JPH01169861A - Ion microanalyzer - Google Patents

Abstract

PURPOSE:To perform the analysis in the depth direction without reducing the separation capability in an energy separator when primary ions are scanned by correcting the voltage of the electric field applied as an energy analyzer in response to the primary ion scanning width. CONSTITUTION:When the scanning voltage is applied to a deflecting electrode 5 by a scanning power source 22, a primary ion beam 2 is moved on an analysis sample 7 in proportion to the voltage, secondary ions extracted by a secondary ion extracting electrode 11 reach a sector electric field 14 through a lens 12 and an aperture 13. The image of the aperture 13 is focused on a beta slit 15, when the primary beam is moved on the sample 7, the convergence point on the beta slit 15 fluctuates. The signal of the scanning power source 22 is sent to an electric field power source 24 to correct this fluctuation, the normal electric field voltage is corrected, and an analyzer is operated so that the convergence point is not drifted when the beam on the beta slit 15 scans the primary ion beam. The analysis precision in the depth direction can be thereby improved in the measurement to scan the primary ion beam.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ion microanalyzer, and particularly to an improvement in a secondary ion analysis section suitable for performing depth direction analysis with high precision.

[Conventional technology]

As described in Japanese Patent Application Laid-open No. 47-37792, the conventional device has a correction deflection electrode in the secondary ion path, a means for correcting fluctuations in the secondary ion convergence point due to primary beam scanning, and It was designed to detect secondary ion images with high resolution.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into consideration the energy distribution of secondary ions, and has a problem in that it is not possible to separate ions with slight differences in energy to improve the accuracy of analysis.

An object of the present invention is to perform depth analysis without reducing the separation ability of an energy separator even when scanning secondary ions.

[Means for solving problems]

The above object is achieved by correcting the voltage of the electric field acting as an energy analyzer depending on the primary ion scanning width.

[Effect]

When a scanning voltage is applied to the deflection electrode 5 from the scanning power source, the secondary ion beam 2 moves over the analysis sample 7 in proportion to the voltage, and as a result, the secondary ions extracted from the secondary ion extraction electrode 11 , lens 12, and aperture 13 to reach the resector electric field 14. The image of aperture 13 is β
Although it converges on the slit 15, as the primary beam moves over the sample 7, the position of the convergence point on the β slit 15 changes.

In order to correct the above fluctuation, the signal from the scanning power supply 22 is sent to the electric field power supply 24 to correct the normal electric field voltage, and
It operates so that the beam on the primary ion beam does not shift even when the primary ion beam is scanned.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Ions such as Oz+ generated by ion gun 1 have a temperature of 10 to 20K.
It is accelerated to y and becomes a primary ion beam 2. This primary ion beam 2 is passed through a condenser lens 3. Objective aperture 4. Deflection electrode5. The primary ions pass through the objective lens 6, etc., and are narrowly focused and irradiated onto the sample 7. When the sample is irradiated with primary ions, the sample is gradually dug up due to the sputtering phenomenon, and a portion of the dug sample is ionized. There is. These secondary ions are extracted by a secondary ion extraction electrode 11 and focused onto an aperture 13 by a lens 12 .

This aperture 13 acts as the object point of the mass spectrometer.

The ions that have passed through the aperture undergo energy dispersion and angular focusing in the sector electric field 14 and are focused on the β slit 15. Therefore, if ions have an energy range, β
Ions with a specific energy that have passed through the β slit through which ions with a specific energy can selectively pass through the slit are separated by mass in the sector magnetic field 16 and converge on the collector slit 17 again. The mass-separated ions are detected by a secondary ion detector, amplified by an amplifier 19, and recorded by a recorder 20. This signal is also used for brightness modulation of the CRT 23.

On the other hand, the primary ion beam 2 can be scanned over the sample by a scanning power source 22 and a deflection electrode 5.

This scanning signal is sent to the CRT 23 and the electric field power supply.

Further, secondary ions are detected by a secondary ion detector 10, passed through an amplifier 21, and also recorded on a CRT 23. amplifier 1
If the 0 signal is used for brightness modulation and the deflection voltage is used as an XY times signal, an image of all the ions sputtered from the sample 7 can be recorded. On the other hand, if the strength of the sector magnetic field 16 is set so that a specific number of masses can pass through it, and the signal from the amplifier 19 is used to modulate the brightness of the CRT 23, an image of a specific ion can be recorded. Furthermore, by connecting the signal from the amplifier 19 to the recorder 20 and scanning the beam with the deflection electrode 5, it is possible to dig into a certain area of the sample surface and monitor specific ions emitted from that area. This method is called depth direction analysis and is used to study the surface layer and sometimes to measure the concentration distribution of B and P implanted into silicone wafers. In the case of depth direction analysis, in addition to ions sputtered from the same phase that should be analyzed, ions combined with gas phase gas may appear.

Furthermore, if these ions have the same mass number, for example S
When analyzing P in i, SiH and P have the same mass number of 29.

In this case, the energy of both ions is often about 10 eV lower for SiH than for P. Therefore, both ions can be separated by a β slit, as explained earlier. For example, this energy width is approximately 0.6 when the secondary ion accelerating voltage is 3 KV in an electric field with an orbital radius of 200 nu.
It is about nm. - On the other hand, when performing depth direction analysis, if the primary ions are scanned, for example, 0.61m, if the image magnification of the electric field is 1, they will be deflected by 0.6no on the β slit, and the P ions will be deflected by 0.6no on the SiH This will be replaced by an ion peak. Therefore, in reality, even 0 and 6 on cannot be scanned.

However, when the electric field voltage is scanned by about 0.3% in synchronization with the scan of the primary ions, the peak of P does not change at the position of the β slit. Therefore, a peak of P can always be set on the collector slit 17, and since the influence of SiH is small, the accuracy of depth direction analysis can be improved.

FIG. 2 shows an example of the effects of the present invention. The sample was a P-implanted Si wafer, and the P+ intensity was measured as a function of time. The figure shows two measurement curves (
(a) shows the results of the conventional method, and (b) shows the results of the present invention. Although the horizontal axis is a function of time, it is equivalent to the depth from the surface because sputtering occurs due to ion irradiation while the sample is constantly scanning primary ions for about 0.2 mm''.

In (a), there is a region of maximum concentration near the surface, and gradually P
The amount of + is decreasing, but it does not decrease beyond a certain depth. On the other hand, in (b), the P+ ions are significantly reduced compared to (a). At the point where are almost parallel (a
) value is approximately 1017/C! 118, about 10 in (b)
5 pieces/a113. As a result, an approximately two-digit improvement in accuracy was observed. The reason why the P+ value does not decrease in the result of (a) is that the main peaks of SiH mentioned above overlap.

〔Effect of the invention〕

According to the present invention, it is now possible to accurately select energy using an electric field even in measurements using a scanning primary ion beam, making it possible to improve the accuracy of depth direction analysis. Si
In the analysis of P in the middle, the accuracy improved by about two orders of magnitude.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing the effects of the present invention. 1...Ion gun, 2...Primary ion beam, 3...
・Condenser lens, 4...Objective aperture, Deflection electrode, 6...Objective lens, 7...Analysis sample, 8...
・Sample holder. 9... Shield electrode, 1o... Secondary ion detector,
DESCRIPTION OF SYMBOLS 11... Secondary ion extraction electrode, 12... Correction lens, 13... Aperture, 14... Sector electric field, 1
5... β slit, 16... Sector magnetic field, 17...
・Collector slit, 18...Secondary ion detector, 1
9...Amplifier, 2o...Recorder, 21...Amplifier, 22...Scanning power supply, 23...CRT, 24...
Electric field power supply. Figure 1 Figure 2

Claims (1)

[Claims] 1. In an ion microanalyzer consisting of a primary ion source, a primary ion irradiation system including a scanning means for scanning the primary ions on the sample surface, and a mass spectrometer having a sample chamber energy separation means, the primary ions are scanned on the sample surface. An ion microanalyzer characterized in that the voltage of an electric field electrode of a secondary ion mass spectrometer section is scanned in proportion to the scanning width.