JP2001343227A - Method for measuring film thickness of thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a film thickness of extremely thin films to be measured even when common elements are included in substrates and the thin films. SOLUTION: An energy distribution of photoelectrons excited by applying X rays to a measurement object with the thin film formed on the substrate is measured. Elements not common are obtained from elements contained in the substrate and the thin film with the use of the photoelectron energy distribution. An atomic concentration of the element peculiar to the substrate and an atomic concentration of the element peculiar to the thin film are obtained. A photoelectron intensity ratio is obtained from a ratio of the atomic concentrations of the elements peculiar to the substrate and the thin film. The photoelectron intensity ratio is applied to a relation expression between the film thickness and the photoelectron intensity ratio, whereby the film thickness of the thin film is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring the thickness of a thin film formed on a substrate, and more particularly to a method for measuring the thickness of a DLC thin film or a carbon thin film used for a protective film of a magnetic head or a magnetic disk. This is a film thickness measuring method.

[0002]

2. Description of the Related Art In recent years, the recording density of magnetic recording devices such as hard disks has increased remarkably, and higher recording densities have been demanded. One of the technical issues required to increase the recording density is to reduce the thickness of a protective film provided on a magnetic head or a magnetic disk.

A magnetic recording device such as a hard disk reads data from a magnetic disk or writes data to a magnetic disk by arranging a magnetic head at a minute interval with respect to a magnetic disk rotating at high speed. A thin film mainly composed of carbon is formed on the surface of a magnetic head and a magnetic disk, and a protective film is formed. In order to increase the recording density, it is necessary to increase the sensitivity of the magnetic head, and it is necessary to reduce the distance between the magnetic head and the magnetic disk. To narrow the interval,
There is a demand for a thinner protective film.

In order to evaluate thinning, a measuring method for accurately measuring the thickness of a thin film is required. Conventionally, a measuring method using ellipsometry has been known as a method for measuring the thin film thickness. The measurement method using ellipsometry is a measurement method using optical interference and has the advantage that it can be easily measured. However, a protective film used recently has a thickness of several nm.
The thickness is extremely small, and the error becomes large at such a small thickness, and there is a problem in practicality.

[0005] A measurement method using an atomic force microscope (AFM) is also known. In this measuring method, a step formed between a portion where the protective film is formed and a portion where the protective film is not formed is measured by contact of a probe, and the film thickness can be actually measured. There is an advantage. However, in order to measure the film thickness, there is a problem that it is necessary to form a portion where the protective film is not formed by masking a part of the protective film and form a step portion corresponding to the film thickness. Because it is a measurement method that contacts the probe,
There is also a problem that the measurement target may be damaged.
Further, there is a problem that a magnetic head or a magnetic disk in which a step is formed for measurement is difficult to use as a magnetic head or a magnetic disk, or its use is restricted.

[0006]

As described above, the conventional method for measuring the thickness of a thin film has a problem that the measurement accuracy becomes impractical for a very thin film thickness of about several nm, and a step is formed. There is a problem that a pretreatment for measurement is required, and a problem that the measurement target may be damaged by the pretreatment or measurement. On the other hand, as a method for measuring the elemental composition and the bonding state of the material surface, a measurement method by ESCA (or XPS) is known. ESCA (or XP
S) irradiates the sample with a soft X-ray having a known specific energy and measures the photoelectron energy excited by the irradiated X-ray to identify the constituent elements of the sample, determine the chemical bonding state, and determine the constituent elements. Quantitation can be performed.

[0007] The measurement method using this ESCA (or XPS) measures the number of photoelectrons generated from a theoretically determined specific depth. Therefore, it is conceivable to measure the thickness of the sample from the relationship between the number of photoelectrons generated and the depth of the generation region. However, the photoelectron generation state varies depending on the elemental composition and chemical bonding state of the thin film and the substrate (or underlayer), the roughness of the substrate (or underlayer), the surface distribution of the thin film, etc., so the film thickness of the thin film is actually measured. It is difficult to do. In particular, when the thin film is mainly composed of carbon, the thin film contains hydrogen inside and the C—C bond as the main component is a chemical bond having different hardness.
Since the p3 orbital (diamond bond) and the sp2 orbital (graphite bond) are complexly mixed,
It is theoretically difficult to numerically predict the effect on photoelectrons generated from the underlayer.

At present, a substrate for a magnetic head is AlT.
An alloy called iC is used, the substrate and the thin film both contain a carbon element, and a carbide compound contained in the substrate;
It is necessary to distinguish carbon contained in the protective film. In addition, it is necessary to consider how the attenuation of photoelectrons by both carbons affects the film thickness measurement. Therefore,
The application of the measurement method by ESCA (or XPS) to the measurement of the thickness of a thin film is merely theoretical, and its practical application involves various problems.

Accordingly, the present invention has been made to solve the above-mentioned problems of the conventional film thickness measuring method, has an object to perform non-destructive film thickness measurement of an extremely thin film, and has an element common to a substrate and a thin film. It is an object of the present invention to be able to measure the film thickness even when it is included.

[0010]

According to the present invention, a measurement method using ESCA (or XPS) is applied to the measurement of the thickness of a thin film. By using different elements on the thin film side, the thickness of an ultrathin film having a configuration including an element common to the substrate and the thin film is measured nondestructively. The method for measuring the thickness of a thin film of the present invention measures the energy distribution of photoelectrons excited by irradiating a measurement target having a thin film formed on a substrate with X-rays, and uses the energy distribution of the photoelectrons. From among the elements contained in the substrate and the thin film, elements that are not common to each other are determined, and the atomic concentration of the element specific to the substrate and the atomic concentration specific to the thin film are determined. Next, an atomic concentration ratio is determined from an atomic concentration of an element peculiar to the substrate and the thin film, and the atomic concentration ratio is applied to a relational expression between the film thickness and the atomic concentration ratio to measure the film thickness of the thin film.

Although the photoelectron intensity ratio is used for measuring the thickness of a thin film, the present invention is characterized in that the atomic concentration ratio is used. As a result, it is possible to eliminate the influence of data variations such as the element composition and chemical bonding state of the thin film, the roughness of the substrate, and the state of the measuring device. By using different elements for measuring the thickness of the thin film between the substrate and the thin film, it is possible to distinguish between the signal from the thin film and the signal from the substrate. In particular, when the thin film contains carbon as a composition component, carbon is selected as an element specific to the thin film, and an element excluding carbon from elements contained in the substrate is selected as an element specific to the substrate.

Examples of the film mainly composed of carbon include a DLC (Diamond Like Carbon) film, a sputtered carbon film, and a cathodic arc film, and are used as a protective film for a magnetic disk or a magnetic head. Further, the present invention can be applied in a manufacturing process of a magnetic disk or a magnetic head. In the first embodiment, the thickness of the substrate of the thin film of the present invention is measured in the process of forming the film, and the thickness distribution and / or the production in each substrate is measured in the process of forming the film. The variation in film thickness between process steps is determined.

In a second aspect, a film formation portion provided on a magnetic disk or a magnetic head is set as a measurement target, and a thin film of a specific portion in a measurement target in a manufacturing process for forming the film is formed by the thin film of the present invention. A thickness measurement is performed to determine a film thickness distribution in each film forming portion and / or a film thickness variation between manufacturing process steps. According to the present invention, it is possible to non-destructively measure the thickness of an extremely thin magnetic layer protective film such as a magnetic disk or a magnetic head. In addition, it is a contact type measurement method, and the film thickness distribution can be quickly measured without damaging the measurement target unlike the AFM method. Further, in an optical measurement method such as ellipsometry, the film thickness can be measured in a limited measurement region, and the measurement region by the optical measurement method can be complemented.

When the thickness measurement of the thin film of the present invention is applied to the measurement of the thickness of a protective film of a magnetic disk or a magnetic head, the thickness measurement can be incorporated into the manufacturing process. A step of taking out from the production line for measurement becomes unnecessary, and time loss can be saved. Further, since the measurement is non-destructive, the film thickness can be measured without damaging the magnetic disk or the magnetic head in the production line.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. As a measurement method for irradiating a sample with X-rays and measuring the energy distribution of photoelectrons excited by the X-ray irradiation, a measurement method called ESCA or XPS is known. The measurement configuration used for this ESCA (or XPS) measurement is, for example, that a sample is irradiated with soft X-rays (for example, AlKα ray: excitation energy 1463.6 eV) generated from an X-ray gun, and the excited photoelectrons are statically irradiated. The light is condensed by an electric lens, the energy is separated by an electrostatic hemispherical analyzer, and the energy of the separated photoelectrons is detected by a detector. The measurement results are processed by data processing.
Recording and quantitative analysis are performed for each element.

In the film thickness measurement of the present invention, when a thin film laminated on a substrate is irradiated with X-rays, photoelectrons excited by the X-ray irradiation are generated from a certain depth region. In the process of photoelectrons emitted from the surface jumping out of the surface, energy loss occurs due to inelastic collision with atoms in the thin film when passing through the laminated thin film, the amount of photoelectrons of a specific element generated from the substrate jumping out of the surface is ,
The property of attenuating at a constant rate depending on the thickness of the laminated thin film is used.

FIG. 1 is a schematic diagram for explaining the arrangement of the film thickness measurement according to the present invention. In Figure 1, when uniform X-rays are irradiated, at a depth z from the sample surface, photoelectron intensity dI _a photoelectron excited from one atom a is emitted into the vacuum without energy loss, dI _{a = F o · S o ·} σ a · n a · exp (-dz / λ · sinα) represented by (1). Note that the number density at F _o is X-ray intensity to be irradiated, S _o is the effective area of the sample photoelectrons detected occurs, sigma is photoionization cross-section, n _a is the depth z of atoms a of interest,
α is the emission angle between the plane parallel to the surface and the analyzer axis, and λ is the inelastic scattering mean free path.

As shown in the above equation (1), as the photoelectrons pass through the thin film, the photoelectron intensity dIa is attenuated according to _a constant probability exp (-dz / λ · sinα). Usually, 95% of the photoelectrons emitted in a vacuum have a depth of 3
Photoelectrons can be generated from a region of constant depth (3λ depth). When the above equation (1) is applied to a two-layer model in which one thin film (thickness d) is formed on a substrate, the photoelectron intensity I _s from the substrate and the photoelectron intensity I _o from the thin film are obtained by integration. It is represented by the following equation.

[0019] _{I s = I ss · exp (} -dz / λ s o · sinα) ... (2) I o = it oo · [1-exp (-dz / λ o o · sinα)] ... (3) It should be noted , I _ss = F _o · S _o · σ _s · _ns · λ _s ^s , I _oo = F _o · S _o
Σ _{o no o} λ _o ^o , λ _s ^s is the mean free path of the photoelectrons of the substrate material in the substrate, λ _s ^o is the mean free path of the photo electrons of the substrate material in the thin film, λ _o ^o Is the mean free path of the photoelectrons of the thin film material in the thin film.

The film thickness d can be expressed by the following equation from the above equations (2) and (3). It should be noted that, when the kinetic energy of the photoelectron is approaching, it is possible to approximate the _{^{λ o o = λ s o =}} λ. d = λ · sin α · ln [(I _o / R _s ) +1] (4) R = I _oo / I _ss (5) Accordingly, the film thickness d is the mean free path λ, the emission angle α,
The comparison coefficient R and the photoelectron intensity ratio between the substrate and the film thickness (I _o /
I _s ) can be obtained by applying the equation (4).

Hereinafter, a first mode of measuring the thickness of a thin film will be described. The first aspect is ESCA (or XP
The atomic concentration of the substrate and the thin film is obtained by S), and the film thickness is obtained by applying the photoelectron intensity ratio (I _o / I _s ) obtained from this atomic concentration ratio to the above equation (4). FIG. 2 is a flowchart for explaining a first mode of measuring the thickness of a thin film. First, ESCA (or XPS)
In the measuring apparatus according to the above, a sample in which a thin film is formed on a substrate (underlying film) is irradiated with soft X-rays (step S1), and the number of photoelectrons for each energy of photoelectrons of a specific element selected by a detector is detected. To measure the photoelectron spectrum (step S2). The constituent elements and the chemical bonding state of the sample are identified (Step S3), and the atomic concentration is quantified (Step S4).

Next, the element compositions of the substrate and the thin film obtained by element identification are compared, different elements are selected for the substrate and the thin film, and an element peculiar to the substrate and an element peculiar to the thin film are selected.
Here, in the case of a film configuration in which a Si film and a DLC thin film are formed on an AlTiC substrate as shown in FIG. 3, both the thin film S and the substrate O contain carbon C. FIG.
The example of the measured spectrum about the film which formed the Si film (2 nm) and the DLC thin film (3 nm) on the AlTiC substrate is shown, the horizontal axis shows the binding energy (eV), and the vertical axis shows the photoelectrons per unit time of photoelectrons. Number (CPS). According to the qualitative result based on the measurement spectrum, O, Ti, C, Si, and Al are detected as constituent elements of the measurement sample.

FIGS. 5 and 6 show measurement data of each constituent element. FIG. 5 (a) shows the measured data of O1s, FIG. 5 (b)
5A shows the measured data of Ti2p, FIG. 5C shows the measured data of C1s, FIG. 6A shows the measured data of Si2p, and FIG.
12 shows measurement data of l2p. The measurement data obtained from the AlTiC substrate are the measurement data of Ti2p in FIG. 5B and the measurement data of Al2p in FIG. 6B, and the measurement data obtained from Si in the intermediate layer is FIG. Si2p
Is the measurement data.

Therefore, here, measurement data of Al2p is used as a signal from the substrate, and C1s is used as a signal of the DLC film.
Use the measurement data of The measurement data obtained from the DLC film is only the measurement data of C1s in FIG. 5C, but the measurement data of C1s includes carbon and hydrocarbon from the DLC film and carbon from the AlTiC substrate. Therefore, in order to distinguish the carbide component contained in the substrate O from the carbon in the thin film S, the spectrum of the carbide contained in the substrate is removed from the measurement spectrum based on the DLC-specific spectrum by a waveform separation method, and the quantification is performed. Perform (Step S5). The concentration ratio of the atomic concentration of the selected element is determined (step S6), and the photoelectron intensity ratio ( _Io / _Is ) is determined from the concentration ratio of the atomic concentration of the selected element (step S7).

Next, the photoelectron intensity ratio (I _o / I _s ) obtained in step S7, the mean free path λ, the emission angle α, and the comparison coefficient R are applied to the above equation (4) to obtain the film thickness d. . In Comparative coefficient R is photoelectron intensity I _o for each single element of the substrate and the thin film selected in the obtains the I _s, respectively photoelectron intensity determined I _oo, and corresponds to I _ss, the intensity ratio R can be obtained from (I _o / I _s ).

The mean free path λ is ln [(I _o / RI _s ) +1] = d / λ (1) obtained by modifying equation (4).
/ Sin .alpha) that can be obtained from, values plotted against 1 / sin .alpha of _{ln [(I o / RI s} ) +1] for an existing thickness can be determined from the slope of this time (step S8) . Therefore, in the first mode of measuring the thickness of a thin film, by ESCA (or XPS),
The film thickness d can be obtained by applying the photoelectron intensity ratio (I _o / I _s ) obtained from the atomic concentrations of the different elements of the substrate and the thin film to the above equation (4).

Next, a second mode for measuring the thickness of a thin film will be described. In the second embodiment, an atomic concentration ratio (photoelectron intensity ratio) is determined for a film having a known film thickness in advance, the relationship between the film thickness and the atomic concentration ratio is determined as a calibration curve, and measurement is performed using the calibration curve. The thickness is determined from the determined atomic concentration. In FIG. 7, the abscissa indicates the film thickness d (nm), and the ordinate indicates the natural logarithm ln (C1s / Al
2p), which constitutes a calibration curve for obtaining the film thickness d.

The measurement points were the Si film (2 nm) and the DLC
The total thickness of the films (3 nm, 6 nm, 8 nm) is 5 nm,
The cases of 8 nm and 10 nm are shown. This example also shows a sufficient linear relationship for a DLC film thickness of less than about 5 nm, so that the reliability of the film thickness measurement of the present invention can be verified. In the above description, DL
Although the measurement of the thickness of the C film is shown, the measurement of the thickness of the Si film can be similarly performed.

The film thickness measurement according to the present invention can be applied to a process for manufacturing a magnetic disk or a magnetic head. The substrate and film formation part of the magnetic disk or magnetic head are measured, and the film thickness of the thin film or substrate is measured during the film formation process, and the film thickness distribution and production within each substrate or each film formation part are measured. Variations in film thickness between process steps can be determined.

[0030]

As described above, according to the method for measuring the thickness of a thin film of the present invention, the thickness of an ultrathin film can be measured without destruction, and an element which is common to the substrate and the thin film is contained. Even in this case, the film thickness can be measured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining an arrangement for measuring a film thickness according to the present invention.

FIG. 2 is a flowchart for explaining one mode of measuring the thickness of a thin film.

FIG. 3 is a schematic diagram for explaining a film configuration.

FIG. 4 is a measured spectrum example of a film in which a Si film and a DLC thin film are formed on an AlTiC substrate.

FIG. 5 is an example of measurement data of each constituent element.

FIG. 6 is an example of measurement data of each constituent element.

FIG. 7 is a diagram showing a correlation between a film thickness and an atomic concentration ratio (photoelectron intensity ratio).

[Explanation of symbols]

 S: thin film, O: substrate (base film).

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2F067 AA28 BB02 BB18 CC00 CC13 EE03 EE04 FF07 HH04 JJ05 KK05 RR24 UU31 2G001 AA01 BA08 CA03 GA01 HA01 KA01 KA11 LA11 MA05 NA03 5D033 CA10 5D112 AA07 AA24 BC05

Claims (4)

[Claims] An energy distribution of photoelectrons excited by irradiating a measurement target having a thin film formed on a substrate with X-rays is measured, and the element contained in the substrate and the thin film is measured using the energy distribution. From among the elements that are not common to each other, the atomic concentration of the element specific to the substrate and the atomic concentration specific to the thin film are obtained, and the atomic concentration ratio obtained from the atomic concentration of the element specific to the substrate and the thin film is represented by A method for measuring the thickness of a thin film, wherein the method is applied to a relational expression of an atomic concentration ratio to measure the thickness of the thin film. 2. The thin film contains carbon as a composition component,
2. The method according to claim 1, wherein carbon is selected as an element peculiar to the thin film, and an element excluding carbon from elements contained in the substrate is selected as an element peculiar to the substrate. 3. A method for measuring a thickness of a substrate by a method for measuring a thickness of a thin film according to claim 1, wherein a film-forming portion provided on a magnetic disk or a magnetic head is set as an object to be measured. 3. The method for measuring the thickness of a thin film according to claim 1, wherein a thickness distribution in each substrate and / or a variation in a thickness between steps of a manufacturing process are obtained. 4. The film thickness measurement according to claim 1, wherein a film forming portion provided on the magnetic disk or the magnetic head is set as a measurement target, and the film thickness measurement according to claim 1 or 2 is performed on a thin film at a specific portion in the measurement target in a manufacturing process of the measurement target. 3. The thin film thickness measuring method according to claim 1, wherein a film thickness distribution in each film forming portion and / or a variation in film thickness between steps of a manufacturing process are obtained.