JP6167610B2 - Thin film evaluation method - Google Patents

Description

The present invention relates to a thin film evaluation method for analyzing composition and film density in a thin film and the like.

  In recent years, in the manufacture of functional materials such as optical components and electronic components, a technique (coating technique) for forming a thin film of 1 μm or less on a substrate material is frequently used. For example, in an optical component, an inorganic oxide such as silicon dioxide (SiO 2) or titanium dioxide (TiO 2) or an inorganic fluoride such as magnesium fluoride (MgF 2) is used to control the refractive index and reflectance of light. Formed on the surface. In addition, indium tin oxide (ITO) is formed on various substrates as a transparent electrode of a touch panel or an organic EL display device.

These thin films are often formed by physical vapor deposition such as vacuum vapor deposition or sputtering. In particular, the sputtering method is frequently used when a thin film having a thickness of 100 nm or less is formed because the composition of the deposited film is uniform and flat and the film thickness is easy to control.
There are a number of different sputtering methods. In general, a coating material for forming a thin film and a thin film raw material called a target are opposed to each other in a high vacuum, and a voltage is applied to both. A phenomenon is utilized in which raw material particles are blown off by collision of ionized gas with a target biased to the negative side.

The repelled raw material particles collide and deposit on the opposite coating material in a high energy state.
By the way, the thin film formed in this way is determined by optical characteristics and electrical characteristics to determine whether or not the functions are sufficiently exhibited. Furthermore, membrane analysis is performed to evaluate the origin of these physical properties. For example, since the electrical characteristics of the transparent electrode are influenced by the film thickness, film composition, and film density of ITO, film observation and chemical composition analysis are performed.

  In many cases, an electron microscope is used for observation of the thin film. When the film is observed in the plane direction of the material to be coated, a scanning electron microscope (SEM) is used. When the film is observed in the depth direction of the material to be coated, it appears by cutting the thin film in the depth direction with a diamond knife or by cutting the thin film with a focused ion beam (FIB). The cross section to be observed is observed using a SEM or a transmission electron microscope (TEM).

  For composition analysis of thin films, energy dispersive X-ray spectroscopy (EDX) for detecting characteristic X-rays of each element generated by applying an electron beam to a sample, Auger electron, and the like. Electron Spectroscopy (AES) for detecting UV, X-ray Photoelectron Spectroscopy (XPS) for detecting photoelectrons generated when a sample is irradiated with X-rays, and fluorescence X generated X-ray Fluorescence (XRF) to detect the energy of the line, or when the sample was irradiated with primary ions such as bismuth (Bi) ions, the substance present on the sample surface was ionized Secondary Ion Mass detecting the following ion mass spectrometry (Secondary Ion Mass Spectorometory: SIMS), there are a wide variety of analytical techniques, such as.

In many cases, these composition analysis methods can obtain composition information of several nm to several tens of nm from the surface layer. However, when analyzing the composition distribution in the depth direction of a thin film, it is necessary to measure the surface of the sample while performing sputter etching with Ar ions. There is no distribution.
For this reason, various methods have been disclosed that can analyze the composition distribution in the depth direction in a non-destructive manner without performing sputter etching.

A typical method is to detect the energy value of ions scattered backward when a sample is irradiated with light element ions such as helium (He) at high energy, and the types and abundances of elements contained in the sample. Are Rutherford Backscattering Spectrometry (RBS), and Recoil Detection Detection Analysis (ERDA) to detect atoms and ions repelled by high energy light element ions.
RBS analysis and ERDA analysis can be measured by irradiating light element ions as described above. Therefore, it has features such as no preparation of a standard sample, no pretreatment, and non-destructive characteristics, and at the same time, the surface density can be measured, so it is an important position in thin film analysis.

  As an RBS measuring apparatus, a measuring apparatus having a resolution in the depth direction of about 1 nm has been recently disclosed (see Patent Document 1). This apparatus can analyze deep position information with high energy resolution using a high energy ion beam. A scattered ion detector, an aperture, and a sample are disposed on the incident beam axis from the upstream side in the incident direction, and a magnetic field parallel to the incident beam axis is applied. The scattered ion detector and the aperture have an opening at the center thereof, and the incident beam can pass through the opening to irradiate the sample. The scattered ions back-scattered from the sample irradiated with the ion beam are converged by the magnetic field, and the scattered ions passing through the aperture opening are detected by the detector. When the magnetic field strength, the sample position, or the position between the aperture and the detector is changed, only the scattered ions having a certain energy can be detected by the detector, so that the energy spectrum of the scattered ions can be measured.

Japanese Patent No. 3273844

However, although the RBS apparatus can measure the number of atoms in the thin film with high resolution, when the composition of the thin film has a concentration gradient in the depth direction, there is a problem that it cannot be determined at which position in the depth direction the target atom is present. It was.
The present invention has been made in view of such circumstances, and an object thereof is to provide a thin-film evaluating how can measure the composition and density distribution in the depth direction.

One aspect of the present invention (shown in example 1, a thin film 3) evaluation of thin film layers of a depth direction of the index of a thin film of the evaluated possess properties different from the thin film of the evaluation A step of generating a laminated body in which a thin film for an indicator is arranged, a step of cutting the laminated body in a depth direction of the thin film to be evaluated and cutting out a thin piece, and a cross section of the cut out thin piece observed with a transmission electron microscope The step of obtaining the thickness of the thin film to be evaluated and the thin film for index by measuring the length, and the energy value of the atomic ions that are scattered forward or backward when the surface of the laminate is irradiated with high-energy atomic ions It was measured, and a film thickness of the thin film and the index thin film of the evaluation obtained from the flakes and the energy value, and a step of evaluating the depth direction of the thin film of the evaluation Thin film evaluation method characterized the door is.
Elemental analysis by detecting the contrast difference between the transmission electron image and reflection electron image of the laminate, or characteristic X-rays generated by electron beam irradiation, or elemental analysis by detecting transmission electron beam energy loss, It is also possible to distinguish between the thin film to be evaluated and the thin film for index.
As an evaluation item of the thin piece of the laminate, the composition and density in the depth direction of the thin film may be obtained.
The thin film to be evaluated may be an inorganic compound having a metal or a metalloid.

The inorganic compound constituting the thin film to be evaluated may be a metal, a semi-metal group, an alloy, an oxide, a nitride, a carbide, or a sulfide.
The indicator thin film may be an inorganic compound made of a metal or a metalloid different from the element contained in the thin film to be evaluated.
The inorganic compound constituting the indicator thin film may be a metal or a semimetal alone, an alloy, an oxide, a nitride, a carbide, or a sulfide.

The thin film and the index for the thin film to be evaluated, not good to be those that are deposited by sputtering.

  According to one embodiment of the present invention, an index thin film layer serving as an index is formed in a thin film, and the thin film is divided in the cross-sectional direction by the index film layer, thereby having a concentration gradient or density difference in the depth direction It is possible to measure the composition and density distribution with high resolution.

It is sectional drawing which shows the structure of the structure for thin film evaluation applied to embodiment of this invention. It is a figure explaining the laminated structure of the thin film 3 and the ultra-thin film 4 among the structures for thin film evaluation.

Embodiments of the present invention will be described below with reference to the drawings.
<Structure of evaluation structure>
FIG. 1 is a configuration diagram showing an example of a thin film evaluation structure 1 according to the present invention, and is a side view.
As shown in FIG. 1, the thin film evaluation structure 1 has a structure in which a thin film 3 to be evaluated is formed on a substrate 2 and an ultrathin film 4 serving as an index is formed in the middle of the thin film 3. Yes. That is, as shown in FIG. 1, the thin films 3 to be evaluated and the ultrathin films 4 that are thinner than the thin films 3 and are the indicators are alternately stacked.
Here, examples of the material of the substrate 2 include glass, metal, or resin.

FIG. 2 is a diagram for explaining a laminated structure of the thin film 3 and the ultrathin film 4.
The first thin film layer 31 is formed by a sputtering method. In the case where the first thin film layer 31 is an insulating film such as SiO2, it is desirable to form the film by a radio frequency (RF) sputtering method or an ion beam sputtering method in order to avoid charging of the target surface. In the case where the first thin film layer 31 is a conductive film such as a single metal or an alloy, it can also be formed by direct current (DC) sputtering.

  When the first thin film layer 31 is formed, the sputtering of the first thin film layer 31 is stopped, and then the first ultra thin film layer 41 is sputtered on the first thin film layer 31. . When the first ultrathin film layer 41 is an insulating film, it is formed by RF sputtering or ion beam sputtering as with the first thin film layer 31, but the first ultrathin film layer 41 is a conductive film. In this case, as with the first thin film layer 31, the film can be formed by DC sputtering.

The composition of the first ultrathin film layer 41 is made of an element different from the elements constituting the first thin film layer 31 so as not to affect the composition and density of the second thin film layer 32 formed thereafter. The film thickness is thinner than the first thin film layer 31, and preferably 5 nm or less.
Next, the second thin film layer 32 is formed on the formed first ultra thin film layer 41. The second thin film layer 32 is formed in the same manner as the first thin film layer 31.

Subsequently, a second ultrathin film layer 42 is formed on the second thin film layer 32. The film forming method is performed in the same manner as the first ultrathin film layer 41. In this way, by forming the thin film layer and the ultra thin film layer alternately, the thin film evaluation structure 1 in which the thin film 3 and the ultra thin film 4 are alternately stacked is manufactured.
In addition, as the thin film 3 to be evaluated, a metal, an inorganic compound having a metalloid, or the like can be applied. As the inorganic compound, a metal, a semimetal, a simple substance, an alloy, an oxide, a nitride, a carbide, a sulfide, or the like can be used.

  Moreover, as the ultrathin film 4 serving as an index, an inorganic compound made of a metal or a semimetal different from the element contained in the thin film 3 can be applied. As the inorganic compound, a simple substance of metal or metalloid, an alloy, an oxide, a nitride, a carbide, or a sulfide can be used. Note that it is preferable that the ultrathin film 4 has a different film thickness in each layer because it is easy to distinguish each layer.

<Evaluation method>
The evaluation method for determining the composition and density in the depth direction of the thin film according to the present invention uses the thin film evaluation structure 1 and the thin film 3 by observing a cross-sectional slice of the thin film evaluation structure 1 with a transmission electron microscope. In addition, after obtaining the film thickness information of the ultrathin film 4, the energy value of the backscattered atomic ions when the thin film evaluation structure 1 is irradiated with the high energy atomic ions is measured, and the information of both is superimposed. It is realized with.

  Specifically, the thin-film evaluation structure 1 is observed by a transmission electron microscope by cutting out a cross-sectional slice with FIB or the like. In the transmission electron microscope image, since the contrast is generated when the constituent elements are different, the thin film 3 and the ultrathin film 4 are recognized separately, and the respective film thicknesses can be measured. If it is difficult to generate contrast, the thin film 3 and the ultrathin film 4 may be separated into layers by EDX (energy dispersive X-ray spectroscopy) installed in a transmission electron microscope. Further, the thin film 3 and the ultrathin film 4 may be discriminated using elemental analysis by detecting transmission electron beam energy loss.

  Moreover, the structure 1 for thin film evaluation can obtain | require the energy value of the backscattered atomic ion by irradiating the surface with the high energy atomic ion. Light element ions such as H + ions and He + ions are used as incident ions. The incident energy of light element ions is preferably 1 MeV or less in consideration of the energy resolution of measurement. In addition, the incident angle and scattering angle of light element ions are limited by the incident energy and the composition and film thickness of the thin film 3 and ultrathin film 4, and are adjusted accordingly.

The energy spectrum obtained by the backscattering of atomic ions has different energy values depending on whether the energy spectrum is scattered by the element contained in the thin film 3 or the element contained in the ultrathin film 4, and therefore differs depending on the existing element. A peak appears at the position.
At this time, since the scattered energy by each element attenuates with the depth direction of the film, the energy spectrum has a certain width. Furthermore, in the depth direction of the thin film 3 and the ultrathin film 4, the peak intensity of each element changes depending on the position where each element exists, so that the energy intensity extremely decreases in a region where no element exists.

That is, the light element ion energy spectrum scattered by the elements contained in the thin film 3 has peaks and valleys, and the portion corresponding to the peak portion of the spectrum shows the element distribution contained in the thin film 3.
Further, the density is calculated by dividing the surface density of the thin film 3 obtained from this distribution by the film thickness obtained by observation with a transmission electron microscope.
In this way, by forming the ultrathin film 4 as an index in the thin film 3 and dividing the thin film 3 in the cross-sectional direction by the ultrathin film 4, it is possible to evaluate the composition and density distribution in the depth direction with high resolution. It becomes.

Next, specific examples of thin film composition and density evaluation realized based on the above embodiment will be described.
First, a thin film evaluation structure 1 was prepared.
A triacetyl cellulose (TAC) sheet was used for the substrate of the thin film evaluation structure 1, and aluminum oxide (AlOx) was formed as the thin film 3 by a sputtering method. An Al target was used as a target, and a film was formed by using a magnetron sputtering apparatus as a sputtering apparatus.

  The TAC sheet was placed on the substrate holder in the film forming chamber of the sputtering apparatus, held at 100 ° C., and the apparatus was sealed, and then evacuated with a vacuum pump. Ar and oxygen (O 2) as discharge gases were introduced into the sputter deposition chamber with their flow rates adjusted by a mass flow controller. The film was formed for 1 minute while the discharge power of the DC power supply was 2.5 kW, the argon gas was 50 sccm, the oxygen gas was 50 sccm, and the pressure in the film formation chamber was maintained at 0.5 Pa. The film thickness of the formed aluminum oxide AlOx was about 6 nm as indicated by a film thickness meter using a crystal resonator.

Subsequently, titanium metal (Ti) was deposited as an ultrathin film 4 using a Ti target attached to the same macetron sputtering apparatus as the aluminum oxide AlOx film. Sputter film formation was performed using argon Ar as a discharge gas. The sputtering film formation was performed for 30 seconds while the discharge power of the DC power source was 2.5 kW, the flow rate of argon gas was 100 sccm, the pressure in the film formation chamber was maintained at 0.5 Pa. The film thickness of the formed Ti was 2 nm as indicated by a film thickness meter using a crystal resonator.
Subsequently, in the same manner as described above, 6 nm of aluminum oxide AlOx was formed on the TAC sheet on which Ti was formed, and further 2 nm of Ti was formed, and finally 6 nm of aluminum oxide AlOx was formed. Thereby, the structure 1 for thin film evaluation of this invention was created.

  Next, in order to obtain the film thickness of the aluminum oxide AlOx, the prepared thin film evaluation structure 1 was observed by a transmission electron microscope. The thin film evaluation structure 1 was cut by FIB in the depth direction of the thin film evaluation structure 1 with a gallium (Ga) ion beam, and a thin piece of about 0.1 μm was cut out. When this thin piece was observed and photographed with a transmission electron microscope, three layers of aluminum oxide AlOx and two layers of Ti could be clearly separated by the contrast of the image in a bright field image. From this image, when the film thickness of the aluminum oxide AlOx was measured, the first aluminum oxide AlOx counted from the substrate side was 6.1 nm, the second aluminum oxide AlOx was 6.0 nm, and the third aluminum oxide was measured. AlOx was 6.0 nm.

Next, in order to obtain the composition of aluminum oxide AlOx, the produced thin film evaluation structure 1 was subjected to RBS analysis. A He + ion beam was used as incident ions, and evaluation was performed under conditions of an incident energy of 500 keV, a beam current of 15 nA, an incident amount of 240 μC, an incident angle of 45 degrees, and a scattering angle of 90 degrees. At this time, the composition of aluminum oxide AlOx was counted from the substrate, the first AlOx was x = 1.8, and the second and third AlOx were x = 1.4.
Further, at this time, when the density of the aluminum oxide AlOx is calculated based on the film thickness information obtained from the observation length measurement of the transmission electron microscope, the first aluminum oxide AlOx is 2.4 g / cm 2 counted from the substrate side. The second and third aluminum oxides AlOx were 2.9 g / cm3.

Thus, by the evaluation method of the present invention, the result was different from the composition and density of aluminum oxide AlOx at the initial stage of sputtering film formation and that of aluminum oxide AlOx with a film grown to some extent.
The embodiment of the thin film evaluation structure 1 made of a laminate according to the present invention has been described in detail with reference to the drawings, but the specific configuration of the present invention is not limited to the contents of the above-described embodiment. Even if there is a design change or the like without departing from the gist of the present invention, these are included in the present invention.

DESCRIPTION OF SYMBOLS 1 Structure for thin film evaluation 2 Substrate 3 Thin film 31 First thin film layer 32 Second thin film layer 4 Ultra thin film 41 First ultra thin film layer 42 Second ultra thin film layer

Claims (8)

Generating a laminate in which an index thin film having a property different from that of the evaluation target thin film and serving as an index in the depth direction of the evaluation target thin film is disposed between layers of the evaluation target thin film;
  Cutting the laminate in the depth direction of the thin film to be evaluated to cut out a slice; and
  Obtaining a film thickness of the thin film for evaluation and the thin film for indicator by observing and measuring the cross section of the sliced piece with a transmission electron microscope; and
  When the surface of the laminate is irradiated with high-energy atomic ions, the energy value of atomic ions that are scattered forward or backward is measured, and the film thickness of the evaluation target thin film and the indicator thin film obtained from the flakes And evaluating the depth direction of the thin film to be evaluated from an energy value. Elemental analysis by detecting the contrast difference between the transmission electron image and reflection electron image of the laminate, or characteristic X-rays generated by electron beam irradiation, or elemental analysis by detecting transmission electron beam energy loss, The thin film evaluation method according to claim 1 , wherein the thin film to be evaluated is discriminated from the thin film for index. As evaluation items of a thin film of the evaluation object, a thin film evaluation method according to claim 1 or 2, characterized in that to determine the composition and density in the depth direction of the thin film. The thin film evaluation method according to any one of claims 1 to 3, wherein the thin film to be evaluated is an inorganic compound having a metal or a metalloid. The inorganic compound constituting the film of the evaluation object, according to claim 4, characterized in that a metal or semi-metal single or alloy, or oxide, or nitrides or carbides or sulfides Thin film evaluation method. The index thin film is a thin film evaluation method according to claim 4 or claim 5, characterized in that the elements contained in the thin film of the evaluation is an inorganic compound made of different metal or metalloid. The inorganic compound constituting the thin film for the indicator, thin film according to claim 6, characterized in that the metal or elemental metalloid, or alloys or oxides, or nitrides or carbides or sulfides Evaluation method. The evaluation thin film and the indicator for thin film target, a thin film evaluation method as claimed in any one of claims 7, characterized in that it is formed by a sputtering method.

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