53 , the measurement apparatus  1  can improve the detection accuracy of the third layer  53 . The measurement apparatus  1  can thereby improve the measurement accuracy of the state of adhesion between the first layer  51  and the second layer  52 . 
     &lt;Scanning of Surface of Sample  50 &gt; 
     As illustrated in  FIG. 11 , the measurement apparatus  1  may scan an electromagnetic wave beam  60 , having a predetermined spread, along the surface of the sample  50 . By scanning in the plane of the sample  50  with the electromagnetic wave beam  60 , the measurement apparatus  1  can calculate the distribution of the third layer  53  in the plane of the sample  50 . The measurement apparatus  1  can also calculate the area where the third layer  53  extends in the plane of the sample  50  with high accuracy. Furthermore, the measurement apparatus  1  can calculate the distribution of the thickness of the third layer  53  in the plane of the sample  50 . The measurement apparatus  1  may map the distribution of the third layer  53  in the plane of the sample  50 . The measurement apparatus  1  may perform a raster scan on the surface of the sample  50 , or may scan the surface of the sample  50  by another method. 
     By scanning the surface of the sample  50 , the measurement apparatus  1  of the present embodiment can measure the distribution of voids contained in the sample  50 . The measurement apparatus  1  can thereby measure the distribution of the state of adhesion between the first layer  51  and the second layer  52 . 
     &lt;Flowchart of Measurement Method&gt; 
     The measurement apparatus  1  may execute a measurement method that includes the procedures of the example flowchart in  FIG. 12 . The procedures illustrated in  FIG. 12  may be implemented as a measurement program to be executed by the measurement apparatus  1 . 
     The controller  10  acquires measurement conditions (step  51 ). The measurement conditions may include the type or physical property parameters of the materials forming the first layer  51  and the second layer  52 . The physical property parameters of the material may include the refractive index. The measurement conditions may include the thickness of the first layer  51 . 
     The controller  10  adjusts the angles of the generation device and reception device based on the measurement conditions (step S 2 ). The controller  10  adjusts the angle of the generation device so that the electromagnetic wave incident from the first layer  51  on the second layer  52  is totally reflected. The controller  10  adjusts the angle of the reception device to match the angle of the generator  20 . 
     The controller  10  adjusts the position of the measurement apparatus  1  above the surface of the sample  50  (step S 3 ). The controller  10  may move the measurement apparatus  1  by controlling moving means such as the tires  3 . The controller  10  may adjust the position of the measurement apparatus  1  based on a map designated in advance. 
     The controller  10  performs measurement by the ATR method at the current position of the measurement apparatus  1  (step S 4 ). Measurement by the ATR method is referred to as ATR measurement. The procedures for ATR measurement are described below. 
     The controller  10  judges whether scanning over the surface of the sample  50  is complete (step S 5 ). When the scanning is not complete (step S 5 : NO), the controller  10  returns to the procedure of step S 3 . When the scanning is complete (step S 5 : YES), the controller  10  advances to the procedure of step S 6 . 
     The controller  10  displays the measurement results of the sample  50  (step S 6 ). After the procedure of step S 6 , the controller  10  ends execution of the procedures of the flowchart in  FIG. 12 . 
     The controller  10  may perform the ATR measurement of step S 4  in  FIG. 12  according to the procedures of the flowchart in  FIG. 13 . 
     The controller  10  generates an electromagnetic wave, causes the electromagnetic wave to be incident on the sample  50 , and receives the electromagnetic wave reflected from the sample  50  (step S 11 ). The controller  10  controls the generation device to generate the electromagnetic wave and causes the electromagnetic wave to be incident on the sample  50  at a predetermined angle. The electromagnetic wave incident on the sample  50  is reflected within the sample  50  and is emitted toward the reception device. The controller  10  acquires the measurement results of the intensity of the electromagnetic wave received by the reception device. 
     The controller  10  calculates the absorption spectrum of the sample  50  (step S 12 ). The controller  10  can calculate the absorption spectrum of the sample  50  based on the difference between the spectrum of the electromagnetic wave generated by the generation device and the spectrum of the electromagnetic wave received by the reception device. The controller  10  may acquire, in advance, the spectrum of the electromagnetic wave generated by the generation device. 
     The controller  10  calculates the total reflection absorption spectrum (step S 13 ). Based on the absorption spectrum of the sample  50  and the absorption spectrum of the first layer  51 , the controller  10  can calculate the total reflection absorption spectrum of the second layer  52 , the total reflection absorption spectrum of the third layer  53 , or the total reflection absorption spectrum at a surface that includes both the second layer  52  and the third layer  53 . The controller  10  may acquire the absorption spectrum of the first layer  51  in advance. 
     The controller  10  judges whether the third layer  53  is present between the first layer  51  and the second layer  52  based on the total reflection absorption spectrum (step S 14 ). The controller  10  may judge whether the third layer  53  is present based on the calculation result of the total reflection absorption spectrum and the total reflection absorption spectrum of the second layer  52 . The controller  10  may, for example, judge that the third layer  53  is not present when the calculation result for the total reflection absorption spectrum matches the total reflection absorption spectrum of the second layer  52 . The controller  10  may, for example, judge that the third layer  53  is present when the difference between the calculation result for the total reflection absorption spectrum and the total reflection absorption spectrum of the second layer  52  is equal to or greater than a predetermined value. 
     When the controller  10  judges that the third layer  53  is not present (step S 14 : NO), the controller  10  ends execution of the procedures of the flowchart in  FIG. 13  and returns to the procedure of step S 5  in  FIG. 12 . When the controller  10  judges that the third layer  53  is present (step S 14 : YES), the controller  10  calculates the area or thickness of the third layer  53  based on the total reflection absorption spectrum (step S 15 ). After step S 15 , the controller  10  ends execution of the procedures of the flowchart in  FIG. 13  and returns to the procedure of step S 5  in  FIG. 12 . 
     According to the measurement method of the present embodiment, the third layer  53  is detected with high accuracy. The measurement accuracy of the state of adhesion between the first layer  51  and the second layer  52  thereby improves. 
     &lt;Determination of Contact State or Tightly Adhered State&gt; 
     As described above, the measurement apparatus  1  of the present embodiment can judge whether the third layer  53  is present between the first layer  51  and the second layer  52  and calculate the area or thickness of the third layer  53 . Here, even when no third layer  53  is present between the first layer  51  and the second layer  52 , the adhesive strength between the first layer  51  and the second layer  52  might be less than a predetermined strength. The state in which the third layer  53  is present between the first layer  51  and the second layer  52  will be referred to as a partial contact state. The state in which the third layer  53  is not present, but the adhesive strength between the first layer  51  and the second layer  52  is less than a predetermined strength, will be referred to as a full contact state. The state in which the third layer  53  is not present, and the adhesive strength between the first layer  51  and the second layer  52  is equal to or greater than a predetermined strength, will be referred to as a tightly adhered state. 
     When the sample  50  is in the full contact state, a void as the third layer  53  can form by at least one of the first layer  51  and the second layer  52  being displaced in a direction away from the other. When the sample  50  is in the tightly adhered state, a void as the third layer  53  does not form even if at least one of the first layer  51  and the second layer  52  is displaced in a direction away from the other. By using the displacer  40  to displace at least one of the first layer  51  and the second layer  52  in a direction away from the other, the measurement apparatus  1  can determine whether the sample  50  is in the full contact state or the tightly adhered state. 
     The displacer  40  may displace the first layer  51  with respect to the second layer  52  by applying a force to the first layer  51  in a direction such that the first layer  51  moves away from the second layer  52  and the substrate  55 . When the second layer  52  is elastic, the first layer  51  can be displaced with respect to the second layer  52  regardless of whether a void is formed between the first layer  51  and the second layer  52 . The displacer  40  may apply a force equal to or greater than a predetermined value so that a void is formed in a portion where the adhesive strength between the first layer  51  and the second layer  52  is less than a predetermined strength. The displacer  40  may displace the second layer  52  with respect to the first layer  51  by applying a force to the second layer  52  or the substrate  55  in a direction such that the second layer  52  moves away from the first layer  51 . The displacer  40  may displace at least one of the first layer  51  and the second layer  52  in a direction away from the other by applying a force to at least one of the first layer  51  and the second layer  52  in a direction away from the other. 
     The displacer  40  may vibrate the sample  50 . The displacer  40  may include an ultrasonic wave generating element that vibrates the sample  50  by ultrasonic waves. The displacer  40  may include a vibrating element such as a piezoelectric element. The displacer  40  may include a striker that causes the sample  50  to vibrate by striking the sample  50 . The displacer  40  may vibrate the sample  50  so that at least one of the first layer  51  and the second layer  52  vibrates. The displacer  40  may vibrate the sample  50  so that the phase of vibration of the first layer  51  differs from the phase of vibration of the second layer  52  and the substrate  55 . The displacer  40  may vibrate the sample  50  so that the amplitude of the first layer  51  differs from the amplitude of the second layer  52  and the substrate  55 . In this way, at least one of the first layer  51  and the second layer  52  can be displaced in a direction away from the other. The displacer  40  may vibrate the sample  50  so that a void is formed in the portion where the adhesive strength between the first layer  51  and the second layer  52  is less than a predetermined strength. 
     The first layer  51 , the second layer  52 , and the substrate  55  each have a unique resonance frequency. When the resonance frequency of the first layer  51  and the resonance frequency of the second layer  52  differ, the displacer  40  can easily cause the phase of vibration of the first layer  51  and the phase of vibration of the second layer  52  to differ. When the second layer  52  vibrates together with the substrate  55 , the displacer  40  can easily cause the phase of vibration of the first layer  51  and the phase of vibration of the second layer  52  to differ based on the difference between the resonance frequency of the first layer  51  and the resonance frequency of the substrate  55 . When the resonance frequency of the first layer  51  differs from the resonance frequency of the second layer  52  or the substrate  55 , the displacer  40  may vibrate the sample  50  at the resonance frequency of the first layer  51  and increase the amplitude of the first layer  51 . The displacer  40  may vibrate the sample  50  at the resonance frequency of the second layer  52  or the substrate  55  and increase the amplitude of the second layer  52  or the substrate  55 . 
     The controller  10  may measure the absorption spectrum of the sample  50  and calculate the total reflection absorption spectrum while displacing the first layer  51  with the displacer  40 . The controller  10  may calculate the total reflection absorption spectrum at various times while the first layer  51  is being displaced. The case in which the displacement of the first layer  51  is maximized is referred to as case 3. The case in which the displacement of the first layer  51  is between zero and the maximum is referred to as case 4.  FIG. 14  illustrates the total reflection absorption spectra for case 3 and case 4. The horizontal and vertical axes of the graph in  FIG. 14  are the same as the horizontal and vertical axes of the graph in  FIG. 4 . The total reflection absorption spectrum for ref is the same spectrum as the total reflection absorption spectrum for ref illustrated in  FIG. 4 . Based on the total reflection absorption spectrum for case 3, which is the timing when the displacement of the first layer  51  is maximized, the controller  10  may judge whether the third layer  53  is present and may calculate the area or thickness of the third layer  53 . Based on the total reflection absorption spectrum for case 4, the controller  10  may estimate the total reflection absorption spectrum at the timing when the displacement of the first layer  51  is maximized. Based on the estimated total reflection absorption spectrum, the controller  10  may judge whether the third layer  53  is present and may calculate the area or thickness of the third layer  53 . 
     When the displacer  40  applies a force to the first layer  51 , the controller  10  may measure the absorption spectrum of the sample  50  at the time the force applied by the displacer  40  is maximized. The absorption spectrum at the time when the maximum force is applied to the first layer  51  can be considered the absorption spectrum of the sample  50  at the timing when the displacement of the first layer  51  is maximized. By including a configuration in which the displacer  40  applies a force to the first layer  51 , the controller  10  can calculate the total reflection absorption spectrum for case 3 with high accuracy. The measurement apparatus  1  can thereby improve the accuracy of judging whether the state of adhesion between the first layer  51  and the second layer  52  is a full contact state or a tightly adhered state. 
     When the displacer  40  vibrates the sample  50 , the controller  10  may measure an absorption spectrum of the sample  50  over a predetermined period of time. Based on the result of measuring the absorption spectrum of the sample  50  within the predetermined period of time, the controller  10  may judge the timing at which the displacement of the first layer  51  was maximized. The controller  10  may judge whether the third layer  53  is present based on the absorption spectrum of the sample  50  at the timing when the displacement of the first layer  51  was maximized. The controller  10  may judge whether the third layer  53  is present based on the absorption spectrum for which the absorption rate at a predetermined frequency was minimized. By including a configuration in which the displacer  40  vibrates the sample  50 , the controller  10  can calculate the total reflection absorption spectrum for case 3. The measurement apparatus  1  can thereby determine, with a simple configuration, whether the state of adhesion between the first layer  51  and the second layer  52  is a full contact state or a tightly adhered state. 
     &lt;Flowchart&gt; 
     The controller  10  may perform the procedures of the flowchart in  FIG. 15 , including the procedure by which the displacer  40  displaces the first layer  51 , as the ATR measurement performed in step S 4  of  FIG. 12 . 
     The displacer  40  displaces the first layer  51  (step S 21 ). In other words, the controller  10  controls the displacer  40  so that the first layer  51  is displaced with respect to the second layer  52 . 
     The controller  10  generates an electromagnetic wave, causes the electromagnetic wave to be incident on the sample  50 , and receives the electromagnetic wave reflected from the sample  50  (step S 22 ). The controller  10  may execute a procedure that is the same as or similar to the procedure of step S 11  in  FIG. 12 . 
     The controller  10  calculates the absorption spectrum of the sample  50  (step S 23 ). The controller  10  may execute a procedure that is the same as or similar to the procedure of step S 12  in  FIG. 12 . 
     The controller  10  calculates the total reflection absorption spectrum (step S 24 ). The controller  10  may execute a procedure that is the same as or similar to the procedure of step S 13  in  FIG. 12 . 
     The controller  10  judges whether data acquisition is complete (step S 25 ). The controller  10  may judge that data acquisition is complete when the presence of the third layer  53  can be judged based on the total reflection absorption spectrum calculated in the procedures of steps S 21  to S 24 . The controller  10  may judge that data acquisition is complete when the calculated total reflection absorption spectrum corresponds to the total reflection absorption spectrum for case 3 in  FIG. 14 , or when the total reflection absorption spectrum for case 3 can be estimated based on the calculated total reflection absorption spectrum. 
     When the controller  10  does not judge that data acquisition is complete (step S 25 : NO), the controller  10  returns to the procedure of step S 21  and continues to calculate the total reflection absorption spectrum. When the controller  10  judges that data acquisition is complete (step S 25 : YES), the controller  10  judges whether the third layer  53  is present based on the calculated total reflection absorption spectrum (step S 26 ). The controller  10  may execute a procedure that is the same as or similar to the procedure of step S 14  in  FIG. 12 . 
     When the controller  10  judges that the third layer  53  is not present (step S 26 : NO), the controller  10  ends execution of the procedures of the flowchart in  FIG. 15  and returns to the procedure of step S 5  in  FIG. 12 . When the controller  10  judges that the third layer  53  is present (step S 26 : YES), the controller  10  calculates the area or thickness of the third layer  53  based on the total reflection absorption spectrum (step S 27 ). After step S 27 , the controller  10  ends execution of the procedures of the flowchart in  FIG. 15  and returns to the procedure of step S 5  in  FIG. 12 . 
     As described above, the measurement apparatus  1  of the present embodiment can determine whether the sample  50  is in a full contact state or a tightly adhered state by displacing the first layer  51  with the displacer  40 . The state of adhesion of the sample  50  can thereby be detected with high accuracy. 
     In analysis using a general ATR method, a prism having a high refractive index is used for electromagnetic waves to be incident on the analysis target. In the present embodiment, the refractive index of the first layer  51  is larger than the refractive index of the second layer  52 , enabling the first layer  51  to function as a prism. The measurement apparatus  1  in the present embodiment can be considered as analyzing the second layer  52  by the ATR method, using the first layer  51  as a prism. The measurement apparatus  1  can also be considered as analyzing the proportion of the third layer  53  within the second layer  52 . 
     (Example for Case of n1&lt;n2) 
     In the above embodiment, the case of assuming that n1&gt;n2 holds has been described. The measurement apparatus  1  can also judge whether the third layer  53  is present when the refractive index of the first layer  51  is smaller than the refractive index of the second layer  52 , that is, when n1&lt;n2 holds. 
     When the refractive index of the first layer  51  is smaller than the refractive index of the second layer  52 , an incident electromagnetic wave  61   a  traveling from the first layer  51  to the second layer  52  is not totally reflected at the surface of the second layer  52 , as illustrated in  FIG. 16 . Although a portion of the incident electromagnetic wave  61   a  is reflected at the surface of the second layer  52 , the majority of the incident electromagnetic wave  61   a  travels into the second layer  52  as a refracted electromagnetic wave  65 . On the other hand, when the third layer  53  is present, the incident electromagnetic wave  61   b  that travels from the first layer  51  to the third layer  53  is totally reflected on the surface of the third layer  53  and is emitted from the first layer  51  as a reflected electromagnetic wave  63 . In other words, the intensity of the electromagnetic wave that can be received by the receiver  30  differs greatly between the case in which the third layer  53  is present and the case in which the third layer  53  is not present. The measurement apparatus  1  may judge that the third layer  53  is present when the intensity of the electromagnetic wave received by the receiver  30  is equal to or greater than a predetermined value. The measurement apparatus  1  may calculate the area or thickness of the third layer  53  based on the intensity of the electromagnetic wave. 
     The measurement apparatus  1  may operate by selecting between a mode for receiving electromagnetic waves totally reflected by both the second layer  52  and the third layer  53  and a mode for receiving electromagnetic waves totally reflected by the third layer  53  only, based on the magnitude relationship between the refractive index of the first layer  51  and the refractive index of the second layer  52 . The measurement apparatus  1  may acquire the respective refractive indices of the first layer  51  and the second layer  52  by, for example, accepting input of measurement conditions, and may judge the magnitude relationship between the refractive indices. The measurement apparatus  1  may change the method of judging whether the third layer  53  is present or of calculating the area or thickness of the third layer  53  in accordance with the mode of operation. 
     Even when n1&gt;n2 holds, the incident electromagnetic wave  61  is not totally reflected on the surface of the second layer  52  when incident from the first layer  51  on the second layer  52  at an angle smaller than the critical angle θ C12 . Conversely, the incident electromagnetic wave  61  is totally reflected on the surface of the third layer  53  when incident from the first layer  51  toward the third layer  53  at an angle greater than the critical angle θ C13 . In other words, in the case of θ C12 &gt;θ C12 , the measurement apparatus  1  may operate in the mode of receiving the electromagnetic wave that is totally reflected only by the third layer  53  when the angle of incidence of the incident electromagnetic wave  61  is larger than θ M  and smaller than θ C13 . 
     The measurement apparatus  1  may further receive electromagnetic waves simply reflected on the surface of the second layer  52 , even when operating in the mode of receiving electromagnetic waves totally reflected only by the third layer  53 . The measurement apparatus  1  may calculate the reflectance of the electromagnetic wave at the surface of the second layer  52  by receiving the electromagnetic wave simply reflected on the surface of the second layer  52 . The reflectance of an electromagnetic wave depends on the frequency of the electromagnetic wave. The relationship between the frequency and the reflectance of the electromagnetic wave at each frequency is expressed as a reflection spectrum. The measurement apparatus  1  may judge whether the third layer  53  exists, and calculate the area or thickness of the third layer  53 , based not only on the total reflection absorption spectrum but also on the reflection spectrum. 
     Embodiments of the present disclosure have been described with reference to the drawings, but specific configurations are not limited to these embodiments, and a variety of modifications may be made without departing from the spirit and scope thereof. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Measurement apparatus 
               2  Housing 
               3  Tire 
               10  Controller 
               12  Memory 
               14  User interface (UI) 
               20  Generator (generation device) 
               22  Incidence angle adjuster 
               30  Receiver (reception device) 
               32  Exit angle adjuster 
               40  Displacer 
               50  Material ( 51 : first layer,  52 : second layer,  53 : third layer,  55 : substrate) 
               60  Electromagnetic wave beam 
               61  ( 61   a ,  61   b ) Incident electromagnetic wave 
               62  Evanescent wave 
               63  Reflected electromagnetic wave 
               64  Evanescent field 
               65  Refracted electromagnetic wave