JP2009099433A - Ion source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate adjustment of a gap between a filament 101 and a cathode 102, at assembly and at operation. <P>SOLUTION: The ion source 100 generating ions by heating the cathode 102 with the filament 101, emitting thermions, and turning raw material gas to plasma, is provided with an ion source body 2 to which the cathode 102 is fixed, a filament holder 3 holding the filament 101 and fitted to the ion source body 2, and an adjustment mechanism 4 provided in interposition between the filament holder 3 and the ion source body 2 enabled to adjust a distance between the cathode 102 and the filament 101 after the assembly. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ion source used in, for example, an ion implantation apparatus. More specifically, the cathode is heated by a filament, and hot electrons for plasma generation are emitted from the cathode into a plasma generation container to ionize a source gas. The so-called indirectly heated ion source.

  As an ion source of this type, as shown in Patent Document 1, thermal electrons emitted from a filament disposed on the cathode back surface opposite to the plasma generation vessel are accelerated by voltage to heat the cathode, The structure has a structure in which thermionic electrons are emitted from the front surface of the cathode facing to the inside of the plasma generation container to cause arc discharge.

  In this ion source, considerable accuracy is required for the gap (gap) between the cathode and the filament, and the accuracy is several mm ± 0.05 mm.

  This gap adjustment is set by inserting a filament set gauge (spacer) when the ion source is assembled. Specifically, a spacer is arranged on the inner surface of the cathode held by the cathode holder, the filament holder holding the filament and the cathode holder are attached with screws so that there is no looseness or looseness, and the filament protruding outward from the filament holder Is pushed so that there are no gaps between the filament, the cathode and the spacer. Thereafter, after confirming that the filaments are attached in parallel, the screws are removed, and the cathode holder is removed. Then, the spacer is removed and reassembled. When reassembling, care must be taken so that the filament position does not shift with respect to the filament holder.

  As described above, since the assembly work is complicated and there are individual differences in the assembly, there is a problem that it is difficult to set an accurate gap between the filament and the cathode.

  Further, since the filament bending process is performed manually, there is a problem that the filament shape varies, and the amount of emitted electrons is different even in the same gap.

  Furthermore, even if the gap is set accurately, the filament foot (terminal) is fixed to the filament holder, so that the filament twists and deforms due to thermal expansion when operated for a long time, and as a result, the gap It will change.

  In addition, the filament itself is consumed and the diameter is reduced, resulting in a gap change.

  In addition, when operated for a long time, a slight depression due to evaporation occurs on the side surface (back surface) of the filament of the cathode, so that the gap changes.

  As described above, it is difficult to accurately adjust the gap at the time of assembly, and even if the gap is accurately set at the time of assembly, the gap changes due to various factors caused by the subsequent operation. There is a problem.

  If the gap becomes small due to various factors during assembly or subsequent operation, and the filament gets too close to the cathode, the amount of emitted electrons (emission) of the thermal electrons becomes too large. At this time, since the current is controlled by the power supply, the voltage between the filament and the cathode (electron impact voltage) is lowered due to the power supply characteristics. As a result, the heating power for heating the cathode decreases and becomes insufficient. Then, it is necessary to adjust the heating power by lowering the current to decrease the amount of emitted electrons and increasing the electron impact voltage. When the gap is small as described above, since the electron current falls in the temperature limited region, there is a condition for adjusting the power, but there is a problem that the control becomes complicated. On the other hand, if the gap is too small, the exhaustion of the filament increases due to thermal radiation from the cathode, and the life of the filament is reduced. Also, in operation, the filament is heated by the cathode, and the emission current increases, so the emission current control becomes unstable.

On the other hand, if the gap is too large, the operation becomes a space charge limited region of the electron current, so even if the filament current is increased and the electron impact voltage is increased, the desired amount of emitted electrons may not be obtained due to the space charge effect. Arise. In this case, it is necessary to disassemble the ion source and adjust the gap between the filament and the cathode again. This is a major problem in the production line because the ion implantation apparatus is stopped. Further, as described above, even in the assembly after disassembly, the work is complicated, and there is a problem that it is difficult to set an accurate gap between the filament and the cathode.
Japanese Patent No. 3758667

  Therefore, the main object of the present invention is to facilitate the adjustment of the gap between the filament and the cathode during assembly and operation.

  That is, the ion source according to the present invention is an ion source that generates ions by heating a cathode with a filament, emitting thermoelectrons from the cathode, and converting the source gas into plasma, and the cathode is fixed. An ion source body, a filament holder that holds the filament, and is provided between the ion source body and the filament holder, and a distance between the filament and the cathode. And an adjustment mechanism that enables adjustment after assembly.

  If it is such, it is not necessary to set the distance of a filament and a cathode correctly at the time of an assembly, for example, and the distance adjustment of a filament and a cathode can be easily performed after the assembly of an ion source. Further, during operation, even when the distance between the filament and the cathode changes due to various factors during operation, the distance between the filament and the cathode can be easily adjusted without having to be disassembled.

  The ion source according to the present invention is an ion source that generates ions by heating a cathode with a filament, emitting thermoelectrons from the cathode, and converting the source gas into plasma, and the cathode is fixed. An ion source main body, holding the filament, a filament holder provided in the ion source main body, and provided on the opposite side of the ion source main body in the filament holder, the distance between the filament and the cathode And an adjusting mechanism that can be adjusted after assembly.

  If it is such, in addition to the effect of the invention mentioned above, the freedom degree of arrangement | positioning of an adjustment mechanism increases, and the arrangement | positioning can be set according to the structure of an adjustment mechanism. As a result, the configuration of the adjusting mechanism can be freely selected, and the fine adjustment of the filament can be facilitated.

  In order to prevent the filament holder, the ion source main body, and screws and insulators for fixing them from being seized by heat from the filament and / or the cathode and preventing disassembly during maintenance, the filament In addition, it is desirable that the filament holder is provided apart from the ion source main body within a range affected by the heat from the cathode.

  As a specific embodiment of the filament holder and the adjustment mechanism, the filament holder is connected to the filament holder that holds the filament, and one end of the filament holder is connected to the base end of the filament holder via an insulating member, A holder fixing member whose other end is fixed to the ion source main body, and the adjustment mechanism adjusts the position of the holder fixing member from the ion source main body, whereby the distance between the filament and the cathode It is desirable to adjust this.

  Further, it is desirable that the contact surface of the holder fixing member with the ion source main body and the surface of the filament facing the cathode are substantially on the same surface. In this case, the parallelism between the face of the filament facing the cathode and the face of the cathode facing the filament can be easily adjusted, and as a result, the cathode can be efficiently heated.

  The adjustment mechanism is connected to a motor provided in the ion source main body or the fixing member, a speed reduction mechanism for reducing the rotation of the motor, and the speed reduction mechanism and the holder fixing member. It is desirable to provide a screw mechanism that converts the movement into movement and moves the holder fixing member forward and backward relative to the ion source body. If it is such, the distance with respect to the cathode of a filament can be adjusted now by a predetermined space | interval with the rotation speed of a motor, the reduction ratio of a reduction mechanism, and the pitch of a screw mechanism.

  In order to realize the speed reduction mechanism easily and in a small size, it is desirable that the speed reduction mechanism uses a worm gear.

  Since the ion implantation apparatus using the ion source described above can supply stable ions, ion implantation can be performed with high accuracy.

  According to the present invention configured as described above, it is possible to easily adjust the gap between the filament and the cathode during assembly and during operation.

  Hereinafter, an embodiment of an ion source 100 according to the present invention will be described with reference to the drawings. 1 is a schematic cross-sectional view of the ion source 100 according to the present embodiment, and FIG. 2 is a partially enlarged schematic view showing the position of the filament 101 after adjustment by the adjustment mechanism 4.

<Device configuration>
An ion source 100 according to the present embodiment is used in an ion implantation apparatus, and as shown in FIG. 1, a cathode 102 is heated by a filament 101 and thermoelectrons are emitted from the cathode 102 into a plasma generation container 22 that also serves as an anode. Then, the source gas is turned into plasma to generate ions, which is called a so-called indirectly heated ion source.

  Specifically, this includes an ion source body 2 to which the cathode 102 is fixed, the filament 101, a filament holder 3 provided in the ion source body 2, and the ions in the filament holder 3. And an adjusting mechanism 4 provided on the opposite side of the source body 2 to adjust the distance between the cathode 102 and the filament 101 after the ion source is assembled.

  Hereinafter, each part 2-4 is demonstrated.

  The ion source main body 2 includes a main body portion 21 having a mount flange 211 attached to an ion source chamber (not shown), and a plasma generation container 22 provided at the distal end portion of the main body portion 21.

The plasma generation container 22 has a rectangular parallelepiped shape, for example, and a predetermined gas for plasma generation (including the case of vapor) is introduced into the plasma generation container 22 through the gas inlet 221. This gas is a gas containing a desired element (for example, a dopant such as boron (B), phosphorus (P), or arsenic (As)). More specifically, the gas includes a source gas such as BF ₃ , PH ₃ , AsH ₃ , B ₂ H ₆ or the like.

  In addition, an ion ejection hole 222 for extracting an ion beam is provided on one wall surface (one of the long side walls) of the plasma generation container 22. The ion injection hole 222 has, for example, an elongated slit shape in the longitudinal direction of the long side wall.

  Furthermore, another wall surface (one of the short side walls) of the plasma generation container 22 is provided with a cathode attachment port 223 for positioning the cathode 102. A reflective electrode 103 that reflects electrons in the plasma is held via an electrical insulator on the inner side of the wall facing the wall having the cathode mounting opening 223.

  The cathode 102 has a columnar shape (more specifically, a cylindrical shape) made of, for example, tungsten (W), and is disposed in the cathode attachment port 223 by the cathode holder 5.

  The cathode holder 5 is made of, for example, molybdenum (Mo), and has a cylindrical holding portion 51 that holds the cathode 102 therein, and a fixing that is fixed to the side surface of the ion source body 2 via an insulating member 53. Part 52. In a state where the fixing part 52 is attached to the ion source body 2, the holding part 51 is inserted into the cathode attachment port 223 from the outside of the plasma generation container 22.

  The filament holder 3 includes a filament holder 31 that holds the filament 101 and a holder fixing member 32 that is fixed to the ion source body 2.

  The filament holder 31 has a substantially rectangular shape, has a function as a filament conductor for energizing the filament 101, and is connected to a filament current conductor (not shown). Further, the filament holder 31 has a filament holding part 311 that holds the filament 101 by its own elastic deformation at the tip part.

  The fixing member 32 has a substantially rectangular shape, one end is connected to the base end of the filament holder 31 via an insulating member 33, and the other end is fixed to the ion source body 2 with a molybdenum screw or the like. Is. The other end of the holder fixing member 32 is provided with a mounting portion 321 having, for example, a step shape for fixing to the ion source main body 2. As shown in FIG. 1, the attachment portion 321 is disposed outside the mount flange 211 in consideration of the influence of heat from the filament 101 and the cathode 102. Examples of the insulating member 33 include ceramic and alumina.

  In the filament holder 3 configured as described above, from the tip end portion (filament holding portion 311) of the filament holder 31 to which the filament 101 is attached to the attachment portion 321 that is fixed to the ion source body 2 of the holder fixing member 32, The ion source body 2 and the cathode holder 5 are provided at a predetermined interval. That is, the attachment portion 321 of the holder fixing member 32 is set in a region where the attachment portion 321, the ion source main body 2, and the fixing screw for fixing them are not seized due to the thermal influence from the filament 101 and the cathode 102. .

  Further, the contact surface of the holder fixing member 32 with the ion source main body 2 and the surface of the filament 101 facing the cathode 102 are located on substantially the same surface. That is, in a state where the filament holder 3 is attached to the ion source main body 2, the cathode-side tip surface (surface facing the cathode 102) of the filament 101 attached to the tip portion thereof and the holder fixing member of the filament holder 3 The side surface of the ion source main body 2 to which 32 is attached is substantially the same surface. Thereby, it is possible to easily adjust the parallelism between the cathode side tip surface of the filament 101 and the filament side end surface of the cathode 102, and as a result, the cathode 102 can be efficiently heated.

  The adjustment mechanism 4 is configured to be able to adjust the distance between the front end face of the filament 101 and the filament side end face (back face) of the cathode 102 from the outside after the assembly of the ion source 2, and is a driving unit provided in the ion source main body 2. A motor 41, a speed reduction mechanism 42 that decelerates the rotation of the motor 41, and the speed reduction mechanism 42 and the holder fixing member 32, and the rotational movement of the motor 41 is converted into a rectilinear movement, whereby the holder fixing member And a screw mechanism 43 that moves the needle 32 forward and backward with respect to the ion source main body 2. Thus, by moving the holder fixing member 32 forward and backward with respect to the ion source main body 2, the filament 101 rotates and moves with the attachment portion 321 of the holder fixing member 32 as the rotational movement center.

  The motor 41 is fixed by a motor holder (not shown) on the atmosphere side of the ion source main body 2 (that is, on the side opposite to the filament 101 with respect to the mount flange). As the motor 41 of this embodiment, a normal motor, a stepping motor, etc. can be used, for example.

  The speed reduction mechanism 42 is provided on the holder fixing member 32, and rotates with the rotation of the drive shaft of the motor 41, a first worm wheel 422 that meshes with the first worm gear 421, and the first Two sets of worm gears each including a second worm gear 423 integrally formed coaxially with the worm wheel 422 and a second worm wheel 424 engaged with the second worm gear 423 are provided.

  The drive shaft of the motor 41 and the first worm gear 421 are connected by a transmission belt 44. The first worm gear 421, the first worm wheel 422, the second worm gear 423, and the second worm wheel 424 are made of tungsten (W), molybdenum (Mo), stainless steel (SUS304), a heat-resistant alloy, Hastelloy, Inconel, or the like. And is rotatably fixed to a protective cover 6 that protects the adjusting mechanism 4 from the outside. The protective cover 6 serves to shield the heat from the filament 101 and the cathode 102 of the adjusting mechanism 4, particularly the speed reduction mechanism 42 and the screw mechanism 43, and prevent metal contamination. Molybdenum (Mo) or stainless steel (SUS304) It is formed from a heat resistant material such as. In FIG. 1, there is no gap between the protective cover 6 and the filament holder 31, but actually, the movement of the filament holder 31 and the holder fixing member 32 relative to the ion source body 2 is not performed. There are enough gaps to allow.

  The screw mechanism 43 includes a female screw portion 431 provided on the fixing member 32 and a male screw portion 432 provided in the vicinity of the tip of the rotary shaft provided coaxially with the rotary shaft of the second worm wheel 424.

When the pitch p of the screw mechanism 43 is set and the reduction ratio of the pair of worm gears in the speed reduction mechanism 42 is N, the linear motion of p / N ² can be transmitted when the motor 41 rotates the first worm gear 421 once. . More specifically, for example, when the reduction ratio N is 32 and the pitch p of the male screw part 432 is 0.5 mm, the male screw part 432 is moved by 0.5 mm with respect to the female screw part 431 by rotating 1024 on the atmosphere side. be able to. Then, the filament 101 has a ratio (L2 / L1) of the distance (L2) from the attachment portion 321 to the filament 101 with respect to the distance (L1) from the attachment portion 321 of the holder fixing member 32 to the screw mechanism 43, and the male screw portion 431. It moves only by the product value (d × L2 / L1) with the moving distance d. For example, when the ratio (L2 / L1) is about 2, the movement distance of the filament 101 is about twice the movement distance (d) of the male screw portion 431. In other words, in this embodiment, when the motor 41 is rotated 512 times, the filament 101 moves 0.5 mm, and the adjustment capability of the adjustment mechanism 4 is 0.001 mm / time.

  <Position adjustment procedure between filament 101 and cathode 102>

  Next, an example of the position adjustment procedure between the filament 101 and the cathode 102 of the ion source 100 will be described with reference to FIG. 2 for the position adjustment after the assembly and before the ion implantation and the position adjustment between the filament 101 and the cathode 102 during the ion implantation. To explain. 2 shows a case where the distance between the filament 101 and the cathode 102 is made smaller than the distance at the time of assembly using the adjustment mechanism 4, and the dotted line in FIG. 2 indicates the filament holder 31 and the filament before adjustment. 101 is shown.

  First, after the assembly, in the case of the position adjustment before the ion implantation, the spacer 101 is used to assemble the distance between the filament 101 and the cathode 102 so as to be approximately a predetermined interval of 2 mm, which is determined in advance. At this time, it is not necessary to accurately adjust the distance between the filament 101 and the cathode 102 to 2 mm as in the prior art. Thereafter, the ion source 100 is operated, the amount of electrons emitted from the filament 101 at a predetermined voltage is measured, and the adjustment mechanism 4 adjusts the position between the filament 101 and the cathode 102 so that a predetermined amount of emitted electrons can be obtained. Perform (see FIG. 2).

  Next, in the case of adjusting the position between the filament 101 and the cathode 102 at the time of ion implantation, when the measured amount of emitted electrons decreases (or increases), the electron impact voltage is first controlled. , Adjust the amount of emitted electrons. The electron impact voltage is a voltage between the filament 101 and the cathode 102, and is a voltage for causing thermal electrons to collide from the filament 101 to the cathode 102. Thereafter, when the amount of emitted electrons cannot be adjusted by the electron impact voltage, the adjusting mechanism 4 adjusts the distance between the filament 101 and the cathode 102 (see FIG. 2).

<Effect of this embodiment>
According to the ion source 100 according to the present embodiment configured as described above, the distance between the filament 101 and the cathode 102 can be adjusted. For example, the distance between the filament 101 and the cathode 102 can be easily adjusted during assembly. Can do. Further, at the time of ion implantation, even when the distance between the filament 101 and the cathode 102 changes due to various factors in operation, the distance between the filament 101 and the cathode 102 can be easily adjusted without being decomposed. Further, even if the distance (gap) between the filament 101 and the cathode 102 is increased, it is not necessary to forcibly increase the filament current, and the filament 101 can always be used under optimum conditions. Can be extended.

  Further, since the filament holder 3 and the ion source body 2 are provided apart from each other, and the filament holder 3 is fixed to the ion source body 2 only by the attachment portion 321, maintenance work such as seizure, specifically, filament holding The cause of hindering the separation work of the body 3 can be removed, and thermal damage of these members can be prevented.

<Other modified embodiments>
The present invention is not limited to the above embodiment. In the following description, the same reference numerals are given to members corresponding to the above-described embodiment.

  For example, regarding the configuration of the adjusting mechanism 4, the adjusting mechanism 4 is not limited to the one using the speed reducing mechanism 42 using the worm gears 421 and 423 and the worm wheels 422 and 424. For example, as shown in FIG. A wedge member provided between the source body 2 and the filament holder 31 and inserted between the holder fixing member 32 and the ion source body 2 may be used.

  Further, the ion source 100 is provided in the order of the filament 101, the adjusting mechanism 4 and the attachment portion 321. In addition, as shown in FIG. 4, the filament 101, the attaching portion 311 and the adjusting mechanism 4 are provided in this order. You may do it. In this case, the attachment portion 321 is provided at a position separated from the filament 101 and the cathode 102 so as not to be seized due to thermal influence.

  Further, the motor 41 of the adjusting mechanism 4 may be provided on the vacuum side using a vacuum motor or the like without being provided on the atmosphere side.

  In addition, regarding the position adjustment method between the filament 101 and the cathode 102, in the above-described embodiment, the physical adjustment by the adjustment mechanism 4 is performed after the control by the electron impact voltage. In addition, physical adjustment by the adjustment mechanism 4 may be performed at the same time, or only physical adjustment may be performed.

  In addition, the mounting portion 321 of the holder fixing member 32 according to the above embodiment is disposed outside the mounting flange 211 (atmosphere side) in consideration of thermal effects, but is disposed inside the mounting flange 211 (vacuum side). You may do it. In this case, the degree of fatigue due to bending of the holder fixing member 32 can be reduced as compared with the case where the holder fixing member 32 is arranged.

  In addition, some or all of the above-described embodiments and modified embodiments may be combined as appropriate, and the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. .

The typical block diagram which shows the ion source which concerns on one Embodiment of this invention. The schematic diagram which shows the position of the filament after adjustment by an adjustment mechanism. The schematic diagram which shows the adjustment mechanism which concerns on deformation | transformation embodiment. The schematic diagram which shows the adjustment mechanism which concerns on a deformation | transformation adjustment mechanism.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Ion source 101 ... Filament 102 ... Cathode 2 ... Ion source main body 3 ... Filament holder 4 ... Adjustment mechanism 31 ... Filament holder 32 ... Holder fixing member 33 ... Insulating member 41 ... Motor 42 ... Reduction mechanism 43 ... Screw mechanism 421, 423 ... Worm gear

Claims (8)

An ion source that generates ions by heating a cathode with a filament, emitting thermoelectrons from the cathode, and converting the source gas into plasma,
An ion source body to which the cathode is fixed;
While holding the filament, a filament holder provided in the ion source body,
An ion source provided between the ion source body and the filament holder, and an adjustment mechanism that allows adjustment of the distance between the filament and the cathode after assembly. An ion source that generates ions by heating a cathode with a filament, emitting thermoelectrons from the cathode, and converting the source gas into plasma,
An ion source body to which the cathode is fixed;
While holding the filament, a filament holder provided in the ion source body,
An ion source provided with an adjustment mechanism provided on the opposite side of the main body of the ion source in the filament holder so that the distance between the filament and the cathode can be adjusted after assembly.   3. The ion source according to claim 1, wherein the filament holder is provided apart from the ion source main body within a range affected by heat from the filament and / or the cathode. A filament holder that holds the filament; a holder fixing member that has one end connected to the base end of the filament holder via an insulating member and the other end fixed to the ion source body; With
4. The ion source according to claim 1, wherein the adjusting mechanism adjusts a distance between the filament and the cathode by adjusting a position of the holder fixing member from the ion source main body.   The ion source according to claim 4, wherein a contact surface of the holder fixing member with the ion source main body and a surface of the filament facing the cathode are located on substantially the same surface.   The adjustment mechanism is connected to a motor provided in the ion source main body or the fixing member, a speed reduction mechanism for reducing the rotation of the motor, and the speed reduction mechanism and the holder fixing member. The ion source according to claim 1, 2, 3, or 4, further comprising: a screw mechanism that converts the movement into movement and moves the holder fixing member forward and backward with respect to the ion source main body.   The ion source according to claim 6, wherein the speed reduction mechanism uses a worm gear.   An ion implantation apparatus using the ion source according to claim 1.