JPH09288981A - Ion beam extracting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extract an ion beam, having about 100% diborane ion from a high-frequency ion source, by extracting the ion beam with sheath electrode voltage, between a high-frequency electrode and plasma, made in a given range. SOLUTION: When plasma 14 is produced in the plasma chamber 10 of a high-frequency ion source 2, the plasma 14 has positive electric potential constantly to a high-frequency electrode 6 and a plasma chamber vessel 4. By this sheath voltage V1 , an electron in the peripheral part of the plasma 14, is accelerated toward the plasma 14 side, to collide with a hydrogen-dilluted diborane gas led into the plasma chamber 10. Here, the energy of the electron, colliding with the hydrogen-dilluted diborane gas, can be made within a range of 4-12eV, by making sheath voltage V1 within 4-12V, thereby extracting an ion beam 28, having nearly 100% of the diborane ion from the high-frequency ion source 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, for implanting impurities into a semiconductor substrate, and extracts an ion beam from a high-frequency ion source, and more specifically, an ion beam in which diborane ions are almost 100%. Regarding how to pull out.

[0002]

2. Description of the Related Art For example, boron (B) is implanted into a predetermined region of a silicon substrate to form a P-type region of a transistor. For this boron implantation, diborane ion B ₂ H _n ⁺ (n =
0-6) are used.

Since diborane self-decomposes when it is a gas having a concentration of 100%, it is usually diluted with hydrogen gas. By the way, it is said that it is difficult to dilute the diborane concentration higher than 20% (that is, 20% diborane and 80% hydrogen) with the current technology.

When plasma is generated by introducing diborane gas diluted with hydrogen into an ion source, hydrogen ions H ⁺ and monomer borane ions BH _n are usually contained in the plasma.
⁺ (N = 0 to 3) and dimer diborane ion B ₂
H _n ⁺ (n = 0 to 6) is generated.

In the case of implanting ions into the substrate, even if hydrogen is implanted, the hydrogen will escape from the substrate surface in the thermal diffusion process as a post process. Therefore, even if hydrogen is implanted, there is no problem in transistor characteristics, but if hydrogen ions are included in the ion beam, extra hydrogen ions are implanted at the same time as the target boron ions, and the implantation amount is usually Since it is measured by the beam current, hydrogen ions are also measured as the implantation amount, and thus the required implantation amount of boron ions is reduced.

Therefore, it becomes necessary to lengthen the implantation time or increase the beam current of the ion beam by the amount of extra hydrogen ions. The former leads to a decrease in throughput (processing ability of the substrate per unit time), and the latter leads to an increase in heat input to the substrate, both of which are not preferable.

On the other hand, even if molecular ions having hydrogen attached to a boron atom (that is, the above-mentioned borane ion and diborane ion) are implanted, the hydrogen attached to the boron escapes from the surface of the substrate in the thermal diffusion step as a post step. Therefore, there is no problem in the characteristics of the transistor. Also, if it is a molecular ion, the boron and hydrogen are measured as an injection amount as one lump, so the required injection amount of boron does not decrease,
Therefore, it is not necessary to inject extra as described above.

Since the borane ion contains one boron and the diborane ion contains two boron, the injection current of diborane ion is half that of borane ion when the same implantation amount is realized. There are advantages.

Further, with the high integration of LSIs, the size of one transistor tends to become smaller and the depth of its PN junction tends to become shallower. For example, the current 16Mbit D
In a RAM, the junction depth is about 100 nm, and boron ions are implanted at an energy of about 10 keV to achieve this. It is expected that the junction depth will be about 50 nm with further integration in the future, and in that case, it is necessary to implant boron ions with energy of about 3 keV.

When ions are electrically accelerated and transported,
The ion beam tends to diverge due to its space charge effect. The lower the accelerating voltage, the greater the effect of this space charge effect, and the more difficult it becomes to transport the ion beam.
Since the diborane ion has a mass number about twice that of the borane ion, a double acceleration voltage is required to make the injection range of diborane the same as that of borane. For example, in order to realize the implantation depth of about 50 nm, the acceleration energy of about 3 keV is used for borane ions, and about 6 keV, which is twice that for diborane ions. Therefore, diborane ions are less affected by the space charge effect and are easier to transport.

As described above, boron ion implantation is
It is preferable to use diborane ions because the beam current is half and easy to transport.

When borane ions are implanted into the substrate at the same time as the diborane ions, the borane ions are implanted at a deeper position as described above, which determines the junction depth. However, an ion beam of almost 100% is required.

[0013]

When a hydrogen-diluted diborane gas is introduced into a high-frequency ion source to extract an ion beam, almost 100% of the diborane ions are emitted from the ion source.
It has been difficult in the past to extract the ion beam.

To explain this in detail, an example of a high frequency ion source is shown in FIG. In this high frequency ion source 2, a gas 36 is introduced and ionized by a high frequency discharge to generate plasma 1
4, a plasma chamber 10 for generating 4 and an extraction electrode system 20 provided near the exit of the plasma chamber 10 for extracting an ion beam 28 from the plasma 14 by the action of an electric field.

The plasma chamber 10 has a cylindrical shape (for example, a cylindrical shape).
Plasma chamber container 4 and its rear surface (extracting electrode system 20
The opening of the plate-shaped high-frequency electrode 6 is covered with an insulator 8 interposed therebetween.

In this example, the plasma chamber container 4 also serves as one high-frequency electrode, and a high-frequency power source 16 is provided between the plasma chamber container 4 and the high-frequency electrode 6 via a matching circuit 18 including a series capacitor and the like. For example, high frequency power having a frequency of 13.56 MHz is supplied. As a result, a high frequency discharge is generated between the high frequency electrode 6 and the plasma chamber container 4, the gas 36 is ionized, and the plasma 14 is generated.

The extraction electrode system 20 is composed of one or more electrodes, usually a plurality of electrodes. Specifically, in this example,
The first electrode 2 arranged from the most plasma side toward the downstream side
The first electrode 22, the second electrode 22, the third electrode 23, and the fourth electrode 24 are included. Reference numeral 26 is an insulator. Each electrode 21-
24 is a porous electrode having a plurality of holes in this example, but may have a plurality of slits.

The first electrode 21 is used for extracting the ion beam 2
8 is an electrode for determining energy, and a positive high voltage (acceleration voltage) is applied from the acceleration power source 31 with reference to the ground potential. The second electrode 22 is an electrode that produces a potential difference between the second electrode 22 and the first electrode 21, and draws the ion beam 28 from the plasma 14 by the electric field generated by the potential difference. The second electrode 22 has a negative potential with respect to the potential of the first electrode 21 from the extraction power source 32. A voltage (drawing voltage) is applied. The third electrode 23 is an electrode that suppresses the backflow of electrons from the downstream side, and a negative voltage (suppression voltage) is applied from the suppression power supply 33 with reference to the ground potential. The fourth electrode 24 is grounded.

In this example, a plurality of permanent magnets 12 for generating a magnetic field for plasma confinement are arranged on the outer periphery of the plasma chamber container 4 and the upper surface of the high frequency electrode 6.

In such a high-frequency ion source 2, by introducing diborane gas diluted with hydrogen as the gas 36, the ion beam 28 containing diborane ions can be extracted.

Typical examples of the conventional operating conditions of such a high-frequency ion source 2 are shown in Table 1, and the proportion of diborane ions in the ion beam 28 extracted under such operating conditions is only about 2%. , Mostly hydrogen ions.

[0022]

[Table 1]

Therefore, conventionally, an analysis magnet (also called a mass separation magnet) is provided between the high-frequency ion source 2 and the substrate to be implanted, and a desired diborane ion is extracted from the ion beam 28 by the analysis magnet. Only the separated one was injected into the substrate.

However, the method using such an analysis magnet requires an analysis magnet and a power source for the analysis magnet, so that it is expensive and the ion implantation apparatus incorporating the same is large, heavy and expensive. There is a problem that becomes.

Moreover, in recent years, the size of the silicon substrate is 8
Although the size has increased from inches to 12 inches, etc., when the target substrate size increases, the ion beam size must be increased accordingly, and the analysis magnet that mass-separates such a large ion beam is also large. The above problem becomes more serious as it has to be realized.

Therefore, the main object of the present invention is to provide a method for extracting an ion beam of which diborane ions are almost 100% from a high frequency ion source using hydrogen-diluted diborane gas.

[0027]

The ion beam extraction method of the present invention uses the high-frequency ion source as described above to introduce hydrogen-diluted diborane gas into the plasma chamber of the high-frequency ion source and to provide a space between the high-frequency electrode and the plasma. Sheath voltage is 4
It is characterized in that the ion beam is extracted in the range of -12V.

According to this method, an ion beam having almost 100% diborane ions can be extracted from the high frequency ion source. The reason is as follows.

When electrons are made to collide with the diborane gas B ₂ H ₆ , diborane ions, borane ions and hydrogen ions are usually generated. In that case, the only reaction in which hydrogen ions are not generated is a reaction in which B ₂ H ₅ ⁺ (5 hydrogen 2 boron ions) is generated among diborane ions, and this is represented by the following formula 1.

[0030]

[Equation 1] B ₂ H ₆ + e → B ₂ H ₅ ⁺ + H + 2e

Other diborane ions B ₂ H _n ⁺ (n = 0 to 0)
4, 6), and in the reaction in which the borane ion BH _n ⁺ (n = 0 to 3) is generated, hydrogen ion is simultaneously generated. Therefore,
It suffices to preferentially cause the reaction of the above formula 1 by properly selecting the electron energy.

The results are shown in FIGS. 2 and 3. Both figures show the amount of ions generated when electrons are made to collide with diborane gas B ₂ H ₆ . As can be seen from FIG. 2, when the electron energy is 12 eV or less, B ₂ H ₅ ⁺
Is generated preferentially, but when it exceeds 12 eV, other diborane ions and borane ions are generated, and at the same time, as shown in FIG. 3, hydrogen ions H _n ⁺ (n = 1,
2) is also generated. If the electron energy is less than 4 eV, the diborane gas is insufficient for ionization, and no diborane ion is generated as shown in FIG. Thus, by setting the electron energy in the range of 4 to 12 eV, only diborane ion B ₂ H ₅ ⁺ can be generated. At this time, it is considered that the reaction of the above formula 1 is preferentially occurring.

FIG. 4 shows the amount of hydrogen ions produced when electrons collide with hydrogen gas. As you can see from this figure,
When the energy of electrons becomes 20 eV or more, the amount of hydrogen ions increases rapidly. This is because the electron energy is 2
This is because the hydrogen gas used for dilution is ionized at 0 eV or more. Therefore, the electron energy is 20e
It must be less than V.

In summary, by setting the energy of the electrons to collide with the hydrogen-diluted diborane gas in the range of 4 to 12 eV, hydrogen ions and borane ions are not generated, and only diborane ions B ₂ H ₅ ⁺ are almost generated. 100
% Can be generated. The inventors of this application have found this.

The method of realizing such electron energy in the high frequency ion source 2 as described above is as follows. That is, when the plasma 14 is generated in the plasma chamber 10 of the high frequency ion source 2, the plasma 14 is always positive with respect to the high frequency electrode 6 and the plasma chamber container 4 due to the difference in mobility of ions and electrons in the plasma 14. Take a potential. Therefore, a voltage difference is generated between the high frequency electrode 6 and the plasma 14 and between the plasma chamber container 4 and the plasma 14. This is the sheath voltage. The sheath voltage is different in magnitude between the high frequency electrode 6 side and the plasma chamber container 4 side, and is inversely proportional to the fourth power of the area. Usually, in addition to the area of the plasma chamber container 4 being larger than the area of the high-frequency electrode 6, the area of the plasma chamber container 4 side may include the area of the first electrode 21 having the same potential as the area. The area on the plasma chamber container 4 side is much larger, and therefore the sheath voltage V ₂ on the plasma chamber container 4 side is much smaller than the sheath voltage V ₁ on the high frequency electrode 6 side. Therefore, the sheath voltage V ₂ can be ignored.

Due to the sheath voltage V ₁ between the high frequency electrode 6 and the plasma 14, the electrons in the peripheral portion of the plasma 14 are accelerated toward the plasma 14 side and collide with the hydrogen-diluted diborane gas introduced into the plasma chamber 10. . The electron acceleration voltage at this time, that is, the sheath voltage V ₁ corresponds to the electron energy described above. Therefore, this high-frequency electrode 6
By setting the sheath voltage V ₁ between the plasma and the plasma 14 to be in the range of 4 to 12V, the energy of electrons that collide with the hydrogen-diluted diborane gas can be set to be in the range of 4 to 12eV. As a result, due to the above-mentioned reason, almost 100 diborane ions are emitted from the high frequency ion source 2.
% Ion beam 28 can be extracted.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION The sheath voltage V ₁ between the high frequency electrode 6 and the plasma 14 described above is, specifically, from the high frequency power source 16 to the high frequency ion source 2 (specifically, the high frequency electrode 6 and the plasma 14). It can be controlled by the frequency of the high-frequency power supplied (between the chamber containers 4), the high-frequency input power thereof, and the partial pressure of diborane in the plasma chamber 10.

In this case, if the high frequency is too low, it is difficult to sustain the discharge, and if it is too high, the high frequency cannot be injected into the high frequency ion source 2, and therefore 13.56 MHz.
To 500 MHz is preferable. The sheath voltage V ₁ tends to decrease as the frequency increases.

If the high-frequency input power is too small, it becomes difficult to sustain the discharge, and if it is too high, the heat load of the high-frequency ion source becomes too large to withstand.
A range of 00W is preferred. When the input power is increased, the sheath voltage V ₁ tends to increase.

If the partial pressure of diborane in the plasma chamber 10 is too high, discharge is generated in the extraction electrode system (specifically, between the first electrode 21 and the second electrode 22), and it is difficult to extract the ion beam 28. If it is too low, it becomes difficult to maintain the discharge in the plasma chamber 10.
It is preferably in the range of × 10 ⁰ Pa to 1 × 10 ^-2 Pa.

The sheath voltage V ₁ is measured, for example, by a voltmeter 38 between a high frequency electrode 6 and the plasma chamber container 4 via a high frequency blocking coil 40, as indicated by a two-dot chain line in FIG. Can be measured by connecting. In that case, the measured voltage also includes the sheath voltage V ₂ on the plasma chamber container 4 side, which is sufficiently smaller than the sheath voltage V ₁ on the high frequency electrode 6 side as described above. Can be ignored.

In the high frequency ion source 2 shown in FIG.
Tables 2 and 3 show the sheath voltage V ₁ , the ratio of the diborane ions B ₂ H ₅ ^{+ in} the extracted ion beam 28, and the overall evaluation when the high frequency, the high frequency input power, and the diborane partial pressure were changed. . Table 2 is a continuation of Table 3. In the comprehensive evaluation, the case where the proportion of B ₂ H ₅ ⁺ was 100% was indicated by a circle, and the other cases were indicated by a cross.

[0043]

[Table 2]

[0044]

[Table 3]

As can be seen from this table, the sheath voltage V ₁
Is in the range of 4 to 12 V described above, the ion beam 28 in which the diborane ions B ₂ H ₅ ^{+ are} almost 100% can be extracted.

Incidentally, conventionally, there was no idea to control the magnitude of the sheath voltage V ₁ between the high frequency electrode 6 and the plasma 14. Therefore, when the sheath voltage V ₁ was examined under the conventional typical operating conditions shown in Table 1 above, it was a very large value of 150 V as shown in the first row of Table 2. . Therefore, as described above, many hydrogen ions were produced, and the proportion of B ₂ H ₅ ⁺ was only about 2%.

The high-frequency ion source 2 shown in FIG. 1 is merely an example, and the structure of the extraction electrode system 20, the structure of the power supply for it, the arrangement of the permanent magnets 12, and the matching circuit 18 are shown.
The configuration and the like may be other than those described above. Even in that case, of course, the above-described ion beam extraction method of the present invention can be applied.

[0048]

As described above, according to the present invention, by extracting the ion beam with the sheath voltage between the high-frequency electrode and the plasma in the range of 4 to 12 V, the high-frequency ion source using diborane gas diluted with hydrogen can be used. , An ion beam with almost 100% diborane ions can be extracted.

As a result, it is possible to omit the analysis magnet and the power supply for the analysis magnet, which is reasonably inexpensive, and the ion implantation apparatus using such an ion beam extraction method can be made compact, lightweight, and low in cost. Cost can be reduced. Moreover, such an effect becomes more remarkable when the ion beam size is increased corresponding to the increase in the substrate size.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a high frequency ion source.

FIG. 2 is a graph showing the amount of boron-containing ions generated with respect to the energy of electrons when the electrons are made to collide with diborane gas.

FIG. 3 is a graph showing the production amount of hydrogen ions with respect to the energy of electrons when the electrons are made to collide with diborane gas.

FIG. 4 is a graph showing the production amount of hydrogen ions with respect to the energy of electrons when the electrons are made to collide with hydrogen gas.

[Explanation of symbols]

 2 high frequency ion source 4 plasma chamber container 6 high frequency electrode 10 plasma chamber 14 plasma 16 high frequency power supply 18 matching circuit 20 extraction electrode system 28 ion beam 36 gas

Claims (1)

[Claims] 1. A plasma chamber container having a cylindrical shape, and a high-frequency electrode having an opening at a rear surface portion thereof covered with an insulator, and a plasma chamber is formed inside the high-frequency electrode. High-frequency electric power is supplied between the electrode and the plasma chamber container to generate a plasma in the plasma chamber by ionizing the gas introduced into the plasma chamber by the high-frequency discharge. A method for extracting an ion beam, which comprises using an ion source to introduce hydrogen-diluted diborane gas into the plasma chamber and extracting the ion beam with a sheath voltage between the high frequency electrode and the plasma being in the range of 4 to 12V. .