JP2011007625A - Standard sample, method of manufacturing the same, and secondary ion mass spectrometry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary ion mass spectrometry for easily and quantitatively measuring concentration distribution of an element to be analyzed of a measuring sample whose base material has two components, a standard sample used for it, and a method of manufacturing the standard sample.SOLUTION: When quantitative determination of the measuring sample of two component base of an element R and an element A is performed, the standard sample used for the secondary ion mass spectrometry is prepared as follows. First, base material composed of the element R is doped with an element M to be measured so as to form known concentration distribution. Then, the base material is doped with an element A so as to form the known concentration distribution including at least a concentration region of 1% or higher, thereby providing the standard sample.

Description

  The present invention relates to a secondary ion mass spectrometry method for measuring the concentration of a trace element in a solid sample and a standard sample used therefor.

  Secondary ion mass spectrometry is often used for the analysis of trace elements such as dopants in semiconductor samples because of its good detection limit. Used to analyze the concentration distribution of trace elements in the depth direction because the sample surface can be etched simultaneously by ion sputtering by using an ion beam as a probe for ionization of elements in the sample to be detected. There are many cases.

  In a secondary ion mass spectrometry method by a known technique, a standard sample is required to perform quantitative analysis of an element in a target sample. For example, to quantify the concentration of an analyte in a sample formed with a matrix, prepare the same matrix and dope the same analyte to a predetermined amount for concentration determination. The standard sample. The sensitivity coefficient of the element to be analyzed in the standard sample is obtained, and converted into a concentration from the secondary ion intensity of the element to be analyzed in the target sample.

At this time, the sensitivity coefficient is usually given from the secondary ion intensity and concentration of the reference element and the element to be analyzed, with the component element having a known concentration in the base material as a reference element (for example, see Non-Patent Document 1). reference.). That is, the reference element R, the known concentration CR of the reference element R, the secondary ion intensity IRi of the isotope Ri of the reference element R, the analyzed element M, the known concentration CM of the analyzed element M, the analyzed Assuming that the secondary ion intensity IMj of the isotope Mj measured for the element M, the sensitivity coefficient K (MR) of the analytical element M with respect to the reference element R is given by the following formula 1.

  Where αMj is the isotope ratio of Mj, αRi is the isotope ratio of Ri, βM is the secondary ion yield IBG of the analyzed element M, and the secondary ion intensity of the isotope Mj measured for the analyzed element M This is the intensity of background noise observed at the same mass position in IMj. The background noise is also mixed in the signal intensity when measuring the secondary ion intensity IRi of the isotope Ri of the reference element R, but as described above, the constituent element whose concentration in the base material is known Is defined as the reference element R, the secondary ion intensity IRi is sufficiently larger than the background noise, and there is almost no influence on the quantification even if the background noise is not subtracted.

Thus, using the sensitivity coefficient K (MR) of the analysis element M with respect to the reference element R obtained from the standard sample, in the actual analysis, the base material is an unknown concentration C′M in the same base material. Is determined by measuring the secondary ion intensity I′Ri of the isotope Ri of the reference element R, the secondary ion intensity I′Mj of the isotope Mj measured for the analyte M, and the background. Using the noise intensity I′BG, the following equation 2 can be used.

Japan Surface Science Society Surface Analysis Technology Selections Secondary Ion Mass Spectrometry Maruzen Co., Ltd. issued in 1999) James F.M. Gibbons, William S .; Johnson, and Steven W. Myloie, Projected Range Statistics-Semiconductors and Related Materials, 2nd Edition-, HALSTED PRESESS, A division of John Wiley & Sons. 1975

As described above, in the secondary ion mass spectrometry method, it is necessary to select the base material of the standard sample according to the target measurement sample. This is because even if the concentration of the element to be quantified is constant, the secondary ion intensity of the element to be analyzed varies greatly depending on the base material. Therefore, as many standard samples as the number of combinations of the target sample base material and the element to be analyzed are required. Further, in an actual measurement sample, the component of the base material of the target region where the concentration distribution is desired is not necessarily one component. For example, when trying to quantify trace elements in a sample using one type of carbon steel as a sample, there are a portion having a composition close to pure iron and a portion having a composition of cementite (Fe ₃ C). In such a case, A huge amount of labor is required to perform a quantitative operation on the portion having each composition as a base material and obtain a concentration distribution from the secondary ion intensity distribution of the element to be analyzed. Furthermore, at the interface portion where the base material switches, the composition is considered to change gradually, the base material component itself is not accurately known, and the base material component of the secondary ionic strength of the element to be analyzed Since the element concentration dependency is unknown, it is difficult to obtain quantitative knowledge about the concentration distribution of the element to be analyzed.

  That is, in the conventional secondary ion mass spectrometry method, when it is desired to obtain the concentration distribution of an analyte element in a sample in which a two-component matrix is present, a quantitative operation is performed on each matrix and the secondary element of the analyte is analyzed. An enormous amount of work is required to obtain the concentration distribution from the ion intensity distribution. Furthermore, in the conventional secondary ion mass spectrometry method, in the interface portion where the base material is switched in the sample of the two-component base material, the base material component itself is unknown and the secondary ion intensity of the element to be analyzed is Since the dependency on the concentration of the base material component element is also unknown, it is difficult to obtain quantitative knowledge about the concentration distribution of the element.

  Therefore, the present invention provides a secondary ion mass spectrometry method capable of easily and quantitatively measuring the concentration distribution of an element to be analyzed in a measurement sample whose base material is a two-component, a standard sample used therefor, and a method for producing the standard sample The purpose is to provide. Here, the concentration refers to the atomic concentration.

  In order to achieve the above object, when quantification is performed with a binary measurement sample of element R and element A, a standard sample used in the secondary ion mass spectrometry method according to the present invention is prepared as follows. First, the base material composed of the element R is doped with the element M to be measured so as to form a known concentration distribution. Further, the base material is doped with element A so as to form a known concentration distribution including a concentration region of at least 1% or more to obtain a standard sample. In this specification, the element R, the element M, and the element A may be referred to as a first element, a second element, and a third element, respectively.

  Specifically, in the standard sample according to the present invention, the base material of the first element (element R) has a known atomic concentration distribution in the depth direction, and the base material is doped with the second element (element M). And a third element (element A) doped in the base material, in which the atomic concentration distribution in the depth direction is known and a part of the atomic concentration distribution exceeds 1%. And used for secondary ion mass spectrometry for specifying the atomic concentration of the second element contained in the measurement sample composed of the first element and the third element.

  By using this standard sample for the secondary ion mass spectrometry method, the concentration distribution of the element to be analyzed in the measurement sample whose base material is two components can be measured easily and quantitatively.

  In the standard sample according to the present invention, the atomic concentration distribution in the depth direction of the second element can be constant.

  The standard sample according to the present invention is manufactured by doping the second element into the base material by ion implantation. By adjusting the ion implantation amount and ion implantation energy, the ion profile in the depth direction of the element M can be controlled to a desired shape. Further, when the concentration distribution in the depth direction of the element M is made constant, it can be realized by preparing a standard sample by a film forming means such as a CVD method or a sputtering method. The concentration of the element M can be made constant in the depth direction by ion implantation. In this case, it is necessary to heat the standard sample under predetermined conditions after ion implantation.

  The standard sample according to the present invention is manufactured by doping the base material with the third element by ion implantation. By adjusting the ion implantation amount and ion implantation energy, the ion profile in the depth direction of the element A can be controlled to a desired shape.

  In the secondary ion mass spectrometry method according to the present invention, the above standard sample is used as the standard sample of the element M to be analyzed in the binary system of the element R and the element A, and the composition ratio of the arbitrary element R and the element A is determined. The element M to be analyzed in the measurement sample is quantified.

  In the secondary ion mass spectrometry method according to the present invention, the atomic concentration of the second element contained in the measurement sample composed of the first element and the third element is specified using the standard sample.

  By performing the secondary ion mass spectrometry method using the standard sample, the concentration distribution of the element to be analyzed in the measurement sample whose base material is two components can be easily and quantitatively measured.

Specifically, the secondary ion mass spectrometry method according to the present invention measures the secondary ion intensity of the third element released from the standard sample by irradiating the standard sample with primary ions, and the standard A third element secondary ion profile of the secondary ion intensity of the third element with respect to the depth direction of the sample is acquired, and from the third element secondary ion profile, the atomic concentration of the third element versus the second element Calculate the third element sensitivity curve of the secondary ion intensity, measure the secondary ion intensity of the second element released from the standard sample by irradiating the standard sample with primary ions, and determine the depth of the standard sample. Obtaining a second element secondary ion profile of the secondary ion intensity of the second element relative to the direction, and from the second element secondary ion profile, the atomic concentration of the second element versus the secondary ion intensity of the second element The second element sensitivity curve is calculated, and the correlation sensitivity between the secondary ion intensity of the third element and the secondary ion intensity of the second element from the secondary ion profile of the third element and the secondary ion profile of the second element. A standard sample measurement procedure to calculate the curve;
The secondary ion intensity of the second element and the secondary ion intensity of the third element which are emitted from the measurement sample by irradiating the measurement sample with primary ions are measured, and calculated by the standard sample measurement procedure Using the third element sensitivity curve, grasp the atomic concentration of the third element from the third element secondary ion profile obtained in the standard sample measurement procedure, if the atomic concentration of the third element is less than a predetermined value, Using the second element sensitivity curve calculated in the standard sample measurement procedure, the atomic concentration of the second element is obtained from the second element secondary ion profile obtained in the standard sample measurement procedure, and the third element When the atomic concentration of the second element is equal to or greater than the predetermined value, the second element secondary ion profile is obtained by using the correlation sensitivity curve calculated in the standard sample measurement procedure to obtain a secondary ion intensity split increment of the second element. A corrected secondary ion profile obtained by subtracting the split increment from the file is calculated, and the atomic concentration of the second element is calculated from the corrected secondary ion profile using the second element sensitivity curve calculated in the standard sample measurement procedure. A measurement sample measurement procedure to be acquired.

  The standard sample of the number of combinations of the base material of the measurement sample and the element to be analyzed, which has been necessary in the past, becomes unnecessary, and the concentration of the element M can be measured easily. Furthermore, since the sensitivity curve of the element A and the element M can be obtained, the concentration of the element M can be quantified even if the ratio of the element R and the element A in the measurement sample is unknown. Therefore, the secondary ion mass spectrometry method according to the present invention can easily and quantitatively measure the concentration distribution of the element to be analyzed in the measurement sample whose base material is the two components.

  The present invention provides a secondary ion mass spectrometry method capable of easily and quantitatively measuring the concentration distribution of an element to be analyzed in a measurement sample whose base material is a two-component material, a standard sample used therefor, and a method for producing the standard sample can do.

It is a figure explaining the concentration distribution of the element contained in the standard sample which concerns on this invention. It is a figure explaining the secondary ion profile of the depth direction of the standard sample which concerns on this invention. It is a figure explaining the sensitivity curve of the density | concentration of the standard sample which concerns on this invention, and secondary ion intensity | strength. It is a figure explaining the secondary ion profile of the depth direction of the standard sample which concerns on this invention. It is a figure explaining the sensitivity curve of the secondary ion intensity about two elements of the standard sample which concerns on this invention. It is a figure explaining the concentration distribution and secondary ion profile of the standard sample for quantification in the conventional secondary ion mass spectrometry method. It is a figure explaining the concentration distribution and secondary ion profile of the standard sample for quantification in the conventional secondary ion mass spectrometry method. It is the figure which showed the example of the 2 component-type measurement sample used as the object of a secondary ion mass spectrometry method. It is a figure of the result of having measured the binary system measurement sample in the depth direction with the conventional secondary ion mass spectrometry method.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

  FIG. 6 is a concentration distribution in the depth direction of a conventional standard sample measured by a secondary ion mass spectrometry method. Since the element R is an element constituting the base material, the concentration is constant in the depth direction, and the concentration is also known. Reflecting this, the depth profile of secondary ions obtained by the secondary ion mass spectrometry method is also constant in the depth direction. On the other hand, the depth direction distribution of the element M is injected into the base material by ion implantation, and is generally a Gaussian distribution having an average range Rp (M) in R as a maximum concentration value. In this case, if the ion implantation energy or acceleration voltage and the crystal structure of the base material are determined, the distribution curve of the element M can be obtained almost accurately by calculation, and a part of the distribution curve is listed (for example, a non-table). (See Patent Document 2).

  On the other hand, the absolute value of the concentration of the element M can be shifted up and down in the figure depending on the ion implantation amount. However, in the case of monovalent ions, the ion implantation amount is a basic value of the current amount during ion implantation. Since it is the same as the value divided by the electric charge, it is obtained accurately. In other words, if the ion implantation amount is set as a predetermined value, the concentration distribution of the element M can be accurately obtained in the same manner as the element R. Therefore, the sample shown in this figure can be a standard sample. Using this sample as a standard sample, the sensitivity coefficient of the analyzed element M in the base material containing the component element R can be calculated from the secondary ion intensity ratio and the concentration ratio of the element R and the element M. Therefore, the element M in the measurement sample can be quantified by making the measurement conditions of the standard sample and the measurement sample having the same base material the same.

  FIG. 7 schematically shows the concentration distribution in the depth direction of a conventional standard sample measured by secondary ion mass spectrometry. This standard sample is used for quantifying the element M to be analyzed in the base material containing the component element A, as in FIG. However, even if the ion implantation amount of the element M is the same as that of the standard sample of FIG. 6 and the measurement conditions are the same, the secondary ion intensity is different. Therefore, the sensitivity coefficient of the element M to be analyzed in the base material containing the element A obtained using the standard sample is the element M to be analyzed in the base material including the element R shown in FIG. This is different from the sensitivity coefficient. That is, in the case of a secondary ion mass spectrometry method using a conventional standard sample, as many standard samples as the number of combinations of the target measurement sample base material and the element to be analyzed are required.

  FIG. 8 shows a method for preparing a reference sample in which the base material changes in the depth direction as a reference. This reference material is obtained by laminating a base material having the same element R as the base material described in FIG. 6 on a base material having the same element A as the base material described in FIG. Element M was prepared by ion implantation. Depending on the lamination conditions and ion implantation conditions, the interface between the two base materials is not steep and often forms an interface layer.

  FIG. 9 shows an example in which the secondary ion profile in the depth direction of the element M is measured in the reference sample described in FIG. In the conventional secondary ion mass spectrometry method, the sensitivity coefficient of the element M to be analyzed is obtained for each of the base material containing the element R and the base material containing the element A, and then the base material containing R as the component. The element M to be analyzed must be quantified in each of the above region and the base material region containing A as a component. In the region of the interface layer between the base material of element R and the base material of element A, the component of the base material itself is unclear, and the secondary ion strength of element M depends on the concentration of the base material component element. Since the nature is unknown, it is difficult to quantify the element M. Since the reference sample is prepared by ion implantation as described in FIG. 8, it is possible to estimate the concentration of the element M to be analyzed in the interface layer, but the element M having an unknown concentration distribution has two mothers. In the case of distribution across the material, the component itself of the base material in the interface layer is unknown, and the dependency of the secondary ionic strength of the element M on the concentration of the base material component element is also unknown, so the concentration distribution of the element M It is difficult to quantify.

  Therefore, in this embodiment, the following standard sample is used. In this standard sample, the base material of the first element (element R) has a known atomic concentration distribution in the depth direction, the second element (element M) doped in the base material, and atoms in the depth direction. And a third element doped with the base material (element A), the concentration distribution of which is known and a part of the atomic concentration distribution exceeds 1%.

  FIG. 1 is a diagram for explaining the concentration in the depth direction of three elements (element R, element A, element M) contained in this standard sample. In this standard sample, a base material composed of the component element R is doped with a target analyte element M so as to form a known concentration distribution, and further doped with an element A as another component. Yes.

  Hereinafter, a secondary ion mass spectrometry method using a standard sample will be described. This standard sample is doped with the element M by ion implantation so that the concentration distribution is constant in the depth direction. In FIG. 1, the concentration of the element M is constant in the depth direction, but may not be constant as long as the concentration distribution is known. In addition, in this standard sample, the element A is ion-implanted with a predetermined ion implantation energy and ion implantation amount in order to form a known concentration distribution. This density distribution may be considered as a Gaussian distribution. The concentration of the element A in the average range Rp (A) of the element A was over 1%.

  FIG. 2 is a secondary ion profile in the depth direction of the element A obtained by measuring the standard sample shown in FIG. 1 by a secondary ion mass spectrometry method. In the vicinity of the average range Rp (A) of the element A, it is considered that the secondary ion intensity released from the base material is changed by the element A itself because the concentration of the element A is high. In this region, the secondary ion profile in the depth direction of the element A obtained by the secondary ion mass spectrometry method is different from the actual distribution. In FIG. 2, a distorted Gaussian distribution is obtained. However, in the two-component system of the element R and the element A, the relationship between the secondary ion intensity and the concentration of the element A can be obtained if the measurement conditions are made constant.

  FIG. 3 is a relationship diagram between the secondary ion intensity and the concentration of the element A calculated from FIG. When both the secondary ion intensity and the concentration are expressed in logarithm, in the low concentration region of the element A, there is a proportional relationship between the secondary ion intensity and the concentration of the element A. Therefore, except for the influence of the background noise, It is on a straight line with an inclination of 45 degrees. Then, since the concentration of the element A exceeds the concentration C0 (A), the proportional relationship does not hold between the secondary ion intensity and the concentration of the element A. However, the relationship between the secondary ion intensity and the concentration of the element A is non-linear, but since it is a monotonically increasing function, the concentration of the element A can be obtained from the secondary ion intensity of the element A using FIG. That is, a sensitivity curve AA (third element sensitivity curve) showing a change in the sensitivity coefficient of the element A due to the element A itself is obtained.

  FIG. 4 is a secondary ion profile in the depth direction of the element M obtained by measuring the standard sample shown in FIG. 1 by a secondary ion mass spectrometry method. In the region other than the vicinity of the average range Rp (A) of the element A, the base material may be considered as a uniform base material composed of the element R. Therefore, the sensitivity coefficient M−M (second) of the element M with respect to the element R Elemental sensitivity curve). With this sensitivity coefficient MM, the element M in the measurement sample whose element M concentration is unknown can be quantified. On the other hand, in the vicinity of the average range Rp (A) of the element A, it is considered that the secondary ion intensity released from the base material changes due to the high concentration of the element A. In this region, the secondary ion profile in the depth direction of the element M obtained by the secondary ion mass spectrometry method is different from the actual distribution. However, if the measurement conditions are made constant, the correspondence between the secondary ion intensity of element A and the secondary ion intensity of element M can be obtained.

  FIG. 5 shows the result of FIG. 4 as a correspondence relationship between the secondary ion intensity of the element A and the secondary ion intensity of the element M. Although the concentration of the element M should be constant, in this example, the secondary ion intensity of the element M increases from the time when the concentration of the element A exceeds the concentration C0 (A). When the secondary ion intensity of the element A shows a certain value under a certain measurement condition, it is possible to know how much the secondary ion intensity of the element M has increased by using FIG. That is, FIG. 5 can be considered as a sensitivity curve MA (correlation sensitivity curve) showing a change in the sensitivity coefficient of the element M.

  Summarizing the above, regarding the trace element M in the binary component measurement sample of the element R and the element A, from the sensitivity curve MA shown in FIG. The degree of sensitization of the next intensity can be known. Then, using the ion profile of element A in FIG. 2, the concentration of element A can be known from the secondary ion intensity of element A, and the composition ratio of element A and element R in the measurement sample can be known. Therefore, this standard sample can be used as a standard sample of the element M in the base material having a composition from 0% of the element A (element R is 100%) to the maximum concentration of the element A in the base material composition. That is, by using this standard sample in the secondary ion mass spectrometry method, the concentration in the binary measurement sample having an arbitrary composition of the element R and the element A with the sample shown in FIG. 1 as the standard sample is unknown. The element M can be quantified.

  A specific measurement method of the secondary ion mass spectrometry method of the present embodiment will be described below. First, the standard sample and the measurement sample are set in the chamber of the secondary ion mass spectrometer. Subsequently, the chamber is evacuated and the standard sample is irradiated with a primary ion beam such as cesium ions, oxygen ions, and argon ions. At this time, secondary ions of element R, element A, and element M released from this standard sample are detected by mass separation, and secondary ion intensity and secondary ion profile in the depth direction are obtained. Since the concentration of each element in the depth direction of the standard sample is known, the sensitivity curve AA for the element A, the sensitivity curve MM for the element M as shown in FIG. A sensitivity curve MA of the element A and the element M as shown in FIG.

  Next, the measurement sample is irradiated with a primary ion beam. At this time, secondary ions of element R, element A, and element M released from the measurement sample are detected by mass separation, and secondary ion intensity and secondary ion profile in the depth direction are obtained. Here, the concentration of the element A in the measurement sample is confirmed using the secondary ion intensity of the element A and the sensitivity curve AA. If the concentration of the element A is less than C0 (A), the concentration of the element M can be known using the secondary ion intensity of the element M and the sensitivity curve MM.

  On the other hand, when the concentration of the element A is C0 (A) or higher, the degree of increase in the secondary ion intensity of the element M is acquired using the sensitivity curve MA. Subsequently, a corrected secondary ion intensity obtained by subtracting the increased intensity from the secondary ion intensity of the element M is acquired. The concentration of the element M can be known using the corrected secondary ion intensity and the sensitivity curve MM.

For example, if the element R is iron, the element A is carbon, and the element A in FIG. 1, that is, the maximum concentration of carbon exceeds 25%, it has an arbitrary composition between pure iron and cementite (Fe ₃ C). Arbitrary element M can be quantified about an iron-carbon compound.

Rp (M): Average range of element M Rp (A): Average range of element A

Claims (6)

The base material of the first element
A second element doped in the base material with a known atomic concentration distribution in the depth direction;
A third element doped in the base material, in which the atomic concentration distribution in the depth direction is known and a part of the atomic concentration distribution exceeds 1%;
Contains
A standard sample used for secondary ion mass spectrometry for specifying an atomic concentration of a second element contained in a measurement sample composed of the first element and the third element.   The standard sample according to claim 1, wherein the atomic concentration distribution of the second element in the depth direction is constant. The standard sample according to claim 1 or 2,
A method for producing a standard sample, characterized in that it is produced by a film forming means or a means for doping the second element into the base material by ion implantation. The standard sample according to claim 1 or 2,
A method of manufacturing a standard sample, wherein the base material is doped with the third element by ion implantation. Using the standard sample according to claim 1 or 2,
A secondary ion mass spectrometry method for identifying an atomic concentration of a second element contained in a measurement sample composed of the first element and the third element. By irradiating the standard sample with primary ions, the secondary ion intensity of the third element released from the standard sample is measured, and the secondary ion intensity of the third element with respect to the depth direction of the standard sample is measured. Acquire a three-element secondary ion profile,
Calculating the third element sensitivity curve of the third element secondary ion intensity versus the third element secondary ion intensity from the third element secondary ion profile;
The secondary ion intensity of the second element emitted from the standard sample is measured by irradiating the standard sample with primary ions, and the secondary ion intensity of the second element with respect to the depth direction of the standard sample is measured. Acquire a two-element secondary ion profile,
Calculating a second element sensitivity curve of the second element atomic concentration versus the second element secondary ion intensity from the second element secondary ion profile;
A standard sample measurement procedure for calculating a correlation sensitivity curve between the secondary ion intensity of the third element and the secondary ion intensity of the second element from the secondary ion profile of the third element and the secondary ion profile of the second element; ,
Measure the secondary ion intensity of the second element and the secondary ion intensity of the third element emitted from the measurement sample by irradiating the measurement sample with primary ions,
Using the third element sensitivity curve calculated in the standard sample measurement procedure, grasp the atomic concentration of the third element from the third element secondary ion profile obtained in the standard sample measurement procedure,
When the atomic concentration of the third element is less than a predetermined value, the second element sensitivity curve calculated in the standard sample measurement procedure is used, and the second element secondary ion profile obtained in the standard sample measurement procedure is used. Get the atomic concentration of the second element,
When the atomic concentration of the third element is equal to or greater than the predetermined value, the percent increment of the secondary ion intensity of the second element is obtained using the correlation sensitivity curve calculated in the standard sample measurement procedure, and the second element Calculate a corrected secondary ion profile obtained by subtracting the percent increment from the elemental secondary ion profile,
Using the second element sensitivity curve calculated in the standard sample measurement procedure, a measurement sample measurement procedure for obtaining the atomic concentration of the second element from the corrected secondary ion profile;
The secondary ion mass spectrometry method according to claim 5, wherein:

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