JP2996210B2 - Sample absorption current spectroscopy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface analysis technique, which measures an absorption current generated in a sample by irradiating an electron beam to a sample surface while changing acceleration energy, and adheres to the surface of the sample. Alternatively, the present invention relates to a method and an apparatus for analyzing elements contained in a sample surface.

[0002]

2. Description of the Related Art Conventional methods for elemental analysis of a surface and a substance attached to the surface include Auger electron spectroscopy (AES) in which an electron beam is irradiated and electrons emitted by an Auger electron excitation phenomenon are subjected to energy analysis. X-ray photoelectron spectroscopy (X
PS or ESCA), EPMA for irradiating an electron beam and analyzing the wavelength of X-rays by characteristic X-ray emission, electron beam energy loss spectroscopy (ELS) for irradiating an electron beam and analyzing the energy of inelastically scattered electrons, ions There is a secondary ion mass spectrometry (SIMS) for mass analysis of the amount of secondary ions generated by irradiation with a beam. All of these measurement methods irradiate a sample with an electron beam, an ion beam, X-rays, or the like, and detect emitted, scattered electrons, ions, or X-rays.

[0003]

In recent semiconductor devices having a very high degree of integration, a vertically elongated deep hole is often formed on the surface of the semiconductor device in the middle of the manufacturing process. However, when the aspect ratio of the hole is very large, the conventional elemental analysis method determines the direction in which electrons, ions, or X-rays enter the surface and the direction in which the detected electrons, ions, or X-rays exit. The orientations should be almost the same, and the elemental analysis at the bottom of this hole was very difficult due to the structure of the device.

The present invention has been made in view of this problem, and has as its object to perform elemental analysis of the bottom of the elongated hole.

[0005]

According to the analysis method of the present invention, a sample surface is irradiated with an electron beam, the acceleration energy of the electron beam is changed, and the current flowing from the sample surface to the back surface is changed with respect to the irradiation electron beam energy. Is characterized by analyzing elements that adhere to the sample surface or are contained in the sample surface.

According to the method of the present invention for analyzing the distribution of elements adhering to or contained in a sample surface, a method of irradiating an electron beam focused by an electron lens on a local region on the sample surface or electron beam. Irradiation while scanning the irradiation position,
Changing the acceleration energy of the electron beam from the sample surface
By measuring a change with respect to the irradiation electron beam energy of a current flowing into the back surface, and measuring the distribution of elements contained in the attachment or the surface of the sample on the sample surface.

According to the present invention, there is provided a device for analyzing an element adhered on or contained in a sample surface, comprising means for irradiating the sample surface with an electron beam while changing acceleration energy.
Means for measuring a change in the current flowing from the front surface to the back surface of the sample during irradiation with the electron beam energy.

The method of measuring a sample absorption current according to the present invention is a method of irradiating a sample with an electron beam and detecting the sample absorption current flowing into the sample. The change in the sample absorption current in the same cycle as the cycle is calculated as the change in the current flowing from the sample front to the back.
And detecting it.

A sample absorption current measuring apparatus according to the present invention is an apparatus for irradiating a sample with an electron beam and detecting the sample absorption current flowing into the sample. Irradiation means and sample absorption current change in the same cycle as the change in acceleration energy
And means for detecting a change in the current flowing from the front surface to the back surface of the sample .

In the present invention, a sample is irradiated with an electron beam, and the sample absorption current flowing through the sample due to the irradiation is measured.
The measurement is performed on the back surface side, and the element attached to the sample surface or contained in the sample surface is analyzed based on the obtained measurement value. For this reason, there is no need to use a detector in the direction in which the sample surface is irradiated with the electron beam, so that the bottom of a very elongated hole , that is, the bottom surface of a concave portion can be analyzed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, an electron beam accelerated to the same energy as the core level binding energy of an element to be detected is irradiated, and the core electrons are excited to a vacuum level or higher. Changes the sample absorption current. Specifically, for example, when the energy of the incident electrons is changed and the change in the sample absorption current at that time is measured, when the energy of the incident electrons is lower than the inner-level binding energy, the inner-shell electrons are excited and the vacuum is obtained. Although the energy can only be lower than the energy level, but the energy is higher than the core level binding energy, the core electrons are excited and become higher in energy than the vacuum level, so that they are emitted into the vacuum. For this reason, a large change occurs in the sample absorption current when the energy of the incident electrons exceeds the core level binding energy. Since the core level binding energy varies greatly depending on the element, the elemental analysis can be performed by changing the energy of the irradiated electrons and examining the energy at which the sample absorption current changes abruptly. is there. The two-dimensional distribution of elements can be examined by measuring the sample absorption current while scanning the surface of the sample using the focused electron beam. Furthermore, when examining the two-dimensional distribution of an element determined in a short time, fix the energy of the focused incident electron beam to the core state binding energy of the element and scan the electron beam to measure the sample absorption current. Analysis is possible.

In the present invention, an electron beam emitted from an electron gun is applied to a target location on a sample. FIG. 1 schematically shows an analyzer according to the present invention. This apparatus includes an electron gun 1 as an electron beam irradiation means and a variable voltage source 4 for changing the acceleration energy of the electron beam from the electron gun 1 and a current detection for measuring a sample absorption current flowing into the sample 2. And a container 3.

In the measurement in this apparatus, an electron beam is irradiated from the electron gun 1 to the surface of the sample 2 while changing the acceleration energy by changing the voltage from the variable voltage source 4. According to the change in the acceleration energy, the element to be analyzed is changed to the sample 2
If the element exists on the surface, a change occurs in the current detected by the current detector 3 in accordance with the above-described principle, and the presence of the element to be analyzed can be detected by measuring a current change specific to the element to be analyzed.

When measuring only a specific location on the sample surface, the electron beam to be irradiated by the electron gun is focused by a control system such as an electron lens, is irradiated to the specific location, and the acceleration energy of the irradiated electron is changed. The fluctuation of the sample absorption current with respect to the energy change is measured. The acceleration energy of the irradiated electron is changed within a range including the core level binding energy of the element to be detected.

On the other hand, when examining the two-dimensional spatial distribution of elements on the surface, an electron beam to be irradiated by an electron lens is focused, and the electron beam is scanned and measured in a desired range. The electron beam scanning system may have a known configuration. FIG. 2 shows an example of an apparatus for measuring such a spatial distribution. The device of FIG. 2 has a configuration in which an electron lens 5 is added to the device of FIG.

At each point of electron beam scanning in the measurement in this apparatus, the acceleration energy of incident electrons is changed, and the fluctuation of the sample absorption current with respect to the change is measured. By examining the energy at which the sample absorption current greatly changes at each point and the amount of the change, the two-dimensional element distribution (spatial distribution) can be examined from the measured data.

Further, when examining the spatial distribution of a two-dimensional amount of a specific element on the surface in a short time, the electron beam to be irradiated is focused by an electron lens, and the acceleration energy of the electron beam is converted into the target element. Near the shell level binding energy,
For example, a range that includes the inner-level binding energy of the element to be measured, that is, a range in which the energy is periodically varied from an energy lower than the inner-level binding energy to an energy that is higher than the inner-level binding energy. Scan and measure. FIG. 3 shows an example of an apparatus that can be used for such a purpose. In the apparatus shown in FIG. 3, the sine wave generator 6 periodically fluctuates the acceleration energy of the electron beam near the core-level binding energy of the target element at each point of scanning, and irradiates the same in the lock-in amplifier 7. A fluctuation component of the sample absorption current at the same frequency as the energy change of the electron beam is detected and extracted as an output signal 8. From the magnitude of the fluctuation signal of the sample absorption current at each scanning point, the spatial distribution of the two-dimensional quantity of the element can be examined.

[0018]

【Example】

Example 1 A diameter of 0.35 on a silicon semiconductor substrate having a trench structure for a dynamic random access memory (DRAM)
The bottom of a cylindrical hole having a depth of 5 μm and a depth of 5 μm was irradiated with a focused electron beam from a direction perpendicular to the substrate surface, and the sample absorption current at that time was measured to analyze the composition of that portion (FIG. 4). The acceleration energy of the irradiated electron beam was changed in the range of 1 keV to 3 keV, and the beam diameter was 0.25.
It was about μm. As a result, it was observed that the sample absorption current greatly changed when the energy of the incident electron beam was about 1840 eV. This 1840 eV signal corresponds to the core level binding energy of the 1s orbit of silicon. From this, it is understood that the main component of the element on the surface portion at the bottom of the hole is silicon. Example 2 On a silicon semiconductor substrate having the same trench structure for a DRAM as in Example 1, a tungsten film having a thickness of about 0.05 μm was formed by a sputtering method from a direction shifted by about 30 ° from a direction perpendicular to the surface (FIG. 5). This sample was irradiated with an electron beam focused from the direction perpendicular to the substrate surface as in Example 1,
By measuring the sample absorption current at that time, the composition of that portion was analyzed. In this experiment, the change in the sample absorption current was observed while changing the acceleration energy of the electron beam from 1 keV to 3 keV at each point where the electron beam was scanned. As a result, in portions other than the holes on the substrate surface, the energy of the incident electron beam is 2820 eV, 2575 eV, 2280 eV.
At the energies of eV, 1870 eV, and 1810 eV, a large change was observed in the sample absorption current.
At an energy of 40 eV, a large change was observed in the sample absorption current. Of these, 2820 eV, 2575 eV,
The signals of 2280 eV, 1870 eV and 1810 eV correspond to the inner-shell binding energies of 3s, 3p and 3d of tungsten, and there is much tungsten on the surface of the substrate other than the holes, while the surface at the bottom of the holes is Indicates that silicon is abundant.

Embodiment 3 A thin film having a thickness of 200.degree. Is deposited on a silicon semiconductor substrate having the same trench structure for a DRAM as in the embodiment and gold is sputtered by argon ions from a direction shifted from the surface perpendicular direction by about 45.degree. (FIG. 6). The sample was irradiated with an electron beam focused from the direction perpendicular to the surface of the substrate, and the sample absorption current at that time was measured to analyze the composition of that portion, as in the above experiment. In this experiment, the acceleration energy of the electron beam was changed from 1 keV to 3 keV at each point where the electron beam was scanned.
The change in the sample absorption current was observed while changing the current.
As a result, in the hole portion on the substrate surface, the energy of the incident electron beam is 2740 eV, 2290 eV and 22 kV.
A large change was observed in the sample absorption current at an energy of 10 eV, and a large change was observed in a portion other than the hole at an energy of 1840 eV. Of these, two
The signals of 740 eV, 2290 eV and 2210 cV correspond to the core-level binding energies of 3p and 3d of gold, and there is a lot of gold on the surface at the bottom of the hole, while silicon is on the surface of the substrate other than the hole. Indicates that there are many.

[0020]

According to the present invention, it is possible to perform elemental analysis on the bottom of a thin and deep hole having a large aspect ratio and formed on a semiconductor device.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a sample absorption current spectrometer.

FIG. 2 is a schematic diagram of a sample absorption current spectrometer for performing local analysis.

FIG. 3 is a schematic view of a sample absorption current spectrometer for performing local analysis at high speed.

FIG. 4 is a schematic diagram of a measurement of a semiconductor sample having a trench structure and an enlarged cross-sectional view of the sample.

FIG. 5 is a sectional view of a trench structure sample in which a tungsten film is formed by a sputtering method.

FIG. 6 is a cross-sectional view of a trench structure sample in which a gold thin film is formed by a vapor deposition method and the surface is polished by an argon ion sputtering method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electron gun 2 sample 3 current detector 4 variable voltage source 5 electron lens 6 sine wave generator 7 lock-in amplifier 8 output signal 9 semiconductor sample having trench structure 10 groove portion of trench 11 formed tungsten film 12 gold Evaporated film

Claims (10)

(57) [Claims] An electron beam is irradiated on the surface of a sample, the acceleration energy of the electron beam is changed, and the change of the current flowing from the surface of the sample to the back surface with respect to the irradiated electron beam energy is measured. An analysis method characterized by analyzing elements attached to or contained in a sample surface. 2. The analysis method according to claim 1, wherein the electron beam is an electron beam focused using an electron lens, and the local region on the sample surface is irradiated with the electron beam. 3. An electron beam focused by an electron lens is irradiated onto a local region on a sample surface or irradiated while scanning an electron beam irradiation position, and the acceleration energy of the electron beam is changed to change the electron beam from the sample surface. By measuring the change in the current flowing into the back surface with respect to the irradiation electron beam energy, the distribution of elements attached to the sample surface or contained in the sample surface can be measured.
Measurement method characterized by that. 4. A concave portion in which the local region is on a sample surface.
A method according to claim 2 or 3, comprising a bottom of 5. The method according to claim 1, periodically changing the acceleration energy of the electron beam in a range including a core level binding energy of an element to be measured. 6. A device for irradiating an electron beam while changing the acceleration energy on the surface of a sample, and a device for measuring a change in current flowing from the surface of the sample to the back surface of the sample during irradiation with the electron beam with respect to the irradiation electron beam energy. An analyzer for an element attached to or contained on a sample surface. 7. An electron lens for focusing an electron beam, and an electron beam control system for irradiating the focused electron beam to a local region on the sample surface or irradiating the focused electron beam while scanning an electron beam irradiation position. An analyzer according to claim 6 . 8. The acceleration energy of the electron beam, spectrometer according to claim 6 or 7 periodically varied in a range including a core level binding energy of an element to be measured. 9. A method for irradiating a sample with an electron beam and detecting a sample absorption current flowing into the sample, wherein the acceleration energy of the irradiating electron beam is periodically changed, and a change in the sample absorption current having the same cycle as the cycle is obtained. Flow from the sample front to the back.
A method for measuring a sample absorption current, which is detected as a change in a current flowing through the sample. 10. A device for irradiating a sample with an electron beam and detecting a sample absorption current flowing into the sample, means for irradiating the sample with the electron beam by periodically changing its acceleration energy, The current flowing from the sample front surface to the back surface by the sample absorption current change of the same cycle as the change cycle
A means for detecting the change in the measurement value.