Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2000-04-04
2002-10-15
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S7230IR, C118S7230AN, C204S298010, C204S298160
Reexamination Certificate
active
06463873
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and apparatus for the production of high density plasmas.
2. Description of Related Art
A variety of different processes are operated in a plasma environment including thin film coating, for example sputtering, evaporation, chemical vapour disposition, cleaning and etching processes.
For example, it has been known for many years that thin film deposition processes and the properties of the deposited films themselves can be Improved by allowing energetic ions to impinge on the growing surface of the film being deposited; this is due to an energy transfer between the energetic ions and the so-called “adatoms” of the thin film being deposited. This increases the surface mobility of the adatoms and allows them to migrate more readily to the preferred lattice sites.
Sputtering processes are widely used for the deposition of thin coatings or films of materials on to substrates. Such processes take place in an evacuated chamber containing a small quantity of an ionisable gas, for example argon. Electrons emitted from a source held within the chamber ionise the gas to form a plasma; a (cathode) target comprising the material to be sputtered is bombarded by the ions causing atoms of the target material to be dislodged and subsequently deposited on to the substrate being coated.
It is also well known that the rate of deposition in sputtering process may be increased by the use of magnetic means, for example an array of permanent magnets positioned in a predetermined manner (commonly as a closed loop) associated with the cathode target to create in use a plasma which is localised and concentrated along a sputtering zone of the target and thereby defined the area or region from which sputtering, or erosion of the target occurs.
In vapour deposition processes, especially plasma enhanced chemical vapour deposition (PECVD), a chemical gad contained within a vacuum chamber is dissociated and activated by the plasma at a rate generally proportional to the density of the plasma.
In plasma etching or cleaning processes, energetic ions and/or chemically active ions and/or chemically active ions produced by a plasma present in a vacuum chamber are employed to remove material from a substrate, for example in the production of semi conductor integrated circuits.
In all such processes, an important parameter is the ability to produce high density plasmas at the lowest possible power consumption. Benefits of high density plasmas include the production of higher grade coatings in general, commonly allow for a greater homogeneity in the coating microstructure,
It has previously been proposed to produce high density plasmas by means of electron cyclotron resonance (ECR) by use of microwaves at a specific frequency of 2.45 GHz and a magnetic field of 875 Gauss in vacuum. Although this produces a useful high density plasma, the size of the required magnetic field is such that it consumes high power levels and is therefore expensive.
A more recent proposal for the production of high density plasmas is the use of high density plasma waves. These can be produced in a chamber at high vacuum, for example 10
−2
to 10
−4
mbar, by interaction between a uniform magnetic field and an electric field profile of an external antenna operating at a radio frequency (RF). Wave energy from the antenna emissions is transferred to the electrons produced in a plasma discharge, for example argon, present in the chamber by the well known mechanism known as Landau damping; with these waves, energy exchange is thought to occur in a much more efficient manner than with other types of discharge. This effect can generally be regarded as a collisionless damping of waves in a plasma due to particles in the plasma which possesses a velocity almost equal to the phase velocity of the wave. Such particles tend to travel with the wave without “seeing” a rapidly fluctuating electric field and can therefore exchange energy with the wave. A plasma containing electrons some of which are faster and some of which are slower than the wave itself. However, in a Maxwellian distribution, there are more slower electrons than faster ones and therefore there are more particles receiving energy from the plasma wave than those Imparting energy to the wave.
The 13.56 MHz frequency discharge is the most widely used to produce high density plasma waves, although related frequencies of 6.78 MHz and 27.12 MHz could also be employed.
High density plasma wave induced plasma generation can usefully be performed in a chamber in which, or about which, field coils are present to effect a uniform magnetic field (commonly cylindrical) in a pre-determined area of the chamber. Three such field coils in a linear array spaced along the length of the relevant past of the chamber are generally sufficient. At one end of the array is positioned the RF antenna to cause, in use of the process, the intense plasma wave produced by interaction between the magnetic field and the RF power supply, which in turn accelerates plasma electrons by the Landau damping mechanism.
The design of the RF antenna required to produce helicon waves and the subsequent generation of a high density plasma is important. The design has been the subject of considerable discussion in original papers by Boswell and subsequently by Chen and thereafter by various other authors.
Previous designs have centred on complex configurations in which the various operating modes are embodied to provide in particular, a double loop system made from a continuous length of conductive material in which:
a first loop having a main axis which is orientated parallel to the direction of the magnetic field present in the chamber;
a second loop also having a main axis which is orientated parallel to the direction of the magnetic field present in the chamber; and
an electrical cross linkage between the first and second loops of varying design.
Although it has been shown that the use of helicon wave systems can produce high density plasmas to good effect, the complexity of the RF antenna and their spatial configuration with the magnetic array required to Interact with the RF power can provide difficulties in the implementation of helicon wave production of helicon wave plasmas.
BRIEF SUMMARY OF THE INVENTION
The invention is concerned with the provision of high density plasma systems embodying an antenna of simpler, easier to use design and having further benefits as described below.
In accordance with the invention, there is provided a high density plasma forming device having a housing comprising an ionisable gas, a process chamber, a target mounted within the process chamber, at least one source chamber completely open at one end to the process chamber, a radio frequency antenna for the formation of a plasma and a magnetic means by which the plasma may be directed and focused onto the target, wherein the antenna is a helical coil associated with the source chamber such that plasma formed within the source chamber is directed into the process chamber and focused onto the target mounted therein.
In accordance with a further aspect of the invention there is provided a process for forming a high density plasma comprising the steps of:
(i) supplying a helical coil radio frequency antenna with a discharge power supply, and
(ii) inducing the ionisation of an ionisable gas within the source chamber completely open at one end to a process chamber to form a plasma, and
(iii) the direction and focusing of the plasma within a process chamber by magnetic means. The invention also provides a process for forming a high density plasma utilising the apparatus of the invention as described above,
It has surprisingly been found that the use of a helically wound coil antenna, as opposed to the complex antennae used previously, can be used to good effect and to provide additional technical benefits leading to a factor of three enhancement in the plasma ion density. The helically wound coil antenna in the invention generally comprises an electrica
Hassanzadeh P.
Mills Gregory
Nixon & Vanderhye P.C.
Plasma Quest Limited
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