JPH11340202A - Method and apparatus for plasma treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma treatment apparatus for reducing damages due to high-energy ions to a workpiece such as a wafer, and realizing high-speed etching with a higher aspect ratio. SOLUTION: A plasma treatment apparatus includes a rotating magnetic field coil 1 for generating magnetic field, in parallel with a wafer 8 to form a uniform plasma distribution in a plasma reaction chamber 4 and rotating the magnetic field in an azimuth direction, a porous electrode 33 for providing ions and radicals with orientation vertical to a surface of the wafer 8 after the ions have been generated in the plasma reaction chamber 3, and decelerating the ions for the ions to bombard the wafer 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing method and a plasma processing apparatus, and particularly useful as a plasma etching apparatus applied to a semiconductor manufacturing line or the like.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional plasma processing apparatus.
Shown in As shown in FIG. 1, the plasma processing apparatus is roughly divided into a plasma generation chamber 3 and a plasma reaction chamber 4.
A process gas is injected into the plasma generation chamber 3 from a gas supply nozzle 11 installed on the side wall.
The internal pressure is maintained at 0.1 to 1 Pa. An RF incident window 5 is attached to the ceiling of the plasma generation chamber 3, and a spiral antenna 23 as shown in FIG. The antenna 23 has a matching device 2 from the high frequency power supply 21.
High-frequency power is supplied via the plasma generation chamber 3
Radiated into. The electromagnetic field radiated from the antenna 23 causes ionization of the gas and generates plasma inside the plasma generation chamber 3. As a process gas, CF ₄ , C ₂ F ₆ or the like is used for etching a dielectric film, and CCl ₄ , BCl ₄ or the like is used for a metal film.

[0003] Between the plasma generation chamber 3 and the plasma reaction chamber 4, a perforated plate 51 provided with a large number of small holes on the entire surface.
Is installed. The plasma in the plasma generation chamber 3 is supplied to the plasma reaction chamber 4 through the holes of the perforated plate 51. A sample stage 7 is provided in the plasma reaction chamber 4, and a wafer 8 is placed thereon. A low frequency power supply 31 is connected to the sample stage 7 via a matching unit 32, and a high voltage is applied to the wafer 8.

[0004] Since the plasma passes through the holes of the perforated plate 51 to form a beam, ions and radicals in the plasma have directivity. Further, ions are accelerated by an electric field perpendicular to the surface of the wafer 8 generated by the high voltage applied to the wafer 8, and collide with the surface of the wafer 8 almost perpendicularly (electrons are diffused and absorbed in the wall direction). As a result, when the wafer 8 having the mask pattern formed on the surface is etched, since the directivity of radicals and ions is good even when the groove is deep, the wafer 8 is penetrated deeply and has a larger aspect ratio (depth of depth relative to groove width). Ratio) can be etched.

[0005]

However, in the above-described plasma processing apparatus according to the prior art, since ions have high energy, more energy than necessary is implanted into the wafer 8, which causes damage. There is.

In view of the above prior art, the present invention reduces the damage of a workpiece such as a wafer due to high energy ions, and enables a plasma processing method and a plasma processing apparatus capable of etching at a higher speed and a larger aspect ratio. The purpose is to provide.

[0007]

The structure of the present invention that achieves the above object has the following features.

1) The magnetic field formed in parallel with the workpiece is rotated in the azimuthal direction to make the generated plasma uniform, while allowing ions and radicals to pass through the respective holes of the porous electrode, thereby obtaining the workpiece. Has a directivity in a direction perpendicular to the surface of the workpiece and decelerates the ions to collide with the workpiece.

According to the present invention, a large-capacity ion flow and radical flow having a strong directivity perpendicular to the surface of a workpiece can be produced, and the movement of ions colliding with the workpiece at this time. Energy is also reduced to an appropriate level.

2) A plasma generation chamber for generating plasma by ionizing a process gas supplied through a gas supply nozzle, and colliding the generated plasma with a surface of the workpiece to etch the workpiece. A rotating magnetic field coil that forms a magnetic field in a direction parallel to a workpiece and turns the magnetic field in an azimuthal direction in a plasma processing apparatus having a plasma reaction chamber for performing the plasma processing. Is disposed between the plasma generation chamber and the plasma reaction chamber to provide directivity in a direction perpendicular to the surface of the workpiece to ions and radicals generated in the plasma generation chamber, and to reduce the speed of the ions. Having a porous electrode for colliding with a workpiece;

According to the present invention, a large-capacity ion stream or radical stream having strong directivity collides with a workpiece. In addition, the collision energy at this time is reduced to an appropriate value by the presence of the porous electrode.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. As shown in the figure, the present embodiment is obtained by adding a rotating magnetic field coil 1 and a porous electrode 33 to the plasma processing apparatus according to the prior art shown in FIG. Therefore, the same parts as those of the prior art shown in FIG.

The plasma generation chamber 3 and the plasma reaction chamber 4 are disposed inside the rotating magnetic field coil 1. The rotating magnetic field coil 1 generates a bipolar magnetic field in a direction parallel to the wafer 8. This rotating magnetic field coil 1 is driven by a polyphase inverter 2 and rotates a bipolar magnetic field at 1 to 10 Hz.

A three-phase inverter 2 which is a polyphase inverter 2 for generating a three-phase alternating current as an example of the rotating magnetic field coil 1
FIG. 2 shows the case where a is used. As shown in the drawing, a yoke 91 forming a magnetic path of the rotating magnetic field coil 1 is formed of a laminated steel sheet or an amorphous steel sheet, and has magnetic poles wound with coils 92a, 92b, 92c at a pitch of 60 degrees. ing. Coils 92a, 92 at facing positions
b, 92c are connected in series so that a magnetic field is generated in the same direction, and the respective coils 92a, 92b, 92c
Currents I ₁ , I ₂ and I ₃ are supplied from the three-phase inverter 2a to the pair. Since the currents I ₁ , I ₂ and I ₃ are each out of phase by 120 degrees, the magnetic field generated by each magnetic pole is 60
It will shift by degrees. As a result, the rotating magnetic field coil 1
, A bipolar magnetic field having a substantially uniform distribution at the center is generated. The lines of magnetic force generated at this time rotate in the azimuthal direction of the rotating magnetic field coil 1 at the frequency of the alternating current.

Here, the polyphase inverter 2 for driving the rotating magnetic field coil 1 may have six phases or twelve phases, and there is no particular limitation on the number of poles. In these cases, the number of magnetic poles of the yoke 91 is set to twelve. And 24 poles.

As shown in FIG. 1, an RF incident window 5 is attached to the ceiling of the plasma generation chamber 3, and a loop-shaped or concentric antenna 23 as shown in FIG. Is installed. High frequency power is supplied to the antenna 23 from the high frequency power supply 21 via the matching unit 22. Further, a gas supply nozzle 11 for supplying a process gas is provided on a side wall of the plasma generation chamber 3.

The porous electrode 33 is a porous plate provided with a large number of small holes on the entire surface, and is arranged so as to partition both spaces in a horizontal plane between the plasma generating chamber 3 and the plasma reaction chamber 4. . The porous electrode 33 is electrically insulated from the plasma generation chamber 3 and the plasma reaction chamber 4 by an insulator 34. The holes provided in the porous electrode 33 are spaced at least twice the diameter of the hole so as not to disturb the electric field distribution on the surface of the porous electrode 33. A low-frequency power supply 31 is connected to the porous electrode 33 via a matching unit 32, and a high voltage is applied. In the plasma reaction chamber 4, there is an electrically grounded sample stage 7, on which a wafer 8 is placed. The oscillation frequency of the low-frequency power supply 31 is
400, which is sufficiently lower than the oscillation frequency of 10 to 20 MHz.
Set to ~ 800 KHz.

After the process gas supplied from the gas supply nozzle 11 of the plasma generation chamber 3 reaches the wafer 8, it is discharged through a vacuum exhaust system.

In general, when plasma is generated in a magnetic field, charged particles such as electrons and ions that make up the plasma orbit around the lines of magnetic force. This rotation describes a circular orbit in a plane perpendicular to the magnetic field lines, the radius of which is proportional to the mass of the charged particle,
It is inversely proportional to the strength of the magnetic field. For this reason, ions having a large mass orbit with a larger radius than electrons having a small mass.
In the plasma processing apparatus according to this embodiment, as shown in FIG. 4, since the magnetic lines of force 82 exist in a direction parallel to the wafer 8, the electrons 71 in the plasma 81 move parallel to the wafer 8 along the lines of magnetic force 82. I do. On the other hand, since the ion 72 has a large turning radius, if the magnetic field is not very strong, the ion 72 diffuses across the magnetic field lines 82 toward the wafer 8. These conditions are satisfied when the magnetic flux intensity H satisfies the following equation (1).

[0021]

(Equation 1)

[0022] In the above equation _{(1), m e, T} e is the distance of the electron mass and temperature m _i, the T _i ion mass and temperature, h is the porous electrode 33 and the RF entrance window 5, k is Boltzmann The coefficient, e is the amount of charge of electrons, and μ ₀ is the magnetic permeability in vacuum.

Since the plasma electrons are diffused along the lines of magnetic force 82, a plasma having a uniform density distribution is formed in the direction of the lines of magnetic force 82. However, since electrons are unlikely to diffuse in the direction perpendicular to the lines of magnetic force 82, the plasma has a long distribution in the direction of the lines of magnetic force 82, as shown in FIG. Therefore, the whole plasma is rotated in the azimuth direction by the rotating magnetic field coil 1 to make the plasma distribution uniform over time.

[0024] When applied to the porous electrode 33 a voltage V _s, the current Is flows between the wall 3a and the porous electrode 33 of the plasma generating chamber 3 through the plasma 81. Since electrons can move only in the direction of the line of magnetic force, the current between the plasma 81 and the wall surface 3a mainly becomes the electron current J _e . On the other hand, since electrons cannot move between the porous electrode 33 and the plasma 81,
The ion current J _i becomes dominant. The relationship between the electron current and the ion current J _i is given by the following equation (2).

[0025]

(Equation 2)

From this, the motion of the ions 72 generated by the ionization of the process gas is dragged by the ion current J _i , and the component perpendicular to the wafer 8 increases, and the radicals 74 generated by the recombination of the ions with the electrons also generate the radicals 74. 8 has a strong directivity in a direction perpendicular to the direction. Further, since only the ion current J _i flows in the direction of the wafer 8, the ion flux becomes larger than that in the case where there is no magnetic field.

The ions 72 and the radicals 74 having a strong directivity by the porous electrode 33 enter the plasma reaction chamber 4 through many small holes provided in the porous electrode 33. The ions 72 entering the plasma reaction chamber 4 are given a large kinetic energy due to the potential difference between the plasma 81 and the porous electrode 33. However, in the plasma reaction chamber 4, the potential of the wafer 8 is higher than that of the porous electrode 33. The ions 72 are decelerated and reach the wafer 8. Since the energy of the ions 72 reaching the wafer 8 is sufficiently low, the probability that the ions 72 enter deep positions from the wafer surface and destroy the crystal structure is reduced.

[0028]

As described in detail with the above embodiments, the invention described in [Claim 1] rotates the magnetic field formed in parallel to the workpiece in the azimuth direction, and makes the generated plasma distribution uniform. On the other hand, by passing ions and radicals through each hole of the porous electrode, directivity in a direction perpendicular to the surface of the workpiece is given, and ions are decelerated to collide with the workpiece. Therefore, large-capacity ion flow with strong directivity perpendicular to the surface of the workpiece,
A radical flow can be created, while at the same time the kinetic energy of the ions colliding with the workpiece is reduced to an appropriate one.

As a result, etching with a large aspect ratio at a high speed by a large-capacity ion flow and a radical flow having a strong directivity becomes possible, while reducing damage to the workpiece due to high-energy ions. It has the effect of being able to do so.

According to the second aspect of the present invention, a plasma generation chamber for ionizing a process gas supplied via a gas supply nozzle to generate plasma, and applying the generated plasma to a surface of a workpiece. In a plasma processing apparatus having a plasma reaction chamber that collides and etches the workpiece, a magnetic field is formed in a direction parallel to the workpiece so as to make the generated plasma uniform. A rotating magnetic field coil that rotates the azimuth direction and a plasma generation chamber are disposed between the plasma generation chamber and the plasma reaction chamber, and directs ions and radicals generated in the plasma generation chamber in a direction perpendicular to the surface of the workpiece. And a porous electrode for decelerating ions and colliding them with the workpiece, so that large-capacity ion and radical flows with strong directivity can be applied. Collide with the object. In addition, the collision energy at this time is reduced to an appropriate value by the presence of the porous electrode.

As a result, it is possible to etch a large aspect ratio at a high speed by a large-capacity ion flow or radical flow having a strong directivity, while reducing damage to a sample by high energy ions. It has the effect of being able to.

[Brief description of the drawings]

FIG. 1 is an explanatory view conceptually showing a plasma processing apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a structure and a circuit configuration of a rotating magnetic field coil in the embodiment shown in FIG.

FIG. 3 is an explanatory diagram showing an example of the shape of the antenna in the embodiment shown in FIG.

FIG. 4 is an explanatory diagram showing the behavior of constituent particles in plasma inside the apparatus in the embodiment shown in FIG.

FIG. 5 is an explanatory diagram showing a positional relationship between magnetic field lines generated by a rotating magnetic field coil and plasma in the embodiment shown in FIG. 1;

FIG. 6 is an explanatory view conceptually showing a plasma processing apparatus according to a conventional technique.

FIG. 7 is an explanatory diagram showing an example of the shape of the antenna in FIG. 6;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 rotating magnetic field coil 2 multiphase inverter 3 plasma generation chamber 4 plasma reaction chamber 8 wafer 33 porous electrode 72 ion 74 radical 81 plasma 82 magnetic lines of force 92a, 92b, 92c coil

Claims (2)

[Claims] A magnetic field formed in parallel to a workpiece is rotated in an azimuthal direction to uniformize a generated plasma distribution, while ions and radicals are passed through each hole of a porous electrode, thereby forming a workpiece. A plasma processing method characterized by providing directivity in a direction perpendicular to the surface of the workpiece and decelerating ions to collide with a workpiece. 2. A plasma generation chamber for ionizing a process gas supplied via a gas supply nozzle to generate plasma, and colliding the generated plasma with a surface of the workpiece to etch the workpiece. A rotating magnetic field coil for forming a magnetic field in a direction parallel to a workpiece and rotating the magnetic field in an azimuthal direction so as to equalize a generated plasma distribution. Is disposed between the plasma generation chamber and the plasma reaction chamber so that ions and radicals generated in the plasma generation chamber have directivity in a direction perpendicular to the surface of the workpiece and are decelerated to form ions. A plasma processing apparatus, comprising: a porous electrode for colliding with a workpiece.