JP2550077B2 - Ion implantation method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an ion implantation method and apparatus for alleviating electrostatic charge during ion implantation with electrons.

(Prior Art) A conventional ion implantation apparatus will be described with reference to FIGS. 3 to 4. FIG. 3 shows an ion implantation apparatus provided with a mechanism for reducing the positive charge on the wafer due to ion implantation. There are an ion source 30 for generating and extracting ions, and a mass spectrometric section 31 for applying only a necessary ion among the extracted ions by applying a strong magnetic field. Then, there are an accelerating unit 32 for accelerating the ion beam that has passed therethrough to a desired energy, a converging unit 33 for converging the ion beam, and a scanning unit 34 for uniformly scanning the converged ion beam on the wafer 39. . Also, a disk on which the wafer 39 is placed
37 and a drive unit 38 that rotates and translates the disk 37.
There is.

Wafer using the ion implanter configured in this way
As a method of uniformly implanting ions into the 39,
At 34, the ion beam is sequentially scanned from one end to the other end on the wafer 39 in the XY directions orthogonal to each other, or the ion beam is fixed, and the disk 37 on which the wafer 39 is mounted is rotated.
And various methods such as a fixed beam method of translation.

When ions are implanted into the wafer 39 by using the above method, the ions implanted into the wafer 39 knock out electrons from the inside of the wafer 39 or implant into the insulator portion of the wafer 39. The wafer 39 is positively charged due to the accumulation of positive charges due to the ions. It is known that the insulator part causes electrostatic breakdown due to this. Therefore, an electron flood system 36 for supplying secondary electrons to the wafer 39 is provided in order to alleviate the positive charging of the wafer 39 and prevent electrostatic breakdown.

Next, the electron flood system 36 will be described with reference to FIG.

A wafer 42 is placed on the disk 41, and is held by a conductive holder 49 so that the wafer 42 does not move due to the rotation and movement of the disk 41. The electron flood system 36 is connected to the filament 46a, a DC power source 46b that heats the filament 46a to emit thermoelectrons 47, a target material 46c that receives the thermoelectrons 47 to generate secondary electrons 48, and a positive side of the target material 46c. The negative side of the DC power source 46b is connected to the negative side of the DC power source 46b.

Electron flood system configured in this way
The operation of 36 is as follows. First, the thermoelectrons 47 emitted from the filament 46a collide with the target material 46c.
Then, using the potential difference of the DC power supply 46d, the target material 46c
Secondary electrons 48 are generated from the surface of the wafer facing the wafer 42.
In this way, the positive charges on the wafer 42 due to the in-on beam 43 were alleviated by supplying the secondary electrons constantly during the ion implantation.

(Problems to be Solved by the Invention) The charge amount of the next wafer 42 scanned by the ion beam 43 is larger in the central portion than in the outer peripheral portion of the wafer 42.
Because the wafer 42 is mounted on the disk 41 in an insulated manner,
Then, it is fixed by a conductive holder 42. Therefore, when the ion beam 43 scans the outer peripheral portion of the wafer 42, the positive load of the ion beam 43 is easily grounded by the holder 42, so that the central portion of the wafer has a larger charge amount. As the number of times the wafer 42 is scanned with the ion beam 43 increases, the difference in the amount of positive charge between the outer peripheral portion and the central portion of the wafer 42 increases.

However, conventional electron flood systems
At 46, the amount of electrons supplied during the time when the wafer 42 is scanned by the ion beam 43 is constant. Therefore, when a constant supply of electrons necessary to effectively mitigate the positive charge when the ion beam 43 scans the central part of the wafer 42, the positive charge in the central part of the wafer 42 is most alleviated, On the contrary, the electrons supplied to the outer peripheral portion of the wafer 42 may become excessive and negative charge may occur.

It is an object of the present invention to provide an ion implantation method and an ion implantation apparatus that alleviate the charge of an object to be implanted.

[Structure of Invention]

(Means for Solving Problems) In order to achieve the above object, in the invention of the method,
The amount of electrons to be injected in order to inject the accelerated ions into the object to be injected and to suppress the charging due to this ion injection,
There is provided an ion implantation method, which is characterized in that it is changed according to a position where the ions are implanted.

Further, in the invention of the apparatus, in the ion implantation apparatus provided with means for injecting ions into the object to be implanted, and means for supplying electrons in order to suppress charging due to the implanted ions, There is provided an ion implantation device characterized in that an amount of supplied electrons is changed according to a position where the ions are implanted.

(Operation) By changing the amount of electrons to be supplied according to the position of the implanted ions with respect to the implantation target, the charging of the implantation target can be mitigated.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings. First, the electron flood system according to this embodiment will be described with reference to FIG.

The wafer 2 is placed on the disk 1 and further held by a conductive holder 9. Then, in the ion implantation apparatus shown in FIG. 3, ions 3 are implanted into the wafer 2 by the fixed beam method.

Then, electrons that neutralize the positive charges of the injected ions are supplied by the electron flood system 6. The electron flood system 6 includes a filament 6a that emits thermoelectrons 7, a pulse generator 6b that can variably control a current flowing through the filament 6a, and a filament 6a that faces the filament 6a and receives the thermoelectrons 7 to receive secondary electrons 8. Of the target material 6c for generating the pulse generator, the positive side of which is connected to the target material 6c, and the negative side of which is the pulse generator
It is connected to 6b and is composed of an acceleration DC power source 6d for extracting secondary electrons from the target material 6c. An ammeter 6e for monitoring the amount of secondary electrons 8 generated from the target material 6c is connected between the target material 6c and the ground. Further, there is provided a disk position detection unit 11 which monitors the movement of the disk 1 such as rotation and translation and detects at which position the ions are implanted into the wafer 2.

Ion implantation is performed by the method shown in FIG. 2 using the ion implantation apparatus configured as described above.

By combining the rotation and translation of the disk 21,
Ions scan from edge a ₁ of wafer 22 to b ₁ and then a ₂
From scanned from b _2, a ₃ to b _3, finally scanned from a _n to b _n. Here, the trajectory 23a of the ions scanned on the wafer 22 is as shown in FIG. As a result, ions are implanted into the entire surface of the wafer 22. Next, similarly, the adjacent wafers are ion-implanted. The amount of electrons supplied by the electron flood system 6 (FIG. 1) when the wafer 22 is being ion-implanted is as shown in FIG. 2 (B). In this figure, the current on the vertical axis is the current flowing through the ammeter (FIG. 1) that effectively monitors the amount of electrons supplied to the wafer 22.

In FIG. 2B, the period T ₁ is the time required for the ions to scan from the edge portions a ₁ to b _n of the wafer 22. Wafer
Electrons are supplied at the same time as Io scans over 22, and most of the electrons are supplied when passing through the center of the wafer 22. A triangular wave current waveform ends the supply of electrons at the same time when the scanning of ions ends. There is. Moreover, the period T ₂ of the up ions start of scanning of the wafer in the next from the first ion scanning end of the wafer 22 is electrons not supplied does not occur positively charged wafer next wafer 22 or by ions.

According to the present embodiment, by increasing the amount of electrons supplied to the central portion of the wafer 22 rather than the outer peripheral portion of the wafer 22, it is possible to reduce the negative charge on the outer peripheral portion of the wafer 22 which has been a problem in the past.
The difference in charge amount between the outer peripheral portion and the central portion of the wafer 22 can be reduced.

In this embodiment, the waveform of the current flowing through the ammeter 6e (Fig. 1) is a triangular wave, but it is not limited to this waveform.

Further, for example, as shown in FIG. 2 (A), when the ions scan from a ₃ to b ₃ , the supplied electrons may be changed. I.e. many electron supplied as the distance of ions to be scanned from a _2, when the ions come in the middle of a ₂ and b _3, and supplies the most electrons, and the electron quantity supplied approaches the b ₂ You can reduce it.

That is, the electrons may be supplied so as to alleviate the different charging depending on the position of the wafer 22.

〔The invention's effect〕

As described above in detail, according to the present invention, it is possible to reduce the dielectric breakdown of the injected object by mitigating the charge amount which differs depending on the position of the injected object.

[Brief description of drawings]

FIG. 1 is a view showing an electron flood system provided in an ion implantation apparatus according to the present invention, FIG. 2 is a current waveform diagram at the time of ion implantation according to the present invention, and FIG. 3 is a conventional ion implantation apparatus and an ion implantation apparatus according to the present invention. Basic configuration diagram, FIG. 4 is a diagram showing a conventional electron flood system. 1 ... Disk 2 ... Wafer 3 ... Ion 4 ... Ion beam introduction tube 6 ... Electron flood system 6a ... Filament 6b ... Pulse generator 6c ... Target material 6d ... DC power supply 6e ... Ammeter 7 ...... Thermionic 8 …… Secondary electron 9 …… Wafer holder 11 …… Disk position detector

Claims (3)

(57) [Claims] 1. An accelerated ion is injected into an object to be injected, and an amount of electrons supplied for suppressing charging due to the ion injection is changed according to a position where the ion is injected. Ion implantation method. 2. The amount of the electrons supplied when the ions are implanted is larger in the central portion than in the peripheral portion of the object to be implanted.
The ion implantation method described in the item. 3. An ion implantation apparatus provided with means for injecting ions into an object to be implanted and means for supplying electrons in order to suppress charging due to the implanted ions, which is supplied from the electron supply means. An ion implanter, wherein the amount of electrons is changed according to a position where the ions are implanted.