Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Conveying or aligning particulate material
Patent
1998-10-07
2000-10-24
Ortiz, Angela
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Conveying or aligning particulate material
264483, 118723R, 425143, B29C 5914, B29C 5916, B29C 3302
Patent
active
061362565
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to dust particle agglomerates. In particular the present invention relates to controlled formation and destruction of such agglomerates as well as to applications of the agglomerates.
The accumulation of dust particles to form agglomerates or clusters, observed during the etching of silicon wafers, has proven to be a major problem in the commercial manufacture of silicon chips. The dust particles which are produced during the etching process usually form agglomerates of around micron size (e.g. 10 microns) which is of the same order as the thickness of the etching patterns. Larger agglomerates of between 100 and 1000 microns also have been observed. These dust particle agglomerates tend to fall into the etching patterns destroying the circuit being fabricated on the wafer and is a major cause of wastage in the industry. To date, only a poor theoretical and experimental understanding of how or why the agglomerates form has been developed.
Following work carried out by the inventors in the study of space plasmas it has been realised that this provides an insight to the forces involved in the formation of dust particle agglomerates and h as enabled methods for the controlled formation and destruction of such agglomerates to be developed. Hence, the present invention provides a method of and the conditions for controlled fabrication of dust particle agglomerates as well as a method of and the conditions for controlled destruction of such agglomerates. The present invention further identifies uses of dust particle agglomerates.
The present invention provides a method of controlling dust particle agglomeration in a plasma comprising adjusting the ratio of temperatures of first and second particle species within the plasma.
Preferably, the ratio of temperatures is adjusted by increasing or decreasing the temperature of the first of the particle species without substantially altering the temperature of the second of the particle species.
In a first embodiment of the invention the ratio of neutral gas particle temperature with respect to dust particle temperature is adjusted. The neutral gas particle temperature may be adjusted by heating or cooling the neutral gas supplied to the plasma. Alternatively, the dust particle temperature is adjusted by heating or cooling the source of the dust particles.
Additionally, movement of dust particle agglomerates formed within the plasma may be controlled preferably by the application of external electric and magnetic fields which are preferably substantially orthogonal.
In a second embodiment dust particle agglomeration is reduced by reducing the ratio of the plasma electron temperature to the plasma ion temperature. Preferably, the ratio is reduced by increasing the plasma ion temperature and ideally the plasma ion temperature is increased so that it is substantially equal to the plasma electron temperature.
The plasma ion temperature may be increased by passing one or more stock waves through the plasma by means of a high pressure gas discharge, a pulsed electron beam or RF injection.
In a further aspect the present invention provides apparatus for controlling formation of dust particle agglomerates in a plasma comprising a plasma containment vessel, plasma generation means including one or more electrodes and temperature control means for controlling the ratio of temperatures of first and second particle species within the plasma.
Preferably, the temperature control means comprises a heat exchanger device which may be in thermal contact with a supply of neutral gas to the plasma containment vessel or may be in thermal contact with the source of dust particles.
Alternatively, the temperature control means may include heat radiative material located within the plasma containment vessel. Separately, the temperature control means may comprise a shock wave generator, means for directing the shock wave through the plasma and valve means for controlling the period of the shock waves through the plasma. Preferably, the shock wave generator is arranged
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patent: 4246208 (1981-01-01), Dundas
patent: 5350454 (1994-09-01), Ohkawa
patent: 5769953 (1998-06-01), Yoshikawa et al.
Dusty Plasmas--'95 Workshop On Generation, Transport, And Removal of Particles in Plasmas, Wickenburg, AZ, USA, Oct. 1-7, 1995, vol. 14, No. 2, ISSN 0734-2101, Journal of Vacuum Science & Technology A (Vacuum, Surfaces, And Films), Mar.-Apr. 1986, AIP For American Vacuum Soc, USA, pp. 644-648, XP002029779 Brattli A et al., "Cooling by dust in levitation experiments and its effect on dust cloud equilibrium profiles" see the whole document.
XP 2029779--Cooling by dust in;levitation experiments and its effect on dust cloud equilibrium pofiles; A Bratti and O. Havnes; Auroral Observatory, University of Tromsb, N-9037 Tromsb, Norway; J. Cac. Scl. Technol. A 14(2), Mar./Apr. 1996; 0734-2101/96/14(2)/644/5/$10.00; .COPYRGT.1996 American vacuum Society.
Bingham Robert
Tsytovich Vadim N.
Council for the Central Laboratory of the Research Councils
Ortiz Angela
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