JPH01232653A - Ion implanter - Google Patents

Abstract

PURPOSE:To neutralize positive electric charges remaining on the surface of a semiconductor wafer effectively by furnishing a magnetic field generating source on a wafer disc, and by forming a line of magnetic force on the surface of semiconductor wafer fixed onto the wafer disc. CONSTITUTION:A magnetic field generating source, for ex. a rod-shaped magnet 5, is installed on a holder 2 of a wafer disc 1. A positive ion 3a which has attained a wafer W intrudes into it, and positive electric charges 7 remain at this time on the surface Wa. An electron 4a, on the other hand, which has attained the wafer W together with the positive ion 3a moves on the surface Wa, but because a line of magnetic force 6 is formed on the surface Wa, the electron 4a makes cycloid motion in either direction depending upon the motion vector at the time of attainment to move in the direction across even the line of magnetic force 6. During this motion, the electron 4a collides with the positive electric charge 7 to neutralize it. This increases provability of collision of electron 4a with positive electric charge 7, and the residual positive electric charges 7 are neutralized effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an apparatus for implanting ions into a semiconductor wafer in semiconductor manufacturing.

<Prior Art> When a semiconductor wafer (hereinafter simply referred to as a wafer) is irradiated with an ion beam to implant ions, charges remain and accumulate on the surface of the wafer. When this charge is discharged to the wafer's substrate, it may partially destroy the semiconductor insulating film formed on the surface of the wafer, or the electric field generated by this charge may deflect the ion beam and cause it to reach the wafer. This causes problems such as hindering uniform ion implantation. Therefore, during ion implantation, it is necessary to remove the 'burden' that remains and accumulates on the surface of the wafer.

For this purpose, for example, an ion implantation device as shown in the schematic diagram of FIG.
6).

That is, a wafer W is mounted on a holder 12 of a conductive wafer disk 11, and B'' and As'' are placed on the wafer W.

Ion implantation is performed by irradiating an ion beam 13 consisting of positive ions 13a such as p", sb+, etc. During ion implantation, in order to release the positive charges 14 remaining on the surface Wa of the wafer W as described above, The wafer disk 11 is grounded.

However, the surface Wa of the wafer W is made of an insulating material such as Sin or photosensitive resin for forming a semiconductor.

Due to the presence of semiconducting materials such as single crystal or polycrystalline silicon, it is impossible to sufficiently remove residual positive charges 14 simply by grounding wafer disk 11.

Therefore, in order to neutralize the positive charge 14 with electrons, an electron generation source 15 and a target 16 for generating secondary electrons are provided near the ion beam 13. That is, primary electrons 17 from the electron source 15 that have traversed the ion beam 13 collide with the target 16 to generate secondary electrons 18. These electrons 19 consisting of secondary electrons 7 and 18 are captured by the beam 13 by being bound by the electric field generated by the ion beam 13, and the space charge of the beam 13 is neutralized. The positive ions 13a travel toward the wafer W along the dotted line 13.

The reason why the configuration uses the secondary electrons 18 from the target 16 in this way is to generate enough electrons from the primary electrons 17 emitted from the electron source 15 to neutralize the space charge of the ion beam 13. This is because it is difficult to capture.

In other words, in order to increase the amount of captured electrons, it is sufficient to reduce the kinetic energy of the electrons, but it is technically difficult to sufficiently reduce the kinetic energy of the primary electrons 17 emitted from the electron source 15. It is.

The positive ions 13a that have reached the wafer W enter into the wafer W, and at this time, positive charges 14 remain on the surface Wa. Then, the electrons 19 that have reached the wafer W together with the positive ions 13a move on the surface Wa, so that the positive charges 14
The positive charge 14 is neutralized by collision with the positive charge 14.

Further, the beam diameter of the ion beam 13 increases as it goes downstream due to repulsion between the positive ions 13a. As the beam diameter increases, the collision cross section with electrons 19 decreases, and the amount of captured electrons 19 decreases. To prevent this, an aperture 20 is provided upstream of the electron source 15 and target 16.

<Problems to be Solved by the Invention> However, in the ion implantation apparatus having the above configuration, the electrons 19 that have reached the wafer W move in random directions on the surface Wa, and thus collide with the positive charges 14 remaining on the surface Wa. The probability is small, and therefore the positive charge 14 cannot be efficiently neutralized. In other words, uniform implantation of ions is hindered.

Examining the uniformity of ion implantation using the above ion implantation device by looking at the sheet resistance of the wafer when the implanted ions are activated, it was found that the ion beam of A s ” was 80 kcV.
With an implantation energy of 10mA and an ion beam current of 10mA,
Further, when ion implantation is performed with the emission current of electrons captured by the ion beam set to an optimum value of 100 to 300 mA, the distribution of sheet resistance is approximately ±10%. Note that when an ion implantation device that does not perform electron neutralization is used, the distribution of sheet resistance is approximately ±20%.

In recent years, as the performance of semiconductor devices has improved, requirements regarding the sheet resistance distribution of ion-implanted impurities have become stricter, and it is desired to achieve ±3% or less with good reproducibility. In addition, since the insulating film formed on the surface of a semiconductor wafer has become thinner, to the order of several hundred, the problem of dielectric breakdown due to charges accumulated on the surface of the urinary wafer during ion implantation has become even more serious.

SUMMARY OF THE INVENTION An object of the present invention is to provide an excellent ion implantation device that can increase the probability that electrons collide with positive charges remaining on the surface of a semiconductor wafer and efficiently neutralize the positive charges.

Means for Solving the Problems> In order to achieve the above object, the ion implantation apparatus of the present invention has the following features:
A magnetic field generating source is provided on the wafer disk to form magnetic lines of force on the surface of a semiconductor wafer mounted on the wafer disk.

Effects> According to the above configuration, the electrons that have arrived at the semiconductor wafer together with positive ions move in a direction across the lines of magnetic force while performing cycloidal motion due to the presence of the lines of magnetic force. This increases the probability of collision between the electrons and positive charges remaining on the surface of the semiconductor wafer.

<Example> Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a schematic side cross-sectional view of the main part of the ion implantation apparatus according to the present invention, in which a semiconductor wafer W (
A state in which a wafer (hereinafter simply referred to as wafer W) is attached is shown. 2 is a schematic front view of the wafer disk 1 shown in FIG. 1. FIG.

As shown in the figure, the ion implantation apparatus of the present invention is B◆.

Ion implantation is performed by irradiating the wafer W with an ion beam 3 consisting of positive ions 3a such as As◆, P◆, and sb"'' together with electrons 4 captured by the ion beam 3. The features of this device are as follows. , in that the holder 2 of the wafer disk l is provided with a magnetic field generating source, for example, six rod-shaped magnets 5. These magnets 5 are used to form magnetic lines of force 6 on the surface Wa of the wafer W. For example, the N poles of the magnets 5 are aligned approximately at the center of the holder 2, and the S poles are located at the periphery of the holder 2. , are embedded radially within the holder 2.

By providing the magnet 5 as described above, the surface Wa is attached to the sea urchin.
Above, lines of magnetic force 6 are formed from the center of the wafer W toward the periphery. Furthermore, by reversing the polarity of the magnet 5,
The direction of the magnetic lines of force 6 may be reversed, that is, from the periphery of the wafer W toward the center.

Further, the magnetic flux density of the magnetic field on the surface Wa of the urchin caused by the magnet 5 is normally desirably 50 to 500 gauss, but the optimum value changes depending on the surface condition of the wafer W and the amount of charge of the ion beam 3. Therefore, the magnet 5 may be an electromagnet, and the magnetic flux density may be made variable.

Next, the operation of the ion implantation apparatus having the above configuration will be explained.

That is, the positive ions 3a that have reached the wafer W enter into the wafer W, and at this time, positive charges 7 remain on the surface Wa. On the other hand, the electrons 4a that have arrived at the wafer W together with the positive ions 3a move on the surface Wa, but since the magnetic lines of force 6 are formed on the surface Wa as described above, the electrons 4a move according to the motion vector at the time of arrival. As shown by curve 12 in FIG. 2, it moves in a direction that crosses the lines of magnetic force 6 while making a clockwise or counterclockwise cycloidal motion. And during this move,
The electron 4a collides with the positive charge 7 and neutralizes the positive charge 7.

In this way, the electrons 4a move in a cycloid on the surface Wa of the wafer W! By moving while moving, electron 4
The probability of collision between a and the positive charges 7 increases, and the positive charges 7 remaining on the surface Wa are efficiently neutralized.

FIGS. 3(a) and 3(b) show that As
'Ion implantation energy of 80 keV.

This is a characteristic diagram showing the sheet resistance distribution when implanted with an ion beam current of 10 m. The numbers in the figure are sheet resistance x 100.
The curves representing the values of and in the figure are equal sheet resistance lines at 5% intervals.

FIG. 3(a) shows the sheet resistance distribution when ions are implanted using the ion implantation apparatus of the present invention, and the average value is 11.5Ω/hole. As shown in the figure, the sheet resistance distribution in this case has a very small variation ranging from -3% to +2%.

On the other hand, FIG. 3(b) shows the sheet resistance distribution when ions are implanted using a conventional ion implantation apparatus without the magnet 5, and the average value is 11.5Ω/port. The sheet resistance distribution in this case varies widely from -3% to +20%.

That is, it can be seen that according to the ion implantation apparatus of the present invention, the characteristics of sheet resistance distribution are significantly improved.

<Effects of the Invention> As described above, in the ion implantation apparatus of the present invention, the positive charges remaining on the surface of the semiconductor wafer can be efficiently neutralized, so that there is no deflection of the ion beam due to the residual positive charges. Ions are uniformly implanted into the wafer, and the sheet resistance distribution characteristics are greatly improved, and can be reduced to ±3% or less. At the same time, the insulating film formed on the surface of the semiconductor wafer is no longer destroyed due to discharge of the residual positive charges.

[Brief explanation of the drawing]

FIG. 1 is a schematic side cross-sectional view of the main part of the ion implantation apparatus according to the present invention, and FIG. 2 is a schematic diagram of the inside of the wafer disk shown in FIG. 1. FIG. 3 is a characteristic diagram showing the sheet resistance distribution of a semiconductor wafer, and FIG. 4 is a schematic configuration diagram showing a conventional example. 1...Wafer disk, 3...Ion beam. 4.4a...electron, 5...magnet, 6...magnetic field lines. 7...Positive charge, W...Semiconductor wafer. Wa... surface. Patent Applicant: Oki Electric Industry Co., Ltd. Figure 1 Figure 2 2. Name of issue 1 Ion implanter 3 Person making correction/Relationship with IG Patent applicant address (105
) 1-7-12 Toranomon, Minato-ku, Tokyo Name (029)
) Oki Electric Industry Co., Ltd. Representative Director and President Nobuko Kosugi 4th Director Address (〒108) 4-10-3-5, Shibaura, Minato-ku, Tokyo, "Detailed Description of the Invention" column of the specification to be amended 6. Details of the amendment (1) "Semiconductor" on page 2, line 17 of the specification is amended to "semiconductor element." (2) Delete "In other words," in the second and third lines of page 5 of the specification. Insert ``Injection was prevented.'' (3) Delete "that is," on page 8, line 11 of the specification. that's all

Claims (1)

[Scope of Claims] An apparatus for implanting ions by irradiating a positively charged ion beam together with electrons captured in the ion beam onto a semiconductor wafer mounted on a wafer disk, comprising: a magnetic field generation source provided in the wafer disk; An ion implantation apparatus characterized in that magnetic lines of force are formed on the surface of the semiconductor wafer.