JP2003065977A - Method and apparatus for inspecting laminated thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for inspecting laminated thin films whereby a film thickness and a density of an nm oxide film of a magnetic resistance type sensor or the like can be quickly measured and analyzed while hardly affected by a change of film thicknesses and densities of the other laminated thin films. SOLUTION: In the method for inspecting the laminated thin film by which a layer structure of the laminated thin film is inspected by sending X rays by a low angle θinto a laminated body having two or more thin films formed on a substrate, measuring an X-ray reflectivity from the laminated thin film and analyzing the reflectivity, when a refractive index of the thin film is made n=1-(λ/4π)<2> (ξ+iη) wherein λ is an X-ray wavelength by a unit of Å, the X-ray wavelength whereby a square of a refractive index difference at an interface of the laminated film other than the test object ΔN<2> =Δξ<2> +Δη<2> becomes 1.5×10<-8> or smaller is used, and a criterion whereby a square sum of a residual between the reflectivity from a laminated thin film as a standard and the reflectivity from the laminated thin film as the test object becomes not larger than an allowable value calculated from the change of the density and the film thickness is set. The apparatus for inspecting the laminated thin film is provided with an analysis means based on the inspection method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated thin film inspection method and a laminated thin film inspection for measuring the X-ray reflectance of a laminated thin film having two or more layers formed on a substrate to rapidly inspect the thickness and density of the laminated thin film. Regarding the device.

[0002]

2. Description of the Related Art In the field of semiconductor integrated circuits, devices using semiconductor integrated circuits, magnetic files, etc., semiconductor layers,
An insulating layer and a metal layer are laminated and a pattern is formed to manufacture an element. The film formed for the purpose of high performance and high performance of the element has become extremely thin and the number of laminated films has been increasing. Since the film thickness and density of such a laminated thin film have a great influence on the characteristics of the element, it is necessary to enhance film formation controllability and evaluate the laminated structure with high accuracy.

The X-ray reflectance measuring method is an effective method for nondestructively evaluating the layer structure of a laminate. Conventionally, after X-rays from an X-ray source are separated by a crystal spectroscope, they are incident on a sample at an oblique incident angle θ, and reflected X-rays from a subject are detected by a detector. The rotating table was driven by the control device, and the reflectance was measured from the θ / 2θ scan.

FIG. 2 is a flowchart showing a conventional inspection processing procedure. The reflectance from the subject measured by the above apparatus is optimized by the least squares method, and the inspection items such as the film thickness and density of the layer structure of the laminated thin film are determined. The inspection item is
If the target value is not satisfied, it is fed back to the film forming process.

Regarding the wavelength of X-rays, Cu-Kα rays are
Commonly used. In addition, JP-A-10-03388
No. 21, JP-A 2000-097883, and JP-A 2001-083108 disclose Cu-Kβ.
It has been reported that the laminated structure can be evaluated with high accuracy by using the X-ray, Co-Kβ line, Ni-Kα line, and Ni-Kβ line.

[0006]

The X-ray reflectivity method is a method for analyzing a vibrating structure in a reflectivity profile caused by interference of X-rays reflected on the surface of a laminate and each interface. If the difference in the refractive index (difference in density) is small, the intensity of reflected X-rays at the interface will be small, and analysis will be impossible depending on the decrease in analysis accuracy for each film and the material composition of the thin film. There was a problem. To overcome this problem, the use of the anomalous dispersion of the refractive index of X-rays by the laminated thin-film constituent material is disclosed in JP-A-10-38821, and the laminated structure can be evaluated with high accuracy.
It has been reported.

However, when this reflectance method is applied to an inspection method for the purpose of controlling and managing the film thickness of a laminated thin film, there are the following problems. (1) It takes several hours to measure the reflectance because Kβ rays having low X-ray intensity are used. (2) Since analysis of reflectance requires experience and knowledge, analysis is difficult and unsuitable for film formation inspection process.

As a magnetoresistive sensor mounted on a magnetic recording / reproducing apparatus, recently, a structure in which an oxide film having a thickness of nm is included in a laminated thin film is becoming mainstream, and control of this oxide film is important. It has become a challenge. In this case, there is a demand to quickly inspect only the thickness and density of the nm oxide film.

An object of the present invention is to provide a laminated thin film inspection method and a laminated thin film device which are not easily affected by variations in the thickness and density of other laminated thin films and which can quickly measure and analyze the thickness and density of a nm oxide film. It is to be.

Another object of the present invention is to provide a magnetic recording / reproducing apparatus equipped with a magnetoresistive sensor having stable performance, which is manufactured by controlling the film thickness and density of nm oxide film by the above-mentioned laminated thin film inspection method. That is.

[0011]

In order to achieve the above object, the present invention makes X-rays from a laminated thin film incident X-rays at a low angle θ on a laminated body in which two or more thin films are formed on a substrate. In the laminated thin film inspection method of measuring the linear reflectance, analyzing the reflectance, and inspecting the layer structure of the laminated thin film, the refractive index of the thin film is n =
1- (λ / 4π) ² (ξ + iη), λ: When the X-ray wavelength is set to Å unit, the square of the refractive index difference ΔN ² = Δξ ² + Δη ² at the interface of the laminated film other than the inspection target is An X-ray wavelength of 1.5 × 10 ⁻⁸ or less is used, and the residual difference between the reflectance from the standard laminated thin film and the reflectance from the laminated thin film to be inspected is 2
We propose a method for inspecting thin film stacks that provides a criterion for making the sum of sums equal to or less than the allowable value calculated from the variations in density and film thickness.

The X-ray wavelength is Mo-Kα ray or C
It is desirable to use o-Kα radiation.

The present invention also provides an X-ray source, a spectroscope for injecting X-rays from the X-ray source at a low angle θ into a sample in which two or more thin films are formed on a substrate, and an X-ray from a laminated thin film. In a laminated thin film inspection device comprising a detector for measuring the linear reflectance, a driving means for the sample and the detector, and a control analysis means for controlling the driving means to analyze the reflectance and inspecting the layer structure of the laminated thin film, The X-ray source changes the refractive index of the thin film to n = 1- (λ / 4π)
² (ξ + iη), λ: When the X-ray wavelength is set to Å unit, the square of the difference in refractive index at the interface of the laminated film other than the inspection target ΔN ² = Δ
ξ ² + Δη ² includes a target that generates a characteristic X-ray with a value of 1.5 × 10 ⁻⁸ or less, and the criterion of the control analysis means is
We propose a laminated thin film inspection system in which the sum of squares of the residuals of the reflectance from the standard laminated thin film and the reflectance from the laminated thin film to be inspected is less than or equal to the allowable value calculated from the variation of the density and the film thickness. .

The X-ray wavelength is Mo-Kα ray or C
Use o-Kα radiation.

In order to achieve the above-mentioned other objects, the present invention provides a magnetic recording medium, a magnetoresistive sensor for reading a magnetic signal from the magnetic recording medium, a write head for writing a magnetic signal on the magnetic recording medium, and a magnetic resistance. Type sensor and a write head are mounted on the tip of the arm to drive in the radial direction of the magnetic recording medium, a control device to control the magnetic recording medium and the driving means of the arm, and the read magnetic signal and the magnetic signal to be written are processed. In the magnetic recording / reproducing apparatus provided with the signal processing means for
A magnetic recording / reproducing apparatus is proposed which is a laminated thin film manufactured by controlling the film thickness by the laminated thin film inspection apparatus.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a laminated thin film inspecting method, a laminated thin film inspecting apparatus, and a magnetic recording / reproducing apparatus according to the present invention will be described below with reference to FIGS.

[0017]

First Embodiment In the present invention, an X-ray wavelength that suppresses reflection from a laminated film other than the inspection target is selected, so that the laminated thin film sensitive to structural changes such as film thickness and density of the laminated thin film to be inspected. The inspection method is obtained.

Consider the X-ray reflectance from the laminated body in which the n-1 layer film is formed on the substrate. Let the complex refractive index be n = 1- (λ
/ 4π) ² (ξ + iη), the oblique angle of the incident X-ray is θ, the X-ray wavelength is λ, the film thickness is t, and the magnitude of the scattering vector is q = 4πsi.
Using nθ / λ and using the approximation of q ² > ξ, η, the reflectance R
Is expressed by Equation 1.

[0019]

[Equation 1] Φ in Expression 1 is an amount representing the phase of the reflected X-ray and is a function of the film thickness or the like. In Equation 1, the first sum term is the reflection from the surface and the interface, and information about the film thickness cannot be derived from this term.

On the other hand, the second sum term is due to the interference of X-rays reflected on the surface and the interface, and as shown in FIG. 3, a vibrating structure appears in the reflectance. This vibrating structure contains information about the film thickness and density of each film of the laminated body. Square of refractive index difference at the interface that determines the amplitude of vibration ΔN ² = (Δξ
² + Δη ² ) depends on the wavelength of the incident X-ray.

If the amplitude of this vibration is increased by the selection of the X-ray wavelength, the intensity of X-rays reflected at the interface becomes high, and the structure of the film in contact with the interface can be analyzed with high accuracy.

On the other hand, if the amplitude of vibration is reduced by wavelength selection, the intensity of reflection at the interface becomes low, and the change in the structure of the film in contact with the interface is not reflected in the reflectance.

The feature of the present invention is that the structural change of the film to be inspected is analyzed by utilizing the fact that the amplitude of vibration is reduced by the wavelength selection as described above, and the structural change of the laminated film other than the inspected film is analyzed. Is not affected by.

Next, the wavelength selection of X-rays was examined.
As described above, as a magnetoresistive sensor mounted on a magnetic recording / reproducing apparatus, recently, a structure including an oxide film having a thickness of nm in a laminated thin film is becoming mainstream, and control of this oxide film is important. It has become a challenge. In this case, there is a demand to quickly inspect only the thickness and density of the nm oxide film. The laminated thin film that constitutes the magnetoresistive sensor includes a magnetic layer and a nonmagnetic layer of a transition metal, and an X-ray wavelength that suppresses reflection from these transition metal films was searched for. Figure 4
Indicates the square of the refractive index difference ΔN ² = (Δξ ² + Δη ² ) at each interface where Cu, NiFe, and CoFe are laminated. As the X-ray wavelength, Kα ray having high intensity was examined.
From FIG. 4, the Mo-Kα line has the smallest ΔN ² at each interface and is the optimum wavelength, and the Co-Kα line also has the next ΔN.
^It turns out that ² is small and promising. From the above, ΔN ²
It can be seen that the intensity of the reflected X-ray from the interface of the laminated film of the transition metal can be suppressed when the value is 1.5 × 10 ⁻⁸ or less.

[0025]

Second Embodiment In a second embodiment, an inspection of a nm oxide film included in a laminated thin film of a magnetoresistive sensor will be described.

FIG. 5 is a block diagram showing the structure of the laminated thin film inspection apparatus according to the second embodiment. The X-rays from the X-ray source 1 are separated into desired characteristic X-rays by the crystal spectroscope 3 and then incident on the sample 6. The reflected X-ray from the sample 6 is slit 7,
After molding with 9 and the solar slit 8 to make them parallel, the detector 10 measures.

Next, each function will be described. As the X-ray target, a Mo target using a Cu rotating anticathode having Mo formed on the rotating surface irradiated with the electron beam from the filament was adopted. The operating conditions of the X-ray source 1 are a tube voltage of 60 kV and a tube current of 300 mA.

Mo-Kα rays from the X-ray source 1 (wavelength: 0.
0709 nm) was taken out by a crystal spectrometer Ge (111) channel cut type crystal. The entrance slit 2 to the spectroscope was set to have a width of 0.1 mm and a height of 10 mm, and the exit slit 4 was set to have a width of 0.1 mm and a height of 5 mm. The slit 7 in front of the detector 10 has a width of 0.2 mm and a height of 5 m.
m, the slit 9 has a width of 0.2 mm, and the solar slit 8 has a width of 5 degrees. The rotary table 5 is composed of two axes of θ−2θ, and the position of the sample holder provided on the θ table can be driven by the controller 11 to adjust the sample 6 in parallel with the incident X-ray. As the detector 10, a scintillation counter having an opening diameter of 1 inch was used. Each drive unit can be controlled by the control device 11.

After the X-ray from the X-ray source 1 is separated by the crystal spectroscope 3, it is made incident on the sample 6 at an oblique incident angle θ, and the reflected X-ray from the object is detected by the detector 10. The rotating table 5 is driven by the control device 11, and the reflectance is measured from the θ / 2θ scan. Entrance slit 2 and exit slit 4
Limits incident X-rays and the slits 7, 9 limit reflected X-rays. The solar slit 8 enhances the parallelism of the reflected X-rays. The analysis device 12 analyzes the obtained reflectance and outputs the analysis result such as the density and film thickness of each layer to the output device 13.

The subject is a tunnel type magnetoresistive film formed on a Si substrate. The film structure is Ru (5) / NiFe
(3) / CoFe (3) / AlO (1.5) / CoFe (3) M
An nPt (23) / NiFe (5) / Ta (5) / Si substrate was used. The thickness in parentheses is the set film thickness and the unit is nm. AlO
Was formed by natural oxidation for 20 minutes at 100 Torr after forming the Al film. The purpose was to evaluate the film thickness and density of this AlO and inspect the process for forming the nm oxide film.

Next, the measurement and analysis procedure will be described. First, the position of the sample 6 is adjusted so as to be parallel to the X-ray, and then the sample 6 is rotated to a set angle and 2θ is rotated to a predetermined angle. For the measurement, the reflected X-ray intensity was measured by θ-2θ scanning at a step angle of 0.004 ° of sample 6. The measuring range of θ is 385 from 0.08 ° to 1.62 °
The point was measured. The measurement time per point is 5-10 seconds,
The total measurement time is ~ 1 hour. The drive of the rotary table 5 was controlled by the control device 11, and the signals from the detector 10 were sequentially recorded in the analysis device 12 via the control device 11.

The reflectance data measured under the condition that the angle θ (degree) and Δθ are constant is used as the scattering vector magnitude q = 4πsin.
The analysis was performed using the q display reflectance obtained by data conversion with constant θ / λ and Δq. To calculate the reflectance, use LGParatt (Phys.Rev.95,3
59 (1954)) and L. Nevot and P. Croce (Rev. Phys. Appl
The theoretical formula by 15,761 (1980)) was used. In the calculation, the complex refractive index of each layer is based on literature values (Sasaki; KEK Report, 88-
14) was used.

The layer structure model used in the analysis is oxide layer / R
u / NiFe / CoFe / AlO / CoFe / MnPt
/ NiFe / reaction layer / Ta / interface layer / Si substrate, and the refractive index, film thickness, and interface width of each layer were optimized using the least square method. The analysis result is shown in FIG. The calculation was performed on the analysis device 12, and the calculation result was output to the output device 13. This analysis requires several hours and is not suitable for inspecting the film thickness and density of AlO.

Therefore, the change in reflectance when the AlO film structure was changed was calculated, and the result is shown in FIG.

With the AlO film thickness fixed at 1.53 nm, the refractive index ξ (proportional to the density) is ± 20% (5.11 × 10 ⁻⁴ ,
(Corresponding to 7.66 × 10 ⁻⁴ ), and the changed reflectance is shown.
Moreover, ξ is fixed at 6.38 × 10 ⁻⁴ , and the film thickness is ± 10.
% (Corresponding to 1.37 and 1.68 nm) and the changed reflectance are also shown.

It can be seen that when the refractive index is changed by ± 20%, the scattering vector q is slightly deviated within the range of 0.10.25. FIG. 7 is an enlarged view of that portion.

On the other hand, when the film thickness is changed by ± 10%, q
It can be seen that is shifted in the range of 0.150.35. Figure 8
FIG. 3 is an enlarged view of that portion. It can be seen that the deviation of the reflectance is larger when the film thickness is changed than when the refractive index is changed.

From these facts, the judgment factor R (%) for inspecting the process of forming the nm oxide film is introduced by the mathematical formula 2.

[0039]

[Equation 2] Here, Istd is the reflectance from the standard sample, and I is the reflectance from the subject. R of the above refractive index change is 1.
8%, R of film thickness change was 5.1%. Therefore, n
5% is appropriate as the allowable value of the judgment factor for inspecting the formation process of the m-oxide film.

FIG. 1 is a flow chart showing the processing procedure of the laminated thin film inspection method according to the present invention. The reflectance of the subject with Mo-Kα rays or Co-Kα rays is measured. If the determination factor calculated from the reflectance of the standard sample and the test object by the mathematical formula 2 is equal to or less than the allowable value, the process for controlling the nm oxide film of the test object is satisfied. On the other hand, if the determination factor is equal to or greater than the allowable value, the film structure of each layer is determined by detailed analysis of reflectance, and the film structure is fed back to the film forming process.

Although the Mo target is used in the second embodiment, a Co-Kα1 ray from a Co target may be used.

In the second embodiment, Mo-Kα having a short wavelength is used.
Since the line is used, the reflectance measurement range is short and the measurement can be performed in a short time. Further, since the X-ray wavelength that suppresses the intensity of the reflected X-ray from the interface of the transition metal laminated film is used, the influence of the change in the transition metal film structure is small. Furthermore, in the second embodiment, since the analysis is performed by the determination factor of Expression 2, the evaluation can be performed in an extremely short time as compared with the detailed analysis.

[0043]

Third Embodiment Next, a magnetic recording / reproducing apparatus equipped with a magnetoresistive sensor whose film thickness is controlled and controlled by the laminated thin film inspection method or laminated thin film inspection apparatus of the present invention will be described.

The film structure of the magnetoresistive sensor is the same as that of the second embodiment.
It is the same as the sample used in. A 5-inch wafer formed by a sputtering apparatus was used as an object to be evaluated by the processing procedure shown in FIG. 1, and only the wafer whose judgment factor satisfied the allowable value was passed to the head processing step.

In each magnetic recording / reproducing apparatus incorporating this magnetoresistive sensor, since the thickness and density of the nm oxide film are controlled, the sensitivity of each magnetoresistive sensor is stable, and as a recording apparatus, It showed a good yield.

According to the third embodiment, the film structure of the nm oxide film, which is the main element of the magnetoresistive sensor, can be more precisely managed and controlled, so that the variation in the performance of each sensor can be suppressed within the allowable range. It is possible to produce a magnetic recording / reproducing device with stable performance.

[0047]

According to the laminated thin film inspection method and the laminated thin film inspection apparatus of the present invention, since the Mo-Kα ray having a short wavelength is used, the reflectance measurement range is short and the measurement can be performed in a short time.

The reflection X from the interface of the transition metal laminated film
The X-ray wavelength that suppresses the intensity of the rays is used, and the influence of the change in the transition metal film structure is small.

Further, since the analysis is based on the judgment factor of Equation 2, the film structure can be evaluated in an extremely short time as compared with the detailed analysis.

Since the film structure of the nm oxide film, which is the main element of the magnetoresistive sensor, can be more precisely managed and controlled, the variation in the performance of each sensor can be kept within the allowable range, and the magnetic recording / reproducing apparatus with stable performance. Can be produced.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a processing procedure of a laminated thin film inspection method according to the present invention.

FIG. 2 is a diagram illustrating a processing procedure of a conventional laminated thin film inspection method based on detailed analysis of X-ray reflectance.

FIG. 3 shows a change in the refractive index of AlO by ± 20%, or
It is a figure which shows the reflectance when changing a film thickness ± 10%.

FIG. 4 is a square of a refractive index difference ΔN ² = Δξ ² + Δη ² at each interface of a transition metal laminated film forming a magnetoresistive sensor.
It is the figure which calculated with various wavelengths.

FIG. 5 is a block diagram showing a configuration of a laminated thin film inspection apparatus according to a second embodiment.

FIG. 6 Oxide layer / Ru / NiFe / CoFe / AlO /
CoFe / MnPt / NiFe / reaction layer / Ta / interfacial layer / Si substrate, each layer having a minimum refractive index, film thickness and interface width of 2
It is a figure which shows the analysis result optimized using the multiplication method.

7 is a diagram showing changes in reflectance with respect to changes in the refractive index of 20% in FIG.

8 is a diagram showing a change in reflectance with respect to a change in film thickness of 10% in FIG.

[Explanation of symbols]

1 X-ray source 2 incident slit 3 Crystal spectrometer 4 exit slit 5 turntable 6 samples 7 slits 8 solar slits 9 slits 10 detector 11 Control device 12 Analyzer 13 Output device

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Claims (5)

[Claims] 1. A laminated thin film in which two or more thin films are formed on a substrate, X-rays are incident on the laminated thin film at a low angle θ, X-ray reflectance from the laminated thin film is measured, and the reflectance is analyzed. In the laminated thin film inspection method for inspecting the layer structure of, the thin film has a refractive index of n = 1− (λ / 4π) ² (ξ + iη), λ:
The square of the refractive index difference ΔN ² = Δξ ² + Δη ² at the interface of the laminated film other than the inspection target is 1.
Using the X-ray wavelength of 5 × 10 ⁻⁸ or less, the sum of squares of the residuals of the reflectance from the standard laminated thin film and the reflectance from the laminated thin film to be inspected is the variation of the density and the film thickness. A method for inspecting a laminated thin film, wherein a judgment criterion is set to be equal to or less than an allowable value calculated from. 2. The method for inspecting a laminated thin film according to claim 1, wherein Mo-Kα rays or Co-Kα rays are used as the X-ray wavelength. 3. An X-ray source, a spectroscope for injecting an X-ray from the X-ray source at a low angle θ into a sample having two or more thin films formed on a substrate, and an X-ray reflectance from a laminated thin film. A laminated thin film inspection apparatus comprising: a detector for measuring the sample, a driving means for the sample and the detector, and a control analysis means for controlling the driving means to analyze the reflectance and inspect the layer structure of the laminated thin film. In the X-ray source, the refractive index of the thin film is n = 1- (λ / 4π).
² (ξ + i η), λ: When the X-ray wavelength is in units of Å, the square of the difference in refractive index at the interface of the laminated film other than the inspection target ΔN ² =
The target includes a target that generates a characteristic X-ray with Δξ ² + Δη ² of 1.5 × 10 ⁻⁸ or less, and the criterion of the control analysis means is the reflectance from the laminated thin film which is the standard and the laminated layer which is the inspection target. A laminated thin film inspection apparatus, wherein a sum of squares of residuals with respect to reflectance from a thin film is equal to or less than an allowable value calculated from variations in density and film thickness. 4. The laminated thin film inspection apparatus according to claim 3, wherein Mo—Kα rays or Co—Kα rays are used as X-ray wavelengths. 5. A magnetic recording medium, a magnetoresistive sensor for reading a magnetic signal from the magnetic recording medium, a write head for writing a magnetic signal on the magnetic recording medium, and a tip portion of the magnetoresistive sensor and the write head. An arm that is mounted on a disk and drives in the radial direction of the magnetic recording medium, a control device that controls the magnetic recording medium and a driving unit of the arm, and a signal processing unit that processes a read magnetic signal and a magnetic signal to be written. 5. A magnetic recording / reproducing apparatus comprising: the laminated thin film of the magnetoresistive sensor;
A magnetic recording / reproducing apparatus, which is a laminated thin film manufactured by controlling and controlling the film thickness by the laminated thin film inspecting apparatus described in 1.