JPH09115850A - Method and device for implanting ion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ion implanting method and device which simultaneously form a plurality of impurity areas that have different impurity concentrations. SOLUTION: Ions discharged from an ion source 1 are accelerated at a primary accelerating part 6, and only impurity ions with a prescribed weight are selected by a weight analyzing magnet 3. Electrons emitted from a heated filament 13 are permitted to collide with rare gas to obtain low-speed electrons. The electrons are injected to the ion beam so that they may be electrically combined with part of the impurity ions. Then, the impurity ions which are not combined with the electrons are further accelerated or decelerated by an accelerating part 7, and implanted to the wafer together with the electrically neutral impurity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation method and an ion implantation apparatus for implanting impurity ions into an ion implantation target such as a wafer in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art FIG. 4 is a schematic view showing a conventional ion implantation apparatus. The vacuum chamber 42 is bent into an L shape, the ion source 41 is provided on one side of the vacuum chamber 42, and the wafer mounting portion 45 is provided on the other side. The wafer mount 4 is provided in the wafer mounting portion 45.
7 is provided, and a wafer to be ion-implanted is mounted on the wafer mount 47. The wafer mount 47 is connected to the ground via an ammeter 48.

A mass analysis magnet (analyzer magnet) 43 is arranged at the bent portion of the chamber 42. The mass analysis magnet 43 generates a magnetic field in the chamber 42, and selects, as will be described later, impurity ions having a desired mass from ions emitted from the ion source 41 by the magnetic field. An accelerating unit 44 is provided between the mass analysis magnet 43 and the wafer mounting unit 45. This acceleration unit 44
An electric field is generated by a high voltage in the axial direction of the chamber where the accelerating unit 44 is arranged, and the electric field accelerates the ions.

A lens (not shown) for converging the ion beam and a scanner (not shown) for deflecting the ion beam are provided in the chamber 42 so that the ion can be placed at an arbitrary position on the wafer. Can be injected. There is also a wafer mounting part 47 that can move on a plane perpendicular to the ion beam. In the ion implantation apparatus configured as described above, the ion source 4
The traveling direction of the impurity ions emitted from 1 is bent by the magnetic field formed by the mass analysis magnet 43. In this case, the bending ratio of the impurity ions is related to the mass of the impurity ions. Therefore, by adjusting the strength of the magnetic field, only the impurity ions of a specific mass are transferred to the wafer mounting portion 45.
The other ions can be removed by taking out in the direction toward.

The impurity ions of a specific mass selected by the mass analysis magnet 43 are then accelerated by the acceleration unit 44. By implanting this impurity ion into the wafer mounted on the wafer mount 47, an impurity region can be formed in the wafer. In this case, the charge due to the impurity ions implanted into the wafer flows from the wafer mount 47 through the ammeter 48 to the ground, so the amount of the impurity ions implanted into the wafer should be known based on the value of the ammeter 48. You can Further, the implantation depth of impurities can be adjusted by adjusting the acceleration of the impurity ions by the acceleration unit 44.

[0006]

However, in the above-described conventional ion implantation apparatus, the implantation depth of the impurities is determined by the energy applied to the ions in the accelerating portion 44, so that, for example, as shown in FIG. A mask used when the high-concentration impurity layer 53 is formed in the shallow portion of the surface of the wafer 51 and the low-concentration impurity layer 54 is formed in the deep portion through the opening of the resist 52 formed on the wafer 51 ( Although the resist 52) is common, it is necessary to carry out the ion implantation a plurality of times, which is complicated.

The present invention was created in view of the above-mentioned problems of the conventional example, and provides an ion implantation method and an ion implantation apparatus capable of simultaneously forming a plurality of impurity regions having different impurity concentrations. The purpose is.

[0008]

Means for Solving the Problems The above-mentioned problems are solved by applying an electric field to impurity ions emitted from an ion source to accelerate the impurity ions, and injecting electrons into the accelerated impurity ion beam to remove impurities. This is solved by an ion implantation method characterized in that the portion is electrically neutralized, an electric field is then applied to the impurity ions to change the speed of the impurity ions, and the impurities are ion-implanted with the neutralized impurities.

Secondly, the above-mentioned problems are accelerating by applying a vacuum chamber, an ion source for generating impurity ions and discharging them into the vacuum chamber, and an electric field applied to the impurity ions discharged from this ion source. A first accelerating means, an electron supplying means for supplying electrons to the beam of impurity ions accelerated by the first accelerating means, and an electron electric field provided in front of the electron supplying means in the ion advancing direction. Second to further accelerate or decelerate the impurity ions by adding
And an accelerating means for the ion implantation device.

In the present invention, electrons are injected into the beam of impurity ions accelerated by the first accelerating means to electrically neutralize a part of the impurities. This electrically neutral impurity is implanted into the ion implantation target without being accelerated by the second accelerating means. On the other hand, the impurity ions that have not been combined with the electrons are further accelerated or decelerated by the second accelerating means, and are injected into the ion implantation target with energy different from that of the neutral impurities. Accordingly, it is possible to simultaneously form a plurality of impurity regions at different depths in the ion implantation target.

It should be noted that the slower the speed of the electrons injected into the ion beam, the easier the electrons and the impurity ions are to combine.
Therefore, when the velocity of the electrons emitted from the electron generator is high, it is preferable to collide the electrons with the rare gas to reduce the velocity of the electrons.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. (First Embodiment) FIG. 1 is a schematic view showing an ion implantation apparatus according to the first embodiment of the present invention. The vacuum chamber 2 is bent in an L shape, the ion source 1 is provided at one end of the vacuum chamber 2, and the wafer mounting portion 5 is provided at the other end. A mass analysis magnet 3 is provided in the bent portion of the chamber 2.

The ion source 1 puts a gas such as a halide into a plasma state and emits ionized impurities into the vacuum chamber 2. Mass analysis magnet 3 is chamber 2
A magnetic field is generated therein, and as will be described later, this magnetic field selects only impurity ions having a predetermined mass. Further, a wafer mount 17 is arranged in the wafer mounting portion 5, and a wafer to be ion-implanted is mounted on the wafer mount 17. The wafer mount 17 is connected to the ground via an ammeter 18.

A pre-stage acceleration section 6 is provided between the ion source 1 and the mass analysis magnet 3, and a post-stage acceleration section 7 is provided between the mass analysis magnet 3 and the wafer mounting section 5. Each of these accelerating units 6 and 7 generates an electric field due to a high voltage in the chamber axial direction of the portion where the accelerating units 6 and 7 are arranged, and the electric fields accelerate or decelerate the ions.

An electron generator 10 is provided between the mass analysis magnet 3 and the post-stage acceleration unit 7. The electron generator 10 includes a sub chamber 11 and a communication part 12 that connects the space inside the sub chamber 11 and the space inside the vacuum chamber 2.
And the filament 13 arranged in the sub chamber 11.
And a power supply 14 for supplying power to this filament 13.
And a power adjustment unit 15 connected between the power source 14 and the filament 13. Further, the sub chamber 11 is provided with a gas supply port 19, and He or Ar is supplied into the sub chamber 11 through the gas supply port 19.
Noble gas such as is supplied.

The high potential side of the filament 13 is electrically connected to the housing of the sub chamber 11, and an ammeter 16 is connected between the high potential side of the filament 13 and the ground. Further, in the vacuum chamber 2, a cryopump 20 is arranged near the communication section 12. A lens (not shown) for focusing the ion beam and a scanner (not shown) for deflecting the ion beam are provided in the vacuum chamber 2, and the wafer mount 17 is also provided.
Can be moved on a plane perpendicular to the ion beam by a mount drive mechanism (not shown). An ion beam can be injected to an arbitrary position on the wafer by these lens, scanner, and mounting base drive mechanism.

The ion implantation method according to the present invention using the ion implantation apparatus constructed as described above will be described below. First, a vacuum pump (not shown) inside the chamber 2
Then, the chamber 2 is evacuated, and the vacuum degree in the chamber 2 is adjusted to about 10 ⁻⁵ Torr. Then, for example, BF ₃ gas is introduced into the ion source 1, and this gas is put into a plasma state to generate ions. The ions are accelerated to a predetermined energy by the pre-accelerator 6. Here, it is assumed that the pre-stage acceleration unit 6 accelerates the ions to an energy of about 50 keV.

The direction of travel of the accelerated ions is bent by the magnetic field generated by the mass analysis magnet 3. In this case, the rate of bending by the magnetic field is related to the mass of the impurity ions. Therefore, by adjusting the strength of the magnetic field, only desired impurity ions can be extracted in the direction toward the wafer mounting portion 5. Here, the energy is about 50 ke
It is assumed that only BF ₂ ⁺ ions of V are taken out in the direction toward the wafer mounting portion 5.

On the other hand, in the electron generator 10, electric power is supplied from the power source 14 to heat the filament 13, and the heated filament 13 emits electrons into the sub chamber 11. The electrons collide with a rare gas such as He or Ar supplied from the gas supply port 19 and secondary electrons of low energy (low speed) are emitted. Then, the electrons enter the vacuum chamber 2 through the communication portion 12 and are electrically coupled with a part of the BF ₂ ⁺ ions selected by the mass analysis magnet 3. The BF ₂ ⁺ ion becomes an electrically neutral BF ₂ by combining with an electron. Since the inside of the chamber 2 is maintained in a high vacuum, the electrically neutral BF ₂ moves toward the wafer mounting unit 5 while maintaining the speed accelerated by the pre-accelerating unit 6.

By adjusting the voltage applied to the filament 13 by the power adjusting unit 15, the amount of electrons emitted from the filament 13 and, consequently, the amount of electrically neutral impurities can be adjusted. Mass analysis magnet 3
Some of the impurity ions selected by the above are combined with the electrons emitted from the electron generator 10 as described above to become electrically neutral impurities (BF ₂ ), but the impurity ions that are not combined with the electrons (BF ₂ ⁺ ) is further accelerated or decelerated by the post-acceleration unit 7. Here, it is assumed that the post-acceleration unit 7 applies an electric field in the direction opposite to the ion flow direction to reduce the ion energy to 25 keV.

In this way, the energy is 50 keV
Of electrically neutral impurities (BF ₂ ) and energy of 2
Impurity ions (BF ₂ ⁺ ) of 5 keV can be simultaneously implanted into the wafer. In this case, the charge due to the impurity ions implanted in the wafer flows to the ground via the ammeter 18, so that the amount of ions implanted in the wafer can be known based on the value indicated by the ammeter 18.

Further, the electrons emitted from the filament 13 and not combined with the ions are absorbed by the chamber housing.
Then, an amount of electric charge corresponding to the electrons emitted from the filament 13 and combined with the ions flows from the ground through the ammeter 16 to the circuit constituted by the filament 13, the power supply 14 and the power adjusting unit 15, so that the ammeter 16 Based on the indicated value of, the amount of electrically neutralized ions can be known.

The rare gas supplied into the sub-chamber 11 flows into the chamber 2 through the communicating portion 12, but the volume of the sub-chamber 11 is set sufficiently smaller than the volume of the chamber 2. Further, the amount of the rare gas flowing into the chamber 2 from the sub chamber 11 is limited by the communication portion 12, and the cryopump 20 is arranged in the vicinity of the communication portion 12, so that the inside of the chamber 2 caused by the rare gas is reduced. The change in vacuum degree can be suppressed.

FIG. 2 shows a semiconductor wafer 21 and this wafer 2.
FIG. 2 is a schematic diagram showing a resist 22 formed on 1
An opening is provided in a predetermined area of the resist 22.
The impurity ions and the electrically neutral impurities 25 with which the wafer 21 is irradiated are implanted into the wafer 21 at a depth corresponding to the energy thereof. That is, the energy is 50 ke
The electrically neutral impurity of V (BF ₂ ) is implanted into a relatively deep portion of the wafer 21, and the impurity ion (BF ₂ ⁺ ) having an energy of 25 keV is implanted into a shallow portion of the wafer 21. In this way, for example, the impurity concentration is 4 × 10
Impurity region 24 of ¹⁵ atom / cm ² and impurity concentration of about 1
The impurity region 23 of 0 ¹² atom / cm ² can be formed at the same time.

In the present embodiment, such two impurity regions having different impurity concentrations can be formed by one ion implantation step. As a result, the manufacturing process of the semiconductor device can be simplified, and the productivity of the semiconductor device is significantly improved. FIG. 3 is a diagram showing an example in which this embodiment is applied to doping of a gate electrode of a MOS transistor. First, a field oxide film 32 and a gate oxide film 33 are formed on the surface of the wafer 31,
A gate electrode 34 made of polysilicon is formed on the gate oxide film 33.

After that, by the above-mentioned ion implantation apparatus and ion implantation method, impurities are implanted into the gate electrode 34 at a high concentration, and ions are implanted at a low concentration into the substrate portion below the gate electrode 34. Ion implantation is performed by adjusting the accelerating voltage of the rear accelerating units 6 and 7 and the electric power supplied to the filament 13. As a result, the gate electrode 34 can be doped with impurities at a high concentration, and the source / drain regions 35 can be formed on the surface of the substrate 31 on both sides of the gate electrode 34. Further, the low-concentration impurity regions 36 and 37 can be simultaneously formed in the substrate portion below the gate electrode 34 and the portion below the source / drain region 35.

Since the low-concentration impurity regions 36 and 37 are provided around the source / drain region 35 in the MOS transistor thus formed, the concentration gradient at the edge of the source / drain region 35 is gentle. Become. (Other Embodiments) In the above-described embodiment, the case where the electron generator 10 and the post-stage acceleration unit 7 are both one set has been described, but a plurality of sets of the electron generator and the post-stage acceleration unit are provided along the traveling direction of the ions. As a result, three or more impurity regions having different impurity concentrations can be simultaneously formed.

Further, in the above embodiment, the case where the high-concentration impurity region is formed in the shallow portion of the wafer surface and the low-concentration impurity region is formed in the deep portion by decelerating the impurity ions in the post-accelerating portion 7 As described above, for example, by accelerating the ions to 25 keV in the pre-accelerating section 6 and accelerating the impurity ions to 50 keV in the post-accelerating section 7, a low-concentration impurity region is formed in a shallow portion of the wafer surface and a deep portion is formed. A high-concentration impurity region can be formed in the.

Further, in the above embodiment, the case where the rare gas is supplied into the sub chamber 11 has been described.
It is not necessary to supply the rare gas. But filament 1
Since the speed of electrons emitted from No. 3 is relatively high, if no rare gas is supplied into the sub-chamber 11, it is difficult for electrons and impurity ions to combine, and it is difficult to neutralize a sufficient amount of ions. Is. Therefore, as described above, it is preferable to supply a rare gas into the sub chamber 11 and collide electrons with the rare gas to obtain constant energy electrons.

[0030]

As described above, according to the present invention,
Electrons are supplied to the beam of impurity ions accelerated by the first accelerating means to electrically neutralize a part of the ions, and the remaining impurity ions are further accelerated or decelerated by the second accelerating means. It is possible to simultaneously form a plurality of layers having different impurity concentrations on the target of ion implantation such as. As a result, there is an effect that the productivity of the semiconductor device is improved.

[Brief description of the drawings]

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

FIG. 2 is a schematic view showing a semiconductor device having an impurity region formed by the ion implantation device according to the present invention.

FIG. 3 is a schematic diagram showing an example in which the present invention is applied to doping of a gate electrode of a MOS transistor.

FIG. 4 is a schematic view showing a conventional ion implantation device.

FIG. 5 is a schematic diagram showing a conventional problem.

[Explanation of symbols]

 1,41 Ion source 2,42 Vacuum chamber 3,43 Mass analysis magnet 5,45 Wafer mounting part 6,7,44 Accelerating part 10 Electron generator 11 Sub chamber 13 Filament 16,18,48 Ammeter 17,47 Wafer mounting Table 19 Gas supply port 21, 31, 51 Wafer 22, 52 Resist

Claims (3)

[Claims] 1. An electric field is applied to impurity ions emitted from an ion source to accelerate the impurity ions, and electrons are injected into a beam of the accelerated impurity ions to electrically neutralize a part of the impurities, After that, an electric field is applied to the impurity ions to change the speed of the impurity ions, and the impurities are ion-implanted together with the neutralized impurities into an ion implantation target. 2. A vacuum chamber, an ion source for generating impurity ions and discharging them into the vacuum chamber, a first accelerating means for accelerating the impurity ions emitted from the ion source by applying an electric field thereto, 1. An electron supply unit for supplying electrons to the beam of impurity ions accelerated by the first acceleration unit, and an electron supply unit provided in front of the electron supply unit in the ion advancing direction to further accelerate the impurity ions by applying an electric field to the impurity ions. Alternatively, an ion implantation device having a second accelerating means for decelerating. 3. The electron supply means supplies a sub-chamber having a space communicating with the space in the vacuum chamber, an electron generating means arranged in the sub-chamber, and a rare gas supplied to the sub-chamber. 3. The ion implantation apparatus according to claim 2, wherein the ion implantation apparatus is configured by a rare gas supply unit that operates.