JPH0618330A - Optical absorption coefficient measuring method and optical absorption coefficient measuring device - Google Patents

Abstract

PURPOSE:To obtain a measuring method for accurately measuring absorption coefficient by one time measurement for a material such as thin film having a low absorption coefficient. CONSTITUTION:Behind a thin film 2 formed on a base 1, a reflector 3 having a high reflectivity is arranged. Light is introduced from the front of this thin film 2 and, by measuring the reflection light L1 from the thin film 2 and the reflection light L2' refelcted by the reflector 3 via the thin film 2, light absorption coefficient of the thin film 2 is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring a light absorption coefficient of a thin film.

[0002]

2. Description of the Related Art In the production of thin films for various semiconductor devices, optical properties, particularly light absorption coefficient, are measured as an index for monitoring the electronic properties of the devices or for keeping the film thickness of the thin films constant. .

When the light absorption coefficient of a thin film is measured by a conventional spectrophotometer, for example, in a thin film transistor or the like, the semiconductor layer has a small thickness and the light absorption coefficient has a low value. Therefore, the transmittance and the reflectance are different from each other. You have to measure
It was difficult to measure the absorption coefficient accurately due to the error between the measured values.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a measuring method and a measuring apparatus capable of accurately measuring the absorption coefficient of a thin film or the like having a low absorption coefficient by one measurement.

[0005]

The optical absorption coefficient measuring method of the present invention has a high reflectance at the rear of a thin film 2 formed on a substrate 1, as shown in the schematic view of FIG. Is arranged, the light is incident from the front side of the thin film 2, the reflected light L ₁ from the thin film 2 and the reflected light L ₂ reflected by the reflector 3 through the thin film _2. The light absorption coefficient of the thin film 2 is measured by measuring ′ and.

Further, according to the present invention, in the above-mentioned optical absorption coefficient measuring method, the above-mentioned reflector 3 is composed of a dielectric multilayer film.

The optical absorption coefficient measuring apparatus of the present invention is an optical absorption coefficient measuring apparatus for a thin film 2 formed on a substrate 1, as shown in a schematic diagram of an example thereof, and at least the light receiving coefficient The portion 11, the light receiving portion 12, and the reflector 3 having a high reflectance are provided, and the thin film 2 is arranged between the light receiving portion 11 and the reflector 3 and between the light emitting portion 12 and the reflector 3. Then, the incident light L ₁ incident on the thin film 2 from the light emitting unit 12 is reflected by the thin film 2 and the reflector 3, and the reflected light L ₀ is incident on the light receiving unit 11 to measure the light amount of the reflected light L _0. And

[0008]

As described above, in the method and measuring apparatus of the present invention, the reflector 3 having a high reflectance is provided behind the thin film 2 as shown in FIGS. The light absorption coefficient of the thin film 2 is measured by injecting light and measuring the reflected lights L ₁ and L ₂ ′ reflected by the surface of the thin film 2 and the reflector 3. The method of calculating the light absorption coefficient will be described below.

As described above, in the present invention, for measurement
Incident light L_iIs incident from the front surface 2S side of the thin film 2.
However, at this time, the arrow on the incident side surface
Mark L ₁Some light is reflected and some light is
Is an arrow L directly through the thin film 2 and the substrate 1.₂Indicated by
Thus, the light is reflected on the surface of the reflector 3. This reflected light
L₂Again passes through the thin film 2 through the substrate 1 and the arrow L₂′
It is radiated to the outside as shown by. At this time, the substrate 1 and the thin film
Arrow L at the interface with 2₃As shown by₂
Part of is reflected.

Here, the reflectance when the incident light L _i is incident on the thin film 2 from the outside is r ₁ . r ₁ is generally expressed as a function of wavelength (r ₁ (λ)), and changes depending on the wavelength of light. Similarly, the reflectance when light enters the thin film 2 from the substrate 1 side is r ₂ (r ₂ (λ)). The reflectance of the reflector 3 having a high reflectance is r ₃ .

At this time, if the thickness of the substrate 1 is sufficiently long with respect to the coherent length of light, the light L _i that first enters the thin film and the reflected light L ₂ reflected by the reflector 3 hardly interfere with each other. The reflectance R measured as a result can be expressed by a simple geometric series shown in the equation (1). _{R = r 1 + t 1 r} 3 t 2 / (1-r 2 r 3) ‥‥ (1)

Where t₁And t₂From the outside to the thin film 2
The absorption amount of light when light is incident is a ₁And the base 1 side
The amount of light absorption when light enters the thin film 2 from₂To
And the following equations (2) and (3) respectively.
It t₁= 1-r₁-A₁ (2) t₂= 1-r₂-A₂ (3)

Therefore, by substituting them into the above equation (1), R = r ₁ + r ₃ (1−r ₁ −a ₁ ) · (1−r ₂ −a ₂ ) / (1−r ₂ r ₃ )… (4)

Here, a ₂ is a ₂ = a ₁ (1-r ₂ ) /
Since it can be written as (1-r ₁ ), and the second term of the above formula (4) can be approximated by a linear expression of a ₁ , the reflectance R is R = {r ₁ + r ₃ −r ₃ (r ₁ + r ₂ )} / (1-r ₂ r ₃ ) -2r ₃ (1-r ₂ ) a ₁ / (1-r ₂ r ₃ ) ... (5) and a ₁ = (1-r ₂ r ₃ ). become _{[{r 1 + r 3 -r 3} (r 1 + r 2)} / (1-r 2 r 3) -R] / 2r 3 (1-r 2) ‥‥ (6).

Assuming that the reflectance of the reflector 3 is sufficiently high and can be approximated to 1, the above equation (6) can be expressed very simply as the following equation (7). a ₁ = (1-R) / 2 (7)

That is, the absorption coefficient of the thin film 2 can be directly investigated by measuring only the reflectance R of the reflected light in front of the thin film 2. When there is almost no absorption amount, the reflectance R is a constant amount regardless of the wavelength. If the absorption coefficient of the thin film 2 is α and the film thickness is d, the absorption amount a ₁ is
It is expressed as shown in Equation 1 below.

[Equation 1]

Therefore, the absorption coefficient α is α = − {ln (1-a ₁ / (1-r ₁ ))} / d (8)

Therefore, according to the measuring method and the measuring apparatus of the present invention, the light quantity of the above-mentioned reflected light L _O (L ₁ and L ₂ ′) is measured, and the reflectance R is calculated from the ratio to the light quantity of the incident light L _i. By measuring, it is possible to accurately measure even a thin film having a low absorption coefficient.

According to another aspect of the present invention, since the reflector 3 is made of a dielectric multilayer film, the reflectance r ₃ of the above-mentioned reflector 3 can be made approximately 1, so that
The absorption coefficient can be measured more accurately.

[0020]

EXAMPLES Each example of the measuring method of the present invention will be described in detail below with reference to the drawings. In the optical absorption coefficient measuring method of the present invention, as shown in FIG. 1, a reflector 3 having a high reflectance is arranged behind a thin film 2 formed on a substrate 1. In this case, the substrate 1 is made of SiO ₂ or the like which transmits the measuring light, for example, visible light,
The thickness is the coherent length of the measuring light (about 10 μm)
The thickness is made sufficiently larger, and a thickness of about 0.5 mm to 1 mm, for example, 0.5 mm is used. Then, the thin film 2 to be measured is deposited on the surface 1S of the base body 1, and the reflector 3 is attached to the rear side of the thin film 2, that is, the surface opposite to this side, ie, the base body 1.
A high reflectance material such as Al or Au is deposited on the back surface 1R of the above. Then, the measurement light L _i is incident from the front side of the thin film 2, that is, the surface 2S side of the thin film 2 in this case, and the reflected light reflected from the thin film 2 and the reflector 3 is measured to obtain the light absorption coefficient. taking measurement.

An example of the measuring apparatus of the present invention for carrying out this measurement will be described with reference to FIG. In this case, the device is
1, the light emitting unit 12, the reflector 3, and the half mirror 1
3, the controller 14, and the thin film 2 is disposed between the light receiving unit 11 and the reflector 3 and between the light emitting unit 12 and the reflector 3. Then, the light L _i from the light emitting unit 12
Is incident on the thin film 2 through the half mirror 13, and the reflected light from the thin film 2 and the reflected light from the above-mentioned reflector 3 arranged behind the thin film 2 are reflected by the half mirror 13 to be received by the light receiving unit 11. Is made incident on. Light receiving unit 11
The reflected light detected by is converted into an electric signal and sent to the controller 14, and the amount of reflected light is measured. In addition, the controller 14 controls the wavelength of the light emitting unit 12.

In FIG. 1, the incident light L _i is reflected by the thin film 2
Surface 2S incident is inclined with respect to the, although the optical path so as not to overlap the incident light L _i and the reflected light L ₁ and L ₂ ', as shown in FIG. 2, the incident light L _i film 2 substantially perpendicularly to be incident to the surface 2S of the reflected light L by forming as L ₁ and L ₂ 'are substantially superimposed in _O words 1, accurately reflected light L _O in the light receiving unit 11
The light intensity of can be measured. In this case, the inclination angle of the thin film 2 of the incident light L _i may be about 10 ° or less when the thin film 2 to be measured has a relatively small thickness.
More preferably, by setting the angle to about 5 ° or less, the amount of reflected light can be measured more accurately.

In the embodiment of the present invention, a hydrogenated amorphous Si (a-Si: H) film having a thickness of 12 nm and a laser beam are irradiated on the film, in the embodiment of the present invention, using the measuring apparatus having the structure described in FIG. Polycrystalline Si (po produced by crystallization)
Amorphous Si (a-S) film prepared by irradiating the ly-Si) film with a laser again and making it amorphous.
i) The absorption coefficient of the film was measured. A quartz substrate having a thickness of 0.5 mm is used as the substrate 1 of these thin films 2, and the reflector 3 having a high reflectance has an Al film formed on the back surface of the substrate 1 opposite to the side on which the thin film 2 is deposited. It was formed by vapor deposition with a thickness of about 100 nm. In this case, the measurement accuracy was 0.01%.
Therefore, the absorption coefficient α that can be measured using this method of the present invention
The lower limit of is about 2 when calculated from the above equations (5) to (8).
It becomes × 10 ² cm ^-1 .

FIG. 3 shows an a-Si: H film and a poly-Si film.
The solid line A shows the measurement results of the reflectance of the film and the a-Si film.
~ C. As can be seen from this result, aS
The reflectance was constant irrespective of wavelength at a wavelength of 800 nm or more for the i: H film and at a wavelength of 825 nm or more for the poly-Si film.

Since the portion where the reflectance is constant can be a region where the absorption coefficient is sufficiently small, the light absorption coefficient spectrum was obtained from the amount of decrease in the reflectance with this reflectance as a reference. In this case, it is assumed that the reflectance of the reflector 3 made of Al is sufficiently high, and since the absorption coefficient is sufficiently small in the region where the reflectance is 80% or more, it is assumed that the above equations (5) to (7) hold. The absorption coefficient was calculated. The result is shown in FIG. In FIG. 4, solid lines D to F are a-Si: H, respectively.
The measurement results of the film, the poly-Si film, and the a-Si film are shown.
The absorption coefficient was determined in the range of 10 ⁵ to 10 ² cm ⁻¹ over the incident light energy range of 2.5 eV to 1.4 eV. In FIG. 4, the arrow N indicates the noise level.

The above a-Si: H film, poly-Si and
And transmitted light and reflected light for the a-Si film
The spectrophotometer is used to obtain the absorption coefficient.
The measured results are shown in FIG. Solid lines G to I in FIG.
A-Si: H film, poly-Si film, a-Si, respectively
The light absorption coefficient spectrum of a film is shown. Using a spectrophotometer
In the conventional method, the transmittance and reflectance must be measured.
Therefore, each measurement error occurs, and the noise
5x10 as shown on the bell³cm^-1The following cannot be measured
Yes. On the other hand, in the present invention, the absorption coefficient is measured by one measurement.
Because you can do 10 ²cm^-1Up to the absorption coefficient of
It will be possible.

Next, a case where a dielectric multilayer film having a higher reflectance than Al, Au, etc. is used as the reflector 3 will be described. The reflectance of the dielectric multilayer film depends on the wavelength, and the range in which 100% reflectance can be realized is limited. Therefore, when measuring a wide absorption spectrum, the reflectance is 100% as shown in FIG. % By using a plurality of types of dielectric multilayer films whose characteristics are controlled so that the wavelength ranges of
As shown in FIG. 5, by forming various dielectric multilayer films 3d on the substrate 1 on the side opposite to the side on which the thin film 2 is deposited, the light absorption coefficient can be measured over a wide wavelength range. it can.

That is, in a relatively long wavelength region, a dielectric multilayer film having a characteristic of a reflectance of 100% in a long wavelength region as shown by a solid line J, and in a medium wavelength region, similarly reflected in a medium wavelength region shown by a broken line K. Dielectric multilayer film having characteristics of 100%
In the short wavelength region, by forming each of the dielectric multilayer films having the characteristics of reflectance of 100% in the short wavelength region as a reflector as shown by the broken line L, the absorption coefficient can be more accurately measured by the above-described measuring method and apparatus of the present invention. It can be measured well.

Further, particularly when a plurality of types of reflectors 3 are prepared in this way, as shown in FIGS. 8 and 9, the reflecting film 3a is provided on the substrate 4 which is a separate body from the substrate 1 on which the thin film 2 is deposited. By using the reflector 3 formed by being attached, the measurement can be performed more easily. As shown in FIG. 8, the reflection film 3a is made to face or adhere to the back surface 1R of the substrate 1, and light is incident from the thin film 2 side as shown by an arrow L _i for measurement, or as shown in FIG. As described above, the reflection film 3a is opposed to the thin film 2 via the spacer 6 and the like with a space of about 0.1 mm, and light is incident from the back surface 1R side of the substrate 1 to perform the measurement. .

Further, in the measuring method and apparatus of the present invention,
Not only visible light but also infrared light can be measured. For example, a thin film 2 is deposited on a substrate 1 made of a material that transmits infrared light, such as Si or Ge, and a reflective film 3a is deposited on a separate substrate 4 facing it. The reflector 3 is arranged. In this case, the reflection film 3d is made of, for example, Au that reflects infrared light with high reflectance.
Can be arranged so as to face the front surface 2S of the thin film 2, and the measurement light L _i can be incident from the back surface 1R side of the substrate 1 to perform the measurement.

Further, in FIG. 11, A is formed on the substrate 1.
1, a reflector 3 having a high reflectance such as Au is adhered and formed,
A low absorption layer 5 having a small absorption coefficient for infrared light, such as SiO ₂ , Al ₂ O ₃ and Si, and a thin film 2 to be measured are sequentially deposited thereon, and a thin film 2 for measurement is applied from the surface 2S side. Light L _i
Can be incident to perform the measurement. In such a configuration, the thin film 2 can be directly deposited on the reflector 3 for measurement.

Also, when light other than infrared light is used, the measurement can be performed by appropriately selecting the materials of the reflector 3 and the low absorption layer 5 by the configuration shown in FIG. With such a configuration, even when a substrate that is not transparent to the measurement light such as infrared light, for example, a substrate such as glass or metal is used, the reflector 3 and the thin film 2 are provided thereon as shown in FIG. By providing it through the low absorption layer 5, the absorption coefficient of the thin film 2 can be accurately measured.

It is needless to say that the present invention is not limited to the above-mentioned embodiment, and various modifications and changes can be made.

[0034]

As described above, according to the present invention, the absorption coefficient of the thin film can be measured by measuring the reflected light once, and it is possible to reduce the error and improve the measurement accuracy. Therefore, it becomes possible to control electronic properties and film thickness of the thin film more accurately.

By using a dielectric multilayer film,
A thin film having a low absorption coefficient can be measured more accurately.

Further, by making the reflector separate, the measurement can be performed more easily.

The absorption coefficient can be measured from infrared light to ultraviolet light.

[Brief description of drawings]

FIG. 1 is a schematic view of an example of a light absorption coefficient measuring method of the present invention.

FIG. 2 is a schematic diagram showing an example of an optical absorption coefficient measuring device of the present invention.

FIG. 3 is a diagram showing wavelength dependence of reflectance of each thin film.

FIG. 4 is a diagram showing a light absorption coefficient spectrum by the light absorption coefficient measuring method of the present invention.

FIG. 5 is a diagram showing a light absorption coefficient spectrum by a conventional light absorption coefficient measuring method.

FIG. 6 is a conceptual diagram of reflection spectra of various dielectric multilayer films.

FIG. 7 is a schematic view of another example of the optical absorption coefficient measuring method of the present invention.

FIG. 8 is a schematic view of another example of the optical absorption coefficient measuring method of the present invention.

FIG. 9 is a schematic view of another example of the optical absorption coefficient measuring method of the present invention.

FIG. 10 is a schematic view of another example of the optical absorption coefficient measuring method of the present invention.

FIG. 11 is a schematic view of another example of the optical absorption coefficient measuring method of the present invention.

[Explanation of symbols]

 1 Substrate 2 Thin Film 3 Reflector 3d Dielectric Multilayer Film 4 Substrate 5 Low Absorption Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Durham Palgosign 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (72) Inventor Setsuo Usui 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo No. Sony Corporation

Claims (3)

[Claims] 1. A reflector having a high reflectance is arranged behind a thin film formed on a substrate, and light is incident from the front side of the thin film to reflect the reflected light from the thin film and the thin film. A light absorption coefficient measuring method for measuring the light absorption coefficient of the thin film by measuring the reflected light reflected by the reflector via. 2. The light absorption coefficient measuring method according to claim 1, wherein the reflector is formed of a dielectric multilayer film. 3. A light absorption coefficient measuring device for a thin film formed on a substrate, comprising at least a light receiving part, a light emitting part, and a reflector having a high reflectance, wherein the thin film is the light receiving part. And the reflector, and between the light emitting unit and the reflector, the incident light incident on the thin film from the light emitting unit is reflected by the thin film and the reflector. An optical absorption coefficient measuring device, characterized in that the reflected light is incident on the light receiving portion and the amount of the reflected light is measured.