JPH11224633A - Ion generation method using SF6 plasma - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a chemically stable, non-toxic SF ₆ gas as a sample gas for generating plasma, and to convert a solid sample fluoride with fluorine in SF ₆ plasma into an ion source plasma chamber. A method for generating ions of a sample element by generating the ions in the above step. SOLUTION: SF ₆ or a gas mixed with SF ₆ is supplied into a plasma chamber to generate SF ₆ plasma, and a solid sample placed in or near the plasma and fluorine or fluoride in the plasma are mixed. A chemical reaction is performed to generate fluoride of the solid sample, thereby increasing the vapor pressure of the solid sample to generate fluoride vapor containing the sample element, and the fluoride vapor is decomposed and ionized in the plasma to form the solid sample. Generate ions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In recent years, ion implantation into materials has been performed using accelerators and the like for the development of highly functional materials and semiconductor devices. Various ions to be implanted are supplied to a Freeman ion source or ECR (Electr).
The method is effective when generating with a well-known ion source such as an on-cyclotron resonance ion source.

[0002]

2. Description of the Related Art When a solid sample at a normal temperature is ionized by an ion source, the solid sample is vaporized by heating, and the gas is introduced into a plasma chamber to be ionized. As a method for heating a solid sample in this vaporization method, a method in which a solid material is put into a crucible and heated is generally known.

At this time, for example, a solid sample of a low vapor pressure substance having a high melting point, such as tungsten or silicon, is vaporized,
In order to obtain that sufficient vapor pressure, simply heating them in a crucible is not enough because the heating temperature is not enough.
A highly corrosive or toxic compound such as WF ₆ or SiF ₄ is used as a sample gas, and the substance is corroded and vaporized.

[0004]

Therefore, when vaporizing a solid sample of the above-mentioned low vapor pressure substance, special attention is required for the vaporizing operation or handling of the sample, and an accelerator or the like including an ion source is required. There was a problem of being corroded.

[0005] A method of directly vaporizing a solid sample by the heat of an ion source plasma or a method of irradiating a sample with an external laser to vaporize the sample have been disclosed as solid sample vaporization methods without using a crucible. It is difficult to maintain a good plasma, and requires additional equipment and power supplies such as lasers.

[0006] The method of the present invention eliminates these disadvantages,
It is possible to ionize a low vapor pressure substance having a high melting point efficiently without using a toxic gas and stably for a long time without using an additional device such as a laser.

[0007]

SUMMARY OF THE INVENTION The method of the present invention is chemically stable as a sample gas for generating a plasma.
The above disadvantage is eliminated by using non-toxic SF ₆ gas and generating fluoride of a solid sample in the ion source plasma chamber with fluorine in SF ₆ plasma.

Namely, the method of the present invention, SF ₆ plasma chamber of Freeman ion source device or ECR ion source device
Alternatively, a gas containing SF ₆ is supplied to generate SF ₆ plasma, and a solid sample placed in or near the plasma is chemically reacted with fluorine or fluoride in the plasma, and the fluorine of the solid sample is subjected to a chemical reaction. By generating a fluoride, the vapor pressure of the solid sample is raised to generate fluoride vapor containing the sample element, and the fluoride vapor is decomposed and ionized in plasma to generate ions of the solid sample.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where ions are generated using a Freeman ion source will be described below with reference to FIG. A hole is made in the center of the disk-shaped sample 1 and an arc chamber (plasma generation chamber) is passed through the hole through the filament 2.
3 Place it inside and below. SF ₆ gas 4 in this arc chamber
And SF ₆ plasma 5 is generated by collision with thermoelectrons generated from the filament (tungsten). This SF ₆ gas is mixed with an Ar gas for improving the plasma stability. The sample placed in SF ₆ plasma
The sample reacts with fluorine in the plasma to generate a fluoride of the sample.

[0010] When fluoride is used, many substances have an increased vapor pressure, and the temperature in the arc chamber becomes 1000 ° C or higher, so that it can be easily vaporized. The vaporized fluoride returns to the plasma again, is decomposed and ionized, and can generate target ions. These ions become an ion beam 7 by the action of the extraction electrode 6.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in the case where ions are generated using a Freeman ion source.

[0012]

Example 1 A hole was made in the center of a disk-shaped (10 mmφ × 5 mm) Nb sample, and a filament was passed through the hole and placed on the lower side in an arc chamber (plasma generation chamber). An SF ₆ gas was supplied into the arc chamber, and a thermal electron generated from a filament (tungsten) was collided with the SF ₆ gas to generate an SF ₆ plasma. The SF ₆ gas used was a mixture of Ar gas for improving the plasma stability. The Nb sample placed in the SF ₆ plasma reacted with fluorine in the plasma and vaporized to generate Nb fluoride gas. The vaporized fluoride returned to the plasma again, was decomposed and ionized, and Nb ions were generated. As a result, 15 μA of Nb ions could be obtained. This was about 150 times the amount of current when generating ions by Ar plasma generated by supplying only Ar gas.

FIG. 2 shows a mass spectrum when Nb ions are generated by SF ₆ plasma. As can be seen from this mass spectrum, a large amount of Nb fluoride was generated in the arc chamber. This indicates that niobium fluoride has a high vapor pressure and is easily vaporized to generate Nb ions. Therefore, a new ion generation method using SF ₆ has made it possible to generate high-current ions of a high-melting substance, which were difficult to generate without using a toxic gas or CCl ₄ gas with a Freeman ion source until now.

Similarly, when boron (B) and silicon (Si) were used as a sample by this method, 13 μA and 7 μA of B and Si ions were obtained, respectively. This was about 13 times and 30 times as large as the current amount when ions were generated by Ar plasma generated by supplying only Ar gas.

[0015]

[Embodiment 2] An ECR (Electron Cyclotron Re) utilizing ion confinement by a mirror magnetic field and electron cyclotron resonance by a microwave will be described below.
An embodiment of the ion source will be described with reference to FIG. The solid sample 1 is set in the plasma chamber. There S
F ₆ gas is introduced, and SF ₆ plasma 5 is generated by microwaves. At this time, SF ₆ contains S ions and F
Dissociated into ions.

In the case where the solid sample is tungsten, fluorine in the plasma reacts with tungsten to produce tungsten fluoride. Since tungsten fluoride has a boiling point of about 18 ° C., it is vaporized even at room temperature. This tungsten fluoride vapor is introduced into the SF ₆ plasma, and can be dissociated by electrons in the plasma to generate tungsten ions. Even when the solid sample is tantalum (Ta), it is fluorinated and its vapor flows into the plasma.

[0017]

According to the present invention, ions that have been difficult to generate stably without the use of a toxic gas or the like or an additional device such as a laser can be generated safely and efficiently and stably. Was. Furthermore, since fluoride is generated in the plasma chamber, the corrosive gas can significantly reduce the corrosion of the ion source and the accelerator as compared with the conventional method.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method of ionizing a solid sample using SF ₆ gas in a Freeman ion source.

FIG. 2 is a diagram showing a mass spectrum when Nb ions are generated by SF ₆ plasma.

FIG. 3 is a diagram illustrating a method of ionizing a solid sample using SF ₆ plasma in an ECR ion source.

[Explanation of symbols]

1: solid sample, 2: filament, 3: arc chamber, 4: SF ₆ gas, 5: SF ₆ plasma, 6: extraction electrode, 7: ion beam

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/265 H01L 21/265 603A

Claims (1)

[Claims] 1. Using a chemical reaction between a solid sample placed in or near a plasma of SF ₆ or a gas containing SF ₆ and fluorine or fluoride in the plasma,
A method of increasing the vapor pressure of a sample by generating fluoride of a solid sample and introducing fluoride vapor containing a sample element into plasma to generate ions of the solid sample.