JP2940090B2 - Ion source having mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion source capable of generating a large-area ion beam containing only ions having a certain mass number.

[Prior art]

In a case where ions are applied to a sample with a thin beam and the physical properties of the sample are examined (for example, SIMS), only a specific ion must be selected, so a mass spectrometer is provided. When the primary ions hit the sample, the secondary ions are emitted. If the type and mass number of the primary ions are not constant, the physical properties of the sample cannot be determined by the energy analysis of the secondary ions. In such a case, ions pass through the static magnetic field created by the electromagnet. The ions emitted from the ion source have the same acceleration energy but different mass numbers, so the arcs drawn in the same magnetic field have different Larmor radii. If the trajectory has a different radius, the ions can be separated after deflecting by the magnetic field because the trajectory of the ion is different. An apparatus for mass-analyzing such a thin ion beam with a deflection magnetic field is well known. Since the beam diameter is small, the cross-sectional area of the magnet is relatively small. However, on the contrary, a large area ion beam may be required. This is a case where some surface treatment is performed over a wide area, such as when ions are implanted on a semiconductor wafer or when ions are irradiated for surface modification of a sheet material. For the purpose of surface treatment, it is more efficient that the ion beam is spread widely. An apparatus for producing such a large-area ion beam already exists. However, these devices do not have a mechanism for mass spectrometry. For mass spectrometry of large area ion beams, electromagnets having a cross section many times the cross section of these beams are required. For a large area ion beam, such an electromagnet is not used because it is huge. If the portion that generates the magnetic field is large, the portion around which the coil is wound is large and the whole becomes an extremely large electromagnet. It is also conceivable that an ion beam having a small diameter is produced without producing a large-area ion beam, mass-separated from the ion beam, and then the beam is expanded into a large-area parallel beam.

[Problems to be solved by the invention]

It is known to use a bending electromagnet to mass analyze a thin ion beam. However, the same means cannot be used for a large-area ion beam. If this were to be done, a huge electromagnet would be required, and almost all of the ion source would be occupied by the electromagnet, its mount, cooling water system, and power supply. This is unrealistic and there is currently no mass spectrometer for large area ion beams. If the beam is narrowed down, it should be possible to perform mass analysis with a deflection magnet. However, this requires a distance to narrow the beam. In addition, a distance is required to spread a narrow beam after mass analysis. In addition, since the method using the bending magnet bends the ions into a ヘ -shaped trajectory, the entire apparatus must be large. In addition, the ions that have exited the ion source have a high energy of about several tens keV to several hundred keV, and the magnet must be large in the longitudinal direction in order to bend with a magnet. After all, there is currently no ion source with a mass spectrometer that produces a large area beam. SUMMARY OF THE INVENTION It is an object of the present invention to provide an ion source that generates a large-area ion beam that can perform mass analysis without impairing large-area characteristics.

[Means for Solving the Problems]

In the ion source, the gas is turned into plasma by, for example, arc discharge. An electrode plate with a large number of holes, called an extraction electrode, is provided at the outlet of the chamber for performing arc discharge. A negative voltage is applied to the high-potential chamber to extract positive ions. Further, an acceleration electrode is provided in front of the extraction electrode, where a negative voltage is further applied to the extraction electrode to accelerate ions. The energy of the ions exiting the extraction electrode is low. Number 10
It is about 0 eV to several keV. The acceleration electrode accelerates to a desired high energy. It is about several tens keV to several hundred keV. Since a large number of holes are provided in the electrode plate in the vertical and horizontal directions, ions can pass through the large number of holes and become an ion beam having a large area as a whole. Ion sources for large areas are known. In the present invention, furthermore, an insulation attached to two conductors having vertical and horizontal through holes matching the holes of the extraction electrode and the acceleration electrode between the extraction electrode and the acceleration electrode or at the subsequent stage of the acceleration electrode. A large number of electric quadrupoles consisting of a plate and a number of columnar electrodes arranged in a row around each hole at the same pitch as the through-holes between these insulating plates are provided, and linearly arranged without impairing the large area of the beam. By moving straight through the passage, only ions having a certain mass number can be extracted.

[Operation]

The extraction electrode, the two insulating plates, and the accelerating electrode are perforated plates having substantially the same size, and are perforated vertically and horizontally so that the holes match. Since the ion beam goes straight in the normal direction of the electrode plate,
Almost all the ions that have passed through the extraction electrode can pass through the holes of the insulating plate and the acceleration electrode as they are. This is the case where no voltage is applied between the electrodes forming the electric quadrupole in the middle of the insulating plate. In the present invention, a set of electrodes arranged four diagonally around the hole, each of which is present at a pitch equal to the pitch of the hole, and a set of electrodes arranged diagonally downward to the right with respect to an arbitrary hole, A pair of electrodes arranged in a diagonal direction is formed, and an AC voltage on which a DC is superimposed is applied therebetween. That is, the columnar electrodes are divided into two sets, and a voltage such as U ₀ = U + Vcosωt (1) is applied between them. Then, in the path from the hole in the insulator to the hole in the other insulator, the ions are subjected to the action of the electric field generated by the voltage as shown in (1) in the direction perpendicular to the path, so that the ions vibrate in the direction perpendicular to the path. I do. Only ions with a certain mass and energy oscillate stably. Other ions oscillate diverging in a right angle direction. Therefore, only ions having a specific mass number and energy can pass through the hole of the second insulator. No other ions can pass through this hole. Thus, the two insulators having many through holes, the many columnar electrodes, and the power supply constitute an electric quadrupole analyzer. This is because only ions having a specific energy mass number can pass through the through holes before and after the two insulators. There are many through holes vertically and horizontally, and there are electric quadrupoles as many as the number of through holes, so that all holes have a mass analysis effect.
For this reason, the ion beam is subjected to mass analysis while maintaining the same area. That is, the large area of the ion beam does not impair the writing. It is well known to perform mass spectrometry with a single electric quadrupole. However, there has been no one that arranges a large number of quadrupole analyzers vertically and horizontally and mass-analyzes a large-area ion beam as it is. In this case, one columnar electrode functions as an electrode for the four holes, so that a fourfold function is achieved. The quadrupling of the role of one electrode also saves space, meaning that the space required for the electrodes is reduced by a factor of four. The vertical and horizontal holes of the extraction electrode, the two insulating plates, and the acceleration electrode have the same dimensions and arrangement so as to match the axial direction (the direction of the normal to the plate). Therefore, since the mass analyzer of the present invention is inserted, the intensity of the ion beam having a desired mass number does not decrease. That is, there is no insertion loss of the ion beam. The resolution of the electric quadrupole increases in proportion to the length of the columnar electrode. In order to increase the resolution, the columnar electrodes must be long and the space for analysis must be long. A mass spectrometer for a thin beam used in a measuring device requires isotope separation and the like. That is, those having different mass numbers must be separated. However, in the case of a large area ion source, isotope separation is not required. A coarser mass separation can be used. For example, it is only necessary to separate substances having considerably different mass numbers such as PH ₃ ⁺ and P ⁺ . Therefore, the length L (the distance between two insulating plates) of the mass spectrometer of the present invention is not so large. The mass analyzer composed of a large number of electric quadrupoles is referred to as a composite electric quadrupole analyzer. This can be provided between the extraction electrode and the acceleration electrode, or can be provided after the acceleration electrode. However, the resolution of mass analysis is better between the extraction electrode and the acceleration electrode. This is because the ion energy is low here. In the latter stage of the accelerating electrode, the resolution is low because the energy is high.

【Example】

FIG. 1 is a schematic sectional view of an ion source according to an embodiment of the present invention. In this method, gas introduced by arc discharge is converted into plasma, and ions are extracted and accelerated by a porous electrode plate to form an ion beam. The filament 1 is heated in the arc chamber 2 and emits thermoelectrons. An arc voltage V _ARC is applied between the arc chamber 2 and the filament 1. This is on the order of tens of volts to 100 volts. Gas is introduced from the gas inlet 21 and is turned into plasma by arc discharge generated between the arc chamber 2 and the filament 1. Around the arc chamber 2, there are a number of permanent magnets for forming a cusp magnetic field near the wall surface, but are not shown here. The filament 1 is connected to a filament power supply 23 by a current introduction terminal passing through an insulator 22. There is an arc power supply 24 between the filament 1 and the arc chamber 2, which produces the arc voltage V _ARC . The arc chamber 2 is a large space that can be evacuated, but one of the openings is an opening, and several openings are provided in the opening. The insulator 3 supports the extraction electrode 4 and the introduction electrode 5 having a large number of vertical and horizontal holes. These holes are axially aligned. A negative voltage V _ARC is applied to the extraction electrode 4 with respect to the arc chamber 2 by an arc power supply 24. Positive ions are attracted to the extraction electrode 4 by this voltage. Then, it passes through the hole of the extraction electrode 4 and goes out of the arc chamber 2. The next introduction electrode 5 is supplied with a further negative voltage V _e by the introduction power supply 25.
Is hanging. Ions gains kinetic energy further qV _e through here. q is the charge of the ion. V _e is 1 kV
About several kV. In this embodiment, a mass analyzer 6 is provided next to the introduction electrode 5. The mass spectrometry section 6 has a first slit plate 7 and a second slit plate 8 which are porous electrode plates at the front and back, and a space sandwiched between them has an insulating plate and a columnar electrode sorting space. Subsequent to the mass spectrometer 6, an acceleration electrode 9, a deceleration electrode 10, and a ground electrode 11, which are porous plates supported by the insulator 3, are provided. These electrodes 4, 5, 7, 8, 9, 10, 11 are all porous electrode plates, but the holes have the same size, position, arrangement and the like in the axial direction. If the ions traveling perpendicular to the surface can pass through the first extraction electrode 4, they can pass through other electrodes. It is under positive voltage V _i by the compensation power supply 26 between the input electrode 5 and the first slit plate 7. This has the effect of decelerating ions, and by setting V _i <V _e , the speed of ions immediately before the first slit plate 7 can be extremely reduced. Then, the ion energy incident on the mass spectrometry unit 6 is low, and the time required for the ion energy to pass therethrough is long, so that the mass resolution improves. The first slit plate 7 and the second slit plate 8 are at a higher potential than the acceleration electrode 9. The accelerating electrode 9 is connected to the ground by an accelerating power supply 27.
To maintain _a high voltage of Va. q (Ve + Va) becomes the kinetic energy finally obtained by the ions. This value is set appropriately according to the purpose. For example, it is several tens kV to several hundreds kV. The deceleration electrode 10 is connected to the ground by
A voltage of V _s is applied. The voltage applied between the extraction electrode 4 and the deceleration electrode 10 is (Ve + Va + V _s ), and the potential increases by V _s by passing through the deceleration electrode, so that the acceleration energy is q (Ve + Va). The mass analyzer 6 will be described. This is because a first insulator 12 and a second insulator 13 are sandwiched between a first slit plate 7 and a second slit plate 8 which are conductors, and a number of columnar electrodes 14 are sandwiched between the first and second insulators 12 and 13. It has a shape that sandwiches both ends of 15. In order to support both ends of the columnar electrodes 14, 15, the insulator 12,
A circular recess is provided on the inner surface of the
It is convenient to insert 4 and 15. Instead, a third insulator plate for supporting the columnar electrodes 14 and 15 at an intermediate portion may be used. Through holes 17 and 18 are formed to match the vertical and horizontal holes of the first slit plate 7 and the second slit plate 8, including the insulators 12 and 13 and the intermediate insulator, if any. After all,
Holes for all electrodes 4, 5, 7, 8, 9, 10, 11 and insulator 1
The through holes 2 and 13 are dimensioned, arranged and numbered so that they all match in the axial direction. The columnar electrodes 14 and 15 are provided at the same vertical and horizontal pitches as the through holes 17 and 18 of the insulators 12 and 13, but are shifted vertically and horizontally by 1/2 pitch. For this reason, when viewed from the central axis of one through hole 17, 18, there is a columnar electrode in four directions. Also, when viewed from one columnar electrode, it seems that there are through holes in four directions. FIG. 2 is a cross-sectional plan view of the mass spectrometer. The direction of the columnar electrode and through hole is the z-axis, and xy
It is assumed that these electrodes and through holes are evenly distributed on a plane. The vertical and horizontal pitch of the through hole and the columnar electrode is 2p. The center coordinate is point O, and the center of one through hole is assumed to overlap here. Since the through holes are arranged in the x and y directions by ± 2p, their coordinates can be expressed as Q _mn = (2mp, 2np) (2). Here, m and n are positive and negative integers. The columnar electrode can be expressed as a value obtained by adding ± p to this. However, there are two types of columnar electrodes. This is for making the electrodes positive and negative. As viewed from the center lines of the arbitrary through holes 17 and 18, positive electrodes are arranged in one diagonal direction, and negative electrodes are arranged in the other diagonal directions. In other words, if attention is paid to the columnar electrodes, every other electrode having the same polarity is arranged. The coordinates of the positive columnar electrode R are And the coordinates of the negative columnar electrode S are It can be expressed as follows. The columnar electrode is with respect to the x and y axes.
Lined up in a 45 ゜ direction. The same applies to the negative columnar electrode. Thus, the positive and negative columnar electrodes can be distinguished. Seen from one hole, there are always columnar electrodes in four directions of 45 °.
The columnar electrode 14 has a sum of its x and y coordinates that is not a multiple of 4,
The negative columnar electrode 15 can be distinguished by the fact that the sum of the x and y coordinates is a multiple of four. Rather, the positive columnar electrode 14 can be defined by the x, y coordinate difference being a multiple of four, and the negative columnar electrode 15 being the x, y coordinate difference not being a multiple of four. The columnar electrodes 14 are all connected to give the same potential. The negative columnar electrodes 15 are all connected to give the same potential. A quad electrode power supply is provided between the positive column electrode 14 and the negative column electrode 15.
16 AC voltage U ₀ obtained by superimposing a direct current by is applied. U _o = U + Vcosωt (5) FIG. 3 is a simplified connection diagram with a quadrupole power supply.
The quadrupole power supply 16 includes a DC power supply _Vb and an AC power supply _Vrf , and generates a DC voltage U and an AC voltage V, respectively. The electric field is zero at the center of the quadrupole. The electric field is also zero on a line connecting the positive electrode and the negative electrode (in a direction forming 45 ° with the x and y axes). The electric field strength increases near the center of the origin in proportion to the distance from the origin. Therefore, consider a coordinate system rotated 45 ° from the original x and y axes. That is, it is assumed that there is a negative electrode on the new X axis and a positive electrode on the new Y axis. FIG. 3 is written in such a coordinate system. In this coordinate system, the electric field has only components along the X and Y axes. This is due to symmetry. The electric field is anti-symmetric on the X axis. It is also antisymmetric on the Y axis. At any point, the position vector (X, Y) and the electric field vector ( _Ex ,
E _y ) is orthogonal. For this reason, it can be written as (X, Y) electric field at point _{E x = kU o X (6} ) E y = -kU o Y (7). Here, k is a constant. If the pitch of the columnar electrodes is 2p and the radius of the columnar electrodes is b, the distance from the origin to the electrode is (p−b). This as a r _o, by integrating the E _x Since it is (potential U of the origin and the electrode _o / 2 So) k is obtained becomes ^{_{kr o 2/2 = 1/}} 2 (9). In this coordinate system becomes a differential equation of variable separation, the equation of motion of the ions, M = q (U + Vcosωt ) X / r 0 2 (10) M = -q (U + Vcosωt) Y / r 0 2 (11) M = 0 (12) q is the charge of the ion and M is the mass of the ion. ξ = ωt / 2 (13) Is the standard form of Matthew's differential equation. It has divergent and stable solutions. The regions a and b having stable solutions are already well known. If b = 0, this is a simple constant factor 2
It becomes a linear differential equation. If a> 0, (17) is a stable oscillatory solution, and (16) is a divergent solution. If a <0, the opposite is true. That is, if b = 0, there is no stable vibration solution based on (16) and (17). On the contrary, if a = 0, all divergent solutions are obtained when b ≠ 0.
In order for both equations to have stable oscillation solutions, both a and b must be 0.
Should not be. (17) is the standard form of Matthew's differential equation. This has a band-like stable solution range in the region of a> 0. a
The region of <0 has a slight stable solution range. (16),
(17) Having both stable solutions means that a> 0 and a
This is a superposition of stable solutions in the region of <0, which is a small range. FIG. 4 shows a range where a and b are closest to 0 and have a stable solution. The area with double oblique lines is the range. Parameters a and b are parameters including a DC component U and an AC component V, and the ion mass and the like are included in the same form. If the ion mass M and charge q are different, a and b change, but the value of the ratio
a / b does not change. The portion indicated by the double oblique line has a downwardly convex OKL curve and a substantially triangular shape surrounded by LN and NO. The slope a / b of the straight line OL is 0.33. Then, a / b = k becomes
Change the values of U and V so that they are smaller than 0.33 If set, the straight line of this slope changes to a stable area curve at two points R ₁ and R ₂ . For any such ions, the ratio of a / b is constant, a, b is between OR _1, if there from R ₂ to the outside, will have a divergent solution. It has a stable solution only when a and b are between line segments R _{1 and} R ₂ . Assuming that the value of b at the time of R ₁ R ₂ is b ₁ and b ₂ , ions of mass number M having a value of b satisfying b ₁ <b <b ₂ oscillate stably. Through the two through holes 17,18. These are already well known as principles of an electric quadrupole mass spectrometer. This story is based on the assumption that the electrode length is infinite. When actually used for an ion beam of a measuring instrument, a long electrode is used because it is necessary to remove isotopes. However, in the case of the present invention, it is rare that ions having various and close masses are contained in the plasma, and it is not necessary to distinguish isotopes, so that the resolution does not need to be very high. Therefore, the length (length of the columnar electrode) L of the mass analyzer may be short. If the energy of the incident ion is E _o , this is the length L
It is considered that the time to fly over is longer than 2π / ω. Also because there is a short length L of the mass analyzer, in Figure 4, R ₁ R ₂
The ions may pass through the through holes 17 and 18 even at a position (a, b) slightly deviated from the above. Therefore, the value of a / b is 0.3
Even close to 3, it is quite possible to pass ions of the desired mass. When a / b approaches 0.33, the analytical effect increases even if L is short.

【The invention's effect】

This is the first mass spectrometer installed in an ion source for producing a large-area ion beam. Even if many types of ions are extracted from the ion source, only ions having a single mass number can pass through the mass analyzer. Rather than using a magnetic field to bend the beam, we select only ions of a particular mass number by going straight. When a magnetic field is used, a huge magnet is required, which is not practical for a large-area beam. In addition, since the beam is bent in the shape of "", a large space is required. This is different from narrowing down the beam once, deflecting it with a magnetic field, and expanding the beam again. A large area beam is passed through many through holes, and mass analysis is performed in each hole by a quadrupole mass analyzer provided here. The large area of the generated ion beam is not impaired. Since mass analysis is performed using voltage, neither a ferromagnetic core nor a bulky winding is required. Since only electrodes are required, space utilization efficiency is high. In addition, one electrode also serves as an electrode of the four mass analyzers, so that the electrode material and space can be effectively used. According to the present invention, since the ion source produces a large-area beam, if high-precision uniformity is not required,
The rotation of the irradiation target can be omitted.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of an ion source according to an embodiment of the present invention. FIG. 2 is a cross-sectional plan view of the mass spectrometer in the apparatus of FIG. FIG. 3 is a wiring diagram for applying a direct current, an alternating current, and a voltage to the columnar electrode of the mass spectrometry unit. FIG. 4 is a graph showing areas where stable solutions exist for parameters a and b of Matthew's differential equation. DESCRIPTION OF SYMBOLS 1 ... Filament 2 ... Arc chamber 3 ... Insulator 4 ... Extraction electrode 5 ... Introducing electrode 6 ... Mass spectrometer 7 ... 1st slit plate 8 ... 2nd slit plate 9 ... Acceleration electrode 10 … Decelerating electrode 11… Ground electrode 12… First insulator 13… Second insulator 14… Positive columnar electrode 15… Negative columnar electrode 16… Quadrupole power supply 17… Through hole 18… Through hole 21 Gas inlet 22 Insulator 23 Filament power supply 24 Arc power supply 25 Introduction power supply 26 Compensation power supply 27 Acceleration power supply 28 Deceleration power supply

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H01J 27/00-27/26 H01J 37/08 H01J 37/05 H01J 37/317 H01J 49/42

Claims (1)

(57) [Claims] An arc chamber for generating an arc discharge between a filament and a container to convert the introduced gas into a plasma, and a perforated plate having a large number of holes in the vertical and horizontal directions. An extraction electrode for extracting ions, an introduction electrode that has a through hole that matches the hole of the extraction electrode, is provided on the downstream side of the extraction electrode and accelerates positive ions between the extraction electrode, and is provided on the downstream side of the introduction electrode. Mass spectrometer, and an extraction electrode, an introduction electrode, a perforated plate having holes that match the holes of the mass spectrometer, and an accelerating electrode that accelerates ions coming out of the mass spectrometer by applying a high voltage. The mass spectrometer has two front and rear insulating plates having through holes corresponding to the holes of the extraction electrode and the acceleration electrode, and front and rear holes having the through holes matching the holes of the extraction electrode and the acceleration electrode. A front and rear metal slit plate fixed to the outside of the edge plate, and a columnar electrode provided between the front and rear insulator plates and supported by the insulator and arranged four by four around the hole at a pitch equal to the vertical and horizontal pitch of the hole. The columnar electrodes are divided into two sets such that two of the columnar electrodes arranged in the diagonal direction of the hole constitute one set, and two of the columnar electrodes arranged in the other diagonal direction constitute another set. The DC voltage and the AC voltage are superimposed between the set of columnar electrodes so that only ions of a certain mass with respect to a certain energy applied are allowed to pass through the front and rear through holes, and the front and rear slit plates are An ion source having a mass spectrometer, wherein a compensating power source is connected between the front and rear slit plates and the introducing electrode so that ions are decelerated between the front slit plate and the introducing electrode. .