KR19980040612A - Plasma Uniformity Control Method in Plasma Etching Equipment - Google Patents

Abstract

A novel plasma uniformity control method is disclosed. Any waveform, the same frequency in a predetermined frequency range, and a controllable phase inversion between the modulations of the main coil and the subcoil of the electromagnet, change the placement of the magnetic field by time-modulating the current in the main and subcoils. Let's do it. Plasma uniformity may be controlled by controlling phase inversion between time-modulated currents of the electromagnet coil.

Description

Plasma Uniformity Control Method in Plasma Etching Equipment

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling plasma uniformity, wherein a phase between time-modulated currents of an electromagnet coil in an electron cyclotron resonance (hereinafter referred to as ECR) plasma and helicon wave plasma etching equipment A method of controlling plasma uniformity by controlling a phase shift.

Plasma is a partially ionized gas of ions, electrons and various neutral species, which is generated by applying an Rf electric field to the gas at low voltage. When a static magnetic field is applied to the plasma from the outside, charged particles, such as electrons and ions, in the plasma are rotated in order to cancel them, and the radius of rotation is called a Larmor radius. This is a phenomenon that occurs because the plasma is a diamagnetic material (ramo radius), expressed by the equation of the L'amo in the following equation.

[Equation]

Where r _l represents the lamo radius, m represents the diameter of the charged particles, v _ㅗ represents the velocity of the charged particles perpendicular to the magnetic field, and B represents the intensity of the magnetic field.

If the Ramo radius is small compared to the size of the system generating the plasma, e.g. the radius of the reaction chamber or the spacing between the electrodes, the charged particles are defined along the applied magnetic field, while the former is lighter than the ions and therefore much larger than the size of the system. It has a small lamo radius and is affected by the magnetic field.

As such, the magnetic field is one of the most important physical factors controlling plasma parameters. In particular, in a magnetic field enhanced reactive ion etch (MERIE) system, the magnetic field improves the characteristics of the plasma by reducing the process pressure, increasing the degree of ionization and decreasing the ion energy. In addition, the magnetic field is one of the essential factors for generating the helicon wave plasma and the ECR plasma. For example, etch rate and etch uniformity are strongly dependent on the distance between the ECR zone and the wafer location area. These systems require the use of permanent magnets or electromagnets to create a magnetic field. stationary). The magnetic field used by Applied Material's MERIE P-5000 machine rotates around the vertical axis of the reaction chamber to control etch uniformity.

An object of the present invention is to provide a method for controlling plasma uniformity by controlling phase inversion between time-modulated currents of an electromagnet coil in an ECR plasma and helicon wave plasma etching apparatus.

1 is a schematic diagram of an electromagnet coil used in an ECR and helicon wave plasma etching equipment.

2 is a graph showing modulation of current in an electromagnet coil.

3 is a graph showing current modulation in controllable phase inversion between the same frequency and modulation of the main and subcoils, for two coil systems.

In order to achieve the above object, the present invention, in the plasma uniformity control method of the plasma etching equipment having an electromagnet, arbitrary waveforms, the same frequency in a predetermined frequency range, and the main coil and the sub-coil of the electromagnet ( A control method of plasma uniformity characterized by changing the configuration of a magnetic field by time-modulating the current in the main coil and the sub-coil by controllable phase inversion between modulations of a subcoil.

According to the present invention, the etching uniformity is controlled by time modulation of the magnetic field.

The plasma etching apparatus includes an ECR plasma etching apparatus and a helicon wave plasma etching apparatus.

The predetermined frequency range is preferably 0.1 Hz to 10 Hz.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram of an electromagnet coil used in an ECR and a helicon wave plasma etching apparatus. 2 is a graph showing modulation of current in an electromagnet coil.

First, the method of applying the static magnetic field to the plasma, the most typical method is a method of generating a magnetic field in the direction perpendicular to the current by applying a direct current (dc) current to the electromagnetic coil (electromagnetic coil). The magnetic field generated is a function of the magnitude of the current and the distance from the current source (see Ampere's Circuit Law or Bio-Savar's Law). The electromagnet coil is mainly used to generate a magnetic field symmetrical about the axis of the reaction chamber in ECR and helicon wave plasma etching equipment. Occasionally, an electromagnet subcoil having a coaxial axis with the main coil is used to control the placement of the magnetic field and the plasma uniformity. The placement of the magnetic field, ie the spatial distribution of the magnetic field, determines the ionization distribution and dissociation rate in the chamber volume.

At a constant current in the coil, the magnetic field inductance B has a nonuniform static spatial distribution. In order to simplify this, considering only the points of the coil axis as shown in FIG. 1, the magnetic field induction coefficient B can be expressed in a simple manner at these points. Time modulation of the current in the magnetic coil will result in time modulation of the magnetic field arrangement. If the current I is a function of time t as shown in Fig. 2, the magnetic field induction coefficient B is defined by the following equation 1 as a function of time and the point A position on the coil axis.

[Equation 1]

Here, n denotes the number of turns in the coil as (N / L), N denotes the number of turns in the coil, and L denotes the length of the coil, respectively. Also, to be.

On the other hand, the time dependence of the current I may be selected as a sin wave, as shown in Equation 2 below,

[Equation 2]

It may be selected as a triangular wave, a right angle pulse, or the like. Where I ₀ represents the direct current (dc) current in the coil, I ₁ represents the amplitude of the alternating current (ac) current in the coil, and w represents the modulation frequency.

As shown in Equation 1, due to the linear dependence of the magnetic field induction coefficient B on the current I, the time dependency of the magnetic field induction coefficient B becomes the same as that of the current. The upper limit of the modulation frequency also depends on the coil parameters (structure and rotational speed).

On the other hand, in order to generate an ECR plasma, the ECR condition defined by Equation 3 below must be satisfied.

[Equation 3]

Here, w _e represents the electron cyclotron frequency, m _e represents the mass of electrons, and e represents the electron charge.

Since the magnetic field induction coefficient B is a function of both position and time, the position of the region where the above ECR condition is satisfied changes in the plasma. This change in the position of the plasma generation source (ECR region) as well as the change in the magnetic field in the diffusion region results in a change in the time and space of the plasma parameters. Accordingly, changes in the plasma parameters control the etching rate and the etching uniformity.

On the other hand, the helicon wave propagates at a position parallel to the direction of the magnetic field, the length of which depends on the strength of the magnetic field. For example, for a wave frequency of 13.56 MHz, the helicon wave

[Equation 4]

(cm)

do. Thus, the temporal modulation of the magnetic field affects the generation of helicon waves as well as the spatial distribution of charged particles in the diffusion region.

On the other hand, some etching equipments use a multicoil magnet system for a fixed current in the coil to control the placement of the magnetic field. At this time, the modulation of the magnetic field may be performed in single and two coil systems. The magnetic fields for the two coil systems can be represented by Equation 5 below.

[Equation 5]

Here, B _1A (t) represents the induction coefficient of the magnetic field generated by the main coil, B _2A (t) represents the induction coefficient of the magnetic field generated by the sub-coil.

In the two coil systems described above, the modulation of the current is performed in a modulation scheme having the same frequency and controllable phase inversion between the modulation of the main coil and the subcoil (see Fig. 3).

Therefore, according to the present invention as described above, the plasma uniformity can be controlled by controlling the phase inversion between the time-modulated currents of the electromagnet coil in the etching equipment including the ECR plasma and the helicon wave plasma.

Claims (4)

In the plasma uniformity control method of the plasma etching equipment having an electromagnet, Any waveform, the same frequency in a predetermined frequency range, and a controllable phase inversion between the modulations of the main coil and the subcoil of the electromagnet, change the placement of the magnetic field by time-modulating the current in the main and subcoils. Plasma uniformity control method characterized in that. The method of claim 1, wherein the etching uniformity is controlled by temporal modulation of the magnetic field. The method of claim 1, wherein the plasma etching equipment includes an electron cyclotron resonance (ECR) plasma etching equipment and a helicon wave plasma etching equipment. The method of claim 1, wherein the predetermined frequency range is 0.1 Hz to 10 Hz.