JPH06235615A - Measuring apparatus for thickness of film - Google Patents

Abstract

PURPOSE:To provide a film thickness measuring apparatus using a spectropho tometer which can accurately measure even a sample changing the index of refraction depending on wavelengths. CONSTITUTION:An interference spectrum of a to-be-measured film is measured by a spectrophotometer (ST1). A calculating range is designated (ST2). The calculating range is divided to some sections (ST3). The average index of refraction for each section is input (ST4), and the film thickness for every section is calculated with the use of the average index of refraction (ST5). The total sum of the obtained film thicknesses of the sections is divided by the dividing number of sections, thereby to obtain the average value which is the thickness of the to-be-measured film (ST6).

Description

Detailed Description of the Invention

[0001]

This invention uses a spectrophotometer,
The present invention relates to a film thickness measuring device for a film having a thickness of about 0.2 μm to 100 μm.

[0002]

2. Description of the Related Art Generally, a nitride film,
Semiconductor manufacturing field where films such as photoresist films are formed,
In the field of membranes such as LD and CD, other 0.2 μm-100
One method for measuring a film thickness of about μm is to use a spectrophotometer. In the film thickness measurement using this spectrophotometer, as shown in FIG. 6, the film to be measured 1 having a refractive index n is irradiated with light whose wavelength continuously changes at an angle θ from the spectrophotometer to measure the film thickness. The interference spectrum generated by the interference wave reflected on the upper surface and the lower surface of the measurement film 1 is measured, and the following formula is applied to the interference spectrum to obtain the film thickness d of the film to be measured 1.

[0003]

[Equation 1]

However, as described above, n is the refractive index, θ is the angle of incidence on the film to be measured, and Δm is the number of peaks in the calculation range (between λ ′ _S and λ ′ _E ) of the interference spectrum illustrated in FIG. , Λ ₁ is the wavelength corresponding to, and λ ₂ is the wavelength corresponding to (3).

[0005]

In calculating the wavelength range of 'from _E lambda' THE INVENTION It is an object to provide a process in the film thickness measurement using a conventional spectrophotometer the lambda to _S is the refractive index n of the measured film is a constant value The film thickness is calculated as However, in practice,
Many films do not have a constant refractive index within the calculated wavelength. In the case of a film whose refractive index is not constant, there is a problem that the conventional calculation method cannot measure a precise film thickness.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a film thickness measuring apparatus capable of measuring a sample with a higher refractive index than a conventional one even if the refractive index changes depending on the wavelength. I am trying.

[0007]

The film thickness measuring apparatus of the present invention irradiates a film to be measured with light whose wavelength continuously changes at a predetermined angle, and from the reflected wave obtained, interference of the film to be measured is obtained. A spectrophotometer for measuring a spectrum, the interference spectrum, a wavelength range designating means for designating a wavelength range for calculation, a section designating means for designating a division of the designated wavelength range into a desired number of sections, and The refractive index input means for inputting the average refractive index of each film to be measured in each section, and the average refractive index for each section is applied to a predetermined expression including the refractive index to calculate the film thickness for each section. And a means for calculating an average value of the calculated section thicknesses to calculate a measured film thickness.

In this film thickness measuring device, an interference spectrum of the film to be measured is measured by a spectrophotometer, and a calculation range and a desired section are set for the interference spectrum, and an average value of the refractive index is set for each section. Is input, and each average value is applied to the film thickness calculation output, and the average value of the film thickness of each obtained section is used as the film thickness to be measured, so that the refractive index is calculated over the entire calculation range. The thickness is not fixed, but the refractive index is taken into consideration for each section, so that the film thickness can be measured more accurately than before.

[0009]

The present invention will be described in more detail with reference to the following examples. FIG. 1 is a block diagram showing a hardware configuration of a film thickness measuring apparatus according to the present invention. The apparatus of this embodiment includes a spectrophotometer 11 for measuring an interference spectrum of a film to be measured, a RAM 12 for storing the measured interference spectrum and a calculation value for film thickness measurement, and various kinds of film thickness measurement. The CPU 13 includes at least a CPU 13 that performs control and calculation, a ROM 14 that stores a program of the CPU 13, arithmetic expressions, constants, and the like, a display 15 that two-dimensionally displays an interference spectrum, and an operation input unit 16. Operation input unit 16
Has a function 16a for designating a calculation range, a function 16b for designating a section for dividing the calculation range, and a function 16c for inputting an average refractive index for each section. These functions will be described later. Well-known keys, cursors, icons, and the like are used as specific input means of the operation input unit 16.

Next, the operation of measuring the film thickness of the film to be measured by the apparatus of the above embodiment will be described with reference to the flow chart shown in FIG. First, the spectrophotometer 11 measures the interference spectrum of the film to be measured by a method well known in the related art (step ST1). For example, this interference spectrum is represented by taking the wavelength on the horizontal axis and the reflectance on the vertical axis as shown in FIG. Because of the interference wave, the waveform is usually amplitude-like, but the smaller the film thickness, the smaller the number of peaks, and the lower limit of the measurable film thickness is about 0.2 μm. The measured interference spectrum is stored in the RAM 12 and displayed on the display 15.

Next, the wavelength range W for calculating the film thickness from the interference spectrum is designated. This designation is made by the operation input unit 16 by, for example, the wavelength λ _S shown in (b) of FIG.
λ _E is input (step ST2). Then, the operation input unit 16 is used to specify how many sections (N) to divide the calculation range W into (step ST3). 3C shows the calculation range W of FIG. 3B as W ₁ , W ₂ ,
This is an example of division into three W ₃ sections (N = 3).

The reason why the calculation range is divided into several sections is that the refractive index, which is a parameter for calculating the film thickness, differs depending on the wavelength. For example, if a sample has a change in the refractive index shown in FIG. 4 with respect to the wavelength, the calculation range W is, for example, W ₁ , W ₂ ,
Divided into three sections of W _3, each section W _1, W _2, the average refractive index n ₁ of the _{W 3, n 2, n 3} , using the film thickness calculated in each section. The number of sections to be divided may be appropriately selected by the operator depending on the change state of the refractive index.

When the divided section is designated, the refractive index for each section is then input from the operation input unit 16 (step ST4). The refractive index of the sample is shown in FIG. 5A, and the calculation range 300 nm to 1300 nm is 600.
If it is divided into three sections of nm and 800 nm, the refractive indices n ₁ , n ₂ and n _{3 of} each section are input. And
Based on these input refractive indices ni (i = 1, 2, 3), the film thickness di for each section is calculated by the following equation (step ST5).

[0014]

[Equation 2]

In addition, the film thicknesses d ₁ and d calculated for each section
₂ and d ₃ are obtained. Finally, the film thickness d ₁ , d for each section
₂ and d ₃ are added, and the added value is divided into 3
Then, the average value of the film thickness of each section is calculated by the calculation of the following formula, and the film thickness d of the film to be measured is calculated (step S
T6). d = (d ₁ + d ₂ + d ₃ ) / 3 (3)

[0016]

According to the present invention, the calculation range of the interference spectrum measured by the spectrophotometer is divided into several sections, the average refractive index is used for each section, and the film thickness is calculated for each section. Since the average value of the film thickness in each of these sections is taken as the film thickness of the film to be measured, in the case of a sample whose refractive index differs depending on the wavelength, it is assumed that the refractive index is always constant as in the conventional case. Compared with the case of calculation, the change in refractive index can be reflected in the measurement, and more accurate measurement can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a hardware configuration of a film thickness measuring apparatus in which the present invention is implemented.

FIG. 2 is a flow chart for explaining a measuring operation in the film thickness measuring apparatus of the embodiment.

FIG. 3 is a waveform diagram for explaining division of a calculation range into sections in the film thickness measuring apparatus according to the embodiment.

FIG. 4 is a diagram exemplifying a change in refractive index with respect to a wavelength of a sample whose film thickness is measured.

FIG. 5 is a diagram for explaining a relationship between designation of a section and calculation of an average refractive index of each section and a film thickness of each section.

FIG. 6 is a diagram illustrating interference spectrum measurement by a spectrophotometer.

FIG. 7 is a diagram for explaining a principle formula for measuring a film thickness using the same interference spectrum.

[Explanation of symbols]

 1 film to be measured 11 spectrophotometer 12 RAM 13 CPU 16 operation input section

Claims (1)

[Claims] 1. A spectrophotometer for irradiating a film to be measured with light whose wavelength continuously changes at a predetermined angle, and measuring an interference spectrum of the film to be measured from a reflected wave obtained, a calculation for the interference spectrum. A wavelength range designating means for designating a wavelength range for specifying, a section designating means for designating a division of the designated wavelength range into a desired number of sections, and an average refractive index of each film to be measured in each section are input. Refractive index input means, section thickness calculation means for calculating the film thickness for each section by applying the average refractive index for each section to a predetermined expression including the refractive index, and A film thickness measuring device comprising: a means for calculating an average value to calculate a film thickness to be measured.