JPH08248005A - Photothermal displacement measuring apparatus - Google Patents

Abstract

PURPOSE: To measure the photothermal displacement regardless of the surface conditions of a sample. CONSTITUTION: When the photothermal displacement of a sample 5 is measured using a measuring light 6 obtained by irradiating the sample 5 with an exciting light 3, the measuring part of the sample 5 is irradiated with ultraviolet rays 12 having predetermined energy, independently from the exciting light 3 and the measuring light 6, by means of an ultraviolet lamp 10 and an optical fiber 11. With such arrangement, the photothermal displacement can be measured regardless of the surface conditions of the sample.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photothermal displacement measuring device, and more particularly to a photothermal displacement measuring device used for evaluating crystal defects of a sample.

[0002]

2. Description of the Related Art When a sample is irradiated with light whose intensity is modulated periodically, the sample absorbs this light to generate heat, which causes thermal expansion vibration on the surface of the sample. A method for evaluating the thermophysical property quantity of a sample by measuring the thermal expansion vibration is known as a photothermal displacement method or a photoacoustic method. This thermal expansion amount is closely related to thermophysical constants such as the thermal conductivity and thermal expansion coefficient of the sample, and they reflect the physical state of the sample such as crystal defect density. Therefore, the photothermal displacement method is widely applied to the evaluation of crystal defects in samples. Further, it has been considered to use the photothermal displacement method for measuring the ion implantation amount, focusing on the fact that the crystal defects of the sample increase as the ion implantation amount into the sample increases (Evaluation o.
f Subsurface Ion Implant
Damage by Photothermal Di
placement measurement, H.S.
Takamatsu, etc. , Mat. Res. So
c. Symp. Proc. Vol 279 (1993)
PP 261-266).

FIG. 8 is a schematic diagram showing a schematic configuration of an example of such a conventional photothermal displacement measuring device A0. In the figure, a pump laser 1 generates an intensity-modulated pump light 3 by an oscillator 2. The excitation light 3 is irradiated onto the sample 5 by the beam splitter 4, and its surface is subjected to photothermal displacement (Phot
o-Acoustic-Displacement: P
AD) is induced. Since the photothermal displacement changes the phase of the measuring light 6, its amplitude is detected by the interferometer 7. The photothermal displacement converted into an electric signal by the interferometer 7 is amplified and noise-removed by the signal processing circuit 8,
It is transmitted to the computer 9. A well-known homodyne interferometer or heterodyne interferometer is used as the interferometer 7. Here, the phenomenon of photothermal displacement is physically understood as follows. A plasma composed of electrons and holes is generated by irradiation with the excitation light 3 having an energy larger than that of the band cap of the sample 5. The generated plasma is recombined while diffusing in the sample 5 and converted into heat energy. The heat generated also diffuses. The size of the thermal diffusion region at this time is reflected in the thermal expansion amount of the sample 5, and is observed as a phenomenon of photothermal displacement. When the sample 5 has a crystal defect, the thermal conductivity is lowered, and the thermal diffusion region is narrowed and the temperature thereof is increased, resulting in a large photothermal displacement. Therefore,
If the photothermal displacement is measured by this device A0, the crystallinity of the sample 5 can be evaluated.

[0004]

The conventional photothermal displacement measuring device A0 as described above has the following problems. (1) The plasma diffusion region is greatly affected by the surface state of the sample 5. Therefore, even if the sample 5 has the same crystallinity, when the surface state is chemically unstable, the surface becomes a recombination center and the plasma diffusion length becomes short. Therefore, when the surface state is chemically unstable, the thermal diffusion region becomes narrower and the photothermal displacement becomes larger than when it is stable. This phenomenon is shown in FIGS. 2 (a) and 2 (b). This means that due to surface changes such as the growth of a natural oxide film on the surface of the sample 5, the measured photothermal displacement amount changes with time regardless of the crystallinity of the sample 5. To do. (2) Further, when the crystallinity of the sample 5 is improved and the number of crystal defects that are recombination centers is reduced, the degree of recombination of plasma on the surface increases. Therefore, the photothermal displacement at that time strongly reflects the surface condition rather than crystal defects. Therefore, in the above conventional apparatus A0, the measured value of the photothermal displacement varies depending on the surface condition of the sample, and it becomes impossible to accurately evaluate the crystallinity of the sample with less damage. In order to solve the above problems in the conventional technique, the present invention provides an improved photothermal displacement measuring device capable of measuring photothermal displacement without being affected by the condition of the sample surface. The purpose is.

[0005]

In order to achieve the above object, the present invention provides a photothermal displacement measuring apparatus for irradiating a sample with light and measuring the photothermal displacement of the sample by the light. The photothermal displacement measuring apparatus is provided with an electromagnetic wave irradiation mechanism for irradiating the measurement portion of the photothermal displacement of the sample with the electromagnetic wave having the energy of 1. Furthermore, it is a photothermal displacement measuring device in which the electromagnetic waves are ultraviolet rays.

[0006]

According to the present invention, when the sample is irradiated with light and the photothermal displacement of the sample due to the irradiation is measured, the electromagnetic wave irradiation mechanism separates an electromagnetic wave having a predetermined energy from the light by the electromagnetic wave irradiation mechanism. The photothermal displacement measurement area is irradiated. As a result, the recombination velocity of the plasma on the sample surface is reduced, so that the plasma diffusion length does not change depending on the state of the sample surface. As a result, the photothermal displacement can be accurately measured regardless of the state of the sample surface.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the accompanying drawings for the understanding of the present invention. It should be noted that the following embodiments are examples of embodying the present invention, and are not intended to limit the technical scope of the present invention. here,
FIG. 1 is a schematic diagram showing a schematic configuration of a photothermal displacement measuring apparatus A1 according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a relationship between a sample surface state and photothermal displacement, and FIG. 3 is a temporal change of photothermal displacement amount. 6 is an explanatory view showing the relationship between the photothermal displacement amount and the ion implantation amount, FIG. 5 is a schematic diagram showing the schematic configuration of a photothermal displacement measuring device A2 according to another embodiment of the present invention, and FIG. Is an illustration of the light deflection method, and FIG. 7 is an illustration of the mirage method. still,
The same symbols are used for the elements common to the schematic diagram showing the schematic configuration in the example of the conventional photothermal displacement measuring apparatus A0 shown in FIG. Photothermal displacement measuring device A according to one embodiment of the present invention
1 is similar to the conventional example in that the sample is irradiated with light and the photothermal displacement of the sample due to the irradiation is measured. However, this embodiment is different from the conventional example in that an electromagnetic wave irradiation mechanism that irradiates an electromagnetic wave having a predetermined energy to the measurement portion of the photothermal displacement of the sample is provided separately from the light.

The device A1 will be described below in more detail with reference to FIG. As shown in FIG. 1, a pump laser 1 generates pump light 3 (corresponding to light) whose intensity is modulated by an oscillator 2. The excitation light 3 is applied to the sample 5 by the beam splitter 4, and the photothermal displacement PAD is induced on the surface. Since the photothermal displacement changes the phase of the measuring light 6, its amplitude is detected by the interferometer 7. The photothermal displacement converted into an electric signal by the interferometer 7 is amplified and noise-removed by the signal processing circuit 8 and transmitted to the computer 9. Up to this point, the apparatus is the same as the conventional apparatus A0, but in the apparatus A1, an ultraviolet irradiation mechanism (corresponding to an electromagnetic wave irradiation mechanism) including an ultraviolet lamp 10 and an ultraviolet light guide fiber 11 is further added, whereby an ultraviolet ray 12 ( The sample 5 is irradiated with (corresponding to electromagnetic waves). That is, the ultraviolet light 12 generated by the ultraviolet lamp 10 is directed by the ultraviolet light guide fiber 11 to the measurement point where the photothermal displacement occurs. Since the ultraviolet lamp 10 can be turned on and off by the computer 9, the sample 5 can be irradiated with the ultraviolet rays 12 only when the measurement is necessary.

The measurement principle of the device A1 will be described below. Regarding the behavior of electrons and holes when silicon is irradiated with ultraviolet rays, Mechanism of Ultr
abiolet Irradion Effecton
Si-SiO ₂ Interface in Sil
icon Wafers, K .; Katayama, et
c. , Jpn. J. Appl. Phys. Vol. 31
(1992) pt. 2, No. 8A. Here, from the valence band of silicon Si to the conductor of the silicon oxide film SiO ₂ (energy gap is 4.2
By the irradiation of ultraviolet rays (photon energy is 4.9 eV of ultraviolet rays) capable of exciting (eV), the excited electrons move to the surface of the native oxide film, that is, the surface not in contact with silicon, It bonds with oxygen molecules and adheres to the surface of the natural oxide film to become charged. At the same time, the electrons also move to the electron states (slow states) in the natural oxide film.
Therefore, the fast states, which are the recombination centers between the silicon and the native oxide film, shift to a higher energy level, and no electrons are present at that level. As a result, the surface recombination rate of the sample decreases.

If the results of the above-mentioned literature are applied, the surface recombination velocity of a sample, which is, for example, a silicon wafer, decreases due to the irradiation of ultraviolet rays, and the plasma generated by the irradiation of excitation light for causing photothermal displacement is generated. Recombination becomes difficult on the sample surface. Therefore, the plasma diffusion length does not change with the state of the sample surface, and the photothermal displacement can be measured without being affected by the state of the sample surface.
3 and 4 show the measurement results obtained by using the apparatus A1. In FIG. 3, sample 5 is a silicon wafer after cleaning, the horizontal axis is the elapsed time after cleaning,
The vertical axis represents the amount of photothermal displacement. The broken line shows the measurement result when the ultraviolet lamp 10 is turned off, and the same result as the conventional example is obtained. Solid line is UV lamp 10 during measurement
It is a measurement result when is turned on. In the conventional example,
While the amount of photothermal displacement changes with time due to the change in the state of the silicon wafer surface after cleaning, the photothermal displacement is stable regardless of the change in the state of the sample surface by irradiating the sample 5 with ultraviolet rays 12 during the measurement of the photothermal displacement. You can see how it is being measured.

Further, in FIG. 4, sample 5 is one in which low density crystal defects are formed by implanting ions into the silicon surface layer. The broken line shows the measurement result when the ultraviolet lamp 10 is in the off state, and the solid line shows the measurement result when the ultraviolet lamp is in the on state. Since the smaller the amount of ion implantation, the smaller the number of crystal defects, it can be seen that by turning on the ultraviolet lamp 10 of the present apparatus A1, it becomes possible to measure low-density crystal defects that could not be measured conventionally. By the way, in the above-mentioned embodiment, the ultraviolet rays 12 are irradiated to the sample 5 only from the incident direction of the excitation light 3. However, as another embodiment of the present invention, as in the apparatus A2 shown in FIG. Irradiation may be performed from the side. In that case, the influence of the state of the back surface of the sample can be reduced. still,
In each of the above two embodiments, the ultraviolet ray 12 is used as the electromagnetic wave, but in actual use, an electromagnetic wave having a larger photon energy than the ultraviolet ray, for example, soft X-ray may be used. In each of the above two embodiments, the ultraviolet light 12 is applied to the sample 5 from an oblique direction, but in actual use, it may be incident on the excitation light 3 coaxially. In each of the above two embodiments, the ultraviolet lamp 10 is used as the ultraviolet light source, but in actual use, the laser light source may be used to irradiate the excitation light 3 coaxially or non-coaxially.

In each of the above two embodiments, the photothermal displacement is measured by using the interferometer 7, but in actual use, another method for measuring the photothermal displacement, for example, as shown in FIG. There is no problem even if the light deflection method or the mirage method as shown in FIG. 7 is used. Here, the optical deflection method is a method of detecting a change in the photothermal displacement amount of the sample surface as a change amount of the reflection angle of the measuring light, and the mirage method is the method of detecting the measuring light due to the change in the refractive index gradient of the sample surface. The method of detecting the deflection of Although not particularly described in the above two embodiments, the excitation light 3 and the measurement light 6 may be emitted from different light sources or may be emitted from the same light source.

[0013]

Since the photothermal displacement measuring apparatus according to the present invention is configured as described above, the recombination rate of plasma on the sample surface becomes small, and the change of the plasma diffusion length due to the state of the sample surface changes. Disappear. As a result, the photothermal displacement can be measured without being affected by the condition of the sample surface.

[Brief description of drawings]

FIG. 1 is a photothermal displacement measuring device A according to an embodiment of the present invention.
1 is a schematic diagram showing a schematic configuration of 1.

FIG. 2 is an explanatory view showing a relationship between a sample surface state and photothermal displacement.

FIG. 3 is an explanatory diagram showing changes over time in the amount of photothermal displacement.

FIG. 4 is an explanatory diagram showing a relationship between a photothermal displacement amount and an ion implantation amount.

FIG. 5 is a schematic diagram showing a schematic configuration of a photothermal displacement measuring device A2 according to another embodiment of the present invention.

FIG. 6 is an explanatory diagram of a light deflection method.

FIG. 7 is an explanatory diagram of a mirage method.

FIG. 8 is a schematic diagram showing a schematic configuration of an example of a conventional photothermal displacement measuring device A0.

[Explanation of symbols]

A1, A2 ... Photothermal displacement measuring device 1 ... Excitation laser 2 ... Oscillator 3 ... Excitation light (equivalent to light) 4 ... Beam splitter 5 ... Sample 6 ... Measurement light 7 ... Interferometer 8 ... Signal processing circuit 9 ... Computer 10 ... Ultraviolet light Illumination lamp (corresponding to part of electromagnetic wave irradiation mechanism) 11 ... Ultraviolet light guide fiber (corresponding to part of electromagnetic wave irradiation mechanism) 12 ... Ultraviolet light (corresponding to electromagnetic wave)

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Naoyuki Yoshida 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Kobe Steel Works, Ltd. Kobe Research Institute

Claims (2)

[Claims] 1. A photothermal displacement measuring device for irradiating a sample with light and measuring the photothermal displacement of the sample thereby, in which an electromagnetic wave having a predetermined energy is provided separately from the light to a portion for measuring the photothermal displacement of the sample. An apparatus for measuring photothermal displacement, comprising an electromagnetic wave irradiation mechanism for irradiation. 2. The photothermal displacement measuring device according to claim 1, wherein the electromagnetic waves are ultraviolet rays.