JPH0234428B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ion implantation apparatus for wafers, and particularly to an ion implantation apparatus of a type in which a wafer is fixed and an ion beam is moved.

[Background of the invention]

As the demand for semiconductor devices increases, improving the efficiency of ion implantation into wafers, which are the material for semiconductor devices, has become an important issue, and various ion implantation devices are being developed to improve productivity and implantation accuracy. be. For example, a device that scans and implants an ion beam onto a rotating disk with a large number of wafers mounted on the same circumference, or a device that rotates a rotating disk with a large number of wafers mounted on the same circumference and directs the ion beam in its diametrical direction. This is a system in which the ion beam is moved back and forth while the ion beam is fixed. These ion implantation devices have advantages and disadvantages, but the latter ion implantation device, which uses a fixed ion beam, is large and has a complicated structure due to the movement of the rotating disk.

FIG. 1 is a principle diagram showing the basic configuration of an ion implantation device. 1 is an ion source, 2 is an ion source housing, and 3 is an electromagnet. An ion beam 4 emitted and accelerated from the ion source 1 is mass-separated by the electromagnet 3. Of the separated ions, only desired ions are selected by a slit 6 attached to the analysis tube 5 and implanted into the wafer 7 in the implantation chamber 8.

When injecting ions with different masses, use electromagnet 3.
This is done by changing the magnetic force of
In order to increase the amount of ions, a suitable gas is introduced into the ion source housing 2. In addition,
Ion source housing 2, analysis tube 5 and implantation chamber 8
The interior is evacuated to a high vacuum state so that movement of the ion beam 4 cannot be prevented.

Since the ion beam 4 that has arrived at the wafer 7 passes through the slit 6, it has a rectangular cross section that is long in the direction perpendicular to the plane of the paper. Therefore, in order to uniformly implant ions into the wafer 7, it is necessary to scan the ion beam 4 or to move the wafer 7 back and forth.

FIG. 2 is a sectional view of a main part of a conventional wafer moving type ion implantation apparatus. In this device, a large number of wafers 7 are mounted on the same radius of a rotating disk 9.
At the same time, the rotation axis 11 is rotated in the Y-Y′ direction.
This method performs ion implantation by reciprocating. The wafer 7 is inserted into the cassette 25 and attached to the rotating disk 9 by a spring 26. A rotating shaft 11 directly connected to the rotating disk 9 is rotated by a pulse motor 16 via a shaft 15 and a pair of bevel gears 13 . Further, the rotating shaft 11 penetrates a rotating vacuum seal 10 attached to the gear housing 12 to maintain the vacuum in the driving chamber 8.

The gear housing 12 is movably coupled to a flange 21 attached to the driving chamber 8 by bellows 14 and 23 via a ball bearing 20, and a female threaded plate 24 is airtightly fixed between the gear housing 12 and the bellows 23. A threaded rod 22 is screwed together. That is, the driving chamber 8 is equipped with a rotary vacuum seal 1.
A vacuum is maintained by bellows 14 and 23, and gear housing 12 is configured to be able to reciprocate in the Y-Y' direction by bellows 14 and 23. Therefore, the volume of the driving chamber 8 needs to be large enough to allow for movement.

An outline of the operation of such an ion implantation device will be explained below. When the pulse motor 19 is rotated, the threaded rod 22 rotates, moving the gear housing 12 and the rotating disk 9 in the Y-Y′ direction, thereby adjusting the R dimension, which is the distance between the center of the ion beam 4 and the center of the rotating shaft 11. change. Moreover, when the pulse motor 16 is rotated, the rotating disk 9 can be rotated.
Therefore, by rotating the pulse motors 16 and 19 at the same time, uniform ion implantation can be performed on a large number of wafers 7 at the same time. Usually 25 on rotating disk 9
Since one wafer 7 is attached, 25 implanted wafers 7 can be obtained by one implanting operation.

However, since the gear housing 12 is provided in the driving chamber 8 and movably connected to each other by the bellows 14 and 23, the structure becomes complicated and the volume of the driving chamber 8 becomes large. Therefore, the evacuation time when replacing the rotary disk 9 becomes longer, and the production efficiency decreases accordingly. Further, since the rotating shaft 11 is driven by the bevel gear 13, it is difficult to employ a direct cooling method such as providing a water pipe on the rotating shaft 11 and cooling the rotating disk 9 with water. Furthermore, since the wafer 7 is mounted using the cassette 25 and the spring 26, there are drawbacks such as the troublesome mounting of the wafer 7.

In addition, when exchanging wafers, the conventional device uses a rotating disk 9, a gear housing 12, and a pulse motor 1.
The drive mechanism including 6, 19, etc. uses a large-scale opening/closing mechanism to open the wafer 7 and expose the wafer 7, and the weight of the moving parts increases, the opening/closing operation takes time, and a large installation floor space is required. There were problems such as:

A further disadvantage of the mechanical scanning method is that it has a short lifespan. Bellows 14, 23 for scanning
Since it moves up and down repeatedly, its cooling cannot be avoided.
They must be replaced as appropriate, but this requires a great deal of cost and time. A conventional device in which the wafer 7 is fixed and the ion beam 4 is scanned by a magnetic field is composed of a separation magnetic field for separating ions and a deflection magnetic field for irradiating the separated and selected ions onto the wafer 7. However, a correction magnetic field is installed separately to prevent changes in the beam width on the wafer 7 caused by scanning the ion beam, and three large magnetic fields are required, which increases the size of the device. It has disadvantages such as:

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide an ion implantation device that is small, easy to operate, and operates with high efficiency and precision.

[Summary of the invention]

The ion implantation apparatus of the present invention includes an ion source, a mass separation magnet and a mass separation slit that separate ions emitted from the ion source, and a deflection magnet that displaces an ion beam of a specific mass that exits the mass separation slit. and an ion implantation chamber for implanting the ion beam into a wafer, wherein a reduced image of the ion source is placed at the position of the mass separation slit by the mass separation magnet using the ion source as an object point. means for forming an enlarged image of the reduced image in the ion implantation chamber by the deflection magnet using the reduced image at the position of the mass separation slit as an object point; wafer support means for positioning the wafer on a rotating disk in the ion implantation chamber in the ion beam made parallel by means; magnetic field strengths of the mass separation magnet and the deflection magnet; and the mass separation slit. The wafer is characterized in that it has a control means for scanning the wafer in synchronization with the position of the ion source and uniformly implanting the ions emitted from the ion source into the wafer.

[Embodiments of the invention]

FIG. 3 is an ion optical system diagram of an ion implantation apparatus which is an embodiment of the present invention. The ion beam 4 emitted from the exit slit 31 of the ion source 1 is deflected by the magnetic field of the mass separation magnet 32, and specific ions are selected by the mass separation slit 33. The ion beam of equal mass that exits this slit is deflected by the deflection magnet 3.
The ion beam is incident on the ion beam 4 and is deflected here, forming a parallel beam and focusing on an imaging position 35 . The wafer 7 placed around the rotating disk 9 in front of the imaging position 35 is irradiated with this ion beam.

The rotating disk 9 is rotated by a drive motor 36, which includes a magnetic field power source 37 for changing the magnetic field of the mass separation magnet 32, a motor 38 for moving the mass separation slit 33, and a magnetic field for changing the magnetic field of the deflection magnet 34. The deflection magnetic field power source 39 and the like are controlled by signals from the control section 40. That is, by sending a signal synchronized with the magnetic field scanning of the mass separation magnet 32 to the motor 38 and deflection magnet power supply 39, ions of a desired mass are selected and uniformly implanted into the wafer 7.

Note that, assuming that the magnetic field strength is B, the magnetic field radius is r, the ion acceleration voltage is V, and the ion mass number is M, the following relationship is obtained.

Br=144√ This means that when M and V are kept constant and the magnetic field strength B is changed, the trajectory of the ion beam can be known as a change in the magnetic field radius r. Furthermore, it can be understood that the magnetic field strength B changes in proportion to the output currents of the separation magnet power supply 37 and the deflection magnet power supply 39, and that the magnetic field radius r is inversely proportional to the magnet strength B by expanding the above equation.

When a specific ion among the ions emitted from the exit slit 31, which is the object point S of the ion source, is deflected by the magnetic field of the mass separation magnet 32, the magnetic field radius
Following the trajectory of R ₁ , R ₂ , R ₃ , mass separation slit 33
Create image points P ₁ , P ₂ , and P ₃ on the plane of . Therefore, the mass separation slit 33 is moved and the magnetic field strength of the mass separation magnet 32 is changed. Furthermore, when the ion beam is deflected by the deflection magnet 34, it is performed in synchronization with the magnetic field sweep of the mass separation magnet 32, so that the ion beam is emitted in parallel through the orbits of r ₁ , r ₂ , and r ₃ , and the imaging position is Images P ₁ ′, P ₂ ′,
We get P ₃ ′.

Since the wafer 7 is placed in front of the images P ₁ ', P ₂ ', and P ₃ ', the shape of the ion beam 4 is constant on any surface of the wafer 7. Furthermore, in order to obtain uniformity of the ion beam, the deflection magnet 34 is an expanding system. For example, if the slit width of the exit slit 31 is 2 mm and the reduction ratio of the mass separation magnet 32 is 1/2, the imaging width of P ₁ , P ₂ , and P ₃ will be 1 mm (within 2 mm even if aberrations are included). ). The width of the images P ₁ ′, P ₂ ′, and P ₃ ′ formed by the deflection magnet 34 with a magnification of 10 times is 10 mm.
(20mm even if the amount of aberration is added), and even if the wafer 7 is placed in front of it, the image width on the wafer 7 surface is
It is extremely easy to keep it within 30mm.

In the apparatus of this embodiment, the mass separation slit 33 is the only mechanical scanning section, but this slit is essential to all ion implantation apparatuses and is not particularly added. Only the control for moving this mass separation slit 33 in synchronization with the magnetic field scanning is added. In addition, the mass separation slit 33
It is easy to move small parts in a straight line.

In order to uniformly implant ions into the wafer 7, magnetic field scanning is performed at a speed inversely proportional to the radius R of the rotating disk 9 on which the wafer 7 is mounted. Further, at this time, the scanning of the mass separation slit 33 and the deflection magnetic field, which are performed synchronously, is also performed at a speed inversely proportional to R. In this way, completely uniform ion implantation becomes possible.

The ion implantation apparatus of this embodiment has the following effects.

1 The rotating disk 9 to which the wafer 7 is attached is the rotating shaft 1
1 is merely rotated without being moved laterally, the driving chamber 8 is made smaller, the evacuation time is shortened, and the driving efficiency is improved.

2. The driving chamber 8 must be clean, but since there is no mechanical system for moving the rotary shaft 11 laterally as described above, contaminants will not be diffused.

3. Since only one deflection magnet 34 is required and the correction magnetic field required in the conventional magnetic field scanning method is not required, a relatively inexpensive and compact device can be obtained.

4 Since the structure of the rotating disk 9 is simple, the wafer 7
can be easily cooled.

〔Effect of the invention〕

The ion implantation apparatus of the present invention can carry out uniform ion implantation while moving the ion beam onto the wafer on the rotating disk, and therefore has the advantage of being compact and highly efficient.

[Brief explanation of drawings]

Fig. 1 is a principle diagram showing the basic configuration of an ion implantation device, Fig. 2 is a sectional view of main parts of a conventional wafer movement type ion implantation device, and Fig. 3 is an ion implantation device according to an embodiment of the present invention. FIG. 3 is an ion optical system diagram of the implantation device. DESCRIPTION OF SYMBOLS 1... Ion source, 4... Ion beam, 7... Wafer, 8... Implanting chamber, 9... Rotating disk, 31... Exit slit, 32... Mass separation magnet, 33... Mass separation slit, 34... Deflection magnet, 35... Imaging position, 36...
Drive motor, 37... Separation magnet power supply, 38... Slit motor, 39... Deflection magnet power supply, 40... Control unit.

Claims (1)

[Claims] 1. An ion source, a mass separation magnet and a mass separation slit that separate ions emitted from the ion source, a deflection magnet that displaces an ion beam of a specific mass that has exited the mass separation slit, and a deflection magnet that drives the ion beam onto a wafer. an ion implantation apparatus having an ion implantation chamber in which the ion source is inserted into the ion implantation chamber;
means for forming an enlarged image of the reduced image in the ion implantation chamber by the deflection magnet using the reduced image at the position of the mass separation slit; a wafer support means for positioning the wafer on a rotating disk in the ion implantation chamber into the ion beam that has been heated, and synchronizing the magnetic field strength of the mass separation magnet and the deflection magnet with the position of the mass separation slit. an ion implantation apparatus comprising: control means for scanning the ion source and uniformly implanting ions emitted from the wafer into the wafer.