JP3157638B2 - Plasma processing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing apparatus used, for example, for etching or film formation in the manufacture of semiconductor devices.

[0002]

2. Description of the Related Art In recent years, a plasma processing apparatus capable of using high-density and low-energy plasma has been developed in order to reduce damage to a semiconductor substrate, improve processing accuracy, and improve productivity when manufacturing a semiconductor device. Is required,
For this reason, those utilizing electron cyclotron resonance (ECR) and those utilizing helicon waves have attracted attention (for example, Document I: "Nikkei Microdevice", 19).
October 1991, pp89-95).

[0003] By the way, both the devices utilizing the ECR and the devices utilizing the helicon wave require a magnetic field and a high-frequency electromagnetic wave for plasma generation, and furthermore, the incidence of ions in the plasma on the workpiece to be processed. Since it is necessary to apply a high-frequency bias to the plasma processing object in order to control the energy, a plasma source having a magnetic field generating unit and an electromagnetic wave supplying unit and a high-frequency power source for bias are provided (for example, the above-mentioned document I). Hereinafter, such a configuration will be briefly described with respect to an example of an ECR plasma processing apparatus called a diffusion plasma type disclosed in the above-mentioned Document I and an example of a plasma processing apparatus using a helicon wave.

First, as shown in FIG. 3A, an ECR plasma processing apparatus called a diffusion plasma type has a chamber 11 made of aluminum or non-magnetic stainless steel and a predetermined magnetic field in the chamber 11. Solenoid coil 1 provided on the outer periphery of chamber 11 to generate
3 and a quartz window 17 provided in a part of the chamber 11 for introducing the microwaves transmitted from the microwave generation unit (not shown) as the electromagnetic wave supply means via the waveguide 15 into the chamber 11. And a holding unit 21 for holding the plasma processing object 19 and a high frequency power supply 23 for applying a bias to the plasma processing object 19. Here, a plasma source is mainly configured by the chamber 11, the solenoid coil 13, and a microwave generation unit (not shown). Further, the holding unit 21 is provided at a position distant from the plasma source to some extent.

As shown in FIG. 3B, a plasma processing apparatus using a helicon wave includes a container 31 made of a dielectric material, an antenna 33 for helicon wave excitation, and a high-frequency power supplied to the antenna 33. An electromagnetic wave supply unit composed of a source high-frequency power supply 35 for applying a magnetic field, a plasma source 39 mainly composed of a magnetic field generation unit 37, and a holding unit 21.
And a high-frequency power supply 23 for applying a bias to the plasma processing object 19 placed in the apparatus.

In each of these conventional plasma processing apparatuses, a frequency of 40
A power supply capable of applying a high frequency power of 0 KHz to 13.56 MHz has been used.

[0007]

However, in any of the conventional plasma processing apparatuses, the frequency of the bias high-frequency power applied to the object to be processed is at most 13.56 MHz. In addition, the cyclotron frequency of electrons on the surface of the plasma processing object is shown in FIG.
In the diffusion plasma type ECR plasma processing apparatus described with reference to (A), if the magnetic field intensity on the surface of the plasma processing target is, for example, 50 gauss, a known ECR conditional expression (f _C = 2.8B) × 10 ^{6, where} f _C is the cyclotron frequency (Hz) of electrons on the surface of the object to be plasma-processed,
B is the magnetic flux density (Gauss) on the surface of the plasma processing object. ), And in a plasma processing apparatus using helicon waves, if the magnetic field intensity on the surface of the plasma processing object is, for example, 5 gauss, the frequency is 14 MHz according to the same conditional expression. As described above, in each of the conventional apparatuses, the frequency of the bias power is smaller than the cyclotron frequency of the electrons on the surface of the plasma processing object by EC.
The R type was extremely small, and the one using helicon waves was also small. This causes a phenomenon in which the high-frequency power applied to the plasma processing object propagates along the magnetic field to the plasma source. This causes fluctuations in plasma potential and floating potential.
The above phenomenon is caused by the electromagnetic wave supply means (EC
In the case of the R type, the power from the microwave generator (not shown) and the power from the high frequency power supply 35) and the power from the high frequency power supply for bias 23 in the case of the helicon wave use cause mutual interference. And the bias condition cannot be controlled independently of each other. Note that the phenomenon described above occurs because electromagnetic waves having a frequency lower than the counterclockwise cutoff frequency in plasma cannot propagate in the plasma in principle, but even lower than this counterclockwise cutoff frequency is lower than the electron cyclotron frequency. Electromagnetic waves at frequencies are explained by the well-known phenomenon that they propagate through the plasma in the presence of a magnetic field. FIG. 4 is a diagram specifically showing this, and is a well-known ω (angular frequency) -k (wave number = 2π / wavelength) characteristic diagram showing a dispersion relationship of an electromagnetic wave propagating along a magnetic field. In FIG. 4, ω _Pe is the plasma angular frequency of the electrons, | Ω _e | is the cyclotron angular frequency of the electrons, c is the speed of light, R is the right-polarized wave, L is the left-polarized wave, and ω _R is the plasma being generated. Is a clockwise cutoff angular frequency, and ω _L is a counterclockwise cutoff angular frequency. The frequency band indicated by I in FIG. 4 is the frequency used in the conventional bias high-frequency power supply.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is therefore an object of the present invention to prevent a high frequency power used for applying a bias to an object to be processed from influencing a plasma source, or to prevent a plasma source from being affected. It is an object of the present invention to provide a plasma processing apparatus that can be further reduced.

[0009]

According to the present invention, there is provided a plasma source having a magnetic field generating means and an electromagnetic wave generating means, and a bias for applying a high frequency bias power to a plasma processing object. High-frequency power supply for applying a high frequency power higher than the cyclotron frequency of electrons on the surface of the object to be processed and lower than the counterclockwise cutoff frequency of the generated plasma in a plasma processing apparatus having a high frequency power supply for plasma. A high-frequency power supply for bias that can be used.

In practicing the present invention, it is preferable that the above-mentioned plasma source is a plasma source utilizing a helicon wave.

[0011]

According to the structure of the present invention, bias high-frequency power having a frequency higher than the cyclotron frequency of electrons on the surface of the plasma processing object and lower than the counterclockwise cutoff frequency of the generated plasma is applied to the plasma processing object. Thus, a plasma processing apparatus capable of performing the plasma processing can be obtained. With such a high frequency power of a predetermined frequency, even if it is applied to the object to be processed, the electromagnetic wave cannot propagate to the plasma source, thereby preventing the high frequency power supply for bias from affecting the plasma source. Alternatively, it can be reduced more than before.

In the case of a plasma source utilizing a helicon wave, the magnetic field strength on the surface of the object to be processed is smaller than that of other plasma sources such as ECR. Can be lowered.
For this reason, the high frequency power supply for bias does not need to be used for a high frequency, so that the present invention can be easily applied.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment will be described below with reference to an example in which the present invention is applied to a plasma etching apparatus having a plasma source using a helicon wave. This description is made with reference to some drawings. However, the drawings used in the description merely schematically show the dimensions, shapes, and arrangements of the components so that the present invention can be understood. Therefore, illustrations of a gas introduction system, an exhaust system, and the like are omitted.
In each figure, the same components are denoted by the same reference numerals.

FIG. 1 is a diagram showing a configuration of a plasma processing apparatus according to an embodiment. The plasma processing apparatus of this embodiment uses a dielectric material (for example, quartz or alumina ceramics).
, A hollow container 51 into which a process gas is introduced, an antenna 53 for helicon wave excitation, a high-frequency power source 55 for applying high-frequency power to the antenna 53, and matching for matching these antennas 53 and the power source 55. A plasma source 60 mainly comprising a box 57 and a magnetic field generating means 59 for generating a predetermined magnetic field in the container 51 is provided. Further, the plasma processing apparatus uses the plasma generated by the plasma source
A plasma processing chamber 63 (hereinafter referred to as a plasma processing chamber 63), and a magnetic field generating means 65 provided on an outer wall of the plasma processing chamber 63 for forming a bucket magnetic field in the plasma processing chamber 63; The plasma processing chamber 63 includes a holding unit 67 for holding the plasma processing target 61 and a bias RF power supply 69 for applying a bias RF power to the plasma processing target 61. The high frequency power for bias is a blocking capacitor 7
The voltage is applied to the object to be plasma-processed 61 via the holding member 1 and the holding portion 67.

In the plasma processing apparatus of this embodiment,
The components other than the high frequency power source for bias 69 can be configured in the same manner as those conventionally known. The biasing high-frequency power source 69 according to the present invention is higher than the cyclotron frequency of electrons on the surface of the plasma processing object 61 and has a counterclockwise cutoff frequency (counterclockwise cutoff) of plasma generated in the hollow container 51. Assuming that the angular frequency is ω _L , high frequency power of a frequency lower than ω _L / 2π) can be applied.
Hereinafter, a configuration example of the bias high-frequency power supply 69 will be described.

First, as is well known, the cyclotron frequency f _C (Hz) of the electrons on the surface of the object to be processed is
It is represented by the following equation (1). Here, B is the magnetic flux density (Gauss) on the surface of the plasma processing object.

F _C = 2.8 B × 10 ⁶ (1) The magnetic field distribution in the space between the vessel 51 of the plasma source 60 and the plasma processing chamber 63 in the plasma processing apparatus using the helicon jacket generally has , As shown in FIG. However, the unit of the magnetic field strength in FIG. 2 is Gauss. That is, in the plasma processing apparatus using the helicon wave, the magnetic field required to generate plasma in the plasma source 60 may be smaller than that of the ECR plasma processing apparatus (for example, 100 to 150 Gauss), and the plasma processing apparatus may perform the plasma processing. Since the object 61 is typically placed at least 10 cm away from the plasma source 60, the magnetic field strength or magnetic flux density B on the surface of the plasma processing object 61 becomes 10 gauss or less. Then, assuming that the magnetic field strength, that is, the magnetic flux density B on the surface of the plasma processing object 61 is, for example, 5 gauss, the cyclotron frequency f _C of the electrons on the surface of the plasma processing object 61 is obtained from the above equation (1). , F _C = 2.
8 × 5 × 10 ⁶ = 14 MHz. When the magnetic field strength on the surface of the plasma processing object 61 is 10 gauss, 15 gauss, and 20 gauss, the cyclotron frequency f _C of the electrons on the surface of the plasma processing object 61 is 2
8 MHz, 42 MHz and 56 MHz.

On the other hand, if the counterclockwise cut-off frequency of the generated plasma is represented by f _L (Hz), this f _L and the counterclockwise cut-off angular frequency ω _L are f _L = ω _L /
Since it has a relationship of 2π and ω _L is expressed by the following equation (2) as is well known, the counterclockwise cutoff frequency f _L is eventually expressed by the following equation (3).

Ω _L = [− Ω _e + (Ω _e ² + 4ω _Pe ² ) ^1/2 ] / 2 (2) f _L = [− Ω _e + (Ω _e ² + 4ω _Pe ² ) ^1/2 ] / 4π (3) In the equations (2) and (3), Ω _e is the cyclotron angular frequency of the electrons on the surface of the object to be processed, and ω _Pe is the plasma angular frequency of the electrons. (3-
It is expressed by the expression 1) and the expression (3-2).

[0020] _{Ω e = 2π · f C ···} (3-1) ω Pe = (n e e 2 / mε 0) 1/2 ··· (3-2) However, (3-1) In the formula 's f _C is a value obtained in the above (1), (3-2) wherein, n _e is the density of electrons, e is the electron charge, m is the electron mass, epsilon ₀ is a dielectric constant of vacuum is there.

[0021] Then, the n _e in the helicon wave Normal 10 ¹²
Ω _Pe is about 2π · 10 ¹⁰ (radian / s) since the number is pcs / cm ³ . Therefore, assuming that the electron cyclotron frequency f _C is, for example, 14 MHz, this f _C
Is substituted into the above equation (3-1) to obtain Ω _e, and the obtained Ω _e = 28π × 10 ⁶ (radian / s) and the above ω _Pe
= 2π · 10 ¹⁰ (radians / s) and 10 ⁶
And then substitute in the above equation (3). Then, the equation (3) becomes the following equation (4).

F _L = [− 28π + ｛(28π) ² +4 (2π · 10 ⁴ ) ² ｝ ^1/2 ] / 4π (4) In the equation (4), 4 (2π · 10 ⁴ ) ² Is sufficiently larger than the other terms, so equation (4) is
1) It can be approximated as in the equation.

F _L ≒ ｛4 (2π · 10 ⁴ ) ² ｝ ^1/2 / 4π = 10 ⁴ (MHz) = 10 (GHz) (4-1) Therefore, in this embodiment, the bias is It can be said that a high-frequency power source 69 for applying high-frequency power having a frequency higher than the cyclotron frequency f _C of electrons on the surface of the object to be processed and lower than 10 GHz can be used. The bias high-frequency power supply 69 has a bias effect, a practical effect,
It is preferable to select one in consideration of economy, industrial radio frequency allocation, and the like.

The frequency range of the high-frequency power output from the biasing high-frequency power source 69 determined in this way is shown in FIG.
Are included in the range indicated by II in the ω-k characteristic diagram. The difference between the present invention and the related art can be seen in comparison with the case of the related art in the range indicated by I in FIG.

Although the embodiment of the plasma processing apparatus of the present invention has been described above, the present invention is not limited to the above-described embodiment.

For example, in the above-described embodiment, an example in which the present invention is applied to a plasma etching apparatus using a helicon wave is shown. It can also be applied to processing equipment. Further, there is a magnetic field generating means such as an ECR plasma processing apparatus called a diffusion plasma type, and an electromagnetic wave supply means for a plasma source (microwave power supply,
The present invention can also be applied to various plasma processing apparatuses including a plasma source having a high-frequency power supply and a high-frequency power supply for bias.

[0027]

As is clear from the above description, according to the plasma processing apparatus of the present invention, a power supply capable of outputting high frequency power in a specific frequency range is provided as a high frequency power supply for bias. Electromagnetic waves of the high-frequency power supply can be prevented from affecting the plasma source or can be reduced more than before. For this reason, (1) the fluctuation of the plasma potential and the fluctuation of the floating potential due to the high frequency power supply for bias can be prevented or reduced as compared with the conventional case. (2) Since interference between the high-frequency power source of the plasma source and the high-frequency power source for bias can be prevented or reduced as compared with the related art, the plasma generation condition and the bias condition can be independently optimized.

[Brief description of the drawings]

FIG. 1 is a view for explaining a plasma processing apparatus according to an embodiment, and is a side view showing an overall configuration of the apparatus.

FIG. 2 is a diagram for explaining a magnetic field intensity on a surface of an object to be processed in a plasma processing apparatus in a case where a helicon wave is used as a plasma source.

FIG. 3A shows a conventional EC called a diffusion plasma type.
It is a figure used for description of R plasma processing equipment, and (B) is a figure provided for explanation of the conventional plasma processing equipment using a helicon wave.

FIG. 4 is a diagram provided for explanation of the related art and the present invention, and is a ω-k characteristic diagram showing a dispersion relationship of an electromagnetic wave propagating along a magnetic field.

[Explanation of symbols]

 51: hollow container made of dielectric material 53: helicon wave excitation antenna 55: source high-frequency power supply 57: matching box 59: magnetic field generating means 60: plasma source 61: plasma processing object 63: plasma processing chamber 65: magnetic field Generation means (for forming a bucket magnetic field) 67: Holder for a plasma processing target 69: High-frequency power supply for bias according to the present invention 71: Blocking capacitor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01L 21/3065 H05H 1/24 H05H 1/24 H01L 21/302 B

Claims (2)

(57) [Claims] 1. A plasma processing apparatus comprising: a plasma source having a magnetic field generating means and an electromagnetic wave supplying means; and a bias high-frequency power supply for applying a high-frequency bias power to an object to be processed. A plasma processing apparatus comprising: a bias high-frequency power supply capable of applying a high-frequency power having a frequency higher than a cyclotron frequency of electrons on a surface of an object to be processed and lower than a counterclockwise cutoff frequency of generated plasma. 2. The plasma processing apparatus according to claim 1, wherein the plasma source is a plasma source using a helicon wave.