Method and apparatus to produce large inductive plasma for...

Coating apparatus – Gas or vapor deposition – With treating means

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

C118S733000, C156S345420

Reexamination Certificate

active

06321681

ABSTRACT:

The present invention relates generally to apparatus and their use for surface treatments using plasma assisted processing and more particularly, but not exclusively, for the treatment of large flat substrates.
Such treatments can include etching, deposition, cleaning, passivation and ion implantation.
The new requirements for the plasma processing of large substrates become more and more critical for plasma sources available on the market. The success of the plasma assisted processing depends on the scalability of these plasma sources.
To fulfil these requirements, new plasma sources must be envisaged to process large substrates with plasma features like the generation of high densities of reactive species with low and controllable energy over a wide pressure range, and with an excellent homogeneity throughout the substrate.
Plasma processing generally uses a vacuum chamber connected to a gas inlet and a pumping device for controlling the gas flows and pressure. Electrical energy is applied to the vacuum chamber to accelerate the free electrons in the gases to the energy of ionization of the gas molecules, which thereby creates plasma. Ionization phenomena free some electrons which can also be accelerated to the ionization energy.
The added energy of the free electrons in the gas is generally accomplished by an electric field, a varying magnetic field, or both.
One traditional method used in plasma processing to generate plasma is by a technique known as called Capacitively Coupled Plasma. The plasma results from the application of an AC voltage between two electrodes creating an electric field which accelerate the free electrons. Generally, one of the two electrodes is the substrate holder. The applied energy generated by the AC voltage applied between the two electrodes controls at the same time the flux and kinetic energy of the ions. Because the two parameters are coupled, this process is difficult to optimise.
Another plasma source used in plasma processing is based on the Electron Cyclotron Resonance (ECR). In this process, microwave power is applied to the gas together with a constant magnetic field which transforms the electron paths into a circular path. The intensity of the magnetic field is such that the frequency of gyration of the electron is the same as the frequency of the electric field, which leads to a resonance effect increasing the efficiency of electron acceleration. This type of excitation mode can provide a plasma with high ion flux and low ion energy. The ion energy can be controlled by applying an independent bias to the substrate. However, such an apparatus is complex and expensive. Moreover, it is still too limited as regards the plasma expected processing expected features, in particular for scaling up and homogeneity of the plasma source.
A new generation of plasma source has been developed during the last years which give good promise. These are known as Inductively Coupled Plasmas (ICPs), such as described e.g. in U.S. Pat. Nos. 4,948,458 and 5,277,751. The plasma is created by a varying magnetic field generated by a spiral planar coil. The electrons are accelerated in a circular path parallel to the coil plane and the insulating window of the plasma chamber. This configuration provides a high density plasma with low kinetic energy, but has an inherent problem of homogeneity at the center and at the boundary of the coil when the size of the apparatus is increased. This problem limits the scability of the process.
U.S. Pat. No. 5,435,881 presents an apparatus for generating a suitably low pressure planar plasma. This apparatus comprises a two-by-two or a larger array of alternating magnetic poles (multipoles). The advantages cited in this patent are the possibility to generate a large plasma by adding more varying magnetic poles, therefore having very small area on non uniform plasma.
However, such a design creates a dependency between the spacing of the two-by-two magnetic poles and the excitation frequency as well as the in-use operation pressure. This spacing depends on the mean free path of the electrons which decreases when the pressure increases. Accordingly, when a high operating pressure is necessary for process requirements, the spacing between the two-by-two poles must be drastically decreased. This becomes critical from a technical point of view. The process also requires different multipole distributions for different process pressures, which decreases its flexibility and applicability to industrial applications.
It is therefore an object of the present invention to provide means to enable optimum plasma conditions to be obtained in a reliable manner, even when workpieces of large dimensions need to be processed.
According to a first aspect of the invention, there is provided an apparatus adapted for generating a time-varying magnetic field through a field admission window of plasma processing chamber to create or sustain a plasma within the chamber by inductive coupling, the apparatus being characterized in that it comprises:
a magnetic core presenting a unipolar pole face structure adapted to be applied against or in proximity to the window and having an active field emission area whose size and shape substantially matches the field emission window, and
an inductor means associated with the magnetic core, for generating a substantially uniformly distributed time-varying magnetic field throughout the unipolar pole face structure.
The combination of a magnetic core with the inductor serves to increase and homogenize the magnetic field produced by the inductor, the magnetic flux lines being uniformly distributed over the pole face structure. This effect is particularly pronounced given that a typical core material that can be used in accordance with the invention would possess a very high permeability (&mgr;) e.g. in the region of 1000 or more. Such a material can be soft iron, an iron alloy or a ferrogmagnetic material. The latter can be in the form of a ceramic such as ferrite, or any other material. Irrespective of the material chosen, the core can be produced by a sintering process where appropriate.
The combination of the magnetic core and unipolar pole face structure ensures that the magnetic field does not have a “dead area” at the center of the inductor, as is usually the case with magnetic field energy sources based on just an inductor having a spiral path formed parallel to the plane of the chamber window.
As a result, the apparatus according to the first aspect of the present invention makes it possible to employ plasma processing chambers having large window areas and thereby to process correspondingly large workpieces under homogeneous plasma conditions throughout the active area. For instance, the present invention can be used for processing substrates of flat panel displays such as LCDs having dimensions of around 0.5 m square or more.
The magnetic core can easily be matched to the shape and dimensions of the window; it can present e.g. a circular, rectangular or polygonal unipolar pole face as required.
The window(s) of the processing chamber need not necessarily be flat, but may be curved, e.g. to follow the contour of a wall portion from which it/they depend(s). The magnetic core can likewise present a unipolar pole face structure configured to follow the curvature of the window(s) to provide uniform conditions inside the chamber.
Preferably, the unipolar face structure is constituted by a single pole face of unitary construction. In this way, the window of the plasma processing chamber is confronted with a substantially continuous surface, which further contributes to enhance uniformity.
It is nevertheless envisageable to divide the unipolar pole face structure into two or more unipolar pole faces that confront respective portions of the plasma processing chamber window. This alternative solution may be considered if the window area to be covered is particularly large. The pole faces may then be associated to respective inductors and power supplies whilst being kept in phase to ensure that all the pole faces have th

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Method and apparatus to produce large inductive plasma for... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method and apparatus to produce large inductive plasma for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus to produce large inductive plasma for... will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-2591565

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.