JP2008232838A - Depth-directional element concentration analytical method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To acquire information about only a desired area, without taking information in the periphery of an analytical area in, and to obtain a precise depth-directional distribution of a trace element, when carrying out a secondary ion mass spectrometry, as to a depth-directional element concentration analytical method. <P>SOLUTION: A voltage is impressed to an object to be measured, in one part of a primary ion beam scanning area emitted toward the object to be measured. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a depth direction element concentration analysis method capable of acquiring only desired information with high accuracy when measuring a depth direction distribution of trace elements by irradiating a sample with primary ions and extracting secondary ions. About.

  In general, in secondary ion mass spectrometry, accelerated primary ions are squeezed with a condenser lens to form an ion beam, and the ion beam is irradiated to the sample position to be analyzed. However, the intensity has an in-plane distribution, and the central part has the maximum intensity.

FIG. 3 is a diagram showing the in-plane distribution when primary ions are focused by a condenser lens, where f is the focal point of the ion beam on the sample surface, and I is the uniform current density. The total current amount of the primary ion beam below, j is the current density, j ₀ is the maximum value of the current density, and the ion beam current density j is the highest in the central part, forming a Gaussian distribution shape. ing.

The upper half of FIG. 3 shows how the primary ion beam converges at the focal point f on the surface of the sample, and the lower half shows how the primary ion beam is distributed in the sample as a beam image. The distribution of the primary ion beam when the current density j is uniform is shown by a broken line under the condition indicated by the solid line and the total current amount I is I = j ₀ r _s ² π And j ₀ is the maximum current density.

  For this reason, when performing element concentration analysis in the depth direction, if the sample is irradiated with the ion beam as it is, information on the depth corresponding to the intensity distribution will be detected in a lump, and accurate depth direction elements will be detected. The concentration distribution cannot be measured.

  Therefore, the primary ion beam usually employs a method of scanning a certain region and selectively extracting information only from the central portion thereof, for example, an electric gate method and an optical aperture method.

  FIG. 4 is an explanatory diagram when the electric gate method is performed. In the figure, 11 is a sample, 11A is a crater generated by irradiation with a primary ion beam, 12 is a primary ion scanning region, 13 Indicates the area where the electric gate is turned on.

  In the electric gate method, only when the primary ion beam to be scanned is located in the analysis region, a voltage is applied to the secondary ion extraction electrode to detect the secondary ions.

  As is apparent from the above, in the electric gate method, the secondary ion extraction electrode is applied with a voltage by applying a voltage to the secondary ion extraction electrode only when the primary ion beam reaches the center of the sample in the scanning process of the primary ion beam. Ions are detected.

  FIGS. 5A and 5B are explanatory diagrams when the optical aperture method is performed. FIG. 5A shows a case where the primary ion beam is not scanned, and FIG. 5B shows a case where the scanning is performed. 1A is the diameter of the analysis region, 1B is the crater, 1C is the depth of the crater, 1D is the step generated in the crater, 2 is the aperture, 2A is the diameter of the aperture, 3 is the primary ion beam, and 3A is the diameter of the primary ion beam 3B denotes an incident angle of the primary ion beam, 4 denotes a secondary ion beam, and 5 denotes a raster plate.

  Specifically, the numerical value 1A of the analysis region is 350 μm, the depth 1C of the crater 1B is 1 μm, the step 1D generated in the crater 1B is 0.017 μm, the aperture diameter 2A is 50 μm, and no scanning is performed. The diameter 3A of the primary ion beam is 250 μm, the diameter 3A of the primary ion beam when scanning is 50 μm, and the incident angle 3B of the primary ion beam is 45 °.

  In the optical aperture method, during irradiation of the primary ion beam, a secondary ion is extracted by applying a voltage to the secondary ion extraction electrode. An aperture is placed behind the extraction electrode and the sample is applied to the sample. Only secondary ions from the center are introduced into the detection system.

  As seen in FIG. 5A, when the primary ion beam 3 is not used for scanning, the bottom of the sample 1 that has been shaved is not flat, and a step of 0.017 μm is generated in the analysis region. However, as seen in FIG. 5B, when scanning with the primary ion beam 3, the bottom of the shaved sample 1 becomes flat.

  The electric gate method and the optical aperture method described above are effective as they are. However, in the recent manufacturing field of semiconductor devices and the like, in order to inject a high concentration impurity into the extremely shallow region, the depth direction The distribution is very shallow and steep.

  For this reason, primary ions used for analysis are forced to be accelerated, and it is difficult to narrow the beam diameter. And along with this, the edge of the crater formed by the primary ion scan loses its steepness, the effective secondary ion extraction region in the center becomes narrow, and the information around the secondary ion extraction region is easily mixed in It is in.

In recent semiconductor analysis, the two extraction methods described above are used, or a voltage is applied to a sample by SIMS analysis (see, for example, Patent Document 1), but deep. There are many cases where the information accuracy of the vertical direction distribution is insufficient.
JP-A-63-226867

  In the present invention, when performing secondary ion mass spectrometry, information on only a desired region can be obtained without acquiring information around the analysis region, and an accurate depth direction distribution of trace elements is obtained.

  In the depth direction element concentration analysis method according to the present invention, a voltage is applied to the object to be measured in a part of the scanning region of the primary ion beam irradiated to the object to be measured. .

  By adopting the above-mentioned means, the distribution in the depth direction of the ion-implanted element is improved as shown in FIG. 1, so that the steepness is improved. Only information from the region can be detected.

  In the present invention, when the conventional secondary ion extraction method, that is, the electric gate method or the optical aperture method is performed, an excellent effect can be achieved by adding the means described below. Can be enjoyed.

  That is, during scanning of the sample with primary ions, the voltage applied to the sample is changed between the analysis region (secondary ion detection region) and its peripheral portion. That is, when viewed from the relationship between the energy distribution of secondary ions and the voltage applied to the sample, a voltage that increases the energy distribution intensity of the secondary ions is applied in the analysis region, and the energy of the secondary ions is applied in the periphery. A voltage that lowers the distribution intensity is applied.

  FIG. 1 is a diagram showing energy distribution of secondary ions generated by irradiating a sample with primary ions. The vertical axis represents normalized secondary ion intensity, and the horizontal axis represents sample potential. It is taken.

  Since the secondary ion intensity varies depending on the voltage applied to the sample, the secondary ion energy distribution shown in FIG. 1 can be obtained by plotting the secondary ion intensity against the sample potential.

  Incidentally, in the conventional electric gate method, the secondary ion extraction voltage is turned on / off in conjunction with the scanning of the primary ions, but in the present invention, the voltage applied to the sample is primary. The major difference is that it is changed in conjunction with the scanning of ions.

  FIG. 2 is a diagram showing the results obtained by carrying out the analysis method of the depth direction distribution of trace elements according to the present invention in comparison with the results obtained by carrying out the conventional electric gate method, In addition, an example of a primary ion scanning pattern when the present invention is implemented is appended to the diagram.

  FIG. 2 shows the depth distribution of In ion-implanted into Si, with the vertical axis representing the secondary ion intensity (pieces / second) and the horizontal axis representing the depth (nm). Yes, A shows the result obtained by carrying out the analysis method of the present invention, and B shows the result obtained by carrying out the conventional electric gate method.

  According to FIG. 2, the result obtained by performing the analysis method of the present invention has a larger dynamic range of the depth direction distribution and the distribution is steeper than the result obtained by performing the conventional electric gate method. It is caught that there is. This means that information from surroundings can be effectively prevented from being mixed.

  In the first embodiment, when scanning the primary ion beam, instead of normal raster scanning, that is, XY scanning, spiral scanning that scans in a spiral shape is added as shown in FIG. The object in the present invention can be easily achieved by performing the annealing and changing the voltage applied to the sample between the outer periphery and the inside of the spiral scanning.

  Since the present invention can be implemented in many forms including the above-described embodiment, it will be exemplified as an additional note hereinafter.

(Appendix 1)
An element concentration analysis method in a depth direction, wherein a voltage is applied to a measurement object in a part of a scanning region of a primary ion beam irradiated to the measurement object.

(Appendix 2)
The depth-direction element concentration analysis method according to (Appendix 1), wherein the region to which a voltage is applied to the object to be measured is a secondary ion detection region.

(Appendix 3)
A relationship between the voltage applied to the object to be measured and the secondary ion intensity corresponding to the voltage is obtained in advance, and the secondary ion intensity in the periphery of the secondary ion detection region is the second ion intensity in the secondary ion detection region. The element concentration analysis method in the depth direction according to (Appendix 2), wherein a voltage is applied to the object to be measured so as to be smaller than the secondary ion intensity.

(Appendix 4)
A relationship between the voltage applied to the object to be measured and the secondary ion intensity corresponding to the voltage is obtained in advance, and the voltage is applied to the object to be measured so that the secondary ion intensity becomes maximum in the secondary ion detection region. (Appendix 2) or (Appendix 3), the element concentration analysis method in the depth direction.

(Appendix 5)
The element concentration analysis method in the depth direction according to (Appendix 1) to (Appendix 4), wherein the primary ion beam scan is a spiral scan.

(Appendix 6)
In the spiral scanning, the element concentration analysis method in the depth direction according to (Appendix 5), wherein a voltage applied to the object to be measured is changed in a scanning region.

It is a diagram showing the energy distribution of the secondary ion generated by irradiating a sample with primary ions. It is the diagram which represented the result obtained by implementing the analysis method of the depth direction distribution of the trace element by this invention compared with the result obtained by implementing the conventional electric gate method. It is a diagram showing the in-plane distribution when primary ions are focused by a condenser lens. It is explanatory drawing in the case of implementing an electric gate method. It is explanatory drawing in the case of implementing an optical aperture method.

Claims (5)

  An element concentration analysis method in a depth direction, wherein a voltage is applied to a measurement object in a part of a scanning region of a primary ion beam irradiated to the measurement object.   2. The element concentration analysis method in the depth direction according to claim 1, wherein the region to which a voltage is applied to the object to be measured is a secondary ion detection region.   A relationship between the voltage applied to the object to be measured and the secondary ion intensity corresponding to the voltage is obtained in advance, and the secondary ion intensity in the periphery of the secondary ion detection region is the second ion intensity in the secondary ion detection region. 3. The element concentration analysis method in the depth direction according to claim 2, wherein a voltage is applied to the object to be measured so as to be smaller than a secondary ion intensity.   A relationship between the voltage applied to the object to be measured and the secondary ion intensity corresponding to the voltage is obtained in advance, and the voltage is applied to the object to be measured so that the secondary ion intensity becomes maximum in the secondary ion detection region. The element concentration analysis method in the depth direction according to claim 2, wherein:   5. The element concentration analysis method in the depth direction according to claim 1, wherein the scanning of the primary ion beam is spiral scanning.

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