JP2000030658A - Total reflection x-ray photoelectron spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a total reflection X-ray photoelectron spectrometer capable of easily setting the sample tilt angle for XPS measurement under the total reflection condition. SOLUTION: This total reflection X-ray photoelectron spectrometer is provided with an X-ray monochromator 3 monochromating the radiated X-rays, a sample tilt mechanism capable of adjusting the sample tilt angle for radiating the monochromated X-rays to a sample surface under the total reflection condition, and an electrostatic semispherical photoelectron energy analyzer 1 energy- distinguishing and detecting the photoelectrons emitted from the sample. This device is provided with a data collection unit 7, a sample stage control unit 8 and an XPS measurement computer 9 for setting the optimum tilt angle based on the profile indicating the relation of the P/B ratio between the sample tilt angle and the perceived photoelectron peak or the relation of the sample tilt angle and the intensity ratio between the photoelectron peak of a sample electrode surface layer and the photoelectron peak of a substrate layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray photoelectron spectrometer (XPS) equipped with an X-ray monochromator, and particularly to an X-ray photoelectron spectrometer (hereinafter, referred to as XPS measurement) under total reflection conditions. The present invention relates to a total reflection X-ray photoelectron spectrometer capable of easily setting a sample tilt angle.

[0002]

2. Description of the Related Art In general, an X-ray photoelectron spectrometer equipped with an X-ray monochromator can remove continuous X-rays due to bremsstrahlung compared with an apparatus using an ordinary non-monochromatic X-ray source. In the observed spectrum, the background component due to inelastic scattered electrons is significantly reduced, and a spectrum having a good peak-to-background ratio (P / B ratio) is obtained. However, it is difficult for a measuring apparatus equipped with such an X-ray monochromator to detect trace elements on a semiconductor wafer or the like.

One of the factors that makes it difficult to detect such a trace element is a background signal of a photoelectron spectrum. This background signal is generated by secondary electrons (including photoelectrons, Auger electrons, etc.) generated inside the substance.
Loses kinetic energy due to inelastic scattering while being transported to the material surface, resulting in a continuous energy distribution. If the signal intensity of the background component is large, the photoelectron signal of the trace element is governed by the S / N ratio due to the statistical fluctuation of the background signal, and it becomes difficult to detect the photoelectron peak of the trace element.

[0004] To detect the photoelectron peak of a trace element, reduction of the background signal is an effective means. The reduction of the background signal can be realized by reducing the penetration depth of the excitation X-ray used for the excitation source of the photoelectrons into the sample and shortening the distance that the generated photoelectrons travel in the substance.

[0005] The penetration depth of the X-ray is determined by the incident angle of the X-ray (θ ₀ :
When the angle of the incident X-ray beam with respect to the sample surface) is set to be equal to or less than the critical angle of total reflection of the X-rays (θ _C ) determined by the wavelength of the excitation X-ray and the sample material, the penetration depth of the X-rays under the condition of total reflection is As shown in FIG. 6, the area is about several nm to about 10 nm. FIG. 3 is a diagram showing a simulation result of the penetration depth of X-rays when the Alα ray (0.833 nm) is irradiated onto the Si substrate while changing the incident angle. The horizontal axis represents θ ₀ / θ _C. The vertical axis indicates the X-ray penetration depth Labs (nm) in consideration of absorption.

[0006] Therefore, conventionally, under total reflection conditions, XP
In order to perform the S measurement, the critical angle of total reflection θ _C determined by the constituent elements in the sample to be measured and the wavelength of the incident X-ray is calculated, and the sample tilt angle is set. In addition, in order to perform XPS measurement under total reflection conditions, the X-ray source, the dispersive crystal, and the sample to be measured are accurately adjusted on the Rowland circle, and then monochromatized to the critical angle of total reflection or less with respect to the sample surface. It is necessary to set the incident angle of the reflected X-ray. When adjusting this incident angle, it is necessary to monitor the intensity / image of the reflected X-ray with an X-ray detector or monitor the absorption current of the sample. A method is used.

[0007]

However, it is necessary to calculate the total reflection critical angle θ _C determined by the constituent elements of the sample to be measured and the wavelength of the incident X-rays, and to calculate the intensity / image of the reflected X-rays using an X-ray detector. There is a problem in that it is quite complicated to monitor the data by using the method or monitor the absorption current of the sample to adjust the incident angle.

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, and XPS measurement is performed 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 a sample tilt angle for performing the above.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an X-ray monochromator for monochromaticizing irradiated X-rays and an X-ray monochromator for irradiating monochromatic X-rays to a sample surface under total reflection conditions. In the total reflection X-ray photoelectron spectrometer, which has a mechanism that can adjust the tilt angle of the sample and an electrostatic hemispherical photoelectron energy analyzer that separates the photoelectrons emitted from the sample by energy, focuses on the tilt angle of the sample with respect to the incident X-ray. Means for setting an optimal sample tilt angle based on a profile representing the relationship between the background intensity ratio with respect to the photoelectron peak obtained, or the relationship between the sample tilt angle and the intensity ratio of the photoelectron peak of the substrate layer with respect to the photoelectron peak of the sample pole surface layer. It is characterized by having.

As described above, the relationship between the sample tilt angle with respect to the incident X-ray and the background intensity ratio with respect to the focused photoelectron peak, or the relationship between the sample tilt angle and the intensity ratio of the photoelectron peak of the substrate layer with respect to the photoelectron peak of the sample pole surface layer. Means for setting an optimum sample tilt angle based on a profile representing the relationship of the following formulas: In XPS measurement under total reflection conditions, the critical angle of total reflection determined by the constituent elements of the sample to be measured and the wavelength of the incident X-ray is determined. The X-ray incident angle can be easily set without calculation, and XPS measurement can be easily performed on various samples having a flat surface under the condition of total reflection.

[0011]

Next, an embodiment will be described. FIG. 1 is a schematic view showing the appearance of a total reflection X-ray photoelectron spectroscopy apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes an electrostatic hemispherical photoelectron energy analyzer that separates and detects photoelectron energy generated from a sample, 2 denotes a sample stage unit,
Reference numeral 3 denotes an X-ray monochromator, and 4 denotes a standard X-ray source for irradiating the sample with X-rays.

FIG. 2 is a sectional view of the sample stage section X in FIG.
FIG. 3 is an enlarged cross-sectional view illustrating an internal configuration of a line monochromator and an excitation X-ray source unit. 2, reference numeral 11 denotes a sample stage, 12 denotes a sample to be measured such as a silicon wafer mounted on the sample stage 11, 13 denotes a sample tilting mechanism, 14 denotes an X-ray monochromator spectral crystal, and 15 denotes an X-ray monochromator. An X-ray source for irradiating the spectral crystal 14 with X-rays, 16 is a photoelectron collection lens for collecting photoelectrons generated from the sample, and 17 is an observation chamber.

In a conventional X-ray photoelectron spectrometer using a conventional ordinary X-ray monochromator having the same structure as described above, the X-rays generated by the X-ray source are separated by using a monochromator spectroscopic crystal. The sample is illuminated on the sample, but in the normal spectroscopic method, the sample is −10 ° so that the solid angle of the monochromator crystal is used in order to increase the amount of light.
It is inclined to about -30 degrees. On the other hand, in the present invention, since it is assumed that the XPS measurement is performed under the condition of total reflection, a very shallow inclination angle is set.

When the tilt angle is set so as to satisfy the total reflection, the range of the photoelectrons generated in the sample to the sample surface is short due to the shallow penetration depth of the X-rays, and the inelasticity is low. The probability of energy loss of photoelectrons due to scattering is small, and the background intensity of the spectrum caused by inelastic scattering is smaller than the spectrum measured at a normal X-ray incident angle larger than the critical angle of total reflection. This aspect,
FIGS. 3A and 3B show a background shape when the Al substrate is irradiated with Alk α-rays on the Si substrate. (A) of FIG.
Is the XPS measurement spectrum under the condition of total reflection, FIG.
Indicates an XPS measurement spectrum under normal conditions, in which the horizontal axis represents binding energy and the vertical axis represents intensity in arbitrary units. As can be seen from these figures, the background intensity B is smaller under the total reflection condition than under the normal condition. In addition, (A) of FIG.
In (B), P indicates the peak spectrum intensity.

As a feature of the XPS measurement spectrum under the condition of total reflection, since the penetration depth of X-rays is small, photoelectrons originating from elements existing near the pole surface are dominant. FIG. 4 shows a comparison of photoelectron peaks caused by the extreme surface layer and the substrate layer under total reflection conditions and normal conditions.
(A) and (B). These are obtained by irradiating the Si substrate on which an extremely thin natural oxide film exists with Al2α radiation to the Si2 substrate.
FIG. 4A is a diagram showing the intensity of the photoelectron peak, and FIG. 4A is a diagram showing the case of the total reflection condition, and FIG. 4B is a diagram showing the case of the normal condition. As can be seen from these figures, when X-rays are irradiated under total reflection conditions, the intensity P _SUR of the Si2p photoelectron peak due to the oxide layer present on the substrate surface and the intensity of the Si2p photoelectron peak due to Si in the substrate layer. The intensity ratio of P _SUB changes.

As described above, in the XPS measurement spectrum under the condition of total reflection, the background intensity is smaller than the background intensity of the spectrum measured at a normal X-ray incident angle, and the surface intensity of the sample is very small. The present invention is characterized in that the intensity ratio of the photoelectron peak due to the element present and the photoelectron peak due to the substrate layer of the sample changes. The present invention focuses on these points and performs XPS measurement under total reflection conditions. The setting of the incident angle of the incident X-ray with respect to the sample surface is performed in the profile showing the relationship of the P / B ratio (or the reciprocal thereof) of the focused photoelectron peak with respect to the tilt angle, or in the extreme surface layer of the sample with respect to the sample tilt angle. A profile showing the relationship between the intensity ratio of the photoelectron peak caused by the element and the photoelectron peak caused by the substrate layer of the sample is created, and the profiles are created. And it is to set the optimum sample tilt angle based on the file.

Therefore, in the present invention, as shown in the embodiment of FIG. 1, the drive motor 5 for driving the tilt mechanism 13 for setting the tilt angle of the sample stage 11 and the drive motor 5 are controlled. Stage control unit 6 and XPS
A data collection unit 8 for acquiring spectral data via the photoelectron detector 7, a profile is created based on the acquired data to determine an optimum sample tilt angle,
An XPS measurement computer 9 for controlling each unit is provided. In FIG. 1, reference numeral 10 denotes a gate valve.

Next, the operation of setting the sample tilt angle in the embodiment configured as described above will be described with reference to the flowchart of FIG. First, the sample to be measured 12 is set on the sample stage 11, and a deep inclination angle to be used in normal XPS measurement is set (step S1), and wide spectrum measurement of the entire region of the sample is performed (step S2). Next, based on the wide spectrum measurement result, which spectrum is determined as the target peak spectrum is detected and determined,
The inclination angle evaluation peak is set (step S3).
Next, a measurement step (step S4) for creating a profile for evaluating the tilt angle is started. 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), an intensity ratio or a P / B ratio is calculated (step S4-3). Here, a photoelectron peak caused by an element existing in the very surface layer of the sample and a photoelectron caused by the substrate layer of the sample are calculated. The peak intensity ratio or the P / B ratio of the focused photoelectron peak is calculated.

By repeating the operations of steps S4-1 to S4-3, a profile for evaluating the inclination angle is created. In the illustrated example, the sample inclination angle θ /
4 shows a profile representing a reciprocal of the P / B ratio with respect to θ _C. From the profile created in this way, the peak intensity ratio between the extreme surface layer and the substrate layer or the inclination angle that is near the minimum of the reciprocal of the illustrated P / B ratio is obtained, and the spectrum measurement under the total reflection condition is performed. The optimum sample tilt angle to be performed is determined (Step S5). By setting the sample tilt angle on the sample stage via the stage control unit and performing measurement, XPS measurement under total reflection conditions is performed.

[0020]

As described above with reference to the embodiments, according to the present invention, upon XPS measurement under total reflection conditions, the total reflection criticality determined by the constituent elements of the sample to be measured and the wavelength of the incident X-rays. The X-ray incident angle can be easily set without calculating the angle, and XPS measurement can be easily performed on various samples having a flat surface under the condition of total reflection.

[Brief description of the drawings]

FIG. 1 is a schematic external view of an embodiment of a total reflection X-ray photoelectron spectroscopy apparatus according to the present invention.

FIG. 2 is a 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 the extreme surface layer and the 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 a penetration depth of X-rays when an Alkα ray is irradiated onto a Si substrate while changing an incident angle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrostatic hemispherical photoelectron energy analyzer 2 Sample stage part 3 X-ray monochromator 4 Standard X-ray source part 5 Sample tilting mechanism drive motor 6 Stage control unit 7 Photoelectron detector 8 Data collection unit 9 Computer for XPS measurement 10 Gate valve 11 Sample stage 12 Sample 13 Sample tilt mechanism 14 X-ray monochromator spectral crystal 15 X-ray source 16 Photoelectron collection lens 17 Observation chamber

Claims (2)

[Claims] An X-ray monochromator for monochromaticizing irradiated X-rays, a mechanism for adjusting a sample tilt angle for irradiating monochromatic X-rays to a sample surface under total reflection conditions, and a photoelectron emitted from the sample -Reflection X-ray photoelectron spectrometer having an electrostatic hemispherical photoelectron energy analyzer that separates energy into energy for detection, based on a profile representing the relationship between the sample tilt angle with respect to incident X-rays and the background intensity ratio with respect to the focused photoelectron peak Total reflection X-ray photoelectron spectroscopy apparatus comprising means for setting an optimum sample tilt angle by using the method. 2. An X-ray monochromator for monochromaticizing irradiated X-rays, a mechanism capable of adjusting a sample inclination angle for irradiating monochromatic X-rays on a sample surface under total reflection conditions, and a photoelectron emitted from the sample. Represents 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 surface layer of the sample in a total reflection X-ray photoelectron spectrometer having an electrostatic hemispherical photoelectron energy analyzer that separates and detects energy. A total reflection X-ray photoelectron spectroscopy apparatus comprising means for setting an optimum sample tilt angle based on a profile.