Plasma processing apparatus and method with controlled biasing functions

This is a continuation of U.S. application Ser. No. 11/053,236, filed Feb. 9, 2005, which is a divisional of U.S. application Ser. No. 09/946,491, filed Sep. 6, 2001 (now U.S. Pat. No. 6,875,366). This application relates to and claims priority from Japanese Patent Application No. 2000-276667, filed on Sep. 12, 2000. The entirety of the contents and subject matter of all of the above is incorporated herein by reference.

1. Field of the Invention

The present invention relates to plasma processing apparatus and method, and particularly to a plasma processing apparatus and method suitable for making surface treatment of a sample such as a semiconductor device by use of plasma.

2. Description of the Related Art

In the plasma etching process, the processing gas is ionized to be activated for fast processing, and radio frequency (RF) biasing power is supplied to a sample to be processed (or a processed sample) so that the ions in the plasma can be incident perpendicularly to the sample to be processed, thereby achieving high-precision etching for anisotropic shape and so on.

A plasma processing apparatus for this purpose is disclosed in Yokogawa et al U.S. Pat. No. 5,891,252. This apparatus, as described in that document, has an air-core coil provided on the outer periphery of the outside of a vacuum vessel, and a circular conductor plate provided to oppose a wafer stage within the vacuum vessel. In addition, an UHF band power supply and a first RF power supply are connected to the circular conductor plate, while a second RF power supply is connected to the wafer stage, so that an electric field of UHF band and anther electric field of frequencies different from the UHF band are applied superimposed upon each other to the circular conductor plate. Thus, plasma is generated by use of electron cyclotron resonance due to the mutual action between the electromagnetic waves from the UHF band power supply and the magnetic field from the air-core coil. The superimposed RF voltage from the first RF power supply increases the bias voltage to the circular conductor plate so that the circular conductor plate and the plasma can be reacted to more produce activated species that contribute to the etching, and the second RF power supply connected to the wafer stage controls the energy of ions within the plasma, incident to the sample.

Also, it is generally known that in a plasma with a static magnetic field applied, the impedance of the plasma perpendicular to the magnetic filed is larger than that parallel to the field as described in “DIFFUSION ACROSS A MAGNETIC FIELD 5.5” in “INTRODUCTION TO PLASMA PHYSICS AND CONTROLLED FUSION” written by F. F. Chen, and published by Plenum Press, PP. 169-172, 1974.

In the above plasma processing apparatus, since the electric path of the RF power supplied to the sample to be processed propagates to cross the magnetic field, the impedance of the plasma perpendicular to this magnetic field may act to form a potential distribution in the surface of the sample to be processed, which causes charging damage. In addition, the energy of ions incident to the sample to be processed is determined by the self-bias potential due to the biasing power fed to the sample to be processed, and there is the problem that the efficiency of the bias application is reduced since the rate of the earth area to the substrate electrode is decreased with the increase of the wafer size toward a large diameter.

Also, in the conventional apparatus, since the vacuum vessel is grounded, the plasma is spread within the vacuum vessel of ground potential, and diffused up to the outer peripheral region so that the plasma cannot be confined enough within the processing region of the vacuum vessel\'s inside. Therefore, in this apparatus, the inner wall of the vacuum vessel is sputtered, thereby increasing the amount of partial produced.

In recent years, as the integration degree of semiconductor integrated circuits has been increased, the thickness of, for example, the gate oxide film of MOS (Metal Oxide Semiconductor) as a typical example of the semiconductor device has been so decreased that the gate oxide film may cause dielectric breakdown (charging damage). Moreover, as the size of semiconductor devices has become very small, the mask selectivity as represented by SAC (Self Aligned Contact) about the processing precision has been requested to improve. Also, since the generation of particle or the like within the apparatus reduces the yield and the operation rate of the apparatus, the apparatus with less particle produced is demanded.

It is the first object of the invention to provide a plasma processing method and apparatus capable of suppressing the charging damage in the plasma processing.

It is the second object of the invention to provide a plasma processing method and apparatus capable of high-precision surface treatment.

It is the third object of the invention to provide a plasma processing method and apparatus capable of reducing the amount of particle produced.

It is the fourth object of the invention to provide a plasma processing method and apparatus capable of high throughput.

The first object can be achieved by providing an electrode opposite to a substrate electrode on which a sample is placed; supplying RF power for plasma generation to the opposite electrode; and supplying, to both the electrodes, other RF power having lower frequencies than the RF power for plasma generation and opposite phases.

The other RF power of opposite phases supplied to both the electrodes have a phase difference of 180°±45°.

The other RF power of opposite phases supplied to both the electrodes also have a phase difference of 180°±30°.

The other RF power supplied to both the electrodes have the same frequency of 5 MHz or below.