JP3087139B2 - Mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass spectrometer suitable for obtaining a one-dimensionally or linearly spread ion beam. Apparatuses for performing various processes by applying an ion beam emitted from an ion source to an object to be processed have already been used in a wide range. In many cases, a mass analyzer using a sector magnet is provided next to the ion source, and only ions of a constant mass passing through the analyzer are irradiated on the object to be processed. In this case, the beam is a single thin line, and the irradiated part is a point. If the processing capacity is insufficient, the ion beam is swung right and left by using a scanning system. Then, a linear or one-dimensional beam is obtained. The scanning of the ion beam is performed by applying an alternating magnetic field and an alternating electric field using a coil or an electrode.

[0002]

2. Description of the Related Art When a beam is scanned left and right by a scanning system, the surface of an object to be processed does not become a parallel beam but an oblique beam. The linear density of the ion beam is not constant. If this is not desired, the beam spread by the scanning system must be turned into a parallel beam. As an apparatus for obtaining such a linear beam, for example, an apparatus as shown in FIG. 8 has been proposed. The raw material gas is ionized by the ion source 41 and turned into an ion beam by the action of the extraction electrode system. This enters a mass analyzer 42 composed of a sector magnet and draws an arc-shaped trajectory. Only ions having a desired mass are analyzed by the analysis slit 43.
Can pass. Ions of different mass cannot pass through the analysis slit 43 because the radii of the arc trajectory are different. Since this mass spectrometer utilizes a sector magnet and a slit having a single hole at the outlet, it can perform mass spectrometry only on a narrow beam (zero dimension). The beam is enlarged after exiting the mass spectrometer. This is the beam sweep electrode 46. By applying an alternating electric field between the electrodes, the ion beam is vibrated to the left and right to form a beam having a substantially one-dimensional spread.
A beam sweep controller 47 generates an alternating voltage and supplies it to the beam sweep electrode 46. A beam collimator 48 is provided at the front and converts the oblique beam into a beam in a fixed direction. This is also done by the action of an electric or magnetic field.
The required electric or magnetic field is provided by beam collimator controller 49. This, of course, must be synchronized with the beam sweep controller. The ion beam, which has become a parallel beam, is irradiated onto the workpiece 50 as it is.

[0003]

A beam having a one-dimensional spread can be substantially produced by an apparatus as shown in FIG. However, this must first start with a zero-dimensional beam in order to use a sector magnet mass analyzer. This is because a beam having a one-dimensional spread, that is, a linear spread cannot be mass-analyzed by the action of a sector magnet. Of course, if the size of the magnet is increased and the distance between the magnetic poles is increased, the one-dimensional beam should be able to perform mass analysis. However, in order to obtain the required magnetic flux density, the magnet becomes too large and the entire device becomes too large. In order to avoid this, it is necessary to start from a zero-dimensional beam, and a scanning system for expanding the beam is required. Further, even if a linear beam is required by a scanning system, if a beam is required to be incident on the workpiece at right angles, a beam collimator is required to make the beam parallel. . The scanning system and the parallelizer must be operated synchronously. Further, even if the beam is swung right and left by the scanning system, the beam does not spread unless there is a sufficient distance, so that a considerable distance is required between the scanning system and the parallelizer. For this reason, the entire apparatus becomes large and extremely complicated.

The ion source itself can generate a one-dimensional ion beam by devising the shape of the extraction electrode. If starting from a ribbon-like ion beam which originally has a one-dimensional spread, such a mechanism as scanning and collimating should be unnecessary. However, in such a case, it is not possible to use a mass spectrometer using a sector magnet which is most frequently used in the past. The existence of a mass spectrometer is a source of difficulty. Of course, it is also conceivable to irradiate the object to be processed directly with a wide beam emitted from the ion source. This avoids the difficulties of the mass analyzer. However, in this case, since mass spectrometry is not performed, there is a drawback that the object to be processed is irradiated with a mixture of different ions. If it is desired to eliminate irradiation of different ions, a mass spectrometer must be inserted somewhere. SUMMARY OF THE INVENTION It is an object of the present invention to provide a mass spectrometer capable of mass spectrometry even for a beam having a one-dimensional spread.

[0005]

SUMMARY OF THE INVENTION An analysis in which an ion beam passes through the center of a magnet pair and a pair of electrodes having a pair of magnets having opposite poles and a pair of electrodes facing at right angles thereto. A plurality of analysis rows in which a plurality of units are linearly arranged are provided.
Only ions having a constant mass are converged on a straight line through an ion beam having a dimensional spread. The opposing magnets are arranged in the same direction in adjacent analysis units. That is, adjacent analysis units share the same magnet. The principle of mass spectrometry is different from that using a sector magnet, and is based on an electric field and an orthogonal magnetic field, and is sometimes called a Wien filter. When charged particles travel in a direction perpendicular to them in an electric field and a magnetic field, the property that only those whose velocity v is equal to E / B can pass straight through them is used. Such analysis units are arranged in two, three, or more rows. The direction of the magnetic field and the direction of the electric field are the same inside the same row. As described above, the permanent magnet can be shared between adjacent analysis units, but the electrodes for generating the electric field cannot be shared. Each analysis unit must have a pair of electrodes. That is, if the i-th analysis unit in the j-th column is Q _ij , the same j
, The directions of the magnetic field and the electric field are the same. However, analysis units belonging to different analysis columns do not always have the same magnetic field and electric field. Between adjacent analysis rows, the positions of the magnets are shifted by a half pitch, and the directions of the magnetic field and the electric field are opposite. That is, the direction of the magnetic field and the electric field is determined so as to be sequentially inverted with respect to the plurality of analysis rows. The number of rows is m and the number of columns is n. The number n of columns may be two or more. If the number of rows n is large, the ion beam becomes strong. The number of rows m is required to be larger. The line length is equal to the required ion beam line length. That is, the length S
Is required, the values of a and m should be determined so that am = S, where a is the pitch of the analysis unit. This eliminates the need for a scanning mechanism and provides a parallel beam.

[0006]

[Function] A wire for mass analysis by the action of an orthogonal magnetic field and electric field.
Filters are well known. A large number of these are arranged in a matrix as an analysis unit. The magnetic field of the magnet becomes parallel in the row direction,
The electric field generated between the electrodes is made parallel in the column direction. In the analysis row, the direction of the magnetic field and the electric field is constant. Since ions having the same mass are bent in the same direction in the same analysis row, they always become parallel beams. Since the pitch of the analysis unit is a and the number of rows is m, the beam has a spread of ma. The directions of the magnetic field and the electric field are reversed between adjacent analysis rows. The ion beams coming out of this analysis line are also parallel if they have the same mass. The holes through which the ion beams pass and the magnets are shifted by a half pitch between adjacent analysis rows. This is to reduce the interference of the lines of magnetic force between the adjacent magnets and to minimize the disturbance of the magnetic field. However, the number of rows may differ by 1 such as m and m + 1. Easily organize directional relationships. The direction of the ion beam is the z direction, and the direction of the row, that is, the direction of the magnetic field is the y direction. The column direction, that is, the direction of the electric field is defined as the x direction. The analysis units are arranged in the y direction. The analysis rows are arranged in the x direction. In one analysis row, the magnetic field is indicated by (0, -B, 0) and the electric field is indicated by (-E, 0, 0). The velocity vector of the ions is (0, 0, v), and the Lorentz force is zero for ions having an appropriate mass. Analysis columns that differ from this by even column numbers have the same magnetic field. Analysis columns that differ by odd column numbers have opposite magnetic field fields. That is, it has a magnetic field of (0, B, 0) and an electric field of (E, 0, 0). In order to generate such magnetic and electric fields, the magnets in the analysis train must be arranged with different polarities in the y direction. The electrodes are provided so as to face each other in the x direction.

The horizontal spread, that is, the spread in the y direction, is made equal to the irradiation width S of the object to be processed. This is the length of one analysis sequence (ma = S). The vertical spread of the entire mass analyzer is W = bn, where b is the pitch in the column direction.
The position of the middle point is (n + 1) / 2, but considering the coordinates brought about the center, the position of the j-th analysis column in the y direction is b {(n + 1) / 2-j}. As mentioned above, the purpose is to create a one-dimensional ion beam. The ion beams from each analysis row must be converged so that the vertical spread is zero. Let L be the distance between the mass analyzer and the slit or workpiece placed in front. Let the z coordinate of the exit of the mass analyzer be z = 0. The point to converge is z = L. At z = 0, the position of the j-th analysis column in the x direction is x _j = b {(n + 1) / 2−j} (1). Since this progresses by L and converges to (z = L) x = 0, the argument Θ _j is not Θ _j = tan ⁻¹ b ｛(n + 1) / 2-j｝ / L (2) No. That is, the analysis sequence j has a non-zero argument unless it is exactly the middle analysis sequence. Otherwise, the ion beam exiting the mass analyzer will not converge at a distance L.

It is easy to have such a declination. The force of the magnet and the force of the electric field should be different for the ion beam having the desired mass and energy. To do this, it is possible to keep the magnetic field constant and change the electric field for each analysis row. Conversely, it is also possible to keep the electric field constant and change the magnetic field. Of course, both may be changed little by little. For example, assume that the magnetic field B is constant. This is B ₀ . Assuming that the velocity of the desired ion beam in the z direction is w, the electric field E of the analysis row at the center position
Is wB ₀ . Let this be the reference electric field E ₀ (= wB ₀ ), and determine the deviation from the reference electric field in each analysis row. Let h be the thickness of the mass analyzer. That is, it is assumed that the length of the action of the magnetic field is h. When passing through this, the excess force is qΔE (3), assuming that the electric field strength is ΔE greater than the reference electric field. Since the ions pass through the mass analyzer for a time of h / w, the impulse received here is qΔEh / w (4). Since this increases the velocity in the x direction, the impulse is divided by the mass M of the ion, and the velocity u in the x direction becomes u = qΔEh / Mw (5). If Θ _j is ± u / w, since the ion beam from each analysis row should converge to x = 0 before L in the z direction, the excess electric field ΔE _j of the j-th analysis row is , ΔE _j = (− 1) ^j Mw ² b {(n + 1) / 2−j} / hqL (6) However, (−1) ^{j at the} beginning is a factor due to the direction of the magnetic field and the electric field being reversed for each adjacent analysis row. That is, if the electric field is in the −x direction in the odd-numbered analysis row, the electric field is in the + x direction in the even-numbered analysis row.

Equation (6) reveals one of the advantageous properties of the present invention. This equation includes the energy of the incident ion beam. It does not include only the speed w. If the velocity w is included as it is, the ion beam
When the energy of the system is changed, the velocity w must be calculated in order to make it converge for each analysis row, thereby recalculating the magnitude of the excess electric field of each analysis row. If the type of ion beam is different, even if the energy is the same, the speed is different, so that it is necessary to recalculate the value of the electric field even when the ion is changed. Not so in the present invention,
The denominator in the deflection angle equation contains energy, not ion velocity. The energy is readily apparent since it is equal to the acceleration energy of the ion source. It does not depend on the ion species. Therefore, no matter what kind of ions are irradiated, if the acceleration energy is constant, the value of the excess electric field Δ
It is not necessary to change E _j . The magnitude E _j of the electric field in each analysis row is determined by E _j = E ₀ + ΔE _j (7). Isn't this mass spectrometer capable of mass spectrometry because the magnitude of the excess electric field is constant regardless of the ion species? The question may arise. But it is not. Mass spectrometry is performed by the action of orthogonal magnetic and electric fields. The problem here is that the mass spectrometry has been completed and the desired ion species is z = L
At the point, the condition for converging to the line x = 0 is determined.

In the above equation, the electric field is changed by the analysis sequence with the magnetic field being a fixed value. Conversely, the magnitude of the magnetic field can be changed to make the electric field the same. The magnet is shared by the analysis units, but this is possible because the shared analysis units belong to the same analysis column. If the reference magnetic field is B ₀ and the constant electric field is E ₀ , E ₀
= WB ₀ . The excess magnetic field ΔB _j is given by ΔB _j = (− 1) ^j Mwb {(n + 1) / 2−j} / hqL (8) However, when a permanent magnet is used, the value of the magnetic field cannot be changed.
To converge at = L, the speed w is fixed.
However, such control is easy if all magnets are electromagnets. The magnetic field B _j of each analysis row is B _j = B ₀ + ΔB _j (9) obtained by adding the excess magnetic field to the reference magnetic field.

[0011]

FIG. 1 shows a schematic configuration of an ion irradiation apparatus including a mass spectrometer according to an embodiment of the present invention. Ion source 10
Is to introduce a source gas and excite it by discharge to generate plasma. It contains a cathode filament and a radiation shield for suppressing thermal radiation and causes an arc discharge between the chamber and the cathode filament to excite the gas. There is a permanent magnet outside and a cusp magnetic field inside. There are also different ion sources. The structural principle of the ion source is arbitrary. This is extracted as an ion beam by the extraction electrode 11. This is one in which a large number of holes are formed in three electrodes, a positive electrode, a negative electrode, and a ground electrode. The position of the hole must correspond to the ion passage hole of the mass spectrometer described later. A positive high voltage is applied to the positive electrode. This is the acceleration voltage. A small negative voltage is applied to the negative electrode. Extraction electrode system 11
Is provided with an E × B-type mass analyzer 12 of the present invention. Here, two beams 20 are illustrated, because this is an embodiment having only two analysis columns. If there are n analysis columns, n beams are emitted. However, this is because a linear beam is viewed from a direction parallel to the line when the beam is to be formed. At a right angle to this, you should see many more m beams. An analysis slit 13 is provided at a position L in front of the mass analyzer. Further, a beam target 14 as an object to be processed is provided behind it.

The traveling direction of the beam is defined as the z-axis, and the direction in which the beam is converged linearly is defined as the y-axis. FIG. 1 shows the xz plane. Let h be the thickness of the mass analyzer. FIG. 2 is an enlarged sectional view of the mass analyzer. The analysis units are arranged in the y direction. The analysis unit is composed of a pair of magnets 15 of opposite polarity and a pair of electrodes 16 in a direction orthogonal to these. The electrodes are for applying an electrostatic field. The positive electrode is indicated by p and the negative electrode is indicated by n. The magnets oppose each other in the y direction. The N pole is represented by N and the S pole is represented by S. The magnetic field is therefore y
Occurs in the direction. The ion beam passes through the magnetic field in the z-direction. The beam cross section is uniform in each analysis unit. This is equivalent to the beam hole 17 of the extraction electrode. FIG. 3 shows a beam hole of the extraction electrode. There are three electrode plates but all have the same array of holes. It has almost the same extent as the dimension of the mass analyzer in the direction perpendicular to the beam, and the position of the hole corresponds to the center of each analysis unit. The electrode in each analysis unit is x
It is provided so that it may oppose a direction. An electric field is generated in the x direction. There are m such analysis units arranged in the y direction. 2
Each of the analysis rows has a counter magnet and a counter electrode.

However, the direction of the magnet and the direction of the electrode are reversed for different analysis rows. In the analysis row on the left, the direction of the magnetic field is in the -y direction (downward), and the direction of the electric field is -x
Direction (rightward). In the analysis row on the right, the direction of the magnetic field is in the + y direction and the direction of the electric field is in the + x direction.
The left analysis column has m analysis units and the right analysis column has m-1 analysis units, but both may have m analysis units. In that case bee
The beam becomes 2 × m beams in the xy plane. However, in this embodiment, there are m and (m-1) beams. Each analysis row is shifted by a half pitch in the y direction. This is as described above. The reason will be described later. The analysis unit alone has a mass spectrometry effect. The orthogonal electric and magnetic fields exert forces on the ions in opposite directions. The value of the electric field magnetic field is adjusted so that the desired ion beam just balances the force. The same applies to the analysis sequence in which m analysis columns are arranged. However, since the m beams are arranged in a straight line, the cross section of the beam passing therethrough is expanded in a straight line. In a normal Wien filter, desired ions are set to pass straight and straight in the z direction. However, in the present invention, the beams from the two sets of analysis rows must converge in a single ribbon. Therefore, the magnitude of the electric or magnetic field is slightly different for the left and right analysis rows.
Assuming that the magnetic field is constant, from equation (6), n = 2 and j = 1, and for the analysis column on the left,

ΔE ₁ = −Mw ² b / 2hqL (10) For the analysis column on the right side, ΔE ₂ = −Mw ² b / 2hqL (11), where n = 2 and j = 2. This happens to coincide, but this value differs for more than two columns. The electric field is a value obtained by adding these excess electric fields to the reference electric field E ₀ = wB ₀ . That electric field of the first analysis column, E ₁ is E ₀ + Delta] E _1, electric field of the second analysis column is _{E 2 = E 0 + ΔE 2} . FIG. 4 is an example of a mass analyzer having four analysis columns. This means that adjacent analysis columns have electric fields in opposite directions. The point that each analysis row is shifted by a half pitch is also the same as the previous example. Again, if the magnetic field is constant for all magnets, the excess electric field Δ
E _j is n = 4, and j = 1, 2, 3, and 4,

ΔE ₁ = −3 Mw ² b / 2hqL (12) ΔE ₂ = + Mw ² b / 2hqL (13) ΔE ₃ = −Mw ² b / 2hqL (14) ΔE ₄ = + 3 Mw ² b / 2hqL (15) Will be. In any case, the adjustment is easy because the velocity of the ions only enters in the form of energy. The number of magnets can also be reduced. In this case, it is preferable to provide two pairs of electrodes having the same polarity in the same opposed magnet. This embodiment is shown in FIG. Here, the magnet has only two rows, but since it has two analysis units, there are four analysis rows. The cathode, anode, cathode, and anode are arranged between a pair of opposed permanent magnets. Excess electric field Δ of the electric field in this case from the reference electric field
E _j is slightly different from the above. j = 1, 2, and j =
This is because the direction of the electric field magnetic field is the same in 3 and 4. ΔE ₁ = −3 Mw ² b / 2hqL (16) ΔE ₂ = −Mw ² b / 2hqL (17) ΔE ₃ = + Mw ² b / 2hqL (18) ΔE ₄ = + ₃ Mw ² b / 2hqL (19)

As described above, if two sets of electrode plates in the same direction are provided in one magnet, the number n of analysis rows is an even number, and the excess electric field ΔE _j is k = [j / 2-0. 5], an integer k can be defined, and instead of (6), ΔE _j = (− 1) ^k Mw ² b {(n + 1) / 2−j} / hqL (6) Here, [x] is a symbol that takes only an integer part of x. The reason for shifting the analysis unit of the adjacent analysis row by a half pitch will be described with reference to FIG. FIG. 6A shows an example in which the analysis unit is not shifted. In this case, since the directions of the magnetic poles of the magnets are reversed, adjacent magnets exert a strong attractive force. Therefore, the lines of magnetic force do not go from one magnet to the opposing magnet, but to the adjacent magnet. Since most of the magnetic field lines are used between the adjacent magnets, the magnetic field lines between the opposed magnets are insufficient. That is, the magnetic field is weakened between the opposed magnets. Then, the function as a mass spectrometer is reduced. Since such difficulties occur when magnets in adjacent analysis units interfere with each other, they are shifted by a half pitch as shown in FIG. 6B. In this case, since the same poles are opposed between the adjacent magnets, the magnetic field lines are not exchanged during this time, and the magnetic field lines at the end portions only turn in the direction of their own different poles. In this way, most of the magnetic field energy of the magnet can be used for mass analysis. For this reason, the analysis units are shifted by a half pitch in the adjacent analysis rows.

However, in the case where the direction of the electric field and the direction of the electric field are the same in the adjacent analysis rows as shown in FIG. 5, it is of course unnecessary to shift the analysis unit by a half pitch. In each embodiment, a plurality of ion beams traveling in the z-direction are not converged in the y-direction, and x
It is possible to obtain a linear ion beam having a strong density by converging in the direction. FIG. 7 shows the end of the magnet. In the case where the magnets are displaced by a half pitch and the directions of the magnetic poles are different as described above, the ferromagnetic material is joined to both ends to terminate. Since the N-pole and the S-pole are at the end, the lines of magnetic force pass through the ferromagnetic material from one magnet to the other, so that there is no loss of magnetic force. Further, the magnetic field does not leak to the outside and adversely affect external devices.

[0018]

According to the present invention, a linear ion beam having a ribbon-shaped cross section is condensed in one direction without converging in one direction while mass analysis is performed on the ion beam exiting from a large number of ion beam through holes.
You can get a bunch of mums. In FIG. 8, one beam is scanned left and right and spread, so that a long distance is required between the mass spectrometer and the beam collimator. In the present invention, the beam is used from the beginning. Such a distance is unnecessary because it is wide. If the object to be processed is a wide band-shaped member that moves at right angles to the direction of the spread of the linear ion beam, the efficiency of ion implantation is extremely improved. The operation is easier and an ion beam having a larger current amount can be obtained as compared with a method in which one ion beam is mass-analyzed through a fan-shaped magnet and then scanned and spread linearly.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an ion beam irradiation apparatus using a mass analyzer of the present invention.

FIG. 2 is a schematic front view of a mass spectrometer according to an embodiment of the present invention having two analysis columns.

FIG. 3 is a front view showing an example of distribution of holes of extraction electrodes provided immediately before the mass spectrometer of the present invention shown in FIG. 2;

FIG. 4 is a schematic front view of a mass spectrometer according to an embodiment of the present invention having four analysis rows.

FIG. 5 is a schematic front view of a mass spectrometer according to another embodiment of the present invention having four analysis rows.

FIG. 6 is a diagram for closing a magnetic field line distribution for explaining that it is better to shift an analysis unit by a half pitch when the magnetic field direction of an adjacent analysis row is opposite. (A) is the one shifted by a half pitch, and (b) is the one shifted by a half pitch.

FIG. 7 is a diagram showing a configuration for preventing a line of magnetic force from leaking outside at the end of an adjacent analysis row.

FIG. 8 is a schematic configuration diagram of an ion beam irradiation apparatus using a fan-shaped magnet mass analyzer for obtaining a linear beam.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ion source 11 Extraction electrode 12 Mass analyzer 13 Analysis slit 14 Beam target 15 Permanent magnet 16 Electrode 17 Beam cross section 20 Ion beam

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takatoshi Yamashita 47 Nisshin Electric Co., Ltd., Umezu Takaune-cho, Ukyo-ku, Kyoto-shi (72) Inventor Hiroshi Inuchi 47 Nisshin Electric Co., Ltd. 47 Umezu-Takaune-cho, Ukyo-ku, Kyoto-shi ( 72) Inventor Koji Matsunaga 47 Nisshin Electric Co., Ltd. 47 Umezu Takaune-cho, Ukyo-ku, Kyoto (56) References JP-A-1-97363 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB H01J 49/00-49/42 H01J 27/00-27/26 H01J 37/05 H01J 37/08

Claims (2)

(57) [Claims] 1. A plurality of analysis units each having a pair of magnets having opposite poles and a pair of electrodes facing each other in a direction perpendicular to the magnets, wherein an ion beam passes through the center of the pair of magnets and the pair of electrodes. A plurality of analysis rows arranged in a straight line are provided, and the declination of ions having a desired mass is changed for each analysis row through an ion beam having a two-dimensional spread so that only ions of a constant mass are aligned in a straight line in front. A mass spectrometer characterized by focusing. 2. A plurality of analysis units each having a pair of magnets having opposite poles and a pair of electrodes facing each other at right angles to each other so that an ion beam passes through the center of the magnet pair and the electrode pair. A plurality of analysis rows arranged in a straight line parallel to the electrode plate are provided in such a manner that the directions of the magnetic field and the electric field are opposite to each other and are shifted by a half pitch in the row direction. A mass spectrometer characterized in that the declination of mass ions is changed so that only ions of a constant mass are focused on a straight line in front.