JPH09159630A - Epma analyzing method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To analyze only an area near the surface of a sample which is not uniform in depth direction with an optimum acceleration voltage. SOLUTION: An X-ray intensity C2 is an apparent intensity, the half of sum (C1 +C3 ) of X-ray intensities C1 and C3 is a background intensity B, and a value obtained by subtracting the background intensity B from the apparent intensity C2 becomes an actual intensity A. Then, when the acceleration voltage of electron rays is changed, the increase/decrease of the apparent intensity C2 and those of the background intensity B are not necessarily proportional and hence S/N ratio which is the ratio of the actual intensity A to the background intensity B does not become constant. Therefore, an acceleration voltage where the S/N ratio is maximized is obtained, thus analyzing the acceleration voltage.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an EPMA (Electro
n Probe Micro Analysis) Analytical method and its apparatus.

[0002]

2. Description of the Related Art In the EPMA analysis method, the wavelength and intensity of a characteristic X-ray generated from a sample surface area irradiated with an accelerated electron beam are detected, and the characteristic X-ray spectrum thus obtained is used to detect the peak wavelength and the X-ray. Read the line strength,
The type of element in the sample surface area is analyzed from the read wavelength, and the content of the element is analyzed from the X-ray intensity.

The shape and size (depth) of the characteristic X-ray generation region in the sample surface region depend on the acceleration voltage of the electron beam and the like. When the accelerating voltage is high, the penetration depth of the electron beam becomes deep, and the shape of the characteristic X-ray generation region is almost water droplet-shaped, as schematically shown in FIG. On the other hand, when the accelerating voltage is low, the penetration depth of the electron beam becomes shallow, and the characteristic X-ray generation region has a substantially hemispherical shape, as schematically shown in FIG. Therefore, in the case of a sample that is homogeneous in the depth direction, the vicinity of the sample surface can be accurately analyzed even if the acceleration voltage is increased. However, in the case of a sample that is not homogeneous in the depth direction, increasing the accelerating voltage is not preferable because characteristic X-rays are generated not only in the vicinity of the sample surface to be analyzed but also in the lower part thereof. For example, in the case of a thin film laminated device such as a thin film transistor, the thickness of the thin film is several tens to several hundreds of nm, while the penetration depth of the electron beam is several μm depending on the electron beam irradiation conditions and the like. In some cases, characteristic X-rays will be generated from the lower part of the thin film to be analyzed. Therefore, conventionally, when only the vicinity of the surface of a sample that is not homogeneous in the depth direction is analyzed, the accelerating voltage is lowered to make the electron beam penetration depth shallow.

[0004]

However, since each element has a unique minimum voltage capable of generating a characteristic X-ray, it cannot be analyzed at an acceleration voltage below this unique minimum voltage. For this reason, when analyzing only the surface vicinity of a sample that is not homogeneous in the depth direction, we want to make the accelerating voltage as low as possible to make the electron beam penetration depth as shallow as possible, but depending on the type of element to be analyzed, the accelerating voltage Since the lower limit value depends, the optimum value of the acceleration voltage varies depending on the type of sample. Further, the shape and depth of the characteristic X-ray generation region do not only depend on the accelerating voltage of the electron beam, but also on the state of the sample, the contained elements, etc. The optimum value will be different. Therefore, under the present circumstances, the analyst may decide the setting of the acceleration voltage based on the theoretical value or experience,
There is a problem in that analysis is performed with a non-optimal accelerating voltage, because it is determined by the method of greatest common divisor, knowing that it is not optimal. An object of the present invention is to make it possible to perform analysis at an optimum accelerating voltage when analyzing only the surface vicinity of a sample that is not homogeneous in the depth direction.

[0005]

According to the first aspect of the present invention,
EP for detecting the wavelength and intensity of characteristic X-rays generated from a sample surface area irradiated with an accelerated electron beam and analyzing the type and content of elements in the sample surface area from the detection result
In the MA analysis method, an electron beam is irradiated multiple times by changing its accelerating voltage, an optimum accelerating voltage is obtained based on the characteristic X-rays generated, and an electron beam is irradiated at this optimum accelerating voltage for analysis. It is the one. The invention according to claim 2 detects the wavelength and intensity of the characteristic X-ray generated from the sample surface region irradiated with the accelerated electron beam, and analyzes the type and content of the element in the sample surface region from the detection result. In the EPMA analysis method described above, the acceleration voltage of the electron beam is set in an arbitrary range with an arbitrary step amount, the electron beam is sequentially irradiated with the set plurality of acceleration voltages, and the optimum value is obtained based on the characteristic X-rays generated respectively. The optimum accelerating voltage is obtained, and an electron beam is irradiated at this optimum accelerating voltage for analysis. The invention according to claim 3 detects the wavelength and intensity of the characteristic X-ray generated from the sample surface region irradiated with the accelerated electron beam, and analyzes the type and content of the element in the sample surface region from the detection result. In the EPMA analyzer, the electron beam is sequentially irradiated with the acceleration voltage setting means for setting the acceleration voltage of the electron beam with an arbitrary step amount within an arbitrary range, and the plurality of acceleration voltages set by the acceleration voltage setting means. Then, based on the characteristic X-rays generated respectively,
SN, which is the ratio of the actual X-ray intensity to the X-ray background intensity
Computation means for obtaining the ratio, and each S obtained by the computation means
A comparison means for comparing N ratios to obtain the maximum SN ratio of them, and irradiating an electron beam with an acceleration voltage corresponding to the maximum SN ratio obtained by the comparison means for analysis. Is.

According to the present invention, when only the vicinity of the surface of a sample that is not homogeneous in the depth direction is analyzed, the electron beam is radiated a plurality of times by changing its accelerating voltage, and it is optimal based on the characteristic X-rays generated respectively. If an optimum accelerating voltage is obtained and the electron beam is irradiated at this optimum accelerating voltage, analysis can be performed at the optimum accelerating voltage.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic configuration of an EPMA analyzer according to an embodiment of the present invention.
This EPMA analyzer includes a stage 2 on which a sample 1 is placed. An electron beam irradiation unit 3 is provided above the stage 2.
And the characteristic X-ray detection unit 4 is arranged diagonally above and to the right of the stage 2. The electron beam irradiation unit 3 is connected to the control unit 5. The control unit 5 is for controlling the operation of the entire device. In addition to the electron beam irradiation unit 3, the control unit 5 is connected with an input unit 6, a calculation unit 7, a comparison unit 8, a storage unit 9, an output unit 10, and the like.

The input section 6 includes an input mode selection button, a ten-key pad, a start button and the like. The electron beam irradiation unit 3 irradiates the surface of the sample 1 with the electron beam 11 with an acceleration voltage according to the irradiation drive signal from the control unit 5. When the characteristic X-ray detection unit 4 detects the characteristic X-rays 12 generated in the surface area of the sample 1, the characteristic X-ray detection unit 4 sends the detection signal to the calculation unit 7. The calculation unit 7 performs a predetermined calculation based on the detection signal from the characteristic X-ray detection unit 4,
The calculation result is sent to the comparison unit 8.
The comparison unit 8 compares the calculation result sent from the calculation unit 7 with the previous comparison result received from the storage unit 9 and sends the comparison result to the storage unit 9. The output unit 10 is composed of a display unit, a printer, and the like, and is for displaying input data and other displays.

Here, the operating principle of this EPMA analyzer and the actual experimental results will be described. FIG. 2 schematically shows the characteristic X-ray spectrum. Peak wavelength λ
X-ray intensity at ₂ is C _2, the wavelength of the predetermined ± [Delta] [lambda] lambda
The X-ray intensities at ₁ and λ ₃ are C ₁ and C ₃ . in this case,
The X-ray intensity C ₂ is the apparent intensity, and the X-ray intensities C ₁ and C ₃
The half of the sum (C ₁ + C ₃ ) (average of C ₁ and C ₃ ) is the background intensity B, and the value obtained by subtracting the background intensity B from the apparent intensity C ₂ is the actual intensity A. However, the apparent intensity C ₂ and the background intensity B change when the acceleration voltage of the electron beam 11 is changed.
However, the increase / decrease in apparent intensity C _{2 and} the increase / decrease in background intensity B are not necessarily proportional. As a result, the actual strength A
Is the signal and the background intensity B is the noise,
The SN ratio, which is the ratio of signal to noise, is not constant.

For example, Sample 1 was prepared by forming a phosphorus thin film having a thickness of about 50 nm on the surface of a silicon substrate. Then, electron beams are sequentially irradiated in a range of an acceleration voltage of 6 kV to 15 kV with a step amount of 1 kV, and based on the characteristic X-rays generated, the SN which is a ratio of the X-ray actual intensity A and the X-ray background intensity B is obtained. When the ratio was obtained, the results shown in FIG. 3 were obtained. As is apparent from FIG. 3, the relationship between the increase / decrease in acceleration voltage and the increase / decrease in SN ratio is non-linear. In this case, the SN ratio becomes maximum at the acceleration voltage of 7 kV. Since the optimum accelerating voltage is when the SN ratio is maximum, the optimum accelerating voltage in this case is 7 k.
V. The operation principle of this EPMA analyzer is focused on such a point.

Next, an example of a specific operation of this EPMA analyzer will be described with reference to the flow chart shown in FIG. First, in step S1, the input mode selection button of the input unit 6 is operated to enter the acceleration voltage setting range lower limit value input mode, and then the numeric keypad is operated to set a numerical value as the lower limit value (6 kV in the case of FIG. 3) of the acceleration voltage setting range. Enter 6. Next, the input mode selection button is operated to enter the acceleration voltage setting range upper limit value input mode, and then the ten key is operated to operate the acceleration voltage setting range upper limit value (1 in the case of FIG. 3).
Input the numerical value 15 as 5 kV). Next, the input mode selection button is operated to enter the set acceleration voltage step amount input mode, and then the numeric keypad is operated to input the numerical value 1 as the set acceleration voltage step amount (1 kV in the case of FIG. 3). The above input data is temporarily stored in the control unit 5.

Next, in step S2, the start button of the input section 6 is operated. Then, in step S3, the control unit 5 selects the lower limit value (6 kV) of the set acceleration voltage as the irradiation acceleration voltage, and sends the irradiation drive signal corresponding thereto to the electron beam irradiation unit 3. Then, in step S4, the electron beam 11 from the electron beam irradiation unit 3 accelerates the acceleration voltage 6 k.
The surface of the sample 1 is irradiated with V. Then, the characteristic X-rays 12 generated in the surface area of the sample 1 are detected by the characteristic X-ray detection unit 4, and this detection signal is sent to the calculation unit 7.

Next, in step S5, the calculation unit 7
Performs a predetermined calculation based on the detection signal from the characteristic X-ray detection unit 4. First, it is assumed that the characteristic X-ray spectrum obtained based on the detection signal from the characteristic X-ray detection unit 4 is as schematically shown in FIG. Then, the calculation unit 7 obtains the X-ray intensities C ₂ , C ₁ and C ₃ at three points of the peak wavelength λ ₂ and the wavelengths λ ₁ and λ ₃ of ± Δλ, and then the actual intensity A and the background intensity B. The SN ratio, which is the ratio of In this case,
As shown in, when the acceleration voltage is 6 kV, the SN ratio becomes 3.5. If the type of element to be analyzed is known in advance, numerical values corresponding to the wavelengths λ ₂ , λ ₁ , and λ ₃ may be input in advance from the input unit 6.

As described above, in the calculation unit 7, the acceleration voltage 6k
The SN ratio (3.5) in the case of V is obtained, and the calculation result is sent to the comparison unit 8. Next, in step S6, the comparison unit 8 compares the calculation result sent from the calculation unit 7 with the previous comparison result received from the storage unit 9. In this case, since the previous comparison result does not exist, The calculation result sent from the calculation unit 7, that is, S when the acceleration voltage is 6 kV
The N ratio (3.5) is sent to the storage unit 9 as the comparison result.
Then, in step S7, the storage unit 9 stores the SN ratio (3.5) and the acceleration voltage value (6) when the acceleration voltage is 6 kV. Next, in step S8, the control unit 5 determines whether or not the acceleration voltage of the comparison target that has just ended is the upper limit value (15 kV) of the set acceleration voltage. In this case, since it is not so (No), the process returns to step S3.

Next, in step S3, the controller 5
Is the lower limit value (6k) of the set acceleration voltage as the irradiation acceleration voltage.
A value (7 kV) obtained by adding a step value (1 kV) to V) is selected, and an irradiation drive signal corresponding thereto is sent to the electron beam irradiation unit 3. Then, in step S4, the electron beam irradiation unit 3
The electron beam 11 is applied to the surface of the sample 1 at an acceleration voltage of 7 kV. Then, the characteristic X-rays 12 generated in the surface area of the sample 1 are detected by the characteristic X-ray detection unit 4, and this detection signal is sent to the calculation unit 7. Next, in step S5, the calculation unit 7 obtains the SN ratio (4.0; see FIG. 4) when the acceleration voltage is 7 kV, and sends the calculation result to the comparison unit 8.

Next, in step S6, the comparison unit 8
Compares the calculation result sent from the calculation unit 7 with the previous comparison result received from the storage unit 9. That is, the SN ratio (4.0) when the accelerating voltage is 7 kV and the SN ratio (3.5) when the accelerating voltage is 6 kV are compared, and the larger SN ratio (4.0) is used as the comparison result in the storage unit. 9 is sent. Then, in step S7, the storage unit 9 stores the larger S
The N ratio (4.0) and its acceleration voltage value (7) are stored. Next, in step S8, the control unit 5 determines that the acceleration voltage of the comparison target that has just ended is the upper limit value (15 kV) of the set acceleration voltage.
It was determined whether or not In this case also, since this is not the case (No), the process returns to step S3.

Thereafter, the above-mentioned processing is repeated.
Then, when the comparison with the SN ratio (2.0; see FIG. 4) in the case of the acceleration voltage of 15 kV (that is, the upper limit value of the set acceleration voltage) is completed, as is apparent from FIG.
The maximum SN ratio among the SN ratios for each acceleration voltage set in increments of 1 kV within the range of 15 kV
The ratio (4.0) and its acceleration voltage value (7) will be stored. Next, in step S8, when it is determined that the acceleration voltage of the comparison target that has just ended is the upper limit value (15 kV) of the set acceleration voltage (Yes), step S9
Proceed to. Next, in step S9, the control unit 5 reads the maximum SN ratio (4.0) and its acceleration voltage value (7) from the storage unit 9 and causes the output unit 10 to output the information. Then, it will be understood that the optimum accelerating voltage is around 7 kV.

Thus, in this EPMA analyzer,
The optimum accelerating voltage (7 kV) can be obtained when analyzing only the vicinity of the surface of a sample that is not homogeneous in the depth direction. Irradiation with an electron beam allows continuous analysis at an optimum acceleration voltage. In this case, the calculation unit 7
At the same time, a graph as shown in FIG. 2 is created based on the detection signal sent from the characteristic X-ray detection unit 4, and the actual intensity A, the background intensity B and the SN ratio thereof are obtained, and these data are obtained. The output unit 10 may display or print out immediately. Needless to say, if the step size is made smaller, for example, 0.5 kV, it becomes possible to perform analysis at a more optimal acceleration voltage.

[0019]

As described above, according to the present invention, when only the vicinity of the surface of a sample that is not homogeneous in the depth direction is analyzed, the electron beam is irradiated multiple times while changing its accelerating voltage,
Since the optimum accelerating voltage is obtained based on the respective characteristic X-rays generated and the electron beam is irradiated at this optimum accelerating voltage for analysis, the analysis can be performed at the optimum accelerating voltage.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an EPMA analyzer according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing a characteristic X-ray spectrum.

FIG. 3 is a diagram shown for explaining the acceleration voltage dependence of the SN ratio.

FIG. 4 is a flowchart shown to explain a case of obtaining an optimum acceleration voltage.

FIG. 5 schematically shows the shape and size of a characteristic X-ray generation region, FIG. 5A shows a case where the acceleration voltage is high,
FIG. 6B is a diagram showing a case where the acceleration voltage is low.

[Explanation of symbols]

 1 sample 3 electron beam irradiation unit 4 characteristic X-ray detection unit 5 control unit 6 input unit 7 calculation unit 8 comparison unit 9 storage unit 10 output unit

Claims (4)

[Claims] 1. An EPMA analysis for detecting the wavelength and intensity of characteristic X-rays generated from a sample surface region irradiated with accelerated electron beams, and analyzing the type and content of elements in the sample surface region from the detection result. In the method, the electron beam is irradiated a plurality of times by changing its accelerating voltage, and each characteristic X is generated.
An EPM characterized by obtaining an optimum accelerating voltage based on a beam and irradiating an electron beam at this optimum accelerating voltage for analysis.
A analysis method. 2. An EPMA analysis for detecting the wavelength and intensity of a characteristic X-ray generated from a sample surface area irradiated with an accelerated electron beam and analyzing the type and content of elements in the sample surface area from the detection result. In the method, the accelerating voltage of the electron beam is set in an arbitrary range in an arbitrary step amount, the electron beam is sequentially irradiated with the set plurality of accelerating voltages, and the optimum accelerating voltage is generated based on the characteristic X-rays generated respectively. And an electron beam is irradiated at this optimum accelerating voltage for analysis to analyze the EPMA. 3. An EPMA analysis for detecting the wavelength and intensity of characteristic X-rays generated from a sample surface area irradiated with an accelerated electron beam, and analyzing the type and content of elements in the sample surface area from the detection result. In the device, the acceleration voltage setting means for setting the acceleration voltage of the electron beam in an arbitrary step amount in an arbitrary range, and when the electron beam is sequentially irradiated with a plurality of acceleration voltages set by the acceleration voltage setting means, Based on the characteristic X-rays respectively generated, the calculating means for obtaining the SN ratio which is the ratio of the X-ray actual intensity and the X-ray background intensity is compared with the respective SN ratios obtained by the calculating means, and the maximum of them is calculated. And an electron beam irradiation at an accelerating voltage corresponding to the maximum SN ratio obtained by the comparison means for analysis. 4. The EPMA according to claim 3, further comprising output means for outputting an acceleration voltage value corresponding to the maximum SN ratio obtained by the comparison means.
Analysis equipment.