JP3321886B2 - Attenuated total reflection thin film evaluation system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an attenuated total reflection type thin film evaluation apparatus for evaluating and measuring the refractive index, attenuation coefficient (light absorption), film thickness and the like of a thin film.

[0002]

2. Description of the Related Art An attenuated total reflection type thin film evaluation method is disclosed in, for example, the Journal of the Physical Society of Japan, Vol. 43, No. 11, 1988, pp. 863-868.
The optical constant of the thin film is evaluated by utilizing the phenomenon described above.

[0003] Compared with the ellipsometry widely used for the same purpose, the evaluation by the ATR shows that the ellipsometry is suitable for a transparent thin film or an absorbing bulk material, whereas the ATR is not suitable for a thin film to be evaluated such as a metal. It is suitable for a thin film having light absorption.

[0004] In this ATR evaluation, light incident from a medium A having a high refractive index to a medium B having a small refractive index has a certain incident angle,
That is, the phenomenon of total reflection that occurs when the total reflection critical angle determined by the refractive index of both media is exceeded is used. At this time, if there is a thin film of a substance that absorbs light, for example, a metal thin film, at the interface between the two media A and B, the light power oozing out of the medium B is absorbed by this thin film and the light power reflected is reduced.

[0005] The phenomenon of ATR has a resonant character. This is because the mode that can absorb the optical power most effectively is the plasma oscillation (electric polarization wave) on the surface of the metal thin film.
Which is a unique dispersion relation determined by the optical constant of the medium.
(A constant relationship that is satisfied by the angular frequency ω and the surface direction component k _H of the metal thin film having the wave number k), a high efficiency is obtained only when the seeping light has the same ω and k _H. Then, energy is transferred to the plasmon, and the reflectivity is drastically reduced.

This ATR thin film evaluation method is, for example, as shown in FIG. 5 which shows a basic configuration of one example of the thin film to be evaluated 11 formed on the bottom surface of a prism 1 having a columnar refractive index _np having a rectangular cross section at right angles. angle of incidence of the laser beam required apparent incident light 2 for example the angular frequency omega _L for measurement with respect to Ag vapor-deposited film (the light incident on the prism is referred to as the angle of incidence apparent angle between the normal to the prism bottom surface Let's say) θ
Irradiation with _i is performed.

FIG. 6 is a diagram showing the dispersion relationship of surface plasmons in this case.

In the ATR thin film evaluation apparatus of the present invention, for example, the frequency ω _{L of the} incident light is fixed, but the wave number k _H is selected by the following equation 1 by changing the incident angle θ _{i of the} light. Thus, a point P on the dispersion curve in FIG. 6 can be obtained.

[0009]

[Number 1] _{k H = ω L n p sinθ} i / c c represents the speed of light.

FIG. 7 shows the change in reflectance with respect to the incident angle θ _i of light. The broken line curve indicates the case where only the prism is used, the solid line curve indicates the case where the Ag thin film is used, and the case where only the prism is used.
total reflection at _{i> θ c,} if the Ag thin film i.e. the metal thin film is present, A is caused sinking by ATR by the dispersion relation of a point P in FIG. θ _c is the critical angle for total reflection.

The angle dependence of the reflectance is determined by the optical constant of the medium (refractive index n, extinction coefficient k) and the thickness d of the metal thin film.
Can be obtained by assuming that n, k, and d can be simultaneously estimated so that the calculation result reproduces the actual measurement.

By the way, in a commonly used polarization analyzer with a fixed incident angle and a single wavelength, n and d are obtained by assuming literature values for k, or after determining the film thickness by another method. It is something that can only be estimated by the two, like
Here is a great advantage of the ATR thin film evaluation method.

By the way, in the above-described ATR film evaluation method, as apparent from the above, although the measurement light beam 2 comprises a range exceeding the total reflection critical angle theta _c is for angular sweep, now view As shown by 5, when an isosceles triangular prism, for example, a right-angled triangular prism is used as the optical coupling prism 1, the incident angle of the light beam on the prism 1 is 90 ° (in the case of a right-angled triangular shape, the apparent incident angle θ _i). Is 4
In this case, the reflectance for the apparent incident angle, that is, the ATR spectrum is 45 ° as shown in FIG.
Disturbance occurs in the vicinity.

As shown in FIG. 5, this phenomenon occurs when the measuring light beam is incident at right angles to one of the slopes of the prism 1 and the point of incidence A on the prism 1 and the thin film 1 to be evaluated.
Since the optical path connecting the point B where the total reflection is performed on the bottom surface where the light-receiving element 1 is disposed and the emission point C from the prism 1 is symmetrical with respect to the normal passing through the point B with respect to the bottom surface, the point B moves from the point B to the point C. This is considered to be due to the reciprocal reciprocal resonance that a part of the light reflected at the lever C takes the same optical path again from the point C to the point B and the part of the light is reflected.

That is, the amplitude of the original measurement light that is detected from the point C to the outside after passing through the point AC only once is:
If the light amplitudes due to the above-described resonance are superimposed, interference occurs in which the detection light is strengthened or weakened depending on whether or not the phases of these waves are the same, and the interference region I shown in FIG. 8 occurs. Conceivable.

As a method of avoiding noise due to optical interference in the prism, for example, a method of changing the refractive index of the prism or the angle of the prism so as to move the target ATR spectrum so that the target ATR spectrum appears in the noise-free angle region. Can be considered.

In this case, this method is quite effective when the medium that causes total internal reflection to the prism is always the same medium, for example, air.

However, for example, when used in a chemical sensor or the like, the critical angle of total reflection is not always constant, and it may be difficult to apply this method.

[0019]

The present invention relates to the above-mentioned A
It is possible to effectively avoid the occurrence of the interference region I, that is, the unstable region in the TR spectrum, and to surely achieve the AT even when the critical angle for total reflection is not determined as described above.
It is possible to effectively avoid the generation of an interference region in the R spectrum and hence the generation of noise.

That is, in the present invention, the optical resonator is not fundamentally formed in the optical coupling prism for the thin film to be evaluated.

[0021]

According to the present invention, FIG.
As shown in FIG.
In the attenuated total reflection type thin film evaluation apparatus which irradiates the thin film to be evaluated 11 with the measuring light beam 2 through the through hole and performs the analysis and evaluation by the attenuated total reflection, the prism 1 is used to set the surface on which the to be evaluated thin film 11 is disposed to the bottom surface. both the base angle on both sides α and β to
Select acute and different angles. That is, β = α +
δ. Here, δ> 0 or δ <0.

[0022]

According to the structure of the present invention described above, as shown in FIG. 1, the measuring light beam 2 is applied to the bottom surface of the prism (in this specification, as apparent from the above description, the thin film 1 to be evaluated).
1 is defined as a bottom surface), that is, when light that is incident at right angles on the slope of the prism toward point B at the center of the bottom surface at right angles is totally reflected at point B, Part of the light reflected at the point C on the inclined surface is reflected to the other without going to the point B as shown by the broken line in FIG.

Therefore, the ATR obtained by this configuration
As shown in FIG. 2, the spectrum has a smooth characteristic without an interference area, that is, an unstable area, and a reliable evaluation (measurement) with small noise can be performed with respect to the ATR evaluation.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an ATR type thin film evaluation apparatus according to the present invention will be described with reference to FIG. This ATR thin film evaluation apparatus can be a standard ATR measurement system.

In this case, a turntable 61 for performing angular scanning.
A sample 62 having a thin film to be evaluated is placed thereon.

As shown in FIG. 1, the sample 62 can have a configuration in which the thin film 11 to be evaluated is formed directly on the bottom surface of the optical coupling prism 1. The configuration proposed in -72245 can be adopted. That is, for example, when an Al thin film or the like attached to a light-transmitting substrate such as glass or plastics is used as an evaluation thin film 11 in an optical disk such as a CD (compact disk), as shown in FIG. The light-transmitting substrate 12 is provided on the bottom surface of the optical coupling prism 1 on the side opposite to the side having the thin film 11 with a coupling layer 15.
And optically coupled to each other.

The coupling layer 15 is a liquid in which the critical angle of total reflection at the interface between the prism 1 and the coupling layer 15 is larger than the critical angle of total reflection at the interface between the light transmitting substrate 12 and air. layer, for example, water, almond oil, a layer such as methylene iodide.

As described above, the coupling by the liquid layer in which the critical angle of total reflection of the interface disk between the prism 1 and the coupling layer 15 is larger than the critical angle of total reflection at the interface between the light transmitting substrate 11 and air. When the ring layer 15 is used, as described in Japanese Patent Application No. 5-72245, it is possible to avoid a substantial influence on the ATR evaluation of each interface between the prism and the substrate 12.

In particular, in the present invention, the configuration of the prism 1 is set such that the base angles α and β on both sides of the surface on which the thin film 11 to be evaluated is arranged are different from each other. That is, β = α + δ. Here, δ> 0 or δ <0.

The mounting table 61 can be constituted by a so-called goniometer stage. That is, for example, it includes first and second stages 63 and 64 that rotate in a relationship between 2θ and θ, respectively.
The sample 62 can be further moved in two directions x and y orthogonal to each other, and the sample 62 is placed on the stage 75.

Then, a light source such as a He-Ne laser 65
Is introduced into the prism 1 through the polarizer 66, the beam splitter 67, and the beam shifter 68 at a required apparent incident angle θ _i shown in FIG.

The diameter of the measuring light beam 2 is selected to be smaller than the thickness D of the light transmitting substrate 11.

Then, the reflected light 2R from the sample 62 with respect to the incident angle is measured while rotating the first and second stages in a relationship of 2θ and θ. For this reason, for example, detection is performed by a first photodetector 69 such as a photodiode disposed on the first stage 63. At this time, the beam shifter 6
By rotating the stage 8 and moving the stage 75 in the x and y directions, adjustment is made so that a predetermined measurement position at the interface between the light transmitting substrate 11 and the thin film 1 is irradiated with incident light.

On the other hand, a part of the laser beam split by the beam splitter 67 is detected by a second photodetector 70 such as a photodiode to detect the power of the laser beam, that is, the power of the measuring light beam. The respective outputs A and B are amplified by amplifiers 71 and 72, respectively, and the outputs A and B are introduced into an analog divider 73 (Analog Devices, Inc .: AD-533) 73 to obtain A / B. Multiply and calculate the reflectance.

The output of the divider 73 is introduced into a personal computer (PC-9801) via a digital oscilloscope. Here, the calculation of the theoretical reflectance and the inter-comparison with the measured values are all performed on this personal computer. Thus, the optical constant of the metal thin film 1 is evaluated by the ATR.

As described above, according to the present invention, the prism 1 for the optical coupling has an unequal triangular shape with the base angles different from each other, thereby forming an optical resonator inside the prism. Figure 2
Thus, it is possible to avoid the occurrence of the interference region in the ATR spectrum described above, and to accurately evaluate (measure) the optical constant and the like of the thin film to be evaluated by the ATR.

Each of the ATR spectra shown in FIGS. 2 and 8 is a case where an Au thin film is deposited on a glass substrate and optically coupled to each prism 1 with the above-described liquid coupling layer.

[0038]

According to the above-described ATR type thin film evaluation apparatus of the present invention, since the occurrence of an optical resonator in the prism is avoided, the AT generated by the configuration of this resonator is avoided.
The generation of unstable regions in the R spectrum can be avoided, and ATR
Reliable evaluation (measurement) with small noise can be performed.

[Brief description of the drawings]

FIG. 1 is a plan view of an example of a prism of the apparatus of the present invention.

FIG. 2 is an ATR spectrum diagram of the apparatus of the present invention.

FIG. 3 is a configuration diagram of an example of the device of the present invention.

FIG. 4 is a plan view showing a relationship between a prism and a sample in an example of the apparatus of the present invention.

FIG. 5 is a plan view of a prism of the conventional device.

FIG. 6 is a diagram showing a dispersion relationship of surface plasmons.

FIG. 7 is a diagram illustrating a relationship between a reflectance and an apparent incident angle for explaining an ATR thin film evaluation method.

FIG. 8 is an ATR spectrum diagram of the conventional device.

[Explanation of symbols]

 Reference Signs List 1 prism for optical coupling 11 thin film to be evaluated 12 light-transmitting substrate 15 coupling layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-161041 (JP, A) JP-A-49-12876 (JP, A) JP-A-6-288900 (JP, A) JP-A-6-288900 288902 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 21/00-21/74 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. An attenuated total reflection type thin film evaluation apparatus for irradiating a light beam for measurement to a thin film to be evaluated via an optical coupling prism and performing analysis and evaluation by attenuated total reflection. The attenuated total reflection type thin film evaluation device, wherein the bottom surface on which the surface is disposed is the bottom surface and the base angles on both sides thereof are both acute angles and are selected to be different from each other.