JP2009121933A - Secondary-ion mass spectrometry method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an analysis method capable of performing an accurate analysis by eliminating the influence of the sidewall of an analysis crater when especially analyzing a deep region exceeding 10 μm. <P>SOLUTION: The analysis is interrupted in a range where the depth of the analysis crater of a region to be analyzed does not affect resolution in a depth direction; a part around the analysis crater is dug so that the part is flush with the bottom of the analysis crater; and the height of a sample is adjusted when resuming the analysis to set an analysis surface to an initial height. Therefore, the irradiation state of primary ions to the analysis surface can be maintained fixedly, and the detection sensitivity of secondary ions can also be maintained stably, thus accurately analyzing a deep region. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a secondary ion mass spectrometry method, and more particularly, to a secondary ion mass spectrometry method for analyzing a deep portion of an analysis target region of a sample.

  The secondary ion mass spectrometry method is a method for irradiating a sample with primary ions, mass analyzing the secondary ions released from the sample, and performing elemental analysis of the constituent components of the sample. By digging, the element distribution state in the depth direction can be obtained. Secondary ion mass spectrometry methods are classified according to the type of mass spectrometer, and examples of the mass spectrometer include a magnetic field type mass spectrometer, a quadrupole mass spectrometer, and a time-of-flight mass spectrometer.

  Since secondary ion mass spectrometry analyzes in the depth direction while digging a sample with primary ions, the region of the sample irradiated with the primary ions has a crater shape. This crater-like region cut into primary ions is called an analytical crater.

  FIG. 5 shows a schematic diagram of the analysis crater 501. In the vicinity of the analysis crater side wall 502, secondary ions 505 may be generated from the analysis crater side wall 502 and the surroundings due to partial contact of the primary ions 504 as shown in FIG. Unlike the composition of the target region (secondary ions 506 generated from the bottom of the crater), becomes an interfering ion. In order to avoid the mixing of the interfering ions, the secondary ion collection region 507 is a central portion away from the normal analysis crater side wall 502 as shown in FIGS. 5A and 5B, and is a primary ion irradiation region. It becomes several tens of percent out of 508.

  When the analysis region is large in the depth direction, the depth of the analysis crater 501 becomes deep, and the primary ions 504 are blocked by the analysis crater side wall 502 so that only a part of the analysis target region can be irradiated. FIG. 6 shows a schematic diagram of the deep analysis crater 601. As the analysis crater becomes deeper, the area where the primary ions 504 do not reach the crater bottom 503 increases, and when the area approaches the secondary ion collection area 507, the detected amount of secondary ions decreases. Further, the secondary ions generated are also disturbed by the side wall, the number of secondary ions 510 that cannot be detected by colliding with the side wall increases, the number of detectable secondary ions 509 decreases, and the detection sensitivity decreases. Further, the solid surface roughness increases as the analysis depth increases (see, for example, Patent Document 1). For the above reasons, there is a problem that the resolution in the depth direction decreases depending on the analysis depth.

  As a method of avoiding this, there is a method in which the primary ion irradiation region is made large and the ratio of the secondary ion collection region to the primary ion irradiation region is made sufficiently small to eliminate the influence of the analysis crater side wall. As an example of this, a method is disclosed in which a side surface in the incident direction of primary ions is excavated by etching in a concave analysis region (see, for example, Patent Document 2). As other methods, there are a method in which several samples polished stepwise to a target depth are prepared and the analysis results thereof are integrated, and a cross section of the sample is analyzed.

  In addition, in an analysis method in which composition analysis in the depth direction of a sample by sputtering and structure observation by a microscope are combined, a technique is disclosed in which the sample is excavated around the analysis crater to the bottom (for example, Patent Document 3). reference).

JP 2001-174421 A (page 3, FIGS. 1-2) Japanese Patent Laid-Open No. 11-23497 (pages 2 and 3, FIG. 2) Japanese Unexamined Patent Publication No. 2004-144635 (page 6, FIG. 2)

  However, if the primary ion irradiation area is made large, the analysis speed of the secondary ion mass spectrometry becomes slower with the expansion of the primary ion irradiation area, and the detected secondary ion intensity decreases with the reduction of the collection area ratio. Resulting in. There are cases where the analysis target region of the sample to be analyzed is very small or the concentration of the analysis element is low, and there is a limit to the reduction of the secondary ion collection region ratio.

  In addition, the method described in Patent Document 1 removes only the side wall corresponding to the incident direction of the primary ions, and when the analysis depth becomes deep, the detection sensitivity of the secondary ions is increased by the peripheral side walls that are not removed. May decrease.

  Further, in the case of a method in which a plurality of samples polished in stages are prepared and the results are integrated, the distribution of the boundary portion at each polishing depth may be ambiguous. Further, the polishing of the sample requires a lot of time and a lot of sample area.

  Further, in the method of analyzing the cross section of the sample, since the surface analysis and the line analysis are performed, the lower limit of detection is worse than that in the normal analysis. When the distribution depth is about several tens of μm, when analyzing from a cross section, the analysis target region is very small and analysis is difficult.

  Moreover, although the method of patent document 3 describes excavating the circumference | surroundings of an analysis crater, it aims at creating the specific observation surface to pay attention to correctly, and also excavates the bottom of an analysis crater. (For example, refer to Patent Document 3).

  The present invention has been made in view of such problems, and the object of the present invention is to provide an analysis method capable of performing an accurate analysis by eliminating the influence of the side wall of the analysis crater, particularly in the analysis of a deep region exceeding 10 μm. Is to provide.

  In order to solve the above problems, the present invention provides a secondary ion mass spectrometry method in which primary ions are irradiated onto a solid sample, and secondary ions released from the sample are subjected to mass separation to perform elemental analysis of constituent components of the sample. , After analyzing the analysis target area to a certain depth, excavate the area around the analysis crater, set it to the same height as the bottom of the analysis crater, and then repeat the analysis of the analysis target area to repeat the analysis of the target depth. Elemental analysis shall be performed.

  The present invention interrupts the analysis in such a range that the depth of the analysis crater in the analysis target area does not affect the depth resolution, and excavates the surrounding area of the analysis crater to make it the same height as the bottom of the analysis crater. In addition, when the analysis is resumed, the height of the sample is adjusted to bring the analysis surface to the initial height. Thereby, the primary ion irradiation state with respect to the analysis surface can be kept constant, and the detection sensitivity of the secondary ions can be stably maintained. Therefore, it is possible to accurately analyze a deep region.

  A focused ion beam apparatus can be used as means for excavating the sample analysis crater. The focused ion beam apparatus can narrow the ion beam finely and can excavate the surroundings without affecting the analysis crater. By incorporating the function of the focused ion beam device into the secondary ion mass spectrometer so that it can be processed in the same sample chamber, rapid analysis becomes possible. Further, a laser displacement sensor may be used as a method for measuring the depth of the analysis crater in the analysis target region.

  As described above, in the secondary ion mass spectrometry method, after analyzing the analysis target region to a certain depth, a portion around the analysis crater is excavated to have the same height as the bottom of the analysis crater, and then the analysis target is again By repeating the analysis of the region and performing the elemental analysis to the target depth, it is possible to analyze up to a deep region without being affected by the side wall of the analysis crater.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows the configuration of a standard magnetic field type secondary ion mass spectrometer 100 used for secondary ion mass spectrometry according to the present invention.

  The secondary ion mass spectrometer 100 includes a primary ion supply unit 110 that supplies a primary ion beam 113, a secondary ion generation unit 120 that generates and detects secondary ions 124, and a focused ion beam 135 that generates a focused ion beam 135. It is roughly divided into an ion beam unit 130.

  The primary ion supply unit 110 includes a cesium ion source 111 and an oxygen ion source 112 in order to generate the primary ion beam 113. As the primary ion beam 113, either cesium ions generated from the cesium ion source 111 or oxygen ions generated from the oxygen ion source is selected according to the element to be measured. The primary ion beam 113 is narrowed down in a vacuum and irradiated on the surface of the sample 121 described later at about several kV to 20 kV.

  The secondary ion generation unit 120 includes a sample 121, an electromagnet 122, and a secondary ion detector 123.

  The sample 121 is installed in the sample chamber and irradiated with the primary ion beam 113 generated from the primary ion sources 111 and 112. On the surface of the sample 121 irradiated with the primary ion beam, particles in the sample jump off due to a phenomenon called sputtering, and secondary ions 124 are generated. Here, the sample chamber is evacuated by an exhaust device (not shown).

  The electromagnet 122 deflects and converges the secondary ions 124 generated by irradiation and mass-separates them, and sends the target ions to the secondary ion detector 123. The secondary ion detector 123 detects the input target secondary ion 124.

  The focused ion beam unit 130 includes an ion gun 131, a secondary electron detector 132, a monitor 133, and a laser displacement sensor 134.

  The ion gun 131 generates gallium (Ga) ions from metal gallium, narrows the gallium (Ga) ions, generates a focused ion beam 135, and irradiates the sample 121 with it to process it.

  The secondary electron detector 132 detects the secondary electrons 136 generated when the focused ion beam 135 is irradiated by the secondary electron detector 132 and sends the detection result to the monitor 133.

  The monitor 133 is connected to the secondary electron detector 132 and displays the detection result detected by the secondary electron detector 132 as a secondary electron image of tens of thousands of times. The measurer can process the sample 121 by using the image displayed on the monitor 133, and can thereby precisely process a minute portion of the sample 121.

  The laser displacement sensor 134 measures the crater depth of the analysis target region, and based on the measurement result, the periphery of the analysis crater is excavated by the focused ion beam so that the entire sample surface becomes the same height as the bottom of the analysis crater. To do.

FIG. 2 is an explanatory diagram of a secondary ion mass spectrometry method according to an embodiment of the present invention.
FIG. 2A shows a cross section of the sample 121. Here, a Si substrate cut into a 2 mm square is used as the sample 121. The sample 121 includes a B distribution region 202 in which B (boron) is distributed at a constant concentration from a region of 200 μm × 200 μm to a depth of 50 μm at the center upper part. The B concentration is about 1 × 10 16 atoms / cm 3. This is affixed on the sample stage 201 and set in the apparatus.

  First, oxygen (O2 +), primary acceleration energy 15 keV, primary current 300 nA, primary ion irradiation region 100 μm × 100 μm, and data capturing region 30 μmφ are set as the primary ion beam 113, and secondary ion mass spectrometry is performed. As secondary ions, B and Si which is a main constituent element of the substrate are measured. Since Si exists in a sufficient amount at any depth, it should be detected with a constant intensity.

  FIG. 2B shows a cross section of the sample 121 when the analysis is interrupted in a range where the secondary ion mass spectrometry does not affect the depth resolution. Here, mass analysis is interrupted at a depth of about 10 μm, and the depth of the analysis crater 203 in the analysis target region is measured by a laser displacement sensor 134 attached in the apparatus. Next, while the depth is checked by the laser displacement sensor 134, the analysis crater periphery removal unit 204 is excavated by the focused ion beam so that the entire sample surface is flush with the bottom of the analysis crater. Thereby, the analysis crater 203 is eliminated, and the primary ion beam 113 is irradiated without being affected by the side wall of the analysis crater.

  FIG. 2C shows a cross section of the sample 121 after excavating the entire sample surface to the same height as the bottom of the analysis crater. Next, the height of the sample stage is adjusted to adjust the measurement surface of the sample 121 to the initial height. Thereby, since the primary ion beam 113 is irradiated to the same position as the measurement start time of the measurement surface of the sample 121, the measurement can be performed under the same conditions as the measurement start time, and the detection sensitivity of the secondary ions can be stably maintained. .

  FIG. 2D shows a cross section of the sample 121 after the sample measurement surface is adjusted to the initial height. After adjusting the sample measurement surface to the initial height, the measurement is resumed. Thereafter, the above-described process is repeated until B is not detected.

  The depth at which the analysis is interrupted may be in a range where the strength of the main constituent element (in this case, Si) is constant. The analysis result is converted from the depth of the analysis crater measured for each measurement into the total distribution depth.

  FIG. 3 is a diagram showing a comparison in the depth direction distribution of B and Si by a secondary ion mass spectrometry method according to an embodiment of the present invention and a conventional method in which analysis is performed without interruption until B is no longer detected. is there.

  In FIG. 3, the thick line A shows the B distribution measured by the secondary ion mass spectrometry method of the present invention, the thick dotted line B shows the Si distribution measured by the secondary ion mass spectrometry method of the present invention, and the thin line C shows The B distribution measured by the conventional method is shown, and the thin dotted line D shows the Si distribution measured by the conventional method.

  When the characteristics of the thin line C and the thin dotted line D, which are the measurement results obtained by the conventional method, are observed, both the Si intensity and the B concentration are decreased from the vicinity of the analysis depth of 15 μm, and the secondary ion detection sensitivity is decreased. On the other hand, in the measurement by the secondary ion mass spectrometry method of the present invention, the Si intensity is constant, the B concentration distribution is constant up to 50 μm, and then rapidly decreases.

  In other words, it was confirmed that the secondary ion mass spectrometry method of the present invention eliminates the influence of the analysis crater side wall and enables accurate analysis in deep region analysis.

  FIG. 4 is a flowchart illustrating a secondary ion mass spectrometry method according to an embodiment of the present invention.

  In step S401, first, mass spectrometry is performed to a depth of about 10 μm. Next, the depth of the analysis crater in the analysis target region is measured by the laser displacement sensor (step S402). Next, while checking the depth by the laser displacement sensor, the periphery of the analysis crater is excavated by the focused ion beam so that the entire sample surface is at the same height as the bottom of the analysis crater (step S403).

  Next, the height of the sample stage is adjusted to adjust the sample measurement surface to the initial height (step S404). After the sample measurement surface is adjusted to the initial height, the analysis is resumed, and the analysis is performed to a depth of about 10 μm as described above (step S405). Next, it is determined whether or not the analysis has been performed up to the target depth (step S406). If it is determined in step S406 that the target depth has been analyzed, the process ends. If not, the process proceeds to step S402 to repeat the process.

  According to the present invention configured as described above, in the secondary ion mass spectrometry method, after analyzing the analysis target region to a certain depth, a portion around the analysis crater is excavated, and the same height as the bottom of the analysis crater is obtained. Then, it is possible to perform analysis up to a deep region without being affected by the side wall of the analysis crater by repeating the analysis of the analysis target region again and performing elemental analysis up to the target depth.

It is a block diagram of the standard magnetic field type | mold secondary ion mass spectrometer used for the secondary ion mass spectrometry method by one Embodiment of this invention. It is explanatory drawing of the secondary ion mass spectrometry method by one Embodiment of this invention. It is a figure which compares and shows the depth direction distribution of B and Si by the secondary ion mass spectrometry method by one Embodiment of this invention, and the conventional method. 3 is a flowchart illustrating a secondary ion mass spectrometry method according to an embodiment of the present invention. It is a schematic diagram explaining the influence of an analysis crater side wall in a secondary ion mass spectrometry method. It is a schematic diagram explaining the case where a deep part is analyzed in the secondary ion mass spectrometry method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Secondary ion mass spectrometer 110 Primary ion supply part 111 Cesium ion source 112 Oxygen ion source 113 Primary ion beam 120 Secondary ion generation part 121 Sample 122 Electromagnet 123 Secondary ion detector 124 Secondary ion 130 Focused ion beam Part 131 Ion gun 132 Secondary electron detector 133 Monitor 134 Laser displacement sensor 135 Focused ion beam 136 Secondary electron

Claims (5)

A secondary ion mass spectrometry method for irradiating a predetermined analysis target region of a solid sample with a primary ion, mass-separating secondary ions released from the solid sample, and performing elemental analysis of components of the analysis target region Because
Analyzing the predetermined analysis target area to a certain depth;
Drilling a portion of the analysis crater around the analysis area to the same height as the bottom of the analysis crater;
Re-analyzing the predetermined analysis target area;
A secondary ion mass spectrometry method comprising the step of performing elemental analysis to a target depth by repeating the excavation step and the re-analysis step. After the analyzing step,
Measuring the depth of the analysis crater further,
The secondary ion mass spectrometry method according to claim 1, wherein in the excavating step, excavation is performed to the same height as the measured depth of the analysis crater. After the drilling step,
Further comprising adjusting the height of the analysis surface of the solid sample to the initial height;
The secondary ion mass spectrometry method according to claim 1, wherein in the reanalyzing step, irradiation of primary ions is started at the initial height.   The secondary ion mass spectrometry method according to claim 1, wherein a focused ion beam device is used as a method of excavating a portion around the analysis crater in the analysis target region.   The secondary ion mass spectrometry method according to claim 2, wherein a laser displacement sensor is used as a method of measuring the depth of the analysis crater in the analysis target region.

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