JP3460953B2 - Method of controlling the amount and energy of ions extracted from plasma - 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 controlling the amount and energy of ions extracted from plasma used in semiconductor manufacturing processes and the like.

[0002]

2. Description of the Related Art As a conventional control method for simultaneously controlling the amount and energy of ions, the control method is performed without using a resonance state. In addition, conventionally, various methods for controlling the amount and energy of ions using the resonance state have been proposed. Typical examples are the ion control method using electron cyclotron resonance, helicon wave, and alphen wave. Further, as a technique using another resonance state, a method of extracting ions while maintaining the plasma density by using a resonance method similar to that of the present invention has been proposed.

[0003]

However, the control method which does not use the resonance state controls the amount and energy of ions by changing the discharge parameters such as frequency, voltage, pressure, etc. Since the energy (electron temperature) and density change with these parameters, the controllable range of ion quantity and energy is narrow,
In addition, there is a problem that the distribution of electron collisions differs depending on the change in pressure, and the types of ions generated are different. Also, the former control method using the resonance state requires a strong magnetic field, and it is difficult to design a device for generating a uniform magnetic field. There was a problem that it was difficult to obtain the characteristics.

Further, the latter control method using the resonance state relates to the control of ion energy and is a control method in which the amount of ions, the plasma density and the electron energy cannot be controlled simultaneously. The present invention provides a method for controlling the amount and energy of ions extracted from plasma while keeping the electron energy distribution, the ion density distribution, and the electron collision distribution constant.

[0005]

A method of controlling the amount and energy of ions extracted from a plasma according to the present invention is such that a pair of parallel plate electrodes are installed across the plasma, and a high frequency power source supplies a high frequency electric field to the parallel plate electrodes. And controlling the plasma by applying a magnetic field to the plasma and controlling the amount and energy of the ions extracted to the parallel plate electrodes, the intensity of the high frequency electric field and the following formula Resonance frequency ω _res corresponding to the frequency of the high frequency power source, cyclotron frequency ω related to the strength of the magnetic field
_ce , the applied angle θ of the magnetic field to the high frequency electric field, and the distance d between the parallel plate electrodes to select the amount of ions extracted from the plasma while keeping the electron energy distribution, plasma density distribution and electron collision distribution constant. And that is what controls the energy.

[Equation 2]

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described based on the embodiments shown in FIGS. FIG. 1 is a schematic diagram for explaining a method of controlling the amount and energy of ions extracted from plasma of the present invention. In FIG. 1, 1 is plasma, 2 is a pair of parallel plate electrodes sandwiching the plasma 1, 3
Is a high-frequency electric field applied to the plasma 1 by the high-frequency power source 4, and 5 is a magnetic field applied by a magnetic field generator (not shown), which is slightly deviated from the angle (90 °) orthogonal to the high-frequency electric field, that is, parallel. A magnetic field is applied from a direction not parallel to the flat plate electrode 2.

In the structure shown in this schematic diagram, the high frequency of the high frequency power source 4 is adjusted to the vicinity of the inherent vibration frequency of the plasma 1, and the strength of the high frequency electric field 3 penetrating into the plasma 1 is adjusted by adjusting the voltage of the high frequency power source 4. Change the amount of ions to control. Further, the sheath thickness is changed so as to meet the resonance condition by adjusting the strength of the magnetic field 5, and the ion energy is controlled. A condition expression of resonance called sheath plasma resonance for controlling the amount of ions extracted from the plasma 1 and the energy of the ions is shown below.

[0008]

[Equation 3]

Where ω _res is the resonance frequency, ω _pc is the plasma frequency, ω _ce is the cyclotron frequency, θ is the angle between the electric field and the magnetic field, s is the sheath thickness, d is the electrode spacing, and n is the plasma density. Since the plasma frequency is proportional to the square of the plasma density and the electron cyclotron frequency is proportional to the magnetic field strength, the above equation can be expressed as follows.

[0010]

[Equation 4]

As a result, the product of the square of the plasma density and the sheath thickness is determined by matching the applied frequency of the high frequency power source 4 with the resonance frequency ω _res and determining the direction and strength of the magnetic field 5. Therefore, under the resonance condition, the plasma is kept such that the product of the square of the plasma density and the sheath thickness is constant.

[0012]

Example: Argon (Ar) model gas was used with a gas pressure of 1 mTorr and an applied frequency of the high frequency power source 4 of 13.56M.
Hz, the electrode spacing of the parallel plate electrode 1 is 20 mm, and the angle θ formed by the electric field 3 and the magnetic field 5 is 95 degrees. And the plasma density under a certain condition when the magnetic field strength (magnetic flux density) is changed. As is clear from this result, it is understood that the plasma density can be continuously controlled by the applied voltage and the magnetic field strength.

In FIG. 2, the applied voltage and magnetic field strength at which the plasma densities are almost equal, 200 V, 5.52 mT,
The distribution states of electron energy, plasma density, and ionization collision, which is one of electron collisions, are compared for three types of 150 V, 5.70 mT, 200 V, and 5.80 mT. The comparison results show that the electron energy distribution in FIG. 3, the ion density distribution in FIG. 4, and the ionization collision distribution in FIG. 5 show that the above three patterns are almost equal under these three conditions.
The fact that the electron energy distributions are equal means that the reactions due to electron collisions in plasma are equal, and one example is that the ionization collision distributions are equal. Therefore, the generated plasma has the same amount of ion species and excited species. Further, since the plasma density distribution is the same, the reaction between the ions and the neutral molecules is also the same, and the process of annihilation of the ions is only diffusion to the electrode, so that the amount of the ions reaching the electrode is also the same.

On the other hand, the resonance state is different under the above three conditions. Since the magnetic field strength is different, the value of Expression 3 is different, and therefore n ² s is also different. Moreover, since the plasma densities are the same, the sheath thicknesses are different. As a result, as shown in FIG. 6, the energy of the ions incident on the electrode 2 is different.

Another embodiment of the present invention will be described with reference to the schematic diagram shown in FIG. The configuration of FIG. 7 is a method in which a DC power source 6 is connected to the high frequency power source 4 of the schematic diagram shown in FIG. 1 and a DC electric field 7 is applied to the plasma 1 together with the high frequency electric field 3. By applying the DC electric field 7, it is possible to control the ion energy distribution. That is, as shown in FIG. 8, the ion energy distributions when no DC voltage is applied (0 V) and when 50 V is applied have different ion energy spreads depending on the presence or absence of a DC electric field.

Therefore, by changing the voltage and the magnetic field strength of the DC electric field 7 applied to the plasma 1 sandwiched between the parallel plate electrodes 2, it is possible to control the ion energy to a different state while keeping the ion amount constant. is there. Further, since electron collision and electron energy are equal to each other, when a gas for a semiconductor manufacturing process is used, ion species and excited species are equally generated, and only ion energy can be controlled. Further, the change in magnetic field strength is small, and the influence on the substrate in the semiconductor manufacturing process is small.

[0017]

By applying a high frequency electric field and a magnetic field to the plasma sandwiched by the parallel plate electrodes, a resonance state occurs between the electrodes, and the sheath thickness changes depending on the resonance condition.
It is possible to control the amount and energy of the ions extracted to the electrode. Further, since the resonance condition can be changed by the distance between the electrodes, the frequency, the electric field strength, the direction of the magnetic field and the magnetic field strength, it becomes possible to control the ions while keeping the electron collision, the plasma density and the electron energy constant.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an embodiment of a method for controlling the amount and energy of ions extracted from plasma according to the present invention.

FIG. 2 is a diagram showing a change in plasma density when an applied voltage and a magnetic field strength of a high frequency electric field applied to plasma are changed according to the present invention.

FIG. 3 is a diagram showing an electron energy distribution when an applied voltage and a magnetic field strength of a high frequency electric field applied to plasma are changed in three ways.

FIG. 4 is a diagram showing an ion density distribution when an applied voltage and a magnetic field strength of a high frequency electric field applied to plasma are changed in three ways.

FIG. 5 is a diagram showing an ionization collision distribution when an applied voltage and a magnetic field strength of a high frequency electric field applied to plasma are changed in three ways.

FIG. 6 is a diagram showing an ion energy distribution when an applied voltage and a magnetic field strength of a high frequency electric field applied to plasma are changed in three ways.

FIG. 7 is a schematic diagram for explaining another embodiment of the method for controlling the amount and energy of ions extracted from plasma according to the present invention.

FIG. 8 is a diagram showing an ion energy distribution when a high frequency electric field and a magnetic field strength are applied to a plasma according to the present invention and a direct current electric field is applied.

[Explanation of symbols]

1 plasma 2 parallel plate electrodes 3 high frequency electric field 4 high frequency power supply 5 magnetic field 6 DC power supply 7 DC electric field

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields investigated (Int.Cl. ⁷ , DB name) H01J 27/00-27/26 H01J 37/08 H05H 1/24-1/52

Claims (2)

(57) [Claims] 1. A pair of parallel plate electrodes sandwiching the plasma, a high frequency electric field is applied to the parallel plate electrodes from a high frequency power source, and a magnetic field is applied to the plasma to control the plasma, thereby forming the parallel plate. In a method of controlling the amount and energy of ions extracted to an electrode, a resonance frequency ω _res corresponding to the intensity of the high frequency electric field and the frequency of the high frequency power source based on the following equation, and a cyclotron frequency ω _ce relating to the intensity of the magnetic field. , The applied angle θ of the magnetic field to the high frequency electric field and the distance d between the parallel plate electrodes are selected to keep the electron energy distribution, the plasma density distribution and the electron collision distribution constant and the amount of ions extracted from the plasma. A method for controlling the amount and energy of ions extracted from a plasma, which is characterized by controlling energy. [Equation 1] 2. The method for controlling the amount and energy of ions extracted from plasma according to claim 1, wherein a direct current electric field is applied to the plasma to control the energy of the ions while keeping the amount of the ions constant.