JP2022122125A - Electron and ion source - Google Patents

Abstract

To provide an electron and ion source capable of stably supplying thermal electrons from a cathode to a plasma generating container over a long period of time.SOLUTION: An ion source 100 and an electron source 10 including a cathode 20 having an electron emitting surface 21a that emits thermal electrons toward a plasma generating container 101 in which plasma is generated includes a cover member 30 having the same potential as that of the cathode 20 and having a cover portion 32 covering at least a part of the outer edge of the electron emitting surface 21a, and the cathode 20 is formed to have a first region A1 covered with the cover portion 32 and a second region B1 in which the electron emitting surface 21a becomes hotter than the first region A1 and can emit thermal electrons.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to an electron source and an ion source, and more particularly to an electron source that supplies electrons to a plasma generating container in which plasma is generated, and an ion source that includes the electron source.

An ion source disclosed in Patent Document 1 is known as an ion source that includes a plasma generation container in which plasma is generated and an electron source that supplies electrons to the plasma generation container. The ion source of Patent Document 1 is used to generate an ion beam in an ion implanter used in a semiconductor manufacturing process or the like, and includes a cathode that emits thermoelectrons and a filament that heats the cathode from the outside. ing. In other words, the ion source of Patent Literature 1 supplies thermionic electrons emitted from the cathode to the plasma generation container to ionize the raw material gas introduced into the plasma generation container to generate plasma.

In this ion source, an anode electrode maintained at a positive potential with respect to the cathode is arranged near the cathode. The anode electrode also has an opening through which thermoelectrons emitted from the cathode can pass. More specifically, the cathode and anode electrodes are positioned with respect to the plasma-generating vessel such that thermionic electrons emitted from the cathode can pass through the opening of the anode electrode and reach the interior of the plasma-generating vessel.
Alternatively, thermoelectrons may be supplied into the plasma generation container by maintaining the plasma generation container at a positive potential with respect to the cathode without providing the anode electrode. In this case as well, thermoelectrons emitted from the cathode pass through an opening formed in the plasma generation container or a member attached to the plasma generation container.

JP 2014-183040

In general, a cathode that emits thermoelectrons is made of metal such as tungsten or tantalum. When heated, thermoelectrons are emitted from the cathode, and the metal that forms the cathode is also vaporized and emitted to the surroundings. become. The metal forming the cathode is also emitted to the surroundings when particles in the plasma generated in the plasma generating container or near the anode electrode collide with the cathode and the surface of the cathode is sputtered. Then, the metal particles emitted from the cathode to the surroundings adhere and accumulate near the opening formed in the anode electrode or the like through which thermoelectrons pass. In this way, when the metal particles are deposited near the opening of the member such as the anode electrode, which has a potential different from that of the cathode, the deposited metal narrows the opening region of the member. Therefore, it becomes difficult for the electrons emitted from the cathode to sufficiently reach the inside of the plasma generation chamber, and the plasma generation efficiency decreases with time. Therefore, in order to sufficiently supply electrons into the plasma generation chamber, if an operation such as increasing the voltage value applied to the cathode is performed, the vaporization of the metal from the cathode is further promoted, and as a result, near the opening of the member, The rate at which metal particles are deposited will increase. Furthermore, in the vicinity of the opening of the member, the deposited metal brings the member and the cathode closer together, which may cause a short circuit between the member and the cathode.

As described above, in the conventional ion source, the metal vaporized from the cathode or the metal sputtered from the cathode accumulates in the vicinity of the opening formed in the member such as the anode electrode, resulting in a decrease in plasma generation efficiency over time. However, there is a risk of eventually causing a short circuit between the member and the cathode. That is, in the conventional ion source, the plasma generation efficiency decreases over time due to metal vaporized from the cathode, and the short circuit between the cathode and members arranged near the cathode causes long-term contamination from the cathode to the plasma generation container. It was not possible to stably supply thermal electrons.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electron source and an ion source capable of stably supplying thermal electrons from a cathode to a plasma generating container over a long period of time.

The electron source in the present invention is an electron source comprising a cathode having an electron emitting surface that emits thermoelectrons toward a plasma generating container in which plasma is generated, and has the same potential as that of the cathode. The cathode further comprises a cover member having a cover portion covering at least a portion of the outer edge of the electron emission surface, and the cathode includes a first region covered with the cover portion, and the electron emission surface facing the first region. It is formed to have a second region that can reach a high temperature and emit the thermoelectrons.

According to this configuration, the electron source of the present invention includes the cover member having the cover portion that covers at least a part of the outer edge of the electron emission surface. At least part of the metal is deposited on the cover. That is, the cover prevents the metal from being released to the outside of the cover member. Furthermore, since the cover prevents particles in the plasma within the plasma generation container from reaching the electron emission surface, metal particles generated by plasma sputtering of the cathode are also reduced. Further, in the electron source of the present invention, since the cover is at the same potential as the cathode, even if the metal deposits on the cover, a short circuit between the cover and the cathode does not occur. Therefore, according to the electron source of the present invention, deposition of the metal around the electron source is suppressed, and as a result, the metal emitted from the cathode is deposited on the member arranged around the electron source. By doing so, a short circuit between the member and the cathode, which has conventionally occurred, is suppressed.
Also, the cathode is formed to have a first region covered with the cover portion and a second region where the electron emission surface becomes hotter than the first region and can emit thermal electrons. Therefore, the second region, which is not covered with the cover, has a higher temperature than the first region and emits relatively more thermal electrons. It is possible to suppress a decrease in thermionic electrons supplied to the generation container.
That is, the electron source of the present invention can stably supply thermal electrons over a long period of time without lowering the efficiency of plasma generation in the plasma generation chamber.

Further, in the electron source of the present invention, the cathode has a surface to be heated which is formed on the back surface side with respect to the electron emission surface and is heated by a heat source arranged outside the cathode, and the second region may be formed by reducing the thickness dimension from the electron emitting surface to the surface to be heated with respect to the first region.

According to this configuration, the thickness dimension from the electron emitting surface of the cathode to the surface to be heated is made smaller than that of the first region in the second region that emits relatively more thermal electrons. can be formed.

Further, in the electron source of the present invention, the cathode has a surface to be heated which is formed on the back surface side with respect to the electron emission surface and is heated by a heat source arranged outside the cathode, and the second region may be formed by increasing the distance from the heat source to the surface to be heated with respect to the first region.

According to this configuration, the second region that emits relatively more thermal electrons can be formed by increasing the distance from the heat source to the surface to be heated as compared with the first region.

Further, in the electron source of the present invention, the cover section is formed in a plate shape and is positioned along a member arranged outside the cover member and closest to the cover section. may be configured.

According to this configuration, since the cover portion is formed in a plate shape and is positioned along the member arranged at the position closest to the cover portion, it is possible to secure a larger space inside the cover member. can be done. Therefore, a larger cathode can be arranged inside the cover member, and one cathode can be used for a longer period of time.

Further, in the ion source of the present invention, a plasma generating container in which plasma is generated; a cathode attached to the plasma generating container and having an electron emitting surface for emitting thermal electrons toward the plasma generating container; and further comprising a cover member having the same potential as the cathode and having a cover portion covering at least a part of the outer edge of the electron emission surface, wherein the cathode is covered with the cover portion It is formed to have a first region and a second region where the electron emitting surface becomes hot with respect to the first region and can emit the thermoelectrons.

According to this configuration, the ion source of the present invention includes the cover member having the cover portion covering at least a part of the outer edge of the electron emission surface. At least part of the metal is deposited on the cover. That is, the cover prevents the metal from being released to the outside of the cover member. Furthermore, since the cover prevents particles in the plasma within the plasma generation container from reaching the electron emission surface, metal particles generated by plasma sputtering of the cathode are also reduced. Further, in the ion source of the present invention, since the cover portion is at the same potential as the cathode, even if the metal deposits on the cover portion, a short circuit between the cover portion and the cathode does not occur. Therefore, according to the electron source of the present invention, deposition of the metal around the electron source is suppressed, and as a result, the metal emitted from the cathode is deposited on the member arranged around the electron source. By doing so, a short circuit between the member and the cathode, which has conventionally occurred, is suppressed.
Also, the cathode is formed to have a first region covered with the cover portion and a second region where the electron emission surface becomes hotter than the first region and can emit thermal electrons. Therefore, the second region, which is not covered with the cover, has a higher temperature than the first region and emits relatively more thermal electrons. It is possible to suppress a decrease in thermionic electrons supplied to the generation container.
That is, the ion source of the present invention can stably supply thermal electrons over a long period of time without lowering the efficiency of plasma generation in the plasma generation container.

According to the electron source and ion source of the present invention, thermal electrons can be stably supplied from the cathode to the plasma generation container over a long period of time.

1 is a longitudinal sectional view showing an electron source and an ion source in one embodiment of the invention; FIG. FIG. 4 is a vertical cross-sectional view of an ion source showing a first modified example of the present invention; The longitudinal cross-sectional view of the electron source which shows the 2nd modification of this invention. The longitudinal cross-sectional view of the electron source which shows the 3rd modification of this invention.

The electron source and ion source of the present invention are used in an ion beam irradiation apparatus used in semiconductor manufacturing processes and the like. First, the ion source 100 provided with the electron source 10 and the electron source 10 in one Embodiment of this invention is demonstrated.

As shown in FIG. 1, an ion source 100 in this embodiment includes a plasma generation container 101 in which plasma is generated, and an electron source 10 that supplies electrons to the inside of the plasma generation container 101 . The plasma generating container 101 has a substantially rectangular parallelepiped shape as a whole, and includes a first side wall 101a and a second side wall 101b facing each other. The first side wall 101a is formed with a beam extraction port 102, which is an opening for taking out an ion beam from the plasma generated inside the plasma generation container 101. Outside the beam extraction port 102, an extraction port (not shown) is formed. An electrode group composed of electrodes and the like is arranged. Further, the second side wall 101b is formed with a gas introduction port 103 through which a raw material gas, which is a raw material of plasma generated inside the plasma generation container 101, is introduced. That is, the ion source 100 ionizes a raw material gas introduced from the outside through the gas inlet 103 by electrons supplied from the electron source 10 to generate plasma, and the plasma is generated by the action of an electrode group (not shown). In this configuration, the positive ions inside are taken out as an ion beam from a beam outlet 102 .

The plasma generating container 101 has a first bottom wall 101c and a second bottom wall 101d facing each other, and thermal electrons emitted from a cathode 20 provided in the electron source 10, which will be described later, pass through the first bottom wall 101c. An aperture member 106 having an aperture 106a is arranged. Further, a magnet (not shown) is arranged outside the plasma generation container 101 to generate a magnetic field directed from the first bottom wall 101c side to the second bottom wall 101d side in the plasma generation container 101, and the cathode Thermal electrons emitted from 20 are captured by this magnetic field and move inside the plasma generating container 101.

Inside the plasma generating container 101, a reflective electrode 104 is arranged on the side of the second bottom wall 101d, and the reflective electrode 104 is supported by a support positioned so as to pass through an opening formed in the second bottom wall 101d. It is supported by member 105 . Further, the anode electrode 50 and the electron source 10 are arranged outside the opening member 106 with respect to the plasma generation container 101 in a state of being spaced apart from each other. More specifically, the anode electrode 50 has an opening 50b that accommodates a part of the cover member 30 of the electron source 10. The cover member 30 of the electron source 10 is separated from the opening 50b by a predetermined distance. are arranged as It should be noted that the opening member 106 in this embodiment may be considered to correspond to the ground electrode in Patent Document 1, but is not limited to this. Further, without providing the reflective electrode 104, the electron source 10 is arranged also on the second bottom wall 101d side, and electrons enter the plasma generation chamber 101 from both the first bottom wall 101c side and the second bottom wall 101d side. A configuration in which electrons are supplied may be employed.

As shown in FIG. 1, the electron source 10 in this embodiment includes a cathode 20 having an electron emitting surface 21a that emits thermal electrons toward the inside of a plasma generating container 101. As shown in FIG. The electron source 10 also includes a cover portion 32 that covers at least a portion of the outer edge of the electron emission surface 21a while being separated from the electron emission surface 21a, and a side portion that surrounds the cathode 20 while being slightly separated from the cathode 20. A cover member 30 having 31 is further provided. Also, the cover member 30 in this embodiment is a cathode seal that surrounds the entire circumference of the cathode 20, is made of carbon or metal, and has the same potential as the cathode 20 while the ion source 100 is in operation. In this embodiment, the outer shape of the electron emitting surface 21a is circular, and the side surface portion 31 of the cover member 30 is cylindrical, but these shapes are not limited.

The cathode 20 includes a body portion 21 capable of emitting thermoelectrons, an electron emission surface 21a formed on the side of the body portion 21 facing the plasma generating container 101, and formed on the back side of the electron emission surface 21a of the body portion 21. and has a heated surface 21b that is heated by a filament 40 that is a heat source. Further, the cathode 20 has a cylindrical side portion 22 formed to stand from the outer edge of the heated surface 21b, and the filament 40 is a space defined by the side portion 22 and the heated surface 21b. are placed in

The cathode 20 further includes a first region A1 covered by the cover portion 32 of the cover member 30, and an electron emission surface 21a not covered by the cover portion 32, the temperature of which is higher than that of the first region A1. It has a second region B1 capable of emitting thermal electrons. In the second area B1, the thickness dimension T from the electron emitting surface 21a of the main body 21 to the heated surface 21b is gradually reduced from the outer edge of the electron emitting surface 21a toward the center, with respect to the first area A1. Specifically, the electron emission surface 21a is formed as a substantially conical concave portion of the cathode 20. As shown in FIG. Due to this shape, the region included in the second region B1 of the electron emission surface 21a is shorter in distance from the heated surface 21b than the region included in the first region A1, and tends to be heated to a higher temperature. Relatively more electrons can be emitted.

The cathode 20 is heated by the filament 40 to emit thermal electrons from the electron emission surface 21 a toward the inside of the plasma generating container 101 . During operation of the electron source 10 and the ion source 100, the cathode 20 becomes hot, and the metal such as tungsten that forms the cathode 20 is vaporized and emitted to the surroundings. Metal particles forming the cathode 20 are also emitted to the surroundings when the cathode 20 is sputtered by particles contained in plasma generated in the plasma generation container 101 or near the anode electrode 50 . On the other hand, in the electron source 10 and the ion source 100 of this embodiment, at least part of the emitted metal is deposited inside the cover member 32, so that the metal is diffused to the surroundings by the cover member 32. is suppressed.

If the electron source 10 does not have the cover member 30, or if the cover member 30 does not have the cover part 32, the metal emitted from the cathode 20 is arranged at the position closest to the cathode 20. It will be deposited in the opening 50b of the anode electrode 50, which is the member that is attached. Therefore, the opening area of the opening 50b is narrowed by the deposited metal, and thermionic electrons emitted from the cathode 20 do not sufficiently reach the inside of the plasma generation container 101. Therefore, the plasma in the plasma generation container 101 generation efficiency decreases over time. Furthermore, since a potential different from that of the cathode 20 is applied to the anode electrode 50, the distance between the anode electrode 50 and the cathode 20 changes over time as the metal is deposited in the opening 50b of the anode electrode 50. , and eventually short circuit.

On the other hand, in the electron source 10 and the ion source 100 of the present embodiment, at least part of the metal emitted from the cathode 20 mainly adheres and accumulates inside the cover portion 32 of the cover member 31 . Become. Therefore, since the deposition of the metal on the anode electrode 50 is suppressed, the plasma generation efficiency in the plasma generation container 101 is suppressed from being lowered, and furthermore, the short circuit between the anode electrode 50 and the cathode 20 is prevented. occurrence is also suppressed. As a result, in the electron source 10 and the ion source 100 of this embodiment, electrons can be stably supplied into the plasma generation container 101 for a long period of time. Since the cover member 30 has the same potential as the cathode 20 , even if the metal is deposited on the cover member 30 and comes into contact with the cathode 20 , a short circuit will not occur.

Moreover, the metal emitted from the cathode 20 causes metal contamination inside the plasma generation container 101. At least a part of the obtained metal is adhered and prevented from reaching the inside of the plasma generation container 101, so metal contamination inside the plasma generation container 101 can also be reduced.

Further, if the entire electron emission surface 21a has a flat shape, part of the thermoelectrons emitted from the electron emission surface 21a are blocked by the cover portion 32 and reach the inside of the plasma generation container 101. As a result, the number of electrons supplied to the plasma generation container 101 is reduced, and the efficiency of plasma generation is lowered. On the other hand, in the electron source 10 and the ion source 100 of the present embodiment, the second region B1 not covered with the cover part 32 has a higher temperature than the first region A1 and relatively more thermal electrons are generated. Since the thermal electrons are emitted, it is possible to avoid a situation in which the thermal electrons supplied to the plasma generating container 101 are reduced due to the first area A1 being covered with the cover part 32 as a whole. In other words, in the cathode 20 of the present embodiment, the first region A1 of the electron emission surface 21a is covered with the cover portion 32, so that the amount of electrons that can be supplied into the plasma generation container 101 is reduced. It is configured to have a second region B1 that can emit relatively more electrons by being heated to a higher temperature than the region A1. That is, the cathode 20 is configured so that the electron emission surface 21a is partially covered with the cover portion 32, but the electrons supplied into the plasma generation container 101 as a whole are not reduced.

Therefore, the electron source 10 and the ion source 100 of the present embodiment can stably supply thermoelectrons for a long period of time without reducing the efficiency of plasma generation in the plasma generation container 101, and short-circuiting due to metal emitted from the cathode 20 is possible. can be suppressed, and thermal electrons can be supplied without lowering the efficiency of plasma generation in the plasma generation container 101 . Furthermore, metal contamination of the plasma generation container 101 by the metal can also be reduced.

Next, the ion source 101 provided with the electron source 11 and the electron source 11 which are the 1st modification of this embodiment is demonstrated. The same components as those of the electron source 10 and the ion source 100 are assigned the same reference numerals as in the above-described embodiment in FIG.
As shown in FIG. 2, the electron source 11 includes a cathode 201 and the same cover member 30 as in the above-described embodiment. It has a body portion 211 having a heating surface 211b. The electron source 11 also includes a cylindrical holding member 231 that holds the cathode 201 outside the heated surface 211b. That is, as shown in FIG. 1, in the electron source 10, the side portion 22 and the body portion 21 of the cathode 20 are integrally formed, whereas the cathode 201 and the cathode 201 are integrally formed as in this modification. Alternatively, a separate holding member 231 may be used, and the filament 40 may be arranged in a space defined by the heated surface 211 b and the holding member 231 .

Further, in the electron source 11, the electron emitting surface 211a of the cathode 201 is formed in a hemispherical shape. In this case also, the cathode 201 is formed such that the thickness dimension T from the electron emitting surface 211a to the heated surface 211b in the body portion 211 is gradually reduced, and the same effect as the above-described embodiment can be achieved. is clear. That is, the shape of the electron emission surface in the present invention is not limited to a specific shape. For example, the electron emission surface of the present invention may have a shape having a plurality of concave portions such as a hemispherical shape. Moreover, the shape of the cover portion is not limited to a shape that covers only the outer edge of the electron emission surface.

Further, the ion source 101 does not have the anode electrode 50 in the above-described embodiment. That is, in the first modification, the electron source 11 is arranged such that the cover member 30 is spaced apart from the opening member 16 by a predetermined distance, and thermoelectrons emitted from the cathode 201 pass through the opening 106a of the opening member 106. and supplied into the plasma generation container 101 . In the first modified example, the metal forming the cathode 201 can also be emitted from the cathode 201, but at least part of the emitted metal is deposited inside the cover part 32 and reaches the inside of the plasma generation container 101. The amount of the metal to be used is reduced.

Next, the electron source 12, which is a second modified example of this embodiment, will be described.
The electron source 12 is configured to be replaceable with the electron source 10 in the ion source 100 shown in FIG. 1, and the main difference from the electron source 10 is the shape of the cover member 302 as described later. As shown in FIG. 3 , the electron source 12 has a cathode 202 and a cover member 302 . Further, as shown in FIGS. 1 and 3, the anode electrode 50 has an inclined portion 50a that is inclined so as to narrow the opening width as it approaches the plasma generating container 101. As shown in FIG. As shown in FIG. 3, in the electron source 12, the cover portion 322 of the cover member 302 is formed in a plate-like shape, and is positioned outside the cover member 302 and closest to the cover portion 322. is positioned along the inclined portion 50 a of the anode electrode 50 . In this modified example, the cover part 322 is formed parallel to the inclined part 50a, but the alignment along the inclined part 50a of the anode electrode 50 is not limited to being parallel.

In FIG. 3, the electron emission surface 21a of the cathode 20 in the electron source 10 is indicated by a chain double-dashed line. Since the cover part 322 is positioned along the anode electrode 50 which is the member arranged at the position closest to the cover part 322 , the space inside the cover member 302 is made larger in the thickness direction of the cathode 20 . can be secured. Therefore, as is clear from the positional relationship between the electron emission surface 21a and the electron emission surface 212a of the cathode 202 in FIG. A cathode 202 having a larger thickness dimension of the cathode 20 in the direction toward 101 can be used. As a result, one cathode 202 can be used for a longer period of time.

Next, the electron source 13, which is a third modified example of this embodiment, will be described.
As shown in FIG. 4, the electron source 13 has a pair of cathodes 203,203. Each cathode 203 is formed to stand from the outer edge of a heated surface 213b, which will be described later, and has a cylindrical holding portion 233 that defines a space for housing the filament 43 together with the heated surface 213b. The electron source 13 also has a cover member 323 that covers part of the outer edge of the cathodes 203 , 203 and a cover member 303 that has the same potential as the cathode 203 .

Each cathode 203 has an electron emitting surface 213a that emits thermoelectrons and a heated surface 213b that is formed on the back side of the electron emitting surface 213a and heated by a filament 43 that is a heat source arranged outside the cathode 203. I have. In this modified example, two filaments 43, 43 are arranged so as to face each heated surface 213b.

The electron source 13 also has a first area A2 covered with the cover part 323 and a second area B2 where the electron emission surface 313a becomes hotter than the first area A2 and can emit thermoelectrons. formed. In this modification, the second area B2 is formed by increasing the distance D from the filament 43 to the heated surface 302 with respect to the first area A2.
In this way, the first area A2 that emits relatively more thermoelectrons is formed by increasing the distance from the filament 43, which is the heat source, to the surface to be heated 302 with respect to the second area B2. can also

Further, the present invention is not limited to the above-described embodiments and modified examples, and it goes without saying that various modifications are possible without departing from the spirit of the present invention.

10 Electron source 100 Ion source 101 Plasma generating container 20 Cathode 30 Cover member 32 Cover part 40 Filament A1 First region B1 Second region

Claims (5)

An electron source comprising a cathode having an electron emitting surface that emits thermal electrons toward a plasma generating vessel in which plasma is generated,
a cover member having the same potential as the cathode and having a cover portion that covers at least part of the outer edge of the electron emission surface;
The cathode is formed to have a first region covered with the cover portion and a second region where the electron emitting surface is heated to a higher temperature than the first region and the thermoelectrons can be emitted. electron source. the cathode has a heated surface formed on the back side of the electron emitting surface and heated by a heat source arranged outside the cathode;
2. The electron source according to claim 1, wherein said second region is formed by making the thickness dimension from said electron emitting surface to said surface to be heated smaller than said first region. the cathode has a heated surface formed on the back side of the electron emitting surface and heated by a heat source arranged outside the cathode;
2. The electron source according to claim 1, wherein said second region is formed by increasing the distance from said heat source to said surface to be heated with respect to said first region. 4. The cover portion is formed in a plate-like shape and is positioned along a member arranged outside the cover member and closest to the cover portion. The electron source described in . An ion source comprising: a plasma generating container in which plasma is generated; and a cathode attached to the plasma generating container and having an electron emitting surface for emitting thermal electrons toward the plasma generating container,
a cover member having the same potential as the cathode and having a cover portion that covers at least part of the outer edge of the electron emission surface;
The cathode is formed to have a first region covered with the cover portion and a second region where the electron emitting surface is heated to a higher temperature than the first region and the thermoelectrons can be emitted. ion source.

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