JP3084307B2 - Ion implanter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation apparatus.

[0002]

2. Description of the Related Art As shown in FIG. 3, a conventional ion implantation apparatus converts an ion source A, an ion analysis magnet B, an acceleration tube C, a Q lens D, and an ion beam in a Y direction (vertical direction). It comprises an ion beam deflection Y electrode E for deflection, an ion beam deflection X electrode F for deflecting the ion beam in the X direction (horizontal direction), and an ion implantation chamber G having a wafer.

In such an ion implantation apparatus, only ions necessary for ion implantation are selected by an ion analysis magnet B after ions generated in an ion source A are accelerated by an extraction electrode. Then, after the selected ions are accelerated by the acceleration tube C, the ions are converged by the Q lens D so that the ion beam having the optimum beam shape can be implanted into the wafer in the ion implantation chamber G. The ion beam converged by the Q lens D is deflected by the ion beam deflection Y electrode E and the ion beam deflection X electrode F, respectively, and is scanned on the wafer in the ion implantation chamber G. In that case, the energy and the number of ions of the ion beam implanted into the wafer are determined according to the purpose of the device.
The number of ions of the ion beam injected into one wafer is controlled by applying or not applying a DC high voltage gate voltage to the ion beam deflection Y electrode E at a high speed. That is, when the number of ions of the ion beam to be implanted into one wafer reaches a predetermined number, a gate voltage is applied, and the implantation of the ion beam into the wafer is stopped. However, when the application of the gate voltage is released, the ion beam is injected into the wafer.

[0004]

When the number of ions of the ion beam to be implanted into one wafer reaches a predetermined number as described above, the conventional ion implantation apparatus applies a direct current to the ion beam deflection Y electrode E. By applying a gate voltage, the implantation of the ion beam into the wafer is stopped. The reason why the injection of the ion beam into the wafer is stopped is that by applying a gate voltage to the ion beam deflection Y electrode E,
The ion beam is splashed and does not reach the wafer,
This is because it hits the inner wall of the vacuum container. When the ion beam hits the inner wall of the vacuum container, the inner wall of the vacuum container is sputtered, and particles of the material of the inner wall of the vacuum container scatter in the vacuum container. Therefore, some of the particles of the inner wall material of the vacuum vessel that are scattered adhere to the wafer. As a result, a foreign substance such as a metal impurity is mixed into a device formed from a wafer, and a problem occurs in that the performance of the device is deteriorated. Further, since the degree of vacuum in the region where ions enter the accelerator tube C is relatively poor in the entire apparatus, ions necessary for implantation between the ion analysis magnet B and the accelerator tube C collide with the residual gas and dissociate. I do.
For example, when BF ₂ (mass 49) ions are selected, 30 KeV is used for the ion source A and 20 KeV for the acceleration tube C, and the total is 50 KeV, which is implanted into the wafer. However, the ion required for implantation is B (Polon mass 11), and the energy is 50 KeV × 11/49 = 11.2 KeV from the mass ratio. However, if the BF ₂ collides with the residual gas before entering the accelerator C and dissociates into B ions and F ₂ , the energy of the B ions before the accelerator C becomes 30 KeV.
× 11/49 = 6.7 KeV. Thereafter, the B ions are given an energy of 20 KeV by the accelerator tube C, and have an energy of 26.7 KeV. Therefore, B ions having an energy of 26.7 KeV, which is higher than the energy of 11.2 KeV required for implantation, are mixed. This is not limited to BF _2, and ions having different energies are all mixed in with molecular ions due to dissociation. Similarly, even when divalent ions capture electrons and become monovalent, or when electrons are stripped and become trivalent, ions that are lower or higher than the energy to be implanted are mixed. become. Therefore, a problem arises in that ions having energy other than the intended purpose are mixed into the device formed from the wafer, and the performance of the device is deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the performance of a device by solving the above-mentioned conventional problems and preventing foreign matter such as metal impurities from being mixed into the device and implanting ions having different energies. It is intended to provide an ion implantation apparatus capable of improving the yield.

[0006]

In order to achieve the above object, the present invention provides a method for selecting only ions necessary for ion implantation from an ion beam extracted from an ion source with an ion analysis magnet, In an ion implantation apparatus that accelerates a beam with an acceleration tube and injects it into a wafer, a silicon liner is attached to the inner surface of the vacuum vessel of the ion analysis magnet, and between the ion analysis magnet and the acceleration tube, Beam mask, gate electrode,
Slit and low energy ion reflective electrode are arranged in this order,
Applying an output from a beam gate power supply to the gate electrode to deflect the ion beam by θ degrees, further arranging a deflection electrode behind the accelerator tube to deflect the ion beam by −θ degrees. Is what you do.

[0007]

According to the present invention, when only ions necessary for ion implantation are selected by the ion analysis magnet, a part of the ion beam sputters a silicon liner attached to the inner surface of the vacuum vessel of the ion analysis magnet. However, the ions generated by the sputtering are bent at the gate electrode, are further reflected by the electric field formed between the slit and the low-energy ion reflecting electrode, and do not reach the acceleration tube. The ion beam selected by the ion analysis magnet passes through the beam mask and reaches the gate electrode. When an output from the beam gate power supply is applied to the gate electrode, the ion beam is deflected by θ degrees. The ion beam deflected by θ degrees passes through the slit, further passes through the low-energy ion reflection electrode, and reaches the acceleration tube. At this time, when ions necessary for implantation collide with the residual gas and dissociate between the ion analysis magnet and the gate electrode, a voltage (V ₁ ) from a beam gate power supply is applied to the gate electrode to change the ion beam by θ. When the ions are deflected by degrees, the dissociated ions are deflected to an angle different from θ degrees, so that they cannot pass through the slit and can be removed. For example, when BF ₂ ⁺ (mass 49) ions are selected, the ions are accelerated to 30 KeV by the ion source and reach the gate electrode. The voltage (V ₁ ) from the beam gate power supply is applied to the gate electrode, and BF ₂ ⁺ ions of 30 KeV are deflected by θ degrees. When the BF ₂ ⁺ ion dissociates, the energy of the B ⁺ ion is 30 KeV × 11/49 = 6.7 K
eV. The 6.7 KeV B + ion is bent at θ × 30 / 6.7 = 4.5θ at the gate electrode to which the voltage (V ₁ ) is applied, and therefore cannot pass through the slit. Even if molecular ions are dissociated in this manner, all ions having energy different from the energy of ions necessary for implantation can be removed. When the monovalent ions become divalent ions or neutral particles, or when the divalent ions become monovalent ions or trivalent ions, the energy does not change, but the valences are different. The deflection angles are different. For example, when B ²⁺ (divalent ions) capture electrons between the ion analysis magnet and the gate electrode and become B ⁺ (monovalent ions), a voltage (V ₂ ) is applied to the gate electrode. When B ²⁺ is deflected by θ degrees so as to pass through the slit, unnecessary B ⁺
Cannot be passed through the slit because it is deflected by only 1 / 2θ degree compared to θ degree of B ²⁺ . In this manner, ions having a valence different from the valence of ions necessary for implantation can be removed. Then, only ions necessary for implantation pass through the low-energy ion reflecting electrode and reach the acceleration tube. The ions passing through the accelerating tube are bent by −θ degrees by a multipole or parallel plate deflection electrode through a focusing system.
The reason for bending by −θ degrees is to remove neutral particles between the slit and the focusing system.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show an ion implantation apparatus according to a first embodiment of the present invention.
An ion extraction power supply 12 is connected to the ion source 11, and the ions generated by the ion source 11 are extracted as a beam by the output. The extracted ion beam passes through the inside of the ion analysis magnet 13, and at this time, only ions necessary for ion implantation are selected there. A liner 14 made of silicon is attached to the inner surface of the vacuum vessel of the ion analysis magnet 13. A silicon beam mask 15 having a hole for passing an ion beam is disposed in the direction toward the exit of the ion analysis magnet 13. The beam mask 15 prevents the ion beam from hitting a gate electrode 16 described later. I have. Behind the beam mask 15, a gate electrode 1 for splashing an ion beam
A beam gate power supply 17 is connected to the gate electrode 16. The beam gate power supply 17 includes:
When the number of ions to be implanted into the wafer described later reaches a required value, a signal from a dose measuring device (not shown) for measuring the number of ions is sent, and the output from the beam gate power supply 17 is sent to the gate electrode 16. No longer applied. A slit 18 made of silicon is arranged behind the gate electrode 16,
Further, a low-energy ion reflection electrode 19 for applying a high voltage lower by about 10 KV than an extraction voltage for extracting an ion beam from the ion source 11 is disposed behind the slit 18, and the slit 18 and the low-energy ion reflection electrode 19 are arranged. And an electric field is formed between them. An accelerating tube 20 is disposed behind the low-energy ion reflecting electrode 19. Behind the accelerating tube 20, a Q lens 21, an ion beam deflecting X electrode 22 for deflecting the ion beam in the X direction (horizontal direction), and an ion beam deflecting Y electrode 23 for deflecting the ion beam in the Y direction (vertical direction) are provided. The ion beam is deflected by −θ degrees by the ion beam deflection Y electrode 23. Behind the ion beam deflection Y electrode 23, an ion implantation chamber where a wafer exists is arranged.

In the first embodiment, ions generated by the ion source 11 are extracted as an ion beam by the output of the ion extraction power supply 12. The extracted ion beam passes through the ion analysis magnet 13, where only ions necessary for ion implantation are selected there. In addition, a part of the ion beam passing through the ion analysis magnet 13 sputters a silicon liner 14 attached to the inner surface of the vacuum vessel of the ion analysis magnet 13. The ion beam that has passed through the ion analysis magnet 13 passes through the beam mask 15, the gate electrode 16, the slit 18, and the low-energy ion reflection electrode 19 in this order, and reaches the acceleration tube 20. During the passage, the beam mask 15 has a function of preventing the ion beam from hitting the gate electrode 16. The gate electrode 16 is deflected by θ degrees and passes through the slit only when the energy and valence of ions necessary for implantation match. Further, the electric field formed between the slit 18 and the low-energy ion reflecting electrode 19 reflects ions which are generated by sputtering the silicon liner 14 and the slit 18 and the like, and cause contamination.
The ions are prevented from reaching the acceleration tube 20. The ion beam reaching the accelerating tube 20 is accelerated there, passes through a Q lens 21, an ion beam deflecting X electrode 22, is bent by -θ degrees by an ion beam deflecting Y electrode 23, and is injected into a wafer in an ion implantation chamber. .

Note that, between the ion analysis magnet 13 and the ion beam deflection Y electrode, some of the ions capture electrons and become neutral particles. The neutral particles go straight without being bent by the ion beam deflection Y electrode, and sputter the inner wall of the vacuum vessel. In order to prevent the generation of foreign matter such as metal impurities due to the sputtering, a silicon liner is attached to a portion irradiated with neutral particles. In addition, a graphite material, which has been conventionally used to prevent generation of foreign matter such as metal impurities, is replaced with a silicon material. For example, a mask or the like in an ion implantation apparatus.

In the embodiment, when the number of ions to be implanted into the wafer reaches a required value, a signal from a dose measuring device (not shown) for measuring the number of ions is supplied to a beam gate power supply 17.
And the output from the beam gate power supply 17 is not applied to the gate electrode 16. As a result, the ion beam is jumped up by the gate electrode 16 and goes straight,
The ion does not pass through the slit 18 and the ion implantation to the wafer is stopped. Then, when the application to the gate electrode 16 is started after the replacement of the wafer, the ion beam is again implanted into the wafer.

Instead of attaching the silicon liner 14 to the inner surface of the vacuum vessel of the ion analysis magnet 13, the vacuum vessel itself of the ion analysis magnet 13 may be made of a silicon block. In addition, a conventional method for reducing foreign substances such as metal impurities by incorporating a vacuum pump in the gate electrode portion can be added. Further, the low energy ion reflection electrode 19 may partially use an electrode of an acceleration tube. During the time when the ion implantation into the wafer is stopped, the ion beam travels straight through the gate electrode 16 and hits the upper portion of the slit 18. Another slit and a beam current cup may be attached to this part as a beam monitor. Instead of the ion beam deflecting X electrode 22 and the ion beam deflecting Y electrode 23, a multipolar electrode capable of simultaneously deflecting the XY axes may be used.

[0013]

According to the present invention, when the output from the beam gate power supply is applied to the gate electrode, the ion beam is deflected by θ degrees and the ion beam can pass through the slit, so that the ion beam is generated between the ion analysis magnet and the gate electrode. To prevent ions with different energy and ion valence from interfering with each other, and prevent ions generated by sputtering the silicon liner attached to the inner surface of the vacuum vessel of the ion analysis magnet from passing through the slit. To remove ions that are not necessary for a small amount of implants that pass through an impossible orbit, they are reflected by the electric field formed between the slit and the low-energy ion reflective electrode so that they do not reach the accelerator tube. . In this way, it is possible to prevent ion species and ion energy that are not necessary for implantation into the device from being mixed, prevent foreign substances such as metal impurities from being mixed into the device, improve the performance of the device, and increase the yield. Be improved. Further, since the gate electrode is arranged before the accelerating tube, the ion beam deflected by θ degrees has low energy. Therefore, the size of the gate electrode can be reduced, the output from the beam gate power supply applied to the gate electrode can be reduced, and the rise and fall times of ON and OFF can be shortened. Furthermore,
Since a liner made of silicon is attached to the inner surface of the vacuum vessel of the ion analysis magnet, the release of gas from the inner surface of the vacuum vessel of the ion analysis magnet is suppressed. As a result, the probability that divalent positive ions such as boron, phosphorus, and arsenic collide with the residual gas in the ion analysis magnet vacuum vessel decreases, and the beam current of divalent positive ions such as boron, phosphorus, and arsenic increases. I do.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an ion implantation apparatus according to a first embodiment of the present invention;

FIG. 2 is an explanatory view showing a part of a main part of the first embodiment of the present invention.

FIG. 3 is an explanatory view showing a conventional ion implantation apparatus.

[Explanation of symbols]

 11 ... Ion source 12 ... Ion extraction power supply 13 ... Ion analysis magnet 14 ... Liner 15 ... Beam mask 16 ... ... Gate electrode 17 ... Beam gate power supply 18 ... Slit 19 ... Low energy ion reflective electrode 20 ... Accelerator tube 21 ...・ Q lens 22 ・ ・ ・ ・ ・ ・ Ion beam deflection X electrode 23 ・ ・ ・ ・ ・ ・ Ion beam deflection Y electrode

Claims (1)

(57) [Claims] 1. An ion beam selected from only an ion beam extracted from an ion source, which is necessary for ion implantation, is selected by an ion analysis magnet, and then the ion beam is accelerated by an acceleration tube and implanted into a wafer. In the injection device, while attaching a silicon liner to the inner surface of the vacuum vessel of the ion analysis magnet, between the ion analysis magnet and the accelerator tube, a beam mask, a gate electrode,
Slit and low energy ion reflective electrode are arranged in this order,
Applying an output from a beam gate power supply to the gate electrode to deflect the ion beam by θ degrees, further arranging a deflection electrode behind the accelerator tube to deflect the ion beam by −θ degrees. Ion implanter.