JPH0388249A - Ion implantation device - Google Patents

Abstract

PURPOSE:To obtain a stable acceleration potential without forming an insulation film on a counter metal electrode for generating secondary electrons by providing an electron shower chamber parted by a partition wall to be separate from an ion implantation chamber. CONSTITUTION:An ion implantation chamber 26 encloses secondary electrons generated when ions are implanted to the surface of a semiconductor wafer 20 to prevent them from leaking out. In this case, an electron generation source for electron shower is not provided in the ion implantation chamber 26, but an electron shower chamber 27 is provided at a rotation angle position apart form the ion implantation chamber. Electron shower is this achieved at a different timing from ion implantation for each time of ion implantation, so the potential in the surface of a semiconductor wafer 20 is decreased because an accumulated positive charge is neutralized at each ion implantation. Formation of an insulation film on a counter metal electrode for emitting secondary electrons in the electron shower chamber 27 is thus prevented, thereby stable and correct electron shower can be achieved.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an ion implantation device, and particularly to a charge-up prevention device.

[Conventional technology]

Ion implanters ionize impurities, accelerate the ions to high energy, and implant them into a semiconductor substrate, such as a semiconductor wafer. In this case, there are two types of ion implantation devices: a medium current type whose ion beam current is 2 mA or less, and a high current type whose ion beam current is 2 mA or more.
The ions extracted from the ion source are given a portion of the necessary energy by the accelerating tube, then enter the mass analyzer, where only ions with the desired mass are selected. After energy is added to the selected ions by an acceleration tube, the ions enter an ion implantation chamber and are implanted into a semiconductor wafer on a disk, which is a rotary mounting table for the semiconductor wafer. By the way, when ions are implanted into a semiconductor wafer in this way, the insulating layer on the surface of the wafer is charged (charged up) with ion charges (positive charges) in the state of surface charge, and this surface charge causes the wafer to become There is a risk that the insulating layer will be destroyed. For this reason, conventionally, in the ion implantation chamber, at the same time as ion implantation, the wafer is irradiated with electrons called an electron shower to neutralize the positive charges and prevent charge-up. . In other words, this electron shower generates hot electrons from the filament, causes these hot electrons to collide against the metal electrode (wall surface of the ion implantation chamber) facing the filament, and generates secondary electrons. is applied to the wafer to neutralize its surface charge. In this case, the amount of secondary electrons generated is as follows:
This corresponds to the accelerating voltage, which is the potential difference with the opposing metal electrode for secondary electron emission, and is determined according to the amount of ion beam current.

[Problem to be solved by the invention]

By the way, this electron shower is ineffective if the amount of secondary electrons irradiated to the semiconductor wafer is small, and if it is large, the insulating layer will be destroyed by discharge due to the electrons. However, conventionally, the insulating film on the surface of the semiconductor chip is sputtered by the ion beam into droplets, which adhere to the wall of the ion implantation chamber to form the insulating film. Therefore, charges accumulate on the wall surface of this ion implantation chamber, and the potential of the opposing metal electrode changes. In this way, when the potential of the opposing metal electrode changes, 2
When the amount of secondary electrons changes and the amount of secondary electrons increases,
This time, there was a drawback that the insulating layer was destroyed by discharge due to electrons. An object of the present invention is to provide an ion implantation device that improves the above-mentioned drawbacks.

[Means to solve the problem]

The present invention provides an apparatus for injecting ionized impurities into an object to be processed while scanning the ions over the object to be processed, which is placed on a mounting table. An ion implantation chamber is provided so that the ion implantation chamber is installed at a location different from the installation location of the ion implantation chamber, and is separated from the ion implantation chamber by a partition wall to neutralize the charge accumulated on the object to be processed. It is characterized by the provision of an electron shower room.

[Effect]

In the ion implantation apparatus according to the present invention configured as described above, the electron shower chamber is separated from the ion implantation chamber by a partition and is provided separately, so that the opposing metal electrode for secondary electron generation is provided with an insulating film. There is no such thing as formation, and a stable acceleration potential can be obtained. Therefore, neutralization of charges accumulated on the object to be processed can be achieved as initially.

【Example】

An embodiment of an ion implantation apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of an ion implantation apparatus according to the present invention, and in the figure, 21 is a semiconductor wafer 20.
It is a disk that is a rotating mounting table. FIG. 2 is a front view of this disk 21 viewed from the direction of ion entry. That is, the disk 21 has a disk-like shape, and a plurality of, for example, eight, semiconductor wafer holders 23 are provided at equal positions in the radial direction from the center on the ion-implanted surface of the disk 21.
The semiconductor wafer holding parts 2 are arranged at equal angular intervals.
3 respectively hold and fix disk-shaped semiconductor wafers 20 into which ions are to be implanted. The disk 21 is rotated about its central axis 17 by a spin motor 22 at a high rotational speed, for example, 11,000 rpm, as shown by an arrow 18. Further, as shown by a single arrow, the disk 21 is linearly moved, for example, vertically in a reciprocating manner by a scan motor 13, so that the ion beam scans the surface of the semiconductor wafer. Therefore, the ion beam is applied to eight semiconductor wafers 2
0 and the entire surface of each semiconductor wafer 20 is irradiated almost uniformly. Then, at a predetermined rotational angle position of the disk 21, a holder 23 is placed so as to face the semiconductor wafer 20.
An ion implantation chamber 26 is provided. This ion implantation chamber 26
is made of a metal hollow cylinder, through which an accelerated ion beam 24 passes, and the surface of the semiconductor wafer is irradiated with the ion beam 24. That is, as shown in FIG. 3, the ions 11 extracted from the ion source 12 are given a part of the necessary energy by the accelerator tube 13, and then enter the mass analyzer 14 to obtain the desired mass. Only ions are selected. After energy is added to the selected ions 11 by the acceleration tube 15, they enter the ion implantation chamber 26 and are implanted into the semiconductor wafer on the disk 21, which is a rotary mounting table for the semiconductor wafer. The ion implantation chamber 26 is for confining secondary electrons generated when ions are implanted into the surface of the semiconductor wafer 20 so that they do not flow out. That is, if the secondary electrons flow to the outside, the potential changes when measuring the amount of ion implantation, making it impossible to accurately measure the amount of implanted ions. In this case, the ion implantation chamber 26 is not provided with an electron generation source for the electron shower, and the electron shower is performed at a separate location. That is, as shown in FIG.
Electron shower chambers 27 are provided at positions spaced apart by degrees. Further, at a position preceding the position of the electron shower chamber 27 in the rotational direction, a semiconductor wafer 2 is placed for monitoring the amount of charge accumulated on the surface of the semiconductor wafer 20.
A conductive plate (so-called Q
A monitor 28 is provided, and a charge amount detection circuit 29 detects the amount of charge on the surface of the semiconductor chip 20. The electron shower room 27 is configured as shown in FIG. 4, for example. That is, like the ion implantation chamber 26, the electron shower chamber 27 is made of metal such as aluminum and has a cylindrical shape. A filament 31 made of, for example, tungsten, serves as a primary electron emitting electrode.
A counter metal electrode 32 is provided opposite to. Since the filament chamber 27 is made of metal, for example aluminum, as described above, the wall surface of the opposing metal electrode 32 can be used as is. Then, a voltage E1 is applied to both ends of the filament 31. In addition, the potential of the filament 31 is set to a voltage E2 with respect to the wall of the electron shower chamber 27 (opposed metal electrode 32).
Keep it as low as possible. Furthermore, the opposing metal electrode 3
2, a bias voltage E3 is applied from a variable bias voltage supply source 33. Then, the detection output from the charge amount detection circuit 29 is supplied to the controller 34, and the variable bias voltage supply source 33 is controlled by the output of this controller 34, and the voltage E
3 is controlled. In the above configuration, the filament 31 has a voltage E
1 generates heat, which generates thermal electrons (primary electrons e+). The primary electrons el are extracted from the filament 31 at a speed corresponding to an accelerating voltage (for example, 300 V), which is the potential difference between the filament 31, which is the primary electron emitting electrode, and the wall surface of the opposing metal electrode 32, and electrode 32
Collision with the wall. Then, secondary electrons e2 are emitted from the wall surface of the opposing metal electrode 32. The emitted secondary electrons e2 enter the semiconductor wafer 20 and act to neutralize its surface charge. In this case, by controlling the polarity and magnitude of the voltage applied from the variable bias voltage supply source 33 to the opposing metal electrode 32, the acceleration voltage for the primary electrons can be controlled. Energy can be controlled. Therefore, in this example, the detection output of the amount of charge on the surface of the wafer 20 from the charge amount detection circuit 29 is supplied to the controller 34. The controller 34 controls the voltage E3 of the variable bias voltage supply source 33 according to the amount of charge on the surface of the semiconductor wafer 20, and uses the value necessary for neutralizing the amount of charge on the surface of the semiconductor wafer 20. Na2
Set the value so that the next electron e2 can be obtained. That is, when the amount of positive charge on the surface of the semiconductor wafer 20 is large, the voltage E3 of the variable bias voltage supply source 33 is increased in accordance with a control signal from the controller 34 so as to increase the acceleration voltage, and the semiconductor wafer 20 is drawn out from the filament 31. Control is performed to increase the amount of primary electrons and increase the energy of secondary electrons emitted from the wall surface of the opposing metal electrode 32. Further, when the amount of positive charge on the surface of the semiconductor wafer X20 becomes smaller than before, the voltage E3 of the variable bias voltage supply source 33 is controlled by a control signal from the controller 34 to lower the acceleration voltage. This reduces the amount of primary electrons extracted from the filament 31,
The energy of the secondary electrons emitted from the wall surface of the opposing metal electrode 32 is controlled to be lowered. In this case, unlike the conventional method, positive charges accumulated on the surface of the semiconductor wafer 20 are neutralized at a time different from the ion implantation. The potential change due to positive charge on the surface of the semiconductor wafer 20 during ion implantation is as shown in FIG. 5 unless electron shower is performed, and the number of implantations (corresponding to the number of rotations of the disk 21) is 1. It has been confirmed that the potential is not high enough to cause dielectric breakdown in ~2 injections, and that as the number of injections increases, the surface potential of the wafer 20 increases, making dielectric breakdown more likely to occur. On the other hand, in the case of the present invention, since an electron shower is performed for each ion implantation, the potential of the surface of the semiconductor wafer 20 is as shown in FIG.
With each ion implantation, the positive accumulated charge is neutralized and reduced. Therefore, the surface potential of the semiconductor wafer 20 does not become high enough to cause dielectric breakdown, and dielectric breakdown of the insulating film on the surface of the semiconductor wafer 20 can be reliably prevented. As described above, according to the present invention, positive charges on the surface of the semiconductor wafer 20 are transferred to the electron shower chamber 27.
is reliably neutralized and no dielectric breakdown occurs. Then, on the wall of the ion implantation chamber 26, as in the past,
Splashes generated when the insulating film on the surface of the semiconductor wafer is sputtered by ions may adhere and form an insulating film, but they are not scattered outside the ion implantation chamber 26 . Meanwhile, in the electron shower room 27,
Since only the electron shower is performed, an insulating film is not formed on the counter metal electrode 32, which is the secondary electron emission electrode. Therefore, the potential of the opposing metal electrode 32 does not change with the voltage applied from the variable bias voltage supply source 33, and can be accurately controlled by the controller 34. It goes without saying that the arrangement position of the electron shower chamber 27 is not limited to the above example as long as it is at a rotational angle position different from that of the ion implantation chamber 26.

【Effect of the invention】

As explained above, according to the present invention, the electron shower chamber is provided separately from the ion implantation chamber to neutralize the charges accumulated on the surface of the semiconductor wafer. An insulating film does not adhere to the opposing metal electrode that emits electrons, allowing stable and accurate electron showering.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of the main part of the ion implantation apparatus according to the present invention, FIG. 2 is a diagram showing an example of the configuration of the negative part thereof, and FIG. FIG. 4 is a diagram showing an example of the configuration of an electron shower chamber, and FIGS. 5 and 6 are characteristic diagrams showing the relationship between the number of ion implantations and the surface potential of a semiconductor wafer. . 20; semiconductor wafer 21; disk 26 as a rotating mounting table; ion implantation chamber 27; electron shower chamber 29; charge amount detection circuit 31; filament 32; opposing metal electrode 33; variable bias voltage supply source

Claims (1)

[Scope of Claims] An apparatus for implanting ionized impurities into an object to be processed while scanning ions onto the object placed on a mounting table, wherein the object to be processed is placed at a predetermined position on the mounting table. An ion implantation chamber is provided opposite to the ion implantation chamber, and the ion implantation chamber is located at a different location from the installation position of the ion implantation chamber,
An ion implantation apparatus characterized in that an electron shower chamber for neutralizing charges accumulated on the object to be processed is provided separated from the ion implantation chamber by a partition wall.