JPH0915213A - Sample holder for photoabsorption measuring device - Google Patents

Abstract

PURPOSE: To enhance the reliability and efficiency of measurements by providing a suction holding mechanism for samples using a sample elastic support member. CONSTITUTION: As for the pressing by a suction holding mechanism which uses an elastic support member 2 for a sample 7, since the pressing pressure is determined by the difference between atmospheric pressure and a sucked vacuum pressure, if evacuation up to more than a certain degree of vacuum is performed the pressing condition can be held constant easily. Therefore, this sample holder 1 for a photoabsorption measuring device can hold the acoustic contact condition with a solid sample constant. Therefor, the reliability and efficiency of measurements can be enhanced. Detection of acoustic signals is performed by means of a piezoelectric element 3 mounted on the holder 1. The element 3 is firmly secured to the holder with an adhesive 4, etc. Therefore, stable acoustic matching between the element 3 and the holder 1 is secured, further enhancing the reliability of the measurements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample holder for an optical absorption measuring device.

[0002]

2. Description of the Related Art With the progress of various optical application technologies, the demand for optical measurement has become more sophisticated. In particular, as a recent trend, attention is being paid to the evaluation of physical properties of light having a wavelength extremely longer or shorter than that of visible light. For example, with light of ultrashort wavelength, various excimer lasers and the like are used for microfabrication and lithography, and measurement and evaluation of optical elements and the like are becoming indispensable.

Among the evaluation items required for optical elements and the like, one of the important items is absorption of light. In the light absorption measurement, generally, a method of directly measuring optically (a method of detecting the light intensity by an optical sensor) is used, but this method has a limit. That is, when the light source light has a short wavelength (200 nm or less), a stable light source and a light quantity measuring method have not been established at present, and the stability is large especially when a minute absorption amount (a minute light amount difference) is observed. Fall

Further, when a pulse laser such as an excimer laser is used, a problem may occur due to the slow response speed of the optical sensor when detecting the pulse laser. Further, it is difficult to separately measure only the absorption amount by an optical method, and it is always detected as a value including the scattering amount on the surface or the like. Therefore, some methods of measuring a minute amount of light absorption, which do not rely on the conventional optical method, have been proposed and implemented. Most of them are methods of measuring light absorption as heat which is a non-radiative transition.

A typical method is known as calorimetry, in which the temperature rise due to light absorption of the sample is directly measured by a temperature measuring means such as a thermocouple. There is also a method called a photoacoustic measurement method in which an acoustic signal generated by deformation and (relaxation of) deformation of a sample or an atmosphere in the vicinity of the sample due to temperature rise is detected and the amount of light absorption is calculated backward from the acoustic signal.

More recently, a method of detecting the refractive index distribution and displacement of the sample or its vicinity caused by absorption heating by light (deflection of light beam, detection of optical path difference, etc.) has been actively used. Among them, the photoacoustic measurement method for performing acoustic measurement (hereinafter, sometimes abbreviated as photoacoustic method) is relatively easy to perform and has high measurement sensitivity.
Widely tried for thin film materials.

In this method, in a sample or an atmosphere in the vicinity thereof, sound that is a volume change caused by heating and cooling by irradiation of intermittent light is converted into an electric signal by a microphone or a piezoelectric element transducer attached to the sample or sample holder. To detect. By analyzing the intensity or phase of the electric signal, various information about the non-radiative transition of the substance can be obtained, but the magnitude of the acoustic wave is usually thermal energy (that is, light absorption amount).
(For detailed theory, see the paper J.Appl.Phy, for example.
s, vol.47, No1, pp64. J.Appl.Phys, vol.51, No6, pp33
43. Can.J.Phys, vol.64, pp147 etc.), from which the amount of light absorption can be calculated.

According to this method, even if the absorption is minute, the amount of detection signal can be increased by using the one having high light intensity, and the measurement can be performed with high sensitivity. The photoacoustic method is used as an analytical method such as an analysis of a non-radiative transition process of a substance, and has been attracting attention as a method of measuring a light absorption amount in terms of its sensitivity and ease of measurement.

[0009]

One of the major problems in measuring the amount of light absorption by the photoacoustic method is the dependence of the signal intensity on the acoustic wave propagation conditions. Since the intensity of the acoustic wave changes depending on the acoustic wave propagation condition from the absorption point, even if the light irradiation condition to the sample is the same, the distance between the sample (and the acoustic source that is the light irradiation part) and the acoustic detection element It depends on the acoustic bonding conditions of. Therefore, care must be taken when comparing signal strengths between separate samples.

In the telemetry using the microphone, the reproducibility of the sound propagation from the sample is relatively easy to obtain and the standardization of the signal is easy. Also, in the case of measurement with liquid samples and gas samples, with the cell that encloses them,
By keeping the light source light and the settings of the acoustic sensing element constant, it is possible to obtain reproducibility of the signal intensity.

However, in the measurement of a solid sample such as a thin film sample formed on a glass substrate, it is not easy to keep the acoustic propagation condition constant when trying to detect a contact type acoustic with a large signal intensity. There is a problem. Here, what is particularly important is the contact condition of the contact portion between the solid sample and the acoustic detection element or the sample holder, and when the sound propagation condition (that is, contact condition) at the contact portion is different when the sample is exchanged. However, there is a problem that the signal strength changes.

For example, when the solid sample and the sample holder (or the acoustic detecting element) are brought into contact with each other by directly pressing them, the sample and the holder (or the acoustic detecting element) are generally rigid solids. Therefore, a slight void layer is formed due to unevenness (or dirt) on the surface. Therefore, it has been confirmed that it is difficult to keep the acoustic contact condition constant, and the signal strength is largely deviated (distributed) and the reliability of measurement is deteriorated.

Further, when the two are contacted with each other by grease or the like which is often used as an acoustic matching material, the thickness of the matching material layer and the contact state with the sample change unless the pressing is carefully performed, resulting in a large acoustic intensity. There is a problem in that there are many deviations (variations), and as a result, the reliability of measurement decreases. There are other problems when using grease or the like. That is, in this case, since grease or the like adheres to the sample or the holder during the sample setting, it is necessary to wash the sample or the holder and apply (supplement) the matching material every time the sample is exchanged, and the measurement efficiency is improved. There is a problem that it decreases.

The present invention has been made in view of the above problems, and it is a sample holder used in an optical absorption measuring device, and it is possible to easily maintain a constant acoustic contact condition with a solid sample. Therefore, as a result, it is an object of the present invention to provide a sample holder for an optical absorption measurement device that can improve the reliability and efficiency of measurement.

[0015]

Therefore, in the first aspect of the present invention, "the light absorption of the sample is measured by measuring the acoustic signal generated by the volume change of the sample caused by the light absorption when the sample is irradiated with light. A sample holder for an optical absorption measuring device (claim 1), which is a sample holder used in an optical absorption measuring device for measuring, and is provided with a sample suction holding mechanism using an elastic supporting member of the sample.

A second aspect of the present invention is that the sample holder for an optical absorption measuring device according to claim 1 is characterized in that the acoustic measuring sensor is provided in an acoustically matched state. )"I will provide a. A third aspect of the present invention is "a sample holder for an optical absorption measuring device according to claim 1 or 2, wherein the sample holder is configured and / or arranged so as not to block the optical path of the irradiation light (claim 3). "I will provide a.

Further, in a fourth aspect of the present invention, "a member constituting the sample holder, wherein a member located on the optical path of the irradiation light transmitted through the sample has a loss corresponding to absorption and scattering of the irradiation light. A sample holder for an optical absorption measuring device according to claim 1 or 2, characterized in that 0.1% or less of a material is used. Also,
Fifthly, the present invention relates to "a sample holder for an optical absorption measuring device according to claim 4 (claim 5), characterized in that the member is subjected to a treatment for preventing reflection of the irradiation light."
I will provide a.

A sixth aspect of the present invention provides a "sample holder for an optical absorption measuring device (claim 6)", wherein a sample positioning mechanism is provided.

[0019]

The sample holder for an optical absorption measuring device and the optical absorption measuring device according to the present invention will be described with reference to the drawings, but the present invention is not limited to the examples of the drawings. The optical absorption measuring device illustrated in the drawing is a system in which light from a light source is condensed by various optical systems and irradiated onto a sample. When irradiating, a system that changes the irradiating light intensity (light intensity) at an appropriate light intensity adjusting part, monitors the irradiating light intensity in a branch optical path, and calculates the light absorption amount from the correlation between the irradiating light intensity and the acoustic signal. Is.

In the example of FIG. 1, the measurement sample 7 is a thin film formed on a glass substrate. Both the material and size of the substrate are constant, and the substrate surface is sufficiently smooth. The amount by which the substrate absorbs the measurement light is preferably sufficiently smaller than the amount by which the thin film to be measured absorbs the measurement light. In this example, a circular pellet-shaped glass substrate is used. When the sample substrate 7 is set in the sample holder 1 as shown in FIG. 1, for example, an O ring (an example of an elastic support member, for example, a rubber O ring such as Viton) 2
It is held by suction 5 (an example of a suction holding mechanism using an elastic support member) from the suction device in the state of being supported by.

As the suction device, a general vacuum pump such as an oil rotary pump may be used. Before the sample 7 is suction-held, it is preferable that the contact surface of the elastic support member 2 with the sample 7 be wiped off in advance to hold the contact surface clean. Therefore, in the sample replacement work, keep the contact surface clean.
It is preferable to carry out in a clean atmosphere (clean room, etc.) that is free of dust.

Since the material of the elastic support member 2 such as the O-ring is an elastic and flexible material, when the sample 7 and the holder 2 are suction-pressed, voids which are problematic in contact pressure-bonding of solids do not occur. Therefore, there is an effect that the matching of the acoustic impedance is improved, the signal intensity to be detected is increased, and the reproducibility of the acoustic propagation condition is improved.

On the other hand, in the case of crimping the sample to the holder with a screw or a spring, which is a general pressing method, it is troublesome to adjust the pressing force uniformly (for example, adjusting the torque of the screw). There is a problem such as the occurrence of fluctuations in the pressing pressure or the weakening of the spring. However, according to the pressing by the suction holding mechanism using the elastic support member 2 of the sample 7 according to the present invention, the pressing pressure is determined by the pressure difference between the atmospheric pressure and the sucked vacuum pressure. For example, if the vacuum is applied to about 10 ^-2 torr, the pressing condition can be easily kept constant.

Therefore, the sample holder for the optical absorption measuring device of the present invention can keep the acoustic contact condition with the solid sample constant, and as a result, the reliability of the measurement can be improved. Also, suction ON / OFF
Can be easily performed by opening and closing a valve, and no matching material such as grease is required. Therefore, quick and simple measurement can be performed without the trouble of supplying and removing the matching material.

Therefore, by using the sample holder for the optical absorption measuring device of the present invention, the measurement efficiency can be improved. The detection of the acoustic signal according to the present invention is performed by a piezoelectric element (an example of an acoustic measurement sensor) 3 attached to the sample holder 1 as shown in FIG. 1, for example. The piezoelectric element 3 is firmly fixed to the holder 1 with an adhesive 4 or the like. Thereby, the piezoelectric element 3 and the holder 1 are stably acoustically matched, and the reliability of measurement is improved.

That is, in order to improve the reliability of measurement, it is preferable that the sample holder is provided with an acoustic measurement sensor in an acoustically matched state (claim 2).
One of the things to be noted when measuring with the optical absorption measuring device is the relationship between the sample holder and the irradiation light optical path.
Consider, for example, the case of the relationship between the sample holder 1 and the irradiation light 6 optical path as shown in FIG. In this case, the irradiation light after passing through the sample 1 reaches the constituent member 9 of the sample holder located on the back side of the sample holder 1, and this member 9 is a material that absorbs the irradiation light. Since sound is generated here as well, it may affect the sound detection as noise.

Therefore, it is preferable to separate the member 9 from the piezoelectric element 3 as acoustically as possible. Therefore, the member 9
Is preferably made of a material such as an elastic body that hardly transmits sound. Alternatively, the sample holder is preferably constructed and / or arranged so as not to block the optical path of the irradiation light (claim 3). For example, as shown in FIGS. 2 and 4, only a part of the samples 7 and 16 is suction-held so that the sample holders 1 and 23 do not block the optical path of the irradiation light.

Alternatively, if a material that constitutes the sample holder and is located on the optical path of the irradiation light that has passed through the sample is made of a material having a loss corresponding to absorption and scattering of the irradiation light of 0.1% or less, It is preferable because the generation of sound in the member and the adjacent atmosphere can be suppressed (Claim 4). In addition, the irradiation light reflected by the member may reach the sample or the holder again, and the sound there may similarly affect the detection signal as noise, so that the reflectance of the member with respect to the irradiation light may be changed. It is preferable to make it small.

That is, it is preferable that the member is subjected to a treatment for preventing reflection of the irradiation light (claim 5). Examples of such treatment include antireflection coating performed by laminating a thin film on a member. By adopting the above-mentioned configuration, the influence of sound other than the sample due to the irradiation light can be suppressed to a small level, so that the reliability of measurement is further improved.

The sample holder of the present invention is preferably provided with a sample positioning mechanism (claim 6). For example, when a guide (an example of a sample positioning mechanism) 8 as shown in FIG. 1 is provided and the sample 7 is positioned, the sample is always set to the same position even if the sample is exchanged. It is preferable because the reliability is further improved.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0032]

[Embodiment 1] FIG. 3 shows a sample holder 15 of this embodiment.
It is a schematic block diagram of the optical absorption measuring device using 23 (refer FIG. 4), and photoacoustic measurement was performed using this device. The light source is an ArF excimer laser (wavelength 193 nm) 10 having a pulse width of about 20 nsec. The pulse irradiation (measurement) light is condensed by the lens optical system 12 and irradiated on the sample 16, and the light diameter on the sample surface is about 2 mm.
Is Φ.

The intensity of the irradiation light is adjusted by a zoom lens inserted in the optical system 12, and the irradiation light intensity is an optical sensor (biplanar type photomultiplier) 14 in a branch optical path using reflection of the quartz glass 13. Is being monitored by. The light transmitted through the sample 16 is blocked by the absorber 18 to prevent the return. In addition, it is preferable that the absorber 18 be made of a material such as an elastic body that hardly transmits sound.

Since the irradiation light is absorbed by ozone generated in oxygen, the optical system is arranged in the chamber 11 purged with nitrogen. Sample holder 23
Is made of aluminum and has an O-ring 32 as shown in FIG.
It is a cylindrical type in which the guide grooves 26, 26 'of 25 mmΦ and 15 mmΦ are double provided. In addition, the guide groove 26,
A suction hole 27 is provided between 26 '.

The Viton O-ring 32 is inserted into the guide grooves 26, 2
After being set to each of 6 ', the sample 16 is set in the sample holder 23, and suction 24 is performed from the suction port of the holder 23 by an oil rotary pump. Sample 16 is a sample having a thickness of 1 μm or less formed on a quartz glass substrate (transmission of light having a measurement wavelength) in the shape of a circular pellet having a diameter of 30 mm and a thickness of 2 mm.
A guide (an example of a sample positioning mechanism) provided in No. 3 28
Thus, the sample holder 23 is always set at a fixed position.

The acoustic signal is detected by a sensor (an example of an acoustic measurement sensor) having a structure in which a receiving plate 30 made of alumina is attached to PZT (lead zirconate titanate) 31 which is a piezoelectric material. The sensor is a holder 2 with a heat sensitive adhesive 29.
The sensor and the holder are stably acoustically matched. The sample 16 set in this way is irradiated with light while driving the zoom lens 12 and changing the light intensity, and the output (voltage) of the optical monitor sensor 14 is measured.

The signal is appropriately filtered to remove noise. In this example, the main frequency of sound is 10
It is about 0 kHz, and the wavelength around this is selected (FF
Recording (according to T19). The acoustic signal 22 ′ and the light intensity signal 22 are measured by the computer 20 controlling the zoom lens 12 in an interlocking manner.

A sample in which a thin film having an absorption of about 5% at the measurement (irradiation) wavelength is formed on the substrate is set in the sample holder 23 of this embodiment, and the result of measurement using the measuring device of FIG. 3 is shown in FIG. Shown in. In Figure 5, incident (irradiation)
The light intensity and the signal intensity have a linear relationship, and the slope represents the absorption coefficient. As a result of measuring by replacing the same sample,
The measured values were on the same straight line (the same was true for the third and subsequent measurements), demonstrating that the measurement using the sample holder 23 of this example has excellent reproducibility.

FIG. 6 shows the result of measurement by replacing the same sample in the same manner as in this example except that the sample was set in an aluminum sample holder via silicon grease. Comparing with this result, it can be seen that the measurement using the sample holder 23 of the present embodiment is extremely excellent in reproducibility.

[0040]

Second Embodiment FIG. 7 shows a sample holder 23 'of this embodiment.
FIG. Using this sample holder 23 ′, the same measurement as in Example 1 was performed. In this holder 23 ′, the sample 16 is fixed by one O-ring 32, and the measurement light transmitted through the sample 16 enters the suction cell and then enters the member 34.

This member 34 is made of synthetic quartz glass and has an absorption rate of 0.1% / irradiation light (193 nm).
The loss is 0.1% or less because the thickness is about 3 mm or less and the scattering rate is 0.2% / cm or less. Further, the surface of the member 34 is provided with an antireflection coating 35 for 193 nm wavelength. By doing so, the signal when the sample is not set in the sample holder 23 'can be suppressed to 0.1% or less as compared with the signal at the time of measurement (when the sample is set). In addition, the measurement results showed good reproducibility as in Example 1.

In the above embodiments, for example, a measurement system for irradiating a pulse laser of a single wavelength is shown as an example, but the present invention is not limited to this, and for example, a continuous wave laser is intermittently used. It can also be applied to an irradiation measurement system.

[0043]

As described above, according to the sample holder for the optical absorption measuring device of the present invention, the acoustic contact condition with the solid sample can be easily kept constant, and as a result, the measurement Reliability and efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view (top) and a schematic front view (bottom) showing an example of a sample holder of the present invention.

FIG. 2 is another example of the sample holder of the present invention,
FIG. 3 is a schematic cross-sectional view (upper) and a schematic front view (lower) showing an example of a sample holder having a configuration in which a member is not arranged on the optical path of irradiation light.

FIG. 3 is a schematic configuration diagram of an optical absorption measuring device used for measurement in Examples.

FIG. 4 is a schematic cross-sectional view (upper) and a schematic front view (lower) showing the sample holder of Example 1.

FIG. 5 is a data diagram showing a result of optical absorption measurement performed using the sample holder of Example 1.

FIG. 6 is a data diagram showing the results of optical absorption measurement performed using a conventional sample holder that holds a sample via grease.

FIG. 7 is a schematic cross-sectional view (top) and a schematic front view (bottom) showing a sample holder of Example 2.

[Explanation of symbols]

1 .. Cylindrical sample holder 2 .. O-ring (an example of elastic support member) 3 .. Piezoelectric element (an example of acoustic measurement sensor) 4 .. Adhesive 5 .. Vacuum pump suction 6 .. Light) 7 ・ ・ Measurement sample 8 ・ ・ Sample guide (an example of sample positioning mechanism) 9 ・ ・ Sample holder back member 10 ・ ・ ArF excimer laser light source 11 ・ ・ Nitrogen purge chamber 12 ・ ・ Light intensity adjustment optical system (zoom lens 13) · Quartz glass plate 14 · · Light intensity monitor sensor 15 · · Sample holder 16 · · Thin film measurement sample 17 · · Acoustic detection element (an example of acoustic measurement sensor) 18 · · Optical block absorber 19 · · Amplifier, Frequency selection device (FFT) 20 Personal computer 21 Zoom lens control is shown. 22..Optical signal (or representing acquisition of optical signal) 22 '.. Acoustic signal (or representing acquisition of acoustic signal) 23..Aluminum sample holder 24..Suction from oil rotary pump 25..ArF laser Light 26..Outer O-ring groove 26 '.. Inner O-ring groove 27..Suction port 28..Sample guide (an example of sample positioning mechanism) 29..Heat sensitive adhesive 30..Alumina receiver plate 31..PZT piezoelectric Element (example of acoustic measurement sensor) 32 ··· Viton O-ring (example of elastic support member) 33 · · O-ring groove 34 · · Quartz glass 35 · · Antireflection coating

Claims (6)

[Claims] 1. A sample holder used in a light absorption measuring device for measuring the light absorption of a sample by measuring an acoustic signal generated by a volume change of the sample caused by light absorption when the sample is irradiated with light. And a sample holder for an optical absorption measuring device, comprising a sample suction-holding mechanism using the sample elastic support member. 2. The sample holder for an optical absorption measurement device according to claim 1, wherein the acoustic measurement sensor is provided in an acoustically matched state. 3. The sample holder for an optical absorption measuring device according to claim 1, wherein the sample holder is constructed and / or arranged so as not to block the optical path of the irradiation light. 4. The member constituting the sample holder, which is located on the optical path of the irradiation light transmitted through the sample, is made of a material having a loss of 0.1% or less corresponding to absorption and scattering of the irradiation light. Claim 1 characterized by the fact that
Alternatively, the sample holder for the optical absorption measuring device described in 2. 5. The sample holder for an optical absorption measuring device according to claim 4, wherein the member is subjected to a treatment for preventing reflection of the irradiation light. 6. The sample holder for an optical absorption measuring device according to claim 1, further comprising a sample positioning mechanism.