JPH0326499B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an ion microanalyzer (Ion microanalyzer).
It is related to the sweep method of primary ions during depth direction analysis using Micro Analyzer, which enables highly accurate measurement of samples in which the target of analysis is widely distributed down to very low concentrations in the depth direction. Regarding microanalyzer.

[Background of the invention]

An ion microanalyzer is a device that irradiates the surface of a solid sample with accelerated ions and performs mass analysis of the spattered secondary ions.
Compared to other surface analyzers, it has the feature of being able to measure the concentration distribution of elements in the depth direction with high sensitivity.
The configuration of such an ion microanalyzer will be explained with reference to FIG. 1. In the figure, primary ions generated and accelerated by an ion source 1 are focused by lenses 2 and 3 and irradiated onto a sample 5. The secondary ions spattered from the surface of the sample 5 are transferred to the extraction electrode 6.
into the mass spectrometer. This mass spectrometer is composed of an electric field 7, a magnetic field 8, a detector 9, etc., and the secondary ions are detected by the detector 9 after passing through the electric field 7 and the magnetic field 8. The ion current detected by the detector 9 passes through the amplifier 10, is digitized by the AD converter 11, and is taken into the data processing device 12. It is now possible to control the primary ion beam.

In this way, when the primary ion beam is irradiated onto the sample 5, atoms on the surface of the sample 5 are spattered and new surfaces are formed one after another. In other words, analysis in the depth direction becomes possible. However, during depth direction analysis, if the primary ion beam is fixed at one point on the sample 5 as shown in Figure 2a, the cross section of the etched sample will have a parabolic shape as shown in Figure 2b; This is because the density of the primary ion beam is generally high at the center and low at the periphery. Therefore, if depth analysis is performed in such a state, it has the disadvantage that it is impossible to obtain a correct concentration distribution in the depth direction due to ions emitted from the etched wall. .

The following method has been proposed to reduce the influence of this etched surface. As shown in Figure 3,
The primary ion beam is raster-swept by the deflector 4, and the secondary ion current is measured only in the center 5A of the sweep area, as shown in FIG. 4a. When such a raster sweep is performed, it becomes possible to perform flat etching without being affected by the density of the primary ion beam, as shown in FIG. 4b. Also,
The influence of the crater wall can also be minimized.

However, when sample 5 is Si, for example, and when we analyze the ultrafine elements implanted into the Si, we expect a profile like the dotted line A in Figure 5, but instead we get a profile like the solid line B. You may get a profile. This is because when the element to be measured exists at a high concentration at a certain depth and is etched beyond that layer, a large amount of the element 22 with high concentration is sputtered at the end of the raster sweep, as shown in Figure 6. This is because it contaminates the center of the raster sweep.
For this reason, the problem of contamination cannot be ignored when measuring a concentration distribution with a dynamic range of several orders of magnitude or more.

[Purpose of the invention]

An object of the present invention is to provide an ion microanalyzer that eliminates the influence of etched walls that cannot be overcome even with the raster sweep limited area measurement method, thereby improving the accuracy of concentration distribution measurements. .

[Summary of the invention]

In order to achieve such an objective, the present invention
As a means of avoiding the influence of the raster sweep from the wall surface, the sweep area is successively reduced. That is, in order to avoid being affected by the wall surface, it is sufficient to continuously reduce the raster sweep area. but,
Continuously reducing the area is not practical because the reduction speed sets a limit in the depth direction. Fourth
As shown in Figure a, on sample 5, 128 points x
Trying to do a 128 point sweep. At this time, assume that two peripheral points in the sweep area are affected by the wall surface, and that the measurement target area is within the sweep area.
If the center is 64 points x 64 points, the ratio of the raster sweep area to the peripheral area affected by the wall is 128 ² −124 ² /128 ² = 0.06.

Also, the ratio of the sweep area to the measurement area is 64 ² /128 ² = 0.25.

If contaminants spattered from the wall are spread evenly to the surrounding area, the influence on the central measurement area will be reduced to 1/4.

Therefore, the influence from the periphery to the central measurement area is 0.06 x 0.25/4 = 3.75 x 10 ^-3 .

In other words, if a component with a concentration of three orders of magnitude or more is exposed on the wall surface, this effect can no longer be ignored. On the contrary, it is shown that if the concentration difference is two orders of magnitude or less, sufficiently accurate measurements can be made using the limited area method. If there is a concentration difference of three orders of magnitude or more, it is necessary to narrow the sweep width to avoid etching the wall surface. The timing of this narrowing can be done using the following method. The secondary ion current values in the etching peripheral area and the wall surface area may be measured, and the sweep area may be reduced when the ratio of the two exceeds a predetermined level. To explain using the above example, the ratio of the measurement area at the periphery to the center is 0.06 x 1/0.25 = 0.24, so if the concentration is uniform, the ion current value at the periphery will be around 0.24 of the center. If this ratio were to be as large as 2.4 or 24, this would indicate that a component with high concentration is exposed in the periphery, and conversely, this component is absent in the center. Therefore, if the sweep area is reduced when the ratio becomes large beyond a certain predetermined level, the influence of the wall surface can be avoided.
FIG. 7 shows an etched cross-sectional view of sample 5 measured by the above method. In the same figure,
When the impurity substance 22 is completely exposed, it can be seen that the sweep area is being narrowed. Further, in FIG. 8, the profile at the periphery is shown by a broken line aa', and the solid line b-b' is the density profile at the center. Suppose that the ratio of both exceeds a certain level at _P1 point. If you reduce the sweep area here, the peripheral profile will shift to a''.If it exceeds the level at point _P2 again, you can limit the area again. This allows profile measurement with a range.

[Embodiments of the invention]

FIG. 9 is a block diagram showing an embodiment of the ion microanalyzer according to the present invention. In the figure, the sweeper 16 is
An XY sweep signal is now created. This XY sweep signal is sent to the deflector 4 via the deflector power supply 15, and the primary ion beam is swept by the deflector 4. The sweep signal is also sent to a primary ion position discriminator 18, and the primary ion position discriminator 18 discriminates whether the primary ion is at the periphery or at the center, which is the measurement area. On the other hand, secondary ions are detected by a detector 9 and measured by a counter 19. During this measurement, a gate signal sent from the primary ion position discriminator 18 is used to separately measure the periphery and the center. The two measured values obtained here are sent to a comparator 20, the ratio of which is determined, and the comparison is made with a predetermined level value. If the determined ratio exceeds the level, a signal is sent to the sweeper 16 to reduce the sweep area. The signal output from the counter 19 is sent to a recorder 21 and recorded.

In this way, the degree of influence of impurities from the periphery to the center can be determined based on whether the ratio of the measured values of the periphery and the center exceeds a certain level value, and based on this, the sweep area can be reduced. Since it is determined whether or not to use the sensor, it is possible to perform measurement while preventing contamination from the periphery to the center due to impurities, and therefore it is possible to perform measurement with a high dynamic range in the depth direction.

Although the embodiment shown in FIG. 9 is constructed using a logic circuit, it is also possible to use a data processing unit (CPU) to measure the secondary ion current, determine the position of the primary ions, and reduce the sweep area. (For example, the data processing device 12 shown in FIG.
). Furthermore, it goes without saying that the sweep method is not limited to raster sweep.

〔Effect of the invention〕

As is clear from the above, the ion microanalyzer according to the present invention eliminates the influence of the etched wall surface, which could not be overcome even with the limited area measurement method using raster sweep, and thereby improves the accuracy of concentration distribution measurement. It is possible to improve the

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of an ion microanalyzer, Figures 2a and b are explanatory diagrams showing an example of the conventional fixed beam method for measuring concentration using an ion microanalyzer, and Figure 3 is an illustration using an ion microanalyzer. FIGS. 4a and 4b are explanatory diagrams showing an example of the conventional raster scan method for measuring density using the raster scan method, and FIG. Figure 6 is an explanatory diagram showing the drawbacks of the raster scan method.
The figure is a cross-sectional view showing the etched state of a sample when concentration is measured using the ion microanalyzer according to the present invention, and FIG. 8 is an output example of a depth direction profile when concentration is measured according to the present invention. The graph shown in FIG. 9 is a configuration diagram showing an embodiment of the ion microanalyzer according to the present invention. 4... Deflector, 9... Detector, 15... Deflector power supply, 16... Sweeper, 17... Oscillator, 18... Primary ion position identifier, 19... Counter, 20... Comparator, 21... Recorder.

Claims (1)

[Claims] 1. An ion microanalyzer that includes an ion source that generates accelerated primary ions, a deflector that can sweep the ion source two-dimensionally over a sample, and a mass spectrometer that analyzes secondary ions emitted from the sample. means for separately extracting secondary ion signals from the periphery and the center of the sample; and means for comparing the secondary ion signals from the periphery and the center of the sample, and when the ratio exceeds a predetermined value, the center of the sample is detected. 1. An ion microanalyzer, comprising: a means for reducing a sweep width so as to sweep a portion of the ion microanalyzer.