TWI575548B - Ion source - Google Patents

Description

source of ion

The present invention relates to an ion source used in an ion implantation apparatus that irradiates carbon ions to a semiconductor substrate such as a germanium wafer. In particular, it relates to an ion source that uses a mixed gas of a carbon-containing process gas and a diluent gas in the process of ion beam generation.

Conventionally, a method of irradiating a semiconductor substrate with an ion beam containing carbon ions is used to suppress diffusion of a dopant in a depth direction of a substrate or to reduce crystal defects or the like under the amorphous layer.

However, in the case of generating carbon ions, there is a problem that the life of the ion source becomes short. For example, carbon dioxide is a representative example of a gas that generates carbon ions. When carbon dioxide is used as the processing gas, oxygen reacts with the metal member constituting the ion source to oxidize the metal member. Owing to this oxidation, for example, there arises a problem that the release of hot electrons from the filament or the reflection of electrons by the reflective electrode does not function smoothly, and the performance of the ion source deteriorates.

In order to solve the above problems, the technique described in Patent Document 1 has been used in recent years. In Patent Document 1, carbon dioxide is used as a processing gas, and hydrogen is mixed as a diluent gas in the processing gas.

Since oxygen which is decomposed from carbon dioxide by hydrogen mixing reacts with hydrogen, the reaction between oxygen and the metal member constituting the ion source is suppressed, and deterioration of performance of the ion source is alleviated. Therefore, it is considered that the ion source can be stably operated for a long period of time.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] US Application Publication No. 2012/0118232

However, even if a gas obtained by mixing carbon dioxide and hydrogen is used, the period during which the performance of the ion source can be maintained is limited. On the other hand, there is no limit to the requirements for the productivity improvement of semiconductor manufacturing apparatuses, and it is required to make the ion source stably operate for a longer period of time.

Further, carbon decomposed from carbon dioxide reacts with a metal member such as a filament of an ion source to form a carbon compound. Metal members such as filaments used in ion sources are generally composed of tungsten, with the concern that the reactants of the materials and carbon evaporate during operation of the ion source and enter electrically independent components within the ion source. Between, causing a short circuit between the components. Further, there is also concern that if the reactant evaporates after the filament reacts with carbon, the filament becomes fine, and the life of the ion source becomes extremely short. Regarding these aspects, even when hydrogen is used as a mixed gas, it still exists as a concern.

In order to achieve the above requirements and improve the concerns, the inventors of the present invention have repeatedly worked on the research, and as a result, helium has been successfully used as a gas instead of hydrogen to stabilize the ion source in a period far longer than hydrogen.

The specific configuration of the ion source is an ion source that generates an ion beam containing carbon ions, and includes: a plasma generation container that is supplied with a treatment gas containing at least carbon and a diluent gas containing at least ruthenium; and a thermoelectron release The outlet portion is disposed at an end portion of the plasma generation container so as to be electrically separated from the wall surface of the container to release hot electrons.

Although not explicitly explained in theory, it is considered that by using hydrazine as a diluent gas, the temperature of the plasma generated in the ion source can be lowered as compared with the case of using hydrogen as a diluent gas, thereby suppressing self-control. The evaporation of the reactants from which the carbon which is decomposed by the gas and the metal member constituting the ion source are evaporated. As a result, the ion source can be stably operated for a longer period of time than when hydrogen is used as the diluent gas.

The above treatment gas is desirably carbon dioxide.

Carbon dioxide is relatively inexpensive and readily available. Further, when ruthenium is used as the diluent gas, there is a special effect of suppressing the formation of O ⁺ ions in the plasma generation chamber. When carbon dioxide is decomposed, O ⁺ ions equivalent to C ⁺ ions are generated. The O ⁺ ion is a cause of oxidizing the metal member constituting the ion source, but the formation of O ⁺ ions can be remarkably suppressed by using ruthenium, and therefore, oxidation of the metal member constituting the ion source is suppressed, so that the ion source can be long-term The ground is stable.

The above diluent gas is desirably helium and argon.

Argon is relatively inexpensive and has a large mass. Moreover, it has properties that are not easily reacted with other substances. By using such a gas together with ruthenium, the reactant formed on the surface of the metal member constituting the ion source can be removed by the sputtering effect.

It is preferable that the thermoelectron emitting portion includes a cathode that discharges hot electrons into the plasma generating container and a filament that heats the cathode.

The life of the ion source can be further extended by using the above-described configuration and using an ion source of a type well known as a parathermal ion source.

It is desirable to arrange a ring-shaped heat shield around the cathode.

By using the configuration as described above, the cathode that emits hot electrons can be maintained at a high temperature. Moreover, since hydrazine is used as the diluent gas, the following can be suppressed: That is, an annular heat shield is arranged around the cathode, and the reactant of the cathode and the carbon is also adhered between the two members by evaporation, thereby causing an increase in the contact area between the two members. When the contact area between the two members is increased, the heat of the cathode is dissipated through the heat shield, but the physical contact between the two members can be suppressed by using the crucible, so that the temperature of the cathode can be maintained at a high temperature.

By using ruthenium as a diluent gas, evaporation of the reactants decomposed from the process gas and the metal member constituting the ion source can be suppressed, and the ion source can be stably operated for a longer period of time than when hydrogen is used as the diluent gas.

1‧‧‧Plastic generation container

2‧‧‧ cathode

3‧‧‧filament

4‧‧‧Reflective electrode

5‧‧‧First gas bottle

6‧‧‧Second gas bottle

7‧‧‧Flow Regulator

8‧‧‧ Magnet

10‧‧‧First gas supply road

11‧‧‧Second gas supply road

12‧‧‧ slot

13‧‧‧ line

14‧‧‧hot screen

B‧‧‧ Magnetic field

IS‧‧‧Ion source

Vf‧‧‧ filament power supply

Vh‧‧‧thermal power supply

Varc‧‧‧Arc Power Supply

Vsub‧‧‧ secondary arc power supply

Y, Z‧‧‧ axis

Fig. 1 is a schematic view showing an example of an ion source to which the present invention is applied.

Fig. 2 is a graph showing the temporal change of the thermal voltage under the conditions of different dilution gases.

Figure 3 is an enlarged view of the vicinity of the cathode of the ion source of Figure 1.

Figure 4 is a cross-sectional view taken along line A-A of Figure 3.

An outline of an example of an ion source to which the present invention is applied is depicted in FIG. The ion source IS is one of a type called a side heat type ion source that heats the cathode 2 by the filament 3 and releases hot electrons from the cathode 2 into the plasma generation container 1. Such an ion source IS is considered to have a longer lifetime than the conventional Berners type ion source.

The ion source IS to which the present invention is applied is not limited to the side heat type ion source, but by using the present invention in combination with such an ion source, the ion source can be stably operated for a longer period of time. Further, a Berners-type ion source of the cathode 2 (not shown) may be used instead of the parathermal ion source. In the present invention, when a side heat type ion source is used, the combined cathode 2 and The filament 3 is referred to as a thermoelectron emission portion, and when a Bernas ion source is used, the filament 3 is referred to as a thermoelectron emitting portion.

The first gas supply path 10 and the second gas supply path 11 are connected to the plasma generation container 1. These gas supply paths are connected to the first gas bottle 5 and the second gas bottle 6 via the flow rate adjuster 7, respectively. For example, carbon dioxide is enclosed in the first gas bottle 5, and a mixed gas containing helium and argon is sealed in the second gas bottle 6.

Further, as shown in the figure, the ion source IS includes the reflective electrode 4 at the end of the plasma generating container 1 opposed to the cathode 2. The reflective electrode 4 is used to return the hot electrons released from the cathode 2 to the cathode 2 side. Further, a pair of magnets 8 are provided outside the plasma generation container 1, and a magnetic field B is generated inside the plasma generation container 1 by the magnets 8. Here, it is assumed that the magnet 8 disposed outside the plasma generation container 1 is a permanent magnet, but an electromagnet may be used instead.

Various power sources are connected to the respective parts constituting the ion source. A filament power source Vf is connected between the terminals of the filament 3, and the amount of current flowing to the filament 3 is adjusted by the power source. Further, a thermal power source Vh is connected between the filament 3 and the cathode 2, and the temperature of the cathode 2 is adjusted by the thermal power source Vh. Further, an arc power source Varc is connected between the cathode 2 and the plasma generation container 1, and arc discharge between the cathode 2 and the plasma generation container 1 is realized by the power source. Further, a sub-arc power source Vsub is connected between the plasma generation container 1 and the reflection electrode 4, and the potential of the reflection electrode 4 is adjusted by the power source.

The gas supplied into the plasma generating container 1 is released by the hot electrons released from the cathode 2, and plasma is generated in the plasma generating container 1. The plasma beam is taken out from the lead opening of the wall surface of the plasma generating container (not shown) provided on the Z-axis direction side.

The thermal voltages representing the different dilution gases are depicted in Figure 2. A graph of time changes. The graph is a model representation of the experimental data.

2 is a graph showing an arc current (flowing between the cathode 2 and the plasma generation container 1) after the various parameters (gas flow rate or value of each power supply voltage) other than the value of the heat removal power source Vh of the ion source IS are kept fixed. When the current is changed in a fixed manner, the value of the thermal power source Vh is changed.

Further, three kinds of graphs are depicted in FIG. 2 in which the types of gases supplied to the plasma generation container 1 are different. A graph drawn by a one-dot chain line indicates a case where only the carbon dioxide is supplied to the plasma generating container 1, and a graph drawn by a broken line indicates a case where the plasma generating container 1 is supplied with a gas obtained by mixing hydrogen into carbon dioxide, by a solid line. The graph of the drawing shows a case where the plasma generating container 1 is supplied with a gas obtained by mixing cerium with carbon dioxide.

Generally, the cathode 2 is reduced by the change over time, and therefore, when the same arc current is to be obtained, the voltage value applied by the thermal power source will become larger with time. However, the rating of the thermal power source is determined by the specifications of the power supply, so that it is not possible to apply a voltage higher than the rated voltage.

According to the graph of Fig. 2, when the thermal power source is rated at 80 V, if there is no dilution gas, the desired arc current cannot be obtained after about 36 hours. Similarly, when hydrogen is used as the diluent gas, the desired arc current cannot be obtained after about 44 hours, and when hydrazine is used as the diluent gas, the desired arc current cannot be obtained after about 52 hours.

According to the results of this experiment, the use of hydrazine as a diluent gas allows the ion source IS to be stably operated for about 1.2 times as compared with the case of using hydrogen. That is, the life of the ion source IS becomes about 1.2 times longer. In view of the results of the experiment, in the present invention, hydrazine is used as a mixed gas mixed with the processing gas instead of the hydrogen used in the conventional patent document 1. The reason why strontium is superior to hydrogen is not clearly explained in theory, but it is considered Compared with the case where hydrogen is used as the diluent gas, the temperature of the plasma generated in the ion source IS can be lowered by using hydrazine as a diluent gas, whereby the carbon which is decomposed from the process gas and the ion source IS can be suppressed. Evaporation of the reactants of the metal member (the cathode 2 or the reflective electrode 4 in the example of Fig. 1).

An enlarged view of the vicinity of the cathode 2 of the ion source IS shown in Fig. 1 is depicted in Fig. 3. In the side heat type ion source IS, the release of hot electrons from the cathode 2 is performed. In order for the hot electrons to be efficiently released, the cathode 2 must be maintained at a high temperature. In order to achieve this, an annular heat shield 14 is disposed around the cathode 2. The heat shield 14 is used to keep the temperature of the cathode 2 at a high temperature in order to block the radiant heat from the cathode 2.

A cross-sectional view taken along line A-A of Fig. 3 is depicted in Fig. 4 . An annular groove 12 is formed at the end of the cathode 2, and the wire 13 is stopped there. The heat shield 14 which doubles as the holder of the cathode 2 protrudes toward the cathode 2 side, and the protruding portion abuts against the lower portion of the wire 13. Further, when the cathode 2 is mounted on the ion source IS, the Y-axis direction is vertically downward, and thus the wire 13 is hung on the heat shield 14, so that the cathode 12 does not fall off from the heat shield 14. Further, a filament 3 is disposed on the back surface of the cathode 2, and the filament 3 and the heat shield 14 are individually supported by a holder (not shown).

In the case where hydrogen is used as the diluent gas, if the material of the cathode 2 or the heat shield 14 is tungsten and the processing gas contains carbon, tungsten carbide is formed on the surface of the cathode 2 or the heat shield 14 due to the reaction with carbon. It is considered that the tungsten carbide has a relatively low melting point and evaporates in the plasma generating vessel 1 at a high temperature, and enters a gap formed between the cathode 2 and the heat shield 14, thereby being restored to tungsten.

As such, the heat shield 14 is in physical contact with the cathode 2. When the contact area is increased, the heat of the cathode 2 is dissipated via the heat shield 14. Therefore, if the thermal voltage is not set to a higher value, the same arc current cannot be obtained.

On the other hand, when ruthenium is used as the mixed gas, as described above, evaporation of the reactant of the metal member and carbon in the ion source IS can be suppressed, and therefore, physical contact between the cathode 2 and the heat shield 14 can be suppressed. The temperature of the cathode 2 is maintained at a high temperature. For the reason as described above, hydrazine is used as a mixed gas instead of hydrogen.

In the embodiment up to this point, carbon dioxide is used as a processing gas because it is inexpensive and easily available. If carbon dioxide is used as the processing gas and helium is used as the diluent gas, special effects can be obtained in the following respects.

When carbon dioxide is plasmad, an O ⁺ ion equivalent to C ⁺ ions is generated. The O ⁺ ions are responsible for oxidizing the metal members constituting the ion source. However, when the ruthenium is mixed, the formation of O ⁺ ions can be remarkably suppressed. Therefore, the oxidation of the metal member constituting the ion source can be suppressed, and the ions can be made. The source operates stably for a long time.

Even if ruthenium is used as the diluent gas, the reactants with the treatment gas are deposited on the metal member constituting the ion source. Since the deposit adversely affects the performance of the ion source, it is considered that argon is used as a diluent gas together with ruthenium as in the configuration shown in FIG. If argon is mixed in advance, it can be removed by sputtering by argon before the deposit becomes a larger block. Further, other rare gases such as helium may be used instead of argon. The reason for using argon is that the price is relatively low and easy to obtain, and the mass number is also somewhat large.

<Other Modifications>

Since the wall surface of the plasma generating container 1 is also composed of a high melting point metal, it is considered that the reactant with the processing gas is deposited in this portion. There is a concern that if the deposit becomes large and peels off, a short circuit is caused between members having different potentials disposed in the ion source. Therefore, in order to suppress the peeling of the deposit, the wall surface of the plasma-forming container 1 may be processed into a concavo-convex shape.

According to the experimental data, it is ideal to set the ratio of cesium to carbon dioxide. To the same extent, and argon is less than, for example, it is set to 30% or less of yttrium. The reason for this is that if the enthalpy is excessively excessively increased (for example, twice or more as carbon dioxide), the amount of current of the ion beam containing carbon ions is reduced, and if it is excessively reduced, problems such as evaporation of the metal member occur.

In the above embodiment, carbon dioxide is sealed in the first gas bottle 5, but carbon monoxide may be used instead. Further, an oven which can be used for a hydrocarbon such as cyclohexane or cyclopentene can be used instead of the gas bottle. Further, when a solid material such as dibenzyl is used, an evaporator capable of heating the material to a high temperature may be used instead of the gas bottle, and the material may be vaporized to be supplied to the plasma generation container 1.

Further, the supply path of the gas toward the plasma generation container 1 does not need to be separated by the treatment gas and the dilution gas. For example, the supply path from each gas bottle may be connected in the middle, and the supply path of the gas toward the plasma generation container 1 may be one. Further, it is not necessary to allow the diluent gas to be mixed in the second gas bottle 6 at the beginning, and it is also possible to independently supply the gas to the inside of the plasma generation container 1 by sealing the argon and argon into individual gas bottles in advance.

Further, in FIG. 1, the cathode 2 is disposed outside the plasma generation container 1, but the arrangement of the cathode 2 may be disposed inside the plasma generation container 1.

It is a matter of course that various modifications and changes can be made without departing from the spirit and scope of the invention.

1‧‧‧Plastic generation container

2‧‧‧ cathode

3‧‧‧filament

4‧‧‧Reflective electrode

5‧‧‧First gas bottle

6‧‧‧Second gas bottle

7‧‧‧Flow Regulator

8‧‧‧ Magnet

10‧‧‧First gas supply road

11‧‧‧Second gas supply road

B‧‧‧ Magnetic field

IS‧‧‧Ion source

Vf‧‧‧ filament power supply

Vh‧‧‧thermal power supply

Varc‧‧‧Arc Power Supply

Vsub‧‧‧ submerged arc power supply

X, Y, Z‧‧‧ axes

Claims (5)

An ion source for generating an ion beam containing carbon ions, and comprising: a plasma generation container supplied with a treatment gas containing at least carbon and a diluent gas containing at least ruthenium; and a thermoelectron emission portion, which is The electrode wall is electrically spaced apart from the wall surface of the container to discharge hot electrons. The ion source of claim 1, wherein the process gas system carbon dioxide. The ion source of claim 1, wherein the diluent gas comprises helium and argon. An ion source according to claim 1, wherein the thermoelectron emitting portion includes a cathode that discharges hot electrons into the plasma generating container and a filament that heats the cathode. An ion source according to claim 4, wherein a ring-shaped heat shield is disposed around the cathode.