JPS59143904A - Monitoring method of characteristics of dielectric thin film - Google Patents

Abstract

PURPOSE:To monitor the characteristics of a dielectric thin film in a forming process of the dielectric thin film accurately, by measuring the transmittance or reflectivity in a wavelength on the short-wavelength side of two wavelengths, and obtaining the refractive index of the dielectric thin film during the formation based on the extreme value of the transmittance or reflectivity. CONSTITUTION:One light beam L1 is transmitted through a glass substrate 13, wherein a thin film is being formed, and guided to the outside of a vacuum evaporating container 11. The light beam is reflected by a mirror 43 and the direction is changed. The light beam is divided into the light having the equal intensity by a beam splitter 32 for 1/2 splitting. The two light beams passed a filter 51, which transmits a wavelength lambda1, and a filter 52, which transmits a wavelength lambda2(lambda1<lambda2). The light beams are converted into electric signals by light receiving devices 611 and 621. The transmitting wavelengths lambda1 and lambda2 of the filters 51 and 52 are different in correspondence with the desired optical film thicknesses. The signals are amplified by amplifiers 61 and 62 by the same amount, and the difference is obtained by a differential amplifier 72. The output of the diffeential amplifier 72 is monitored by a voltmeter 9. At a point when the output of the differential amplifier 72 becomes zero, the film formation is stopped and the optical film thickness is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for monitoring dielectric thin film characteristics, which monitors film thickness and refractive index when a dielectric thin film is formed on a substrate. The method of the present invention can be used, for example, in the production of glass with special optical properties, such as automobile window glasses, camera lenses, eyeglass lenses, optical filters, etc., when producing multi-dimensional optical thin films using multi-dimensional vacuum evaporation equipment or multi-dimensional sputtering equipment. This is used when it is necessary to keep the optical thickness of each layer constant and to be able to easily measure its refractive index and physical thickness.

Conventionally, in order to form an optical thin film with a thickness of λ/4 with high precision, it is necessary to detect the end point of the formation of 1 point, for example.
Color methods have been used. In other words, the workpiece is irradiated with light, the transmitted light or reflected light is divided into two parts, each passes through a filter with a different wavelength, and then the transmittance or reflectance is measured. This is a method of terminating film formation. However, in this method, the optical film thickness is kept constant, and the refractive index and physical film thickness are not measured. Therefore, even if the refractive index changes due to changes in conditions, it cannot be detected. Therefore, there are 711 points in the characteristics of the subsequent layer (by composition change) that cannot be sacrificed.

In view of the above-mentioned problems, the purpose of the present invention is to control the optical film thickness using a two-color method, measure the transmittance or reflectance on the short wavelength side independently, and determine the refractive index by knowing the minimum transmittance. Based on the idea of finding the physical film thickness from the optical film thickness and refractive index, we formed a dielectric (5) thin film!
The object of this invention is to accurately monitor dielectric thin film characteristics at different temperatures.

In the present invention, light is projected onto the dielectric thin film being formed,
The transmitted light or reflected light is split into two predetermined wavelengths (1η), and the thin film formation is stopped when the amount of transmitted light or reflected light at these two wavelengths becomes equal, thereby increasing the optical film thickness. At the same time, the transmittance or reflectance at the shorter wavelength of the two wavelengths is measured, and the refractive index of the dielectric thin film being formed is determined from the extreme value of the transmittance or reflectance. A method for monitoring characteristics of a dielectric thin film is provided.

An apparatus for carrying out a method for monitoring dielectric thin film characteristics as an embodiment of the present invention is shown in FIG. In the apparatus shown in FIG. 1, an evaporation source 12 and a glass substrate 13 are installed in a vacuum evaporation container 11 of a vacuum evaporation apparatus 1, and a substance 1d evaporated from the evaporation source 12 is deposited on the glass substrate 13 to form a dielectric thin film. form.

White light source 2 of the light source section 2 placed outside the vacuum deposition container 11
1 is split into two by a beam splitter 31, and each light is guided into the vacuum evaporation container 11. One light L1 is guided to the outside of the vacuum deposition container 11 after passing through the glass substrate 13 on which a thin film is being formed. The direction of the light is changed by reflection by a mirror 43, and the light is divided into equal intensities by a 1/2 beam splitter 32. These two lights (
The rJ knee passes through a filter 51 that transmits the wavelength λ1 and a filter 52 that transmits the wavelength λ2 (λ1 > λ2), and is converted into an electrical signal by the light receivers 611 and 621.

The transmission wavelength λ1 of the filters 51 and 52. λ2 varies depending on the desired optical film thickness, and will be described in detail later. each, amplifier 6
1.62, and a differential amplifier 72 takes the difference. The optical film thickness is controlled by monitoring the output of the differential amplifier 72 with the voltmeter 9 and stopping film formation when the output of the differential amplifier 72 reaches D.

The other light L2 passes through a reference glass 14 of the same quality as the glass substrate 13, which is placed in a position where evaporated substances do not adhere, and then is guided outside the vacuum evaporation container 11 and passes through a filter 53 that transmits the wavelength λ2. The light is then converted into an electrical signal by the light receiver 631. This signal is amplified by an amplifier 63. The output of this amplifier 63 is adjusted to be the same as the output of the amplifier 62 which amplifies the light transmitted through the glass substrate 13 before the film is attached. During film formation, the outputs of the amplifiers 62 and 63 are divided using a divider 71 to form one signal. This signal is taken into the calculation device 8 to calculate the transmittance, and from this transmittance, the refractive index of the thin film being formed is determined.

Here, in order to eliminate the influence of light emitted from the evaporation source, the chopper 22 chops the light and amplifies only the alternating current component.

The process of independently monitoring the optical thickness and refractive index of a dielectric thin film during deposition using apparatus d in FIG. 1 will be described below.

First, the principle of monitoring optical film thickness will be described below.

In the apparatus shown in FIG. 1, a method is used in which film formation is stopped by detecting a point where the optical film thickness becomes λ/4. Here, λ is the design wavelength. In the case of a thin film whose optical film thickness (film thickness x refractive index) is λ/4, its spectral transmittance takes an extreme value at the design wavelength λ, and the wave number at wavelength λ is 1/λ (hereinafter this will be referred to as k). ) and is symmetrical with respect to him. Figure 2 shows that the refractive index n is 2.4 and the film thickness is 60.80.
Now, let us consider the case where a material with a refractive index of 2.4 is formed to a thickness of 1100 nm, while the wave number at 100 nm shows the characteristic of transmittance T. The optical film thickness is expressed as 1 sample thickness x refractive index, so in this case the desired optical film thickness is 240 nm.
This is λ/4. Therefore, the design wavelength λ=96
0 nm and k-10417crn-1.

Looking at the 100 nrn curve (solid line) in Figure 2, it is symmetrical with the wave number k as the center, and the wave number is ``?1''.
It is recognized that the transmittance T takes an extreme value. Furthermore, it can be seen that for other film thicknesses, the film is not symmetrical about the wave number k. Therefore, the wave number 1 (centered on the wave number 1) and the wave number shifted in the opposite direction is 1, that is, the wave number (k-
Δk) and (k+Δk) (here Δk = 2000
cm'-1), the optical film thickness is 24
Only when the optical film thickness is 0 nm, the transmittance at (k - Δk) and (k + Δk) is equal, and when the optical film thickness is other than 240 nm, the transmittance is equal to (k
-Δk) and (k 0 m k), the expansion rate is L, etc. [7 k]. This can also be seen in Figure 2/)1, that is,
7 skin length λ1 corresponding to these wave numbers: 1/(k− to k
) and λ2=1/(k0ζ・k), if the film formation is stopped at the point when the transmittance becomes equal, the film thickness will be 24 [1 nm].
becomes.

An example of a five-layer film is shown in Figure 3. This is the fourth
1 to less than (t7) assumes the case where the optical film thickness of the fifth layer that has already been formed and is being formed is monitored.Group; ej' from the 1 nos side; 2.4, film thickness 100 m, 2.4] Coma IJ: Jirl refractive index 1,
5 has a film thickness of 160n, and each has an optical film thickness of 2.40n.
m. Then, the fifth layer is q((+y thickness D with refractive index 2.4 == 80 layers m.

It also shows the characteristic of transmittance T at the wave number when the wavelength is 100 nm. Figure 2: Same as the single layer case, the film thickness is 8
When it is 0 nm, that is, when the optical film thickness is not λ/4, the desired film thickness is 1100 nm, which has a transmittance of wave number (k + Δk) and (k - Δk).

That is, when the optical film thickness becomes λ/4, the transmittance at these two points becomes equal. That is, even in the case of multi-r1★, the optical film thickness can be monitored by monitoring the difference in transmittance of two wavelengths.

The spectral transmittance obtained by converting the horizontal axis wave number in FIG. 2 to the wavelength λ is shown in FIG. λ1 is 1/(k-Δk),
In other words, 1188.1 nm) λ2 is 1/(
k+Δk), which is 805.4 layers m here. As shown in Figure 4, refractive index 2.4, film thickness D = 100
nm, that is, when the optical film thickness is λ/4, it is confirmed that the transmittance at both wavelengths is equal.

Although the optical film thickness can be monitored by the above method, as described above, this is the product of the refractive index and the film thickness, and the values of each are unknown. However, when using a thin film optically, its refractive index is a very important value, and it is necessary to know this value in order to estimate its optical properties.

In the apparatus shown in FIG. 1, it is possible to monitor the optical film thickness using the method described above, and also measure the h-Y'fi refractive index using the method shown below. That is, the minimum value of the transmittance at the short wavelength side filter 520 wavelength (λ2) is measured, and the refractive index is determined independently from that value. This method will be explained below.

The relationship between refractive index "+I thickness" and 7j transmissivity T is theoretically given by the following equation.

Here, T: transmittance R(n): energy reflectance of the n-th layer n (n): refractive index of the n-th layer Dll: film thickness of the n-th layer λ: wavelength of light θ (b): n-th layer Output angle of layer r(n): Amplitude reflectance of the upper surface of the n-th layer r(n-+): Amplitude reflectance of the lower surface of the n-th layer. This is expressed as λ=λ1 −805. 4 nff1 , that is, the transmission wavelength of the short wavelength side filter 52 is calculated for the case of a layered film as shown in FIG.

That is, it can be seen that the extreme value of the transmittance changes depending on the value of the refractive index (minimum value when the refractive index of the single 7-layer film is larger than that of the glass substrate, and maximum value when it is small). Therefore,
If we know the extreme value of the transmittance, we can calculate the refractive index by back calculation.

In order to calculate the transmittance from the measured value, it is necessary to measure the amount of transmitted light through glass of the same quality as the substrate (reference glass) in order to cancel the absorption and reflection of the glass substrate.

Here, if the amount of light transmitted through the sample is I(S), the amount of light transmitted through the reference glass is 1(S), and the reflectance on the substrate surface is r, the transmittance T is expressed by the following equation.

Actually, the output of the divider 71 is one direction/I(F).

If this is 5(71), then equation (3) becomes 1 r(1
-11) (/IJ J.

The transmittance at the shorter wavelength (here, 805.4 nm) used for optical film thickness control is calculated one by one using equation (3), and the calculation device calculates its extreme value T (M
1) Determine (minimum value when the refractive index of the single layer film is higher than that of the glass substrate). From the moment the extreme value T (M) is known, the refractive index is immediately calculated by the calculation device. This calculation is performed by changing n (n) in 2(1) and (2), and calculating the extreme value T(M2) of the 7L pass rate in each case.
), select the extreme value T (M2) of transmittance that is closest to the extreme value T (Ml) of transmittance found by actual measurement, and use n (n) at this time as the refractive index of that layer. . The calculation procedure of the calculation device at this time is shown in steps 81 to S9 in the flowchart of FIG. In Figure 5, Id
Although the example of a single layer is shown, the refractive index can be measured in exactly the same way even in the case of a multilayer, as long as the refractive index and film thickness of the lower layer are known.

The device shown in Figure 1 measures the transmittance for the shorter wavelength of the two wavelengths used for optical film thickness control, so it always passes through one extreme value before reaching the desired optical film thickness. do. Therefore, the refractive index can be determined in any case, and if necessary, it is possible to know the physical film thickness from the set optical film thickness and the refractive index.

In addition, in the above, the desired optical film thickness is 24011 n
Although the thickness is not limited to 1, it is possible to control any optical film thickness by changing the design wavelength λ. Further, in the above description, t\=2000 go 1, but the value is not limited to this, and can be appropriately selected depending on the film thickness, the number of refractive index layers, etc.

The method of monitoring dielectric thin film characteristics using the apparatus shown in FIG. 1 has the following advantages. That is, since the optical film thickness is always maintained at λ/4 only by conventional monitoring of the optical film thickness, the λ/4 multilayer film can also be used as a multilayer film.

However, for some reason, for example, temperature, pressure.

Even if the refractive index of the formed film differs from the initially expected refractive index due to changes in the film formation rate, etc., it is impossible to know this fact. Therefore, it is necessary to fabricate the subsequent layers as designed, and the design ff1-Q'i property is 1.
The only thing you can get is a lot of savings. An example of this is shown in FIG. Figure 7 shows an example of a three-layer heat ray reflective film.

a is the design characteristic and the first. Fold A'S 2 on the 6th layer.
．． 4 films with a thickness of 100 nm and a refractive index of 1 in the second M.
．． These are the characteristics when the film No. 5 was formed to a thickness of 160 nm. If the first layer /iT! For some reason, the refractive index is 2.2.
Suppose that I didn't know that, and I didn't know that.
2. When the fifth layer is completely formed, the characteristics are as shown in b,
The maximum transmittance of the thermal spinning zone increases by about 5010 culms compared to a. In other words, the characteristics deteriorate.

Here, if the refractive index is monitored by the method using the device shown in Figure 1, even if the refractive index of the formed film changes, the refractive index of the subsequent layer will change to an appropriate value. By doing so, desired characteristics can be obtained.

The refractive index of the first layer is 2.2.
2 is replaced with a substance having a total refractive index of 1.38 in the 2nd month, and almost the same characteristics as characteristic a are obtained.

As described above, by monitoring the refractive index of the film formed using the apparatus shown in FIG. 1, the film configuration can be controlled so that desired characteristics are finally obtained.

In carrying out the present invention, 1-L, it is possible to take various modifications of the above-mentioned embodiments, and perform an audio-visual method of dielectric thin film characteristics as an example of the modification. The apparatus is shown in FIG. At the 11th flash station, the optical film thickness and refractive index were monitored by measuring the transmitted light.
The optical film thickness and refractive index are monitored by measuring the reflected light using the device shown in FIG.

In the device shown in FIG.
5. It uses a mirror 15 that has a metal mirror with a reflectance of 100% on the lower surface of high-quality glass.

This determines the reflectance γL11] and the mirror 15
The energy reflectance is determined by the following equation, where J(M) is the amount of reflected light from the sample 13, J(S) is the amount of reflected light from the sample 13, and r is the amplitude reflectance on the substrate surface.

(i-2r)J(M)+reJ(S) Further, the theoretical reflectance is expressed by the following formula.

Equation (1) '+ (2), f3 in the device shown in Figure 1
) by replacing equations (5), (61, and (7)), it becomes possible to monitor the optical film thickness and refractive index in the same manner as in the first illustration fi.

Note that 16 in FIG. 8 is a screen for preventing evaporated substances from adhering to the mirror.

In addition, in each of the above-mentioned practical examples, the formation of the dielectric thin film was described as being by vacuum evaporation, but it is not limited to this.
Monitoring can be performed in the same manner even in the case of film formation by sputtering V.

According to the present invention, the flexibility of the dielectric material during the formation process of the dielectric thin film is monitored.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an apparatus for monitoring the characteristics of a dielectric thin body as an embodiment of the present invention; , Figure 4 is a diagram showing the characteristics of wavelength vs. transmittance, Figure 5 is a diagram showing the characteristics of film thickness vs. transmittance, and Figure 6 is a flowchart of the calculation of the calculation device in the device shown in Figure 1. Fig. 7 is a diagram showing the inertia of wavelength versus transmittance, and Fig. 8 is a diagram explaining another embodiment of the present invention. (Explanation of symbols) 1... True nitrogen evaporation device, 11...・A vapor deposition passenger equipment,
12... Evaporation source, 13... Crow substrate, 14.
...Reference glass, 2...Light source section, 21...Light source, 22...Chopper, 31, 32...Beam splitter, 41.42, 46.44...Mirror,
51.52.53... Filter, /+1.62.63... Masu Ii Shoki, 611.621
, 631... Light receiver, 71... Divider, 72.
...Differential amplifier, 8...Calculating device, 9...Voltmeter. Patent Applicant Nippon Mekoku Parts Research Institute Patent Application Representative Patent Attorney Akira Aoki Patent Attorney Kazuyuki Nishidate Patent Attorney Matsushita Akira Akira Yamaguchi Figure 1-21 Figure 2-11 Fig. 3-〉k Fig. 4+o7. +l -shi ^ Figure 5 0 100 200 300 400 5
00 (nml--1-) [) Fig. 6 Fig. 7 1111 =>). Figure 8-

Claims (1)

[Claims] Light is projected onto the dielectric thin film being formed, the transmitted light or reflected light is separated into two determined wavelengths, and thin film formation is stopped when the amount of transmitted light or reflected light at these two wavelengths becomes equal. In addition to controlling the optical film thickness, the transmittance or reflectance at the shorter wavelength of the two wavelengths is measured, and the extreme value of the transmittance or reflectance is used to determine the dielectric thin film being formed. A method for monitoring dielectric thin film properties characterized by determining the refractive index.