JPH02135657A - Secondary ion mass spectrometry method and apparatus therefor - Google Patents

Abstract

PURPOSE:To accurately perform mass spectrometry of an element having a large concentration variation range or an element having a high concentration by executing arithmetic processing to compensate the difference in energy on the basis of physical quantities detected at different states of energy. CONSTITUTION:An acceleration voltage of a secondary ion is applied from a secondary ion acceleration power source 11 to a sample. A voltage divided in association with the acceleration voltage is applied to a drawing electrode 5 and an electrostatic lens 6 via a bleeder 12. The output of an electric field power source 13 is applied to an electric field electrode 7 so that an electric field is formed between electrodes, thereby controlling the strength of a magnetic field formed at an electromagnet 8 by means of a magnetic power source 14. The respective power sources 11, 13, 14 are controlled by a computer 15, and then, the output of a pulse counter 10 is stored in a first memory 16. Data stored in the memory 16 is operated by the computer 15 so as to be stored in a second memory 17. Data stored in the memory 17 is outputted to a printer 18. Therefore, a dynamic range in a detection system can be taken-up two places or more.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an analyzer for various materials such as semiconductors, and is particularly suitable for analyzing elements with large concentration differences or large concentration change widths. The present invention relates to an ion mass spectrometry method and apparatus.

[Conventional technology]

Conventional devices often use a pulse measurement method to detect secondary ions. In the pulse measurement method, a secondary electron multiplier tube, high-speed pulse amplifier, etc. are used in the secondary ion detection unit to convert each secondary ion to be detected into pulses, and the number of pulses is counted. . At this time, since the pulses are counted in a time-division manner, the maximum count of secondary ions is limited by the response speed of the high-speed pulse amplifier and the pulse counting circuit. Due to the above limitations, the dynamic range of analysis using the pulse measurement method was limited to 8 digits. For this reason, the analysis is subject to the following constraints.

(1) The concentration difference between elements is within 8 digits.

(2) The range of element concentration changes is within 8 digits.

When analyzing extremely low concentration impurities in a matrix,
Although it is necessary to detect both the matrix element and the impurity element, if the difference in concentration between the two exceeds eight orders of magnitude, it becomes impossible to detect both due to the above-mentioned restriction (1). For this purpose, both matrix elements and impurity elements can be detected by detecting multivalent ions and compound ions of matrix elements, which have a smaller amount of secondary ions than monovalent ions of matrix elements. However, determining and setting multivalent ions and compound ions is an extremely complicated operation. In addition, when measuring the state of diffusion at the multilayer film interface,
The concentration change of the diffused element can only be measured within 8 orders of magnitude from the above-mentioned limit (2).

[Problem to be solved by the invention]

The above conventional technology does not take into account the expansion of the dynamic range when detecting secondary ions, and it is not possible to simultaneously analyze high-concentration elements and extremely low-concentration elements, or to analyze elements whose concentration changes significantly from high to extremely low concentrations. There was a problem that analysis could not be performed.

The purpose of the present invention is to expand the dynamic range when detecting secondary ions, so that elements with large concentration differences or
It is an object of the present invention to provide a secondary ion mass spectrometry method and apparatus that can analyze elements with a large concentration change range in a single measurement, do not require selection of analysis elements, etc., and have good operability.

[Means to solve the problem]

In order to achieve the above object, the present invention comprises a step of irradiating a sample with primary ions, a step of detecting a physical quantity of secondary ions released from the sample, a step of storing the detected physical quantity, and a step of storing the physical quantity. A process of varying the energy of secondary ions emitted from a sample when the value exceeds a preset value and when it does not exceed a preset value, and based on each physical quantity detected in each state of different energy. This is a secondary ion mass spectrometry method including the step of performing mass analysis by performing calculation processing to compensate for the difference between the different energies.

The present invention also includes a step of irradiating a sample with primary ions;
A step of detecting the physical quantity of secondary ions emitted from the sample, and varying the energy of the secondary ions emitted from the sample depending on the trend of the physical quantity, so that the physical quantity of the secondary ions is within the measurement range of the detection means. and a step of performing mass spectrometry by expanding the measurement range and performing calculation processing by correcting the stored physical quantity in accordance with the different changes in energy. A secondary ion mass spectrometry method involving

In the analysis method, it is preferable that the physical quantity of the secondary ions is detected at predetermined intervals during the analysis of the sample with respect to the energy possessed by the secondary ions, and the difference between the different energies to be compensated for is always known.

Alternatively, it is preferable to analyze the same component by changing the energy of the secondary ions multiple times, and compare the analysis data for each energy value to determine the difference in different energies to be compensated for.

Further, in the analysis method, it is preferable that the range of concentration differences between a plurality of analytes or the concentration distribution range of one analyte exceeds the range of the detection means. Further, the sample to be analyzed is a semiconductor formed by ion implantation, and the amount of implanted impurity ions in the depth direction of the semiconductor can be cited.

Further, the secondary ion mass spectrometer according to the present invention includes means for irradiating a sample with primary ions, means for detecting a physical quantity of secondary ions emitted from the sample, and means for storing the detected physical quantity. means for varying the energy of secondary ions emitted from the sample when the physical quantity exceeds a preset set value and when the physical quantity does not exceed a preset value; and means for performing calculation processing to compensate for the difference between the different energies based on physical quantities. Here, examples of means for varying the energy possessed by the secondary ions include an acceleration power source provided in the flow path of the secondary ions emitted from the sample, that is, an acceleration voltage or the intensity of the electric field.

[Effect]

The amount of secondary ions introduced into the detection system can be increased or decreased by changing the selected value of the energy of the secondary ions emitted from the sample by changing the energy of the secondary ions emitted from the sample. Further, the detected value of the physical quantity of the secondary ion is constantly monitored by a means for determining whether or not the detected value of the physical quantity of the secondary ion exceeds a predetermined value within the measurement dynamic range of the detection system. If the detected value exceeds a predetermined value, the energy selection means changes the energy selection value to reduce the amount of secondary ions so that the detected value does not exceed the dynamic range of the detection system. can do. The data detected in the above manner is temporarily stored in memory.

When outputting data, the amount of secondary ions is reduced and the detected data is divided by the reduction rate of secondary ions using means for calculating the stored data to compensate for the change in energy. By performing calculation processing, the output data does not become saturated at the upper limit of the dynamic range of the detection system, and can output data that has a large dynamic range and faithfully reflects the analysis value.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The primary ion irradiation unit 1 generates, accelerates, focuses, and
The sample 3 is irradiated by scanning or the like. The sample 3 is, for example, a semiconductor formed by ion implantation, and the amount of impurity ions in the depth direction thereof is measured.

The sample 3 irradiated with the primary ions 2 emits secondary ions 4 . The secondary ions 4 are extracted from the surface of the sample 3 by an extraction electrode 5 and an electrostatic lens 6, are focused, and energy is focused while passing through an electric field formed by an electric field electrode 7, and then formed by an electromagnet 8. The mass is separated while passing through a magnetic field,
Secondary ions with a specific mass-to-charge ratio reach the detector 9.

The detector 9 generates a pulse for each arriving secondary ion, and the pulse counter 10 counts the number of pulses. Sample 3
A secondary ion accelerating voltage is applied from a secondary ion accelerating power source 11, and a divided voltage is applied to the extraction electrode 5 and the electrostatic lens 6 via the bleeder 12 in conjunction with the accelerating voltage.

The output of the electric field power supply 13 is applied to the electric field electrode 7 to form an electric field between the electrodes, and the intensity of the magnetic field formed by the electromagnet 8 is controlled by the magnetic field power supply 14. Then, in the computer 15, the secondary ion accelerating power source 11, the electric field power source 13, and the magnetic field power source 14 are
The output of the pulse counter 10 is sent to the first memory 1.
Save to 6.

The data stored in the first memory 16 is transferred to the computer 15
The calculation process is performed and stored in the second memory 17. The data stored in the second memory 17 is output to the printer 18.

By the way, FIG. 2 is a diagram showing the energy distribution of the secondary ions 4. The vertical axis represents the amount of secondary ions, and the horizontal axis represents the output voltage of the secondary ion accelerating power source 11, which corresponds to the energy of the secondary ions. Normally, the accelerating voltage V is set to VM at which the secondary ion preciousness becomes the maximum IN. The reason for this is to detect the analytical element down to a lower concentration region.

Here, a case will be considered in which a sample is analyzed in the depth direction of an element whose concentration changes from a minimum Cmin to a maximum Cmax. FIG. 3 shows the correspondence between the measurement results of the depth direction profile with a conventional device and the true values, where the vertical axis is the concentration and the horizontal axis is the sputtering time (corresponding to the depth from the surface of the sample). Cw
If the range of change from in to Cmax is large, the detected value will be saturated at the upper limit of the dynamic range of the device detection system, and accurate data (indicated by the dashed-dotted line in Figure 3) will not be obtained in the region where the concentration is above Csat. I can't get it.

Therefore, in this embodiment, within the dynamic range of the detection system, a first predetermined level C1 and a second predetermined level C1 are set.
8 is set in advance and the set values are set in the computer 15. The levels of C and C2 are shown in FIG.

FIG. 4 shows data stored in the first memory 16, with the vertical axis representing the concentration and the horizontal axis representing the sputtering time.

At time tl when the concentration of the element under analysis exceeds a first predetermined level C1, the computer 15 changes the output voltage of the secondary ion accelerating power supply 11 from vM to Vs to reduce the amount of secondary ions. If the reduction rate at this time is set as A, the maximum concentration Cmax is stored in the first memory 16 as A-C118. During measurement with the accelerating voltage set to Vs, at time t2 when the accelerating voltage becomes lower than the second predetermined level C2, the computer 15 returns the output voltage of the secondary ion accelerating power supply 11 from Vs to vH. Among the data stored in the first memory 16 as described above, the computer 15 divides the data between tl and t2 by the reduction rate A, and then divides the data into a second memory.
It is stored in the memory 17 of. Figure 5 shows the second memory 1
In the data stored in 7, the vertical axis is the concentration and the horizontal axis is the sputtering time. This FIG. 5 corresponds to profile data of a wide dynamic range from Cmax to CflIin, including the region from C5at to Cmax shown by the dashed line in FIG. The data stored in this second memory 17 is output to the printer 18.

When energy is selected by changing the output of the secondary ion accelerating power source 11, the reduction rate A can be set to 10''1 to 10-, so the dynamic range of the detection system is expanded by one to two orders of magnitude.

Incidentally, if the amount of secondary ions (physical quantity) relative to the energy possessed by the secondary ions is detected at predetermined intervals during analysis of the sample and the reduction rate A is always known, the measurement can be made with higher accuracy. Another method for determining the reduction rate A may be to analyze the same component by changing the energy of the secondary ions multiple times, and compare the analysis data for each energy value to determine the optimum one.

In addition, in the above explanation, a case has been described in which the concentration distribution range in the depth direction of the sample of the analysis target exceeds the range of the detection means. The present invention can be applied in the same way even when the value exceeds the range of the detection means.

〔Effect of the invention〕

According to the analysis method according to the present invention, the dynamic range of the detection system can be expanded by two or more orders of magnitude, so that it is possible to accurately analyze elements with a large range of concentration changes or elements with large concentrations.

Further, according to the analyzer according to the present invention, the above analysis method can be carried out with a simplified device structure.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of a secondary ion mass spectrometer according to the present invention, FIG. 2 is a diagram showing energy distribution characteristics of secondary ions, and FIGS. 3 to 5 are diagrams showing analysis data. 1... Primary ion irradiation part, 2... Primary ion, 3...
...Sample, 4...Secondary ion, 5...Extraction electrode, 6
... Electrostatic lens, 7... Electric field electrode, 8... Electromagnet, 9... Detector, 1o... Pulse counter, 11...
・Secondary ion acceleration power supply, 12...Bleeder, 13...
- Electric field power supply, 14... Magnetic field power supply.

Claims (1)

[Claims] 1. A step of irradiating a sample with primary ions, a step of detecting a physical quantity of secondary ions emitted from the sample, a step of storing the detected physical quantity, and a step of storing the physical quantity in advance. A process of varying the energy of secondary ions emitted from the sample when the set value is exceeded and when it is not, and determining the difference based on each physical quantity detected in each state of the different energy. A secondary ion mass spectrometry method comprising the step of performing mass spectrometry by performing calculation processing to compensate for the difference in energy. 2. A step of irradiating the sample with primary ions, a step of detecting the physical quantity of the secondary ions emitted from the sample, and a step of detecting the detection by varying the energy of the secondary ions emitted from the sample depending on the trend of the physical quantity. A process of storing the physical quantity of the secondary ions while keeping it within the measurement range of the detection means, and expanding the measurement range by correcting the stored physical quantity in accordance with the different changes in the energy. A process of processing and mass spectrometry;
secondary ion mass spectrometry methods including; 3. In claim 1, the secondary ion detects the physical quantity of the secondary ion with respect to the energy possessed by the secondary ion at predetermined time intervals during analysis of the sample, and always grasps the difference between the different energies to be compensated for. Ion mass spectrometry methods. 4. In claim 1, the secondary ion analyzer analyzes the same component by changing the energy of the secondary ions multiple times, and compares the analysis data for each energy value to determine the difference between different energies to be compensated for. Ion mass spectrometry methods. 5. The secondary ion mass spectrometry method according to claim 1 or 2, wherein the range of concentration differences between a plurality of analytes or the concentration distribution range of one analyte exceeds the range of the detection means. 6. The secondary ion mass spectrometry method according to claim 5, wherein the sample to be analyzed is a semiconductor by ion implantation, and the amount of impurity ions implanted in the depth direction of the semiconductor is determined. 7. means for irradiating a sample with primary ions; means for detecting a physical quantity of secondary ions emitted from the sample; means for storing the detected physical quantity; and a means for storing a preset value of the physical quantity. A means for differentiating the energy of secondary ions emitted from the sample when the energy is exceeded and when it is not exceeded, and compensating for the difference in the different energies based on each physical quantity detected in each state of the different energies. A secondary ion mass spectrometer comprising means for performing arithmetic processing. 8. A secondary ion mass spectrometer according to claim 7, wherein the means for varying the energy of the secondary ions is an accelerating power source provided in the flow path of the secondary ions emitted from the sample.