JPS58704A - Film thickness measuring device - Google Patents

Abstract

PURPOSE:To exactly measure thickness of a thin film, by constituting so that a light reflected by the surface of a substrate which has formed the thin film on both its surfaces is made to pass through from a transmission part, and intercepting a light refleted by the opposite surface of the substrate, by a light shielding plate. CONSTITUTION:A white light emitted from a white light source 8 is reflected by a reflector 10 through a spectroscope 9, passes through a slit 5a of a light shielding plate 5, and is made incident at a 15 degree incident angle to a substrate 2 which has formed a thin film on both its surfaces. A light reflected by the lower surface of the substrate 2 passes through the slit 5a, and a light reflected by the upper surface is intercepted by the light shielding plate 5. The light which has passed through the slip 5a is made incident to a detector 12 through a reflector 11 and intensity of its light is recorded in a recording meter 13 as a function of spectral wavelength of the spectroscope 9. Since thickness of a film is measured by detecting only an interference light from a film to be measured, thickness of a thin film is measured exactly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a film thickness measuring device for measuring the thickness of a thin film formed on both sides of a transparent substrate.

Thickness measurements of magnetic garnet films epitaxially grown on thin films with low light absorption, such as Gd5Gα5012 single crystal substrates (hereinafter referred to as GGG substrates) used as crystals for magnetic bubble memories, are usually performed using magnetic garnet films.・This is done by utilizing the original reflection characteristics of the film. An example will be explained based on FIG. 1(a). Since the light 3 incident on the magnetic garnet film is reflected on the surface of the magnetic garnet film 1 and also on the interface between the magnetic garnet film 1 and the GGG substrate 2, interference occurs due to the optical path difference between these reflected lights 4. . Therefore, by recording the reflection intensity at each wavelength, five interference waveforms as shown in Figure 1 (kl) can be obtained. Assuming that the wavelength of the Nth peak is λ2, the thickness of the magnetic Garient film is calculated from the following formula based on the light interference condition, where θ is the incident angle shown in Figure 1 ta>, n, , n
2 and 2 each have a wavelength λ1. It is the refractive index of magnetic garnet at λ2. Therefore, in principle, the film thickness can be measured accurately with an error of less than 1% by accurately reading the weight of the interference waveform or the wavelength at the trough position.

However, if the substrate 2 is transparent and the thin film 1 is
When trying to measure the thickness of a thin film formed on both sides of the surface, as shown in Figure 2(a), the reflected light includes the reflected light 4 from the surface to be measured and the reflected light 4 from the opposite side. Light 4' is included. FIG. 2(b) shows the front board 20.
This is an example of measurement of interference waveforms in which magnetic garnet films 1 are formed on both sides. Figure 2 (The waveform of tel is the interference waveform of the two magnetic garnet films 1 interfering with each other and deforming the interference waveform of the target magnetic garnet film, so the measurement accuracy is significantly reduced. Therefore, the measurement accuracy is significantly reduced. To accurately measure the thickness of a magnetic garnet film, it is necessary to weaken the reflected light from the opposite surface.To weaken the reflection from the opposite surface, apply a liquid with the same refractive index to the opposite surface. There are ways to prevent reflection, but the refractive index of magnetic garnet is greater than 2 in visible light, and there is no readily available liquid, and if a special liquid gold is applied, it must be completely washed away. When forming a bubble memory element or the like at 5%, contaminating the substrate causes a decrease in yield in the element process, and is an industrially disadvantageous method.

The present invention solves the above-mentioned problems by disposing a light-shielding plate having transmission parts periodically in the optical path of the light incident on the thin film to be measured, so that the light that passes through the transmission parts and is reflected on the surface of the substrate is transmitted. The film thickness was measured by detecting only the interference light from the thin film to be measured by blocking the light that passed through the thin film and reflected on the opposite side of the substrate through the transparent part using a light shielding plate. It is characterized by this.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a diagram showing the principle of the present invention. In the figure, a light shielding plate 5 having a row of slits 5a having a width ω1 and a period 2ω and perpendicular to the incident direction is arranged parallel to the substrate 2 at a distance l from the surface 6 of the transparent substrate 2. Place. When the thickness of the substrate 2 is t, the light incident at an incident angle θ passes through the sleeve 5a and is reflected on the surface 6 of the substrate 2, and the condition that all of the reflected light passes through the sleeve 5a is as follows. .

Nω=ltanθ・・・・・・・・・・・・(2
) However, N is a positive integer including 0, and when N=O, 1'=0
At this time, the S source plate 5 is in close contact with the substrate 2, and the light reflected from the surface 6 passes through the same slit 5a as the incident light. Third
The figure shows an example of N-1, and the reflected light of the light incident from the slit 5a passes through the Nth slit. Next, pickpocket
The following equation is obtained to find the conditions under which all the light that enters from the nozzle 5a and is reflected on the opposite surface 7 of the substrate 2 is blocked by the light shielding plate 5.

. =t tmα・・・・・・・・・・・・(3) However
fθ=nnotα (4) n is the refractive index of the substrate.

Therefore, by providing a light shielding plate having a shape that satisfies equations (2), (3), and (4) at the same time, it is possible to extract only the reflected light from one flush of the substrate. However, strictly speaking, the light reflected from the opposite surface 7 of the substrate 2 returns to the surface 6.
When the light is reflected from surface 7 and goes out from surface 6 (indicated by the broken line in the figure), it passes through Surin) 5ai, but the intensity of the light that is repeatedly reflected in this way is weak, so it is necessary to reduce the measurement accuracy. Not enough.

FIG. 4 is a schematic diagram of a film thickness measuring device to which the present invention is applied. The substrate 2 is placed on the edge of the sample stand 14 with the side with the thin film to be measured facing downward, and the light shielding plate 5 is placed on the edge of the sample stand 14.
The light shielding plate 5 is mounted on the sample stage 14 at the opening 14a at the bottom of the sample table 14, and even if the substrate 2 is attached or detached, the substrate 2 and the light shielding plate 5 are always kept parallel to each other and at a constant distance. Since this device uses a GGG substrate with a thickness of 0.5 sm and a refractive index of n = 1.97, the parameters of equations (2) and (3) are J = 0.5 m and ω = 0.066 m, respectively. It is said that

A light-shielding plate 5Fi was used by partially machining and notching an aluminum plate having a thickness of 10 μm to form a slot 1-5a f, and pasting it on a sample stage 14. FIG. 4(b) is a plan view thereof.

In FIG. 4 (aJ), 8 is a white light source, and this white light passes through a spectroscope 9, is reflected by a reflection @10, passes through a slit 5a of a light shielding plate 5, and enters the substrate 2 at an incident angle of 15°. Here, according to the above-mentioned principle, the light reflected from the lower surface of the substrate 2 shown in the figure passes through the slit 5a, but the light reflected from the upper surface of the substrate 2 hits a portion of the light shielding plate 5 other than the slit 1-5a and is blocked. The light that has passed through the slit 5a is incident on the detector 12 by the reflecting mirror 11, and its intensity is converted into an electrical signal.The intensity of this light and the wavelength of the light separated by the spectroscope 9 are recorded by a recorder. By recording at 15,
Even in a sample where a thin film is formed on both sides of the substrate, Fig. 1 (b)
An interference waveform of only one plane, indicated by J, was obtained. Similar results were also obtained when the light shielding plate 5 was formed by vapor-depositing aluminum on a glass plate, forming lines of width ω at a period of 2ω, and providing slits 5ai. The shape of the slit in the light shielding plate is the most efficient if it is in the form of a straight strip as shown in Figure 4 fbl, and the slit shape of the light shielding plate is the most efficient, as shown in Figure 4 fbl.
However, it does not necessarily have to be in the form of a strip with a width ω and a period of 2ω.For example, even if circular holes with a diameter ω are opened every 2ω, reflection from the opposite surface can be blocked using the same principle. I can do it. Furthermore, in the embodiment, the direction of the slit is arranged perpendicular to the direction of the incident light, but according to the above-mentioned principle, the width in the perpendicular direction only needs to satisfy equations (2), (3), and (4). Therefore, it is also possible to adjust the effectiveness of the slit by making a narrower slit and shifting the direction of the slit from the direction perpendicular to the direction of the incident light.

As described above, according to the present invention, the light reflected from the surface of the substrate with thin films formed on both sides is allowed to pass through the transmitting portion, and the light reflected from the opposite surface of the substrate is blocked by the light shielding plate.
This has the effect of preventing deformation of the interference waveform due to the film to be measured and accurately measuring the thickness of the thin film formed on both sides of the transparent substrate.

[Brief explanation of the drawing]

Figure 1 (a) is a reflection characteristic diagram when a thin film is formed on only one side of the substrate, Figure 1 (bJ is an interference waveform diagram, and Figure 2 (a) is a reflection characteristic diagram when a thin film is formed on both sides of a transparent substrate. FIG. 2 ib) is an interference waveform diagram, FIG. 3 is a principle diagram of the present invention, and FIG. 4 is a configuration diagram showing an embodiment of the present invention. 1... Thin film formed on the substrate, 2... Substrate, °6
...Incoming light. 4...Reflected light, 4'...Reflected light from the opposite surface, 5.
... Light shielding plate. 609. Surface of the board, 7... Opposite side of the board Patent applicant NEC Corporation No. 21!8 To the slope

Claims (1)

[Claims] (1) In a film thickness measuring device that measures the total thickness of a thin film by making light obliquely incident on a thin film formed on both sides of a transparent substrate and utilizing the reflection characteristics of the light reflected by the thin film at each wavelength, A film thickness measuring device characterized in that a light-shielding plate having a plurality of transmission parts periodically provided on the optical path of incident light and reflected light is installed parallel to a thin film to be measured.