JPH0636738A - Ion implanter - Google Patents

Abstract

(57) [Abstract] [Purpose] To reliably prevent the dielectric breakdown of the object to be processed due to ion implantation, and to suppress the contamination of the object to be processed. [Structure] A Faraday cup 2 is arranged in front of a rotating disk 31 in which a plurality of wafers W are arranged in the circumferential direction, and a plasma generating unit 4 is provided outside the Faraday cup 2. A current detector 6 for detecting a negative current flowing from the rotating disk 31 to the ground is provided, the rotating disk 31 is rotated at a high speed, and the power supplies 51 and 52 of the plasma generator 4 are turned on to set the negative current. Beam gate 21 after exceeding the value
A control unit 7 is provided to perform control so as to open. Since the negative current corresponds to the arrival amount of the plasma, the generation of the plasma can be confirmed by detecting it. Therefore, when the wafer W is irradiated with the ion beam, the charge can be surely neutralized.

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, the separated ion beam of the desired ions is accelerated to the final energy through the accelerating tube 94, and then irradiated onto the wafer W, so that desired impurities are introduced into the surface of the wafer W. The wafer W also has a rotating disk 95 that rotates about a horizontal axis.
Ions are arranged on the upper side in the circumferential direction while rotating the rotating disk 95 by the motor 96.

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. 7, 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 rotating disk 95 is erected as shown in FIG.
When each wafer W is irradiated with the ion beam from the ion source 9, the amount of positive charges accumulated on the surface of the wafer W becomes too large due to the irradiation of the ion beam before the plasma is sufficiently raised. In some cases, the wafer W is subject to dielectric breakdown.

The plasma generating unit 98 is constructed such that a filament made of tungsten is provided in a plasma generating chamber made of, for example, molybdenum, and the filament is heated and its thermoelectrons collide with argon gas to generate plasma. However, there is a small amount of filament vapor in the plasma generation chamber and sputtered particles on the inner wall of the plasma generation chamber due to plasma, and some of these heavy metal particles such as molybdenum and tungsten that are hit by plasma and ionized. is there.

On the other hand, when the plasma generator 98 is started up,
From here, the plasma sheath flows out into the Faraday cup 97, diffuses, and contacts the wafer W facing the Faraday cup 97. At this time, the ionized heavy metal particles in the plasma sheath adhere to the surface of the wafer W,
Further, some of the heavy metal particles generated in the plasma generation unit 98 and flying out as neutral particles may be reflected by the inner wall of the Faraday cup 97 or may directly reach the surface of the wafer W and be attached thereto. As a result, the specific wafer W
Regarding the above, there was a problem that the plasma generation chamber of the plasma generation unit 98 and the degree of contamination by the heavy metal that is the material of the filament are large.

Further, the temperature of the power supply member for supplying power to the plasma generating portion becomes high, and thus the specific wafer W is exposed to high temperature for a long time, the photoresist pattern on the wafer surface is changed, and the photoresist is scorched. There is a risk of damage to the pattern such that it becomes difficult to peel off due to peeling.

The present invention has been made under the circumstances as described above, and an object thereof is to reliably prevent dielectric breakdown of an object to be processed due to ion implantation, and to prevent the object from being processed. An object of the present invention is to provide an ion implanter capable of suppressing contamination.

[0012]

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 charge on the surface of the object to be processed, plasma generation confirmation means for confirming generation of plasma by the plasma generation part, and the plasma generation confirmation means. After the generation of plasma is confirmed by the above, a control unit for performing control so as to irradiate the object to be processed with the ion beam is provided.

According to a second aspect of the present invention, a plurality of objects to be treated, into which ions are injected by irradiation of an ion beam, are arranged in a circumferential direction on a rotary mounting table, and a plasma generator is arranged in the vicinity of the objects to be treated. Then, in the ion implantation apparatus in which the electrons in the plasma generated in the plasma generation unit are attracted to the surface of the target object to neutralize the positive charges on the surface of the target object, the generation of plasma by the plasma generation unit is prevented. Plasma generation confirming means for confirming and rotating the rotary mounting table to generate plasma in the plasma generating part, and confirming the generation of plasma by the plasma generation confirming means, and then irradiating the object with an ion beam And a control unit for performing such control.

According to a third aspect of the present invention, the plasma generating portion is arranged in the vicinity of the object to be implanted with the ions by the irradiation of the ion beam, and the electrons in the plasma generated in the plasma generating portion are on the surface of the object to be treated. In an ion implantation apparatus that attracts and neutralizes positive charges on the surface of the object to be processed, it is arranged so as to be openable and closable between the plasma generating section and the object to be processed so as to block plasma flowing out from the plasma generating section. And a plasma shutter that is closed before plasma is generated in the plasma generation unit, opens the plasma shutter after confirming the generation of plasma by the plasma generation confirmation means, and irradiates an ion beam. And a control unit for controlling the above.

[0015]

For example, when a plurality of objects to be processed are arranged on the rotary mounting table in the circumferential direction, the rotary mounting table is set to 100 r.
p. While rotating at m, plasma is generated in the plasma generating part. Therefore, even if ionized or neutral heavy metal particles come into contact with the object to be processed due to the generation of plasma, the rotary mounting table is rotating, so that the contamination is dispersed in each object to be processed.

Further, by providing a shutter and closing it until the plasma is generated in the plasma generator, it is possible to suppress contamination of the object to be processed. After confirming the generation of plasma, the target object is irradiated with the ion beam.Therefore, even if a positive charge is accumulated on the surface of the target object due to the irradiation of the ion beam, the plasma is always generated at this point. Therefore, the dielectric breakdown of the object to be processed can be reliably prevented.

[0017]

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 mounted and held on the rotary disk 31 which is the rotary mounting table rotated by the motor 3.

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 21 for irradiating or blocking the wafer W with the ion beam by opening and closing the path of the ion beam by the gate driving unit 22 is provided between the and the acceleration tube 16. Further, on the outside of the Faraday cup 2, in order to neutralize the electric charge on the surface of the wafer W, a plasma generating portion 4 is formed.
Are arranged.

Next, the main part of the embodiment of the present invention will be described in detail with reference to FIG. On the side of the Faraday cup 2 that penetrates the ion beam IB, for example, −1000 V is used so that secondary electrons do not jump out of the Faraday cup 2.
The suppress electrode 23 to which the voltage Es is applied is provided.

The plasma generating section 4 is constructed by providing a filament 42 made of, for example, tungsten in a plasma generating chamber 41 made of, for example, carbon or molybdenum, and the plasma generating chamber 41 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 40 is provided on the Faraday cup 2 side of the plasma generation chamber 41.
The opening 20 is formed in the wall of the Faraday cup 2 facing the plasma outlet 40 so that plasma can flow into the Faraday cup 2.

A DC power supply 51 for applying a filament voltage is connected between both ends of the filament 42, and a discharge voltage is applied between the filament 42 and the wall of the plasma generating chamber 41. Is connected to the DC power supply unit 52.

As shown in the schematic perspective view of FIG. 3, the rotary disk 31 includes a plurality of wafers W, for example, ten wafers W (illustrated as eight wafers in FIG. 3 for convenience of illustration) in the circumferential direction. The wafer W is loaded or unloaded when the wafer W is horizontal, and the ion implantation is performed when the wafer W is erected. Done. In order to detect the current flowing from the wafer W to the ground via the rotary disk 31, the rotary disk 31 is connected to the ground by a current detection unit 6 via the exterior part of the motor 3 in this example. There is.

The motor 3 is driven by a motor drive circuit 32, and the motor drive circuit 32 is provided with a control unit 7 which gives a command signal for controlling the drive of the motor 3.
Are connected. This control unit 7 has a function of controlling the motor 3 as well as a DC power supply unit 5 related to the plasma generation unit 4.
A function to control ON / OFF of 1, 52 and a command to open the gate drive unit 22 of the beam gate 21 when the detected current value of the current detection unit 6 is compared with a set value and the detected current value exceeds the set value. It is provided with a function of outputting the above, and is composed of a CPU and a memory storing a predetermined program for performing such control. However, in this example, the current detector 6 and
The circuit section for comparing the detected current value and the set value in the control section 7 constitutes a plasma generation confirmation means for confirming the generation of plasma.

Next, the operation of the above-described embodiment will be described with reference to the flowchart of the control section 7 shown in FIG. 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 21 is closed so that the ion beam IB is not irradiated to the Faraday cup 2 side. On the other hand, for example, 10 wafers W are transferred onto the rotating disk 31 by a transfer mechanism (not shown). The rotating disk 31 is set in a horizontal state when the wafer W is transferred, and after receiving the wafer W and placing and holding the wafer W, the rotating disk 31 is in an upright state as shown in FIG.

Next, the controller 7 controls the motor drive circuit 32.
A rotation command is output to the rotation disk 31 and the rotation disk 31 starts to rotate. The speed is set to a speed set value ra, for example 1000 r. p. After confirming that m has been reached, the plasma generator 4 is started up. This startup is performed by turning on the DC power supply units 51 and 52 by the control unit 7. First, the filament 42 is heated to generate thermoelectrons, and the discharge between the filament 42 and the plasma generation chamber 41 is performed. A voltage excites a discharge gas such as argon gas with thermoelectrons to generate plasma.

When the discharge gas is excited, the plasma sheath P flows into the Faraday cup 2 through the plasma outlet 40 and the opening 20 and diffuses. When the plasma W touches the surface of the wafer W or the rotating disk 31, the plasma sheath P Of electrons flow toward the ground, and this negative current is detected by the current detector 6. The detected current value (current detection value) is taken into the control unit 7, and when the current value reaches a predetermined value Ia (for example, about several mA), the control unit 7 causes the rotating disk to reach a predetermined rotation speed, for example, 1200 rpm. After confirming that it has reached, an opening command is output to the gate drive unit 22 to open the beam gate 21 as shown by the solid line in FIG. As a result, the ion beam IB emitted from the ion source 1 is applied to the wafer W, and impurities such as phosphorus and arsenic are implanted into the wafer W. Considering the reason why a negative current flows from the rotating disk 31 toward the ground,
Anode potential of plasma chamber (plasma generation chamber 41
Potential) is the same as that of the rotating disk, and the potential of the whole plasma is usually several volts lower than the anodic potential.
The electric potential of the whole plasma becomes several volts lower than the electric potential of the disc, and electrons flow from the plasma to the disc. Further, since a negative bias voltage is applied to the suppress electrode 23, ions are attracted to the suppress electrode 23, so that more electrons are present than the ions in the rotating disk 31.
It is presumed that it has reached. Therefore, the current detector 6
The detected current value corresponding to the negative current detected in step 1 is an index of the plasma generation state in the plasma generation unit 4, and it is confirmed that sufficient plasma is generated by confirming that this value has reached a predetermined value. Can be confirmed.

When the wafer W is irradiated with the ion beam IB, positive charges are accumulated on the surface of the wafer W.
Since the beam gate 21 is opened after confirming the generation of plasma, when the positive charges are accumulated, they are always neutralized by the electrons in the plasma, and the DC power supply unit 51,
Although 52 is charged, the beam gate 21 is not opened when the plasma outlet 20 is clogged with sputtered particles or the like, so that dielectric breakdown of the wafer W due to accumulation of positive charges can be reliably prevented.

As described in the section "Problems to be solved by the invention", vapor from the filament and sputtered particles on the inner wall of the plasma generation chamber 41 are ionized by being hit by plasma, and these ionized heavy metal particles are generated. The diffusion of the plasma sheath makes contact with the wafer W on the rotating disk 31, and the neutral heavy metal particles that are not ionized go straight on or are reflected by the inner wall of the Faraday cup 2 to come into contact with the wafer W. Since the rotating disk 31 is rotating when plasma is generated in the plasma generating section 4, these contaminants are dispersed to each wafer W on the rotating disk 31, so that the specific wafer W facing the plasma generating section The amount of pollutants attached to
For example, when 10 wafers W are arrayed on the rotating disk 31, the number is about 1/10 of that when the rotating disk 31 is not rotated. For example, some devices have an allowable critical density of heavy metals of 10 per square centimeter.
^Since it is on the order of ¹⁰ atoms, it is very significant that the amount of heavy metal attached can be reduced by an order of magnitude.

Further, in such an embodiment, contamination by heavy metals can be suppressed, and it is also possible to prevent only a specific wafer W from being exposed to high heat of the power supply member in the plasma generating section 4 for a long time.

For an apparatus for holding one wafer by a platen and performing ion implantation one by one without using a rotating disk, as shown in FIG. A plasma shutter 82 is provided between the plasma generator 4 and the wafer W on the platen 81 so that the plasma shutter 82 can be opened and closed, and the shutter 82 is closed before the plasma is generated in the plasma generator 4. If the control unit 7 confirms the generation of plasma based on the value and then the shutter 82 and the beam gate 21 are opened, the contamination of the wafer W by the heavy metal particles from the plasma generation unit can be suppressed.

Such a shutter 82 may be provided in an ion implantation apparatus in which a plurality of wafers W are arranged on a rotating disk, but according to the method of rotating at high speed as described above,
The device configuration is simpler than when a separate shutter is provided. However, in the present invention, high-speed rotation may be performed and a shutter may be provided. Further, the position at which the shutter 82 is provided may be the exit of the plasma generator 4.

The discharge gas used in the plasma generator 4 is a gas that has a large ionization cross-sectional area and does not adversely affect the semiconductor, for example, xenon (Xe) gas or krypton in order to generate plasma at a discharge voltage as low as possible. It is preferable to use (Kr) gas or the like. The reason is as follows. If a gas with a large ionization cross section is used,
(1) It is possible to generate plasma with a small amount of gas. As a result, the amount of gas knocked on to the injection target can be suppressed to a small amount. (2) It is also possible to lower the discharge voltage, which has the effect of suppressing the generation of sputtered substances. It also lowers the maximum energy of electrons in the plasma, thus reducing the possibility of charge breakdown due to negative charges. (3) The filament current can be further reduced, and the consumption of the filament can be suppressed. As described above, there are many advantages of using a gas having a large ionization cross section. In the above, in order to confirm the generation of plasma, a negative current flowing from the Faraday cup 2 or the plasma shutter 82 to the ground may be detected, or a probe such as a Langmuir probe may be used at the plasma outlet. It may be detected by being provided in the vicinity, or may be confirmed by a method other than current detection.

As the object to be implanted with ions,
Not limited to semiconductor wafers, various types can be applied. The present invention can also be applied to a device that does not include an accelerating tube, or a device in which a Faraday cup 85 is arranged on the back side of a rotating disk 84 having a cutout portion 83 as shown in FIG.

[0034]

According to the first aspect of the present invention, the ion beam is applied to the object to be processed after confirming the generation of the plasma in the plasma generating portion. Therefore, positive charges are accumulated in the object to be processed. Since it is always neutralized by the electrons in the plasma when going, it is possible to reliably prevent the dielectric breakdown of the wafer due to the accumulation of positive charges.

According to the invention of claim 2, in addition to the effect of the invention of claim 1, since the plasma is generated in the plasma generating part by rotating the rotary mounting table, contamination from the plasma generating part is caused. Since the substance is dispersed in each object to be processed, it is possible to suppress the contamination of each object to be processed.

According to the invention of claim 3, in addition to the effect of the invention of claim 1, since the plasma shutter is closed before the plasma generation in the plasma generation part, the object to be treated by the contaminants from the plasma generation part The contamination of can be suppressed.

[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 a flowchart illustrating the operation of the above embodiment.

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

FIG. 6 is a configuration diagram 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 Accelerating tube 2 Faraday cup 21 Beam gate 3 Motor 31 Rotating disk 4 Plasma generation part 6 Current detector 7 Control part 82 Plasma gate

Claims (3)

[Claims] 1. A plasma generating part is arranged in the vicinity of a target object into which ions are injected by irradiation of an ion beam, and electrons in plasma generated in the plasma generating part are attracted to the surface of the target object to be treated. In the ion implantation apparatus for neutralizing the positive charges on the surface of the object to be treated, a plasma generation confirmation means for confirming generation of plasma by the plasma generation part, and an object to be treated after confirming generation of plasma by the plasma generation confirmation means An ion implantation apparatus comprising: a control unit that controls to irradiate an ion beam to the. 2. A plurality of objects to be treated, into which ions are implanted by irradiation of an ion beam, are arranged in a circumferential direction on a rotary mounting table, and a plasma generator is arranged in the vicinity of the objects to be treated. In the ion implantation device in which the electrons in the plasma generated in 1 are attracted to the surface of the object to be processed to neutralize the positive charge on the surface of the object to be processed, the generation of plasma is confirmed by the plasma generation unit. Means for rotating the rotary mounting table to generate plasma in the plasma generating part, and confirming the generation of plasma by the plasma generation confirming means, and then irradiating the object to be processed with an ion beam. An ion implantation apparatus comprising: a control unit. 3. A plasma generating part is arranged in the vicinity of an object to be treated into which ions are injected by irradiation of an ion beam, and electrons in plasma generated in the plasma generating part are attracted to the surface of the object to be treated. In an ion implantation device that neutralizes the positive charges on the surface of a processing object, a plasma shutter that is openably and closably disposed between the plasma generating part and the object to be processed so as to block the plasma flowing out from the plasma generating part. Control for closing the plasma shutter before plasma is generated in the plasma generation unit, opening the plasma shutter after confirming the generation of plasma by the plasma generation confirmation means, and controlling to irradiate an ion beam And an ion implantation device.