JPH0527955U - Ion implanter - Google Patents

Abstract

(57) [Summary] [Purpose] The main purpose is to simplify the structure of the gate power supply and thereby reduce the cost of the gate power supply. [Structure] The gate power source 32 is configured by connecting a circuit in which a transistor 34 and a resistor 36 are connected in series and a capacitor 38 is connected in parallel to the resistor 36 to the emission power source 20 in parallel. And this transistor 3
The connection 40 between the resistor 4 and the resistor 36 is connected to the gate 14 and the transistor 34 is controlled by the control circuit 24.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an ion implantation apparatus provided with a neutralizing means for supplying electrons to a substrate to be ion-implanted to prevent charging (charge-up) of a substrate accompanying ion implantation.

[0002]

[Background technology]

 The same applicant has separately proposed an ion implanter of this type, which can control the holder current flowing through the holder with good response and has a long filament life. One example thereof will be described with reference to FIG.

This ion implantation apparatus is basically configured to irradiate the substrate 8 held by the holder 7 with the ion beam 2 in the vacuum container 4 to perform ion implantation.

In addition, a Faraday case 6 is provided from the periphery of the holder 7 to the upstream side, and this and the holder 7 via a holder current measuring resistor 22, which is an example of the holder current measuring device, are electrically connected in parallel to each other. It is connected to the beam current measuring device 30 so that the beam current Ib of the ion beam 2 can be accurately measured.

On the other hand, in order to prevent the surface of the substrate 8 from being positively charged due to the irradiation of the ion beam 2 and causing a defect such as discharge, the following neutralizing means is provided. .. That is, the filament 10 is provided on the side of the Faraday case 6, and the primary electron 11 emitted from this is applied to the inner wall of the Faraday case 6 in this example to emit the secondary electron 12 therefrom, and the secondary electron 12 is emitted. Is supplied to the substrate 8 to neutralize the positive charge due to the ion beam 2. The filament 10 has a box shape in this example, and is surrounded by a gate 14 having an opening 14 a along the filament 10 inside the Faraday case 6. 16 is an insulator.

A filament power source 18 for heating the filament 10 is connected between both ends of the filament 10. Between the filament 10 and the Faraday case 6, a direct-current emission power source 20 for extracting primary electrons 11 from the filament 10 is connected with the filament 10 on the negative side. Further, as a characteristic of this prior art example, a direct current voltage variable gate power supply 32 is connected between the gate 14 and the Faraday case 6 with the former on the negative side. The relationship between the potential Ee of the filament 10, the potential Eg of the gate 14 and the potential Ef of the Faraday case 6 is such that Ee <Eg <Ef as shown in FIG.

Further, in this example, a positive bias voltage is applied to the holder 7 or the like between the holder 7 or the like and the beam current measuring device 30 to efficiently guide the secondary electrons 12 to the substrate 8 on the holder 7. The holder bias voltage 26 of and the Faraday bias voltage 28 for giving a positive bias voltage to the Faraday case 6 to prevent the secondary electrons 12 from escaping are inserted in series. It may be omitted.

At the time of ion implantation into the substrate 8, the holder current Ih (= Ib −) is generated in the holder current measuring resistor 22 by combining the beam current Ib by the ion beam 2 and the secondary electron current I ₂ by the secondary electron 12. I ₂ ) flows, but this is taken into the control circuit 24, and by controlling the gate power supply 32 by this control circuit 24 to change its output voltage Vg, the primary voltage emitted from the filament 10 is as follows. By controlling the amount of the electrons 11 and thus the amount of the secondary electrons 12, the holder current Ih is controlled to a desired constant value (usually a value close to 0) to prevent the substrate 8 from being charged. There is.

That is, conventionally, the filament current was controlled to control the amount of the primary electrons 11, but this has problems such as poor responsiveness and a short life of the filament 10. In order to solve the problem, in this prior art example, the gate power supply 32 is provided to control the output voltage Vg.

The amount of primary electrons 11 emitted from the filament 10 is determined by the difference between the gate potential Eg and the filament potential Ee in the space charge limited region, and is expressed as follows by the primary electron current I ₁ . K is a constant. I ₁ = K ・ (Eg −Ee) ^3/2

Therefore, even if the filament current is kept constant by changing the output voltage Vg of the gate power supply 32 and controlling the gate potential Eg, the amount of the primary electrons 11 emitted from the filament 10 is reduced. As a result, the amount of secondary electrons 12 can be controlled. Moreover, since this control is based on the electric field, the response is much better than the conventional control based on the filament current.

The primary electrons 11 emitted as described above are further accelerated by the electric field between the gate 14 and the Faraday case 6 (that is, by the difference between the Faraday case potential Ef and the gate potential Eg) (that is, 2). It collides with the Faraday case 6 (accelerated by one step), and secondary electrons 12 are emitted from it. The secondary electrons 12 can prevent the substrate 8 from being charged by the ion beam 2, and in this example, the holder current Ih can be controlled with good responsiveness by controlling the output voltage Vg of the gate power supply 32. It is possible to effectively prevent the substrate 8 from being charged. Further, since it is sufficient to keep the filament current constant, the life of the filament 10 becomes longer than in the case where the filament current is controlled as in the conventional example.

In addition, in the above-described prior art, since the energy distribution of the secondary electrons 12 does not change even if the amount of the primary electrons 11 is changed, a condition that prevents the substrate 8 from being charged most effectively. Has a merit that it is easy to determine, and a sufficient amount of primary electrons can be taken out even if the structure is simple compared to the one in which primary electrons are accelerated and then decelerated.

[0014]

[The purpose of the device]

 However, the ion implanter requires an extra gate power source 32, and if the gate power source 32 is composed of an ordinary power source, the cost is high and there is room for improvement.

Therefore, the main object of the present invention is to simplify the configuration of the gate power supply and thereby reduce the cost of the gate power supply.

[0016]

[Means for achieving the purpose]

 In order to achieve the above object, the ion implanter of the present invention is configured by connecting the gate power source with a circuit in which a transistor and a resistor are connected in series and a capacitor is connected in parallel with the resistor and the emission power source is connected in parallel. The connection between the transistor and the resistor is connected to the gate, and the transistor is controlled by the control circuit.

[0017]

[Action]

 According to the above configuration, the output voltage of the emission power supply can be divided by the transistor and the resistor, and this can be applied to the gate as the output voltage of the gate power supply. However, the output voltage of the gate power supply can be continuously changed by controlling the transistor by the control circuit.

[0018]

【Example】

 FIG. 1 is a diagram showing an ion implantation apparatus according to an embodiment of the present invention. The same or corresponding parts as those in the previous example of FIG.

In this embodiment, the gate power source 32 described above is connected in parallel to the emission power source 20 described above with a circuit in which a transistor 34 and a resistor 36 are connected in series and a capacitor 38 is connected in parallel to the resistor 36. It consists of. The connecting portion 40 between the transistor 34 (more specifically, the emitter thereof) and the resistor 36 serves as an output portion, and the connecting portion 40 is connected to the gate 14 described above. Further, the control signal from the above-mentioned control circuit 24 is given to the base of the transistor 34 so that the control circuit 24 controls the transistor 34.

According to the above configuration, the output voltage Ve of the emission power supply 20 can be divided by the transistor 34 and the resistor 36 and applied to the gate 14 as the output voltage Vg of the gate power supply 32. In addition, the output voltage Vg can be continuously changed by controlling the transistor 34 by the control circuit 24, which allows the emission amount of the primary electrons 11 and thus the emission amount of the secondary electrons 12 to be desired. Can be controlled.

According to the above, the gate power supply 32 can be configured by the three parts of the transistor 34, the resistor 36, and the capacitor 38. Therefore, the configuration of the gate power supply 32 is extremely simple, and The cost of the gate power supply 32 can be reduced.

By the way, the reason why the capacitor 38 is connected in parallel to the resistor 36 is as follows. That is, since the ion beam 2 with which the substrate 8 is irradiated is scanned by a scanning device (not shown) and is overscanned (scanned to the outside of the holder 7) to a certain extent, the beam current Ib flowing through the beam current measuring device 30 or the like. Has a trapezoidal wave shape of, for example, about 500 Hz. It is confirmed by experiments that a part of the trapezoidal wave current Ib passes through the gate power supply 32, although the reason is not clear. When the gate power supply 32 is an ordinary power supply device, its internal resistance is sufficiently low so that there is no problem even if a part of the trapezoidal wave current as described above passes through the gate power supply 32. If the transistor is composed of only the transistor 34 and the resistor 36, the value of the resistor 36 is, for example, about 20 KΩ, so that the internal resistance of the gate power source 32 is too large and the beam current passing therethrough is distorted, so that the beam current measuring unit Alternatively, a beautiful trapezoidal wave of the beam current Ib cannot be observed with an oscilloscope or the like instead, and it becomes difficult to confirm the overscan of the ion beam 2 and the like. On the other hand, if a capacitor 38 (whose value is, for example, about 1 μF) is connected in parallel to the resistor 36 as in this example, the impedance of the AC component of the gate power supply 32 can be lowered by this capacitor 38. Therefore, the above problems will not occur.

The transistor 34 and the resistor 36 and the capacitor 38 are turned upside down so that the transistor 34 is placed on the negative side of the emission power source 20 and the resistor 36 and the capacitor 38 are placed on the positive side of the emission power source 20. You may come. Further, an FET may be used instead of the transistor 34.

[0024]

[Effect of the device]

 As described above, according to the present invention, the structure of the gate power supply is extremely simple, and the cost of the gate power supply can be reduced.

In addition to the above, in comparison with the conventional example in which the filament current is controlled, the following effects can be obtained as in the case of the above-mentioned prior example. That is, according to this invention, it is possible to control the holder current flowing in the holder to a predetermined value with good responsiveness, thereby effectively preventing the electrification of the substrate even when the beam current fluctuates. it can. However, since it is sufficient to keep the filament current constant, the life of the filament becomes longer than in the case of controlling the filament current as in the conventional example. Moreover, even if the amount of primary electrons is controlled, its energy is constant, and the energy distribution of secondary electrons is also constant, which makes it easier to determine the conditions that prevent the charging of the substrate most effectively. Furthermore, since the present invention has a structure in which primary electrons are accelerated in two stages, a sufficient amount of primary electrons can be extracted even if the structure is simple as compared with a structure in which primary electrons are accelerated and then decelerated.

[Brief description of drawings]

FIG. 1 is a diagram showing an ion implantation apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of an ion implantation apparatus which is the background of the present invention.

FIG. 3 is a diagram showing an example of a relationship of electric potentials of a filament, a gate, and a Faraday case in FIG.

[Explanation of symbols]

 2 Ion beam 6 Faraday case 7 Holder 8 Substrate 10 Filament 11 Primary electron 12 Secondary electron 14 Gate 18 Filament power supply 20 Emission power supply 22 Holder current measuring resistance 24 Control circuit 32 Gate power supply 34 Transistor 36 Resistance 38 Capacitor

Claims (1)

[Scope of utility model registration request] 1. An ion implanter in which primary electrons emitted from a filament are applied to a Faraday case to emit secondary electrons, and the secondary electrons are supplied to a substrate to be ion-implanted on a holder. A filament power supply for heating the filament, a direct current emission power supply connected between the filament and the Faraday case with the former on the negative side, and a gate surrounding the filament and having an opening inside the Faraday case. , A DC voltage variable gate power supply connected between the gate and the Faraday case with the former on the negative side, a holder current measuring device that measures the holder current flowing in the holder, and a holder current measuring device. And a control circuit for controlling the voltage output from the gate power supply so that the holder current has a predetermined value. In, the gate power supply,
A circuit in which a transistor and a resistor are connected in series and a capacitor is connected in parallel to the resistor is configured to be connected in parallel to the emission power source, and the connection between the transistor and the resistor is connected to the gate, and the transistor is connected. Is controlled by the control circuit.