JPH0636739A - Ion implanter - Google Patents

Abstract

PURPOSE:To prevent the dielectric breakdown of an object to be processed by the accumulation of positive charges due to ion implantation. CONSTITUTION:A plasma generation section 5 is provided near a rotary disk 3 mounted with a wafer W, and positive charges on the surface of the wafer W are neutralized by electrons in plasma. A current detection section 7 is provided between a plasma generation chamber 51 and the earth, and a controller 8 outputs the closing command of a beam gate 4 when the current detected value of the current detection section 7 becomes lower than the preset value. The current detected value is the preset magnitude when electrons are normally extracted from the plasma generation section 5, however the current detected value becomes low and the beam gate 4 is closed when no electron is extracted due to the plugging of an plasma outlet 50. The similar function may be provided by detecting the current flowing from the rotary disk 3 to the earth.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an ion implanter.

[0002]

2. Description of the Related Art The ion implantation technique is a method of accelerating impurity ions generated in an ion source in a high electric field and mechanically introducing impurities into a semiconductor wafer by utilizing the kinetic energy thereof. This is a very effective method in that the total amount of the impurities thus removed can be accurately measured as the charge amount.

Conventionally, such ion implantation is performed by, for example, FIG.
It is performed using the device shown in. That is, gas or solid vapor is turned into plasma in the ion source 9, positive ions in this plasma are extracted with a constant energy by the extraction electrode 91, and then mass analysis is performed on the ion beam by the mass analyzer 92. The desired ions are separated, and further the separation slit 93 completely separates the ions. Then, after accelerating the separated ion beam of desired ions to the final energy through the accelerating tube 94, the wafer W arranged on the rotating disk 95 driven by the motor 96 is irradiated with the desired beam, and thus the surface of the wafer W is desired. Introduce impurities.

Reference numeral 97 is a Faraday cup for confining secondary electrons generated when ions are implanted on the surface of the wafer so as not to flow out to accurately measure the amount of ion implantation. .

By the way, when the wafer W is irradiated with an ion beam, positive charges of ions are accumulated in the insulating film exposed on the surface of the wafer W, and when the charge amount exceeds the dielectric breakdown charge amount, the insulating film is destroyed. The device becomes defective.

Therefore, conventionally, as shown in FIG. 6, a plasma generator 98 is provided near the wafer W at a position facing the ion beam, and electrons in the plasma generated by the plasma generator 98 are generated in the plasma generator 98. The potential gradient between the wafer W and the wafer W attracts it to the surface of the wafer W to neutralize the positive charges on the surface of the wafer W, thereby suppressing the amount of the insulating film accumulated on the wafer W to be small.

[0007]

By the way, the plasma generating part 98 has a filament 98b made of tungsten in a plasma generating chamber 98a made of, for example, molybdenum.
Is provided, and the filament 98b is heated to collide the thermoelectrons with argon gas or the like to generate plasma. In the plasma generation chamber 98a, vapor of the filament 98b and plasma generation chamber 98 by plasma are generated.
There is a small amount of sputtered particles on the inner wall of a.

On the other hand, if the plasma outlet of the plasma generating chamber 98a is made too large, the degree of vacuum in the Faraday cup 97 is lowered, and therefore it is very small, for example, about 1 mm.
Therefore, the vapor of the filament 98b and the sputtered particles may adhere to and deposit on the wall surface surrounding the plasma outlet, thereby blocking the plasma outlet. However, if the plasma outlet is blocked, the electrons that should neutralize the positive charges on the surface of the wafer W are not sufficiently extracted or not extracted at all, and the positive charges are accumulated on the surface of the wafer W by the irradiation of the ion beam. There is a problem that the amount becomes too large and the insulating film on the surface of the wafer W is destroyed and the device characteristics are impaired.

The present invention has been made under such circumstances, and an object thereof is to provide an ion implantation apparatus capable of reliably preventing dielectric breakdown of an object to be processed due to ion implantation. is there.

[0010]

According to a first aspect of the present invention, a plasma generating section is arranged in the vicinity of an object to which ions are injected by irradiation of an ion beam, and electrons in plasma generated in the plasma generating section are generated. In an ion implantation apparatus that is attracted to the surface of the object to be processed and neutralizes the positive charges on the surface of the object to be processed, current detection for detecting a current flowing between the plasma generating section and ground It is characterized by having a section.

According to a second aspect of the present invention, in the ion implantation apparatus according to the first aspect, the current detection value of the current detection unit is compared with a preset set value, and when the detected current value deviates from the set value, the object to be processed is processed. A control unit for prohibiting the irradiation of the body with the ion beam is provided.

[0012]

When the ion beam is irradiated onto the object to be processed and positive charges are accumulated on the surface of the object to be processed, the electrons in the plasma generated in the plasma generating part are attracted to the positive charges and the positive charges are generated. Neutralize. At this time, the electrons flow from the ground to the plasma generation portion as much as the electrons are extracted from the plasma generation portion to the surface of the object. Therefore, for example, when the plasma outlet of the plasma generation unit is clogged and the electrons are not sufficiently neutralized, the current detection value of the current detection unit becomes low, and the ion beam irradiation is performed, for example, when the current detection value becomes less than a set value. It is possible to prevent the dielectric breakdown of the object to be processed by prohibiting.

If the electrons are not sufficiently neutralized, the current flowing from the mounting table to the ground becomes large.
The same effect can be obtained by providing a current detector between the mounting table and the ground.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram showing the entire ion implantation apparatus according to an embodiment of the present invention. The entire apparatus will be briefly described with reference to the same figure. In the figure, reference numeral 1 is an ion source for converting gas sublimated from a solid raw material in a vaporizer 11 into plasma, and the ions in the plasma are extracted electrodes. An ion beam is extracted to the outside by an extraction voltage applied between 12 and the main body of the ion source 1. A mass spectrometer 14 is arranged on the downstream side of the extraction electrode 12 via a slit portion 13, where only desired ions are taken out, and then the slit portion 1 is provided.
Entering into the accelerating tube 16 via 5. The ion is the acceleration tube 1
After being accelerated by the accelerating voltage at 6, the wafer is passed through the Faraday cup 2 and injected into the object to be processed, for example, the semiconductor wafer W, which is placed and held on the rotating disk 3 made of conductive aluminum, which is rotated by the motor 31. To be done.

The Faraday cup 2 is "prior art".
As mentioned in the section above, the purpose is to confine secondary electrons generated during ion implantation so that they do not flow out, and to accurately measure the amount of ion implantation.
A beam gate 4 for irradiating or blocking the ion beam to the wafer W by opening and closing the path of the ion beam by the gate driving unit 41 is provided between the and the acceleration tube 16. Further, on the outside of the Faraday cup 2, a plasma generating section 5 is arranged to neutralize charges on the surface of the wafer W.

Next, the main part of the embodiment of the present invention will be described in detail with reference to FIGS. In order to prevent secondary electrons from jumping out of the Faraday cup 2, a suppress electrode 61 is provided along the path of the ion beam IB of the Faraday cup 2 in order to prevent secondary electrons from jumping out of the Faraday cup 2. This suppress electrode 61 is arranged.
, A voltage of −1000 V, for example, is applied by the DC power supply unit 62.

The plasma generating unit 5 is constructed by providing a filament 52 made of, for example, tungsten in a plasma generating chamber 51 made of, for example, carbon or molybdenum, and the plasma generating chamber 51 is provided with a discharge gas from a gas supply source (not shown). For example, a gas supply pipe (not shown) for introducing argon gas is connected. A plasma outlet 50 is provided on the Faraday cup 2 side of the plasma generation chamber 51.
The opening 20 is formed in the tube wall portion of the Faraday cup 2 facing the plasma outlet 50 so that the plasma can flow into the Faraday cup 2. The side surface of the plasma generating chamber 51 is surrounded by a frame portion 21 made of, for example, aluminum having a cooling water passage (not shown), and the plasma generating chamber 51 is made to flow through the cooling water passage. Is cooled. The plasma generation chamber 51 and the frame portion 21 are insulated from the Faraday cup 2 by the insulating layer 22. A DC power supply 53 for applying a filament voltage is connected between both ends of the filament 52, and between the filament 42 and the wall of the plasma generation chamber 51,
A DC power supply unit 54 for applying a discharge voltage is connected.

Between the wall of the plasma generating chamber 51 and the connection point A of the DC power supply 54 for the discharge voltage and the ground,
A current detection unit 7 is provided to detect the amount of electrons flowing from the ground to the plasma generation unit 5, that is, the amount of current flowing from the plasma generation unit 5 to the ground, and between the current detection unit 7 and the ground. Is provided with a dose counter 71 for detecting the dose of ions to the wafer W.

The Faraday cup 2, the rotating disk 3, and the positive electrode side of the DC power source 63 are electrically connected to the input end side (current detecting section 7 side) of the dose counter 71, and therefore the beam is emitted. Secondary electrons, ions and electrons in plasma generated when the disk hits the disk 3 are exposed to the outside from the clearance between the Faraday cup 2 and the disk 3, the clearance between the Faraday cup 2 and the suppress electrode 61 and the center of the suppress electrode 61. Since it does not leak (the device is designed so that it does not leak), an amount of electrons equal to the beam current is emitted from the ground.
It is possible to accurately measure the beam current by flowing to the counter 71.

The signal line of the current detection value detected by the current detection unit 7 is connected to the control unit 8, and this control unit 8
Compares the current detection value from the current detection unit 7 with a predetermined set value, and when the current detection value becomes lower than the set value, the ion beam IB is prohibited from being irradiated, for example, by the beam gate 4 It has a function of outputting a close command to the drive unit 41 and closing the beam gate 4.

Next, the operation of the above embodiment will be described. First, the ion source 1 shown in FIG. 1 is started up, an ion beam IB containing ions of impurities such as phosphorus and arsenic is extracted from this, and the beam gate 4 is closed so that the ion beam IB is not irradiated to the Faraday cup 2 side. On the other hand,
The rotating disk 3 on which, for example, 10 semiconductor wafers W, which are the objects to be processed, are placed is rotated, and the plasma generating unit 5 is started up. In the plasma generator 5, the filament 52 is heated to generate thermoelectrons, and the discharge voltage between the filament 52 and the plasma generation chamber 51 excites a discharge gas such as argon gas with thermoelectrons to generate plasma. .

Next, the beam gate 4 is opened as shown by the solid line in FIG. 2 to irradiate the wafer W with the ion beam IB, whereby impurities such as phosphorus and arsenic are implanted into the wafer W. Then, the positive charges are accumulated on the surface of the wafer W by the irradiation of the ion beam. However, if the plasma generation part 5 is normal, the electrons in the plasma generated here are generated between the surface of the wafer W and the plasma generation part 5. Is attracted to the surface of the wafer W by the potential gradient of and the positive charge is neutralized. In this case, in order to scan the ion beam IB with respect to the wafer W, for example, the rotating disk 3 is moved along a vertical plane by a driving mechanism (not shown).

For this reason, a current flows from the plasma generation chamber 51 toward the ground as much as electrons are extracted from the plasma generation unit 5. This current is supplied from the ion beam IB, and as shown in FIG.
a, the current flowing from the plasma generation chamber 51 toward the ground is Ib, and the current reaching the wafer W is Ic, I
a is almost the sum of Ib and Ic.

Therefore, if the plasma generator 5 is normal, the current Ib has a predetermined magnitude, for example, about 10 mA.
As described in the section “Problems to be Solved by the Invention”, when the vapor of the filament 52, sputtered particles, etc. adhere to the plasma outlet 50 of the plasma generation chamber 51 and become deposited, and the plasma outlet 50 becomes narrower, the plasma generation chamber 51 becomes smaller. The amount of electrons traveling from the wafer to the wafer W becomes small, and the current Ib
Becomes smaller and the plasma outlet 50 is completely blocked, it becomes zero.

As described above, the current Ib is applied to the plasma generating unit 5
In order to correspond to the amount of electrons extracted from the wafer W toward the wafer W, a current value that can sufficiently neutralize the positive charge is input as a preset value in the control unit 8 in advance, so that the plasma generation unit 5 operates normally. In this case, since the current detection value of the current detection unit 7 is larger than the set value, the beam gate 4 remains open, and the surface of the wafer W is irradiated with the ion beam. When the ions cannot be sufficiently extracted from the generator 5, the current detection value becomes smaller than the set value. Therefore, the controller 8 outputs a close command to the gate driver 41 to close the beam gate 4 as shown by the chain line in FIG. And the ion beam is blocked here. The irradiation amount (ion implantation amount) of the ion beam to the wafer W and the scan position of the wafer W up to this point are stored, and after the maintenance, the remaining ion implantation is performed based on this stored value. .

Therefore, according to such an embodiment, the beam gate 4 is closed when no electrons are drawn from the plasma generating section 5 or when electrons are not sufficiently drawn out, such as when the plasma outlet 50 is clogged. It is possible to prevent dielectric breakdown of the insulating film on the surface of the wafer W due to charge accumulation.

In the above, the current detecting section 7 is shown in FIG.
It may be provided between the plasma generation chamber 51 and the connection point A as shown in FIG. Furthermore, in order to monitor whether or not the electrons are sufficiently extracted from the plasma generating section 5, a current detecting section 72 is provided between the rotating disk 3 and the ground as shown in FIG. The control unit 8 may output a close command to the gate drive unit 41 when the detected value exceeds the set value. In this case, if the electrons are not sufficiently drawn out or not completely drawn out from the plasma generating portion 5, the Ic shown in FIG. 4 becomes smaller by the amount of Ic, so that Ic exceeds the set value.

In the present invention, the above-mentioned current detectors 7 and 7 are used.
When the current detection value of 2 deviates from the set value, a visual display with a lamp or an audible display with an alarm sound may be performed, or the current detection value may be displayed with a meter or a numerical value, and the operator can make such a display. Alternatively, the ion beam irradiation may be manually prohibited to prevent the dielectric breakdown of the wafer W in advance.

As the object to be implanted with ions,
Not limited to semiconductor wafers, various types can be applied. The present invention also relates to a device that does not include an accelerating tube, a device that includes a Faraday cup 83 on the back side of a rotating disk 82 that has a cutout 81 as shown in FIG.
The present invention can also be applied to an apparatus in which one target object is placed on the platen and ion implantation is performed one by one.

[0030]

According to the first aspect of the invention, the state of neutralization of the positive charge of the object to be processed by the electrons extracted from the plasma generating section is monitored through the current detection value in the current detecting section. For example, it is possible to know clogging of the plasma outlet of the plasma generation unit before the dielectric breakdown of the object to be processed, and as a result, it is possible to prevent the dielectric breakdown of the object to be processed.

According to the second aspect of the invention, since the irradiation of the ion beam is prohibited when the current detection value detected by the current detection unit deviates from the set value, the object to be processed due to the clogging of the plasma outlet or the like. It is possible to reliably prevent dielectric breakdown of the body.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an entire embodiment of the present invention.

FIG. 2 is a configuration diagram showing a main part of the embodiment.

FIG. 3 is a perspective view showing an overview of a main part of the above embodiment.

FIG. 4 is an explanatory diagram illustrating an operation of the above embodiment.

FIG. 5 is a schematic diagram showing a main part of another embodiment of the present invention.

FIG. 6 is a perspective view showing a main part of still another embodiment of the present invention.

FIG. 7 is a configuration diagram showing an outline of a conventional ion implantation apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ion source 14 Mass spectrometer 16 Accelerator tube 2 Faraday cup 3 Rotating disk 4 Beam gate 41 Gate drive unit 5 Plasma generation unit 7, 72 Current detection unit 8 Control unit

Claims (2)

[Claims] 1. An object to be treated into which ions are implanted by irradiation of an ion beam is placed on a conductive placing table, and
An ion implantation apparatus in which a plasma generating unit is arranged in the vicinity of an object to be processed, and electrons in plasma generated in the plasma generating unit are attracted to the surface of the object to be processed to neutralize positive charges on the surface of the object to be processed. The ion implantation apparatus according to claim 1, further comprising a current detection unit provided between the plasma generation unit or the mounting table and the ground to detect a current flowing therethrough to monitor the state of the plasma generation unit. 2. A control unit is provided, which compares a current detection value of the current detection unit with a preset set value, and prohibits irradiation of an ion beam to the object to be processed when the detected current value deviates from the set value. The ion implanter according to claim 1.