JP2008241301A - Non-destructive three-dimensional nano-meter analyzing apparatus by time of flight analysis type back scattering, and non-destructive three-dimensional nano-meter analysis method by time of flight analysis type back scattering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To analyze impurity identification using a focused ion beam, element analysis, composition, crystallinity, and surface boundary state in a minute region of nano-meter order. <P>SOLUTION: In the three-dimensionally visualizing method, ions of intermediate energy 100-400keV focused to 10 nm or less are scanned and radiated to a sample, the time of flight measurement of Rutherford back scattered ions is performed by detecting a secondary electron ion as a start signal, TOF (Time Of Flight)-RBS data corresponding to each irradiation position is obtained with a nano-meter resolution, and the three-dimensional visualization is allowed by time-energy conversion. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention measures and analyzes the time of flight (TOF: Time Of Flight) of backscattered ions generated when a sample to be measured (hereinafter simply referred to as a sample) is irradiated with a focused ion beam. And improvement of Rutherford Backscattering Spectrometry (hereinafter referred to as RBS) for structural analysis. The present invention is particularly non-destructive and includes not only a plane (two-dimensional) but also a depth direction in a nanometer-order region in the vicinity of the surface of a semiconductor device or other fine-structured material that has been miniaturized. It is suitable for an apparatus capable of three-dimensional analysis.

  Until now, SIMS (Secondary Ion Mass Spectrometry), which is a destructive measurement method, has been used for measurement of impurity identification, element distribution, composition, etc. It is difficult to calibrate the sheath concentration, and problems such as beam mixing and the spatter yield due to destructive measurement have made it extremely difficult to measure with a focused ion beam in the nanometer order. On the other hand, in a scanning electron beam analyzer such as SEM (scanning electron microscope) or TEM (transmission electron microscope), a secondary electron image or a transmission intensity image is obtained. However, in order to measure the above-described impurity identification, element distribution, composition, etc., it is necessary to use a secondary reaction excited by an electron beam such as EDX (energy dispersive X-ray analyzer). In order to obtain the information of the direction, there was a problem that it would be a destructive measurement.

On the other hand, Rutherford backscattering analysis is known in which a sample is irradiated with a focused ion beam and the time of flight of ions backscattered there is measured to perform mass analysis of the sample. Such an analysis method has an advantage that the sample can be measured nondestructively. As an example of such a time-of-flight analysis type RBS, a continuous ion beam is converted into pulsed ions using chopping means for controlling passage / non-passage as in Non-Patent Document 1, and a chopping signal is flying. It was the time reference time. This is because the diameter of the conventional focused ion beam is several tens of nanometers, the value of the beam current is 30 pA or more, and it can be practically regarded as a continuous ion beam in relation to the chopping time width. In the following description, such a method is referred to as a “pulsed method using a gate of a continuous ion beam”.
J. Tajima, S. Kado, YKPark, R. Mimura, and M. Takai. “Medium energy nuclear microprobe with enhanced sensitivity for semiconductor process analysis“, Nuclear Instruments and Methods in Physics Research B 181 (2001) 44-48

  Next, another conventional embodiment as a comparison with the present invention will be described with reference to FIG. In FIG. 4, ions generated from the ion source, for example beryllium ions, are accelerated by the acceleration electrode 13 to which 100 kV to 200 kV is applied, and proceed toward the sample 6 in the lower part of FIG. At this time, a rectangular wave signal of 1 MHz shown in FIG. 7 is applied to the chopping plate 72 provided for the purpose of deflecting the path of the continuous ion beam and making it into a pulse shape. Here, when the potentials of the chopping plates A and B are the same, the ion beam travels straight without being influenced and passes through a hole of about 0.1 mm provided in the center of the chopping aperture 73. However, when the potential difference between the chopping plates A and B becomes larger than a certain level, the ion beam is affected by the electric field between the chopping plates A and B, and its path is deflected, so that it cannot pass through the hole at the center of the chopping aperture.

  In this conventional embodiment, a gate time of 1 ns width is created by adjusting the amplitude, rise time and fall time of a 1 MHz rectangular wave signal. The ion beam generated from the ion source is irradiated to the sample 6 as pulsed ions having a repetition period of 500 ns and a time width of 1 ns by a chopping plate, a chopping aperture, and a 1 MHz rectangular wave signal.

  The pulsed ions irradiated on the sample 6 reach the ion sensor 51 (Micro Channel Plate) and are detected as ions scattered back on the surface of the sample 6. A signal detected by the ion sensor 51 is input to a TOF (time-of-flight) measuring device through an ion system amplifier 55. As shown in FIG. 5, the TOF measuring device is equipped with a multiscaler, which is a high-speed frequency counter, and starts counting with the gate signal from the chopping plate, and counts when the signal from the ion sensor arrives. Works to stop.

As shown in FIG. 6, the time of flight of the backscattered ions is Tx.
Tx = Tc- (Ta + Tb)
Can be calculated as Here, Ta is the flight time of ions from the chopping plate 72 to the sample 6 and is a known value. Tb is a sensor delay time, which is also a known value.
The above is an explanation of one-time ion irradiation, but in actual analysis work, a large number of data are collected by scanning a predetermined location in the X and Y directions of the sample 6 with a deflection electrode, and processed by a CPU (computer). As a result, the distribution of foreign matter and the like near the surface of the sample 6 is three-dimensionally displayed on the display unit.

  The reason why the gate period is set to 500 ns and the gate time width is 1 ns in this conventional embodiment will be described below. Table 2 shows examples of flight times of backscattered ions of various metals in the case of an ion beam obtained by accelerating beryllium ions at 100 kV. If the gate period is shorter than the maximum time of flight of the element to be analyzed, the backscattering phenomenon at a certain time may overlap with the backscattering phenomenon that precedes or follows it, leading to erroneous measurement. It will be. For this reason, 500 ns was selected as the gate time. Since the gate time width determines the limit of time resolution, 1 ns is selected as a small value that can be realized.

表２は、BeイオンおよびSiイオンを使用した場合の被分析元素の飛行時間を示す表である。

Table 2 is a table | surface which shows the flight time of the to-be-analyzed element at the time of using Be ion and Si ion.

In recent years, there has been a demand for analysis of foreign matters in a narrow region of a nanometer order on a semiconductor circuit, for example. If the thickness of the ion beam is reduced to the nanometer order to meet such a demand, the ion beam current becomes a value of pA (picoampere) order. When the ion beam current is I [A], the charge amount of monovalent ions such as beryllium and silicon is
1.6022 × 10 ^-19 [C (Coulomb)]
Therefore, the average time interval Te of ions is from the definition of current value “1A = C / sec”.
Te = 1.6022 × 10 ^-19 / I
As shown in Table 1.

表１は、イオンビーム電流値とイオンの平均時間間隔を示す表である。

Table 1 is a table showing ion beam current values and average time intervals of ions.

  In the conventional example, when the beam thickness is narrowed down to the nanometer order, as shown in Table 1, the ions are not regarded as continuous in a comparison with the gate time width of 1 ns, and are in a single state. For example, when the beam current is 0.3 pA, the average time interval of the singulated ions is approximately 500 ns. When the analysis operation is performed in this situation, that is, when the analysis operation is performed by the “pulsing method by the gate of the continuous ion beam”, one or more ions pass within the gate time of 1 ns as shown in FIG. This is the case when the beam current is larger than 160 pA.

  When the beam current is smaller than 160 pA, the average time interval of ions is larger than 1 ns, and one or more ions are not necessarily passed within the gate time of 1 ns. When the beam current is 0.3 pA, the average time interval of the singulated ions is about 500 ns, and there is no correlation between the gate time and the movement of the ions, so that the ions are within the gate time of 1 ns. The probability of passing is 1/500. This is that the work efficiency of the analysis work becomes 1/500. In other words, the analysis work time is 500 times longer than that of the conventional case where the ion beam current is 160 pA or more. For example, the analysis work completed in several hours requires several hundred hours or more, As a result, the efficiency will be significantly reduced.

  The present invention has been made in view of the problems of the prior art, and provides an analysis apparatus and an analysis method that can accurately perform mass spectrometry of a sample by Rutherford backscattering analysis without taking a long measurement time. With the goal.

The non-destructive three-dimensional nanometer analyzer using time-of-flight analysis type backscattering according to the first aspect of the present invention irradiates the sample with a focused ion beam, and thereby the sample based on the time of flight of backscattered ions emitted from the sample. An analysis device for performing analysis of
A secondary electron detection sensor that detects secondary electrons emitted simultaneously with the backscattered ions from the sample and outputs a first detection signal;
A backscattered ion detection sensor that detects the backscattered ions emitted from the sample and outputs a second detection signal;
The first detection signal and the second detection signal are input, a time TD from the time when the first detection signal is input to the time when the second detection signal is input is obtained, and the time TD And an arithmetic unit that obtains the time of flight of the backscattered ions.

The non-destructive three-dimensional nanometer analysis method by time-of-flight analysis type backscattering according to the second aspect of the present invention is configured to irradiate the sample with a focused ion beam, and thereby the sample based on the time of flight of backscattered ions emitted from the sample. An analysis method for analyzing
The time of flight of the backscattered ions is obtained by detecting secondary electrons emitted simultaneously with the backscattered ions from the sample.

  According to the present invention, for example, beryllium ions from a liquid metal ion source are focused to 10 nanometers or less by a focusing lens system, and raster scanning is performed on the sample, whereby secondary electrons and backscattered ions from the scanning position are obtained. Each can be measured. In addition, by measuring the time of flight of backscattered ions using the signal from the secondary electron detection sensor as a start trigger (reference time), analysis of impurities in the sample, element distribution, composition, crystallinity, surface interface state, etc. It can be performed. Furthermore, the backscattering spectrum data corresponding to the ion raster scanning position can be loaded into a computer, and impurity identification, element distribution, composition, crystallinity, surface interface state, etc. in the sample can be analyzed and displayed in two and three dimensions. it can.

  The time-of-flight detection of backscattered ions is generated at the same time as ions are irradiated and backscattered without irradiating the sample surface for the purpose of shortening the analysis time without using the conventional technique of “pulsing with a continuous ion beam gate”. The secondary electron signal to be measured is used as a trigger. Further, the surface of the measurement sample can be observed by a secondary electron image, and targeted three-dimensional measurement can be performed. Here, “time of flight” refers to the time from when the backscattered ions generated by irradiating the sample with the focused ion beam are released until they are detected by the backscattered ion detection sensor.

  In the present invention, the gate time is not used as the reference time for measuring the time of flight of backscattered ions, but secondary electrons generated simultaneously when the ions are irradiated on the sample surface and backscattered are detected by the secondary electron detection sensor. The time of day is used as a reference for time-of-flight measurement. According to this method, the sample is irradiated with all of the ion beam current emitted from the ion source, and the analysis can be executed with an analysis time substantially equivalent to the conventional method based on the gate time.

  Compared with the conventional method of “Pulsing method by gate of continuous ion beam” when the beam current is 160 pA or more and an analysis time of 1 hour is required, when the beam current is 0.3 pA, the time is 500 times 500 times. In other words, there is a risk that the time will be significantly increased and the system will be unusable. On the other hand, according to the present invention, even when the beam current is 0.3 pA, it is possible to realize an analysis time of almost the same level as the conventional method. In the present invention, it can be used under the condition that the time interval of the singulated ions is about 500 ns or more.

  According to the present invention, in a nanometer resolution analyzer using Rutherford backscattering and channeling effect of an ion beam focused to 10 nanometers or less, impurity identification in the nanometer region, element distribution, composition, crystallinity In addition to analysis of the surface interface state and the like, three-dimensional visualization of element distribution, composition, and the like is possible. As for crystallinity, channeling contrast images of individual depths can be obtained by raster scanning along the channeling axis direction of focused ions. Three-dimensional visualization is also possible. RBS measurement has the advantage that the scattering yield is theoretically determined, absolute measurement is possible if there is a standard signal of measurement, and it does not include depth and concentration uncertainty like other measurement methods. Yes.

When the flight time of secondary electrons is TA, the response delay time of the secondary electron detection sensor is TB, and the response delay time of the backscattered ion detection sensor is TC, the flight time TX of the backscattered ions is It can be obtained by the following equation (see FIG. 3).
TX = (TA + TB + TD) −TC

  Backscattered ions have the characteristic that the energy after backscattering decreases as the backscattering angle with respect to the straight direction of ion irradiation increases. Decreasing energy means decreasing the speed of backscattered ions, and means that the flight time after backscattering is increased. For this reason, even if the elements to be measured on the sample are the same, if the backscattering angle is different, the flight time is different, which is an error factor of the analyzer for obtaining the mass from the flight time.

  The difference in flight time due to the backscattering angle is that when the backscattering angle is large and the flight time is long, the distance to the sensor is shortened, and when the backscattering angle is small and the flight time is short, the distance to the sensor is short. Correction can be made by increasing the distance. In this invention of Claim 3, the measurement error by a scattering angle can be reduced by adjusting the angle of an ion detection sensor from the exterior of a sample chamber.

  According to the present invention, non-destructive three-dimensional analysis relating to impurity identification, element distribution, composition, crystallinity, surface interface state, etc. in the nanometer region that does not require calibration using a standard substance is possible without taking a long time. Therefore, it can be used as a non-destructive local analysis device for a state-of-the-art semiconductor integrated circuit, as well as being the only measuring means for the process and structure analysis for the structural design production in the nanometer order. In particular, the surface structure of a local portion of several hundred nanometers or less can be directly observed with a two-dimensional electron image, and a targeted non-destructive three-dimensional analysis can be performed in a short time.

  Hereinafter, a focused ion beam irradiation apparatus which is an analysis apparatus according to an embodiment of the present invention will be described. FIG. 1 is a schematic configuration diagram of a focused ion beam irradiation apparatus according to the present embodiment. In FIG. 1, the CPU 39 includes an EOS (electro-optical system) control unit 31 for driving and controlling the ion gun 9, the acceleration electrode 13, and the lens system power supply unit 25 according to an operation from the operation unit 37, and a blanking electrode. The blanking control unit 33 for driving and controlling the deflection 12, the deflection control unit 35 for driving and controlling the deflection electrode 17, the TOF measuring device 41 for calculating the flight time TOF, and the degree of vacuum in the sample chamber 4 are controlled. The vacuum system control unit 36 is controlled, and predetermined information is displayed on the display device 38.

  FIG. 2 is an enlarged view showing the vicinity of the sensor in the sample chamber 4. In the sample chamber 4, a sample 6 is placed on a sample stage 5 (see FIG. 1) that can move in the XY directions orthogonal to the ion irradiation direction, and an ion sensor (backscattered ion detection) is further provided above the sample 6. Sensor) 51 and secondary electron detection sensor 61 are arranged. The ion sensor 51 is connected to the ion system amplifier 55 and outputs a detection signal (second detection signal) to the ion system amplifier 55 in response to detection of backscattered ions. The secondary electron detection sensor 61 is composed of a scintillator and a photomultiplier tube and is connected to the secondary electron system amplifier 65 to receive a detection signal (first detection signal) in response to detection of secondary electrons. This is output to the secondary electron amplifier 65. The ion system amplifier 55 and the secondary electron system amplifier 65 amplify the detection signals, respectively, and input them to the TOF measurement device 41 as an arithmetic device.

  As shown in FIG. 1, in the ion beam column 3 provided in the upper part of the sample chamber 4, the condenser lens 15 and the object lens 19 are installed apart from each other in the height direction. The focal position of the focused ion beam is controlled by the voltage value of each electrostatic lens.

  An EOS (electron optical system) control unit 31 drives an emitter power source 21 and a high voltage power source 22 for emitting ions from the ion gun 9, and a lens system power source unit 25 for operating the condenser lens 15 and the object lens 19. And a high voltage power source 22 for driving a high voltage to the acceleration electrode 13 for accelerating the ions emitted from the ion gun 9 at 100 to 400 keV.

  The blanking control unit 33 can pass ions by applying a voltage to the blanking electrode 12 via the blanking circuit 27. In other words, here, the operation of allowing the ions to pass is performed only from the time when the sample analysis operation is started to the time when the analysis operation is completed.

  The deflection control unit 35 applies a voltage to the deflection electrode 17 via the deflection circuit 29, thereby energizing ions passing between the deflection electrodes 17 to change the traveling direction, thereby performing raster scanning on the sample. It is like that. Although not shown, the deflection electrode 17 is composed of an X-axis electrode and a Y-axis electrode that are orthogonal to each other, and is adjusted so that ions are irradiated to predetermined positions on the surface of the sample 6 on the X-axis and Y-axis. .

  Next, an analysis method according to this embodiment will be described. In FIG. 1, beryllium ions emitted from the ion gun 9 (hereinafter simply referred to as ions. Although not shown, the ions proceed downward along a broken line extending downward from the ion source) are accelerated by the acceleration electrode 13. Accelerated. The blanking electrode 12 allows ions to pass through only when the sample is analyzed.

  After that, the condenser lens 15 and the object lens 19 adjust the ion focusing and the like, and the deflection electrode 17 irradiates a predetermined position on the surface of the sample 6 arranged in the sample chamber 4.

  In FIG. 2, ions emitted toward a predetermined position on the surface of the sample 6 are back-scattered therefrom, become back-scattered ions 52, reach the ion sensor 51, and are converted into electrical signals here. The electrical signal from the ion sensor 51 is further amplified by the ion system amplifier 55 and then input to the TOF measuring device 41. Further, secondary electrons 62 are generated at the same time as ions are backscattered on the surface of the sample 6. The secondary electrons 62 are detected by the secondary electron detection sensor 61 and converted into electrical signals. The electric signal from the secondary electron detection sensor 61 is further amplified by the secondary electron amplifier 65 and then input to the TOF measuring device 41.

  In the present embodiment, the secondary electron detection time is always earlier than the ion detection time because of the relationship between the movement speed of the secondary electrons and ions and the relationship between the arrangement of the ion sensor and the secondary electron detection sensor. Designed to.

  Here, the concept from when the sample 6 is irradiated with ions until it is measured by the TOF measuring device will be described with reference to the drawings. FIG. 3 is a diagram showing a time chart from ion irradiation to time-of-flight measurement of backscattered ions. In FIG. 3, the secondary electron flight time is TA, the response delay time of the secondary electron detection sensor 61 is TB, the flight time of the backscattered ions 52 is TX, the response delay time of the ion sensor 51 is TC, and the TOF measuring device 41 The measured value by the multiscaler is TD.

Here, since the times TA, TB, and TC are data that can be obtained in advance by a data book, a theoretical formula, an experiment, or the like, if TD is obtained as an actual measurement value, the backscattered ion flight time TX is Formula TX = TA + TB + TD-TC
It can ask for. Here, the target element (sample) having a short flight time TX is an atom having a large mass, and the target element having a long flight time TX is an atom having a small mass, that is, the flight time TX is a value specific to a substance determined by a backscattering factor. Therefore, mass analysis of the target element can be performed from the measured flight time TX.

In the present invention, for the purpose of correcting the difference in flight time due to the scattering angle of backscattered ions,
As shown in FIG. 8, an angle adjusting external handle 53 that can operate the ion detection sensor 51 from the outside of the sample chamber is provided. By operating the angle adjusting external handle 53, the angle of the ion detection sensor 51 with respect to the scattering angle of the backscattered ions is changed via a mechanism (not shown). Backscattered ions have the characteristic that the energy after backscattering decreases as the backscattering angle with respect to the straight direction of ion irradiation increases. Decreasing energy means decreasing the speed of backscattered ions, and means that the flight time after backscattering is increased. For this reason, even if the elements to be measured on the sample are the same, if the backscattering angle is different, the flight time will be different, which is an error factor of the analyzer for obtaining the mass from the flight time.

  This difference in flight time due to the backscattering angle is adjusted by adjusting the angle of the ion detection sensor, and when the backscattering angle is large and the flight time is long, the distance to the sensor is shortened, the backscattering angle is small, and the flight time is Can be corrected by increasing the distance to the sensor. According to the present invention, by adjusting the angle of the ion detection sensor from the outside of the sample chamber, the measurement error due to the backscattering angle can be reduced as a result.

  The above description describes the operation per ion. In actual analysis work, the necessary amount of data can be obtained by raster scanning the ion beam over the measurement range of the sample 6. In the conventional method, it takes a long time, for example, several hundred hours to obtain the necessary amount of data. However, according to the present invention, the necessary amount of data can be obtained in a short time, for example, several hours. Once the data is obtained, the three-dimensional distribution information of the sample surface and the near-surface material can be easily displayed by applying computer processing. The present invention makes it possible to perform ultra-high resolution analysis in the nanometer region of the ultra-shallow impurity distribution on the semiconductor surface in a non-destructive manner in a short time as the semiconductor device structure becomes highly integrated and ultrafine.

It is a schematic block diagram of the focused ion beam irradiation apparatus concerning this Embodiment. It is a figure which expands and shows the sensor vicinity in the sample chamber. It is a figure which shows the time chart from ion irradiation to the time-of-flight measurement of backscattered ion. It is a schematic block diagram of the focused ion beam irradiation apparatus concerning conventional embodiment. It is a figure which expands and shows the sensor vicinity in the sample chamber 4 of conventional embodiment. It is a figure which shows the time chart of conventional embodiment. It is a figure which shows the relationship between singulated ion and gate time. It is a figure which shows the angle adjustment example of an ion detection sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ion beam 3 Ion beam column 4 Sample room 5 Sample stand 6 Sample 9 Ion gun 12 Blanking electrode 13 Accelerating electrode 15 Condenser lens 17 Deflection electrode 19 Object lens 21 Emitter power supply 22 High voltage power supply 25 Lens system power supply part 27 Blanking circuit 29 Deflection circuit 31 EOS control unit 33 Blanking control unit 35 Deflection control unit 36 Vacuum system control unit 37 Operation unit 38 Display device 41 Measurement device 51 Ion detection sensor 52 Back scattered ions 53 Angle adjustment external handle 55 Ion system amplifier 61 Secondary Electron detection sensor 62 Secondary electron 65 Secondary electron amplifier 71 Chopping control unit 72a Chopping plate A
72b Chopping plate B
73 Chopping aperture

Claims (4)

A mass spectrometer that analyzes a sample based on the time of flight of backscattered ions backscattered by the sample by irradiating the sample with a focused ion beam,
A secondary electron detection sensor that detects secondary electrons emitted simultaneously with the backscattered ions from the sample and outputs a first detection signal;
A backscattered ion detection sensor that detects the backscattered ions in the previous sample and outputs a second detection signal;
The first detection signal and the second detection signal are input, a time TD from the time when the first detection signal is input to the time when the second detection signal is input is obtained, and the time TD A non-destructive three-dimensional nanometer analyzer using time-of-flight analysis type backscattering, comprising: When the flight time of secondary electrons is TA, the response delay time of the secondary electron detection sensor is TB, and the response delay time of the backscattered ion detection sensor is TC, the flight time TX of the backscattered ions is The non-destructive three-dimensional nanometer analyzer by time-of-flight analysis type backscattering according to claim 1, wherein the non-destructive three-dimensional nanometer analyzer is obtained by a formula.
TX = (TA + TB + TD) −TC   The non-destructive three-dimensional nanometer analyzer by time-of-flight analysis type backscattering according to claim 1, wherein an ion detection surface of the backscattering ion detection sensor is variable. An analysis method for analyzing the sample based on the time of flight of backscattered ions backscattered by the sample by irradiating the sample with a focused ion beam,
Non-destructive three-dimensional nanometer analysis by time-of-flight analysis type backscattering, wherein the time of flight of the backscattered ions is obtained by detecting secondary electrons emitted simultaneously with the backscattered ions from the sample. Method.

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