Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of coating supply or source outside of primary...
Reexamination Certificate
1999-02-23
2001-06-12
Bueker, Richard (Department: 1763)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of coating supply or source outside of primary...
C427S563000, C118S7230ER
Reexamination Certificate
active
06245396
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns CVD apparatus, and in particular CVD apparatus which use plasma and which are suitable for depositing films on large flat panel substrates.
2. Discussion of Related Art
The use of high temperature polysilicon type TFT (thin film transistors) and the use of low temperature polysilicon type TFT were known in the past as methods for the production of liquid crystal displays. A quartz substrate which can withstand high temperatures of 1,000 C or above is used for obtaining a high quality oxide film and oxide film interface with polysilicon in the method of production where high temperature polysilicon type TFT is used. On the other hand, a glass substrate as generally used for a TFT is used in the production of low temperature polysilicon type TFT liquid crystal display and so film deposition must be carried out in a low temperature environment, such as at 400 C. The production of liquid crystal displays using low temperature polysilicon type TFT has the advantages of not requiring the use of a special substrate and so this method has come into practical use in recent years and the amount of production continues to expand.
Plasma enhanced CVD is used in those cases where an appropriate silicon oxide film is deposited at a low temperature as a gate insulating film in the production of a liquid crystal display using low temperature polysilicon type TFT. Silane and tetraethoxysilane (referred to hereinafter as TEOS) are used as precursor gases when depositing silicon oxide films using plasma enhanced CVD.
When a silicon oxide film is deposited using plasma enhanced CVD with TEOS as the precursor gas, the precursor gas is delivered directly into the plasma which is formed in a conventional plasma processing apparatus. The precursor gas and oxygen react vigorously and the reaction product is formed in the gas phase. The reaction product forms dust particles which cause the formation of defects in the TFT elements. There is a problem in that the yield is reduced by the formation of dust particles. Moreover, there is also a problem in that the film properties are adversely affected by the implantation in the silicon oxide film of the high energy ions which are present in the plasma which is in contact with the substrate.
Plasma enhanced CVD apparatus in which a remote plasma system is used has been suggested in the past as a means of resolving the abovementioned problems. In a remote plasma system, the region in which the plasma is generated and active species such as radicals are formed is separated from the substrate in the plasma processing apparatus and the precursor gas is delivered close to the region in which the substrate is disposed. The radicals which are formed in the plasma region are diffused toward the region in which the substrate has been disposed and reach the space in front of the surface of the substrate which is being processed. The vigorous reaction between the plasma and the precursor gas is suppressed in a plasma processing apparatus of the remote plasma system and there is little dust particle formation, and there is a further advantage in that the implantation of ions into the substrate is also suppressed.
However, the plasma generating region and the region in which the substrate is disposed are formed separately with an intervening Joining space in a plasma processing apparatus of the remote plasma system. The radicals which are produced at a location remote from the substrate are delivered to the substrate by a diffusion process through the joining space. The rate of film deposition is reduced in a remote plasma system and there is a further problem in that the distribution in the vicinity of the substrate surface is poor. In particular, problems arise in that the system cannot be applied to the substrates which have a large surface area which are used for large liquid crystal displays because of the poor distribution in the vicinity of the substrate surface.
OBJECTS AND SUMMARY
An aim of this invention is to resolve the problems referred to above and to provide a CVD apparatus which can be used effectively for the deposition of films on substrates which have a large surface area while suppressing the formation of dust particles, preventing the implantation of ions into the substrate and providing a good plasma distribution in the vicinity of the substrate when depositing silicon oxide films using a precursor gas such as TEOS in CVD with large area substrates in the production of large liquid crystal displays in which low temperature polysilicon type TFT are used.
In order to realize the aforementioned aims, a CVD apparatus has a reactor in which plasma is generated, and active species (radicals) are formed and a film deposition process is carried out on a substrate with these active species and a precursor gas. The CVD apparatus has a partitioning plate in which a plurality of holes are formed. The partitioning plate divides the reactor into a plasma generating space and a film deposition process space. The precursor gas which is delivered to the reactor is passed through the plasma generating space and the partitioning plate and conducted and dispersed directly into the film deposition process space through a plurality of electrically conductive pathways. The active species which have been formed in the plasma generating space pass through the plurality of holes which are formed in the partitioning plate and are delivered into the film deposition process space. The precursor gas is delivered directly into the film deposition process space in front of the substrate, avoiding the region in which the plasma is being generated. By this means the occurrence of a vigorous chemical reaction between the precursor gas and the plasma is prevented and the formation of dust particles is suppressed.
The holes which are formed in the partitioning plate satisfy the condition that uL/D>1, where u is the flow rate of reaction gas (oxygen) in the holes, L is the characteristic length of the holes and D is the binary diffusivity (which is to say the binary diffusion constant of oxygen gas and the precursor gas). This condition is set so that if it is assumed that the reaction gas (oxygen gas) is passing through the holes by convection and the precursor gas is migrating to the other side by diffusion, the extent of the migration of the precursor gas by diffusion is suppressed.
The partitioning plate is connected to an RF power supply which provides RF power for cleaning purposes. Plasma for cleaning purposes is generated in the film deposition process space by supplying RF power to the partitioning plate at a suitable time.
A gas reservoir which is furnished with an equalizing plate is established on the entry port side of the plurality of pathways. The precursor gas which is being delivered into the film deposition process space is caused to diffuse and equalized out so that a film can be deposited on a substrate which has a large surface area.
Plasma is generated in the spaces between a discharge electrode and the partitioning plate and the top plate which form the plasma generating space by establishing the electrode at an intermediate position within the plasma generating space.
Plasma is generated between the discharge electrode and the partitioning plate by establishing the electrode in a position in the upper part of the plasma generating space.
A method of film deposition in a CVD apparatus involves carrying out film deposition on a substrate with a precursor gas and an active species which has been formed by a plasma. The reactor is divided into a plasma generating space and a film deposition process space by a partitioning plate in which a plurality of holes have been formed. The precursor gas which is delivered to the reactor is introduced directly into the film deposition process space. The active species which have been formed from the reaction gas in the plasma generating space pass through a plurality of holes which have been formed in the partitioning plate and are introduce
Anelva Corporation
Bueker Richard
Burns Doane , Swecker, Mathis LLP
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