JP3643484B2 - Total reflection X-ray photoelectron spectrometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray photoelectron spectrometer (XPS) equipped with an X-ray monochromator, and in particular, easily sets an optimal sample tilt angle for performing X-ray photoelectron spectroscopy measurement (hereinafter referred to as XPS measurement) under total reflection conditions. The present invention relates to a total reflection X-ray photoelectron spectrometer that can be used.
[0002]
[Prior art]
In general, an X-ray photoelectron spectrometer equipped with an X-ray monochromator can remove continuous X-rays due to bremsstrahlung compared to an apparatus using an ordinary X-ray source that is not monochromatic, so the observed spectrum is A background component due to inelastically scattered electrons is significantly reduced, and a spectrum having a good peak / background ratio (P / B ratio) can be obtained. However, even in a measuring apparatus equipped with such an X-ray monochromator, it is difficult to detect a trace element on a semiconductor wafer.
[0003]
One factor that makes it difficult to detect such trace elements is the background signal of the photoelectron spectrum. This background signal has a continuous energy distribution because the secondary electrons (including photoelectrons, Auger electrons, etc.) generated inside the material lose kinetic energy due to inelastic scattering while being transported to the material surface. Is attributed. When the signal intensity of the background component is high, the trace element photoelectron signal is governed by the S / N ratio due to statistical fluctuation of the background signal, and it is difficult to detect the trace element photoelectron peak.
[0004]
Therefore, in order to detect the photoelectron peak of a trace element, reduction of the background signal is an effective means. Reduction of the background signal can be realized by reducing the penetration depth of the excitation X-ray used for the photoelectron excitation source into the sample and shortening the distance that the generated photoelectron travels in the substance.
[0005]
The penetration depth of X-rays is defined as the X-ray incident angle (θ ₀ : the angle of the X-ray incident flux with respect to the sample surface), the X-ray total reflection critical angle (θ _C ) determined by the wavelength of the excited X-ray and the sample material. When set to the following, as shown in FIG. 6 showing the penetration depth of the X-rays under the total reflection condition, it becomes a region of several nm to 10 nm. FIG. 6 is a diagram showing a simulation result of the penetration depth of X-rays when the Si substrate is irradiated with Alkα rays (0.833 nm) while changing the incident angle. The horizontal axis represents θ ₀ / θ _C. The vertical axis represents the penetration depth Labs (nm) of X-rays taking absorption into consideration.
[0006]
Therefore, conventionally, in order to perform XPS measurement under total reflection conditions, the sample tilt angle is set by calculating the total reflection critical angle θ _C determined by the constituent elements in the sample to be measured and the wavelength of the incident X-ray. I am doing so. In addition, in order to perform XPS measurement under total reflection conditions, the X-ray source, the spectroscopic crystal, and the measurement sample are accurately adjusted on the Roland circle, and then are monochromatic below the critical angle of total reflection with respect to the sample surface. It is necessary to set the incident angle of the X-ray, but when adjusting the incident angle, the intensity / image of the reflected X-ray is monitored with an X-ray detector, or the absorption current of the sample is monitored. The method is used.
[0007]
[Problems to be solved by the invention]
However, the total reflection critical angle θ _C determined by the constituent element of the sample to be measured and the wavelength of the incident X-ray is calculated, the intensity / image of the reflected X-ray is monitored by an X-ray detector, the absorption current of the sample In order to adjust the incident angle by monitoring the above, there is a problem that a considerably complicated work is required.
[0008]
The present invention has been made to solve the above-mentioned problem in setting the sample tilt angle when XPS measurement is performed under total reflection conditions in a conventional X-ray photoelectron spectrometer. In order to perform XPS measurement under total reflection conditions. It is an object of the present invention to provide a total reflection X-ray photoelectron spectrometer capable of easily setting the sample inclination angle.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides an X-ray monochromator for monochromatic irradiation X-rays, a mechanism capable of adjusting a sample tilt angle for irradiating the monochromatic X-rays on the sample surface under total reflection conditions, and , have a electrostatic hemispherical photoelectron energy analyzer for detecting the photoelectrons emitted from the sample and energy separation, the total reflection X-ray photoelectron spectrometer having a reduced background components due inelastic scattered electrons in the observed spectrum, incident Based on the profile representing the relationship between the sample tilt angle with respect to X-rays and the background intensity ratio to the focused photoelectron peak, or the relationship between the sample tilt angle and the photoelectron peak intensity ratio of the substrate layer to the photoelectron peak of the sample electrode surface layer. Means for setting an optimum sample inclination angle is provided.
[0010]
In this way, in the total reflection X-ray photoelectron spectrometer in which the background component due to inelastically scattered electrons in the observation spectrum is reduced using an X-ray monochromator for monochromatic irradiation X-rays, the sample tilt angle with respect to the incident X-ray and the focus Means for setting the optimum sample tilt angle based on the profile representing the relationship between the background intensity ratio to the measured photoelectron peak or the relationship between the sample tilt angle and the intensity ratio of the photoelectron peak of the substrate layer to the photoelectron peak of the sample electrode surface layer By setting the X-ray incident angle, it is possible to easily set the X-ray incident angle without calculating the total reflection critical angle determined by the constituent element of the sample to be measured and the wavelength of the incident X-ray. This makes it possible to easily perform XPS measurement under total reflection conditions on various samples having a flat surface.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments will be described. FIG. 1 is a schematic view showing the appearance of a total reflection X-ray photoelectron spectrometer according to the present invention. In FIG. 1, 1 is an electrostatic hemispherical photoelectron energy analyzer that separates and detects the energy of photoelectrons generated from a sample, 2 is a sample stage unit, 3 is an X-ray monochromator, and 4 is for irradiating the sample with X-rays. Standard X-ray source unit.
[0012]
FIG. 2 is an enlarged cross-sectional view showing the internal configuration of the sample stage unit, X-ray monochromator, and excitation X-ray source unit in FIG. In FIG. 2, 11 is a sample stage, 12 is a sample to be measured such as a silicon wafer placed on the sample stage 11, 13 is a sample tilting mechanism, 14 is an X-ray monochromator spectral crystal, and 15 is an X-ray monochromator. An X-ray source for irradiating the spectral crystal 14 with X-rays, 16 a photoelectron collecting lens for collecting photoelectrons generated from the sample, and 17 an observation chamber.
[0013]
In an X-ray photoelectron spectrometer using a conventional ordinary X-ray monochromator having the same structure as described above, X-rays generated by an X-ray source are spectrally separated using a monochromator spectral crystal and applied to a sample. Although the irradiation is performed, the sample is tilted to about −10 ° to −30 ° so that all solid angles of the monochromator spectral crystal are used in order to increase the amount of light in the normal spectroscopic method. On the other hand, in the present invention, since it is premised that XPS measurement is performed under the total reflection condition, a very shallow inclination angle is set.
[0014]
When the tilt angle is set to satisfy total reflection in this way, the X-ray penetration depth is shallow, so the range of photoelectrons generated in the sample to the sample surface is short, and thus photoelectrons due to inelastic scattering are generated. The energy loss probability of the spectrum is small, and the background intensity of the spectrum caused by inelastic scattering is small compared to the spectrum measured at a normal X-ray incident angle larger than the total reflection critical angle. This mode is shown in FIGS. 3A and 3B showing the background shape when the Alkα ray is irradiated on the Si substrate. 3A shows the XPS measurement spectrum under the total reflection condition, FIG. 3B shows the XPS measurement spectrum under the normal condition, the horizontal axis indicates the binding energy, and the vertical axis indicates the intensity in arbitrary units. Yes. As can be seen from these figures, the background intensity B is smaller in the total reflection condition than in the normal condition. In FIGS. 3A and 3B, P indicates the peak spectrum intensity.
[0015]
Further, as a feature of the XPS measurement spectrum under the total reflection condition, since the penetration depth of X-rays is shallow, photoelectrons caused by elements existing near the pole surface are dominant. This mode is shown in FIGS. 4A and 4B showing a comparison of photoelectron peaks caused by the extreme surface layer and the substrate layer under total reflection conditions and normal conditions. These are diagrams showing the intensity of the Si2p photoelectron peak when an Si substrate having an extremely thin natural oxide film is irradiated with Alkα rays. FIG. 4A shows the total reflection condition, and FIG. It is a figure which shows the case of normal conditions. As can be seen from these figures, when X-rays are irradiated under total reflection conditions, the intensity of the Si2p photoelectron peak P _SUR caused by the oxide layer existing on the substrate surface and the intensity of the Si2p photoelectron peak caused by Si of the substrate layer. The intensity ratio of _PSUB changes.
[0016]
As described above, in the XPS measurement spectrum under the total reflection condition, the background intensity of the spectrum measured at a normal X-ray incident angle is small, and the elements present in the extreme surface layer of the sample The present invention is characterized in that the intensity ratio between the photoelectron peak caused by the photoelectron peak and the photoelectron peak caused by the sample substrate layer changes, and the present invention pays attention to these points, and the incident X for performing the XPS measurement under the total reflection condition. The incident angle setting of the line to the sample surface is caused by the profile indicating the relationship of the P / B ratio (or the reciprocal) of the focused photoelectron peak with respect to the tilt angle, or the element existing in the extreme surface layer of the sample with respect to the sample tilt angle. Create a profile that shows the relationship between the photoelectron peak and the intensity ratio of the photoelectron peak due to the substrate layer of the sample. And it is to set the optimum specimen rotation angle Zui.
[0017]
Therefore, in the present invention, as shown in the embodiment of FIG. 1, the drive motor 5 that drives the tilt mechanism 13 for setting the tilt angle of the sample stage 11, and the stage control unit that controls the drive motor 5 6 and a data acquisition unit 8 for acquiring XPS spectral data via the photoelectron detector 7, and a profile is created on the basis of the acquired data to determine the optimum sample tilt angle and control of each part is performed. A computer 9 is provided. In FIG. 1, 10 is a gate valve.
[0018]
Next, the operation of setting the sample inclination angle in the embodiment configured as described above will be described based on the flowchart of FIG. First, the sample 12 to be measured is set on the sample stage 11, a deep tilt angle is set for normal XPS measurement (step S1), and wide spectrum measurement is performed on the entire region of the sample (step S2). Next, based on the wide spectrum measurement result, it is detected and determined which spectrum is the target peak spectrum, and a peak for tilt angle evaluation is set (step S3). Next, a measurement step (step S4) for creating a profile for tilt angle evaluation is entered. Here, the sample tilt angle is changed little by little (step S4-1), and XPS measurement is performed each time (step S4-1). In step S4-2), the intensity ratio or P / B ratio is calculated (step S4-3) . Here, the intensity ratio between the photoelectron peak due to the element existing in the extreme surface layer of the sample and the photoelectron peak due to the substrate layer of the sample, or the P / B ratio of the focused photoelectron peak is calculated.
[0019]
By repeating the operations in steps S4-1 to S4-3, an inclination angle evaluation profile is created. In the illustrated example, a profile representing the relationship of the reciprocal of the P / B ratio to the sample tilt angle θ / θ _C is shown. From the profile created in this manner, the peak intensity ratio between the extreme surface layer and the substrate layer or the inclination angle near the minimum of the reciprocal of the P / B ratio shown in the figure is obtained, and spectrum measurement under total reflection conditions is performed. The optimum sample tilt angle for performing is determined (step S5). XPS measurement under total reflection conditions is performed by setting the sample tilt angle to the sample stage via the stage control unit and performing measurement.
[0020]
【The invention's effect】
As described above based on the embodiments, according to the present invention, the total reflection critical angle determined by the constituent element of the sample to be measured and the wavelength of the incident X-ray is calculated in the XPS measurement under the total reflection condition. Therefore, the X-ray incident angle can be easily set, and XPS measurement can be easily performed on various samples having a flat surface under total reflection conditions.
[Brief description of the drawings]
FIG. 1 is a schematic external view of an embodiment of a total reflection X-ray photoelectron spectrometer according to the present invention.
2 is a cross-sectional view showing an internal structure of a main part of the embodiment shown in FIG.
FIG. 3 is a diagram showing background intensity under total reflection conditions and normal conditions.
FIG. 4 is a diagram showing photoelectron peaks caused by an extreme surface layer and a substrate layer under total reflection conditions and normal conditions.
FIG. 5 is a flowchart for explaining the operation of the embodiment shown in FIG. 1;
FIG. 6 is a diagram showing a simulation result of an X-ray penetration depth when an Alkα ray is irradiated on an Si substrate while changing an incident angle.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electrostatic hemispherical type photoelectron energy analyzer 2 Sample stage part 3 X-ray monochromator 4 Standard X-ray source part 5 Sample tilt mechanism drive motor 6 Stage control unit 7 Photoelectron detector 8 Data collection unit 9 XPS measurement computer
10 Gate valve
11 Sample stage
12 samples
13 Sample tilt mechanism
14 X-ray monochromator crystal
15 X-ray source
16 Photoelectron collection lens
17 Observation chamber

Claims (2)

X-ray monochromator for monochromatic irradiation X-rays, mechanism for adjusting the sample tilt angle for irradiating the monochromatic X-rays to the sample surface under total reflection conditions, and photoelectrons emitted from the sample are detected by energy separation possess the electrostatic hemispherical photoelectron energy analyzer that, in the total reflection X-ray photoelectron spectrometer having a reduced background components due inelastic scattered electrons in the observed spectrum, for photoelectron peak which focuses the specimen rotation angle with respect to the incident X-ray A total reflection X-ray photoelectron spectrometer comprising means for setting an optimum sample inclination angle based on a profile representing a relationship with a background intensity ratio. X-ray monochromator for monochromatic irradiation X-rays, mechanism for adjusting the sample tilt angle for irradiating the monochromatic X-rays to the sample surface under total reflection conditions, and photoelectrons emitted from the sample are detected by energy separation substrate have a electrostatic hemispherical photoelectron energy analyzer, in the total reflection X-ray photoelectron spectrometer having a reduced background components due inelastic scattered electrons in the observed spectrum, for photoelectron peak of specimen rotation angle and the sample electrode surface layer A total reflection X-ray photoelectron spectrometer comprising means for setting an optimum sample inclination angle based on a profile representing a relationship with the intensity ratio of the photoelectron peak of the layer.

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