JP3417176B2 - Ion irradiation equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion irradiation apparatus for irradiating a substrate on a holder with an ion beam and performing a process such as ion implantation on the substrate. The present invention relates to an improvement in means for suppressing charge (charge-up) of the substrate. 2. Description of the Related Art Conventionally, there has been proposed an ion irradiation apparatus in which low-energy electrons in plasma are used to suppress charging of a substrate due to ion beam irradiation. One example of the ion irradiation apparatus will be described with reference to FIGS. 2 and 3. This ion irradiation apparatus basically includes a substrate (for example, a wafer) held by a holder 10 housed in a vacuum vessel (not shown). ) 8 is irradiated with the ion beam 2 and subjected to a treatment such as ion implantation. [0004] The holder 10 may be a wafer disk for batch processing or a platen for single wafer processing. The illustrated one is an example of the former case, and is rotated in the direction of arrow A in a vacuum vessel. And in the direction of arrow B. [0005] The substrate 8 is irradiated with the ion beam 2.
The following measures are taken in order to prevent the occurrence of problems such as electric discharge due to positive charging when the surface is an insulator, especially when the surface is an insulator. That is, in this example, the cylindrical reflector electrode 24 surrounding the periphery of the ion beam 2 passing therethrough is provided at the portion immediately upstream of the holder 10 in this example. The reflector electrode 24 is made of a non-magnetic material such as aluminum or carbon, and has a hole 25 on a side surface thereof. Near the outside of the hole 25 of the reflector electrode 24, there is provided a plasma shower device 30 for generating a plasma 32 and introducing the plasma 32 into the reflector electrode 24 through the hole 25. 28 is an insulating plate. [0008] In this example, the plasma shower device 30 generates plasma in two stages. As shown in FIG.
A plasma generation container 64, a coil 68, and various power supplies for them are provided. Both plasma generation vessels 46, 64
Is made of a non-magnetic material such as carbon in this example. The first plasma generation container 46 has a small hole 48 at a portion on the reflector electrode 24 side, and an ionization gas 52 such as xenon gas is introduced into the inside. In the first plasma generation container 46, a filament 54 is provided.
Are provided at both ends thereof, and a heating filament power source 58 is connected to both ends thereof. On the reflector electrode 24 side of the first plasma generation container 46, a second plasma generation container 64 is provided. The second plasma generation container 64 has small holes 66 and holes 67 before and after it. The first plasma generation container 46 and the second plasma generation container 64 are electrically insulated by a ring-shaped insulator 62. A coil 68 to which a DC power source 70 for excitation is connected is wound around the outside of the vicinity of the first plasma generation container 46, whereby the first plasma generation container 46 is
A magnetic flux is generated along the axial direction, that is, along the introduction direction of the plasma 32, in a region from the inside to the vicinity of the outlet of the second plasma generation container 64. Reference numeral 76 in FIG. 2 schematically shows an example of the magnetic flux. However, the direction of the magnetic flux may be opposite to that shown in the drawing (the same applies to the embodiment of FIG. 1). A DC plasma generation power supply 74 is connected between the second plasma generation container 64 and the filament 54 with the former being on the positive side. Second plasma generation vessel 6
4 and the first plasma generation container 46, for example, 15
A limiting resistor 72 of about 0Ω is connected. Thermions emitted by heating the filament 54 are drawn toward the first plasma generation container 46 by the voltage applied from the plasma generation container 74 via the limiting resistor 72, and on the way, Gas 52 introduced into first plasma generation container 46
And ionizes it, thereby generating a plasma 60 in the first plasma generation container 46. At this time, the magnetic flux 76 contributes to generation and maintenance of the plasma 60. When the plasma 60 is generated, the limiting resistor 7
2, a voltage drop occurs there, and a potential difference of, for example, about several tens of volts is generated between the second plasma generation container 64 and the first plasma generation container 46. As a result, the voltage applied to the first plasma generation container 46 decreases, and the plasma 60 becomes relatively thin. The plasma 6 in the first plasma generation vessel 46
The electrons in 0 are constricted by the magnetic flux 76 and, at the same time, are extracted into the second plasma generation container 64 by the accelerating electric field due to the potential difference. Although the energy of the electrons is low, for example, about 20 eV, the electrons are guided by the magnetic flux 76 and efficiently extracted into the second plasma generation container 64. The gas 52 flows into the second plasma generation container 64 from the first plasma generation container 46 through the small holes 48 and 66, and is drawn into the second plasma generation container 64. The electrons collide with the gas and ionize it, and the plasma 32 is created again in the second plasma generation vessel 64. The ionization energy of the gas 52 is 1
Since it is about 0 eV, it can be sufficiently ionized by electrons having an energy of about 20 eV. In addition, in the second plasma generation container 64, electrons collide with gas molecules in the process of circling around the magnetic flux 76, so that the ionization efficiency of the gas 52 is high. , First plasma generation container 46
A plasma 32 having a higher density (for example, about 3 to 4 times) than the plasma 60 in the inside is generated. The hole 6 of the second plasma generation vessel 64
From 7, the plasma 32 is introduced into the reflector electrode 24 by the potential or pressure difference of the ion beam 2. The energy of the electrons in the plasma 32 remains as it was when the plasma 32 was generated, and since no acceleration has been performed thereafter, the energy is low, for example, about several eV to tens eV. Between the plasma shower device 30 (more specifically, the second plasma generation container 64) and the reflector electrode 24, a direct current for applying a negative voltage to the reflector electrode 24 with respect to the plasma shower device 30 is used. Reflector power supply 26 is connected. The output voltage of the reflector power supply 26 is set to a voltage enough to push back electrons in the plasma 32 introduced into the reflector electrode 24, for example, about -20V to -30V. The ions in the plasma 32 introduced into the reflector electrode 24 as described above are attracted and captured by the reflector electrode 24 having a negative potential. On the other hand, the electrons in the plasma 32 are pushed back by the negative voltage of the reflector electrode 24 and are drawn into the ion beam 2 by its positive potential. When the substrate 8 is charged, a potential gradient is generated in the axial direction of the ion beam 2 due to this, so that the electrons drawn into the ion beam 2 are attracted to the substrate 8 by the potential gradient, and the surface of the substrate 8 is charged. Neutralizes the positive charge associated with the ion beam irradiation. When the positive charges are neutralized, the attraction of electrons into the substrate 8 automatically stops. In this manner, the electrons are supplied to the substrate 8 without any excess or shortage, so that the positive charging of the substrate 8 due to the ion beam irradiation can be suppressed. In addition, since the potential of the substrate surface due to the electrons does not become higher than the energy of the electrons incident thereon on the negative side, by utilizing the low energy electrons in the plasma 32 as described above, the substrate 8 Negative charging can also be suppressed. As described above, most of the electrons supplied from the plasma shower device 30 to the ion beam 2 and used for neutralization thereof are mostly plasma 32
Medium energy (for example, several eV to ten e as described above)
V), but in reality,
High-energy (for example, about 20 eV or more) thermoelectrons emitted from the filament 54 are also mixed, and the high-energy thermoelectrons are supplied to the ion beam 2 and
Incident on the substrate 8 may cause a negative charge at a high voltage on the substrate 8. Accordingly, it is a primary object of the present invention to provide an ion irradiation apparatus improved so that electrons of high energy components from a plasma shower apparatus can be prevented from being supplied to an ion beam. According to the present invention, there is provided an ion irradiation apparatus having a hole at a position corresponding to the hole of the reflector electrode, and a ferromagnetic material having the same potential as that of the reflector electrode. It is characterized by being mounted so as to surround the outer periphery. According to the above configuration, the magnetic flux generated from the coil of the plasma shower device passes through the ferromagnetic material on the outer periphery near the reflector electrode. That is,
Near the hole in the reflector electrode, the magnetic flux is directed to the ferromagnetic material or the reflector electrode inside the ferromagnetic material. As a result, the electrons and other electrons in the plasma introduced from the plasma shower device into the reflector electrode are guided by the magnetic flux, and travel along the magnetic flux toward the ferromagnetic material or the reflector electrode. At this time, electrons having energy smaller than the potential of the reflector electrode and the ferromagnetic material having the same potential are rebounded by the potential and enter the reflector electrode, and are attracted into the ion beam by the potential. Electrons having an energy higher than the potential of the material overcome the potential and enter the reflector electrode or the ferromagnetic material and flow therethrough. By such an action, it is possible to prevent electrons of a high energy component from being supplied to the ion beam from the plasma shower device. FIG. 1 is a cross-sectional view showing an example of the vicinity of a plasma shower device in an ion irradiation apparatus according to the present invention. In this figure, the ion beam 2 travels from the front side to the back side of the paper as in FIG. Parts that are the same as or correspond to those in the embodiment of FIG. 2 are denoted by the same reference numerals, and differences from the conventional example will be mainly described below. In addition, since the overall configuration of the ion irradiation apparatus is the same as that described with reference to FIG. 3, for example, reference is made thereto. In this embodiment, the ferromagnetic material 80 is
The reflector is mounted so as to surround the outer periphery of the reflector electrode 24. That is, a cylindrical ferromagnetic material 80 having the same shape as that of the cylindrical reflector electrode 24 is attached to the outside of the cylindrical reflector electrode 24. The ferromagnetic material 80 is used for the reflector electrode 2
A hole 82 is provided at a position corresponding to the hole 25 of No. 4. The ferromagnetic material 80 is electrically connected to the reflector electrode 24 and has the same potential as that of the ferromagnetic material 80, and the negative side of the reflector power supply 26 is connected to them. The ferromagnetic material 80 is made of, for example, iron, SUS4
It is made of a ferromagnetic material such as a ferromagnetic stainless steel such as 40A. By providing such a ferromagnetic material 80, the magnetic flux 76 generated from the above-described coil 68 of the plasma shower device 30 is generated near the reflector electrode 24, as schematically shown in FIG. Pass through the ferromagnetic material 80 on the outer periphery. That is, in the vicinity of the hole 25 of the reflector electrode 24, the magnetic flux 76 is directed toward the ferromagnetic material 80 or the reflector electrode 24 inside the ferromagnetic material 80,
It does not reach the vicinity of the ion beam 2 passing through the reflector electrode 24. As a result, electrons such as electrons and other thermoelectrons in the plasma 32 generated by the plasma shower device 30 as described above and introduced into the reflector electrode 24 through the holes 25 are generated by the magnetic flux 76. Guided
The ferromagnetic material 80 or the reflector electrode 24 travels along the magnetic flux 76. At this time, electrons having an energy lower than the potential of the reflector electrode 24 and the ferromagnetic material 80 having the same potential (this is set by the reflector power supply 26) are repelled by the potential and enter the reflector electrode 24 to enter the ion beam. 2, electrons having an energy higher than the potential of the reflector electrode 24 and the ferromagnetic material 80, which are attracted into the reflector electrode 24 and the ferromagnetic material 80, enter the reflector electrode 24 or the ferromagnetic material 80 and are collected by them. You. Accordingly, near the entrance of the reflector electrode 24, only low-energy electrons that are not collected by the reflector electrode 24 and the like are present, and are attracted into the ion beam 2 by the positive potential thereof, and
At the same time, it is incident on the substrate 8 (see FIG. 3) and acts to neutralize the positive charge accompanying the ion beam irradiation on the substrate surface. By the above-described operation, it is possible to prevent electrons of high energy components from being supplied to the ion beam 2 from the plasma shower device 30. As a result, negative charging of the substrate 8 by high-energy electrons can be reliably prevented. As can be seen from the above description, in the apparatus of this embodiment, selection is made based on the potential of the reflector electrode 24 and the ferromagnetic material 80, that is, the output voltage of the reflector power supply 26, and used for neutralizing the ion beam 2. The upper limit of electron energy is determined. Therefore, the output voltage of the reflector power supply 26 is
It is preferable to make it sufficiently small. For example, the output voltage of the reflector power supply 26 is preferably in the range of about 0 to -5 V, and it is preferable to make the output voltage variable from the viewpoint of improving controllability. On the other hand, in the conventional device,
Since the electrons introduced into the reflector electrode 24 are all repelled by the negative potential of the reflector electrode 24, the output voltage of the reflector power supply 26 is -20V to -30 as described above.
It was quite large, about V. As described above, the method of using the output voltage of the reflector power supply 26 is completely different between this embodiment and the conventional example. Further, since the inside of the reflector electrode 24 is magnetically shielded by covering the periphery of the reflector electrode 24 with the ferromagnetic material 80 as described above, an external magnetic field, for example, mass separation of the ion beam 2 can be obtained. The effect of the leakage magnetic field from the analysis electromagnet used can be cut off. As a result, the electrons introduced into the reflector electrode 24 can be prevented from being induced in an undesired direction by an external magnetic field, and the electrons can be more reliably drawn into the ion beam 2. Note that instead of providing the ferromagnetic material 80, the reflector electrode 24 itself may be made of a ferromagnetic material, but this is not preferable for the following reasons. That is, it is not preferable to make the reflector electrode 24 so large that the plasma 32 is supplied from as close to the ion beam 2 passing therethrough as possible. Therefore, the peripheral portion of the ion beam 2 It cannot be said that there is no possibility of hitting for some reason, in which case the reflector electrode 24 is sputtered by the ion beam 2. In consideration of this, the reflector electrode 24 has conventionally been made of aluminum or carbon which has little problem of metal contamination (adhesion of metal impurities) to the substrate 8. This is a non-magnetic material. On the other hand, when the reflector electrode 24 is made of a ferromagnetic material, the ferromagnetic material usually contains iron and chromium. 8 are not easily removed even by washing or the like, and the problem of metal contamination is great. Therefore, it is not preferable to configure the reflector electrode 24 itself with a ferromagnetic material. Although the plasma shower device 30 does not necessarily need to generate plasma in two stages as in the above example, the following effects can be obtained by using the one in the above example. . That is, in the plasma shower device 30, the plasma 60 generated in the first plasma generation container 46 may be thin, and the plasma 60
The dark plasma 32 is generated in the second plasma generation container 64 by utilizing the electrons in the zero, and the dark plasma 32 is generated by the reflector electrode 24.
We are trying to introduce it inside. As a result, the amount of electrons emitted from the filament 54 can be reduced, so that the consumption of the filament 54 can be delayed and its life can be prolonged. Moreover, the first plasma generation vessel 4
6 can be reduced, and the gas 52 leaked from the first plasma generation container 46 into the second plasma generation container 64 is converted into plasma there again. Since the conductance to the gas is sufficiently reduced at 66, the amount of gas leaking into the reflector electrode 24 is very small, and thus the degree of vacuum in the reflector electrode 24, that is, in the passage area of the ion beam 2 is reduced (ie, the gas pressure rises) ) Can be kept very small. As a result, it is possible to prevent the ion beam 2 and gas molecules from colliding with each other and generating neutral particles, thereby preventing a problem such as an injection amount error. As described above, according to the present invention, by providing the ferromagnetic material as described above, the electrons introduced into the reflector electrode by the magnetic flux entering the ferromagnetic material and the potential of the reflector electrode. Can be limited to those having energy smaller than the potential of the reflector electrode, so that electrons of high energy components from the plasma shower device can be prevented from being supplied to the ion beam. As a result, negative charging of the substrate by high-energy electrons can be reliably prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing an example around a plasma shower device in an ion irradiation apparatus according to the present invention. FIG. 2 is a cross-sectional view showing an example around a plasma shower device in a conventional ion irradiation device. FIG. 3 is a longitudinal sectional view showing one example of a conventional ion irradiation apparatus as viewed in a direction P in FIG. 2; [Description of Signs] 2 Ion beam 8 Substrate 10 Holder 24 Reflector electrode 26 Reflector power supply 30 Plasma shower device 68 Coil 76 Magnetic flux 80 Ferromagnetic material

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01J 37/317 H01L 21/265 C23C 14/48

Claims (1)

(1) An ion irradiation apparatus for treating a substrate by applying an ion beam to a substrate on the holder, wherein the ion beam is located upstream of the holder and passes therethrough. A reflector electrode formed of a non-magnetic material and having a hole on a side surface thereof, and a plasma generated by introducing the plasma into the reflector electrode through the hole, and the plasma In an ion irradiation device including a plasma shower device having a coil that generates a magnetic flux along an introduction direction, and a DC reflector power supply for applying a negative voltage to the reflector electrode with reference to the plasma shower device, the reflector electrode has a hole. A ferromagnetic material having a hole at the corresponding position and having the same potential as the reflector electrode is attached so as to surround the outer periphery of the reflector electrode. Ion irradiation apparatus according to claim Rukoto.