JPH0621001A - Etching method - Google Patents

Abstract

(57) [Summary] [Purpose] With regard to dry etching, the purpose is to reduce damage to the processed surface, enable fine processing, and reduce the effect on device characteristics and reliability. [Structure] A magnetic field whose magnetic flux density gradually changes is formed in an etching chamber, plasma of a reaction gas is generated in the magnetic field, and an electric field for moving charged particles in the plasma toward a portion having a high magnetic flux density is applied. The workpiece is placed at a position where the velocity of the charged particles in the direction of the magnetic force line becomes substantially zero in the portion having a high magnetic flux density, and the workpiece is etched.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method for surface processing used for manufacturing semiconductor devices and the like.

In recent years, semiconductor devices have been highly integrated, and processing techniques are required to have high uniformity and controllability. For this reason, dry etching technology using plasma and accelerated particles is widely used, but it may damage not only the surface but also the inside, and may affect device characteristics, etc. There is a need for an etching technique with less damage to the surface.

[0003]

2. Description of the Related Art The conventional dry etching technique is to generate a plasma of gas by using a high frequency electric field or the like, and plasma etching utilizing the chemical reaction of the gas, or reactive ion etching (anisotropic) which is anisotropic in this method. RIE), or sputter etching that uses high-energy ions generated by discharging a heavy inert gas, and ion beam etching that accelerates and bombards the inert gas.

In any of these techniques, etching is carried out by using the energy given by an electric field by charged particles for physical change or chemical reaction on the processed surface.

However, the charged particles collide with the processed surface, causing damage to the inside and adversely affecting the device characteristics and reliability. In particular, in order to obtain high processing accuracy, it is necessary to increase the energy of the charged particles, and along with this, the collision energy on the processing surface is also increasing.

[0006]

In the prior art, damage to the processed surface has increased when performing fine dry etching.

It is an object of the present invention to reduce damage to the processed surface during dry etching, enable fine processing, and reduce the influence on device characteristics and reliability.

[0008]

[Means for Solving the Problems] To solve the above problems, a magnetic field whose magnetic flux density gradually changes is formed in an etching chamber,
A plasma of a reaction gas is generated in the magnetic field, and an electric field for moving the charged particles in the plasma toward a portion having a high magnetic flux density is applied. In the portion having a high magnetic flux density, the velocity of the charged particles in the magnetic line direction. It is achieved by an etching method in which a workpiece is placed at a position where is substantially zero.

[0009]

FIG. 1 is a diagram for explaining the principle of the present invention. In the figure, 1 is a workpiece, 2 is a magnetic pole, 3 and 4 are electrodes, and 11 is an etching chamber for generating plasma. The broken line indicates the line of magnetic force, and the magnetic flux density continuously changes toward the magnetic pole. The solid spiral line represents the trajectory of the motion of charged particles in the magnetic field. Here, the method of plasma generation does not matter, but it is appropriate that the magnetic field is not disturbed significantly.

In the present invention, the charged particles in the plasma are accelerated toward the electrode 4 on which the workpiece is placed by the electric field formed between the electrodes, and the locus thereof acts on the charged particles moving in the magnetic field. As shown in the figure, the Lorentz force creates a spiral that entangles with the magnetic field lines, advances toward the magnetic pole, and bounces off at a point determined by the velocity of the charged particles and the size of the magnetic flux density. Perform the movement of charged particles.

In other words, the momentum of the charged particles in the direction of the magnetic force line, that is, the momentum toward the workpiece gradually decreases, becomes 0 at a certain point, and the momentum in the direction away from the workpiece again increases. However, since the energy of the charged particles during this period is stored, the energy of the charged particles is high at the point where the charged particles are reflected and the momentum toward the workpiece is zero.

Therefore, if there is a workpiece at this point,
The charged particles reach the surface softly without giving energy to the work piece in the collision direction. If the particles are selected to cause a chemical reaction with the surface substance, the energy of the particles causes a chemical reaction and etching proceeds.

At this time, the subsurface damage due to the collision of particles can be minimized. In addition, at the point where the particles are reflected, the radius of spiral movement of the particles is minimized, improving the processing accuracy.
Further, the energy of the charged particles, the strength of the electric field, and the strength of the magnetic field can be controlled by adjusting the shape and size of the device and the applied power.

The process of repelling charged particles at a certain position will be described in more detail below. In a stationary magnetic field, the magnetic moment is conserved, so charged particles approaching from a region with a small magnetic field to a region with a large magnetic field have progressively higher velocities in the rotation direction and kinetic energy are conserved, so the velocities in the traveling direction gradually increase. Get smaller. When the magnetic field becomes stronger, the velocity in the traveling direction becomes 0, and finally the direction changes. This is called a mirror magnetic field and is used to confine plasma. The velocity component in the traveling direction along the line of magnetic force of the repelled charged particles gradually increases for the same reason as above. For the velocity component along the magnetic field lines, this acceleration is negative if the direction in which the magnetic field is strong is positive.

The acceleration of the charged particles by the electric field is to give energy to the charged particles so as to advance the charged particles toward the region where the magnetic field is strong, or to repel the charged particles that recoil back to the region where the magnetic field is strong. Done.

Next, the principle of the present invention will be described in more detail. (1) First, for simplicity, consider the case where the voltage applied to the electrodes is zero. Let the magnetic flux density at point A be B ₀ and that at the surface of the workpiece be B _1, and let the velocity of the charged particles parallel to the center line be
Let v _{P be} the velocity of a charged particle perpendicular to the center line, and v _Q be
As long as the magnetic field gradually changes in space, the magnetic moment μ of charged particles is adiabatic invariant and is conserved. Therefore, μ = (1/2) mv _Q ² / B = (1/2) mv _Q0 ² / B ₀ = (1/2) mv _Q1 ² / B ₁
= If the energy of a constant charged particle is E, from the energy conservation law, E = (1/2) mv ² = (1/2) m (v _P ² + v _Q ² ) v _P = ± [(2 / m) E− v _Q ² ] ^1/2 = ± [(2 / m) E− (2 / m) μB
] ^1/2 , so v _P = 0, that is, reflection occurs before the work piece is (2 / m) E− (2 / m) μB ₁ <0, ∴μ> E / B ₁ ( 1/2) mv _Q0 ² / B ₀ ＞ (1 / B ₁ ) [(1/2) m (v _P0 ² ＋ v _Q0 ² ) ∴ v _Q0 ² / (v _P0 ² ＋ v _Q0 ² ) ＞ B ₀ / B ₁ Now, if the direction of the charged particles at point A is defined as tan θ = v _Q0 / v _P0 , sin θ = (B ₀ / B ₁ ) ^1/2 Therefore, the charged particles that reach the surface of the workpiece are Satisfies sin θ ≤ (B ₀ / B ₁ ) ^1/2 .

At this time, (1/2) mv _P1 ² = μ (B ₀ / sin ² θ−B ₁ ) = E [1− (B ₁ / B ₀ ) sin ² θ] (1/2) mv _P1 ² / (1/2) mv _P0 ² = (E−μB ₁ ) / (E−μB ₀ ) = 1 − [(B ₁ / B ₀ ) −1] tan ² θ Therefore, the charged particles on the surface of the workpiece The energy in the direction perpendicular to the surface of is reduced by the factor of the above equation and becomes energy in the direction parallel to the surface of the work piece.

Now, assuming that B ₁ = 2B ₀ , those within θ = 45 ° reach the workpiece. When θ = 40 °, the vertical energy is about 30%, and when θ = 30 °, the vertical energy is about 67%. (2) When the voltage applied to the electrode is V In this case, the energy is not conserved and E ₀ = (1/2) mv ₀ ² = (1/2) m (v _P0 ² + v _Q0 ² ) E ₁ ＝ (1/2) mv ₁ ² ＝ (1/2) m (v _P1 ² ＋ v _Q1 ² ) ＝ E ₀ ＋ eV At this time, the electric field generally does not coincide with the direction of the magnetic field lines, so the energy conservation law does not hold. Therefore, since the acceleration due to the electric field is directed toward the work piece, the work piece reaches the work piece even if the initial direction θ of the charged particles is larger. (3) Etching control (A) Depending on the magnetic flux density distribution inside the device, the relative position between the workpiece and the magnetic pole is changed, that is, the ratio B ₀ / B ₁ of the magnetic flux density is changed to reach the charged particles in the vertical direction. Control the energy of.

(B) By changing the position of the electrode and the applied voltage,
By changing the energy of the charged particle in the traveling direction,
Controls the incoming charged particles and the energy in the vertical direction.
Since the actual control parameters depend on the device, the variables of (A) and (B) above are specifically shaken to find the optimum value.

[0020]

FIG. 2 is a block diagram of an embodiment of the present invention. In the figure, 6 is a thermionic emission filament for plasma generation,
7 is a workpiece, a semiconductor wafer, 8 is a reaction gas inlet, 9
Is an exhaust port, and 10 is an insulating plate.

As the reaction gas, for example, carbon tetrafluoride (CF ₄ )
Fluorine (F) ions are generated when the is discharged. A negative potential is applied to the wafer 7 to accelerate the F ions, and the wafer 7 is swung around the lines of magnetic force to approach the wafer. The wafer is placed at the point where the magnetic flux density is increased and the ions are repelled, and etching is performed by reacting with the silicon dioxide (SiO ₂ ) on the surface of the wafer.

At this time, the accelerating voltage, the distance between the electrodes, the position of the magnetic pole, and the strength of the magnetic field are controlled to optimize and determine the etching conditions. An electromagnet may be used to generate the magnetic field,
Permanent magnets can also be used to reduce power consumption.

In this embodiment, the relative positions of the wafer and the magnetic poles are fixed, but etching may not be performed uniformly depending on the state of the magnetic field. Therefore, the configuration shown in FIG. 3 is effective.

FIGS. 3A and 3B are block diagrams of another embodiment of the present invention. Figure 3 (A) shows an example of a movable wafer,
(B) is an example in which the magnetic poles are movable. By performing the etching while changing the relative positions of the wafer and the magnetic pole, the uniformity of etching can be achieved.

In the embodiment, since the charged particles are concentrated in the portion where the magnetic field is strong near the magnetic pole, the magnetic pole is scanned on the wafer in order to make the distribution uniform when etching a large area.
The etching rate is made uniform on the wafer.

In order to change the relative position between the wafer and the magnetic pole, for example, a means for moving the stage on which the wafer is placed is used. FIGS. 4A and 4B are views for explaining an arrangement example of the permanent magnet and the electromagnet, respectively.

In the figure, 2 is a magnetic pole and N pole, 2A is an iron core forming a magnetic path, and 2B is a coil. An example of control parameter values using these devices is shown below. Electrode spacing: 100 mm Applied voltage: 100 V Surface magnetic flux density of magnetic pole: 0.5 tesla Here, when using a permanent magnet, use Alnicco 5
Formed a pole.

[0028]

According to the present invention, damage to the processed surface during dry etching can be reduced, and as a result, fine processing can be performed and the influence on device characteristics and reliability can be reduced. It was

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the present invention.

FIG. 3 is a configuration diagram of another embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of arrangement of magnets.

[Explanation of symbols]

 1 Workpiece 2 Magnetic pole 3,4 Electrode 6 Thermoelectron emission filament for plasma generation 7 Semiconductor wafer as a work piece 8 Reactive gas inlet 9 Exhaust 10 Insulation plate 11 Etching chamber

Claims (1)

[Claims] 1. An electric field in which a magnetic field having a gradually changing magnetic flux density is formed in an etching chamber, plasma of a reaction gas is generated in the magnetic field, and charged particles in the plasma move toward a portion having a high magnetic flux density. And an object to be processed is placed at a position where the velocity of the charged particles in the direction of the magnetic force line is substantially zero in the portion having a high magnetic flux density, and etching is performed.