JPS63128210A - Measuring method for film thickness and refractive index - Google Patents

Abstract

PURPOSE:To simultaneously measure film thickness and a refractive index of a light transmissive film by irradiating an electromagnetic wave to the light transmissive film while varying its incident angle, and measuring the incident angle at which the reflection or transmission intensity takes an extreme value. CONSTITUTION:A monochromatic light from a laser oscillator 1 travels in order of a rotary reflecting mirror 2 lenses 3a, 3b a measuring film 10 a condensing lens, and its light quantity is detected 5. A reflecting point G on the reflecting mirror 2 coincides with a focus of the lens 3a, and parallel rays which have passed through the lens 3a are all placed so as to pass through a focus of the lens 3b. Also, the surface of the film 10 is positioned on the focus of the lens 3b, therefore, the monochromatic light which has been reflected by the reflecting mirror 2 reaches a point H on the film 10, and a measuring position is not shifted. From a CPU7, an incident angle command signal is sent to a galvanometer 8 and the reflecting mirror 2 is oscillated, and the monochromatic light reaches the point H while varying the incident angle. A detected light quantity signal by the detector 5 is sent to the CPU7 and a light quantity variation by the incident angle is analyzed, the incident angle at which the light quantity takes an extreme value is measured continuously, and film thickness and a refractive index of the film 10 are measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of simultaneously measuring both film thickness and refractive index using electromagnetic wave interference.

[Prior Art] As methods for measuring film thickness and refractive index, an ellipsometer that uses polarization analysis, a spectroscopic analysis method that uses interference, and the like have been put into practical use. However, these conventional techniques have the disadvantage that they are limited to cases where either the film thickness or the refractive index is known, and cannot be measured at all when both are unknown.

[Problems to be Solved by the Invention] The present invention has been made to solve the above-mentioned technical constraints, and its purpose is to provide a light-transmitting material whose film thickness and refractive index are both unknown. It is an object of the present invention to provide a method for measuring film thickness and refractive index that can measure both the film thickness and refractive index in a transparent film.

[Means for Solving the Problems] The structure of the present invention that achieves the above object is a method for measuring film thickness and refractive index by irradiating electromagnetic waves onto a transparent film. irradiating the translucent film with electromagnetic waves while changing the angle of incidence on the translucent film, and detecting at least three incident angles at which the intensity of reflection or transmission caused by the interference effect of the electromagnetic waves on the translucent film takes an extreme value; This is a method for measuring film thickness and refractive index, the gist of which is to obtain the film thickness and refractive index by measuring and solving the two-dimensional simultaneous equations of equations (12) and (13) below.

... (12) ... (13) where d: Film thickness λ: Wavelength of electromagnetic wave d'm+2r, θ''m+r, θ''I: Indicates the incident angle,
At which angle of incidence does the reflected or transmitted intensity observed at each angle take a different maximum or minimum value? m + 2 r and θ”mar.

Between θ″m+″ and θ″m, there are (r−1) angles that take the maximum value or the minimum value (90〉0m〉θ
mar>0m+2r>O).

[Operations] The basic principle of electromagnetic wave interference, which plays an important role in the configuration of the present invention, will be explained with reference to the drawings.

First, in Figure 2, PQR5 is substance I, II (medium)
This is a transparent film 10 in which both outer surfaces existing between the two are parallel planes.

Let us now assume that the substances (1) and (2) are air, and consider the case where an electromagnetic wave is incident from point A to one point B on the surface PQ of the film 10 at an incident angle θ, as shown in FIG. The thickness of the inner membrane 10 is d, the wavelength of electromagnetic waves in air is λ, the refractive index of the membrane with respect to air is n, and the refraction angle is ψ.

A part of the electromagnetic waves irradiated to the film 10 is reflected at point B and travels in the direction indicated by the arrow, and the other electromagnetic waves enter the film 10 at a refraction angle ψ and head toward point C, and at the ridge point C. It is reflected and goes in the direction of arrow M via a dot on plane PQ. The path BL of the electromagnetic wave reflected at point B is parallel to the path DM of the electromagnetic wave going in the direction of M via points C and D.

The electromagnetic waves traveling through these two paths BL and DM interfere on the focal point Fo of the lens 11 after passing through the lens 11.

Here, there are two paths BL in electromagnetic waves.

The optical distance difference Δ of BCDM can be expressed as in the following equation (1), where K is the foot of the perpendicular line drawn from the dot to the route BL.

Since there is a relationship between θ and ψ of sin θ=nsin ψ − (2), the following equation (3) is obtained by substituting equation (2) into equation (1) and rearranging.

Δ=2nd-cosψ ・(3) Now,
Assume that electromagnetic waves are made incident on a film while continuously changing the incident angle θ. When the incident angle θ is 0 m, the intensity takes a maximum value (or minimum value) due to the interference of the reflected waves, then when the incident angle θ is 0 m + 1, the intensity takes a maximum value (or minimum value) again, and then Suppose that θ reaches the maximum value (or minimum value) again when θm+2 (90°〉0m〉0m+1〉)
θm+2〉0). At this point, the incident angle θm measured sequentially
.

Optical distance difference Δm for each of 0m+1 and θm+2,
Δm+1. Between Δm+2, the following (4) and (5)
The relationship of the formula holds true.

1 Δu++1 −Δml= λ
... (4) 1Δm+2−Δm+11
=λ...(5) Therefore, the above (3),
From equations (4) and (5), the following equations (6) and (7) can be obtained.

λ d=-・n... (6) d=2n... (7) In the above equations (8) and (7), the three incident angles θ
m.

θm+1. Since θm+2 can be obtained as a measured value, the thickness d and refractive index n of the film 10 can be measured by combining equations (6) and (7).

On the other hand, from the relationship of equations (6) and (71), the following (8
) formula is obtained.

However, X = 2sin20m+1-5in2θm-5
in'θm+2 Y = X + 2sin20m+1 Therefore θ, θm+1. The measured value of θm+2 may be applied to the above equation (8) to obtain the value of the refractive index n, and then the film thickness d may be obtained from the equation (6) or (7).

In calculating equations (6) and (7), reflected waves were used in the case shown in Fig. 2, but the present invention is not limited to the case where reflected waves are used. Similarly, even when using transmitted waves, the above (6)
, (7) can be obtained from 6 above (8),
The simultaneous equations in equation (7) are based on three different incident angles θ groups, θm+1. The relationship at θm+2 was obtained, and the intensity due to interference is local maximum value - local minimum value →
Three different incident angles θym, θ'ma1, which are sequentially bundled when taking the local maximum value or local minimum value → local maximum value - local minimum value.
Simultaneous equations can be obtained similarly for θ'm+2.

In this case, the phase is shifted by λ/2, so (
In the above case, it is shifted by λ), and (9) below.

Simultaneous equations of (lO) are obtained. However, 90°〉θ
'm>θ'm+1>θ'm+2>O.

... (9) ... (10) In the above equations (9) and (10), the incident angle θ1.
Since θ'm+1°02m+2 is measured, (9),
The film thickness d and the refractive index n can be determined by solving the simultaneous equations (10). Also in this case, as in the case described above, the following equation (11) is obtained from equations (9) and (10), the refractive index n is obtained from this equation (11), and then (9) and (10 ) The film thickness may be determined using either one of the following equations.

However, X = 2sin2θ'm+1-5in20'm
-5in”&'m+2 Y = X + 2sin2 0'm+1 Now, next (
Consider the general formulas 6) to (8) or (9) to (11).

As shown in Figure 4, when the incident angle is changed, it reaches an extreme value at a certain angle θm, and then as it continues to change further, it passes through the maximum and minimum points r times and reaches θmar. Suppose that it takes the extreme value again and, while changing it further, passes through the maximum and minimum points again r times and takes the extreme value again at 0m+2r.

At that time, if d'm >θ"mar> θ-+2r, then the relationship between equations (6) to (8) or equations (9) to (11) is generally the relationship between equations (12) to (14) below. can be expressed as

... (12) ... (13) ,? 7 However, X = 2s+n2θmar -5in2θ″m
-5in2d'm+2r Y = X + 2sin' θ”m + r Above (1
In equations 2) to (14), if r=1, the above (9)
~ (11) formula is obtained, and if r = 2, the above (6) ~
Equation (8) is obtained.

According to the inventor's experimental results, setting r as large as possible can reduce the influence of measurement errors in angles that take extreme values, and improves the measurement accuracy of refractive index and film thickness.

Basically, the present invention uses electromagnetic waves of a known wavelength to determine the film thickness d for a film 10 whose film thickness d and refractive index n are unknown.
and the refractive index n, but if either the refractive index n or the film thickness d is known and the wavelength of the electromagnetic wave to be used is unknown, the above (12), (
It goes without saying that technical applications such as finding the wavelength of electromagnetic waves by applying the relationship in equation 13) are possible.

[Example] FIG. 1 is a schematic explanatory diagram of a film thickness/refractive index measuring device configured to carry out the method of the present invention.

The monochromatic light emitted from the laser oscillator 1 is transmitted to the rotating reflector 2.
- The light progresses in the order of lenses 3a, 3b→film 10 (measurement target)→condensing lens 4, and the reflection intensity (light amount) is measured by the light amount detector 5. The rotating reflecting mirror 2 is configured to be swung by a galvanometer 8, and the traveling direction of the monochromatic light reflected by the rotating reflecting mirror 2 can be arbitrarily changed.

On the other hand, the reflection point G of the monochromatic light reflected by the rotating reflector 2 is configured to coincide with the focal point of the lens 3a, and the monochromatic light reflected at the reflection point G passes through the lens 3a, so that all of the monochromatic light is reflected by the lens 3a. It becomes parallel to the optical axis of 3a. Further, the lenses 3a and 3b are arranged so that their respective optical axes coincide with each other, and the parallel rays after passing through the lens 3a pass through the focal point of the lens 3b after passing through the lens 3b. and lens 3b
The surface of the film 10 is positioned on the focal point of the mirror 2, so that all the monochromatic light reflected by the rotating mirror 2 reaches the same point H on the surface of l1U10, and the measurement position does not shift.

An incident angle command signal is sent to the galvanometer 8 from the central processing circuit (CPU) 7, and the galvanometer 8 swings the rotary reflecting mirror 2 in accordance with the command signal.
The monochromatic light reflected by reaches point H while changing the angle of incidence.

Note that the point F at which the reflection intensity of the monochromatic light in the light amount detector 5 is measured coincides with the focal point of the focusing lens 4 due to the second
As stated in relation to the figure.

The light amount signal detected by the light amount detector 5 is then sent to the amplifier 6.
The signal is sent to the CPU 7, amplified, and further sent to the CPU 7. CPU
In step 7, the changes in the amount of light depending on the angle of incidence are analyzed, and the angle of incidence at which the amount of light takes an extreme value is continuously measured.
14) The film thickness d and refractive index of 1I110 are measured by applying the relationship of formula.

Furthermore, the optical system shown in FIG. 1 can be configured as shown in FIG. 5 (schematic explanatory diagram). In addition, 12 in Figure 5
is a reflector.

In the configuration shown in FIG. 5, the angle of the light emitted from the laser oscillator 1 is changed by a rotating reflector, and then it passes through lenses 3a and 3b and enters the film 10. The reflected light from the film 10 passes through the lens 3b again, its angle is changed by the reflecting mirror 12, passes through the condensing lens 4, and the amount of light is detected by the light amount detector 5.

The method of the present invention can also be implemented in such a configuration. Note that in the configuration shown in FIG. 5 as well, lenses 3a, 3b and lens 4 are used similarly to the optical system shown in FIG.
The focal points are arranged so as to coincide with the center of rotation of the rotating reflecting mirror 2 (coinciding with the irradiation point of the laser beam), the measurement point H1 of the film 10, and the light amount detector 5, respectively.

[Effects of the Invention] As described above, according to the present invention, by employing the above-described configuration, it is possible to measure with high accuracy the film thickness and refractive index of a film whose film thickness and refractive index are unknown. became.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram of a film thickness/refractive index measuring device configured to carry out the method of the present invention, Figs. 2 and 3 are schematic explanatory diagrams showing the principle of the present invention, and Fig. 4 is a general illustration. Equation (12) ~
FIG. 5 is a graph showing waveforms for determining equation (4), and is a schematic explanatory diagram showing another example of a film thickness/refractive index measuring device configured to carry out the method of the present invention. 1... Laser oscillator 2... Rotating reflector 5...
Light amount detector 6...Amplifier 7...Central processing circuit 8...Galvanometer 10...Membrane (measurement target) Fig. 3 Between A and L 11 8U63-128210 (6) Fig. 4 Incident angle

Claims (1)

[Claims] A method for measuring film thickness and refractive index by irradiating electromagnetic waves onto a transparent film, the electromagnetic waves are applied to the transparent film while changing the angle of incidence of the electromagnetic waves on the transparent film. irradiate, measure at least three incident angles at which the reflection or transmission intensity caused by the interference effect of electromagnetic waves on the transparent film takes an extreme value, and solve the two-dimensional simultaneous equations of equations (12) and (13) below. A method for measuring film thickness and refractive index, characterized by determining film thickness and refractive index. ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(12) However, d: Film thickness λ: Wavelength of electromagnetic wave θ″m+2r, θ″m+r, θ″m: Indicates the angle of incidence,
The angle of incidence when the reflected or transmitted intensity observed at each angle takes a different maximum or minimum value, θ″m+2r, θ″m+r, θ″m
There are (r-1) angles between +r and θ″m that take the maximum value or the minimum value (90°>θ″m>θ″m+r>θ″m+2
r>0).