JPH0734399B2 - Radical beam generation method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for generating a radical (active species) beam used for forming a thin film or the like.

[0002]

2. Description of the Related Art Attempts have been made to form a thin film on a substrate by injecting a radical beam into the substrate. For example, attempts have been made to form an amorphous silicon thin film using silane radicals and to form a diamond thin film using methane radicals.

An example of an apparatus for generating such a radical beam is shown in FIG. This apparatus comprises a radical beam source 2 in which a bottomed cylindrical discharge electrode 6 (also called a hollow cathode) is housed in a bottomed cylindrical main body container 4,
It is provided with a high frequency power supply 10 for supplying high frequency power.

A desired source gas (for example, SiH ₄ + H ₂ , CH ₄ + H _2, etc.) 8 is supplied to the radical beam source 2, and the discharge electrode 6 (more specifically, between it and the main container 4) is supplied. When high-frequency power is supplied from the high-frequency power source 10 via the matching box 12, for example, high-frequency discharge mainly occurs inside the discharge electrode 6 and the source gas 8
Is decomposed by discharge to generate plasma 14. Many radicals are present in the plasma 14, and these radicals 16 are obtained by being extruded from the opening of the radical beam source 2 by the flow of the raw material gas 8 and the like. In that case, the high frequency power supplied to the radical beam source 2 is conventionally a continuous sine wave, and the frequency thereof is usually 13.56 MHz.

[0005]

However, although various kinds of radicals are simultaneously generated in the plasma 14, it is impossible to selectively increase the required radical species in the prior art. However, there is a problem in that a large amount of unnecessary radicals are mixed, so that a high-quality radical beam cannot be obtained.

Further, since particles (dust) are generated inside the radical beam source 2 or the like, particularly inside the discharge electrode 6 thereof, due to generation of unnecessary radicals, the radical beam source 2 or the like is frequently cleaned. There was also the problem of having to do it.

Therefore, the main object of the present invention is to provide a method capable of enhancing the selectivity of radicals generated in the above radical beam source.

[0008]

In order to achieve the above object, the method of generating a radical beam according to the present invention interrupts a discharge electrode of a radical beam source with respect to a high frequency wave of a sawtooth wave or a triangular wave. It is characterized in that the high frequency power is supplied by the first modulation and the second modulation which is intermittently performed at a cycle shorter than the first modulation.

[0009]

The main role of energy conversion in the plasma is electrons, and a variety of radicals and ions are generated by repeated collisions of electrons accelerated by an electric field with ions and neutral particles. The ratio of various radicals generated at this time mainly depends on the energy of electrons in the plasma (that is, the electron temperature).

The electron temperature in the plasma has a time transition such that the electron temperature rises sharply when the high frequency power is turned on (the way of rise is mainly determined by the temporal change rate (dE / dt) of the electric field strength) and then falls. By controlling the high frequency power in the region, more specifically, controlling the on time and the off time of the second modulation, and further selecting the original high frequency to be a sawtooth wave or a triangular wave. ,
It becomes possible to control the electron temperature, which can increase the generation of necessary radicals and suppress the generation of unnecessary radicals, thereby improving the selectivity of radicals.

The various radicals produced as described above have different lifetimes depending on their types. For example, radicals having a large molecular weight necessary for forming a thin film have a long life, and radicals unnecessary for forming a thin film and causing particles are short-lived. By applying the first modulation to the high-frequency power and interrupting it at a longer period than the second modulation, it is possible to leave radicals with a long life and extinguish radicals with a short life, which also exists in the plasma. The selectivity of radicals to be processed is improved.

[0012]

1 is a schematic view showing an example of a radical beam generator used in an embodiment of the present invention. The same or corresponding portions as those of the conventional example in FIG. 4 are denoted by the same reference numerals, and the differences from the conventional example will be mainly described below.

In this embodiment, instead of the high frequency power source 10 of the conventional example, a waveform generator 18 capable of generating an arbitrary signal waveform and a high frequency power amplifier 20 for amplifying the power of a high frequency signal from the waveform generator 18 are constituted. The high frequency power supply 10a is used. As a result, for example, as shown in FIG. 2, with respect to the high frequency of the original sawtooth wave (in the case of the illustrated example) or the triangular wave, the first modulation for interrupting it at the cycle T and the cycle shorter than that The high frequency power subjected to the intermittent second modulation (that is, the double modulation) is supplied to the discharge electrode 6 of the radical beam source 2 as described above.

The frequency of the high frequency of the sawtooth wave or the triangular wave which is the source of this is 13.56 MH as in the conventional example.
However, it is not limited to this.

Many radicals and ions are present in the plasma 14 generated by utilizing the high frequency discharge in the radical beam source 2 as described above. The main role of energy conversion in the plasma 14 is electrons, and a variety of radicals and ions are generated by repeated collisions of electrons accelerated by an electric field with ions and neutral particles. The ratio of various radicals generated at this time changes depending on the energy of electrons in the plasma 14 (that is, electron temperature). That is, controlling the electron temperature in the plasma 14 is a key factor for increasing the selectivity of radicals and increasing only necessary radicals.

In order to control the electron temperature and the like, the present invention performs double modulation on the above-mentioned sawtooth wave or triangular wave high frequency instead of the conventional continuous sinusoidal high frequency power. The high frequency power was supplied.

That is, as shown in FIG. 3, for example, the electron temperature in the plasma 14 has a time transition such that it sharply rises when the high frequency power is turned on and then falls, and the way of the rise is mainly the temporal change rate of the electric field strength. (DE / dt). For example, when the high-frequency waveform is a sawtooth wave as shown by A in FIG. 3, the rise of the electron temperature becomes steep as shown by a, and when the high-frequency waveform is a triangular wave as shown by B, The temperature rise is moderate as indicated by b. Therefore, the high frequency power in such a transition region of the electron temperature is controlled, more specifically, the on time t ₁ and the off time t ₂ of the second modulation are controlled, and the original high frequency is sawtooth wave. It is possible to control the electron temperature by selecting whether to use the triangle wave or the triangular wave, which can increase the generation of necessary radicals and suppress the generation of unnecessary radicals, thereby improving the selectivity of radicals. improves.

The various radicals produced as described above have different lifespans depending on their types. For example, a radical having a large molecular weight necessary for forming a thin film (for example, SiH _{3 in} the case of silane) has a long life, and a radical which is unnecessary for forming a thin film and causes particles (for example, in the case of silane, is generated. SiH ₂ , SiH, Si) has a short life. By applying the first modulation to the high-frequency power and interrupting it at a longer cycle than the second modulation, it is possible to leave radicals with a long life and extinguish radicals with a short life, which also exists in the plasma. The selectivity of radicals to be processed is improved.

In the above case, the frequency of the first modulation is preferably selected from the range of 400 Hz to 1 KHz because the life of radicals is generally on the order of msec. The second modulation interval is, specifically,
It is preferable to select the on-time t ₁ within the range of 0.5 μsec to 100 μsec and the off-time t ₂ within the range of 3 μsec to 100 μsec in view of the curve of electron temperature transition in the experiment.

By improving the selectivity of radicals as described above, it becomes possible to obtain a high-quality radical beam 16 containing a large number of necessary radicals and a small number of unnecessary radicals.

Further, since the generation of unnecessary radicals can be suppressed, the generation of particles is greatly reduced,
Since the frequency of cleaning the radical beam source 2 and the like can be reduced, maintenance becomes easy.

Furthermore, since it is possible to suppress the generation of unnecessary radicals, it is possible to input a correspondingly large high frequency power, and it is also possible to obtain a radical beam 16 of higher density.

Further, in the method of the present invention, only the method of modulating the high frequency power is changed and the radical beam source 2 does not need to be modified, so that the cost can be reduced.

The shape of the discharge electrode in the plasma source is not limited to the cylindrical shape as in the above example, but may be another shape such as a coil shape.

Next, two more specific embodiments according to the present invention will be described. Items common to both examples are as follows.

Dimensions of discharge electrode 6: 200 mmφ × 200
mm Original high frequency: 13.56 MHz sawtooth wave (type that rises vertically first) First modulation: Frequency 1 KHz, duty ratio (ON period / cycle) 30% Second modulation: ON time t ₁ = 10 μsec OFF time t ₂ = 10 μsec

Example 1 Required radical: SiH ₃ radical Raw material gas 8: SiH ₄ + H ₂ SiH ₄ flow rate: 50 sccm H ₂ flow rate: 250 sccm Discharge electrode 6 gas pressure: 1 to 5 × 10 ⁻¹ Torr Input high frequency power : 300W

As a result of Example 1, the radical ratio of SiH ₃ (to Si + SiH + SiH ₂ ) was 90% or more. Incidentally, the radical ratio in the case of the conventional example in which the high frequency power was not double-modulated under the same conditions as above was only about 30%. The density of particles having a particle size of 0.3 μm or more on the substrate placed 100 mm from the exit of the radical beam source 2 was 30 particles / 100 mm ² . By the way,
Under the same conditions as above, in the case of the conventional example in which the high frequency power is not double-modulated, the particle density is 80 to 100 particles / 100 mm ²
There was also a degree.

Example 2 Required radical: CH ₃ radical Raw material gas 8: CH ₄ + H ₂ CH ₄ flow rate: 50 sccm H ₂ flow rate: 150 sccm Gas pressure inside discharge electrode 6: 1 to 8 × 10 ⁻¹ Torr High frequency power input : 500W

Results of Example 2 The radical ratio of CH ₃ (to C + CH + CH ₂ ) was 93.
% Or more was obtained. Incidentally, the radical ratio in the case of the conventional example in which the high frequency power is not double-modulated under the same conditions as above is 20.
It was only about 30%. The density of particles having a particle size of 0.3 μm or more on the substrate placed 100 mm from the exit of the radical beam source 2 was 20 particles / 100 mm ² . By the way,
In the case of the conventional example in which the high frequency power is not double-modulated under the same conditions as above, the particle density was about 50 to 70 particles / 100 mm ² .

[0031]

As described above, according to the present invention, by applying the second modulation to the high frequency power and by selecting the original high frequency waveform, the radical beam generated in the radical beam source It becomes possible to control the electron temperature of, thereby increasing the production of necessary radicals and suppressing the production of unnecessary radicals, thereby improving radical selectivity. Further, by applying the first modulation to the high-frequency power, it is possible to leave radicals having a long lifetime and extinguish the radicals having a short lifetime, which also improves the selectivity of radicals existing in the plasma.

As a result, it is possible to obtain a high-quality radical beam containing a large number of required radicals and a small amount of unnecessary radicals. Further, since the generation of unnecessary radicals can be suppressed, the generation of particles is greatly reduced, and the maintenance of the radical beam source becomes easy. Further, since it is possible to suppress the generation of unnecessary radicals, it is possible to input a correspondingly high frequency power, and it is also possible to obtain a radical beam of higher density. Further, in the method of the present invention, only the method of modulating the high frequency power is changed, and no modification of the radical beam source is required, so that the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a radical beam generator used in an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a waveform of high frequency power supplied to the discharge electrode of FIG.

FIG. 3 is a diagram showing an example of the relationship between the waveform of high-frequency power and electron temperature transition in plasma.

FIG. 4 is a schematic view showing an example of a conventional radical beam generator.

[Explanation of symbols]

 2 Radical beam source 4 Main body container 6 Discharge electrode 8 Raw material gas 10a High frequency power supply 12 Matching box 14 Plasma 16 Radical beam

Claims (2)

[Claims] 1. A sawtooth wave or a triangular wave high frequency to a discharge electrode of a radical beam source which has a discharge electrode and discharges and decomposes a source gas by a high frequency power supplied to the discharge electrode to generate a radical beam. Against
A method of generating a radical beam, characterized in that high-frequency power is supplied by applying a first modulation for intermittently performing it and a second modulation for intermittently performing it at a shorter period than the first modulation. 2. The frequency of the first modulation is 400 Hz to
The method of generating a radical beam according to claim 1, wherein the second modulation has an on-time of 0.5 μsec to 100 μsec and an off-time of 3 μsec to 100 μsec in the range of 1 KHz.