JPS63212807A - Measuring method of thickness of thin film - Google Patents

Abstract

PURPOSE:To enable the precise measurement of the thickness of a thin film by a method wherein the peak value of the quantity of light of a wavelength which gives this peak value to a measured film thickness is determined from measured quantities of lights of shorter and longer wavelengths than said wavelength and the thickness of a thin film is measured from said peak value. CONSTITUTION:Above a chamber 11, a light application system 20 and a light reception system 21 are disposed corresponding to a thin film formed on a substrate 14, and these systems are connected to a film thickness measuring system 23. The light application system 20 is provided with a light source 24, a monochromator 25 and a lens system 26, and the light reception system 21 is provided with a detector 27, while the measuring system 23 is provided with CPU 28. A wavelength giving the peak of the quantity of light to the measured film thickness t0 of the thin film 29 is denoted by lambda0, wavelengths shorter and longer than said wavelength by lambda1 and lambda2 respectively, and normalized reflection quantities R1 and R2 of the shorter and longer wavelengths lambda1 and lambda2 are measured. The peak value of the quantity of light for the wavelength lambda0 can be detected from the intersecting point of said reflection quantities R1 and R2, and the thickness t0 of the thin film 29 can be determined from this peak value of the quantity of light.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application Field 1 The present invention relates to a method for measuring the thickness of thin films used in various fields such as semiconductors, optics, and communications.

rPrior art J In the fields of semiconductors, optics, communications, etc., when forming a thin film such as an oxide film or an optical filter to a predetermined thickness on a silicon substrate, the thin film is formed while measuring the film thickness. It is common to do this, and as such a measuring means, an optical film thickness measuring method is widely used.

One of the widely known optical film thickness measuring methods described above is the method shown in FIG.

In the method shown in FIG. 5, a thin film 2 on a substrate 1 is irradiated with measurement light P, and the amount of reflected light PR from the thin film 2 is measured.

The reflected light mPR at this time changes sinusoidally with respect to the thickness t of the thin film 2, and its period is equal to the wavelength of the measurement light P.
When the refractive index of is set to n, it becomes in/2n.

Therefore, when forming a thin film 2 with a known wavelength and refractive index n to a thickness tO, if the reflected light fiP++ is continuously measured in synchronization with the thin film formation, it is possible to measure the change in the thin film 2 over time. If the thickness t is determined from the relationship shown in FIG. 6, and the thin film formation is stopped at the time t-to, the S
The thickness of the film 2 is finished to a predetermined value (a).

In the film thickness measurement method described above, the wavelength λ of the measurement light P is 4
nto, the thickness to of the thin film 2 can be determined by detecting the light intensity peak at 4nto. However, in actual measurement, the measurement wave input is set to 4nto - Δλ, which is slightly smaller than 4nto. , it takes = 4nt (
At 1-Δ, a point slightly exceeding the first light amount peak (A in FIG. 6) is detected to determine the thickness to of the thin film 2.

The reason for this is that, as pointed out in general peak detection, the absolute value of the amount of reflected light PR is affected by optical loss in the measurement system, so this must be avoided to improve measurement accuracy. Furthermore, the peak of the amount of light itself cannot be determined until it exceeds the peak.

"Problems to be Solved by the Invention" However, in the measurement method described above, the change in the amount of reflected light PR is extremely small with respect to the change in film thickness near the peak of the light amount, and in practice it is affected by noise, etc. It is difficult to accurately locate peaks.

As a result, when forming the thin film 2 while measuring its thickness, it may be difficult to finish the thin film 2 to a predetermined thickness.

Of course, such a situation also occurs when the light transmitted through the thin film 2 is used as the measurement light.

In view of the above-mentioned problems, the present invention aims to provide a method that can accurately measure the thickness of a thin film when the thickness of the thin film is measured by optical means.

Means for Solving Problems j In order to achieve the intended purpose of the present invention, the thin film whose thickness is to be measured is irradiated with light, the light from the thin film generated by the light irradiation is used as measurement light, and the In the method of measuring the thickness of a thin film by measuring the light intensity of the measurement light, the wavelength of the measurement light that gives the light intensity peak with respect to the measured thickness of the thin film is λ0, and the wavelength shorter than the wavelength input 0 is used. When input 1 is a wavelength longer than the wavelength λ0, input 2 is measured, the light intensity of the two long and short wavelengths λ1 and λ2 is measured, and the two long and short wavelengths λ1 and input 2 are measured.
From the measured light amount, find the light amount peak at the wavelength λ0,
The method is characterized in that the thickness of the thin film is measured.

``Example 1'' An example of the method for measuring the thickness of a g-film according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a thin film forming apparatus for applying the method of the present invention.

In the apparatus shown in FIG. 1, the chamber 11 includes a rotating system 12,
An exhaust system 13 is provided.

A substrate 14 for thin film deposition is installed in the upper part of the chamber 11, and a shutter 15, a target (thin film material) 10, an electron beam heat source 17. It is equipped with ion guns 18, etc.

Rotating system 12. Exhaust system 13, shutter 15, target 1
6, the electron beam heat source 17, the ion gun 18, etc. are each connected to a device control system 19, and the devices are controlled via the control system 13.

In FIG. 1, a light irradiation system 20 and a light receiving system 2 are located above the chamber 11, corresponding to the thin film formed on the substrate 14.
1 is arranged, and these light irradiation system 20 and light reception system 21 are connected to a film thickness measurement system 23.

Furthermore, the film thickness measurement system 23 is connected to the device control system 18 in order to input the measurement signal thereto.

As shown in FIG. 2, the light irradiation system 20 described above includes a light source 24 such as a halogen lamp, a monochromator 25, and a lens system 2B, the light receiving system 21 includes a detector 27, and the film thickness measurement system 23 includes a It is equipped with a CPU 28.

In the thin film forming apparatus shown in FIG.
When forming an IJ film by electron beam evaporation, the inert gas atmosphere (Ar) in the chamber 11 is maintained at an appropriate degree of vacuum via the exhaust system 13, and the target 16 is heated to a predetermined temperature by the electron beam heat source 17. Retained.

At this time, the rotation system 12 rotates the chamber 11 in order to improve the uniformity inside the chamber 11, and the ion gun 18
substrate 14 to enable low-temperature deposition on the substrate 14.
Emit positive ions towards 4.

In this state, particles evaporated from the target 16 adhere to the substrate 14, forming a thin film 29 as shown in FIG.

Note that before forming the nine films 29 on the substrate 14 through the evaporation means, the target is preheated with the shutter 15 closed.

In the method of the present invention, when forming the thin film 29 on the substrate 14, as shown in FIG. The reflected light from the thin film 29 is used as measurement light,
The measurement light is made to enter the film thickness measurement system 23 from the light receiving system 21 with the detector 27, and the thickness of the thin film 29 is measured.

In this case, the monochromator 25 includes a dual wavelength input l, which will be described later.
input 2 is selected alternately, and the detector 27 selects these two wavelengths λ
1. Measure the amount of reflected light of λ2, and roughly measure the amount of reflected light of λ2.
8 detects a predetermined light intensity peak based on the measured value and stops the film forming means.

To explain the method of the present invention in more detail, among the above measurement lights, the wavelength that gives a light intensity peak with respect to the measured film thickness to of the thin film 29 is λ0, and the wavelength shorter than 0 is input] = input0 - Δ
λI, its wavelength input. Input a wavelength longer than 2 = 1 input G + Δ
2, and measure the amount of light (normalized reflection amount) at two long and short wavelengths λ1 and λ2.

Here, the normalized reflection amount R of the wavelength is expressed by the following formula (1), when the light amount of the measurement light (reflected light) is PR, and the normalized reflection amount R1 of the above two long and short wavelengths λ1 and λ2. ,R2
is as shown in Figure 3.

R(PR-PR-sin)/(PR,ax-PR1i
(1) Therefore, as shown in FIG. 3, the peak of the light intensity at wavelength 0 can be detected from the intersection of the normalized reflection amounts R1 and R2 for the long and short wavelengths 1 and 2.

In this case, the following relational expression (2) is required to hold, but in this case, by setting Δ input 2 kuku input 0, Δ
Input 1 - ∆ Input 2, and even if ∆ Input - ∆ Input 2 - ∆ Input 1, the error is (∆ Input / Input o) 2, which is extremely small.

ΔInput 1-(λ0・Δλ2)Ba Input 0÷ΔInput 2)・・・(
2) Therefore, as described with reference to FIG. 3, the light intensity peak for the wavelength λ0 can be detected from the intersection of the normalized reflection amounts R1 and R2 for the long and short wavelengths λ1 and λ2, and from this light intensity peak , the thickness to of thin H29 is found.

FIG. 4 shows 5i02, which is a typical material of the 6M film 29.
Generally, the refractive index n of 5i02 is a function of wavelength.

Here, if Δ is set to 0, the dependence of the refractive index n on the wavelength can be ignored, and thereby the above-mentioned matter is technically established.

When aiming for more accurate film thickness measurement, it is sufficient to use the calibration method of equation (2), which takes into account these effects.

Thus, when the thickness to of the thin film 28 is determined, the measurement signal is input from the film thickness measurement system 23 to the device control system 19,
The operating state of the thin film forming apparatus (FIG. 1) is controlled.

In the thin film forming apparatus of FIG. 1, for example, a submicron-thick TiO2 film, S1021)51! dozens of layers,
When forming an optical filter (thin film) on the substrate 1 by alternately laminating layers, in order to obtain a high quality optical filter, the film thickness of each layer must be kept within an error of ±1z. When the FIJ film forming apparatus was controlled to be stopped in a timely manner through the method, the film thickness of each layer could be finished within the allowable error range.

In this case, Ti02M, Si0? The film formation time is
The test times were approximately 2 minutes and 4 minutes, respectively, per 1000 nm thick layer.

The deposition rate was slowed near the peak of the light intensity.

The data processing speed of the film thickness measurement system 23 is when a 16-bit personal computer is used.

The time was approximately 0.2 seconds.

In the embodiments described above, the light reflected from the thin film is measured as the measurement light, but the film thickness can be measured in the same manner as described above even when the light transmitted through the thin film is used as the measurement light.

In addition, in the illustrated example, the maximum positive value of the sine wave is used as the light amount peak in the present invention, but the maximum negative value of the sine wave may be used as the light amount peak.

"Effects of the Invention" As explained above, 1. When using the method of the present invention, when measuring the thickness of a thin film through optical means, the wavelength incidence 0 that gives the light intensity peak for the measured thickness of the thin film is directly measured. Instead, the amount of light at a wavelength λl shorter than the wavelength 0 and a wavelength 2 longer than the wavelength λ0 is measured, and these two wavelengths λ! Since the thickness of the thin film is measured by determining the light intensity peak at wavelength 0 from the measured light intensity of , λ2, the light intensity peak can be accurately and easily oriented, and precise film thickness control can be performed during thin film formation. Yield is improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a thin film forming apparatus to which the method of the present invention is applied;
Fig. 2 is an explanatory diagram schematically showing the main parts of the measurement system in the method of the present invention, Fig. 3 is an explanatory diagram showing the relationship between the normalized reflection amount and the measurement wavelength in the method of the present invention, and Fig. 4 is an explanatory diagram showing the relationship between the normalized reflection amount and the measurement wavelength in the method of the present invention. FIG. 5 is an explanatory diagram showing the relationship between the refractive index and wavelength, FIG. 5 is a schematic diagram of the conventional method, and FIG. 6 is an explanatory diagram showing the relationship between the amount of reflected light and the measured film thickness in the conventional method. 20... Light irradiation system 21... Light receiving system 23... Film thickness measurement system 23... Thin film

Claims (3)

[Claims] (1) In a method of measuring the thickness of a thin film by irradiating light onto a thin film whose thickness is to be measured, using the light from the thin film generated by the light irradiation as measurement light, and measuring the light intensity of the measurement light, Among the measurement lights mentioned above, if the wavelength that gives the light intensity peak with respect to the measured thickness of the thin film is λ_0, the wavelength shorter than the wavelength λ_0 is λ_1, and the wavelength longer than the wavelength λ_0 is λ_2, then the two wavelengths λ_1 are the long and short wavelengths. , λ_2, and from the measured light intensities of these two long and short wavelengths λ_1 and λ_2, determine the light intensity peak of the wavelength λ_0 to measure the thickness of the thin film. . (2) The method for measuring the thickness of a thin film according to claim 1, wherein the measurement light is reflected light from the thin film. (3) The method for measuring the thickness of a thin film according to claim 1, wherein the measurement light is light transmitted through the thin film.