JP6331960B2 - Thin film sample pretreatment method and analysis method - Google Patents

Description

  The present invention relates to a sample pretreatment method and an analysis method. Specifically, the present invention relates to a pretreatment method for removing an organic substance attached to a sample surface using a cluster ion beam and a method for analyzing a sample using the pretreatment method.

  X-ray photoelectron spectroscopy (hereinafter also referred to as XPS) makes X-rays incident on a sample and analyzes the kinetic energy of photoelectrons excited by the photoelectric effect, thereby allowing the sample surface (for example, from the surface to a depth of several nm). This is an analytical method that can acquire elemental information on the region) and information on its chemical bonding state. In XPS, by analyzing the binding energy of the core level for a wide range of elements from Li to U, it is possible to analyze the chemical bonding state of the elements constituting the sample. Furthermore, semi-quantitative composition analysis of the sample is possible by using the relative sensitivity coefficient. As a result, XPS has been applied to material analysis in a wide range of fields.

  However, since information obtained by XPS is limited to the extreme surface of the sample, there is a problem that not only information on the elements constituting the sample but also information on contaminants attached to the sample surface is obtained. In particular, contaminated organic substances composed of carbon and oxygen adhering from the atmosphere often adhere to the sample surface even when the sample is handled with great care. Such contaminating organic matter reduces the peak intensity of the element in the target sample. In addition, the presence of contaminating organic matter also affects the composition analysis result of the sample, and depending on the element, the chemical state may be affected.

  For example, in an oxide transparent conductive thin film used for touch panel applications and the like, the degree of oxygen vacancies inside the oxide is an important factor in expressing its electrical characteristics. Therefore, in order to discuss electrical characteristics, a method of analyzing the ratio between oxygen and metal elements and the chemical state of metal elements is important. Since such a transparent oxide conductive thin film is a thin film, it is difficult to apply a method such as a chemical analysis method or a fluorescent X-ray method, and an analysis method with a shallow information depth such as XPS. It is necessary to analyze.

  However, when analyzed by a surface sensitive analysis method such as XPS, as described above, it is affected by organic contaminants adhering to the sample surface, and results of semi-quantitative composition analysis, especially oxygen semi-quantitative analysis results. In addition to the information inherent to the sample, information on oxygen derived from contaminating organic substances is included, making it difficult to evaluate the original oxygen / metal ratio of the sample.

In order to evaluate the original oxygen / metal ratio of the sample, it is necessary to remove contaminants on the sample surface. Therefore, in order to perform analysis while excluding the influence of such contaminants, various pretreatment methods are used in XPS. For example, there are a method of cleaving a sample in a high vacuum in an XPS apparatus and measuring an exposed new surface (Non-Patent Document 1) and a method using ion sputtering (Non-Patent Document 1). The ion sputtering referred to here is an electron having an energy of about 100 eV discharged from a hot filament into argon (Ar) gas at a low pressure (about 1 × 10 ⁻³ Pa) using an ion gun attached to the apparatus. And Ar is positively ionized, then Ar ions are accelerated by applying a voltage of 0.5 to 5 kV in the direction of the target, and in the XY direction on a plane perpendicular to the direction of Ar ion travel. In this method, ions are focused on a certain region by applying an appropriate voltage, collide with a target, cause a sputtering phenomenon, etch the sample surface, and remove the surface layer portion of the sample as well as contaminants.

  However, the method of cleaving the sample in the XPS apparatus has a problem that the sample needs to be a bulk sample having a certain size and cannot be applied to a thin film sample having a film thickness of several tens to several hundreds of nm. Even if the sample can be cleaved, the process required for the cleavage takes time, and as a result, the analysis takes time. In addition, although the method using ion sputtering can remove contaminating organic substances, even the oxide constituting the sample is reduced by selective sputtering on the surface of the sample. As a result, the oxygen / metal ratio before and after sputtering is reduced. There was a problem of changing (Non-Patent Document 2). As described above, in the analysis by XPS, the actual oxygen / metal ratio of a sample in a thin film sample (for example, an oxide transparent conductive film) cannot be evaluated correctly.

Japan Surface Science Society, "X-ray photoelectron spectroscopy", Maruzen Publishing Co., Ltd. Journal of Surface Analysis, Vol. 10, No. 3 (2003), p. 230-236

  The present invention has been made in view of the above situation, and a sample pretreatment method capable of removing organic matter adhering to the surface of a sample composed of an inorganic material without damaging the sample, and a sample using the pretreatment method It is an object of the present invention to provide a method for analyzing a sample after removing organic substances on the surface.

  The present inventor made the reverse idea of removing only the organic matter adhering to the surface of the sample without damaging the sample while using sputtering which is a technique for cutting the sample. That is, it is a technique in which inorganic substances such as oxides are hardly sputtered and only organic substances are sputtered.

  In order to apply this method, the sputtering depth (sputter rate) per unit time may be increased for organic substances and decreased for inorganic substances. Since the sputtering rate of a monoatomic ion beam on an organic sample is very large, the present inventor first reduces the energy of a monoatomic ion constituting the monoatomic ion beam (for example, lowers the acceleration voltage). It was considered that the sputter rate of the inorganic substance can be reduced while maintaining the sputter rate of the organic substance at a large value.

  However, actually, surprisingly, even when the acceleration voltage is lowered, the sputtering rate of the inorganic material becomes a relatively large value, and the ratio of the sputtering rate indicating the sputtering rate of the organic material to the sputtering rate of the inorganic material becomes 2 or less. Obtained. In other words, an unexpected finding was obtained that when the organic substance is removed, the inorganic substance is also removed to some extent.

  Therefore, the present inventor conducted a study based on this knowledge on the premise that the inorganic material is not damaged, and as a result, by using the cluster ion beam used for sputtering of the organic material, the above-described sputtering rate ratio is increased. The present inventors have found that only an organic substance can be removed without damaging a sample composed of an inorganic substance, and the present invention has been completed by solving the above problems.

That is, the first aspect of the present invention is a method for pretreating a thin film sample composed of an inorganic substance using sputtering, and is composed of an organic substance corresponding to the sputtering rate of an inorganic standard sample composed of an inorganic substance. If the sputtering rate of the organic standard sample that is sputter rate ratio, the sputtering rate ratio as a thin film of the sample by sputtering condition that 5 or more was irradiated with argon gas cluster ion beam deposited in a thin film of the sample organics A thin film-like sample pretreatment method characterized by selectively removing the thin film sample.

  In the first aspect, the sputtering rate ratio is preferably 200 or less.

The thin-film second aspect of the present invention, characterized in that analyzing the thin film of the thin film-shaped sample subjected to pretreatment by the pretreatment method of the sample according to any of the first aspect of the This is a method for analyzing a sample.

Said 2nd aspect WHEREIN: It is preferable to analyze the thin film-shaped sample which performed the pre-processing using X-ray photoelectron spectroscopy.

In the second aspect, it is preferable that the thin film sample contains a metal oxide, and the abundance ratio of oxygen and metal in the metal oxide is analyzed.

  According to the present invention, a sample pretreatment method capable of removing organic matter adhering to the surface of a sample composed of an inorganic material without damaging the sample, and organic matter on the sample surface is removed using the pretreatment method. And a method for analyzing a sample afterwards.

FIG. 1 is a process diagram of a sample pretreatment method and analysis method according to this embodiment. 2 (a) is a perspective view of a standard sample, FIG. 2 (b) is a perspective view of an aluminum foil for forming a shielding region, and FIG. 2 (c) is shown in FIG. 2 (b). FIG. 2D is a perspective view of the standard sample shown in FIG. 2C viewed from the Z-axis direction. FIG. 3 (a) is a perspective view of a standard sample in which a recess is formed by sputtering, and FIG. 3 (b) is a schematic cross-sectional view of the standard sample along the line IIIa-IIIa in FIG. 3 (a). FIG. 3C is a schematic cross-sectional view of the concave portion of the standard sample in which the shielding region is not formed as viewed from the X-axis direction. FIG. 4 is a diagram showing XPS spectra (carbon 1s spectra) of the surface of an indium oxide-based thin film sample before and after sample pretreatment in an example of the present invention. FIG. 5 is a diagram showing XPS spectra (oxygen 1s spectra) of the surface of an indium oxide thin film sample before and after sample pretreatment in an example of the present invention. FIG. 6 is a diagram showing XPS spectra (indium 3d _5/2 spectrum) of the surface of an indium oxide-based thin film sample before and after sample pretreatment in an example of the present invention.

Hereinafter, the present invention will be described in detail in the following order based on embodiments shown in the drawings.
1. Sample pretreatment method 1-1 Sample 1-2 Standard sample 1-3 Sputter rate ratio calculating step 1-3-1 Shielding region forming step 1-3-2 Sputtering step 1-3-3 Sputtering depth measuring step 1- 3-4 Sputter rate ratio calculation step 1-4 Organic matter removal step 2. 2. Sample analysis method Effect of the present embodiment 4. Modified example

(1. Sample pretreatment method)
The sample pretreatment method according to the present embodiment mainly includes a step of calculating a sputtering rate ratio using two types of standard samples, a step of removing organic substances attached to the sample based on the calculated sputtering rate ratio, including. The pretreatment method will be described with reference to the process diagram shown in FIG.

(1-1 sample)
First, a sample for pretreatment is prepared. The sample is not particularly limited as long as it is made of an inorganic material, but in this embodiment, the sample is made of a metal oxide. The metal constituting the metal oxide is not particularly limited as long as it is a metal capable of forming an oxide. The metal oxide may be an oxide composed of one kind of metal or a complex oxide composed of two or more kinds of metals. In the present embodiment, the sample is a thin film sample. The lower limit of the thickness of the thin film is 20 nm. This is because if the thickness of the thin film becomes smaller than the lower limit value, depending on the sample analysis method described later, a lot of ground information is included in the analysis result, and an accurate analysis result may not be obtained. Moreover, the upper limit of the thickness of a thin film is 1 mm, and is normally 100 micrometers or less.

  Note that the chemical bond state and composition ratio (oxygen / metal ratio) of the sample are examined by XPS analysis in the sample analysis method described later. An organic substance composed of carbon, oxygen, hydrogen or the like is usually unavoidably attached to the surface of such a sample. Therefore, if the above analysis is performed without any allowance, peaks due to chemical bonds in these organic substances will be observed. In addition, oxygen derived from organic matter also affects the calculation of the composition ratio due to chemical bonds in the sample.

(1-2 Standard sample)
Subsequently, a standard sample is prepared. The standard sample is a sample used for calculating the sputtering rate. In this embodiment, the standard sample composed of an organic material (organic standard sample) and the standard sample composed of an inorganic material (inorganic standard sample). And two kinds of standard samples are used. As will be described later, the sputtering rate (nm / min) is obtained as a value obtained by dividing the sputtering depth (nm) by the sputtering time (min).

  The structure (skeleton, substituent, molecular weight, etc.) of the organic substance constituting the organic standard sample may be different from the structure of the organic substance adhering to the sample, but in this embodiment, it is the same as the structure of the organic substance constituting the organic specimen. Or it is preferable that it is similar. By approximating the structure of the organic matter constituting the organic matter standard sample to the structure of the organic matter adhering to the sample, the sputter rate of the organic matter standard sample can increase the approximation accuracy of the sputter rate of the organic matter adhering to the sample. In the present embodiment, the organic standard sample is composed of an organic polymer material such as polyimide or polyethylene terephthalate (PET). In this specification, “similar” means, for example, a case where an alkyl group is included as a substituent and the number of carbons in the alkyl group is different.

The structure (composition, crystal structure, etc.) of the inorganic substance constituting the inorganic standard sample is preferably the same as or similar to the structure of the inorganic substance constituting the sample, like the organic standard sample, but the inorganic substance has a different structure. However, since the sputter rate does not change as much as the organic substance, the inorganic substance constituting the inorganic standard sample and the inorganic substance constituting the sample may be different. In this embodiment, a standard sample that is usually used for measuring the sputtering rate is used. Specifically, a standard sample composed of a SiO ₂ thin film formed on a Si substrate or a Ta ₂ O ₅ thin film formed on a Ta substrate is exemplified as an inorganic standard sample.

  The dimension of the standard sample is not particularly limited as long as it is a size that can be installed in an apparatus used for calculating the sputtering rate.

(1-3 Sputter rate ratio calculation process)
First, for the organic standard sample and the inorganic standard sample, the sputtering rate when a cluster ion beam is used is calculated, and the sputtering rate ratio is calculated from the calculated sputtering rate. For the inorganic standard sample, the sputtering rate may be calculated by a method of measuring the time required to penetrate a standard sample having a known thickness by sputtering. In this embodiment, at least the organic standard sample is preferably subjected to the following steps in order to accurately calculate the sputtering rate.

(1-3-1 Shielding Region Forming Step S10)
First, a standard sample is placed on the sample holder shown in FIG. 2A, and the surface of the standard sample 1 held on the sample holder 2 is irradiated with a cluster ion beam and sputtered, and the cluster ion beam. And a shield region that is not irradiated and sputtered.

  The method for forming the shielding region is not particularly limited, and may be formed by a known method. In the present embodiment, the shielding region is formed by masking the surface of the standard sample. Specifically, a sputter region and a shielding region are formed by covering the surface of the standard sample with a film-like substance from which a predetermined range shown in FIG. 2 (c)). The film-like substance is not particularly limited as long as it is a substance with little surface contamination, but in the present embodiment, aluminum foil is preferable from the viewpoints of availability, ease of forming holes, and the like.

(1-3-2 Sputtering step S20)
Subsequently, the sample holder 2 including the standard sample 1 in which the sputter region 11 and the shielding region 12 are formed is introduced into the sputtering apparatus to perform sputtering.

  As shown in FIG. 2C, since the surface of the standard sample 1 is covered with the aluminum foil 3 having the hole 4 formed in the center, the surface of the standard sample is composed of the sputter region 11 and the shielding region 12. The In the sputtering step S20, this standard sample is irradiated with a cluster ion beam from the Z-axis direction, and the standard sample is sputtered. In this embodiment, as shown in FIGS. At least a part of the boundary 13 between the sputter region 11 and the shielding region 12 in the XY plane is included in a range 20 (hereinafter also referred to as a raster range 20) for scanning a cluster ion beam used for sputtering. 2C and 2D, the hatched portion indicates the raster range 20, and the entire boundary 13 is included in the raster range 20.

  By doing in this way, the sputtering depth of the recessed part formed by sputtering the sputter | spatter area | region 11 can be accurately calculated in the sputtering depth measurement process mentioned later. In addition, the maximum diameter (Ds) of the sputter region 11 is preferably less than or equal to half the maximum diameter (Dr) of the raster range 20. By doing in this way, the measurement error of sputtering depth can be made small.

  The sputtering apparatus may be an apparatus attached to another analysis apparatus (for example, an X-ray photoelectron spectrometer), or may be a single apparatus.

  In this embodiment, a cluster ion beam is used as the ion beam used for sputtering. In order to achieve the purpose of selectively removing organic substances adhering to a sample composed of an inorganic substance, an ion beam having a low sputter rate for an inorganic standard sample and a large sputter rate for an organic standard sample is used. This is because the present inventor found for the first time that it is a cluster ion beam. In other words, for inorganic materials, the binding state of the constituent elements is preserved, and while the ion beam can be sputtered with low damage so that a damage layer does not occur, for organic materials, bonding between the elements is broken to eliminate adhesion to the sample surface. It is an ion beam that satisfies the condition that it is possible to give as much energy as possible.

  Whether or not the above conditions are satisfied is determined by whether or not the sputter rate of the organic standard sample with respect to the sputter rate of the inorganic standard sample (hereinafter also referred to as a sputter rate ratio) is a predetermined value or more. In the present embodiment, the sputtering rate ratio is 5 or more. Although the upper limit is not particularly limited, the setting value of the acceleration voltage of the argon gas cluster ion gun attached to the commercially available XPS apparatus is normally 20 kV at the maximum, and the sputtering rate ratio at this time is about 200. In the embodiment, the upper limit of the sputtering rate ratio is 200. If the sputtering rate ratio satisfies the above range, the organic substance is much easier to remove than the inorganic substance, and therefore selective sputtering is possible. Here, “selective sputtering” means that elements constituting the sample are hardly removed by sputtering, and organic substances adhering to the sample surface are removed by sputtering. Therefore, this “selective sputtering” does not mean that the elements constituting the sample that are easily removed by sputtering are sputtered and those that are difficult to remove by sputtering remain in the sample.

  Such a sputter rate ratio cannot be realized by a monoatomic ion beam such as an Ar monoatomic ion beam, but can be realized only by a cluster ion beam. When a monoatomic ion beam is used, the sputtering rate of organic matter becomes very large, but the sputtering rate of inorganic matter also becomes relatively large, and as a result, the sputtering rate ratio when using a monoatomic ion beam (of organic matter) (Spatter rate / spatter rate of inorganic substance) is unexpectedly low, for example, 2 or less. This is a finding that the present inventors have found for the first time.

  When the sputtering rate ratio is low, the inorganic material is damaged when the organic material is removed, and therefore selective sputtering that removes only the organic material cannot be performed.

  On the other hand, in the cluster ion beam, the sputtering rate of the inorganic substance remains very low and the sputtering rate of the organic substance becomes high, so that the sputtering rate ratio can be 5 or more. In particular, when the acceleration voltage is increased, the sputter rate of the organic substance is rapidly increased although the sputter rate of the inorganic substance is not increased so much. As a result, the sputtering rate ratio also increases rapidly, which is more advantageous for selective sputtering.

  The reason why the range of the sputtering rate ratio defined by the present invention cannot be realized by a monoatomic ion beam and only a cluster ion beam can be realized is unknown, but the present inventor presumes as follows. In other words, since each ion constituting a monoatomic ion beam has a large energy, even if it is an organic substance or an inorganic substance, collisions between constituent atoms occur continuously when ions enter the inside of them. Finally, atoms present on the surface are released (sputtered) from the surface. Therefore, when such collision between atoms occurs continuously, it is considered that the sputtering rate does not change so much whether it is an organic substance or an inorganic substance.

  On the other hand, in the cluster ion beam, when the cluster collides with the surface of the organic or inorganic material, it is considered that the bonds between the elements existing on the surface are broken. The energy of each ion constituting the cluster ion beam is much smaller than the energy of each ion constituting the monoatomic ion beam. Therefore, in the sputtering by the cluster ion beam, it is considered that the bonds between the constituent elements of the organic substance, which require a relatively small energy for cutting, are easily cut, whereas the bonds between the constituent elements of the inorganic substance are difficult to cut. As a result, it is considered that the spatter rate of the inorganic substance can be kept small although the spatter rate of the organic substance becomes large.

The cluster ion beam, argon gas cluster ion beam _(Ar-GCIB), but _{C 60} cluster ion beam and the like, in the present embodiment using Ar-GCIB. C ₆₀ cluster ion beam are the cluster ion beam of carbon atoms, can cause some C ₆₀ during sputtering remaining in the sample, possibility of organic material of the fullerene from influences the composition ratio or the like of the sample Because there is.

  The sputtering rate mainly depends on the acceleration voltage of the cluster ion beam, the sputtering time, and the like. For example, the higher the accelerating voltage, the more rapidly the sputter rate of the organic standard sample tends to increase. As the sputtering time is longer, the sputtering rate tends to increase. However, depending on the condition of the acceleration voltage, the sputtering rate may be saturated even if the sputtering time is increased.

  Therefore, in order to set the sputtering rate ratio to 5 or more, it is preferable to keep the sputtering rate of the inorganic standard sample small by controlling the acceleration voltage and the sputtering time. Moreover, if the sputtering rate ratio is 5 or more as described above, the organic matter adhering to the sample surface by sputtering can be selectively removed, but depending on the kind, amount, bond type, etc. of the adhering organic matter, It is preferable to appropriately control the sputtering rate ratio. In this embodiment, in order to control the sputtering rate ratio, the acceleration voltage is preferably in the range of 2.5 to 20 kV, and the sputtering time is preferably in the range of 6 seconds to 30 minutes. For example, it is preferable to increase the acceleration voltage when the time required for removing organic substances is short, and the acceleration voltage may be decreased when priority is given to less damage to the sample.

  In the sputtering step S20, Ar-GCIB emitted from the ion gun of the sputtering apparatus is accelerated in the Z-axis direction, and Ar-GCIB collides with the surface of the standard sample to repel atoms constituting the surface of the standard sample. The standard sample is sputtered. In the present embodiment, as shown in FIGS. 2C and 2D, the shielding region 12 is also included in the range 20 (raster range 20) in which the ion beam is scanned on the XY plane. The actual sputtering range does not coincide with the raster range 20, and only the sputter region 11 is sputtered.

  The sputtering conditions and the sputtering time for calculating the sputtering rate ratio are the same for the organic standard sample and the inorganic standard sample.

  After the sputtering is completed, the standard sample is taken out and the aluminum foil is removed. In the standard sample 1 from which the aluminum foil has been removed, only the sputter region is shaved by sputtering, and as shown in FIG. 3A, the sputter region forms a crater-like recess 14.

(1-3-3 Sputtering depth measurement step S30)
In the sputtering depth measurement step S30, the difference (distance in the Z-axis direction) between the height of the surface of the recess 14 and the height of the non-sputtered region (shielding region 12) is measured, and this is used as the sputtering depth. That is, the sputtering rate is not actually calculated from the sputtering time required for penetrating a standard sample with a known thickness as in the prior art, but the sputtering depth is actually measured to calculate the sputtering rate.

  In FIG. 3B, which is a schematic cross-sectional view of the vicinity of the concave portion 14 of the standard sample 1 after sputtering, a boundary 13 a between the concave portion 14 and the non-sputtered region 12 (12 a) is defined as a shielding region 12 and a sputter region 11. It almost coincides with the boundary 13 between. Further, as is apparent from FIG. 3B, the recess 14 formed by sputtering and the non-sputtered shielding region 12a in the vicinity of the boundary 13a can be distinguished very clearly. That is, the step between the recess 14 and the shielding region 12 stands out. This is because at least a part of the boundary 13 between the shielding region 12 and the sputter region 11 is included in the raster region 20, and as a result, within the raster region 20 in the vicinity of the actually sputtered region (recess 14). This is because there is a shielding region 12a that is not sputtered.

  On the other hand, when the shielding region is not formed, as shown in FIG. 3C, not only the region where sputtering is planned (the region included in the raster range 20) but also the peripheral portion of the region. In addition, the region 15 that is not included in the raster range 20 may be sputtered. Since the organic matter is easily sputtered, a part of the region where sputtering is not scheduled, that is, a region outside the raster range 20 may be sputtered due to the influence of sputtering.

  As a result, the boundary 13b between the region actually sputtered and the region not actually sputtered is gently inclined, and the distinction between these regions becomes ambiguous. In order to accurately measure the sputtering depth, it is necessary to set a reference point for measuring the sputtering depth in a non-sputtered region, that is, the surface of the standard sample. In FIG. This becomes difficult. Then, even if the sputtering depth is measured, a measurement error becomes large, and as a result, an accurate sputtering rate cannot be calculated.

  In addition, when the standard sample is made of an organic substance, the rigidity is low, so that there may be a case where the sample is slack that cannot be visually observed during sputtering. Due to the influence of the sag of the standard sample, it becomes more difficult to distinguish between the sputtered region and the non-sputtered region. In some cases, it becomes difficult to know where the concave portions formed by sputtering are formed. Further, since the raster range is usually on the order of several hundred μm to several mm, the surface roughness and surface waviness of the standard sample also affect the measurement error of the sputtering depth.

  Therefore, as shown in FIG. 3B, the reference point for measuring the sputtering depth can be reliably set on the surface of the standard sample by making the step between the concave portion 14 and the shielding region 12 stand out. it can. The sputtering depth 30 can be accurately measured from the difference between the surface height of the recess 14 and the surface height of the shielding region 12.

  It does not restrict | limit especially as a method of measuring sputtering depth, What is necessary is just to measure with a well-known measuring apparatus. In this embodiment, since the sputtering depth is 1 μm or less, it is preferable to measure with a device having a resolution of nm level. Specifically, a white interferometer, a stylus profilometer, an atomic force microscope, and the like are exemplified.

  When measuring the sputtering depth, it is preferable to measure the difference between the height of the surface of the standard sample (shielding region 12) and the height of the surface of the peripheral edge of the recess 14. By doing in this way, even if it is a case where the whole sample inclines, the measurement error of sputtering depth can be made small.

  Moreover, in sputtering depth measurement process S30, as above-mentioned, sputtering depth can be measured correctly from the level | step difference of the formed recessed part 14 and the shielding area | region 12a.

(1-3-4 Sputter rate ratio calculation step S40)
In the sputtering rate ratio calculating step S40, first, the sputtering depth measured above is divided by the sputtering time, or the thickness of the standard sample is divided by the time required to penetrate the standard sample, The sputter rates of the organic standard sample and the inorganic standard sample are calculated. In addition, since the sputtering rate obtained through the above steps is calculated using the accurately measured sputtering depth, the accuracy is high.

  A sputter rate ratio (sputter rate of organic standard sample / sputter rate of inorganic standard sample) is calculated from the sputter rate of the obtained organic standard sample and inorganic standard sample. If the calculated sputtering rate ratio is less than 5, the sputtering conditions may be changed as appropriate, and S10 to S40 may be repeated until a sputtering rate ratio of 5 or more is calculated.

As specific sputtering rate ratios, the sputtering rates of organic standard samples and inorganic standard samples when using an argon gas cluster ion gun with acceleration voltages of 5 kV and 20 kV, and the sputtering rate ratio calculated from these sputtering rates are as follows: Table 1 shows. For reference, Table 1 also shows each sputtering rate and sputtering rate ratio when using an argon monoatomic ion gun with acceleration voltages of 0.5 kV and 2 kV. For both the argon gas cluster ion gun and the argon monoatomic ion gun, a standard sample composed of polyethylene terephthalate (PET) is used as the organic standard sample, and a thin SiO ₂ film is formed on the Si substrate as the inorganic standard sample. Standard samples prepared are used.

  From Table 1, it can be seen that when the argon gas cluster ion gun is used, the sputter rate of the inorganic standard sample is low and only the sputter rate of the organic standard sample is high. As a result, it is understood that the sputtering rate ratio is 5 or more, and selective sputtering is possible. In particular, it can be seen that the sputtering rate ratio is rapidly increased by increasing the acceleration voltage.

  On the other hand, when an argon monoatomic ion gun is used, the sputter rate of the organic standard sample is increased not only when the acceleration voltage is lowered or increased, but also the sputter rate of the inorganic standard sample is relatively increased. It is getting bigger. As a result, it can be seen that the sputtering rate ratio is low and does not satisfy the scope of the present invention. That is, it can be seen that when an argon monoatomic ion gun is used, selective sputtering cannot be realized, and it is difficult to remove organic substances attached to the sample surface without damaging the sample.

(1-4 Organic substance removal process S50)
In the organic matter removing step S50, the sample to be analyzed is pretreated (removing the organic matter) under the sputtering conditions set based on the sputtering rate ratio (5 or more) calculated in the above step. In this embodiment, the surface of the sample is sputtered by using an argon gas cluster ion gun attached to an X-ray photoelectron spectrometer for XPS analysis to be described later, and only organic substances are removed (selective sputtering). Although the organic matter adhering to the surface of the sample is removed by this sputtering, the sample surface is hardly sputtered and is not damaged. Therefore, the chemical bonding state of the elements near the extreme surface of the sample hardly changes before and after sputtering.

(2. Sample analysis method)
Subsequently, the sample from which the organic matter adhering to the sample surface has been removed by the pretreatment of the sample is analyzed. The analysis method is not particularly limited, but is particularly preferably a method for analyzing the surface of a sample. Specific examples include X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS). The In this embodiment, a surface analysis by XPS is performed on a thin film sample made of a metal oxide.

  In XPS analysis, a sample is irradiated with X-rays, and the energy spectrum of photoelectrons emitted from the sample by the photoelectric effect is measured. And the binding energy of the element which comprises a sample is calculated | required by analyzing the energy spectrum of a photoelectron. Since this binding energy shows a value specific to the element and its bonding state, the element constituting the sample can be identified by analyzing the peak position of the binding energy in the energy spectrum of the photoelectrons. Furthermore, by dividing each obtained peak mathematically and calculating the peak area, the abundance ratio of the constituent elements can be calculated, and a semi-quantitative composition analysis of the sample can be performed. At this time, since the analysis can be performed with the surface of the sample kept clean by the pretreatment described above, an analysis result reflecting only the original information of the sample is obtained. Therefore, for example, the oxygen / metal ratio in the metal oxide constituting the sample can be accurately evaluated.

(3. Effects of the present embodiment)
Organic substances are usually attached to the surface of the sample to be analyzed. Such organic matter affects surface analysis such as XPS. For example, oxygen derived from organic matter may be included in the amount of oxygen in the analysis result of the sample, and the original composition ratio of the sample may not be obtained.

  Therefore, in this embodiment, sputtering is performed using a cluster ion beam in order to remove only organic substances adhering to the surface of the sample and prevent the sample from being damaged. When a cluster ion beam is used, it is possible to remove only organic matter adhering to the sample surface by increasing the spatter rate of the organic matter while keeping the inorganic spatter rate small so as not to damage the sample. it can. In other words, the organic substance adhering to the sample surface composed of an inorganic substance can be selectively sputtered. As a result, when the surface analysis of the sample is performed after such pretreatment (selective sputtering), information such as the chemical bonding state and the composition ratio can be obtained as the original information of the sample.

  This is because only the cluster ion beam can make the sputtering rate ratio within the range of the present invention, and when using a monoatomic ion beam, the sputtering rate ratio cannot be made within the range of the present invention. This is an effect obtained because the inventor has found out the knowledge for the first time.

  In addition, since the constituent elements of organic substances are easily removed by sputtering, it is difficult to accurately calculate the sputtering rate. Therefore, in the present embodiment, when the sputtering rate is calculated, the sputtering depth can be accurately calculated by providing the standard sample with the shielding region and the sputtering region, and the sputtering rate can be accurately calculated. Can be calculated.

(4. Modifications)
In the above embodiment, only the extreme surface of the sample is analyzed, but the depth direction analysis may be performed using sputtering.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the embodiment mentioned above at all, and can be variously modified within the range which does not deviate from the summary of this invention.

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

Example 1
An indium oxide-based oxide transparent conductive thin film sample was fixed to a sample holder attached to an X-ray photoelectron spectrometer (Versa Probe II manufactured by ULVAC-PHI Co., Ltd.) using a double-sided tape. Then, the measurement position on the sample was determined, and XPS analysis was performed in order to obtain each spectrum of C1s, O1s, and In3d _{5/2 in} the vicinity of the surface of the sample before and after pretreatment of the sample. The spectrum acquisition conditions were as follows: X-ray condition: 100 μm 25 W, measurement region: 100 μmφ, Tilt Angle: 45 °, measurement chamber vacuum: 7.0 × 10 ⁻⁷ Pa, PassEnergy: 23.5 eV. The results are shown in FIGS.

  Note that sample pretreatment (removal of organic substances) was performed under the following conditions using an argon gas cluster ion gun attached to the apparatus. Sputtering conditions were: Emission: 20 mA, Ionization: 150 V, Beam: 5 kV, Extractor: 2.8 kV, Focus: 86.8%, Objective: 50.55%, Magnet: 25 A, Bend: −100 V, Wien Deflection: 10. 4 V, Target Pressure: 650 kPa, raster range: 2 mm × 2 mm, sputtering time: 10 minutes.

The sputtering conditions in Table 1 are the same as those in the argon gas cluster ion gun having an acceleration voltage of 5 kV. Therefore, from Table 1, the sputtering depth of organic matter (PET) (sputtering rate × sputtering time) is about 3. The sputter depth of 6 nm and inorganic substance (SiO ₂ ) is assumed to be about 0.3 μm.

From FIG. 4, it was confirmed that the peak of the C1s spectrum almost disappeared before and after sputtering. That is, it is considered that the organic matter adhering to the surface of the sample was removed by the pretreatment (sputtering). Further, from FIG. 5, the peak intensity of O1s derived from In ₂ O ₃ increases before and after sputtering, and the bond between carbon and oxygen (CO, C, C) present on the left shoulder of the O1s peak before sputtering. It was confirmed that the peak of the organic substance derived from = O) disappeared.

Furthermore, it was confirmed from FIG. 6 that the intensity of the In3d _5/2 peak was increased before and after sputtering. Further, it was confirmed that there was no change in the shape of the spectrum, no reduction of indium, etc., and no damage to the sample.

  From Table 2, it was confirmed that carbon was detected before the pretreatment, and organic substances were attached to the surface of the sample. Further, after the pretreatment, it was confirmed that the carbon that had been detected before the pretreatment was not detected, while the oxygen and indium concentrations were increased. This shows that the organic substances adhering to the sample surface by the pretreatment were removed by sputtering, as in FIGS. Further, the ratio of oxygen and indium before and after the pretreatment is changed from 60.6: 39.4 to 58.0: 42.0, and the ratio of oxygen and indium before the pretreatment is changed. It is thought that oxygen derived from organic matter was taken into consideration. That is, it was confirmed that the original information of the sample can be obtained as the composition ratio (oxygen / metal ratio) of indium oxide as the sample by performing pretreatment of the sample to remove the organic matter.

DESCRIPTION OF SYMBOLS 1 ... Standard sample 11 ... Sputtering region 12, 12a ... Shielding region 13, 13a ... Boundary 14 ... Recess 3 ... Aluminum foil 4 ... Hole 20 ... Range which scans an ion beam (raster range)

Claims (5)

A method of pretreating a thin film sample composed of an inorganic material using sputtering,
When the sputtering rate of the organic standard sample composed of organic matter with respect to the sputtering rate of the inorganic standard sample composed of inorganic material is defined as the sputtering rate ratio, argon is added to the thin film sample under the sputtering conditions where the sputtering rate ratio is 5 or more. A pretreatment method for a thin film sample characterized by selectively removing organic substances adhering to the thin film sample by irradiation with a gas cluster ion beam. 2. The thin film sample pretreatment method according to claim 1, wherein the sputtering rate ratio is 200 or less. Method for analyzing thin film sample, characterized by analysis of thin-film sample pretreated by the pretreatment method of a thin film-like sample according to claim 1 or 2. 4. The method for analyzing a thin film sample according to claim 3 , wherein the thin film sample subjected to the pretreatment is analyzed using X-ray photoelectron spectroscopy. The method for analyzing a thin film sample according to claim 3 or 4, wherein the thin film sample contains a metal oxide, and an abundance ratio of oxygen and metal in the metal oxide is analyzed.