Coating processes – Direct application of electrical – magnetic – wave – or... – Chemical vapor deposition
Patent
1994-08-01
1996-02-20
Pianalto, Bernard
Coating processes
Direct application of electrical, magnetic, wave, or...
Chemical vapor deposition
118500, 118663, 118723R, 4272481, 427569, C23C 1426
Patent
active
054927374
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus and methods relating to the deposition of films on workpieces and in particular to the stress set up in those films during the deposition process.
The need to deposit thin layers of material particularly arises in the manufacture of semi-conductor devices, but this invention is not limited to the manufacture of such devices. However, in that field it is generally recognised that it is desirable to attempt to control the stress set up in the film during deposition, because if not controlled the stresses can be sufficient to lift the film from the surface of the workpiece. It has been known for a long time that such stresses can be controlled, to a degree, by altering process parameters such as pressure temperature gas flow rates etc. However variations in these parameters generally cause variations in other physical characteristics of the film and so the user of this approach generally settles on a compromise.
In plasma chemical vapour deposition processes it is known that the stress can be controlled by altering the frequency of the AC field which maintains the plasma discharge. However the frequency range in which stress is a minimum is also the band used for aircraft communication and so this technique is prohibited. Other proposals have been made for either switching between high and low frequency or providing a mix of frequencies but these too have their problems.
According to the present invention there is provided reactor apparatus comprising a chamber, means for forming a plasma within the chamber, an electrode for supporting the workpiece, means for allowing gas to be introduced into the chamber such that a film can be deposited on the workpiece, means for connecting the electrode to ground and including adjustable means for varying the effective resistance of the connection between the electrode and ground.
For the purposes of this specification the term "effective resistance" refers to the ease or otherwise with which a voltage on the electrode can drain to ground. It thus includes not only traditional resistance but also other means for affecting the current flow through the connection to ground.
Thus the adjustable means may include a variable resistance, or, alternatively, it may include means for adjusting the current flow through the connecting means and/or the voltage dropped across the connecting means. In this latter case the adjustable means may include a transistor connected to control the rate of voltage drain from the electrode to ground and means for adjustably controlling the transistor. The means for adjustably controlling the transistor may comprise means, such as an operational amplifier, for comparing the voltage on the electrode, or an indication thereof, with a preset voltage, or an indication thereof, and means for controlling the transistor to equate the electrode and preset voltages or indications thereof.
From another aspect the invention consists in apparatus for controlling the stress in a film deposited on an electrode comprising a reactor chamber, means for striking a plasma in the chamber, an electrode for supporting the workpiece in the chamber and means for varying the magnitude of the negative sheath associated with the electrode in the presence of the plasma to alter the film stress.
From a still further aspect the invention consists in a method of controlling the stress in a film deposited on a workpiece comprising, placing the workpiece on an electrode in a reactor chamber, introducing a gas into the chamber, connecting the workpiece electrode to ground via a variable effective resistance means and selecting the resistance of the variable effective resistance means in accordance with the desired stress characteristics.
Although the invention has been defined above it is to be understood that it includes any inventive combination of the features set out above or in the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be performed in various ways and a specific embodiment will now be described, by wa
REFERENCES:
patent: 4543576 (1985-09-01), Hieber et al.
Beekmann Knut
Dobson Christopher
Kiermasz Adrian
Ling Edmond
Shearer Christine
Electrotech Equipments Limited
Pianalto Bernard
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