JP2962073B2 - Measurement method of concentration distribution of trace elements - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a concentration distribution of a trace element, and more particularly, to a method of measuring a distribution of a trace impurity contained in a semiconductor material, a metal material, a ceramic material, and an organic material in a depth direction. And a method for analyzing and evaluating with high sensitivity and high resolution in the plane direction.

[0002]

2. Description of the Related Art In semiconductor materials, metal materials, ceramic materials, organic materials, etc., various processes have been tried to improve their functionality, such as high purification or intentional addition of impurities. . However, the analysis of trace elements contained in these materials is indispensable for the process evaluation and the property evaluation of the materials themselves.

Conventionally, secondary ion mass spectrometry has been mainly used as a method for evaluating trace elements present in these materials. However, a sample surface is irradiated with O ₂ ⁺ ions or Cs ⁺ ions. In general, a technique of detecting monoatomic ions (M ⁺ , M ⁻ ) among secondary ions emitted by the sputtering phenomenon has been common. However, in this method, the matrix effect in which the detection sensitivity depends on the elemental composition of the base material and the interface effect in which the detection sensitivity changes at the layer interface are severe,
It has been extremely difficult to accurately and easily know the information on the elements present in the film. In addition, a technique for detecting a diatomic complex ion (CsM ⁺ ) of Cs ⁺ and the element to be detected (M) has been proposed, but the sensitivity of this technique is by no means high, and it is difficult to analyze trace elements. Not available.
Therefore, it has been desired to develop a method for analyzing trace elements in a solid with high sensitivity.

[0004] By the way, Josephson junction elements and MOS
In an electronic device such as an IC, an extremely thin oxide film is used as a tunnel oxide film or a gate oxide film. In these electronic devices, there are a number of problems in element fabrication related to oxide films, such as deterioration of oxide film function due to heat treatment and breakthrough after ion implantation, and information on element distribution in oxide films is extremely important.

Conventionally, secondary ion mass spectrometry has been mainly used as a method for evaluating the distribution of elements present in an oxide film in the depth direction, but O ₂ ⁺ ions or Cs
^The sample surface is irradiated with ⁺ ions, and among the secondary ions emitted by the sputtering phenomenon, monoatomic ions (M ⁺ ,
A method of detecting M ⁻ ) is generally used. However, in this method, the matrix effect, in which the detection sensitivity depends on the element composition of the base material, and the interface effect, in which the detection sensitivity changes at the layer interface, are intense, and it is very difficult to accurately and easily know information on the elements present in the film. Was difficult. In recent years, a technique for detecting a diatomic complex ion of Cs ⁺ and a detection target element has also been proposed, but the angle of incidence of Cs ^{+ on} the sample surface has not been clarified, and the reliability of the obtained information is not necessarily guaranteed. It was not expensive.

On the other hand, conventionally, when identifying an element present on a fixed surface, the sample has not been subjected to any pretreatment (such as formation of an oxide film), and the sample has been left to mass spectrometry. Therefore, in many cases, the sensitivity is insufficient and the trace element originally present cannot be detected.

[0007]

SUMMARY OF THE INVENTION The present invention provides a high sensitivity analysis and a high resolution analysis in the depth direction and plane direction of trace impurities contained in a semiconductor material, a metal material, a ceramic material, and an organic material. The purpose is to contribute to the functional evaluation of An object of the present invention is to accurately evaluate the concentration distribution in the depth direction of an element present in a film and the oxide film existing between layers of a material used for an electronic device, thereby contributing to the evaluation of element characteristics of the electronic device. The purpose is to do.

Another object of the present invention is to identify trace elements present on a fixed surface with high sensitivity.

[0009]

Means for Solving the Problems The present invention has been made to achieve the above object, and a first invention according to the present application is to provide a method for measuring a trace element in a solid in a plane direction and / or a depth direction. a method of measuring the concentration distribution, to a solid surface, Li, C
Irradiation of ions containing alkali metal elements such as s as an ion beam, and mass separation of triatomic complex ions consisting of the irradiated alkali metal ions, the target element, and the base material element among the particles emitted from the solid surface due to the sputtering phenomenon By detecting the concentration distribution in the plane direction by displaying the intensity distribution of the triatomic complex ions as a two-dimensional image, or by displaying the intensity of the triatomic complex ions together with the sputtering time, It is characterized by measuring the distribution.

In the first aspect of the present invention, it is preferable to set the incident angle of the irradiation ion beam at 45 to 60 degrees with respect to the normal direction of the sample for the purpose of improving the sensitivity. In order to improve the resolution in the depth direction, the incident angle of the irradiation ion beam is set to 60 to 90 degrees with respect to the normal direction of the sample.
The preferred method is to reduce the temperature. Further, for the purpose of improving the resolution in the plane direction, it is preferable to set the incident angle of the irradiation ion beam at 0 to 30 degrees with respect to the normal direction of the sample.

That is, in order to capture an image of secondary ions, the ion beam is scanned, but when the incident angle is inclined, the beam shape becomes elliptical on the sample surface. In order to obtain an image with good resolution, it is necessary to sharpen the beam shape on the sample surface, and the inclination is suitably within 30 °. Furthermore,
For the purpose of high-sensitivity analysis of trace elements contained in the oxide film on a solid sample having an oxide film existing on the surface or between layers, it is preferable to set the incident angle of the irradiated alkali metal ion beam from 60 degrees to 90 degrees.

As described above, in the first invention, the incident angle of the ion beam incident on the sample surface is appropriately selected according to the purpose of high sensitivity analysis, high mass resolution analysis, high plane resolution analysis, and oxide film analysis. By the above means, the matrix effect and the interface effect, which were problems of the conventional method, are removed,
High-sensitivity, high-resolution analysis can be performed according to the purpose.

The first aspect of the second invention according to the present application is:
A plane direction and / or depth direction density fraction measuring method of the fabric of trace elements present in the solid, the solid surface, at the same time while irradiating an oxygen ion beam Li, ions including alkali metal elements such as Cs Is irradiated as an ion beam at an angle of incidence of 30 to 60 degrees with respect to the normal direction of the sample, and sputtering is performed while forming an oxide film on the solid surface. Of the particles emitted from the solid surface, alkali metal ions Detect the diatomic complex ion consisting of the target element and the target element by mass separation and measure the concentration distribution in the surface direction by displaying the diatomic complex ion as a two-dimensional image,
Alternatively, the concentration distribution in the depth direction is measured by displaying the intensity of diatomic complex ions together with the sputtering time.

That is, in the first embodiment, simultaneous irradiation is performed under the condition that the implantation depth of oxygen ions is deeper than the implantation depth of alkali metal ions. This condition is determined by considering the acceleration energy and incident angle of oxygen ions. Alternatively, it is also possible to obtain the condition by operating the acceleration energy of the alkali metal ion (even if the incident angle of the alkali metal ion is limited to 30 to 60 degrees).

[0015] Robert G. Wilson, Fer
d A. Stevie, Charles W. Mage
e, "Secondary for Mass Sp
electro-metry "(JOHN WILEY &
SONS Publishing, 1989) According to P1.2-1 O ₂
⁺ , Ar ⁺ , Cs ⁺ are implanted in the following formulas I to III O ₂ ⁺ : R = 2.15Ecos θ (I) Ar ⁺ : R = 1.622E ^0.84 cos θ (II) Cs ⁺ : R = 1.838E ^0.68 cos θ (III) where R is the penetration depth (mm), θ is the angle of inclination from the normal, and E is the primary energy (keV). It is. Therefore, condition setting is easy.

[0016] A second aspect of the second invention of the present application provides a planar direction and / or depth direction density fraction measuring method of the fabric of trace elements present in the solid, the solid surface ,
And irradiating an oxygen ion beam, Li, against attempts <br/> charge the normal direction as the ion beam containing ions of alkali metal elements such as Cs, irradiation at an incident angle of 60 ° to 30 °
The sputtering is repeated while forming an oxide film on the solid surface, and among the particles emitted from the solid surface, diatomic complex ions composed of alkali metal ions and the target element are detected by mass separation. , To measure the concentration distribution in the plane direction by displaying the diatomic complex ion as a two-dimensional image, or to measure the concentration distribution in the depth direction by displaying the intensity of the diatomic complex ion together with the sputtering time. Features.

In the second invention, the thickness of the oxide film formed on the sample surface is preferably 2 to 5 nm. Thus, the second invention according to the present application forms an extremely thin oxide film of 2 nm to 5 nm on a solid surface by vapor deposition or the like,
In this method, ions containing an alkali metal element such as Li or Cs are irradiated at an incident angle of 30 to 60 degrees in the presence of an extremely thin oxide film. In addition, upon detection, of the particles emitted from the solid surface due to the sputtering phenomenon, a diatomic complex ion composed of an alkali metal ion and the detection target element is captured, and the depth direction and the surface direction of the detection target element are detected by mass spectrometry. This is to evaluate the concentration distribution of.

By the above-mentioned means, the matrix effect and the interfacial effect, which are problems of the conventional method, are eliminated, and high-sensitivity analysis becomes possible. Further, a third invention according to the present application is a method for measuring the concentration distribution in the depth direction of a trace element present in an oxide film, wherein a Cs is applied to a solid sample having a solid surface or an oxide film between layers. ⁺ , Li ^{+ and the} like are irradiated at an incident angle of 60 ° to 90 ° with respect to the normal direction of the sample, and among the secondary ions released by the sputtering phenomenon, the irradiated alkali ions and the detection target element (M ) Is detected by mass separation, and the concentration distribution in the depth direction is measured by displaying the intensity of the diatomic complex ion together with the sputtering time.

As described above, according to the third aspect of the present invention, the solid sample existing on the surface or between the layers is subjected to mass spectrometry by the above-described method, whereby the concentration distribution in the depth direction of the element existing in the film can be accurately determined. It can be measured and contributes to the evaluation of the element characteristics of the electronic device. Still further, according to a fourth aspect of the present invention, there is provided a method for identifying an element present on a solid surface, comprising: forming an extremely thin oxide film on the solid surface;
Irradiation of ions containing an alkali metal element such as Cs as an ion beam at an incident angle of 30 to 60 degrees with respect to the normal direction of the sample, and among the particles emitted from the solid surface due to the sputtering phenomenon, the irradiated alkali metal ions And diatomic complex ions of the elements present on the sample surface
It is characterized by mass spectrometry.

As described above, in the fourth invention, the sensitivity is increased by forming an oxide film on the sample surface in advance and then irradiating ions containing an alkali metal element at a constant angle to reduce the trace elements existing on the solid surface. It is to be identified. Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited to these Examples.

[0021]

【Example】

Example 1 (related to the first invention) ¹⁸ O ⁺ was introduced into a Si substrate at 100 keV and 5 × 10 ¹⁴ atoms /
A sample was prepared by ion implantation at cm ² . Cs
^The sample surface was irradiated with ⁺ at an incident angle of 54 degrees to increase the sensitivity. The results are shown in FIG. FIG. 1 shows that the conventional CsO ⁺
It can be seen that the sensitivity of CsSiO ⁺ detection is much higher than that of CsSiO ⁺ . FIG. 2 shows NbN / Nb / Al / Nb.
In the structure of the / Si substrate, the concentration distribution of O and H in the depth direction was measured, and Cs ⁺ was irradiated at an incident angle of 72 degrees for the purpose of high depth resolution. Conventional CsO ⁺ , CsH ⁺
The detection of CsNbO ⁺ and CsNbH ⁺ is more sensitive than the detection of, and it can be seen that the distribution at the layer interface is clearly understood and the depth resolution is high.

Next, Table 1 shows the detection limit of ¹⁸ O ^{+ in} Si obtained from a sample obtained by implanting ¹⁸ O ⁺ into a Si substrate.

[0023]

[Table 1]

As is apparent from the results shown in Table 1, when the purpose is to improve the sensitivity, the incident angle of the irradiation ion beam is preferably set to 45 degrees to 60 degrees with respect to the normal direction of the sample.

Embodiment 2 (Related to Second Invention) Next, an oxygen ion beam and an alkali metal element ion beam
An example of the invention in which the irradiation is repeated alternately is shown.
FIG. 3 and FIG._Two 5 nm for S
The sample formed on the i (100) substrate was
And Si in the depth direction. Figure
3 is an ion beam of ions containing alkali metal (Cs
⁺Beam) (conventional method), and FIG.
Beam of ions containing ions and alkali metals (Cs
⁺Density distribution obtained by alternate irradiation with
You. Cs⁺The angle of incidence of each beam is 30 °, and the detection is
Diatomic complex ion of Cs and detection target elements O and Si
is there. In FIG. 3, CsSi in Si substrate⁺Is 1 ×
10 ^ThreeIn FIG. 4, 5 × 10^Threecount
It can be seen that the sensitivity is improved five times. Therefore, Si
When trace elements are present in the substrate,
Detection can be performed with five times the sensitivity.

In the second invention, the analysis
In this case, the thickness of the oxide film to be formed on the sample surface is set to 2 to 5 nm.
Is preferred. FIG. 6 shows the sample prepared in Example 2 above.
And SiO_TwoDepth of O and Si although the thickness of O was 10 nm
FIG. FIG. 5 shows that the sample of FIG.
SiO by etching_TwoO, Si depth of 2nm
FIG. CsSi as shown in FIG.⁺Strong
The change can be seen in both FIG. 5 and FIG. However, in FIG.
O _Two/ CsSi gradually toward the Si substrate interface⁺Low strength
I'm down. The oxide film effect is sufficiently observed at 10 nm
It is up to about 5 nm, which is half. Also, when the oxide film thickness is less than 2 nm
In the case of thinner
The concentration of potassium metal ions on the sample surface did not reach a certain level.
(Sputtering is in an unsteady state), the effect of this method is weak
It is considered something. Therefore, the analysis of the present invention
At this time, the oxide film thickness formed on the sample surface is limited to 2 to 5 nm.
Preferably.

Example 3 (related to the third invention)_TwoFor a sample with a film thickness of 10 nm,
Alkali metal ion Cs⁺With the angle of incidence on the sample surface being 3
Irradiation at 0, 45, 60, and 80 degrees
Atomic complex ion CsSi⁺And CsO⁺The result of detecting
It is shown in FIGS. 7 and FIG._TwoDuring ~
CsSi at⁺And CsO⁺Secondary ion intensity of the sample
SiO from the surface_Two/ Si decreases toward the substrate interface, and C
sSi⁺Depth profile is SiO_Two/ Si substrate
Discontinuous at the interface. On the other hand, in FIG. 9 and FIG.
Is SiO_TwoCsSi in⁺And CsO⁺Secondary a
On-strength is almost constant, and both depth profiles
There are no discontinuities. From these results, Cs⁺Incident
Irradiate the sample surface at an angle of 60 to 90 degrees, ⁺To
By detecting, the concentration in the depth direction of the element present in the oxide film
It can be seen that the distribution can be measured accurately.

Embodiment 4 (Related to the Fourth Invention) I) 2 nm thick SiO 2_TwoAfter forming
s⁺Was irradiated at an incident angle of 30 °. Sputtering development
(CsSi) released from the solid surface by ⁺And
And CsO⁺) Are shown in FIG. In FIG.
The CsSi on the sample surface⁺Strength depends on oxide film
It can be seen that the number has increased. II) FIGS. 12 and 13 show the results obtained by doping B into a Si substrate.
3 is a mass spectrometry spectrum of a sample. FIG. 12 shows a conventional method, and FIG.
3 This method (analyze after forming a thin oxide film on the sample surface)
6 is a graph showing the analysis results obtained by (method). In FIG.
Is CsB⁺B is detected as
In No. 2, B is not detected.

[0029]

As described above, the present invention has a high sensitivity in the depth direction and plane direction of trace impurities contained in semiconductor materials, metal materials, ceramic materials, and organic materials. It can be analyzed and contribute to the functional evaluation of the material. Further, it is possible to accurately measure the distribution in the depth direction of an element present in an oxide film used for an electronic device or the like, which can contribute to evaluation of element characteristics of the electronic device.

[Brief description of the drawings]

FIG. 1 is a graph showing the concentration distribution of O in Si in the depth direction.

FIG. 2 is a graph showing the distribution of O and H in the depth direction on an NbN / Nb / Al / Nb / Si substrate.

FIG. 3 is a graph showing the concentration distribution of O and Si in the depth direction by Cs ⁺ irradiation.

FIG. 4 is a graph showing the concentration distribution of O and Si in the depth direction by alternate irradiation of O ₂ ⁺ and Cs ⁺ .

FIG. 5 is a graph showing the concentration distribution of O and Si in the depth direction by Cs ⁺ irradiation.

FIG. 6 is a graph showing the concentration distribution of O and Si in the depth direction by Cs ⁺ irradiation.

FIG. 7 is a graph showing the concentration distribution of O and Si in the depth direction (Cs ⁺ incident angle 30 °).

FIG. 8 is a graph showing the concentration distribution of O and Si in the depth direction (Cs ⁺ incident angle: 45 °).

FIG. 9 is a graph showing the concentration distribution of O and Si in the depth direction (Cs ⁺ incident angle: 60 °).

FIG. 10 is a graph showing the concentration distribution of O and Si in the depth direction (Cs ⁺ incident angle: 80 °).

FIG. 11 is a graph showing measurement results after forming SiO ₂ on a Si surface.

FIG. 12 is a graph showing an analysis result according to the fourth invention.

FIG. 13 is a graph showing an analysis result by a conventional method.

Claims (10)

(57) [Claims] 1. A plane direction and / or depth direction density fraction measuring method of the fabric of trace elements present in the solid, the solid surface is irradiated with ions including alkali metal element as an ion beam, sputtering Among the particles released from the solid surface due to the phenomenon, the triatomic complex ions composed of the irradiated alkali metal ions, the target element and the base element are detected by mass separation, and the intensity distribution of the triatomic complex ions is displayed as a two-dimensional image. Or measuring the concentration distribution in the depth direction by displaying the intensity of the triatomic complex ion together with the sputtering time by measuring the concentration distribution in the plane direction. 2. The measuring method according to claim 1, wherein the incident angle of the irradiation ion beam is set to 45 degrees to 60 degrees with respect to the normal direction of the sample for the purpose of improving sensitivity. 3. In order to improve the resolution in the depth direction, the incident angle of the irradiation ion beam is set to 60 degrees with respect to the normal direction of the sample.
The measuring method according to claim 1, wherein the angle is changed from 90 degrees to 90 degrees. 4. The measuring method according to claim 1, wherein the incident angle of the irradiation ion beam is set to 0 to 30 degrees with respect to the normal direction of the sample for the purpose of improving the resolution in the plane direction. 5. An incident angle of an alkali metal ion beam from 60 degrees to 90 degrees with respect to a solid sample having an oxide film present on the surface or between layers for the purpose of high-sensitivity analysis of trace elements contained in the oxide film. The measurement method according to claim 1, wherein the measurement is performed. 6. A plane direction and / or depth direction density fraction measuring method of the fabric of trace elements present in the solid, the solid surface, ions containing an alkali metal element while simultaneously irradiating an oxygen ion beam Is irradiated as an ion beam at an angle of incidence of 30 to 60 degrees with respect to the normal direction of the sample, and sputtering is performed while forming an oxide film on the solid surface. Of the particles emitted from the solid surface, alkali metal ions Detect the diatomic complex ion consisting of the target element and the target element by mass separation and measure the concentration distribution in the surface direction by displaying the diatomic complex ion as a two-dimensional image,
Alternatively, the measurement method is characterized in that the concentration distribution in the depth direction is measured by displaying the intensity of diatomic complex ions together with the sputtering time. 7. A plane direction and / or depth direction density fraction measuring method of the fabric of trace elements present in the solid include a solid surface, and irradiating an oxygen ion beam, an alkali metal element Irradiate ions as ion beams at an incident angle of 30 to 60 degrees with respect to the normal direction of the sample .
Preparative repeated alternately perform sputtering while forming an oxide film on a solid surface, of the particles emitted from the solid surface, a diatomic complex ions of the detection object elemental alkali metal ions were detected by mass separation, the two It is characterized by measuring the concentration distribution in the plane direction by displaying the atomic composite ions as a two-dimensional image, or measuring the concentration distribution in the depth direction by displaying the intensity of the diatomic composite ions together with the sputtering time. The measuring method. 8. The thickness of an oxide film formed on the surface of a sample is set to 2 to 8.
And 5 nm, claim 6 or method according to 7. 9. A method of measuring the concentration distribution in the depth direction of the trace elements present in the oxide film, a solid surface or to a solid sample oxide film is present between the layers, the sample method alkali metal ions Irradiation is performed at an incident angle of 60 to 90 degrees with respect to the line direction, and among secondary ions emitted by the sputtering phenomenon, diatomic complex ions of irradiated alkali ions and the target element (M) are detected by mass separation. And measuring the concentration distribution in the depth direction by displaying the intensity of the diatomic complex ions together with the sputtering time. 10. A method for identifying an element present on a solid surface, comprising forming an extremely thin oxide film and then using an ion containing an alkali metal element as an ion beam from 30 degrees with respect to the normal direction of the sample. Irradiation at an incident angle of 60 degrees, among particles emitted from the solid surface due to the sputtering phenomenon,
The above-described identification method, comprising detecting a diatomic complex ion of the irradiated alkali metal ion and an element present on the sample surface and performing mass spectrometry.