Electric heating – Metal heating – By arc
Reexamination Certificate
1999-04-27
2001-11-20
Jeffery, John A. (Department: 3742)
Electric heating
Metal heating
By arc
C118S7230IR, C438S715000
Reexamination Certificate
active
06320154
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a plasma processing method for performing a plasma process upon an object to be processed, such as a semiconductor wafer.
BACKGROUND OF THE INVENTION
During the fabrication of a semiconductor device, a plasma is often used to subject a semiconductor wafer (hereinafter called a wafer) to a process such as film-formation or etching. This processing is performed by introducing a processing gas into a vacuum vessel which is provided with a mounting stand for a wafer, then supplying energy such as electromagnetic energy to that processing gas to create a plasma therefrom. Various methods are known as methods of supplying this electromagnetic energy, such as electron cyclotron resonance (ECR), which makes use of the interaction between microwaves and a magnetic field, and a method known as inductive coupled plasma (ICP) in which an electric field and a magnetic field from a coil surrounding a dome-shaped vessel are applied to a processing gas.
A high-density plasma is established in a zone corresponding to the wafer, but a thin plasma is also present throughout the entire interior of the vacuum vessel. This deteriorates an O-ring that acts as a sealing material and also causes peeling of a film that has adhered to the walls of the vessel due the reactions of the processing gas. It is therefore not possible to avoid the generation of particles within the vacuum vessel. Particularly with plasma processing, the speed of movement of electrons within the plasma is greater than that of ions, so a large number of electrons adhere to surfaces such as the walls and internal members of the vessel, as well as the wafer, and are negatively charged. Thus the potential gradient in the vicinity of these surfaces destroys the neutral characteristics of the plasma in the vicinity of the surfaces, without allowing the electrons to approach, thus forming a zone called a sheath of a thickness of a few mm.
Since the particles are negatively charged, they cannot pass through the sheath zone and are pushed back towards the plasma. As seen from a certain point in time, it occurs that these particles appear to be trapped at the boundary between the plasma and the sheath zone. However, when the microwave power and wafer biasing power are cut, the particles trapped at positions floating above the wafer will tend to adhere to the wafer. There is therefore a demand for a method of suppressing the generation of these particles as far as possible, especially since circuitry patterns will continue to become finer in the future.
The present invention was devised in the light of the above problems with the conventional art and has as an objective thereof the provision of a plasma processing method that is capable of suppressing the creation of particles, thus increasing the yield.
SUMMARY OF THE INVENTION
In order to achieve the above described objective, an aspect of the present invention disclosed in a first claim herein relates to a plasma processing method comprising the steps of:
supplying at least electrical power to a processing gas within a processing chamber to form a plasma, and using that plasma to perform a plasma process on an object to be processed;
subsequently forming a plasma that does not promote processing at an electrical power that is lower than that used during the previous step, instead of the plasma of the processing gas, to form a sheath zone above the object to be processed that is thicker than a sheath zone thereabove during the previous step; and
conveying the object to be processed out of the processing chamber.
In another aspect of this invention disclosed in a second claim herein, the plasma processing method comprising the steps of
placing an object to be processed on a mounting stand that is provided within a processing chamber and includes an electrode, supplying at least electrical power to a processing gas to form a plasma, applying biasing power to the electrode, and using that plasma to perform a plasma process on the object to be processed while ions within the plasma are drawn towards the object to be processed;
subsequently forming a plasma that does not promote processing instead of the plasma of the processing gas, and increasing the biasing power to higher than that used during the previous step, to form a sheath zone above the object to be processed that is thicker than a sheath zone thereabove during the previous step; and
conveying the object to be processed out of the processing chamber.
In a further aspect of this invention disclosed in a third claim herein, the plasma processing method comprising the steps of:
forming a magnetic field by a magnetic field formation means in such a manner that magnetic lines of force thereof run from a zone corresponding to a surface to be processed of an object to be processed towards the object to be processed, and also forming a plasma from a processing gas that is supplied into a processing chamber, based on the interaction between an electrical field and the magnetic field, and using that plasma to perform a plasma process on the object to be processed;
subsequently forming a plasma that does not promote processing instead of the plasma of the processing gas, and adjusting the magnetic field in such a manner that the magnetic lines of force thereof in the vicinity of the object to be processed fan out further than during the previous step; and
conveying the object to be processed out of the processing chamber.
A still further aspect of this invention disclosed in a fourth claim herein relates to the method of the third claim, wherein: the magnetic field formation means is disposed so as to surround a central axis of the object to be processed and comprises a first coil provided above the object to be processed and a second coil provided either beside or below the object to be processed; and
the step of adjusting the magnetic field is done by either reducing a current flowing through the second coil to less than that during the plasma processing (including a reduction to zero) or reversing the current.
In a yet further aspect of this invention disclosed in a fifth claim herein, the plasma processing method comprising the steps of:
attracting an object to be processed by electrostatic attraction to a mounting stand that is provided within a processing chamber and includes an electrostatic chuck, and also supplying electrical power to a processing gas within a processing chamber to form a plasma, then using the plasma to perform a plasma process on the object to be processed;
subsequently separating the object to be processed from the mounting stand and applying a negative voltage to a chuck electrode of the electrostatic chuck; and
placing another object to be processed on the mounting stand and performing plasma processing thereon.
In an even further aspect of this invention disclosed in a sixth claim herein, the plasma processing method comprises: a step of supplying a processing gas into a processing chamber and forming a film on an object to be processed;
performing a first cleaning step for cleaning the interior of the processing chamber with a plasma of a halogenized gas; and
performing a second cleaning step for cleaning the interior of the processing chamber with a plasma including at least an oxygen plasma.
In a final aspect of this invention disclosed in a seventh claim herein, the plasma processing method comprising the steps of:
forming a magnetic field by a magnetic field formation means in such a manner that magnetic lines of force thereof run from a zone corresponding to a surface to be processed of an object to be processed towards the object to be processed, and also forming a plasma from a processing gas that is supplied into a processing chamber, based on the interaction between an electrical field and the magnetic field, and using the plasma to form a film on the object to be processed; and
performing a cleaning step for cleaning the interior of the processing chamber with a plasma of a cleaning gas;
wherein the magnetic field is adjusted during the cleanin
Akahori Takashi
Nakase Risa
Oka Shinsuke
Jeffery John A.
Smith , Gambrell & Russell, LLP
Tokyo Electron Limited
Van Quang
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