JPH0346502A - Film thickness measuring method - Google Patents

Abstract

PURPOSE:To simplify the pre-preparation work by deriving the film thickness, based on a correlation of a relative reflection factor obtained by dividing a reflection factor in known correlation data of a reflection factor and the film thickness by a known reflection factor of an arbitrary sample, and the film thickness. CONSTITUTION:Energy of specific wavelength of a reflected light from a sample P with know absolute reflection factor is measured, and a value Ep of this energy detected by a spectroscope 32 is stored in a film thickness calculating mean 36. Also, a reflection factor Rp of the sample P is stored in the means 36. Moreover, correlation data of an absolute reflection factor Rs of a sample S to be measured and film thick ness dx is checked in advance by various literatures, and correlation data of a relative reflection factor Rs/Rp and the film thickness dx is calculated, and stored in a film thickness data memory 35. Next, energy Es of specific wavelength of a reflected light from the sample S is measured, and with respect to the energy Es detected by the spectroscope 32, the means 36 executes 36 executes a division of Es/Ep, inputs a value of Es/Ep as an address to the memory 35, and the outputted film thickness is outputted to an indicator as film thickness is outputted to an indicator as film thickness of a transparent thin film in the sample S.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for measuring the thickness of a transparent thin film on a sample to be measured in which a transparent thin film is formed on a substrate. Concerning technology for measuring with high precision.

<Conventional technology> Conventionally, in the inspection process of semiconductor manufacturing processes, for example, to optically measure the thickness of a silicon oxide film formed on a silicon substrate, it is necessary to measure changes in the polarization state of reflected light. There are two methods of determining the film thickness: one method is to determine the film thickness by measuring the energy of reflected light (hereinafter referred to as the polarization analysis method), and the other is a method of determining the film thickness by measuring the energy of reflected light (hereinafter referred to as the reflected light energy measurement method). A method of determining the film thickness by measuring the reflectance (hereinafter referred to as a reflectance measurement method) has been proposed.

In the polarization analysis method, light is irradiated from diagonally above the sample to be measured, and the change in the polarization state of the reflected light, that is, the relative vibration component P wave parallel to the plane of incidence and the component S wave perpendicular to the plane of incidence, is measured. This method determines the thickness of a transparent thin film in a sample to be measured from changes in the phase shift and changes in the amplitude ratio of both waves.

This polarization analysis method is a film thickness measurement method using a so-called ellipsometer, and is an excellent method that can accurately measure film thicknesses of 10 nm or less. Since it is difficult to specify a specific area and measure the film thickness, the latter reflected light energy measurement method is adopted for such film thickness measurements.

This film thickness measurement method using the reflected light energy measurement method is because among the reflected light from the sample to be measured, the reflected light from the surface of the transparent thin film and the reflected light from the interface between the transparent thin film and the substrate interfere. This is a method of measuring film thickness by utilizing the property that the energy of reflected light from a sample to be measured changes depending on the film thickness of the transparent thin film.

Specifically, obtain correlation data between the reflected light energy and the thickness of the transparent thin film for a sample in which the optical constants of the transparent thin film or substrate are the same as those of the transparent thin film or substrate of the sample to be measured. Then, the reflected light energy of the sample to be measured is measured, and from the correlation data, it is determined whether the reflected light energy approximates the film thickness of the transparent thin film in the sample to be measured. It is said to be thick.

Further, the reflectance measurement method is based on the principle described below.

When the reflectance of the sample to be measured is Rs, the reflectance R3 is the refractive index no and absorptivity ko of the incident side medium of the transparent thin film (usually air since the film thickness is measured in the atmosphere), and the refractive index of the transparent thin film. It is uniquely determined when n1 and absorption coefficient are given as 1, refractive index n2 and absorption coefficient of the substrate are given as 2, wavelength λ and incident angle φ of the measurement light, and film thickness dX of the transparent thin film are given.

Therefore, no, nl, n2, ko, kl, k2,
Under the conditions in which λ and φ are specified, the film thickness dx can be determined when the reflectance Rs becomes clear.

Therefore, we have obtained correlation data between the reflectance Rs and the film thickness dx under the condition that the optical constants of the transparent thin film and substrate are the same as those of the transparent thin film and substrate of the sample to be measured. , the reflectance Rs of the sample to be measured is measured under conditions where the wavelength λ and the angle of incidence φ of the measurement light are set to be the same as the wavelength λ and the angle of incidence φ of the measurement light in the relevant correlation data,
The reflectance Rs is approximated from the correlation data as follows:
The basic principle of film thickness measurement is to find out which film thickness dx is and assume that the film thickness dX is the film thickness dx of the transparent thin film in the sample to be measured.

<Problem to be solved by the invention> As mentioned above, the method for measuring the energy of reflected light relies on correlation data between the energy of reflected light and film thickness.
Since this method measures film thickness, it is essential to obtain correlation data in advance, but obtaining this data is not easy as described below.

The measured value of reflected light energy is a value that includes the effects of characteristics unique to the equipment used for the measurement (e.g., the energy of the light source, various characteristics such as the photoelectric conversion efficiency of the photoelectric exchange means for detecting reflected light energy). Therefore, it can be obtained empirically as described below.

First, a sample (hereinafter referred to as
(referred to as a standard sample). However, several transparent thin films with different thicknesses are prepared. Then, the energy of the reflected light from these standard samples is measured using the same device that measures the energy of the reflected light from the sample to be measured, and the measurement results are used to provide correlation data between the energy of the reflected light and the film thickness. shall be.

By the way, as for the correlation data between the energy of the reflected light and the thickness (19), it is not possible to obtain sufficient film thickness measurement accuracy unless the data is collected in some detail, so a large number of standard samples must be prepared. Therefore, measuring the energy of the reflected light from the standard sample requires a great deal of work. Also,
It is not easy to prepare many standard samples,
That in itself is a huge amount of work.

In this way, the conventional film thickness measurement method based on the reflected light energy measurement method requires a great deal of preparation work, as correlation data between the reflected light energy and film thickness must be obtained empirically in advance. There is a problem in that it requires

In contrast to such an energy measurement method, the reflectance measurement method does not have the above problem because it is a method based on correlation data between the reflectance Rs and the film thickness dx. In other words, since the reflectance Rs is not a value that includes the influence of characteristics specific to the equipment used for measurement, the correlation data between the reflectance Rs and the film thickness dx is similar to the reflectance Rs published in various literatures. By using the correlation data with the film thickness dx (the energy Es of the reflected light and the film thickness d in the reflected light energy measurement method)
This is because there is no need to obtain it empirically like correlation data with x.

However, it is not easy to measure the reflectance Rs of the sample to be measured. This is based on the measurement of reflectance in the literature in which the correlation data between the reflectance Rs and the film thickness dX is manually obtained, and the measurement of the reflectance of the sample to be measured under various measurement conditions, i.e., the refractive index no. This is because the absorption coefficient ko, the wavelength λ, the incident angle φ, etc. of the measurement light must be exactly matched.

The purpose of the present invention is to take advantage of the above-mentioned reflected light energy measuring method which can measure the film thickness by measuring the energy of the reflected light of the sample to be measured, and to obtain the reflectance Rs and film thickness which do not necessarily require empirical manual intervention. It is an object of the present invention to provide a film thickness measuring method that has the advantages of the reflectance measuring method described above and does not require a large amount of preparation work because it uses correlation data with dx. That is, it is an object of the present invention to provide a film thickness measuring method that eliminates the need for a large amount of preparation work even though the measurement of a sample to be measured is simple.

<Means for Solving the Problems> The present invention is a method for measuring the film thickness dx of a transparent thin film in a sample to be measured consisting of a substrate and a transparent thin film on the substrate, the method comprising: A method for making such measurements using known correlation data between the ratio Rs and the film thickness dx of the transparent thin film, characterized in that it is determined by the following steps (a) to (b): (a) the above-mentioned method; The reflectance Rs in the correlation data is divided by the reflectance Rp in any sample for which at least the reflectance is known, and from the correlation data, the relative reflectance Rs/R is calculated.
a step of calculating correlation data between p and film thickness; (b) a step of measuring the energy Ep of the reflected light of any sample for which at least the reflectance is known; (c) an energy of the reflected light of the sample to be measured. (d) By dividing the energy Es of the reflected light of the sample to be measured by the energy Ep of the reflected light of any sample whose reflectance is known at least, the reflected light of the sample to be measured is determined. a step of calculating the energy ratio Es/Ep; (e) a relative reflectance Rs/Rp calculated in the step (a);
The reflected light energy ratio Es/Ep of the sample to be measured calculated in the step (d) from among the correlation data between and the film thickness dx.
A step of searching for a relative reflectance Rs/Rp that approximates the above, and setting the value of the film thickness dx correlated with the searched relative reflectance Rs/Rp as the film thickness dx of the transparent thin film of the sample to be measured.

<Function> When the reflectance of the sample to be measured is Rs, the reflectance R8 is the refractive index no and absorption coefficient kO of the incident side medium of the transparent film (usually air since the film thickness is measured in the atmosphere), and the transparent It is uniquely determined when the refractive index n1 and absorption coefficient of the thin film are given as 1, the refractive index n2 and absorption coefficient of the substrate are given as 2, the wavelength λ and the incident angle φ of the measurement light, and the film thickness dX of the transparent thin film are given. .

Therefore, no, nl, n2, ko, kl, k2,
Under the conditions in which λ and φ are specified, the reflectance Rs and the film thickness d× are correlated.

Therefore, in the present invention, we have obtained correlation data between the reflectance Rs and the film thickness dx under the condition that the optical constants of the transparent thin film and substrate are the same as those of the transparent thin film and substrate of the sample to be measured. First, in step (a), an arbitrary sample whose reflectance is at least known (hereinafter referred to as a known reflectance sample) is prepared, and the reflectance Rs in the correlation data is calculated as the reflectance Rp of the known reflectance sample. By dividing by
The correlation data is converted into correlation data between the relative reflectance Rs/Rp and the film thickness dX.

In the step (b), the energy Ep of the reflected light from the sample with a known reflectance is measured, in the step (c) the energy Es of the reflected light from the sample to be measured is measured, and in the step (d), the energy Ep of the reflected light from the sample to be measured is measured. By dividing the energy Es of the reflected light of the sample by the energy Ep of the reflected light of the sample with a known reflectance, the reflected light energy ratio Es/E of the sample to be measured is calculated.
Calculate p.

Next, in the step (e), the reflected light energy ratio Es/Ep of the sample to be measured is changed to the relative reflectance Rs of the sample to be measured.
/Rp, and from the correlation data between the relative reflectance Rs/Rp calculated in the step (a) and the film thickness d, the reflected light energy ratio Es of the sample to be measured calculated in the step (d). /Ep and find the relative reflectance Rs/Rp, and find the value of the film thickness dx that correlates to the horizontally constructed relative reflectance Rs/Rp, and find the value of the transparent thin film of the sample to be measured. 7.
dx.

Note that the calculated value of the reflected light energy ratio Es/Ep is
The reason why the relative reflectance of the sample to be measured is regarded as Rs/Rp is as follows.

The relationship Ep=-Rp holds between the energy Ep of the reflected light of a sample with a known reflectance and its reflectance R10.

Note that K is a value specific to the device that measures the energy Ep of anti-11 light, and is determined by characteristics specific to the device.

Therefore, when the energy Es of the reflected light from the sample to be measured is measured using the same device, the relationship Es=-Rs also holds true. Therefore, Rs /Rp - Es /Ep.

<Example> Embodiments of the present invention will be described below with reference to the drawings.

The drawing is a schematic diagram of an apparatus using a film thickness measuring method according to an embodiment of the present invention.

In the figure, S is a sample to be measured in which, for example, a transparent thin film such as a silicon oxide film is formed on a silicon substrate.

The light irradiated from the light source 10 is irradiated onto the surface of the sample S to be measured via the condensing element 2, the half mirror 16, and the imaging element 18.

The light reflected on the surface of the sample to be measured S is focused by the imaging element 18, passes through the half-hole 16, is reflected by the pinhole 20 and the mirror 22, and is further passed through the imaging lens 18. The light enters the camera unit 2G via 24.

l The operator operates the sample stage (not shown) on which the sample S to be measured is placed while viewing the pattern of the surface of the sample S to be measured captured by the camera unit 26 and displayed on the CRT (not shown). The energy measurement area of the reflected light on the sample S to be measured by the imaging element 18 is made to coincide with the required film thickness measurement location.

As the light source 10, for example, a halogen lamp that emits visible white light is used.

The light irradiated onto the sample S to be measured is reflected by the surface of the thin film of the sample S to be measured, and also reflected by the interface between the thin film and the surface of the substrate. After being focused by the imaging element 18, these lights pass through the half mirror 16 and the pinhole mirror 20 and enter the spectroscope 32.

The signal detected by the spectrometer 32 is given to a microcomputer 34 for calculating the film thickness of the sample S to be measured. The microcomputer 34 has a film thickness data memory 35.
As described later, the film thickness data memory 35 stores the data for calculating the film thickness used to calculate the film thickness, and the film thickness calculation means 36 has the film thickness calculation means 3G. By referring to the calculation data, the thickness of the transparent thin film in the sample S to be measured is calculated from the energy of the specific wavelength detected by the spectroscope 32.

Next, a method according to an embodiment using a film thickness measuring device will be described. First, as a preparation for measuring the thickness of the transparent thin film in the sample S to be measured, it is important to know whether the optical constants of the transparent thin film or the substrate match those of the transparent thin film or the substrate in the sample to be measured or not. I don't care, again
A transparent thin film may or may not be formed, but at least one sample whose absolute reflectance is known (hereinafter referred to as absolute reflectance known sample 14P) is prepared. Note that the sample P with known absolute reflectance may be any sample as long as it has a clear absolute reflectance, but it is preferable that the sample P be one whose absolute reflectance is not extremely different from that of the sample to be measured. Made of the same material as the iJru board,
It is sufficient to prepare a sample or the like on which a transparent thin film is not formed and whose surface is exposed. Then, the energy of the specific wavelength of the reflected light from the sample P with a known absolute reflectance is measured. At this time, the spectrometer 32
The value of this energy detected at (hereinafter referred to as Ep)
is stored in the memory section within the film thickness calculation means 36. Further, the reflectance of the sample P with known absolute reflectance (hereinafter referred to as Rp) is stored in the film thickness calculating means 36 via input means such as a keyboard (not shown).

Furthermore, as a preparatory step, it is necessary to make sure that the transparent thin film or substrate is the same as the transparent thin film or substrate of the sample to be measured, and that the wavelength λ and the angle of incidence φ of the measurement light are the same as those used when measuring the energy of the reflected light from the sample S to be measured, which will be described later. Correlation data between the absolute reflectance Rs and the film thickness dx under conditions set to be the same as a specific wavelength and incident angle can be found in various documents (for example, l1andbook of
0ptical Con5tans of Solids
+ ^ Academic Press) etc., and calculate the absolute reflectance Rs that corresponds to this correlation data as follows:
Dividing by the absolute reflectance Rp of the sample P with known absolute reflectance,
Correlation data between the relative reflectance Rs/Rp and the film thickness dX is calculated and stored in the film thickness data memory 35.

6. After completing the preparations above, measure the energy E of the specific wavelength of the reflected light from the sample S to be measured.

Then, the energy E detected by the spectrometer 32,
, the film thickness calculating means 36 divides F, , /E P, inputs the value of E S / E P as an address to the film thickness data memory 35, and determines the output film thickness as the measured value. The thickness of the transparent thin film in the sample S is output to a display device such as a printer or CRT (not shown).

Note that the wavelength λ of the measurement light in measuring the reflected light energy of the sample P with a known absolute reflectance and the specific wavelength when measuring the energy of the reflected light from the sample P with a known absolute reflectance and the sample S to be measured are the same. The wavelength must be unified, but any wavelength will do as long as it is unified.

Further, in the step (e) in the configuration of the present invention, a relative reflectance Rs/Rp that approximates the reflected light energy ratio E S / E of the sample to be measured is searched, and the searched relative reflectance Rs/Rp is calculated. Let the value of the film thickness dx that is correlated with Rp be the film thickness dx of the transparent thin film of the sample to be measured." This means that the value of the relative reflection that completely matches the foul light energy ratio Es/E from the correlation data. This is not limited to searching for the ratio Rs/Rp, but also searching for the closest relative reflectance Rs/Rp. Alternatively, some approximate relative reflectance R
This also corresponds to setting a value obtained by interpolation calculation based on the film thickness value correlated with s/Rp as the film thickness of the transparent thin film of the sample to be measured.

<Effects of the Invention> The film thickness measuring method of the present invention is a simple film thickness measuring method in which the film thickness dx is determined by measuring the energy Es of the reflected light from the sample to be measured.

Moreover, the film thickness measurement method of the present invention does not calculate the film thickness based on the direct correlation between the energy Es of the reflected light and the film thickness dx, unlike the film thickness measurement method based on the conventional energy measurement method. Instead, the film thickness dx is determined based on the correlation between the film thickness dx and the relative reflectance Rs/Rp calculated from the correlation between the reflectance Rs and the film thickness dx. Therefore, it is convenient as follows. The correlation data between the energy Es of the reflected light and the film thickness dx is correlation data that can only be obtained empirically because the energy Es of the reflected light includes characteristics unique to the measuring device. It takes a lot of work to get it. On the other hand, the reflectance Rs is the basis for calculating the correlation data between the relative reflectance Rs/Rp and the film thickness dx.
The correlation data between the film thickness dx and the film thickness dx does not include characteristics specific to the measuring device, and can be easily obtained from various literatures without having to be obtained empirically.

Therefore, while the conventional film thickness measurement method based on the reflected light energy measurement method requires a large amount of work to prepare many standard samples and measure the energy of each reflected light, the present invention The method for measuring film thickness does not require such a large amount of work. The film thickness measuring method of the present invention is based on the energy Es of the reflected light from the sample to be measured.
In order to calculate the reflected light energy Es/Ep of the sample to be measured, it is necessary to prepare a sample P with a known absolute reflectance and measure its reflected light energy Ep.
It is sufficient to prepare only one sample P with a known reflectance, and the work of measuring its reflected light energy is only required once. Preparation is also required in the present invention, but it is not necessary to prepare a film according to the conventional method for measuring reflected light energy. Compared to the thickness measurement method, the work involved is significantly less.

[Brief explanation of drawings]

The drawing is a schematic diagram of a film thickness measuring device using a method according to an embodiment of the present invention. S...Measurement sample 10...Light source 18...Imaging element 32...Spectroscope 34...Microcomputer

Claims (1)

[Claims] (1) Consisting of a substrate and a transparent thin film on the substrate, with a reflectance Rs
The film thickness dx of the transparent thin film in the sample to be measured for which correlation data between
A method for measuring film thickness, characterized in that the film thickness is determined by the step of (a) dividing the reflectance Rs in the correlation data by the reflectance Rp in an arbitrary sample for which at least the reflectance is known, to obtain the correlation data. , the relative reflectance Rs/R
a step of calculating correlation data between p and film thickness; (b) a step of measuring the energy Ep of the reflected light of any sample for which at least the reflectance is known; (c) an energy of the reflected light of the sample to be measured. (d) By dividing the energy Es of the reflected light of the sample to be measured by the energy Ep of the reflected light of any sample whose reflectance is known at least, the reflected light of the sample to be measured is determined. a step of calculating the energy ratio Es/Ep; (e) a relative reflectance Rs/Rp calculated in the step (a);
The reflected light energy ratio Es/Ep of the sample to be measured calculated in the step (d) from among the correlation data between and the film thickness dx.
A step of searching for a relative reflectance Rs/Rp that approximates the above, and setting the value of the film thickness dx correlated with the searched relative reflectance Rs/Rp as the film thickness dx of the transparent thin film of the sample to be measured.