TW201602514A - Optical measurement method of film thickness - Google Patents

Abstract

An optical measurement method of film thickness is disclosed, which includes the following steps: (a) providing a sample under thickness measurement, which includes a film body and a rough surface structure; (b) using a reflectometer to obtain an optical wavelength-related reflectance curve of the sample under thickness measurement, in which the optical wavelength-related reflectance curve has a plurality of peak values and each peak value corresponds to a different optical wavelength; (c) calculating the optical thickness of the sample under thickness measurement based on the corresponding wavelengths of the at least two peak values; (d) using effective medium approximation method to calculate the effective reflective index of the film body and the rough surface structure; and (e) dividing the optical thickness by the effective reflective index to obtain the film thickness of the sample under thickness measurement.

Description

Optical film thickness measurement method

The present invention relates to a film thickness measuring method, and more particularly to an optical film thickness measuring method.

The Reflectometer is mainly used for film thickness measurement in the fields of flat panel displays, thin film solar cells, etc., and the measured film thickness data is used as a parameter for coating process parameters. In the calculation of film thickness, the traditional reflective spectrometer uses the fixed optical refractive index with the least squares method for regression analysis, and assumes that each film layer is an ideal optical film layer, that is, the surface of each film layer is optically smooth, parallel and Isotropic, while under ideal film conditions, only the film thickness and optical refractive index affect the intensity of the reflected light.

However, since most of the film layers are not ideal optical film layers, the surface of the film layer usually has a roughness (or surface roughness). However, the above fixed optical refractive index calculation method cannot obtain a refractive index including a change in roughness, so that the film thickness of the film layer cannot be accurately calculated.

Therefore, it is necessary to provide an innovative and progressive optical film thickness measurement method to solve the above problems.

The invention provides an optical film thickness measuring method, comprising the following steps: (a) providing a film thickness sample to be tested, the film thickness sample to be tested comprises a film body and a surface roughness structure; (b) utilizing a reflection type Measuring, by a spectrometer, a light wavelength-dependent reflectance curve of the film thickness sample to be measured, the light wavelength-dependent reflectance curve having a plurality of peaks, each of the peaks corresponding to each (c) calculating the optical thickness of the film thickness sample to be measured by the wavelength of light corresponding to at least two peaks; (d) calculating the equivalent refraction of the film body and the surface roughness by an equivalent medium approximation method; And (e) dividing the optical thickness by the equivalent refractive index to obtain a film thickness of the film thickness sample to be tested.

According to the present invention, an equivalent refractive index including a change in the roughness of the surface can be obtained, and the film thickness of the film thickness sample to be tested can be accurately calculated by using the equivalent refractive index.

The embodiments of the present invention can be more clearly understood, and the objects, features, and advantages of the present invention will become more apparent. The details are as follows.

10‧‧‧ film thickness samples to be tested

11‧‧‧ membrane body

12‧‧‧ Surface roughness

Volume of fsi‧‧‧矽

P‧‧‧ peak

S‧‧‧Light wavelength dependent reflectance curve

1 is a flow chart showing a method for measuring an optical film thickness of the present invention; FIG. 2 is a view showing a film thickness sample to be tested in the method of the present invention; and FIG. 3 is a view showing a light wavelength dependent reflectance curve in the method of the present invention. Figure 4 shows a schematic diagram of the rough microstructure of the ruthenium substrate after etching; Figure 5 shows the equivalent refractive index profile of air and bismuth at different mixing ratios; Figure 6 shows the comparative example of aluminum-doped zinc oxide transparent conductive film (AZO) The wavelength-dependent reflectance curve of the light; and FIG. 7 shows the wavelength-dependent reflectance curve of the aluminum-doped zinc oxide transparent conductive film (AZO) of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart showing the optical film thickness measurement method of the present invention. Figure 2 shows a schematic representation of one of the film thickness samples to be tested in the method of the present invention. Referring to step S11 and FIG. 2 of FIG. 1 , a film thickness sample 10 to be tested is provided. The film thickness sample 10 to be tested includes a film body 11 and a surface roughness structure 12 .

Figure 3 shows a graph of light wavelength dependent reflectance in the method of the present invention. Matching Referring to step S12, FIG. 2 and FIG. 3 of FIG. 1, a light wavelength-dependent reflectance curve S of the film thickness sample 10 to be measured is measured by a reflection spectrometer (not shown), and the wavelength-dependent reflectance curve of the light is measured. S has a plurality of peaks P, each of which corresponds to a different wavelength of light.

Referring to step S13, FIG. 2 and FIG. 3 of FIG. 1, the optical thickness of the film thickness sample 10 to be tested is calculated by the wavelength of light corresponding to at least two peaks P respectively. In this embodiment, the optical thickness calculation formula of the film thickness sample 10 to be tested is:

Where nd is the optical thickness, and λ _i and λ _{i +1} are the wavelengths of light respectively corresponding to the two peaks P. Known by Maxwell's equation:

The solution to the above wave equation is as follows:

c represents the speed of light, and λ represents the wavelength of light.

The solution of the wave equation back to the original equation can be obtained as follows:

Where ε ₀ is the vacuum dielectric coefficient, and the propagation rate C _{m of the} light in the medium can be obtained by solving the equation as follows: C _m =( με ) ^-1⁄2

Where ε is the dielectric coefficient of the substance and μ is the magnetic permeability coefficient of the substance. The physical definition of the refractive index is the speed of light in vacuum divided by the speed of travel in the medium. If the material is not a magnetic substance, the magnetic permeability of the following can be canceled up and down.

The physical parameters of the shielding parameters in the substance are as follows:

Therefore, it can be known that the relationship between the refractive index n of the substance and the shielding parameter κ is as follows: κ = n ²

Referring to step S14 of FIG. 1 and FIG. 2, the equivalent refractive index of the film body 11 and the surface roughness 12 is calculated by an equivalent medium approximation. When the upper and lower undulations of the surface roughness 12 are smaller than the wavelength of light, the surface roughness 12 can be equivalent to a film layer having a clear refractive index medium, and the light reflection behavior of the film layer and the air interface is similar to the surface roughness 12 Light reflection behavior. In other words, the equivalent medium approximation method mainly considers the film body 11 and the surface roughness structure 12 as a two-layer optical film layer, and further calculates an equivalent refractive index of the two-layer optical film layer. In this embodiment, the equivalent dielectric coefficient calculation formula is

Where ε _h is the dielectric constant of the equivalent dielectric of the film, χ is the shielding parameter, ε _i is the dielectric constant of the ith material, and v _i is the ratio of the doping volume of the equivalent dielectric in the ith material.

Referring to Figure 4, it is a schematic view showing the rough microstructure of the surface of the tantalum substrate after etching. Taking bismuth (Si) as an example, the surface of the ruthenium substrate is etched to form a rough microstructure, and the dotted line in Fig. 4 The outer material has a clear refractive index, but the refractive index of the region can be described by the surface microstructure without a clear definition of the optical refractive index. Therefore, if the dotted line area is less than one tenth of the wavelength of the light, the dotted line area can be equivalent to an equivalent dielectric film with a clear refractive index, so that the light reflection behavior of the equivalent dielectric film and the air interface and the light reflection behavior of the rough surface Equivalent approximation.

Referring to Figure 5, there is shown an equivalent refractive index profile for different mixing ratios of air and helium. In Fig. 5, the equivalent refractive index calculated from the range of 0.1 to 0.9 of the volume fsi of the crucible is sequentially shown from bottom to top. It can be seen that the refractive index will change as the microstructure is mixed.

Referring to step S15 of FIG. 1 and FIG. 2, the film thickness of the film thickness sample 10 to be tested can be obtained by dividing the optical thickness nd by the equivalent refractive index.

According to the present invention, an equivalent refractive index including the variation of the surface roughness 12 can be obtained, and the film thickness of the film thickness sample 10 to be tested can be accurately calculated by using the equivalent refractive index.

The invention is illustrated by the following examples, which are not intended to be limited to the scope of the invention.

[Comparative example]

The film thickness sample to be tested in the comparative example is an aluminum-doped zinc oxide transparent conductive film (AZO). Referring to Fig. 6, there is shown a light wavelength-dependent reflectance curve of a comparative aluminum-doped zinc oxide transparent conductive film (AZO). Under the condition that the surface roughness is not considered, the refractive index of the material of AZO is 1.8, and the film thickness is calculated by taking the wavelength of light corresponding to the peak of 5 points in FIG. The calculation results are shown in Table 1. The film thickness was 823 nm, and the calculated film thickness was 153 nm from the 670 nm measured by the α-step contact film thickness measuring instrument.

[Example of the invention]

The film thickness sample to be tested in the invention is an aluminum-doped zinc oxide transparent conductive film (AZO). Referring to Fig. 7, there is shown a light wavelength dependent reflectance curve of an inventive aluminum-doped zinc oxide transparent conductive film (AZO). Under the condition of considering the surface roughness, the equivalent refractive index of AZO is 1.9, and the film thickness is calculated by taking the wavelength of light corresponding to the peak of 5 points in Fig. 7 . The calculation results are shown in Table 1. The film thickness was 783 nm, and the calculated film thickness was 113 nm from the 670 nm measured by the α-step contact film thickness measuring instrument. The film thickness calculation result of the invention example is more accurate than the comparative example.

The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the scope of the present invention. The scope of the invention should be as set forth in the appended claims.

Claims (3)

An optical film thickness measuring method comprises the following steps: (a) providing a film thickness sample to be tested, the film thickness sample to be tested comprises a film body and a surface roughness structure; (b) measuring by a reflection spectrometer An optical wavelength-dependent reflectance curve of the film thickness sample to be measured, the light wavelength-dependent reflectance curve having a plurality of peaks, each of which corresponds to a different wavelength of light; (c) calculating the wavelength of light corresponding to at least two peaks respectively The optical thickness of the film thickness sample to be tested; (d) calculating the equivalent refractive index of the film body and the surface roughness structure by an equivalent medium approximation method; and (e) dividing the optical thickness by the equivalent refractive index, The film thickness of the film thickness sample to be tested can be obtained. The optical film thickness measurement method of claim 1, wherein the optical thickness calculation formula of the step (c) is Where nd is the optical thickness, and λ _i and λ _{i +1} are the wavelengths of light respectively corresponding to the two peaks. The optical film thickness measurement method of claim 1, wherein the equivalent refractive index calculation formula of the step (d) is Where ε _h is the dielectric constant of the equivalent dielectric of the film, κ is the shielding parameter, ε _i is the dielectric constant of the ith material, and v _i is the ratio of the doping volume of the equivalent dielectric in the ith material.