JPH04366541A - Ion beam neutralization device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of charge-up owing to the excessive irradiation of an electron shower by switching a connection condition between an emission electrode and an emission power source so as to form an electron shower intermittently, and reduce the negative polarity charging speed of an objective to be ion-irradiated. CONSTITUTION:An ion beam neutralization device is provided with an emission electrode 8, which emits thermoelectrons from a heated filament, and an emission power source 14, which applies positive potential to the emission electrode 8. The emission electrode 8 and the emission power source 14 are connected via emission voltage switching circuit 15 and the like, which is possible to switch a connection condition with an interval in response to the electric potential increasing speed of an objective to be ion-irradiated 10.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an ion beam neutralization device that neutralizes the positive charge generated when an ion beam is irradiated onto an object to be irradiated, such as a wafer, using an electron shower. relates to an ion beam neutralization device that prevents negative charge-up due to excessive electron shower.

0002

[Prior Art] Ion implantation equipment ionizes impurities to be diffused, selectively extracts these impurity ions using mass spectrometry using a magnetic field, accelerates them using an electric field, and irradiates the ion irradiation target. Impurities are injected into the irradiation target. Since this ion implantation apparatus can implant impurities that determine the characteristics of a device in a semiconductor process to an arbitrary amount and depth with good controllability, it has become an important apparatus in the manufacture of current integrated circuits.

By the way, the above-mentioned impurity ions include, for example, boron ions (positive ions) and arsenic ions (positive ions), and these impurity ions are applied to an ion irradiation target made of, for example, a silicon substrate having a polysilicon film. In the case of irradiation, impurities are implanted into the ion irradiation target and the polysilicon film of the ion irradiation target is positively charged. When the potential difference between the positively charged polysilicon film and the silicon substrate exceeds a predetermined value, discharge occurs and a charge-up occurs that destroys the circuit of the device.

[0004] Therefore, in recent years, ion implantation equipment has been equipped with an ion beam neutralization device that prevents charge-up due to positive polarity that occurs during implantation of impurity ions. Conventionally, as shown in FIG. 4, for example, this ion beam neutralization apparatus has a control circuit 55 consisting of a disk current setting circuit 51, a feedback signal generation circuit 52, a differential circuit 53, and a filament current control circuit 54, and a filament power supply 56 whose output current is set by a circuit 55; a filament 57 which generates heat due to the filament current from the filament power supply 56;
It consists of an emission electrode 58 that emits thermoelectrons from the filament 57, and a neutral cup 59 that generates secondary electrons by collision of the thermoelectrons.

The ion beam neutralization device irradiates the object 60 with secondary electrons from the neutral cup 59 in the form of a shower, and the electron shower 62 consisting of the secondary electrons is turned into a positive polarity by the ion beam 61. By neutralizing the charged polysilicon film of the ion irradiation object, charge-up is prevented.

[0006]

[Problems to be Solved by the Invention] However, in the conventional ion beam neutralization apparatus described above, in the case of a mechanical scan type ion implantation apparatus in which the disk 63 is reciprocated and translated at a constant speed, the ion beam 61 is linearly In contrast to the ion irradiation object 60, the electron shower 62 is irradiated onto the ion irradiation object 60 in a planar manner, resulting in the following problems.

That is, as shown in FIG.
When the ion beam 1 is irradiated onto the ion irradiation target 60, the polysilicon film at the irradiated area is positively charged by the ion beam 61. At this time, the ion irradiation target 60 has
An electron shower 62 is irradiated over the entire surface, and this electron shower 62 is applied to the ion irradiation target 60.
As the polysilicon film is translated in the A direction, the positive charge on the polysilicon film is neutralized, and the polysilicon film is further charged to a negative polarity.

[0008] The above-mentioned negative polarity charging will not cause charge-up if the ion beam 61 is irradiated again before reaching the potential difference that causes charge-up. However, in the conventional ion beam neutralization device, as shown in FIG. 4, even when the heating temperature of the filament 57 is controlled by controlling the filament current, the emission electrode 58 emits thermionic electrons, so the electron shower 62 The object 60 to be irradiated with ions is continuously irradiated, and by the time the ion beam 61 is irradiated again, the negative potential difference tends to exceed the potential difference that causes charge-up.

Therefore, an object of the present invention is to provide an ion beam neutralization device that can prevent charge-up due to negative polarity charging by preventing continuous irradiation with the electron shower 62. There is.

0010

[Means for Solving the Problems] In order to solve the above problems, the ion beam neutralization device of the present invention forms an electron shower from thermionic electrons, and generates a positive polarity by irradiating an ion beam onto an object to be irradiated with ions. The electrostatic charge is neutralized by the above-mentioned electron shower, and it has the following characteristics.

That is, this ion beam neutralization apparatus has an emission electrode which is an emission means for emitting the thermoelectrons from a heated filament, and an emission power supply which is an application means which applies a positive potential to the emission means. are doing. The emission means and the application means include a rotation detection sensor whose connection state can be switched at intervals corresponding to the rate of increase in the potential difference of the ion irradiation target;
It is characterized in that they are connected via switching means consisting of a disk rotation speed detection circuit, a counter circuit, a count number setting circuit, and an emission voltage switching circuit.

0012

[Operation] According to the above structure, the hot electrons from the filament that form the electron shower are emitted only when the emission means has a positive potential.
No emission occurs when the emission means does not have a positive potential. Therefore, switching the connection state between the emission means and the application means by the switching means causes the emission means to apply the voltage intermittently, so that an electron shower is also formed intermittently.

[0013] As a result, the speed at which the electron shower charges to a negative polarity is lower than that in the case of continuous electron shower irradiation because of the intermittent irradiation. This decrease in speed is caused by the fact that electron showers are formed intermittently at intervals corresponding to the rate of increase in the potential difference of the ion irradiation target, so the ion beam has to be irradiated again before reaching the potential difference that causes charge-up. As a result, it is possible to prevent charge-up from occurring due to excessive irradiation of electron showers.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

As shown in FIG. 1, the ion beam neutralization apparatus according to this embodiment is mounted on a mechanical scan type ion implantation apparatus in which a disk 13 is reciprocated and translated at a constant speed. This ion beam neutralization device has a control circuit 5 that sets the output current of the filament power supply 6, and the control circuit 5 outputs a disk current setting signal that changes the disk current according to the position of the disk 13. The disk current setting circuit 1 has a disk current setting circuit 1 for controlling the disk current setting circuit 1.

As shown in FIG. 2, the disk current setting circuit 1 has a disk position detection sensor 25, a counter circuit 24, and a DA conversion circuit 23. For example, by converting the integrated value of the number of revolutions of a drive shaft (not shown) that moves the disk 13 1 cm every rotation into an analog voltage output, the position of the disk 13 that is moving back and forth in translation can be specified by the voltage output. ing.

The above-mentioned DA conversion circuit 23 is connected to a function generation circuit 22 to which a beam current signal generation circuit 26 and a disk current setting circuit 27 are connected. 26 is connected to the differential amplifier 21. These circuits 21, 22, 26, and 27 output a disk current setting signal of a voltage output obtained by converting the voltage output from the DA conversion circuit 23 to a desired disk current. .

The disk current setting circuit 1 described above is connected to one input terminal of a differential circuit 3, as shown in FIG. On the other hand, the other input terminal of the differential circuit 3 is connected to a feedback signal generating circuit 2 that outputs a feedback signal based on the disk current caused by the ion beam 11 irradiating the disk 13. , a signal obtained by superimposing a feedback signal on the disk current setting signal is output. The differential circuit 3 is connected to a filament current control circuit 4, and the filament current control circuit 4 outputs a current setting signal corresponding to the signal input from the differential circuit 3. .

The control circuit 5 described above is connected to a filament power supply 6 which outputs a filament current corresponding to the current setting signal. The filament power supply 6 is connected to both ends of a coiled filament 7, for example, and the filament 7 generates heat when a filament current from the filament power supply 6 is applied thereto.

The filament power supply 6 is also connected to an emission power supply 14 that applies a positive potential to the emission electrode 8, and the emission power supply 14 is connected to the emission electrode 8 via an emission voltage switching circuit 15, which will be described later. ing.

The above-mentioned emission electrode 8 is arranged between the filament 7 and the passage path of the ion beam 11, and an emission hole 8a large enough to surround the filament 7 is formed in the center of the emission electrode 8. It is formed. When the emission electrode 8 is connected to the emission power source 14 in a conductive state, a positive potential is applied to the emission electrode 8, and thermionic electrons are emitted from the filament 7 and passed through the emission hole 8a. It looks like this.

A neutral cup 9 formed to surround the path of the ion beam 11 is disposed in the direction of movement of the thermoelectrons that have passed through the emission hole 8a.

This neutral cup 9 is designed to emit secondary electrons upon collision with thermoelectrons, and the emitted secondary electrons are attracted to the flow of the ion beam 11 and move in the flow direction of the ion beam 11. It is supposed to move to .

In the flow direction of the ion beam 11,
An ion irradiation target 10 such as a wafer is provided. The ion irradiation target 10 is made of, for example, a silicon substrate having a polysilicon film, and impurities are implanted by the ion beam 11 irradiation. The ion irradiation target 10 is attached to a disk-shaped disk 13 in units of a plurality of disks, and the disk 13 is configured to reciprocate and translate in the B direction and rotate at a constant speed in the C direction, for example. .

The disk 13 is provided with a rotating shaft 13a connected to rotational driving means such as a servo motor (not shown). A rotation detection sensor 1 is provided near the rotation shaft 13a to detect the rotational state of the rotation shaft 13a.
9 is provided, and this rotation detection sensor 19 outputs a detection pulse signal every rotation of the rotating shaft 13a.

The rotation detection sensor 19 described above is connected to the counter circuit 16 via a disk rotation speed detection circuit 18 that performs noise removal and waveform shaping of the detection pulse signal. Further, a count number setting circuit 17 is also connected to the counter circuit 16, and this count number setting circuit 17 outputs a predetermined set value, such as a binary number 5 or 10, to the counter circuit 16. ing. and,
The counter circuit 16 counts the detection pulse signals inputted through the disk rotation speed detection circuit 18, compares this counted value with the set value from the count number setting circuit 17, and determines that the counted value has reached the set value. It is designed to output a count-up signal at certain times.

The counter circuit 16 described above is connected to the emission voltage switching circuit 15. This emission voltage switching circuit 15 is a
It has a switch part that is in a contact state. The connection state of this switch section is switched between a conductive state and an insulated state by a count-up signal, and when the count-up signal from the counter circuit 16 is input, the emission power source 14 and the emission electrode 8 are connected to each other. It is designed to bring the two into a conductive state. The connection state of the switch section described above is set at intervals corresponding to the rate of increase in the potential difference of the ion irradiation target 10 to the extent that positive charge-up by the ion beam 11 and negative charge-up by the electron shower 12 are not caused. It needs to be switched with .

The operation of the ion beam neutralization apparatus in the above configuration will be explained.

First, specific impurity ions are selectively extracted by mass spectrometry using a magnetic field, and are accelerated by an electric field to form an ion beam 11. On the other hand, the control circuit 5 causes the filament power supply 6 to output a filament current, thereby causing the filament 7 to generate heat. Thereafter, the disk 13 is driven to rotate at a constant speed via the rotating shaft 13a, and is translated back and forth in the B direction. The entire surface will be irradiated with the ion beam 11.

At this time, the rotation detection sensor 19 detects the rotation state of the rotation shaft 13a that rotates the disk 13, and outputs a detection pulse signal every rotation of the rotation shaft 13a. The detection pulse signal is input to the disk rotation speed detection circuit 18, and after being subjected to noise removal, waveform shaping, etc., it is input to the counter circuit 16.

The counter circuit 16 counts the input detection pulse signals and compares the counted value with the set value from the count number setting circuit 17. and,
When the count value and the set value become equal, a count-up signal is output to the emission voltage switching circuit 15. The emission voltage switching circuit 15 to which this count-up signal is input switches the switch section from the insulated state to the conductive state, thereby bringing the emission power source 14 and the emission electrode 8 into the conductive state.

The emission electrode 8 has a positive potential by being brought into conduction with the emission power source 14, and the positive potential at the periphery of the emission hole 8a causes hot electrons to be emitted from the heated filament 7. I will let you do it. Thermionic electrons emitted from the filament 7 pass through the emission hole 8a and reach the opposing neutral cup 9.
The neutral cup 9 emits secondary electrons due to the collision of the thermionic electrons. The secondary electrons then drift within the neutral cup 9 and move with the flow of the ion beam 11, reaching the ion irradiation target 10 as a shower-like electron shower 12.

By the way, as shown in FIG. 3, the ion beam 11 is linearly irradiated onto the ion irradiation object 10, and the polysilicon film at the irradiated area is positively charged by the ion beam 11. . Then, when the electron shower 12 reaches the ion irradiation target 10, the polysilicon film is positively charged with the ion irradiation target 60.
Along with the translational movement in the direction, it will be neutralized, and furthermore, it will be charged to a negative polarity by the supply of secondary electrons from the electron shower 12.

At this time, the above electron shower 12
Thermionic electrons from the filament 7 that generate the are emitted only when the emission electrode 8 has a positive potential, and are not emitted when the emission electrode 8 does not have a positive potential. Therefore, the electron shower 12 is intermittently irradiated onto the ion irradiation target 10 at a rate of once per rotational speed of the disk 13 which is equal to the set value of the count number setting circuit 17 .

[0035] As a result, the speed of neutralization and negative charging due to translational movement in the A direction is lower than when the electron shower 12 is continuously irradiated, and this decrease in speed is caused by Since it is possible to irradiate the ion beam 11 again and charge it to a positive polarity before reaching the potential difference that causes charge-up, it is possible to prevent charge-up from occurring due to excessive irradiation of the electron shower 12. It has become.

In this embodiment, the occurrence or non-occurrence of the electron shower 12 is controlled based on the rotational speed of the rotating shaft 13a, but the present invention is not limited to this. That is, the electron shower 12 is applied intermittently at intervals corresponding to the rate of increase in the potential difference of the ion irradiation target 10 to the extent that positive charge-up by the ion beam 11 and negative charge-up by the electron shower 12 are not caused. As long as it is controlled, it may be controlled based on time, for example, or it may be controlled based on a charge amount detection sensor capable of detecting the charge amount of the object 10 to be ion irradiated.

[0037]

Effects of the Invention As described above, the ion beam neutralization device of the present invention forms an electron shower from thermionic electrons, and uses the electron shower to positively charge an object to be irradiated with the ion beam. The emission means for emitting the thermoelectrons from the heated filament and the application means for applying a positive potential to the emission means are arranged at intervals corresponding to the rate of increase in the potential difference of the object to be ion irradiated. The configuration is such that they are connected via switching means that can switch the connection state.

[0038] As a result, the switching of the connection state between the emission means and the application means by the switching means causes the emission means to be applied intermittently, so that an electron shower is intermittently formed. This has the effect of reducing the charging speed and preventing the occurrence of charge-up due to excessive irradiation of electron showers.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an ion beam neutralization apparatus of the present invention.

FIG. 2 is a block diagram of a disk current setting circuit.

FIG. 3 is an explanatory diagram showing the state of potential difference of an object to be irradiated with ions.

FIG. 4 shows a conventional example, and is a block diagram of an ion beam neutralization device.

FIG. 5 is an explanatory diagram showing the state of potential difference of an object to be irradiated with ions.

[Explanation of symbols]

1 Disk current setting circuit 2 Feedback signal generation circuit 3 Differential circuit 4 Filament current control circuit 5 Control circuit 6 Filament power supply 7 Filament 8 Emission electrode (emission means) 8a
Emission hole 9 Neutral cup 10 Ion irradiation object 11 Ion beam 12 Electron shower 13 Disk 13a Rotating shaft 14 Emission power supply 15 Emission voltage switching circuit (switching means)

Claims (1)

[Claims] [Claim 1] An ion beam neutralization device that forms an electron shower from thermionic electrons and neutralizes a positive charge caused by ion beam irradiation on an ion irradiation target by the electron shower. It has an emission means for emitting the thermionic electrons, and an application means for applying a positive potential to the emission means, and the emission means and the application means are connected at an interval corresponding to the rate of increase in the potential difference of the object to be irradiated with ions. An ion beam neutralization device characterized in that the ion beam neutralization device is connected via a switching means that can switch states.