KR0128491Y1 - Secondary ion mass spectrometer - Google Patents

Abstract

In a time-of-flight secondary ion mass spectrometry (TOF SIMS), an electrostatic energy analyzer (Electro static analyzer) for adjusting the path so that the secondary ion can perform a circular motion several times in succession is performed. When the ion is rotated one by one after the additional arrangement is arranged in parallel with the third electrostatic energy analyzer, and the second ion is added to the fourth path adjusting electrostatic energy analyzer, the second field is not applied initially. By allowing the electric field to take place, the secondary ion can enter the detector after several circular motions, making it possible to lengthen the passage of ions passing through the electrostatic energy analyzer.

The present invention using the principle as described above has a long time for the secondary ion generated in the sample to reach the detector Two elements with mass difference of △ m Mass spectrometry is performed by reaching at intervals of difference. When the radius formed by the electrostatic energy analyzer is r, the circular motion trajectory becomes 2πr, and thus increases by 2πr every turn.

Since △ t is proportional to the total trajectory L,

As a result, when the mass of each element is mixed when the elements of various components are mixed using a conventionally different arrival time according to the mass m, the problem that may occur, that is, the time difference to reach the detector When elemental or molecular ions are generated, the time of arrival is similar, so mass analysis is difficult, and the shortcomings can be solved.

As a result, Mass Resolving Power can be increased to enable precise mass analysis, and the number of repetitions of circular motion can be determined according to the mass resolution value of the analyzer without increasing other equipment. I can do it.

Description

Secondary ion mass spectrometer

1 is a cross-sectional view showing an electrostatic energy analyzer of a secondary ion mass spectrometer according to the prior art.

2 is a cross-sectional view showing an electrostatic energy analyzer of a secondary ion mass spectrometer according to the present invention.

[Industrial use]

The present invention relates to Secondary Ion Mass Spectrometry (SIMS), and in particular, to adjust the path of the secondary ion in the time-off-flight SIMS (TOF SIMS) It is a mass spectrometer that adds an analyzer and arranges an electrostatic energy analyzer in a circle facing each other.

[Prior Art and Problem]

Secondary ion mass spectrometers have the highest detection sensitivity and depth resolution of any surface analyzer, making them uniquely positioned for trace element depth profiling.

Techniques for such secondary ion mass spectrometry have already been known in Method of Surface analysis, 1989, Cambridge University Press, 9231 and Secondary Ion Mass Spectrometry, P97-101, 1989, Oxford and Application Note, Charles Evans Associations, 1989.

The detection limit of the secondary ion mass spectrometer can be precisely analyzed at the ppm-ppb level over the entire range of the periodic table, but it is difficult to apply to the analysis of the main matrix of the sample. This is because the SIMS detection range is suited for the analysis of trace amounts, so it is difficult to see the change state when the number of detection elements is large.

In the case of trace impurities, the SIMS has a large change in the ionization rate of the element as the matrix element is changed. Therefore, in the case of two or more multilayered membrane samples, the impurity concentration measurement value is different for each layer unlike the actual distribution. do. This phenomenon makes it difficult to quantify the impurity concentration, there is a problem that a standard sample must be present for quantification.

However, since it is impossible to manufacture all the standard samples under the same conditions for each thin film to be analyzed, the Sputtered Neutral Mass Spectrometry was developed to compensate for the shortcomings of the secondary ion mass spectrometer. Has a method using an electron gun or a laser, and recently developed CSX ⁺ , which can be applied to trace impurity element analysis without adding any equipment to SIMS, and also improves quantification. It became.

In the analysis of the composition ratio of principal components, the SIMS analysis method includes a dynamic method showing an impurity distribution according to depth, an imaging method for mapping an impurity distribution, and a kind of surface impurity. There is a static method of examining.

However, the analytical method can investigate all kinds of impurities due to its excellent sensitivity, but it has a disadvantage that the distribution ratio of each element is unknown. CSX ⁺ SNMS can be applied to the analysis of matrix composition, which was impossible with SIMS, and the dynamic range through 10 ppm detection limit and impurity distribution analysis can be secured up to 10 ⁴ .

However, the secondary ion mass spectrometer such as CSX ⁺ SNMS also has a fixed angle to the incident beam of the sample, so that the incident angle of the incident ion beam becomes constant and is incident at a predetermined angle, so that the sample does not cut flat even when the sample is etched. As it is shaved into shape, it is difficult to accurately analyze due to the change of Secondary Ion Yield due to the formation of a tooth-shaped nonuniform surface during the concentration depth profile of the impurity ion implantation sample.

SIMS used in the present invention is a time-of-flight secondary ion mass spectrometer (hereinafter referred to as TOF SIMS), which will be described in detail with reference to the structure and operation of the related art TOF SIMS.

1 is a cross-sectional view of a conventional electrostatic energy analyzer of TOF SIMS.

As shown in FIG. 1, the conventional electrostatic energy analyzer scans the pulse primary ion method 1 into the sample 2 so that the protruding secondary ion 4 has a constant volume 5. ) Through a first circular motion using the first to third electrostatic analyzer (ESA) (9, 11, 12) to reach the detector (13), the electrostatic energy analyzer is pulsed Immersion lens (3) disposed in front of the sample (2) to immerse the sample (2) to be scanned by the primary ion beam of and the secondary ions generated from the sample (2) by the impact of the pulsed primary ion beam. And a transfer lens 6 and a contrast diaphragm 7 sequentially installed at predetermined intervals from the immersion lens 3, and when entering the contrast diaphragm 7, the incident light is rounded. Remove the beams on both sides of the secondary ion beam. Field Aperture (8) for selecting only the pure beam in the middle and the secondary ion beams passing through the field Apache (8) are arranged in the inner charging plate and the outer charging plate respectively so as to enable the circular motion Energy slit 10 for adjusting the detection amount of the secondary ion beam which is circularly moved through the first to third electrostatic energy analyzers 9, 11, 12, and through the field Apache 8, and through the first electrostatic energy analyzer 9. And a detector 13 arranged at a point where the secondary ion beam after one rotation of circular motion will reach.

The operation principle of such a conventional TOF SIMS device will be described below.

The pulsed primary ion (1) hits the sample (2) at regular intervals. At this time, some of the surface elements of the sample come out by sputtering while being ionized. At this time, the ions move in a volume 4 along a predetermined path 5.

The moving secondary ion beam then passes through the transfer lens 6 and the contrast lens 7 and enters the first electrostatic energy analyzer 9 via the field Apache 8.

In the electrostatic energy analyzer 9, two charging plates are charged in concentric circles, and secondary ions are circularly moved. After passing through the energy slit 10, the secondary ions passing through the electrostatic energy analyzer 9 reach the detector 13 through the second and third electrostatic energy analyzers 11 and 12.

At this time, if the passage path length is L and the ions passed are monovalent ions with mass (m), when the secondary ions are moved by the voltage (V), the secondary ions are forced into the electric field. The exercise equation Becomes

Integrating this expression over time gives the path length L = V × t ego, from Becomes

In this case, since the passage length L, the secondary ion charge amount e, and the acceleration voltage V are given values, it can be seen that the arrival time varies depending on the mass m.

Such a conventional SIMS analyzes the mass of various components, and if the mass difference of each element becomes large when various elements are mixed in the sample, the time difference to reach the detector can be easily distinguished. When elemental or molecular ions are generated, the time of arrival is similar, making mass spectrometry difficult.

[Purpose of designation]

Therefore, in order to solve the above problems, the present invention arranges a path control electrostatic energy analyzer in a circular side by side line with a general electrostatic energy analyzer so as to maintain the circular motion of secondary ions several times, thereby increasing the mass path resolution L to increase the mass resolution. An improved secondary ion mass spectrometer is provided.

[Composition of design]

In order to achieve the above object, the present invention provides an imaging lens disposed at one end of a sample 2 to immerse secondary ions generated from the sample 2 by the impact of a pulsed primary ion beam, Field pain that removes the beams on both sides of the incident secondary ion beams by passing the lens and contrast diaphragm sequentially installed at a predetermined interval and the secondary ion beams that enter the round shape when passing through the contrast diaphragm and select only the pure beam in the middle First to third electrostatic energy analyzers disposed in the inner charging plate and the outer charging plate, respectively, so that the secondary ion beams having passed through the field Apache are circularly moved; The energy slit for controlling the detection amount of the ion beam and the secondary ion beam incident through the contrast diaphragm are electric field type. If not, it has a first passage that can go straight and a second passage formed in a direction perpendicular to the first passage, when the electric field is formed secondary ion beam path direction of the secondary ion beam incident from the third electrostatic energy analyzer during circular motion The fourth path control energy analyzer and the fourth path control electrostatic energy, which is composed of one inner charge plate and three outer charge plates so as to form a circular shape in combination with the first to third electrostatic energy analyzers, to form a circular shape. And a detector disposed at the side of the second passage of the analyzer.

[Action]

As described above, since the secondary ion can be circled several times before the secondary ion reaches the detector, the arrival path L can be greatly increased. That is, as the time given in Eq. (A) shows that the time is proportional to the arrival path L, the time difference Δt for each mass is increased by the same amount as the length increases, so that similar masses can be decomposed and other equipment is greatly increased. You can make the path of the circular motion as long as you want without having to.

EXAMPLE

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

2 is a cross-sectional view showing an electrostatic energy analyzer of TOF SIMS according to the present invention.

As shown in FIG. 2, the TOF SIMS according to the present invention is designed to immerse the sample 2 to be scanned by the primary ion beam of the pulse and the secondary ion generated from the sample 2 by the impact of the pulsed primary ion beam. (2) The immersion lens 3 disposed at one end, the transfer lens 6 and the contrast diaphragm 7 sequentially installed at a predetermined distance from the immersion lens, and the contrast diaphragm 7 in a round shape when passing therethrough. Each of the secondary ion beams that enters the straight field is removed so that the beams on both sides are selected and only the pure beams in the middle are selected. First to third electrostatic energy analyzers 9, 11, and 12 disposed as an inner charging plate and an outer charging plate, and an energy slit 10 for adjusting a detection amount of a secondary ion beam circularly passing through the first electrostatic energy analyzer. ) A first passage (a) capable of going straight when the secondary ion beam incident through the contrast diaphragm (7) is not formed in the electric field, and a second passage formed perpendicular to the first passage (a) ( b) with one inner charging plate and three outer charging plates such that when the electric field is formed, the secondary ion beam incident from the third electrostatic energy analyzer 12 moves in the secondary ion beam path direction 15 in circular motion. A fourth path adjustment energy analyzer 14 configured to be generally circular with the first to third electrostatic energy analyzers 9, 11, and 12, and a second of the fourth path adjustment electrostatic energy analyzer 14. It consists of the detector 13 arrange | positioned at the channel | path b side.

At this time, it is noted that the position of the transfer lens 6 and the contrast diaphragm 97 is slightly shifted from the conventional position by the above configuration.

Here, the electrostatic energy analyzer for adjusting the path to be additionally arranged has two holes (first passage and second passage) for straightening the beam, and is used in a conventional magnetic analyzer. That is, the TOF SIMS for achieving the object of the present invention is composed of the first to third electrostatic energy analyzers (9, 11, 12) arrangement and the fourth electrostatic energy analyzer 14 for the path adjustment to maintain a large circular orbit It can be seen that.

When explaining the basic operation principle of the TOF SIMS according to the present invention.

When the pulsed primary ion 1 hits the sample 2, the secondary ion 4 protruding from the sample 2 at this time is a constant path 5 due to the high voltage between the sample 2 and the immersion lens 3. Exercise along.

At this time, it passes through the transfer lens 6 and the contrast diaphragm 7, and enters the fourth path control electrostatic energy analyzer 14. At this time, the secondary ion beam 4 does not apply an electric field to the path control electrostatic energy analyzer 14. This goes straight.

Subsequently, the ions enter the first electrostatic energy analyzer 9 through the field Apache 8 and perform a circular motion, causing the direction to spring out. This is because two charging plates are charged in concentric circles in the electrostatic energy analyzer, and secondary ions move in a circular motion. At this time, the secondary ion beam bounced from the sample passes straight through the secondary ion beam path in the form of a round cylinder when it enters through the fourth path adjusting electrostatic energy analyzer 14.

In this case, when the beam coming straight out of the sample is fixed at an angle with respect to the incident beam of the sample, as described above, the incident angle of the pulsed incident ion beam becomes constant and is incident at a predetermined angle so that the sample is etched at the surface of the sample. Is not flat, but is cut into a sawtooth shape, and the secondary ion generation amount due to the formation of a tooth-shaped nonuniform surface when changing the concentration of the impurity ion implantation sample is changed. Therefore, when it comes out from the sample, the incident ion beam does not come out at the desired depth. Depending on the angle of, it may protrude from the deeper part of the sample, or it may protrude from the nonuniform surface of the sample. Subsequently, the secondary ion beam protruding from the sample 20 changes the composition ratio of the material depending on the depth of the sample. Not generated, but the molecularly coupled beam Come out together.

Therefore, it is necessary to remove the beams on both sides of the round cylindrical beams generated from the sample, and select only the purer beams in the middle, which is the field Apache (8).

After passing through the energy slit 10, it passes through the second and third electrostatic energy analyzers 11 and 12 and enters the fourth path adjusting electrostatic energy analyzer 14 again.

In this case, an electric field is applied to the fourth path adjusting electrostatic energy analyzer 14 to continue the secondary ion beam path 15 in a circular motion. The energy slit 10 is mainly used to reduce or increase the amount of detection of the secondary ion beams that have passed through the first electrostatic energy analyzer 9, and in more detail, the first electrostatic energy analyzer 9 will be described. The secondary ion beam that has passed through is bent inward when it is referred to the ion beam path 4 in the degree of bending, while being bent outward.

At this time, among the secondary ion beams generated from the sample (2), the beams with many molecular bonds are bent inward of the ion beam path (4), and the pure beams without molecular bonds are bent outwards, and when the pure beam is desired, the energy slit moves outwards. For example, if you want a molecularly coupled beam, you can move the energy slit inward from the existing position.

Here, the time interval for applying the electric field is calculated by inputting the pulse interval and the path distance.

According to the above-described principle, the secondary ion, which has been circularly moved in the fourth path, the adjusting electrostatic energy analyzer 14, continues the circular motion passing through the first to fourth electrostatic energy analyzers 9, 11, 12, and 14. After a certain number of circular motions are removed, the electric field of the electrostatic energy analyzer 14 for the path adjustment is removed, and the secondary ions stop the circular motions moving along the secondary ion beam path 15 and go straight to reach the detector 13. The passing path of is increased by the desired length. As a result, the time of arrival (t) and the time difference (Δt) also increase, resulting in large mass resolution.

Here, the arrival time t is the time taken for the secondary ion generated in the sample to reach the detector, which means the time given in Equation (A).

In other words,

When the radius of the first to fourth electrostatic energy analyzer is r, since the circular motion trajectory becomes 2πr, it increases by 2πr every turn.

It can be seen that the mass decomposition is easy even if the Δm is small.

[Effect of design]

As described above, the secondary ion mass spectrometer according to the present invention additionally arranges an electrostatic energy analyzer for adjusting the path so that the secondary ion can perform a circular motion several times in succession. The problem that can occur when analyzing individual masses when the elements are mixed, that is, when elements or molecular ions of similar mass have a similar time difference, the arrival time is similar, making the mass analysis difficult. As can be seen, it can be solved by increasing the total trajectory L, so that the mass resolution can be easily made even if △ m is small, so that the mass resolution power can be increased and the mass resolution value of the analyzer can be increased without increasing other devices. Provide secondary ion mass spectrometer to determine repetition frequency of circular motion It can be so.

Claims (6)

An immersion lens 3 disposed at one end of the sample 2 in order to immerse the secondary ions generated from the sample 2 by the impact of the pulsed primary ion beam, and a transfer lens 6 sequentially installed at a predetermined distance from the immersion lens. And the field diaphragm that removes the beams on both sides of the incident secondary ion beam passing through the contrast diaphragm 7 and the secondary diaphragm 7, and selects only the pure beam in the middle. 8) and first to third electrostatic energy analyzers 9, 11, and 12 arranged as inner and outer charging plates so that the secondary ion beams passing through the field Apache 8 may be circularly moved, respectively, The energy slit 10 for adjusting the detection amount of the secondary ion beam circulating through the first electrostatic energy analyzer and the secondary ion beam incident through the contrast diaphragm 7 are not formed in the electric field. Has a first passage (a) that can go straight, and a second passage (b) formed in a direction perpendicular to the first passage (a), and when the electric field is formed is incident from the third electrostatic energy analyzer 12 It consists of one inner charging plate and three outer charging plates so that one secondary ion beam moves in the secondary ion beam path direction 15 which has a circular motion, so that the first to third electrostatic energy analyzers 9, 11 and 12 A secondary ion mass spectrometer comprising a fourth path adjusting energy analyzer 14 arranged to form a circle, and a detector disposed on the second passage b side of the fourth path adjusting electrostatic energy analyzer 14. . The secondary ion mass spectrometer of claim 1, wherein the fourth path adjusting electrostatic energy analyzer (14) does not form an electric field when a secondary ion beam is incident from the contrast diaphragm (7). 4. The secondary ion mass spectrometer of claim 1, wherein the fourth path control electrostatic energy analyzer (14) is configured to generate an electric field when continuous circular motion of the secondary ion beam is required. 4. The secondary ion mass spectrometer of claim 3, wherein the fourth path adjusting electrostatic energy analyzer (14) forms an electric field after the secondary ion beam passes. The apparatus of claim 1, wherein the fourth path control electrostatic energy analyzer (14) removes an electric field so that the secondary ion is incident on the detector (13) after several circular motions to secure a sufficient trajectory. Secondary ion mass spectrometer, characterized in that. 2. The secondary ion mass spectrometer of claim 1, wherein the fourth path control electrostatic energy analyzer is a time adjustment device for determining a repetition number of circular motions according to a mass resolution value.