JPS638577B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the composition of raw material gas used when forming ions.

Conventionally, an atomic (or molecular) gas having atoms (or molecules) of a desired ion species as a constituent element has been used as a raw material gas for forming ions. Therefore, it is necessary to supply a small amount of raw material gas, so there is a drawback that it is difficult to control the supply amount, or if the raw material gas is chemically active such as oxygen gas or boron trifluoride gas. In the case of
When it is poisonous, such as phosphingas,
The drawback was that it was dangerous for those who handled it.

In order to eliminate these drawbacks, the present invention uses a chemically stable gas that is difficult to ionize into a gas (hereinafter referred to as the first gas) that has atoms (or molecules) of the desired ion species as constituent elements as a raw material gas. A gas mixture of a gas (hereinafter referred to as second gas) and a chemically stable gas that is easily ionized (hereinafter referred to as third gas) is used, and the present invention will be described in detail below.

Although the first gas is essential to obtain the desired ions, alone it has the drawbacks mentioned above. Therefore, by mixing the second gas with the first gas, the total gas supply amount can be increased and the concentration of the first gas can be reduced while reducing the influence on the ionization of the first gas. That is, even if the amount of first gas supplied is small, the total amount of gas supplied is large, making it easy to control the amount of gas supplied. Furthermore, since the concentration of the first gas is reduced, the supply device and the ion source are less likely to be contaminated or damaged, or the toxicity is reduced. For example, when the first gas is oxygen gas, combustion support is weakened and oxidation of the ion source is suppressed. In addition, in a normal ion source, ions are focused at the center by magnetic flux or the like, whereas the inner wall of the ion source is surrounded by a second gas that does not ionize to protect the inner wall of the ion source, thereby reducing contamination of the inner wall of the ion source. for example,
When the first gas is boron trifluoride gas, boron trifluoride reduces clogging of the gas system of the supply device by reacting with air remaining in or leaking into the supply device. Further, for example, when the first gas is arsine gas or phosphine gas, the ratio of toxic gas to all source gases decreases, so the toxicity is weakened even if the amount of leakage is the same.

By the way, in order to fully exhibit the effects of the second gas described above, it is necessary to increase the composition ratio of the second gas, which creates a new drawback that prevents the ionization of the first gas. Therefore, by mixing a third gas and promoting ionization, it is possible to
To prevent ionization of a first gas from being hindered even if the amount of gas is large. In addition, if there is too much third gas,
Only the ionization of the third gas becomes significant and exceeds the ionization of the first gas, resulting in the opposite effect.
The gas composition ratio should not be too high.

As the type of the first gas, a gas type that is normally used as an ion source source gas may be used. As for the type of second gas, it is preferable to use helium gas, neon gas, etc., which have a small atomic number and are difficult to ionize among chemically stable inert gases. Hydrogen gas may be used, or a mixed gas of these gases may be used. Among chemically stable inert gases, argon gas, krypton gas, xenon gas, radon gas, etc., which are easily ionized and have a large atomic number, are preferable as the third gas, and mixtures of these gases are also preferable. It's okay.

Next, as an embodiment of the present invention, the desired ion species is O ⁺ or O ₂ ⁺ , the first gas is oxygen (O ₂ ) gas, the second gas is helium (He) gas, and the third gas is argon (Ar ) Let's discuss the case of gas.

Figure 1 is a block diagram for explaining the outline of a measuring device for measuring ion formation and ion current, in which 1 is a cylinder for supplying a raw material mixed gas to obtain desired ion species, and 2 is a cylinder for supplying a raw material mixture gas to the ion source. A control device for controlling the raw material gas supply amount; 3 an ion source for generating ions; 4 an extraction voltage application device for extracting ions generated by the ion source;
5 is an electromagnet for ion species analysis to obtain only desired ions from among the extracted ions, and 6 is an ion current measuring device for the extracted ions. The cylinder 1 for supplying the raw material mixed gas may be a cylinder in which a gas mixed in advance is sealed, or a cylinder in which a gas mixing device is added to a cylinder in which only gases having respective composition ratios are sealed.

Figure 2 is a diagram showing the characteristics of O ⁺ and ₂ ⁺ ion currents when the composition ratio of the source gas is changed using the _measuring device shown in Figure 1. Curve b is the O ^{2 +} ion current in the case of a two-gas mixture with He gas, curve b is the O ₂ ⁺ ion current in the case of a similar gas mixture, and curve c is O ₂ /He.
Mixed gas with third gas Ar gas against O ₂ gas
O ⁺ ion current in the case of O ₂ /He/Ar three-gas mixture mixed at a ratio of 10%, curve d is the O ₂ ⁺ ion current in the case of a similar mixed gas, curve e
is the O + ion current, curve f, in the case of O ₂ /He / Ar mixed gas, ^which is O ₂ /He mixed gas and Ar gas as the third gas at a ratio of 1% to O ₂ gas.
is the O ₂ ⁺ ion current in the case of a similar mixed gas, and curve g is the gas supply pressure to the ion source at each gas composition ratio.

First, in the measuring device shown in Fig. 1, when a mixed O ₂ /He gas, which is a mixture of O ₂ gas as the first gas and He gas as the second gas, is used as the raw material gas, the curves a and b in Fig. 2 As shown in , both O ⁺ and O ₂ ⁺ ion currents decrease by including He gas as the second gas compared to the ion current in O ₂ gas as the first gas, but the composition of the He gas as the second gas decreases. ratio to 90
Even if the ion current increases to nearly 60%, the ion current decreases by 60% compared to the magnitude of the ion current in the case of only _O2 gas as the first gas.
It can be suppressed to about %.

Next, when Ar gas as the third gas is added to this O ₂ /He two-gas mixture at a ratio of 10% to the O ₂ gas as the first gas, as shown in curves c and d in Figure 2, , the ionic current can be slightly restored. If the amount of Ar gas added is 1% to the O ₂ gas of the first gas, as shown in curves e and f in Figure 2,
The ion current can be significantly improved compared to the case of a two-gas mixture of the first gas and the second gas. Especially the first
The composition ratio of the three mixed gases of O ₂ gas, He gas as the second gas, and Ar gas as the third gas, respectively.
When set to 10%, 90%, and 0.1%, the O ⁺ ion current becomes
In addition, the composition ratio of similar gases was set to 40% and 60%, respectively.
%, 0.4%, the O ₂ ⁺ ion current is 100% the magnitude of the ion current in the first O ₂ gas.
I can recover.

On the other hand, as for the supply pressure of the raw material gas, as shown by curve g in Fig. 2, by increasing the composition ratio of He gas, which is the second gas, the gas supply pressure can be increased.
That is, a large amount of gas can be supplied, and the supply amount can be easily controlled. For example, in curve g in Fig. 2, when the raw material gas is only O ₂ as the first gas, the raw material gas supply pressure is 4 μ;
A mixed gas of O ₂ /He/Ar with a composition ratio of 40% and 60%.
%, 0.4%, the raw material gas supply pressure is 6 μ; when the composition ratio is 10%, 90%, 0.1% with the same mixed gas,
The raw material gas supply pressure increases to 35μ. This is the second
This is an effect achieved by increasing the composition ratio of He gas. Furthermore, the stability of the formed ions can be maintained even if the total amount of supply becomes large because the first gas itself is in a small amount.

Although the case of the O ₂ /He/Ar three-component mixed gas has been described above, similar results can be obtained with other combinations of the first, second, and third gases if the mixing ratio is appropriately selected.

As explained above, the present invention uses a mixed gas consisting of the above-mentioned first, second and third gases as a raw material gas when forming ions by gas discharge. Without reducing the ion current obtained with the raw material gas (first gas) (effect of the third gas), the effect of the second gas makes it very easy to control ion formation, especially the gas supply amount. can,
Moreover, since the ions can be maintained stably after formation,
For example, continuous processing or labor saving of the ion implantation process using the ion formation can be realized. Furthermore, contamination and damage to the ion source caused by the raw material gas, toxicity of the raw material gas, etc., which have traditionally been problems in the ion formation mechanism, can be significantly reduced by the effect of the second gas, extending the life of the ion source, and It has the characteristics of reducing the dangers associated with gas handling.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining the outline of a measuring device for measuring ion formation and ion current, and FIG. 2 is a diagram showing experimental data for demonstrating the effects of the embodiment of the present invention. O ₂ /
O ⁺ when changing the composition ratio of He/Ar ternary mixed gas
FIG. 2 is a diagram showing the relationship between O ₂ ⁺ ion current and mixed raw material gas supply pressure. In the figure, 1... raw material gas cylinder, 2... gas supply amount control device, 3... ion source, 4... ion extraction voltage application device, 5... electromagnet for ion species analysis, 6... ion current measuring device.

Claims (1)

[Claims] 1 When forming oxygen ions by gas discharge,
An ion formation method characterized by using, as a raw material gas, a mixture of oxygen gas, chemically stable helium gas that is difficult to ionize, and chemically stable argon gas that is easy to ionize.