JPS5995406A - Method for measuring thickness of thin film - Google Patents

Abstract

PURPOSE:To enable measurement of a film thickness with good accuracy without damaging a sample surface by irradiating diagonally the light of which the wavelength changes continuously onto the surface of a film to be measured, and knowing the wavelengths of the two adjacent bright peaks produced by the interference of the light reflected from the surface of the film and the light reflected from the base thereof. CONSTITUTION:Light is irradiated from a spectroscope 1 at the wavelength changed continuously to 450-1,100nm onto the surface of a sample 2 inclined at 45 deg.. The light reflected from said surface is received in a luminous intensity detector 3, and the relation between each wavelength and the intensity of the reflected light is plotted. If the sample is assumed to be, for example, a selenium layer 5 deposited by evaporation on a conductive substrate 4, the interference condition of the light 11 reflected on the surface of the layer 5 and the light 12 reflected on the boundary between the layer 5 and the substrate 4 and transmitted through the layer 5 is given by the following equation [II]. In the equation II, d is the film thickness of the layer 5, thetai is an angle of refraction, n(lambdai) is the refractive index of the film dependent on the wavelength lambdai of the incident light, and m is 0, 1, 2, 3- integer. Therefore the film thickness (d) is determined by the equation [ I ] if the wavelengths of the adjacent two bright peaks interfering with each other are designated as lambdai, lambdai+1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the thickness of a thin film deposited on a substrate.

The thickness of a thin film is an indispensable parameter for determining the physical properties of a thin film. For example, in an electrophotographic photoreceptor formed by coating a single layer or multilayer thin film of a photoconductive material on a conductive substrate, the thickness of the thin film controls the characteristics of the photoreceptor;
Alternatively, it is an important item for considering the layer structure, and it is desired that it be measured accurately.

Well-known methods for keeping the 1MJFi of a thin film constant include multiple reflection interferometry and thin current method.

Multiple reflection interferometry, also called repeated reflection interferometry, is a method in which a flat plate with high reflectance is tilted at a small angle on a high reflectance surface with a step between the deposited and non-deposited parts of the thin film, and is placed on the sample surface. On the other hand, when monochromatic light is applied directly to the top, the film thickness is determined by observing interference fringes on the normal θ with steps created by the reflected light. However, there are difficulties in preparing a +pH1 constant sample, and the sample must be flat, making it impossible to measure using the cylindrical photoreceptor itself. In the eddy current method, the film thickness is measured from the deep penetration point of a thin current generated in the sample by a current from a high-frequency oscillator, but the eddy current method is limited to 100% Fi films on non-ferrous metal substrates. It must be a welding type, and in the case of multilayer j′ & gold film)! This method has drawbacks such as measuring J- and not being able to measure arbitrary layers.

The present invention eliminates the above-mentioned drawbacks, provides a method that allows sample preparation to be made easily and reliably, allows for accurate film thickness measurement without damaging the sample surface, and allows for measurement of the film thickness of each layer in a multilayer film. The purpose is to

The purpose of this is to diagonally irradiate the surface of the film to be measured with light whose wavelength changes continuously, and to detect the wavelength λ of two adjacent bright peaks caused by the interference between the reflected light on the surface of the film and the reflected light on the bottom surface. , λ as I 1 + 1 , and λ1 of the membrane. The refractive index for λ1+1 is n(λ1)
.

n(λi++), the refraction angle of light is 01. When θi++ is closed, this can be achieved by finding the film thickness d.

Embodiments of the present invention will be described below with reference to the drawings. In Figure 1, the wavelength of spectrometer 1 is 450 to 1l100.
The light is received by the tilter 3 at a total of 45 degrees while changing continuously to n, and the relationship between each wavelength and the intensity of the reflected light is plotted. For example, if the sample is heated with a selenium layer 5 deposited on a conductive substrate 4 as shown in FIG. The interference condition with the reflected light 12 that has passed through the selenium layer 5 is given by the following equation.

Bright condition 2n(λ7) acosθ+-(m + 2
)λi ・= −(1) Dark condition 2n(λ−)dco
sθ=mλ1 1 1 where d is the thickness of the selenium layer 5, θ is the refraction angle, and n(λ1
) is the refractive index of the film depending on the incident light wavelength λ1, m is 0,
It is an integer of 1, 2, 3... Therefore, assuming interference, the film thickness d can be determined from the following equation.

Including angle of incidence θ. is 45°.

FIG. 3 shows a case in which a pure selenium layer 6 is deposited on a conductive substrate 1, a selenium layer 7 doped with impurities is deposited thereon, and a pure selenium layer 8 is further formed thereon. An oxide film of added impurities is formed on the surface of the noso 7 to have a different refractive index from that of the pure selenium layer 8. Therefore, the light that has passed through layer 8 is reflected on the surface of layer 7 and interferes with the light reflected on the surface of layer 8, and by satisfying the interference condition of equation (1), equation (
214- can be used to measure the thickness of layer 8. An example of measuring the film thickness of the tellurium vapor deposited film 8 shown in FIG. 3 is shown in FIG. 4, where the reflectance on the vertical axis is the ratio of the amount of reflected light to the amount of incident light. In this measurement example, a measurement result was obtained in which the thickness d of the surface layer 8 was 1.17 μm.

As described above, the present invention determines the film thickness based on the interference conditions between the reflected light on the film surface and the reflected light on the bottom surface of the film of light whose wavelength changes continuously, which is incident on the film surface. Not only in a single layer film but also in a multilayer film, by creating a difference in refractive index between the layers, the film thickness of the top layer can be sequentially measured. Further, according to the present invention, even if the sample shape has a curvature, +jf can be suppressed to a high degree by making it sufficiently small compared to the curvature of the light spora 14, and even cylindrical samples can be measured. In addition, since it is non-contact and non-destructive and does not damage the film surface, it can be particularly effectively applied to the photosensitive Jvj thickness measurement of electrophotographic photoreceptors having a multilayer structure.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of an L1111 constant device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of the principle of measuring the film thickness of a single layer film according to the present invention, and Fig. 3 is a diagram illustrating the principle of measuring the film thickness of a multilayer film according to the present invention. FIG. 4, which is an explanatory diagram of the measurement principle, is a relationship diagram between reflectance and irradiation light wavelength in one embodiment of the present invention. 1... Spectrometer, 2... Sample, 3... Light intensity detector.

Claims (1)

[Claims] 1) The surface of the film to be measured is irradiated with light whose wavelength changes continuously obliquely, and two adjacent bright peaks are generated by the reflected light on the surface of the film and the interference on the bottom surface. wavelength λ・
λ・ is known, and the refractive index of the film for λ λ・1+Otori+1llll+1 is 'n(λ, ), n(λ+++L, assuming that the refraction angle of light is θ1.θ1+1.The film thickness d is then determined. Method for measuring thin film thickness.