JP6136847B2 - Analysis method - Google Patents

Description

  The present invention relates to an analysis method.

  X-ray photoelectron spectroscopy (XPS) is an analysis method that irradiates the surface of a solid sample with characteristic X-rays and detects photoelectrons generated by the photoelectric effect. Specifically, the element type, core level, and chemical bonding state can be analyzed from the detected kinetic energy of the photoelectrons.

  In XPS, when analyzing the chemical bonding state of a sample, one kind of element is focused on for the reason that the kinetic energy of the photoelectron is easily changed due to the change of the chemical bonding state and the peak shape is easy to analyze. Analysis is often performed by selecting the core level. That is, in most cases, analysis is performed on photoelectrons emitted from one selected core level.

  In this case, it is predicted whether the detected photoelectron peak includes several different chemical bonding states, and the chemical bonding state is determined by performing peak fitting. At this time, a standard sample corresponding to a chemical binding state that is expected to be detected is measured under the same measurement conditions to obtain an element peak for peak fitting. However, in a region having a depth of about 10 nm from the surface measured by XPS, the surface may be oxidized, and a necessary standard sample may not be available. In addition, the binding energy varies depending on how to prepare a standard sample and correction using adsorbed hydrocarbon. Therefore, the standard sample may not always be an absolute element peak.

JP-A-6-3295 JP-A-6-160314

  By the way, in the case where a standard sample cannot be prepared, etc., reference is made to literature values, etc., but although there are descriptions of binding energy in the literature, etc., elements for determining peak shapes such as half width and asymmetric parameters have not been disclosed. Absent. Therefore, since the element for determining the peak shape is unknown, there are many cases where an element peak that includes the subjectivity of the analyst and the result of fitting often occur, and therefore, variations tend to occur.

  Therefore, there is a need for an analysis method that can perform peak fitting with little variation without relying on the person who analyzes the photoelectron peaks measured under the same apparatus and the same measurement conditions by XPS.

  According to one aspect of the present embodiment, in the analysis method using X-ray photoelectron spectroscopy, the two different core levels in the sample to be analyzed are selected and the sample is irradiated with X-rays. A condition setting step of setting the photoelectron extraction angles at the two different core levels so that the escape depth of the photoelectrons from the sample is substantially the same, and irradiating the sample with X-rays, A first measurement step of measuring photoelectrons at one core level among different core levels at a photoelectron extraction angle corresponding to the one core level, and irradiating the sample with X-rays And a second measurement step of measuring photoelectrons at the other core level of the two different core levels according to the extraction angle of photoelectrons corresponding to the other core level. It is characterized by that.

  Further, according to another aspect of the present embodiment, in the analysis method by X-ray photoelectron spectroscopy, two or more different core levels in the sample to be analyzed are selected, and X-rays are applied to the sample. A condition setting step for setting the photoelectron extraction angles at the two or more different core levels so that the escape depth of the photoelectrons from the sample when irradiated is substantially the same, and X-rays are applied to the sample. Irradiating each of the inner core levels, and measuring the photoelectrons according to the extraction angle of the photoelectrons corresponding to each of the inner core levels.

  According to the disclosed analysis method, in XPS, peak fitting with little variation can be performed without depending on an analyst.

XPS analyzer structural diagram Correlation diagram between binding energy and number of photoelectrons obtained by XPS wide scan Illustration of conventional peak fitting (1) Illustration of conventional peak fitting (2) Explanatory diagram of relationship between extraction angle and photoelectron escape depth Flow chart of peak fitting in analysis method in the present embodiment Structure diagram of analyzer by XPS used for analysis method in this embodiment Explanatory drawing (1) of peak fitting in the analysis method in the present embodiment Explanatory drawing (2) of the peak fitting in the analysis method in this Embodiment

  The form for implementing is demonstrated below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

  First, general XPS will be described with reference to FIG. As shown in FIG. 1, a general XPS includes an X-ray source 10, an analyzer 20, a detector 30, a sample stage 40, and the like, and a sample 50 to be analyzed is installed on the sample stage 40. Yes. When performing analysis by XPS, the X-ray source 10 irradiates the sample 50 placed on the sample stage 40 with X-rays. As a result, photoelectrons are generated in the sample 50, and the generated photoelectrons are detected for each energy by the detector 30 via the analyzer 20.

  FIG. 2 shows the relationship between the binding energy and the photoelectron intensity (the number of photoelectrons) when the sample 50 is GaN and is scanned wide by XPS. The sample 50 is left in the atmosphere, and the surface is oxidized. In such a sample 50, peaks in Ga2p, Ga3p, Ga3d, etc. are detected. In the present embodiment, the X-rays emitted from the X-ray source 10 are AlKα rays (1486.6 eV).

Here, the case where peak fitting is performed using the measurement result when the core level is Ga2p _3/2 will be described. Incidentally, the photoelectron take-off angle is 28 °. Generally, peak fitting is performed for the purpose of separating overlapping peaks or estimating peak positions. FIG. 3A shows the relationship between the binding energy obtained by measurement and the number of photoelectrons when the core level is Ga2p _3/2 and the photoelectron extraction angle is 28 °. FIG. 3B shows the result of peak fitting based on the relationship between the binding energy and the photoelectron intensity thus obtained. Based on this result, the ratio of Ga ₂ O ₃ to be an oxide on the surface of the sample 50 is estimated to be 48%.

On the other hand, the case where peak fitting is performed using the measurement result when the core level is Ga3d will be described. Incidentally, the photoelectron take-off angle is 28 °. FIG. 4A shows the relationship between the binding energy obtained by measurement and the photoelectron intensity when the core level is Ga3d and the photoelectron extraction angle is 28 °. FIG. 4B shows the result of peak fitting based on the relationship between the binding energy and the photoelectron intensity obtained by the measurement. Based on this result, the proportion of Ga ₂ O ₃ to be an oxide on the surface of the sample 50 is estimated to be 17%.

As described above, when the measurement result at the core level of Ga2p _3/2 is used and when the measurement result at the core level of Ga3d is used, the oxide obtained by the result of the peak fitting is used. The ratio is very different. Thus, the reason why the ratio of the obtained oxide is greatly different between Ga2p _3/2 and Ga3d is that the inner shell level is Ga2p _3/2 , as will be described later, This is because the escape depth of photoelectrons in the sample 50 is different from the case where the level is Ga3d.

  On the other hand, in XPS, the angle formed between the surface of the sample 50 and the analyzer 20 can be changed by rotating the sample stage 40 with respect to the analyzer 20. Thereby, the escape depth of the photoelectrons from the sample 50 can be changed, and the analysis in the depth direction of the sample 50 can be performed nondestructively.

Specifically, as shown in FIG. 5A, when the analyzer 20 is installed in a direction that is normal to the surface of the sample 50, the take-off angle TOA (Take-Off Angle) of the photoelectrons is 0 °. The escape depth D of the photoelectrons from the sample 50 becomes deep. On the other hand, as shown in FIG. 5B, when the analyzer 20 is installed inclined with respect to the normal line on the surface of the sample 50, the escape depth D of the photoelectrons from the sample 50 is as shown in FIG. ) Can be made shallower than the case shown in FIG. The photoelectron take-out angle TOA means an angle with respect to the normal line on the surface of the sample 50. Further, the photoelectron extraction depth D in the sample 50 can be obtained by D = 3λ cos θ, where λ is the mean free path and θ is the photoelectron extraction angle TOA. In addition, the mean free path of photoelectrons in Ga2p _3/2 described later is 0.95 nm, and the mean free path of photoelectrons in Ga3d is 2.57 nm.

Table 1 shows the relationship between the photoelectron extraction angle TOA and the photoelectron escape depth when GaN is formed on the surface of the sample 50. As shown in Table 1, when the photoelectron take-off angle TOA is increased, both the escape depth in Ga2p _{3/2 and} the escape depth in Ga3d gradually become shallower. Further, the escape depth of the photoelectrons from the sample 50 differs depending on the inner shell level, and the escape depth in the Ga2p _3/2 inner shell level and the escape depth in Ga3d are the same photoelectron take-out angle TOA. But it is different.

  In the present embodiment, peak fitting is performed by setting the photoelectron take-off angle TOA so that the escape depth is substantially the same for two or more different core levels. Thereby, peak fitting without variation can be performed.

Specifically, the escape depth of Ga2p _3/2 when the photoelectron take-out angle TOA is 28 ° is 2.5 nm, and the escape depth of Ga3d when the photoelectron take-out angle TOA is 68 ° is 2. 9 nm. Therefore, the escape depth of Ga2p _3/2 when the photoelectron take-out angle TOA is 28 ° and the escape depth of Ga3d when the photoelectron take-out angle TOA is slightly higher than 68 ° are approximately the same 2.5 nm. In this way, by measuring information on the same escape depth of the sample 50 under different conditions, it becomes possible to perform peak fitting without variation as will be described later. That is, if the information on the depth measured in the sample 50 is the same, for example, the ratio of Ga oxide and nitride is the same, and therefore, by performing peak fitting based on this, variation can be reduced. Can do.

The Ga2p _3/2 escape depth when the photoelectron extraction angle TOA is 58 ° is 1.5 nm, and the Ga3d escape depth when the photoelectron extraction angle TOA is 78 ° is 1.6 nm. . Therefore, the escape depth of Ga2p _3/2 when the photoelectron take-off angle TOA is 58 ° and the escape depth of Ga3d when the photoelectron take-out angle TOA is slightly over 78 ° are substantially the same 1.5 nm. This is the same as above.

(Analysis method)
Next, an analysis method according to the present embodiment will be described with reference to FIG.

First, as shown in step 102 (S102), the inner shell level and the extraction angle are set so that the escape depth of the photoelectrons in the sample 50 is substantially the same. Specifically, based on the relationship between the extraction angle and the escape depth at a plurality of inner shell levels shown in Table 1, etc., a plurality of combinations of the inner shell level and the extraction angle so that the escape depths are substantially the same. Select and set as measurement conditions. Specifically, the photoelectron extraction angle TOA when the inner core level is Ga2p _3/2 is 28 ° as the first condition, and the photoelectron extraction angle TOA when the inner core level is Ga3d is 68 °. The second condition is assumed. When the photoelectron take-off angle TOA is 28 °, the escape depth of Ga2p _3/2 is 2.5 nm, and when the photoelectron take-off angle TOA is 68 °, the escape depth of Ga3d is 2.9 nm. The escape depth values at are substantially the same. In this way, two different measurement conditions are set.

Next, as shown in step 104 (S104), the relationship between the binding energy and the photoelectron intensity is measured under the first condition. Specifically, when the core level is Ga2p _3/2 , measurement is performed at a photoelectron take-off angle TOA of 28 °. At this time, the apparatus shown in FIG. 1 is provided with a moving mechanism (not shown) for moving the analyzer 20 so that the take-off angle changes, and the analyzer 20 is moved so that the take-off angle is 28 ° and measurement is performed. May be. Further, as shown in FIG. 7, using a device in which a plurality of analyzers 20a and 20b are installed, for example, measurement is performed with the analyzer 20a installed at a position where the photoelectron take-off angle TOA is 28 °. Also good. The analyzer 20a may be connected to the detector 30a, and the detector 30a may be connected to the control unit 60. The control unit 60 includes an interface, a control unit main body, a display device, and the like. In general, the sample 50 is rotated together with the sample stage 40, and the angle with the analyzers 20a and 20b is changed.

  Next, as shown in step 106 (S106), the relationship between the binding energy and the photoelectron intensity is measured under the second condition. Specifically, when the core level is Ga3d, measurement is performed at a photoelectron take-off angle TOA of 68 °. At this time, the apparatus shown in FIG. 1 is provided with a moving mechanism (not shown) that moves the analyzer 20 so that the take-out angle changes, and the analyzer 20 is moved so that the take-off angle becomes 68 °. May be. Further, as shown in FIG. 7, using a device in which a plurality of analyzers 20a and 20b are installed, for example, measurement is performed with an analyzer 20b installed at a position where the photoelectron take-off angle TOA is 68 °. Also good. The analyzer 20b may be connected to the detector 30b, and the detector 30b may be connected to the control unit 60.

  Next, as shown in step 108 (S108), peak fitting is performed in the control unit 60 or the like. Specifically, based on the relationship between the binding energy and the photoelectron intensity in the first condition obtained in step 104, and the relationship between the binding energy and the photoelectron intensity in the second condition obtained in step 106, Perform peak fitting. At this time, peak fitting is performed by defining element peaks so that the ratio of Ga oxide to nitride is substantially the same in both. Specifically, in the graph of the relationship between the binding energy and the photoelectron intensity obtained in the measurement, the peak is such that the ratio of the area of Ga oxide to the area of Ga nitride is substantially the same in both. Perform fitting.

FIG. 8 (a) shows the relationship between the binding energy and the photoelectron intensity obtained by measuring with the photoelectron take-off angle TOA of 28 ° when the core level is Ga2p _3/2 . FIG. 8B shows the relationship between the binding energy and the photoelectron intensity obtained when the photoelectron take-off angle TOA is set to 68 ° when the core level is Ga3d. In FIG. 8A and FIG. 8B, peak fitting was performed by determining element peaks so that the ratio of Ga oxide to nitride was substantially the same in both cases. As a result, the proportion of oxide in the case shown in FIG. 8A is 18%, the proportion of oxide in the case shown in FIG. 8B is 16%, and the proportion of oxide in both is The values were almost the same.

  Thus, in this embodiment, the probability of peak fitting can be improved.

(Other examples of analysis methods)
Next, an example in which the inner core level and the extraction angle different from the above are set as measurement conditions will be described with reference to FIG.

First, as shown in step 102 (S102), the inner shell level and the extraction angle are set so that the escape depth of the photoelectrons in the sample 50 is substantially the same. Specifically, the photoelectron take-off angle TOA when the inner core level is Ga2p _3/2 is 58 ° as the first condition, and the photoelectron take-out angle TOA when the inner shell level is Ga3d is 78 °. The second condition is assumed. When the photoelectron take-off angle TOA is 58 °, the escape depth of Ga2p _3/2 is 1.5 nm, and when the photoelectron take-off angle TOA is 78 °, the escape depth of Ga3d is 1.6 nm. The escape depth values at are substantially the same. In this way, two different measurement conditions are set.

Next, as shown in step 104 (S104), the relationship between the binding energy and the number of photoelectrons is measured under the first condition. Specifically, when the core level is Ga2p _3/2 , measurement is performed at a photoelectron take-off angle TOA of 58 °. At this time, the apparatus shown in FIG. 1 is provided with a moving mechanism (not shown) that moves the analyzer 20 so that the take-out angle changes, and the analyzer 20 is moved so that the take-out angle becomes 58 °. May be. Further, as shown in FIG. 7, using a device in which a plurality of analyzers 20a and 20b are installed, for example, measurement is performed with the analyzer 20a installed at a position where the photoelectron take-off angle TOA is 58 °. Also good.

  Next, as shown in step 106 (S106), the relationship between the binding energy and the number of photoelectrons is measured under the second condition. Specifically, when the core level is Ga3d, measurement is performed at a photoelectron take-off angle TOA of 78 °. At this time, the apparatus shown in FIG. 1 is provided with a moving mechanism (not shown) that moves the analyzer 20 so that the take-off angle changes, and the analyzer 20 is moved so that the take-off angle becomes 78 °. May be. Further, as shown in FIG. 7, using a device in which a plurality of analyzers 20a and 20b are installed, for example, measurement is performed by the analyzer 20b installed at a position where the photoelectron take-off angle TOA is 78 °. Also good.

  Next, as shown in step 108 (S108), peak fitting is performed. Specifically, based on the relationship between the binding energy and the number of photoelectrons in the first condition obtained in step 104, and the relationship between the binding energy and the number of photoelectrons in the second condition obtained in step 106, Perform peak fitting. At this time, peak fitting is performed by defining element peaks so that the ratio of Ga oxide to nitride is substantially the same in both.

FIG. 9 (a) shows the relationship between the binding energy and the photoelectron intensity obtained by measurement with the photoelectron take-off angle TOA of 58 ° when the core level is Ga2p _3/2 . FIG. 9 (b) shows the relationship between the binding energy and the photoelectron intensity obtained when the photoelectron take-off angle TOA is 78 ° and the core level is Ga3d. In FIG. 9A and FIG. 9B, peak fitting was performed by determining element peaks so that the ratio of Ga oxide to nitride was substantially the same in both. As a result, the ratio of oxide in the case shown in FIG. 9A is 37%, and the ratio of oxide in the case shown in FIG. 9B is 35%. The ratio of the oxide became substantially the same value.

In the above description, the case where the extraction angle is set so that the escape depth in the sample 50 is substantially the same due to the restrictions of the apparatus has been described. However, if there are no restrictions on the apparatus or the like, the escape depth of the photoelectrons is The take-out angle may be set so as to be more uniform. Table 2 shows that the escape depth of the photoelectrons when the escape depth in the sample 50 is set to be substantially the same, the take-out angle when the inner core level is Ga2p _3/2 , and the inner core level is Ga3d. The relationship with the taking-out angle in the case is shown.

As shown in Table 2, when the photoelectron escape depth in the sample 50 is measured under the condition that both are 0.5 nm, the extraction angle when the inner core level is Ga2p _3/2 is 80 °. In the case where the inner core level is Ga3d, measurement is performed at an extraction angle of 86 °.

Further, when measurement is performed under the condition that the photoelectron escape depth in the sample 50 is both 1.0 nm, the take-off angle when the inner core level is Ga2p _3/2 is 69 °, and the inner core level is Measurement is performed at an extraction angle of 83 ° in the case of Ga3d.

Further, when measurement is performed under the condition that the escape depth of the photoelectrons in the sample 50 is 1.5 nm, the extraction angle when the inner core level is Ga2p _3/2 is 58 °, and the inner core level is Measurement is carried out at an extraction angle of 79 ° in the case of Ga3d.

Further, when the photoelectron escape depth in the sample 50 is measured under the condition that both are 2.0 nm, the extraction angle when the inner core level is Ga2p _3/2 is 45 °, and the inner core level is Measurement is performed with a take-off angle of 75 ° in the case of Ga3d.

Further, when the photoelectron escape depth in the sample 50 is measured under the condition that both are 2.5 nm, the extraction angle when the inner core level is Ga2p _3/2 is 29 °, and the inner core level is Measurement is carried out with a take-off angle of 71 ° in the case of Ga3d.

  In the above description, the case where two different core levels are selected and the extraction angle is set so that the photoelectron escape depth is substantially the same has been described. However, in the present embodiment, three different core levels may be selected, and the extraction angle may be set so that the photoelectron escape depth is substantially the same. Thereby, the accuracy of peak fitting can be further improved.

  Although the embodiment has been described in detail above, it is not limited to the specific embodiment, and various modifications and changes can be made within the scope described in the claims.

In addition to the above description, the following additional notes are disclosed.
(Appendix 1)
In the analysis method by X-ray photoelectron spectroscopy,
Two different inner core levels in the sample to be analyzed are selected, and the two different inner levels are such that the escape depth of the photoelectrons from the sample when the sample is irradiated with X-rays is substantially the same. A condition setting step for setting each photoelectron extraction angle at the shell level;
First, the sample is irradiated with X-rays, and photoelectrons are measured at one core level of the two different core levels, based on the photoelectron extraction angle corresponding to the one core level. Measuring process,
The sample is irradiated with X-rays, and photoelectrons are measured at the other core level of the two different core levels by the photoelectron take-off angle corresponding to the other core level. Measuring process,
The analysis method characterized by having.
(Appendix 2)
After the first measurement step and the second measurement step,
And a peak fitting step of performing peak fitting on the sample based on the result obtained by measurement at the one core level and the result obtained by measurement at the other core level. 2. The analysis method according to 1.
(Appendix 3)
The sample contains two different substances,
In the peak fitting process, the ratio of the two different substances in the result obtained by the first measurement process and the ratio of the two different substances in the result obtained by the second measurement process are substantially the same. The analysis method according to appendix 2, characterized in that:
(Appendix 4)
In the peak fitting step, the area ratio of the two different substances in the result obtained by the first measurement step and the area ratio of the two different substances in the result obtained by the second measurement step are: The analysis method according to appendix 3, wherein the analysis method is performed so as to be substantially the same.
(Appendix 5)
The analysis method according to appendix 3 or 4, wherein the two different substances are an oxide and a nitride.
(Appendix 6)
In the analysis method by X-ray photoelectron spectroscopy,
The two or more different core levels in the sample to be analyzed are selected so that the escape depth of the photoelectrons from the sample when the sample is irradiated with X-rays is substantially the same. A condition setting step for setting the extraction angles of photoelectrons at different core levels,
A measurement step of irradiating the sample with X-rays and measuring photoelectrons at each of the inner core levels according to the extraction angle of the photoelectrons corresponding to the inner core levels;
The analysis method characterized by having.
(Appendix 7)
After the measuring step,
The analysis method according to appendix 6, further comprising a peak fitting step of performing peak fitting on the sample based on the result obtained in the measurement.
(Appendix 8)
The sample includes a plurality of different substances,
The analysis method according to appendix 7, wherein the peak fitting step is performed such that the ratio of the plurality of different substances is substantially the same in the result obtained by the measurement step.
(Appendix 9)
The analysis method according to appendix 8, wherein the peak fitting step is performed such that the area ratios of the plurality of different substances are substantially the same in the result obtained by the measurement step.
(Appendix 10)
10. The analysis method according to any one of appendices 1 to 9, wherein the sample is made of a material containing Ga.

10 X-ray source 20 Analyzer 20a Analyzer 20b Analyzer 30 Detector 30a Detector 30b Detector 40 Sample stage 50 Sample 60 Control unit

Claims (10)

In the analysis method by X-ray photoelectron spectroscopy,
Two different inner core levels in the sample to be analyzed are selected, and the two different inner levels are such that the escape depth of the photoelectrons from the sample when the sample is irradiated with X-rays is substantially the same. A condition setting step for setting each photoelectron extraction angle at the shell level;
First, the sample is irradiated with X-rays, and photoelectrons are measured at one core level of the two different core levels, based on the photoelectron extraction angle corresponding to the one core level. Measuring process,
The sample is irradiated with X-rays, and photoelectrons are measured at the other core level of the two different core levels by the photoelectron take-off angle corresponding to the other core level. Measuring process,
The analysis method characterized by having. After the first measurement step and the second measurement step,
A peak fitting step of performing peak fitting on the sample based on a result obtained by measurement at the one core level and a result obtained by measurement at the other core level. Item 2. The analysis method according to Item 1. The sample contains two different substances,
In the peak fitting process, the ratio of the two different substances in the result obtained by the first measurement process and the ratio of the two different substances in the result obtained by the second measurement process are substantially the same. The analysis method according to claim 2, wherein the analysis method is performed as follows.   In the peak fitting step, the area ratio of the two different substances in the result obtained by the first measurement step and the area ratio of the two different substances in the result obtained by the second measurement step are: The analysis method according to claim 3, wherein the analysis is performed so as to be substantially the same.   The analysis method according to claim 3 or 4, wherein the two different substances are an oxide and a nitride. In the analysis method by X-ray photoelectron spectroscopy,
The two or more different core levels in the sample to be analyzed are selected so that the escape depth of the photoelectrons from the sample when the sample is irradiated with X-rays is substantially the same. A condition setting step for setting the extraction angles of photoelectrons at different core levels,
A measurement step of irradiating the sample with X-rays and measuring photoelectrons at each of the inner core levels according to the extraction angle of the photoelectrons corresponding to the inner core levels;
The analysis method characterized by having. After the measuring step,
The analysis method according to claim 6, further comprising a peak fitting step of performing peak fitting on the sample based on a result obtained in the measurement. The sample includes a plurality of different substances,
8. The analysis method according to claim 7, wherein the peak fitting step is performed such that the ratio of the plurality of different substances is substantially the same in the result obtained by the measurement step.   The analysis method according to claim 8, wherein the peak fitting step is performed such that the area ratios of the plurality of different substances are substantially the same in the result obtained by the measurement step.   The analysis method according to claim 1, wherein the sample is made of a material containing Ga.

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