JP3140248B2 - Method and apparatus for controlling ion energy - 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 and an apparatus for controlling ion energy, and more particularly, to a method and apparatus for controlling ion energy which collides with a workpiece placed in a plasma. A method and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, in a technical field such as dry etching or film formation of a semiconductor or the like, ions in plasma are used.

That is, since the material to be treated located in the plasma is normally negatively biased when electrically insulated, ions in the plasma are accelerated toward the material to be treated. . The ion energy of the accelerated ions plays an important role in processes such as dry etching and film formation.

At present, in order to control such ion energy, a bias voltage such as a direct current (DC) voltage or a high frequency (RF) voltage is applied from an external power supply according to the conductivity of the material to be processed, and an external power supply is applied. This has been performed by changing the potential of the surface of the material to be processed by a bias voltage.
That is, when the material to be processed is an electrically conductive material, a DC voltage is used as an external bias voltage, and when the material to be processed is an electrically insulating material, an RF voltage is used as an external bias voltage. Was used.

[0005]

However, the above-described DC voltage or RF as an external bias voltage is used.
It is considered that application of a voltage to the material to be treated disturbs the plasma on the surface of the material to be treated, and it has been pointed out that it is not preferable.

In addition, when a DC voltage is applied to a conductor, the potential of the surface of the material to be processed is different from the potential of the surface of the material to be processed when the material to be processed has an insulator mask on the conductor which is often used for dry etching. The potential of the insulator mask is different from that of the insulator mask, and the electric field between the surface of the workpiece and the insulator mask is distorted. For this reason, there is a problem in that the incident trajectory of ions to the material to be processed is bent.

Furthermore, when an RF voltage is applied to the insulator, there is a problem that an excessive voltage is applied to the material to be processed at the peak voltage of the RF voltage.

Further, the use of such an external bias voltage necessitates a new power supply separately, which causes a problem of increasing the manufacturing cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned various problems of the prior art, and an object of the present invention is to apply a bias voltage to a material to be processed without applying a bias voltage from the outside. An object of the present invention is to provide a method and an apparatus for controlling ion energy capable of controlling ion energy incident on a processing material.

[0010]

In order to achieve the above object, a method for controlling ion energy according to the present invention comprises the steps of: positioning an object to be processed and setting an electron beam into an ion generation region in a predetermined reaction gas atmosphere; In the method of controlling ion energy when the plasma is generated by accelerating ions in the plasma by the voltage applied to the ion sheath on the surface of the workpiece and colliding with the workpiece, the electron beam is irradiated with the electron beam. By changing the angle of incidence at the time of incidence on the material, the number of electrons colliding with the surface of the material to be processed is controlled to change the floating potential on the surface of the material to be processed, and the floating potential is applied to the ion sheath based on the change in the floating potential. By changing the voltage, the ion energy is controlled.

Further, in the ion energy control method according to the present invention, a plasma is generated by irradiating an electron beam into an ion generation region having a predetermined reaction gas atmosphere while positioning a material to be processed. The ions are accelerated by the voltage applied to the ion sheath on the surface of the workpiece,
In the method of controlling the ion energy when colliding with the workpiece, the number of electrons colliding with the surface of the workpiece is controlled by changing the acceleration when irradiating the electron beam into the ion generation region. The floating potential on the surface of the processing material is changed, and the voltage applied to the ion sheath is changed based on the change in the floating potential to control the ion energy.

Further, the ion energy control apparatus according to the present invention has an ion generation chamber in a predetermined reaction gas atmosphere, and electron beam irradiation means for irradiating the ion generation chamber with an electron beam to generate plasma. Then, the ion in the plasma is accelerated by the voltage applied to the ion sheath on the surface of the workpiece placed in the ion generation chamber, and the ion energy control device in the electron beam excited ion irradiator that collides with the workpiece, A supporting device is provided for rotatably supporting the material to be processed, so that the angle of incidence when the electron beam is incident on the material to be processed is variable.

Further, the ion energy control apparatus according to the present invention includes an ion generation chamber having a predetermined reaction gas atmosphere, and an electron beam irradiation means for irradiating the ion generation chamber with an electron beam to generate plasma. In the ion energy control device in the electron beam excited ion irradiation device, the ions in the plasma are accelerated by the voltage applied to the ion sheath on the surface of the workpiece placed in the ion generation chamber and collide with the workpiece. A power supply for electron beam acceleration capable of variably controlling the voltage for controlling the acceleration of the electron beam, so that the acceleration at the time of irradiating the electron beam into the ion generation chamber is variable.

[0014]

When the angle of incidence of the electron beam upon the material to be processed changes, the number of electrons reaching the surface of the material to be processed changes, and the floating potential on the surface of the material to be processed changes. This changes the voltage applied to the ion sheath. For this reason, the ion energy accelerated by the voltage applied to the ion sheath and incident on the surface of the workpiece can be controlled by changing the angle of incidence of the electron beam on the workpiece.

By changing the acceleration when the electron beam is incident on the material to be processed, the number of electrons reaching the surface of the material to be processed changes, and the floating potential on the surface of the material to be processed changes. This changes the voltage applied to the ion sheath. Therefore, the ion energy accelerated by the voltage applied to the ion sheath and incident on the surface of the material to be treated is
It can be controlled by changing the acceleration when the electron beam is incident on the workpiece.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an ion energy control method and apparatus according to the present invention;

FIG. 1 shows an electron beam excited ion irradiation apparatus 10 provided with an ion energy control apparatus according to one embodiment of the present invention.

This electron beam excited ion irradiation apparatus 10
Is a sealed container 12 having a diameter of about 95 mm and a total length of about 110 mm.
An anode electrode 14 and an electron beam accelerating electrode 16 made of, for example, a refractory metal such as tungsten or molybdenum are arranged at intervals of about 1 mm. The anode electrode 14 and the electron beam accelerating electrode 16
Is formed in the shape of a disk having a diameter of several cm and a thickness of about 0.2 mm to 0.5 mm.
A large number of through holes 14a and 16b of about 5 mm to 1.0 mm are formed.

On one side wall 12a facing the anode electrode 14 in the sealed container 12, a cathode electrode 18 made of a hot filament is provided so as to project toward the anode electrode 14.

The cathode electrode 18 and the anode electrode 1
4, an electrode 20 having a through-hole 20a is provided. The electrode 20 stabilizes the discharge between the cathode electrode 18 and the anode electrode 14 by increasing the gas pressure in the region of the cathode electrode 18 made of a hot filament, or operates gas for generating ions in the ion generation region described later. When an active gas such as oxygen is used as the gas, the gas pressure of Ar (argon) gas introduced into the region of the cathode electrode 18 is increased to prevent the active gas such as oxygen from flowing into the region, and the heat of the cathode electrode 18 is reduced. Acts as a barrier to protect the filament.

The cathode electrode 18 and the anode electrode 1
4 is set to about 0.1 Torr.

Further, in the ion generation chamber 12c between the electron beam accelerating electrode 16 and the other side wall 12b facing the electron beam accelerating electrode 16, a support device 24 for supporting the material to be processed 22 in an electrically insulated state is provided. Have been. The support device 24 is rotatable around an axis O-O as shown in FIG.
The processing target material 22 is supported rotatably with respect to the sealed container 12.

Further, in order to emit thermoelectrons, a DC or AC heater power supply 26 for applying a voltage Vh for heating a filament as the cathode electrode 18 to about 1500 ° C. to 1600 ° C .;
A discharge power supply 28 for applying a discharge voltage Vd between the power supply and the anode electrode 14 and an electron beam acceleration power supply 30 for applying an electron beam acceleration voltage Va to the electron beam acceleration power supply are provided.

In the above configuration, Ar gas is discharged as a discharge gas into the sealed container 12 through a valve (not shown) provided between the side wall 12a of the sealed container 12 and the electrode 20.
Gas is introduced. Cathode electrode 18 and anode electrode 1
4 between about 60V to 100V from the discharge power supply 28
Is applied to generate a discharge, and a discharge plasma is generated between the cathode electrode 18 and the anode electrode 14.

That is, the cathode electrode 18 and the anode electrode 1
The area between the area 4 and the area 4 is a plasma area, which is an area where the discharge power supply 28 generates plasma containing electrons serving as an electron beam source.

At this time, the cathode electrode 18 is connected to the heating power source 2
1500 to 160 ° C depending on the heating voltage Vh from 6
It is heated to 0 ° C. to emit thermoelectrons, thereby facilitating the start of discharge between the cathode electrode 18 and the anode electrode 14. For this purpose, about 60 V to 1
Discharge can be started with a low energy discharge voltage Vd of 00V.

The anode electrode 14 is about 1 mm
An acceleration voltage Va is applied to the electron beam accelerating electrodes 16 provided at intervals of from the electron beam accelerating power supply 30, and electrons are generated from discharge plasma generated between the cathode electrode 18 and the anode electrode 14. Pull out and accelerate,
An electron beam enters the ion generation chamber 12c. Therefore, a region between the anode electrode 14 and the electron beam acceleration electrode 16 is an electron beam acceleration region in which electrons are accelerated by the electron beam acceleration power supply 30.

The gas pressure between the anode electrode 14 and the electron beam accelerating electrode 16 is, for example, about 0.03 Torr.

In the ion generation chamber 12c, for example, oxygen (O ₂ ) or A
r gas is supplied. And the ion generation chamber 12c
The electron beam introduced therein collides with gas molecules of a working gas for generating ions, and generates a dense plasma. In this manner, plasma is generated in a region with a low gas pressure by using an electron beam having a large ionization cross-sectional area and energy. That is, high-speed electrons collide with gas molecules in the ion generation chamber 12c, and the gas molecules are turned into plasma to generate ions.

Accordingly, the region from the electron beam accelerating electrode 16 to the side wall 12c is an ion generation region which is a region for generating plasma by the electron beam.

The gas pressure in the ion generation region is set to about 10 ^-4 Torr to 0.1 Torr by a vacuum pump.

The ions in the plasma generated in the ion generation chamber 12c as described above collide with the workpiece 22 supported by the support device 24, and perform processing such as etching on the workpiece. Will be.

At this time, by rotating the support device 24, the angle (θ) between the electron beam and the surface of the workpiece 22 is changed from vertical to parallel, so that the workpiece 22 is It can be controlled to change the incident ion energy.

Also, by controlling the acceleration power supply 30 to change the acceleration voltage Va of the electron beam, it is possible to control so as to change the ion energy incident on the workpiece 22.

That is, the material to be processed 2 positioned in the plasma
2 is supported by the support device 24 in an electrically insulated state. For this reason, the target material 22 is normally negatively biased due to the difference in diffusion coefficient between electrons and ions, and an ion sheath is formed on the surface of the target material 22.
The potential on the surface of the material to be processed 22 at this time is called a floating potential Vf, and the spatial potential Vs of the plasma in the ion generation chamber 12c.
The potential difference between the voltage and the floating potential Vf is the voltage applied to the ion sheath (FIG. 3).

Since the ions in the plasma in the ion generation chamber 12c are accelerated by the voltage applied to the ion sheath, the ion energy incident on the surface of the workpiece 22 is Ei, and Ei = q (Vs- Vf) q: electric charge.

Therefore, the ion energy Ei incident on the surface of the workpiece 22 can be controlled by controlling the floating potential Vf if the space potential Vs is constant.

By the way, the floating potential Vf is a potential on the surface of an insulator in plasma, and no current flows on that surface, so that electrons and ions arriving at the surface lose charge due to surface recombination. , The number of electrons and ions reaching a unit time must be equal. That is, the potential at which the electron current and the ion current are equal becomes the floating potential Vf.

Here, the ratio between the electron saturation current Ies and the ion saturation current Iis is as follows: Ies / Iis = 0.66 (mi / me) ^1/2 mi: mass of ions, me: mass of electrons. , Ar gas has a large ratio of about 180.

Accordingly, since the ion saturation current Iis is much smaller than the electron saturation current Ies, the number of electrons having energy larger than the potential difference of the ion sheath reaching the surface of the material to be processed 22 is controlled only slightly. Floating potential V
f can be changed, and the potential difference of the ion sheath can be controlled.

That is, as shown in FIG. 3, when the beam electrons have an angle θ with respect to the workpiece 22, the beam electrons enter the ion sheath at the same angle. At this time, the beam electrons incident on the ion sheath are repelled by the reverse electric field in the ion sheath, and only the electrons whose energy of the component perpendicular to the surface of the material to be processed 22 is larger than the reverse electric field are reduced. To reach the surface. As a result, FIG.
As shown in (2), the potential difference (Vs-Vf) of the ion sheath can be controlled.

That is, FIG. 4 shows the floating potential V of the workpiece 22 with respect to the incident angle θ of the beam electrons to the workpiece 22.
This shows the dependence of f (the space potential Vs is constant). 4 that the floating potential Vf can be controlled by changing the angle θ.

Therefore, since the space potential Vs of the plasma is near the ground potential, the ions entering the material to be processed 22 are accelerated by the potential difference between the space potential Vs and the floating potential Vf. Ion energy to be controlled.

The number of electrons reaching the surface of the workpiece 22 can also be controlled by controlling the acceleration of the beam electrons by changing the acceleration voltage Va. Therefore, when the acceleration voltage Va is changed, the floating potential Vf also changes, and as shown in FIG. 4, the potential difference (Vs-Vf) of the ion sheath can be controlled.

Since the ion energy cannot be controlled unless the electron beam reaches the workpiece 22, the gas pressure of the working gas in the ion generation region 12c and the distance from the electron beam accelerating electrode 16 to the workpiece 22 are controlled. There are restrictions.

That is, as shown in FIG. 5, when the gas pressure (pressure) of the working gas in the ion generation region 12c is high, the probability that the electron beam collides with the gas molecules of the working gas becomes extremely high. The existence probability of the electrons reaching 22 becomes extremely low. Further, even when the distance from the electron beam accelerating electrode 16 to the workpiece 22 is long, the probability that the electron beam collides with the gas molecules of the working gas becomes extremely high, so that the electrons cannot reach the workpiece 22. The probability becomes extremely high. Therefore, the gas pressure is maintained at a predetermined level or less, and the distance from the electron beam accelerating electrode 16 to the workpiece 22 is set to be shorter than several times the length of the mean free path of collision between electrons and atoms. It becomes necessary.

In the experimental example shown in FIG. 5, when the gas pressure becomes about 0.01 Torr or more, the potential difference between the space potential Vs and the floating potential Vf becomes small, and it becomes difficult to control the ion energy.

In the above embodiment, when an inert gas is used as the working gas in the ion generation region, it is not necessary to protect the cathode electrode 18 made of a hot filament, so that the electrode 20 need not be provided.

In the above embodiment, a DC discharge power source 2 is used as the discharge plasma generated in the plasma region.
8 is used, it is only necessary to extract electrons from the plasma region and accelerate the electrons in the electron beam acceleration region. Therefore, high-frequency (RF) discharge plasma, microwave discharge plasma, or ECR (Electron) is used. Cyclotron L
(esonance) plasma (electron cyclotron resonance plasma) or the like may be used.

[0050]

Since the present invention is configured as described above, it has the following effects.

The ion energy incident on the surface of the material to be processed is controlled by changing the angle of incidence of the electron beam on the material to be processed or the acceleration when the electron beam is incident on the material to be processed. Since there is no need to apply a bias voltage to the material to be treated from the outside,
It is possible to solve a problem caused by an external bias voltage such as disturbance of the plasma on the surface of the material to be processed, and to suppress the manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view of an electron beam excited ion irradiation device provided with an ion energy control device according to one embodiment of the present invention.

FIG. 2 is an enlarged explanatory view of a support device.

FIG. 3 is an explanatory diagram showing an electron beam incident state on a material to be processed.

FIG. 4 is a graph showing a relationship between an incident angle θ of an electron beam to a material to be processed, an acceleration voltage Va of the electron beam, and a potential difference of an ion sheath.

FIG. 5 is a graph showing a relationship between a gas pressure of a working gas in an ion generation region, a space potential Vs, and a floating potential Vf.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Electron beam excitation ion irradiation apparatus 12 Hermetic container 14 Anode electrode 14a Through hole 16 Electron beam accelerating electrode 16a Through hole 18 Cathode electrode 20 Electrode 20a Through hole 22 Material to be treated 24 Support device 26 Heating power supply 28 Discharge power supply 30 Acceleration power supply

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05H 1/24 H05H 1/46 H01L 21/3065 C23F 16/50 C23C 4/00

Claims (4)

(57) [Claims] An ion beam is irradiated to an ion generation region in a predetermined reaction gas atmosphere by locating a material to be processed to generate plasma, and ions in the plasma are ion-sheathed on the surface of the material to be processed. In the method for controlling ion energy when the electron beam is made to collide with the material to be processed by accelerating by the voltage applied to the material to be processed, by changing an incident angle when the electron beam is incident on the material to be processed, Changing the floating potential of the surface of the material to be processed by controlling the number of electrons colliding with the surface,
A method for controlling ion energy, wherein the voltage applied to the ion sheath is changed based on the change in the floating potential to control the ion energy. 2. A method for locating a material to be processed and irradiating an electron beam into an ion generation region in a predetermined reaction gas atmosphere to generate plasma, and dissociating ions in the plasma with an ion sheath on the surface of the material to be processed. In the method for controlling ion energy at the time of colliding with the workpiece by accelerating by the voltage applied to the workpiece, by changing the acceleration at the time of irradiating the electron beam into the ion generation region, The number of electrons hitting the surface is controlled to change the floating potential on the surface of the workpiece, and the voltage applied to the ion sheath is changed based on the change in the floating potential to control the ion energy. A method for controlling ion energy, characterized in that: 3. An ion generating chamber having a predetermined reaction gas atmosphere, and an electron beam irradiating means for irradiating the ion generating chamber with an electron beam to generate plasma, wherein ions in the plasma are In the ion energy control device in the electron beam excited ion irradiation device, which is accelerated by a voltage applied to the ion sheath on the surface of the workpiece positioned in the generation chamber and collides with the workpiece, the workpiece is rotatable. A control device for controlling the ion energy, wherein the incident angle of the electron beam incident on the workpiece is variable. 4. An ion generating chamber having a predetermined reaction gas atmosphere, and an electron beam irradiating means for irradiating the ion generating chamber with an electron beam to generate plasma, wherein ions in the plasma are In the ion energy control device in the electron beam excited ion irradiation device, which is accelerated by a voltage applied to the ion sheath on the surface of the material to be processed positioned in the generation chamber and collides with the material to be processed, the acceleration of the electron beam is controlled. An electron beam acceleration power supply capable of variably controlling a voltage for activating the ion beam, wherein an acceleration when irradiating the electron beam into the ion generation chamber is variable.