Electric heating – Metal heating – By arc
Patent
1990-02-20
1992-11-03
Paschall, Mark H.
Electric heating
Metal heating
By arc
21912136, 156345, 373 18, B23K 900
Patent
active
051608251
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process and device for supplying processing gas to a reactor located in a zone subjected to intense electric and/or electromagnetic fields likely to cause ionization of said gas.
It applies more particularly, but not exclusively, to supplying a processing device with processing gas by ionic bombardment, for example an ionic implanter of the type used in the semiconductor industry for incorporating ionized chemical species on silicon substrates for doping thereof.
In this example, the generation, acceleration and focussing of the ions bring into play considerable electric fields, requiring voltage sources of several tens of kilovolts.
This is why, for safety reasons, the reactor (or ionization chamber) in which the processing takes place is isolated, as well as the elements brought to said voltages situated in its environment, in a conducting enclosure serving as electric and/or electromagnetic screen which forms a potential barrier between its inner volume and its outer environment.
Because of the intensity of the intense electric fields present inside the enclosure, it is impossible during processing to admit the processing gases into the ionization chamber from gas sources situated outside the enclosure, particularly because of: (even in the case where these pipelines are sufficiently isolated with respect to the enclosure, these pipelines would be brought to high potentials and would form electric conducting bridges between the inner volume of the enclosure and its outer environment, pipelines, because such gases would be ionized and would become conducting.
Considering these problems, the present solution consists in using processing gas reserves of small capacity (0.6 l in general) placed in a ventilated metal box, itself disposed inside the conducting enclosure and brought to the same potential as that of a high voltage source which supplies the reactor.
This solution has however several major drawbacks: opening the conducting enclosure after interrupting the high voltage supply and after making sure that no residual electric charges remain inside the enclosure, these operations only being able to be carried out during a prolonged shut-down of the reactor; panel associated with the gas sources and its position inside the enclosure, and enclosure during handling, such equipment being furthermore very expensive.
OBJECT AND SUMMARY OF THE INVENTION
The invention has then particularly as object to overcome all these drawbacks.
It proposes generally a process for supplying, with processing gas, a reactor operating by means of a high voltage current and situated in a zone subjected to intense electric and/or electromagnetic fields likely to cause ionization of said gas, said zone being insulated electrically from its outer environment by at least one electrically conducting wall forming a potential barrier.
According to the invention, this process is more particularly characterized in that it consists in supplying said reactor with gas by means of at least one intermediate capacity filled periodically from a gas source situated outside said zone, during interruptions of the high voltage current, by means of at least one pipeline passing through the wall, this pipeline being made from an electrically insulating material at least on its portion passing through said wall.
Furthermore, each phase of filling the intermediate capacity will be followed by closure of said pipeline in a portion situated in said zone, and evacuation of said gas at least in a portion of said pipeline passing through said wall.
Advantageously, such removal will be carried out by scavenging said portion with a gas which is not ionizable by said fields.
Considering the complete electric insulation provided by the electrically insulating material portion of the pipeline and because of said evacuation of the processing gas, at least in this portion, the intermediate capacity may be advantageously brought to a high voltage, like the gas reserves used previously.
BRIEF DESCRIPTION
REFERENCES:
patent: 4659899 (1987-04-01), Welkie et al.
Nuclear Instruments and Methods in Physics Research, vol. B6, No. 1/2, 1-1985 Elsevie Science Publishers Division.
Drucker William A.
Eferel S.A.
Paschall Mark H.
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