JP2016205951A - Film thickness measurement method and film thickness measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film thickness measurement method and film thickness measurement device capable of easily and speedily acquiring the thickness of a thin film formed on a substrate using an XPS.SOLUTION: A film thickness measurement method of a thin film in a sample having the thin film formed on a substrate includes: a process S106 of acquiring a photoelectron spectrum by radiating X rays to the thin film in the sample; a process S108 of acquiring peak areas of two photoelectron peaks of an element that is contained in the substrate and is not contained in the thin film in the photoelectron spectrum, and calculating the peak area ratio on the basis of each peak area; a process S110 of preparing a calibration curve on the basis of the peak area ratio; and a process of acquiring the value of the thickness of the thin film on the basis of the calibration curve.SELECTED DRAWING: Figure 11

Description

  The present invention relates to a film thickness measuring method and a film thickness measuring apparatus.

  In the fields of semiconductors, surface treatment, coating, etc., a thin film is formed on the surface of a substrate or the like. As a method for measuring the film thickness of the thin film thus formed, there is a method using a transmission electron microscope (TEM). Specifically, there is a method in which a film thickness is examined by cutting out a base material on which a film has been formed as a sample and observing a cross section of the cut sample with a TEM.

  However, a sample for TEM observation needs to be made very thin in order to transmit electrons, and producing such a sample requires skillful technique, time, and labor. It took a lot of time and money.

  For this reason, as a method for more easily knowing the film thickness of the thin film, there is a method using X-ray photoelectron spectroscopy (XPS). XPS is an analysis method for irradiating the surface of a solid sample with characteristic X-rays to detect photoelectrons generated by the photoelectric effect. The element type, core level, chemical bonding state from the kinetic energy of the detected photoelectrons. Can be analyzed.

Special table 2008-539433 gazette JP 2012-154950 A Japanese Patent Laid-Open No. 9-14947

In the method of knowing the film thickness of the thin film formed on the base material by XPS, the film thickness of the thin film is calculated based on the following equations (1) and (2) using the obtained photoelectron peak intensity. Is possible. Incidentally, I _S: intensity of photoelectrons from the substrate, I _S0: intensity of photoelectrons When the substrate is a bulk, I _F: intensity of photoelectrons from thin, I _S0: intensity of photoelectrons when a thin film is the bulk, d: film thickness of the thin film, λ: electron mean free path in the thin film, θ: photoelectron extraction angle.

I _S = I _S0 × exp (−d / λ cos θ) (1)

I _F = I _F0 × {1-exp (−d / λ cos θ)} (2)

However, when calculating the film thickness of the thin film based on the equations shown in the above (1) and (2), the value of the electron mean free path λ in the thin film is required. The value varies depending on the material forming the thin film, the density, and the like. For this reason, in order to obtain the value of the mean free path λ of electrons as accurately as possible, since it must be obtained experimentally, a great amount of time and labor are required.

  Therefore, there is a need for a film thickness measurement method that can easily obtain the film thickness of a thin film formed on a substrate as accurately as possible in a short time using XPS.

  According to one aspect of the present embodiment, in the method for measuring the thickness of a thin film in a sample in which a thin film is formed on a substrate, a step of irradiating the thin film of the sample with X-rays to obtain a photoelectron spectrum; In the photoelectron spectrum, each peak area is obtained from two photoelectron peaks of elements that are contained in the base material but not in the thin film, and a peak area ratio is obtained from each of the peak areas. And a step of obtaining a value of the film thickness of the thin film from the peak area ratio.

  According to the disclosed film thickness measuring method, the film thickness of the thin film formed on the substrate can be easily obtained in the shortest possible time using XPS.

Sample structure Correlation diagram between sample binding energy and photoelectron intensity obtained by XPS wide scan Correlation diagram between sample binding energy and photoelectron intensity obtained by XPS narrow scan (1) Correlation diagram between sample binding energy and photoelectron intensity obtained by XPS narrow scan (2) Illustration of background Illustration of peak area Illustration of calibration curve Explanatory diagram of peak area of samples with different film thickness Structure diagram of film thickness measuring apparatus in this embodiment Structure of analysis sample Flowchart (1) of the film thickness measurement method in the present embodiment Flowchart (2) of the film thickness measurement method in the present embodiment Explanatory drawing of the film thickness measuring 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.

FIG. 1 shows a cross-sectional structure of a sample 10 used in this embodiment. In the sample 10, a thin film 12 of Li ₉ Al ₃ (P ₂ O ₇ ) ₃ (PO ₄ ) ₂ is formed on a base 11 of LiFePO ₄ . In addition, the sample 10 used three types from which the film thickness of the thin film 12 differs, ie, the sample 10 whose film thickness of the thin film 12 is 2 nm, 4 nm, and 6 nm. The film thickness of the thin film 12 of the sample 10 is a value obtained by TEM observation or the like.

FIG. 2 shows the relationship between the binding energy and the photoelectron intensity (a value proportional to the number of photoelectrons) when the sample 10 is wide-scanned by XPS. As shown in FIG. 2, when the binding energy is in the vicinity of 720 eV, a peak of Fe2p of iron that is a constituent element of LiFePO ₄ forming the base material 11 is detected. Note that Fe is an element that is contained in the substrate 11 but not in the thin film 12. FIG. 3 shows the relationship between the binding energy and the photoelectron intensity (a value proportional to the number of photoelectrons) when a narrow scan is performed in the range where the binding energy is approximately 700 eV to 770 eV by XPS. As shown in FIG. 3, when the thickness of the thin film 12 of the sample 10 is increased, the peak intensity of Fe2p is decreased and the background on the high energy side is also decreased. Since the background on the high energy side is caused by the peak of Fe2p, when the film thickness of the thin film 12 of the sample 10 increases, the absorption in the thin film 12 increases and decreases.

FIG. 4 shows the peak intensity of Al2p of aluminum which is a constituent element of Li ₉ Al ₃ (P ₂ O ₇ ) ₃ (PO ₄ ) ₂ forming the thin film 12 of the sample 10. Al is an element that is contained in the thin film 12 but not contained in the base material 11. As shown in FIG. 4, as the film thickness of the thin film 12 increases, the peak intensity of Al2p increases, but the background does not change.

By the way, as shown in FIG. 3, when the film thickness of the thin film 12 of the sample 10 is changed, a difference is generated between the 2p _1/2 peak and the 2p _3/2 peak in Fe2p. 2p _1/2 and 2p _3/2 are obtained by splitting the energy eigenvalues of electrons degenerated by the spin-orbit interaction into two.

Here, as indicated by the one-dot chain line in FIG. 5, a background of 2p _1/2 peak is set, and similarly, a background of 2p _3/2 peak is set. Thus, as shown in FIG. _{6, 1/2} peak and peak area _{2p 1/2} S of _2p, to give a peak area _{2p 3/2} S of _{2p 3/2} peak, the peak area ratio of Fe2p (2p _3/2 S / 2p _1/2 S) is calculated. Each peak area is an area of a region surrounded by each peak portion and the background.

The relationship between the calculated peak area ratio of Fe2p (2p _3/2 S / 2p _1/2 S) and the film thickness of the thin film 12 of the sample 10 is shown in FIG. As shown in FIG. 7, since the peak area ratio of Fe2p (2p _3/2 S / 2p _1/2 S) and the film thickness of the thin film 12 of the sample 10 are in a linear relationship, the peak area ratio of Fe2p ( If 2p _3/2 S / 2p _1/2 S) is known, the film thickness of the thin film 12 of the sample 10 can be known. That is, if a calibration curve of the relationship between the peak area ratio (2p _3/2 S / 2p _1/2 S) shown in FIG. 7 and the film thickness of the thin film 12 was obtained in advance, it was obtained by XPS measurement. The value of the film thickness of the thin film 12 can be obtained from the peak area ratio of Fe2p (2p _3/2 S / 2p _1/2 S). For example, the slope of the calibration curve shown in FIG. 7 is α, the thickness of the thin film of the analytical sample to be measured is T, and the peak area ratio of the analytical sample obtained by XPS (2p _3/2 S / 2p _{1 / When 2} S) is R, the film thickness T of the thin film of the analytical sample can be obtained from the equation shown in the following (3). Β is a constant.

T = α × R + β (3)

The calibration curve shown in FIG. 7 changes because the density, film quality, etc. of the thin film 12 change when the maintenance of the film forming apparatus and the film forming conditions when the thin film 12 is formed are changed. For this reason, when the maintenance of the film forming apparatus and the film forming conditions when the thin film 12 is formed are changed, it is necessary to prepare again the sample 10 having a different film thickness of the thin film 12 and create a calibration curve. . However, if the maintenance of the film forming apparatus and the film forming conditions when forming the thin film 12 are not changed, the calibration curve once created can be used as it is. Therefore, based on the result obtained by the XPS measurement, the film thickness of the thin film 12 can be easily obtained in a short time using the same calibration curve.

  FIG. 8 shows a state in which a background is set in the XPS measurement results of the samples 10 having different thicknesses of the thin film 12 shown in FIG. In the present embodiment, the background is set by a method (Linear method) in which bottom regions on both sides of each peak are connected by a straight line. Note that the Shirley method may be used as a method for setting the background in order to obtain individual peak areas.

In the above description, the sample 10 in which the Li ₉ Al ₃ (P ₂ O ₇ ) ₃ (PO ₄ ) ₂ thin film 12 is formed on the LiFePO ₄ base material 11 has been described. 11 and the material for forming the thin film 12 may be materials other than those described above.

In the above description, the case where the 2p _1/2 peak and the 2p _3/2 peak in Fe2p are used has been described. However, any element included in the base material 11 and not included in the thin film 12 may be used. It is also possible to use peaks of elements other than Fe. In addition to the p orbit, photoelectrons from the d or f orbit may be used.

(Thickness measuring device)
Next, the film thickness measuring apparatus in the present embodiment will be described with reference to FIG. The film thickness measurement apparatus shown in FIG. 9 has a structure similar to that of general XPS, and the film thickness of the thin film in this embodiment can also be measured using general XPS. The film thickness measurement apparatus in the present embodiment includes an X-ray source 20, an analyzer 30, a detector 40, a sample stage 50, a control unit 60, and the like. When creating a calibration curve, the sample stage 50 is provided with a sample 10 serving as a calibration curve sample. When measuring the film thickness, an analysis sample 110 as an analysis target shown in FIG. Installed. The analysis sample 110 is prepared by using the same material and the same conditions as the sample 10 except that the thin film 112 is formed on the base material 111 and the film thickness of the thin film 112 is unknown. Has been.

  When creating a calibration curve, the sample 10 placed on the sample stage 50 is irradiated with the X-rays emitted from the X-ray source 20 in the same manner as in the case of analyzing by XPS. Thereby, photoelectrons are generated in the sample 10, and the generated photoelectrons are detected for each energy by the detector 40 via the analyzer 30.

  Similarly, when the thickness of the thin film 112 in the analysis sample 110 is measured, the analysis sample 110 installed on the sample stage 50 is irradiated with the X-rays emitted from the X-ray source 20. Thereby, photoelectrons are generated in the analysis sample 110, and the generated photoelectrons are detected for each energy by the detector 40 via the analyzer 30.

  Information on the photoelectron intensity (number of photoelectrons) detected for each energy is sent to the control unit 60. The control unit 60 creates a photoelectron spectrum, sets a background, calculates a peak area ratio, calculates a film thickness based on a calibration curve, etc., and calculates a film thickness of the thin film 112 of the analysis sample 110 to be analyzed. . The control unit 60 includes a storage unit 61 that stores information on calibration curves and the like, and is connected to a display unit 62 that can display a two-dimensional image.

(Thickness measurement method)
Next, the film thickness measurement method in the present embodiment will be described with reference to FIGS. First, a method for creating a calibration curve will be described with reference to FIG.

  First, as shown in step 102 (S102), a sample 10 to be a calibration curve sample is prepared. The calibration curve sample is used to obtain a calibration curve, and a plurality of, for example, three samples 10 having different thicknesses of the thin film 12 are prepared.

  Next, as shown in step 104 (S104), the film thickness of the thin film 12 of each sample 10 is measured by TEM observation.

  Next, as shown in step 106 (S106), each sample 10 is irradiated with X-rays emitted from the X-ray source 20 and measured by XPS. At this time, the measurement conditions and measurement range of the XPS measurement may be determined in advance.

  Next, as shown in step 108 (S108), the peak area ratio in each sample 10 is calculated based on the measurement result by XPS.

  Next, as shown in step 110 (S110), the thickness of the thin film 12 of each sample 10 obtained in step 104 and the peak area ratio in each sample 10 obtained in step 108 are shown in FIG. Create a calibration curve as shown. The calibration curve obtained in this way is stored in the storage unit 61 in the control unit 60 of the film thickness measuring apparatus in the present embodiment, and when measuring the film thickness of the thin film 112 in the analysis sample 110 to be described later. Use.

  Next, a method for measuring the film thickness of the thin film 112 in the analysis sample 110 will be described with reference to FIG. In the present embodiment, as shown in FIG. 13, a case will be described in which the film thickness is measured in the region where the X coordinate is from 0 to A and the Y coordinate is from 0 to B. Therefore, a case where the measurement position in this region is sequentially irradiated with X-rays emitted from the X-ray source 20 to measure the film thickness distribution of the thin film 112 of the analysis sample 110 will be described.

  First, as shown in step 202 (S202), the analysis sample 110 is placed on the sample stage 50 of the film thickness measurement apparatus in the present embodiment.

  Next, as shown in step 204 (S204), (X, Y) = (0, 0) is set.

  Next, as shown in step 206 (S206), the analysis sample 110 is irradiated so that the X-ray emitted from the X-ray source 20 is irradiated and the measurement position at which the film thickness is measured becomes (X, Y). Move.

  Next, as shown in step 208 (S208), the measurement position (X, Y) of the analysis sample 110 is irradiated with X-rays emitted from the X-ray source 20, and measurement by XPS is performed to obtain a photoelectron spectrum. .

  Next, as shown in step 210 (S210), 1 is added to the current X value to obtain a new X value.

  Next, as shown in step 212 (S212), it is determined whether or not the value of X exceeds A. When the value of X exceeds A, the process proceeds to step 214, and when the value of X does not exceed A, the process proceeds to step 206.

  Next, as shown in step 214 (S214), 1 is added to the current Y value to obtain a new Y value.

  Next, as shown in step 216 (S216), it is determined whether or not the value of Y exceeds B. If the value of Y exceeds B, the process proceeds to step 220. If the value of Y does not exceed B, the process proceeds to step 218.

  Next, as shown in step 218 (S218), the value of X is set to 0, and the routine proceeds to step 206.

  Next, as shown in step 220 (S220), from the acquired photoelectron spectrum, the peak areas of the two split peaks at each measurement position are obtained, and further, from the peak areas of the two peaks obtained, The peak area ratio at the measurement position is calculated.

  Next, as shown in step 222 (S222), based on the calibration curve stored in the storage unit 61 in the control unit 60, the film thickness of the thin film 112 at each measurement position based on the peak area ratio at each measurement position. Get the value of. Thereafter, the distribution of the film thickness of the thin film 112 is two-dimensionally displayed on the display unit 62 connected to the control unit 60.

  As described above, two-dimensional information of the film thickness of the thin film 112 in the analysis sample 110 can be obtained by the film thickness measurement method in the present embodiment.

  Note that by incorporating the film thickness measurement apparatus according to this embodiment into a part of the film formation apparatus, it is possible to know the film thickness of the formed thin film in a nondestructive manner immediately after film formation in the film formation apparatus. .

  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 method for measuring the thickness of a thin film in a sample in which a thin film is formed on a substrate,
Irradiating the thin film of the sample with X-rays to obtain a photoelectron spectrum;
In the photoelectron spectrum, each peak area is obtained from two photoelectron peaks of elements that are contained in the base material but not in the thin film, and a peak area ratio is obtained from each of the peak areas. Calculating
Obtaining a film thickness value of the thin film from the peak area ratio;
A film thickness analysis method characterized by comprising:
(Appendix 2)
The film thickness analysis method according to appendix 1, wherein the two photoelectron peaks are obtained by splitting the energy eigenvalues of electrons degenerated by spin-orbit interaction into two.
(Appendix 3)
By moving the position of X-rays irradiated on the thin film of the sample to obtain the photoelectron spectrum, calculating the peak area ratio, and obtaining the film thickness value of the thin film,
3. The method of analyzing a film thickness according to appendix 1 or 2, wherein the film thickness distribution of the thin film is obtained.
(Appendix 4)
The step of obtaining the value of the thickness of the thin film includes
Supplementary note 1 wherein the value of the film thickness of the thin film is obtained from the calculated peak area ratio based on a calibration curve indicating the relationship between the peak area ratio of the two photoelectron peaks and the film thickness of the thin film. To 4. The film thickness analysis method according to any one of items 1 to 3.
(Appendix 5)
The calibration curve is
Producing a plurality of calibration curve samples with different thicknesses of the thin film formed on the substrate;
Measuring the thickness of the thin film in each of the calibration curve samples;
Irradiating the thin film of the calibration curve sample with X-rays to obtain a photoelectron spectrum;
In the photoelectron spectrum of the calibration curve sample, each peak area is obtained from two photoelectron peaks of the elements that are included in the base material of the calibration curve sample but are not included in the thin film. Calculating a peak area ratio from each of the peak areas;
Appendix 4 characterized in that the calibration curve is obtained from the relationship between the thickness of the thin film in the calibration curve sample obtained by the measurement and the peak area ratio of the calibration curve sample obtained by the measurement. The film thickness analysis method described in 1.
(Appendix 6)
An X-ray source for generating X-rays applied to the thin film of a sample having a thin film formed on a substrate;
An analyzer for detecting photoelectrons generated by irradiating the X-ray;
A control unit for controlling the X-ray source and the analyzer;
Have
In the control unit, a photoelectron spectrum is created from the detected photoelectrons, and in the photoelectron spectrum, from the two photoelectron peaks of elements that are included in the base material but not included in the thin film, respectively. The film thickness analyzer is characterized in that a peak area ratio is calculated from the respective peak areas, and a value of the film thickness of the thin film is obtained from the peak area ratio.
(Appendix 7)
The sample is placed on a sample stage,
7. The film thickness analyzer according to appendix 6, wherein the film thickness distribution of the thin film is obtained by moving the sample stage and repeatedly creating a photoelectron spectrum.

DESCRIPTION OF SYMBOLS 10 Sample 11 Base material 12 Thin film 20 X-ray source 30 Analyzer 40 Detector 50 Sample stage 60 Control part 61 Memory | storage part 62 Display part 110 Sample 111 Base material 112 Thin film

Claims (5)

In the method for measuring the thickness of a thin film in a sample in which a thin film is formed on a substrate,
Irradiating the thin film of the sample with X-rays to obtain a photoelectron spectrum;
In the photoelectron spectrum, each peak area is obtained from two photoelectron peaks of elements that are contained in the base material but not in the thin film, and a peak area ratio is obtained from each of the peak areas. Calculating
Obtaining a film thickness value of the thin film from the peak area ratio;
A film thickness analysis method characterized by comprising:   2. The film thickness analysis method according to claim 1, wherein the two photoelectron peaks are obtained by splitting the energy eigenvalues of electrons degenerated by spin-orbit interaction into two. By moving the position of X-rays irradiated on the thin film of the sample to obtain the photoelectron spectrum, calculating the peak area ratio, and obtaining the film thickness value of the thin film,
The film thickness analysis method according to claim 1, wherein the film thickness distribution of the thin film is obtained. An X-ray source for generating X-rays applied to the thin film of a sample having a thin film formed on a substrate;
An analyzer for detecting photoelectrons generated by irradiating the X-ray;
A control unit for controlling the X-ray source and the analyzer;
Have
In the control unit, a photoelectron spectrum is created from the detected photoelectrons, and in the photoelectron spectrum, from the two photoelectron peaks of elements that are included in the base material but not included in the thin film, respectively. The film thickness analyzer is characterized in that a peak area ratio is calculated from the respective peak areas, and a value of the film thickness of the thin film is obtained from the peak area ratio. The sample is placed on a sample stage,
5. The film thickness analyzer according to claim 4, wherein the film thickness distribution of the thin film is obtained by moving the sample stage and repeatedly creating a photoelectron spectrum.

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