JPH0834129B2 - Method and apparatus for generating microwave plasma - Google Patents

Description

TECHNICAL FIELD The present invention relates to a microwave plasma generation method and apparatus used in a semiconductor plasma process.

[Prior Art] Microwave plasma has been attracting attention as an important one indispensable for a semiconductor plasma process since it is completely electrodeless discharge and therefore has little pollution. Further, since microwave plasma has a high frequency, the rate of accelerating plasma ions is very small, and the increase in kinetic energy of ions can be suppressed, so that it is excellent in that the surface of the semiconductor crystal substrate is not damaged. It has features. Therefore, microwave plasma is widely applied to semiconductor manufacturing, surface modification, thin film formation, and the like.

A conventional configuration of such a microwave plasma generator is shown in FIG. This figure shows a magnetic field microwave plasma generator with a high degree of utilization.
Is a 2.45GHZ microwave source. 2 is an isolator that absorbs reflected power, 3 is a power monitor that measures transmitted power and reflected power, 4 is a tuner that matches the impedance of the microwave oscillation source side and the impedance of the plasma discharge part side, 5 is a rectangular waveguide, Reference numeral 6 denotes a corner, and these 2 to 6 form a waveguide path 10. The rectangular waveguide 5 is a waveguide for passing the microwave mode TE10 fundamental mode of 2.45GHZ, and for example, WRJ-2.6 is used. Reference numeral 11 is a taper connection converter for allowing the TE 11 mode microwaves to pass through the cylindrical waveguide forming the discharge chamber 12, and 12 is the plasma discharge part D.
Is a discharge chamber for generating Reference numeral 13 is an electromagnet that effectively stores plasma and generates a magnetic field for effectively coupling plasma and microwave by utilizing electron cyclotron motion. Reference numeral 14 denotes a plasma generation chamber for processing the semiconductor W to be processed, and a gas discharge port 14a for discharging the processing gas supplied from the gas supply port 12a of the discharge chamber 12 is provided. As this gas, a gas such as silane or argon is used in the case of deposition, and a gas such as CF ₄ is used in the case of etching.

[Problems to be Solved by the Invention] In the above-described microwave plasma generation device, a more effective microwave plasma may be obtained under a higher frequency. This depends on the selection of gas type, plasma density, etc., but when using 4.2 GHz as the high frequency microwave oscillation source, for example, the rectangular waveguide 5 of the waveguide path 10 is used. It had to be changed to WRJ-4, and the cylindrical waveguide forming the discharge chamber 12 also had to be changed to one for the 4.2GHZ fundamental mode. That is, in the conventional microwave plasma generation device, both the waveguide and the discharge chamber were designed according to the fundamental mode of microwave. Therefore, every time the microwave frequency to be used is changed, it is necessary to replace not only the microwave oscillation source but also all the components of the waveguide path 10, and in the end, it is necessary to prepare a plurality of systems. However, there is a drawback that it requires a large amount of equipment cost and a lot of equipment space.

Furthermore, another drawback of the conventional device is that the higher the frequency of the microwave used, the shorter the wavelength,
Therefore, the shape of the waveguide that propagates the fundamental mode, particularly the shape of the discharge chamber, becomes smaller, and therefore the plasma discharge portion D in the plasma generation chamber 14 becomes smaller. Therefore, in CVD and etching using plasma, the size of the semiconductor crystal substrate that can be processed is inevitably made small, and when the Si wafer size that continues to expand is taken into consideration year by year, the reduction of the plasma discharge part D is It was a big problem, and its solution was desired.

[Means for Solving the Problems] Object of the Invention An object of the present invention is to provide a microwave plasma generation method and a microwave plasma generation method that can be commonly used for a plurality of microwave oscillation sources by using a set of microwave waveguide paths and a discharge chamber. By providing the apparatus, it is possible to reduce the equipment cost and the installation place and improve the processing capability of the workpiece.

The present invention is a versatile microwave plasma in which only the microwave oscillation source is replaced and the waveguide path and the discharge chamber are commonly used in an apparatus for generating plasma using microwave oscillation sources of different frequencies. A generation method and an apparatus thereof are provided.

For this purpose, the sizes of the rectangular waveguide 5 and the discharge chamber 12 of the waveguide path are designed in accordance with the fundamental mode of the microwave having the lowest frequency among the plurality of microwave oscillation sources used, and the minimum frequency is set. When using a microwave oscillator with a higher frequency, use the same waveguide path as it is,
A method of propagating only the fundamental mode of this high frequency microwave (hereinafter referred to as oversize propagation) is adopted.

The oversize propagation method also has a problem that higher-order modes are easily excited, but in the present invention, the connection between the microwave oscillation source 21 having a frequency higher than the lowest frequency and the waveguide path 10 has a gentle slope. By coupling with the taper guide 22, excitation of higher order modes is prevented. Rather, in the device using the oversize propagation method of the present invention, as shown in FIG. 5 described later, there is an advantage that the loss of the waveguide is reduced unless the frequency becomes extremely high. As described above, the method and the apparatus of the present invention adopt the oversize propagation method,
The waveguide path 10 and the discharge chamber 12 other than the microwave oscillating source 1 or 21 of the plasma generator can be commonly used.

[Embodiment] The present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 is a block diagram of an apparatus for carrying out the method of the present invention, in which 1 is a first microwave oscillation source that outputs a microwave having a lower frequency of two microwaves used. And, for example, it is a 2.45GHZ 300 [W] magnetron. 21 is a second microwave oscillating source that outputs microwaves of a higher frequency, such as 4.2 GHz
It is a magnetron of 300 [W]. Reference numeral 22 is a taper guide provided in the oversized oscillation source 21, and 23 is a microwave oscillation source switching device for switching the microwave frequency.

Reference numeral 2 is an isolator, 3 is a power monitor, and 4 is a tuner, which is similar to the above-described conventional apparatus. Reference numeral 5 is a rectangular waveguide, and 6 is a corner, which are commonly used for the 2.45GHZ oscillation source 1 and the 4.2GHZ oscillation source 21,
In this embodiment, it is designed according to the lower frequency of 2.45GHZ, specifically, the rectangular waveguide WRJ-2.6 (86.36 × 43.18).
mm) is used to cause oversize propagation for microwaves with a higher frequency of 4.2GHZ. The discharge chamber 12 is also designed according to the lower frequency of 2.45GHZ, and specifically, a cylindrical waveguide having an inner diameter of 100 mm is used. Reference numeral 11 connects the rectangular waveguide forming the corner 6 and the cylindrical waveguide forming the discharge chamber 12, and propagates through the rectangular waveguide.
A taper-connected converter for converting a TE10 fundamental mode into a TE11 fundamental mode propagating in a cylindrical waveguide. Reference numeral 12 denotes a discharge chamber, in which microwaves propagate in the TE11 fundamental mode converted by the taper connection converter formed by the cylindrical waveguide, and form the plasma discharge part D. Reference numeral 13 is an electromagnet, which acts to apply a magnetic field to the plasma as described above with reference to FIG. The strength of the magnetic field is selected so that the microwave frequency and the electron cyclotron frequency substantially match. When the microwave frequency is 2.45GHZ, adjust the value of the current flowing through the electromagnet so that the magnetic field strength is approximately 875 Gauss. Reference numeral 14 denotes a plasma generation chamber that accommodates the semiconductor W to be processed, and the plasma discharge part D generated in the discharge chamber 12 extends to this chamber.
In addition, the gas supply port of the discharge chamber 12 is provided in this chamber.
Gas outlet 14a for discharging the processing gas supplied from 12a
Is provided.

The microwave oscillation source switching device 23 is connected between the taper guide 22 provided on the first microwave oscillation source 1 and the second microwave oscillation source 21 and the isolator 2 of the waveguide path 10. For example, the structure is as shown in FIG. Reference numeral 31 is a first input connector connected to the first microwave oscillation source 1, 32 is a second input connector connected to a taper guide 22 provided on the second microwave oscillation source 21, and 33 is a first input connector. And a connector mounting plate for mounting the second input connector, 34 is an output connector connected to the isolator 2 of the waveguide path 10, 35 is an output connector mounting plate for mounting the output connector, and 36 and 37 are the input connector mounting plate 33 and the output. First and second mounting plate supporting arms that fixedly support the connector mounting plate 35, and 38 is a waveguide for switching and connecting between the first input connector 31 or the second input connector 32 and the output connector 34. , 39 are provided at the centers of the first input connector 31 and the second input connector 32, and are provided on the input connector mounting plate 33.
It is an input side rotating shaft that is rotatable with respect to. 40 is a rotary arm whose one end is fixed to the input side rotation shaft 39, the other end is attached with the handle 41, and the one end 38a of the waveguide 38 is attached to the handle attachment side, and this arm is input by the handle 41. By rotating the side rotation shaft 39 as a center, the one end 38a of the waveguide 38 is moved from the first connector 31 shown in FIG. 2 (A) to the second connector shown in FIG. 2 (B). Connected to 32. Reference numerals 42 and 43 are first and second positioning bolts for connecting the waveguide 38 and the first connector 31 or the second connector 32 for positioning and fixing. Reference numeral 44 denotes an output side rotation shaft to which the other end 38b of the waveguide 38 is fixed and which is rotated with respect to the output connector mounting plate 35 by the rotation of the handle 41.

In this apparatus, the microwave oscillation source switching device 23 is set to the state shown in FIG. 2A, for example, and microwave plasma is generated by the microwave of the lower frequency of 2.45GHZ as in the conventional apparatus, and the semiconductor to be processed is processed. Process W. Also,
Microwave plasma can be obtained even when the microwave oscillation source switching device 23 is set to the state shown in FIG. 2 (B) and the microwave having the higher frequency of 4.2 GHz is propagated.
Can be processed. This is because the higher microwave of frequency 4.2GHZ propagated oversize while maintaining the TE10 fundamental mode in the large-sized waveguide path 10 like the microwave of lower frequency 2.45GHZ. Further, in the discharge chamber 12, similarly, the higher microwave of frequency 4.2GHZ propagates oversize in the TE11 mode. However, the second microwave oscillation source 21
It is important to use the taper guide 22 in order to guide the microwave emitted from the waveguide 10 to the waveguide path 10, and this enables oversize propagation of the TE10 fundamental mode. That is, by using the taper guide 22, only the microwave of the TE10 fundamental mode is propagated and the microwaves of TE20 and TE30 modes higher than the TE10 fundamental mode are not propagated.

Next, the magnetic field intensity is increased to 1500 gauss for microwave plasma of this frequency in order to match the period of electron rotation with the period of microwave (reciprocal of frequency), that is, to cause electron cyclotron resonance. Must be,
Therefore, the current flowing through the electromagnet 13 is increased.

The advantage of this embodiment is that the plasma generator excluding the microwave oscillating source can be commonly used for microwaves of a plurality of frequencies, and the plasma discharge part can be used for microwaves of higher frequency 4.2GHZ. Since D can be increased, a large-area semiconductor wafer can be processed in a small number of times, and since the oversize propagation method is used, the power of the waveguide for the microwave of the higher frequency than the lower frequency can be processed. The loss can be reduced. The reason is as follows. Figure 3 shows a rectangular waveguide
The figure shows the state of guided wave of TE10 mode microwave propagating in WRJ-2.6. As shown in FIG. 3 (B), the reflection angle β at which the microwave of 4.2GHZ propagates oversize is larger than the reflection angle α of 2.45GHZ microwave propagation shown in FIG. 3 (A). It is because it has become. The loss coefficient of the TE10 mode propagating in the WRJ-2.6 of the rectangular waveguide 5 is given by Rs [1+ (fc / f) ² ] /8.14 [1- (fc / f) ² ] ^0.5 . However, the cutoff frequency fc is 1.74GH
Z, the waveguide wall surface resistance Rs is (πfμ ₀ / σ) ^0.5 (where σ
Is the electrical conductivity). In the above equation, the microwave frequency f is
The loss factor at 4.2GHZ is smaller than that at 2.45GHZ.

Next, Fig. 4 shows the loss coefficient of TE10 mode with respect to microwave frequency f.
Since the lowest value of the loss coefficient appears in the vicinity of HZ, this embodiment uses this low loss region. Figure 5 shows
6 shows the TE11 mode loss coefficient of a cylindrical waveguide forming the discharge chamber 12. In the figure, when the radius α of the cylindrical waveguide is 8 cm or less, the loss of 4.2 GHz microwave of oversize propagation is smaller than the loss of 2.45 GHz microwave. Are using.

In this embodiment, two microwave oscillation sources are used, but three or more may be used. In addition, in order to switch the microwave frequency, it is necessary to replace the microwave oscillation source, but without using a microwave oscillation source switching device, the microwave oscillation sources connected to the respective taper guides should be connected to the waveguide path each time. You may remove it.

[Effects of the Invention] As described above, according to the present invention, the plasma generator excluding the microwave oscillation source can be commonly used for microwaves having a plurality of frequencies, and the microwave having a higher frequency of 4.25GHZ can be used. Since the plasma discharge part can be enlarged even against waves, a large area semiconductor wafer can be processed with a small number of times,
The semiconductor processing cost can be reduced, and since the oversize propagation method is used, the power loss of the waveguide with respect to the microwave of the higher frequency than the lower frequency can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a microwave plasma generation apparatus for carrying out the method of the present invention. FIG. 2 (A) is a view showing the structure of a microwave oscillation source switching device used in an apparatus for carrying out the method of the present invention, and FIG. 2 (B) is a rotation of the handle shown in FIG. 2 (A). It is a figure which shows the structure of the microwave oscillation source switching device when it is made to be in another state. FIG. 3 (A) is a diagram showing a reflection angle at which a 2.45GHZ microwave propagates in the waveguide, and FIG. 3 (B) is a reflection when a 4.2GHZ microwave propagates oversize in the waveguide. It is a figure which shows an angle. FIG. 4 is a diagram showing a loss coefficient due to microwave propagation in a waveguide of a device for carrying out the method of the present invention. FIG. 5 is a diagram showing the loss factor due to microwave propagation in a cylindrical waveguide forming the discharge chamber of an apparatus for carrying out the method of the invention. FIG. 6 is a configuration diagram of a conventional microwave plasma generation device. 1 ... First microwave oscillation source 2 ... Isolator 5 ... Square waveguide 10 ... Waveguide path 11 ... Taper connection converter 12 ... Discharge chamber 14 ... Plasma generation chamber 21 ... Second Microwave source 22 …… Taper guide 23 …… Microwave source switch D …… Plasma discharge part W …… Semiconductor to be processed

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Ishida 2-11-1, Tagawa, Yodogawa-ku, Osaka City, Osaka Daihen Co., Ltd.

Claims (2)

[Claims] 1. A microwave plasma generator used in a semiconductor plasma process, wherein a plurality of microwave oscillation sources having mutually different frequencies, and a fundamental mode propagation of a microwave oscillation source having the lowest frequency among the plurality of microwave oscillation sources. A waveguide path, a taper guide for connecting a microwave oscillation source of another frequency of the plurality of microwave oscillation sources to an input end of the waveguide path, and an output end of the waveguide path. A discharge chamber connected to the discharge chamber and a plasma generation chamber connected to the discharge chamber, and a microwave oscillation source having the lowest frequency and a microwave oscillation source having the other frequency to which the taper guide is connected. A microwave plasma generation method for generating plasma with microwaves of different frequencies by replacing and connecting to the input end of the waveguide path 2. A microwave plasma generation device used in a semiconductor plasma process, wherein a plurality of microwave oscillation sources having different frequencies and a fundamental mode propagation of the microwave oscillation source having the lowest frequency among the plurality of microwave oscillation sources. A waveguide path, a taper guide for connecting a microwave oscillation source of another frequency of the plurality of microwave oscillation sources to an input end of the waveguide path, and an output end of the waveguide path. The discharge chamber connected to the discharge chamber, the plasma generation chamber connected to the discharge chamber, the microwave oscillation source of the lowest frequency and the microwave oscillation source of the other frequency to which the taper guide is connected, and the conduction is performed. A microwave plasma generation device comprising: a microwave oscillation source switching device connected to an input end of a wave path.