KR19980041231A - Plasma Uniformity Control Method - Google Patents

Abstract

A method of controlling the uniformity of the plasma is disclosed, in which the density of the plasma is made uniform by adjusting the intensity of the magnetic field applied to the plasma. In the plasma generation mechanism in which the inductively coupled plasma and the helicon wave plasma are mixed, the spatial distribution of the plasma density can be controlled by emphasizing either the inductively coupled plasma or the helicon wave plasma by adjusting the intensity of the magnetic field.

Description

Plasma Uniformity Control Method

The present invention relates to a method for controlling plasma uniformity. In a plasma generating apparatus in which capacitively coupled plasma and helicon wave plasma are mixed, the intensity of a magnetic field is controlled. The present invention relates to a plasma uniformity control method capable of ensuring uniformity of plasma density.

As the manufacturing process of the semiconductor device proceeds to the sub-micron level, the processing dimension becomes smaller and becomes 0.4. Pattern processing of m or less levels is required. Therefore, in the etching process, demand for high etching selectivity with the underlying film, fine line width control, and the like is emphasized. Accordingly, the dry etching method for forming the anisotropic profile takes up the majority of the etching process, and the demand for the vertical profile is increasing with the reduction of design rules.

The dry etching process is largely divided into a physical sputtering method, a reactive ion etching method, and a plasma etching method. Recently, plasma etching having a high selectivity for both the mask and the underlying layer is mainly used, and efforts have been continuously made to reduce the electrical defects and obtain a high anisotropic shape during the plasma etching.

For this purpose, recently attracting equipments have generally adopted a method of generating high density plasma at low pressure to achieve high anisotropic etching while reducing electrical defects from the plasma. Representative equipments having such characteristics include an inductively coupled plasma generator such as inductively coupled plasma (ICP) or transform coupled plasma (TCP) and a helicon wave plasma generator.

Inductively coupled plasma is a plasma using an electric field induced by applying RF power to a coil. A secondary electric field formed around a plasma and formed by a high frequency supplied to a circular or spiral antenna through which an RF current passes is introduced into the plasma. Can't penetrate deeply.

On the other hand, due to the electromagnetic field acting on the surface of the plasma, the high frequency current flowing in the portion is attenuated as it enters from the surface. This is called the skin depth. Depth of the epidermis Obtained by the equation, where c represents the speed of light Represents the electron plasma frequency.

The inductively coupled plasma has a mechanism such that the electrons are accelerated by the secondary electric field only at a distance called the depth of this skin, ie, the plasma surface very close to the antenna. In this case, as shown in FIG. 1, there is a nonuniformity in which the density near the edge of the plasma becomes higher than the density in the center.

When the magnetic field perpendicular to the antenna direction of the inductively coupled plasma generator is applied, the depth of the epidermis increases as the intensity of the magnetic field increases. When the magnetic field is increased to some extent, the secondary electric field generated by the antenna penetrates deeply into the center of the plasma. In this case, electromagnetic waves traveling inside the plasma are formed, which is called a helicon wave. Helicon waves propagate at positions parallel to the direction of the magnetic field, the length of which depends on the strength of the magnetic field. The plasma generated by such a helicon wave has the highest density distribution in the center, as shown in FIG. 2.

In the inductively coupled plasma and the helicon wave plasma as described above, the non-uniformity of the plasma density causes a narrow process margin during the progress of the etching process using the plasma, thereby lowering the yield. In addition, due to the non-uniformity of the plasma density, the gate oxide film is degraded, resulting in an electrical defect of the semiconductor device.

Accordingly, a technical problem of the present invention is to provide a plasma uniformity control method in which a plasma generation mechanism is a mixture of an inductively coupled plasma and a helicon wave plasma. To provide.

1 is a graph showing the density distribution of inductively coupled plasma.

2 is a graph showing the density distribution of the helicon wave plasma.

3 is a graph showing the density distribution of the plasma when the inductively coupled plasma and the helicon wave plasma are mixed.

4 is a schematic diagram illustrating a method of real-time monitoring of plasma density using a charge coupled device.

In order to achieve the above object, the present invention provides a plasma uniformity control method characterized in that the density of the plasma is uniform by adjusting the intensity of the magnetic field applied to the plasma.

According to a preferred embodiment of the present invention, controlling the intensity of the magnetic field is a plasma generating mechanism in which the inductively coupled plasma and the helicon wave plasma are mixed.

In addition, the plasma density may be monitored in real time using a charge coupled device (hereinafter referred to as a CCD).

The present invention can control the spatial distribution of the plasma density by emphasizing either the inductively coupled plasma or the helicon wave plasma by adjusting the intensity of the magnetic field in the plasma generation mechanism in which the inductively coupled plasma and the helicon wave plasma are mixed.

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

First, a brief description of plasma refers to a partially ionized gas consisting 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 rotate in order to cancel the rotation, and the radius of rotation is called a Larmor radius. This is a phenomenon that occurs because the plasma is a diamagnetic material (diamagnetic material), and expressed as the lamo radius as follows.

[Equation]

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

If the lamo 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 system It has a small lamo radius and is affected by the magnetic field.

The most typical method of applying a static magnetic field to the plasma is a method of generating a magnetic field perpendicular to the current by applying a direct current (DC) current to the electromagnetic coil. The magnetic field generated is then 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).

As such, the magnetic field is one of the most important physical factors controlling plasma parameters. In particular, in magnetically enhanced reactive ion etching (MERIE) devices, the magnetic field improves plasma characteristics, such as reducing process pressure, increasing the degree of ionization, and reducing ion energy. In addition, the magnetic field is one of the essential factors for generating a helicon wave plasma and an electron cyclotron resonance (ECR) plasma.

When a weak magnetic field of about 100 gauss is present in a conventional plasma generating apparatus, two modes of plasma described with reference to FIGS. 1 and 2 exist simultaneously. In other words, the mode of high plasma density by inductive coupling and the mode of high plasma density by helicon waves exist simultaneously. This is illustrated in FIG. 3.

At this time, when the strength of the magnetic field is weak, the plasma formation by the inductive coupling is stronger, the density of the edge of the plasma is increased. On the other hand, when the strength of the magnetic field is strong, the plasma formation by the helicon wave becomes strong and the density in the center of the plasma becomes high. Therefore, the spatial distribution of the plasma density can be adjusted by emphasizing either the inductively coupled plasma or the helicon wave plasma by adjusting the intensity of the magnetic field.

According to a preferred embodiment of the present invention, the function of controlling the spatial distribution of the plasma density can be further enhanced by constantly monitoring the distribution of the plasma density. That is, as shown in Figure 4 using a CCD camera to monitor the density of the plasma in real time.

Referring to FIG. 4, light emitted from the plasma generator is analyzed by a CCD camera through an optical filter selectively transmitting only a predetermined wavelength. In this way, the spatial distribution of the plasma density is monitored in real time, and the analyzed results are fed back to adjust the strength of the magnetic field to obtain an optimized spatially uniform plasma density.

As described above, according to the plasma uniformity control method according to the present invention, in the plasma generation mechanism in which the inductively coupled plasma and the helicon wave plasma are mixed, one of the inductively coupled plasma or the helicon wave plasma is controlled by controlling the intensity of the magnetic field. Emphasis can be placed on controlling the spatial distribution of plasma density.

Claims (3)

And controlling the intensity of the magnetic field applied to the plasma to make the density of the plasma uniform. The method of claim 1, wherein the controlling of the intensity of the magnetic field is a plasma generating mechanism in which an inductively coupled plasma and a helicon wave plasma are mixed. 2. The method of claim 1, wherein the density of the plasma is monitored in real time using a charge coupled device (CCD).