Electricity: electrical systems and devices – Electric charge generating or conducting means – Use of forces of electric charge or field
Reexamination Certificate
1998-09-10
2001-07-03
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Electric charge generating or conducting means
Use of forces of electric charge or field
C279S128000
Reexamination Certificate
active
06256186
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electrostatic chucks for clamping semi-conductor wafers and processing apparatus and methods utilising such chucks.
2. Description of the Related Art
In the micro-fabrication of semi-conductor, micro-mechanical, optical and other devices on or from semi-conductor wafers, it is common to pattern the upper layer of or on a semi-conductor wafer by depositing a photo-sensitive coating, defining the pattern using a lithographic process and developing the resultant pattern.
The developed photo-sensitive coating then forms a mask which can either be used to protect certain areas of the wafer from a subsequent etch process or the coating can be utilised as part of a “lift off” process where a subsequent layer is deposited over the patterned material and removal of the patterned material, lifts off the subsequent layer except where there were exposed areas defined by the pattern.
For many such processes the gases or vapours that are used at low pressure have a tendency to condense or otherwise adhere to surfaces which are cooler than the gas or vapour. This is a particular problem where the platen on which the wafer is located in the processing apparatus is cooled, because the build up of such material can effect the intimate contact between the wafer and the platen.
It will be understood that as wafers are exchanged during the production process, there is inevitably a period when the upper surface of the platen is exposed and hence by-products can build up on it. If the platen is constituted by an electrostatic clamp or chuck, this can be particularly problematic because the clamping becomes unreliable resulting in poor wafer cooling and other deleterious results.
Current approaches to this problem include allowing the chuck to warm up to gas ambient temperature, the chamber being pumped out to a high vacuum or an etch process being carried out while the wafer is absent from the chamber. Whilst this latter option is effective, it also etches away the very thin dielectric layers, which exist on prior art chucks, rapidly causing a break-down of the dielectric layer and hence of the clamping. The other options tend to slow down the production cycle and/or increase the cost of the apparatus.
In existing designs the dielectric layers are kept extremely thin, e.g. 4 &mgr;m-200 &mgr;m, so that low voltages can be used on the chuck and thus avoid high voltages appearing on the wafer. These dielectric layers are frequently defective due to pin holes and other faults, which cause failure of the electrostatic chucks.
BRIEF SUMMARY OF THE INVENTION
From one aspect the invention consists in an electrostatic chuck for clamping a semi-conductor wafer during processing, including a platen on which the wafer is received, the wafer receiving surface of the platen having a dielectric coating characterised in that the dielectric layer is between 0.5 and 1.5 mm thick.
The Applicants have determined, contrary to the industry's understanding and expectation, that dielectric layers of this thickness can be used with significantly increased voltages. Thus the voltage range may be between 2½ thousand and 7½ thousand volts and where, for example, the layer is approximately 1 mm thick, the clamping voltage maybe 5 thousand volts. The apparatus may include supply means for charging the platen to these voltages, in which case the voltage means may charge the chuck positively or negatively. Each wafer being clamped with alternatively positive and negative voltage to avoid build up of charge on the chuck.
From another aspect the invention consists in semi-conductor wafer processing apparatus comprising a plasma etching reactor, an electrostatic chuck as defined above and control means for processing, e.g. etching, a wafer when it is on the platen and for etching when no wafer is present.
The apparatus may further comprise heating means to maintain the walls of the chamber above ambient temperature and thus reduce the likelihood of deposition on those walls, whilst the platen may additionally or alternatively have means for cooling it below the ambient temperature of the chamber. Thus for example the chamber walls may be heated to approximately 50° C. where as the wafer may be cooled to approximately 10° C.
The apparatus may further include means for supplying oxygen and sulphur containing gases for the etch process when the wafer is present and means to supply oxygen and fluorine containing gases for processing the wafer and means to supply oxygen and fluorine containing gases for the etch process when the wafer is not present.
From a still further aspect the invention may consist in a method of processing semi-conductor wafers comprising clamping a wafer on an electrostatic chuck as defined above, maintaining the platen below ambient chamber temperature, processing (e.g. etching) an organic layer on the wafer using oxygen and sulphur containing gases, removing the wafer and whilst the wafer is not there using oxygen and fluorine containing gases to etch reaction by-products from the platen.
The chamber walls may be heated to above ambient temperature.
Although the invention has been defined above it is to be understood it includes any inventive combination of the features set out above or in the following description.
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Iacopi Alan Victor
Powell Kevin
Puttock Mark Stephen
Tossell David Andrew
Jones Volentine, L.L.C.
Sherry Michael J.
Trikon Equipments Limited
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