EP0833705A1 - Fabrication sur site d'acide fluorhydrique ultra-pur destine au traitement des semi-conducteurs - Google Patents

Fabrication sur site d'acide fluorhydrique ultra-pur destine au traitement des semi-conducteurs

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Publication number
EP0833705A1
EP0833705A1 EP96919223A EP96919223A EP0833705A1 EP 0833705 A1 EP0833705 A1 EP 0833705A1 EP 96919223 A EP96919223 A EP 96919223A EP 96919223 A EP96919223 A EP 96919223A EP 0833705 A1 EP0833705 A1 EP 0833705A1
Authority
EP
European Patent Office
Prior art keywords
vapor
gas
purity
purifier
flow
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP96919223A
Other languages
German (de)
English (en)
Other versions
EP0833705A4 (fr
Inventor
Joe G. Hoffman
R. Scot Clark
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Air Liquide America Corp
Original Assignee
Startec Ventures Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from PCT/US1995/007649 external-priority patent/WO1996039358A1/fr
Application filed by Startec Ventures Inc filed Critical Startec Ventures Inc
Priority claimed from PCT/US1996/009554 external-priority patent/WO1996041687A1/fr
Publication of EP0833705A1 publication Critical patent/EP0833705A1/fr
Publication of EP0833705A4 publication Critical patent/EP0833705A4/fr
Withdrawn legal-status Critical Current

Links

Definitions

  • the present invention relates to semiconductor manufacture, and particularly to systems and methods for supplying ultra-high-purity HF and hydrofluoric acid for semiconductor manufacture.
  • Contamination is generally an overwhelmingly important concern in integrated circuit manufacturing.
  • cleanup steps of one kind or another such cleanup steps may need to remove organic con- taminants, metallic contaminants, photoresist (or inorganic residues thereof), byproducts of etching, native oxides, etc.
  • Plasma etching has many attractive capabilities, but it is not adequate for cleanup. There is simply no available chemistry to remove some of the most undesirable impurities, such as gold. Thus wet cleanup processes are essential to modern semiconductor processing, and are likely to remain so for the foreseeable future.
  • Plasma etching is performed with photoresist in place, and is not directly followed by high-temperature steps. Instead the resist is stripped, and a cleanup is then necessary.
  • the materials which the cleanup must remove may include: photoresist residues (organic polymers); sodium; Alkaline earths (e.g. calcium or magnesium); and heavy metals (e.g. gold). Many of these do not form volatile halides, so plasma etching cannot carry them away. Cleanups using wet chemistries are required.
  • Integrated circuit structures use only a few dopant species (boron, arsenic, phosphorus, and sometimes antimony) to form the required p-type and n-type doped regions.
  • dopant species boron, arsenic, phosphorus, and sometimes antimony
  • many other species are electrically active dopants, and are highly undesirable contaminants. Many of these contaminants can have deleterious effects, such as increased junction leakage, at concentrations well below 10 13 cm "3 .
  • some of the less desirable contaminants segregate into silicon, i.e. where silicon is in contact with an aqueous solution the equilibrium concentration of the contaminants will be higher in the silicon than in the solution.
  • all liquid solutions which will be used on a semiconductor wafer should preferably have extremely low levels of all metal ions.
  • concentration of all metals combined should be less than 300 ppt (parts per trillion), and less than 10 ppt for any one metal, and less would be better.
  • contamination by both anions and cations must also be controlled. (Some anions may have adverse effects, e.g. complexed metal ions may reduce to mobile metal atoms or ions in the silicon lattice.)
  • Front end facilities normally include on-site purification systems for preparation of high-purity water (referred to as "DI" water, i.e. deionized water).
  • DI high-purity water
  • process chemicals in the purities needed.
  • the present inventors have developed a method for preparing ultra-high-purity ammonia, in an on-site system located at the semiconductor wafer production site, by: drawing ammonia vapor from a liquid ammonia reservoir, passing the ammonia vapor through a microfiltration filter, and scrubbing the filtered vapor with high-pH purified water (preferably deionized water which has been allowed to equilibrate with the ammonia stream).
  • high-pH purified water preferably deionized water which has been allowed to equilibrate with the ammonia stream.
  • the drawing of the ammonia vapor from the supply reservoir serves by itself as a single-stage distillation, eliminating nonvolatile and high-boiling impurities, such as alkali and alkaline earth metal oxides, carbonates and hydrides, transition metal halides and hydrides, and high-boiling hydrocarbons and halocarbons.
  • the reactive volatile impurities that could be found in commercial grade ammonia, such as certain transition metal halides.
  • Group HI metal hydrides and halides, certain Group IV hydrides and halides. and halogens, previously thought to require distillation for removal, were discovered to be capable of removal by scrubbing to a degree which is adequate for high-precision operations. This is a very surprising discovery, since scrubber technology is traditionally used for the removal of macro-scale, rather than micro-scale, impurities.
  • the present application discloses systems and methods for preparation of ultrapure chemicals on-site at a semiconductor manufacturing facility, so that they can be piped directly to the points of use.
  • the disclosed systems are very compact units which can be located in the same building as a front end (or in an adjacent building), so that handling is avoided.
  • Hydrofluoric acid is an important process chemical in semiconductor manufac- turing. It is overwhelmingly important for deglaze (i.e. removal of thin native oxides) and for oxide removal generally. It is also a component of standard wet etches for isotropic etching of silicon (e.g. "CP4A,” which is 3 parts HF, 5 parts HNO 3 , and 3 parts acetic acid).
  • Anhydrous HF is typically manufactured by the addition of sulfuric acid to fluorspar, CaF 2 .
  • fluorspars contain arsenic, which leads to contamination of the resulting HF.
  • arsenic contamination is a dominant problem with HF purification.
  • One source (from China) contains minimal As and is the optimal raw material for Ultra high purity HF.
  • HF manufactured from this material is available from Allied Chemical in the US.
  • Other impurities, in conventional systems, are contributed by the HF generation and handling system. These impurities result from degradation of these systems; these systems were designed for applications much less demanding than the semiconductor industry. These contaminants must be removed in order to achieve good semiconductor performance.
  • the HF process flow includes a batch process arsenic removal and evaporation stage, a fractionating column to remove most other impurities, an Ionic Purifier column to suppress contaminants not removed by the fractionating column, and finally the HF Supplier (HFS).
  • Arsenic will be converted to the +5 state and held in the evaporator during distillation by the addition of an oxidant (KMnO 4 or (NH 4 ) 2 S 2 O 8 ) and a cation source such as KHF-, to form the salt K 2 AsF 7 .
  • an oxidant KMnO 4 or (NH 4 ) 2 S 2 O 8
  • KHF- cation source
  • Groups 3 - 12 (III A - II A) Cr, W, Mo, Mn, Fe, Cu, Zn
  • Group 13 (III) Ga Group 14 (IV) Sn, Pb, and
  • This fractionating column acts as a series of many simple distillations; this is achieved by packing the column with a high surface area material with a counter current liquid flow thus ensuring complete equilibrium between the descending liquid and rising vapor. Only a partial condenser will be installed in this column to provide reflux and the purified gaseous HF will then be conducted to the HF Ionic Purifier (HF IP).
  • HF IP HF Ionic Purifier
  • the HF IP will be utilized as an additional purity guarantee prior to introduction of the HF gas into the supplier systems. These elements may be present in the treatment solution or introduced in the IP to absorb sulfate carried over in the HF stream. IP testing has demonstrated significant reductions in the HF gas stream contamination for the following elements:
  • Figure 1 shows an on-site HF purifier according to a sample embodiment of the disclosed innovations.
  • Figure 1A shows an on-site HF purifier according to an alternative embodiment of the disclosed innovations, wherein high-purity arsenic-reduced hydrofluoric acid is used as the bulk starting material.
  • Figure 2 is a block diagram of a semiconductor fabrication line to which the purification unit of Figure 1 may be directly connected.
  • FIG. 1 shows an on-site HF purifier according to a sample embodiment of the disclosed innovations.
  • HF purification is accomplished by first oxidizing arsenic into the +5 oxidation state and fractionation to remove the As +5 and metallic impurities. See US Patent 4,929,435, which is hereby incorporated by reference. A variety of oxidizing reagents have been used for this purpose, as shown in the literature.
  • Fluorine (F 2 ) has been shown to work (by the published work of others), and is regarded as the presently preferred embodiment. F 2 requires expensive plumbing and safeguards, but has been shown to be workable.
  • An alternative secondarily preferred embodiment uses ammonium persulfate ((NH 4 ) 2 S 2 O 8 ), which is conveniently available in ultra-high purity.
  • oxidizers which do not introduce metal atoms are preferred.
  • other candidates include H- O ⁇ , and O 3 .
  • a less preferred candidate is Caro's acid (persulfuric acid, H-,SO 5 , which produces H 2 O 2 in solution).
  • Another option is ClO 2 . but this has the severe disadvantage of being explosive.
  • Other options include HNO 3 and Cl 2 , but both of these introduce anions which must be separated out. (Reduction of non-metallic anions is not as critical as reduction of metal cations, but it is still desirable to achieve anion levels of 1 ppb or less. Initial introduction of anions thus adds to the load on the ionic purification stage.)
  • KMnO 4 is the most conventional oxidant, and is predicted to be useable for ultrapurification if followed by the disclosed ionic purifier and HF stripping process.
  • this reagent imposes a substantial burden of cations on the purifier, so a metal-free oxidizer is preferred.
  • high-purity 49% HF which is essentially arsenic-free can be used.
  • Such low-arsenic material is expected to be available from Allied as of the third quarter of 1995, and can used, in combination with an on-site ionic purification process which does NOT include an arsenic oxidation reagent, to produce ultrapure HF on-site.
  • the HF process flow includes a batch process arsenic removal and evaporation stage, a fractionating column to remove most other impurities, an Ionic Purifier column to suppress contaminants not removed by the fractionating column, and finally the HF Supplier (HFS).
  • a batch process arsenic removal and evaporation stage includes a fractionating column to remove most other impurities, an Ionic Purifier column to suppress contaminants not removed by the fractionating column, and finally the HF Supplier (HFS).
  • Arsenic will be converted to the +5 state and held in the evaporator during distillation by the addition of an oxidant (KMnO 4 or (NH 4 ) 2 S 2 O 8 ) and a cation source such as KHF 2 to form the salt K 2 AsF 7 .
  • an oxidant KMnO 4 or (NH 4 ) 2 S 2 O 8
  • a cation source such as KHF 2
  • This process requires contact times of approximately 1 hr at nominal temperatures. To achieve complete reaction in a continuous process would require high temperatures and pressures (undesirable for safety) or very large vessels and piping.
  • the HF would be introduced into a batch process evaporator vessel and would be treated with an oxidant while stirring for a suitable reaction time.
  • Group 2 (II) Ca > Sr, Ba, Groups 3 - 12 (III A - II A) Cr, W, Mo, Mn, Fe. Cu. Zn
  • Group 15 (VII) Sb This fractionating column acts as a series of many simple distillations; this is achieved by packing the column with a high surface area material with a counter current liquid flow thus ensuring complete equilibrium between the descending liquid and rising vapor. Only a partial condenser will be installed in this column to provide reflux and the purified gaseous HF will then be conducted to the HF Ionic Purifier (HF IP).
  • HF IP HF Ionic Purifier
  • the HF at this stage is pure by normal standards, except for the possible carry over of the arsenic treatment chemicals or the quench required to remove these chemicals.
  • the HF IP will be utilized as an additional purity guarantee prior to introduction of the HF gas into the supplier systems. These elements may be present in the treatment solution or introduced in the IP to absorb sulfate carried over in the HF stream. IP testing has demonstrated significant reductions in the HF gas stream contamination for the following elements:
  • Figure 1A shows an on-site HF purifier according to an alternative embodiment of the disclosed innovations, wherein high-purity arsenic-reduced hydrofluoric acid is used as the bulk starting material.
  • the first unit in the cleaning line is a resist stripping station 41 where aqueous hydrogen peroxide 42 and sulfuric acid 43 are combined and applied to the semiconductor surface to strip off the resist. This is succeeded by a rinse station 44 where deionized water is applied to rinse off the stripping solution. Immediately downstream of the rinse station 44 is a cleaning station 45 where an aqueous solution of ammonia and hydrogen peroxide are applied. This solution is supplied in one of two ways. In the first, aqueous ammonia 31 is combined with aqueous hydrogen peroxide 46, and the resulting mixture 47 is directed to the cleaning station 45.
  • pure gaseous ammonia 32 is bubbled into an aqueous hydrogen peroxide solution 48 to produce a similar mixture 49. which is likewise directed to the cleaning station 45.
  • the semiconductor passes to a second rinse station 50 where deionized water is applied to remove the cleaning solution.
  • the next station is a further cleaning station 54 where aqueous solutions of hydrochloric acid 55 and hydrogen peroxide 56 are combined and applied to the semiconductor surface for further cleaning.
  • This is followed by a final rinse station 57 where deionized water is applied to remove the HC1 and H 2 O 2 .
  • dilute buffered HF is applied to the wafer (for removal of native or other oxide film).
  • the dilute buffered hydrofluoric acid is supplied directly, through sealed piping, from the generator 70.
  • the reservoir 72 holds anhydrous HF, from which a stream of gaseous HF is fed through the ionic purifier 71 into generator 70.
  • gaseous ammonia is also bubbled into generator 70 to provide a buffered solution, and ultrapure deionized water is added to achieve the desired dilution. This is followed by a rinse in ultrapure deionized water (at station 60), and drying at station 58.
  • the wafer or wafer batch 61 will be held on a wafer support 52, and conveyed from one workstation to the next by a robot 63 or some other conventional means of achieving sequential treatment.
  • the means of conveyance may be totally automated, partially automated or not automated at all.
  • FIG. 2 is just one example of a cleaning line for semiconductor fabrication.
  • cleaning lines for high-precision manufacture can vary widely from that shown in FIG. 2, either eliminating one or more of the units shown or adding or substituting units not shown.
  • the concept of the on-site preparation of high-purity aqueous ammonia, however, in accordance with this invention is applicable to all such systems.
  • ammonia and hydrogen peroxide as a semiconductor cleaning medium at workstations such as the cleaning station 45 shown in FIG. 2 is well known throughout the industry. While the proportions vary, a nominal system would consist of deionized water, 29% ammonium hydroxide (weight basis) and 30% hydrogen peroxide (weight basis), combined in a volume ratio of 6: 1 : 1. This cleaning agent is used to remove organic residues, and, in conjunction with ultrasonic agitation at frequencies of approximately 1 MHz, removes particles down to the submicron size range.
  • the purification (or purification and generation) system is positioned in close proximity to the point of use of the ultrapure chemical in the production line, leaving only a short distance of travel between the purification unit and the production line.
  • the ultrapure chemical from the purification (or purification and generation) unit may pass through an intermediate holding tank before reaching the points of use. Each point of use will then be fed by an individual outlet line from the holding tank.
  • the ultrapure chemical can therefore be directly applied to the semiconductor substrate without packaging or transport and without storage other than a small in-line reservoir, and thus without contact with the potential sources of contamination normally encountered when chemicals are manufactured and prepared for use at locations external to the manufacturing facility.
  • the distance between the point at which the ultrapure chemical leaves the purification system and its point of use on the production line will generally be a few meters or less. This distance will be greater when the purification system is a central plant-wide system for piping to two or more use stations, in which case the distance may be two thousand feet or greater. Transfer can be achieved through an ultra-clean transfer line of a material which does not introduce contamination. In most applications, stainless steel or polymers such as high density polyethylene or fluorinated polymers can be used successfully.
  • the water used in the unit can be purified in accordance with semiconductor manufacturing standards. These standards are commonly used in the semiconductor industry and well known among those skilled in the art and experienced in the industry practices and standards. Methods of purifying water in accordance with these standards include ion exchange and reverse osmosis.
  • Ion exchange methods typically include most or all of the following units: chemical treatment such as chlorination to kill organisms; sand filtration for particle removal; activated charcoal filtration to remove chlorine and traces of organic matter: diatomaceous earth filtration; anion exchange to remove strongly ionized acids; mixed bed polishing, containing both cation and anion exchange resins to remove further ions; sterilization, involving chlorination or ultraviolet light; and filtration through a filter of 0.45 micron or less.
  • Reverse osmosis methods will involve, in place of one or more of the units in the ion exchange process, the passage of the water under pressure through a selectively permeable membrane which does not pass many of the dissolved or suspended substances.
  • Typical standards for the purity of the water resulting from these processes are a resistivity of at least about 15 megohm-cm at 25°C (typically 18 megohm-cm at 25°C), less than about 25ppb of electrolytes, a paniculate content of less than about 150/cm 3 and a particle size of less than 0.2 micron, a microorganism content of less than about 10/cm 3 , and total organic carbon of less than lOOppb.
  • a high degree of control over the product concentration and hence the flow rates is achieved by precise monitoring and metering using known equipment and instrumentation. A convenient means of achieving this is by acoustic velocity sensing. Other methods will be readily apparent to those skilled in the art.
  • concentration control loop using conductivity, etc., in place of acoustic velocity
  • An on- site subsystem in a semiconductor device fabrication facility, for providing ultra-high-purity reagents comprising HF to a semiconductor manufacturing operation, comprising: an evaporation source connected to receive an HF source and to provide a flow of HF vapor therefrom; said flow of HF vapor being connected to pass through an ionic purifier unit which provides a recirculating volume of high-purity water, containing a high concentration of HF in contact with said flow of HF vapor, wherein said purifier exhausts a small amount of HF gas; and a generator unit, connected to receive said flow of HF vapor from said purifier and to combine said HF vapor with an aqueous liquid to produce an ultra-pure aqueous solution comprising hydrofluoric acid; and a piping connection which routes said a- queous solution to points of use in the semiconductor device fabrication facility.
  • An on-site subsystem in a semiconductor device fabrication facility, for providing ultra-high- purity reagents comprising HF to a semiconductor manufacturing operation, comprising: an evaporation source connected to receive HF and to provide a flow of HF vapor therefrom; said flow of HF vapor being connected to pass through an ionic purifier unit which provides a recirculating volume of high-purity water, containing a high concentration of HF in contact with said flow of HF vapor, wherein said purifier exhausts a small amount of HF gas; and a generator unit, connected to receive said flow of HF vapor from said purifier and to combine said HF vapor with an aqueous liquid to produce an ultra-pure aqueous solution comprising hydrofluoric acid; whereby said ultra-pure aqueous solution can be used within the semiconductor device fabrication facility without bulk transfer or exposure of liquid surface to any uncontrolled ambient atmosphere.
  • An on-site subsystem in a semiconductor device fabrication facility, for providing ultra-high- purity HF for use in semiconductor manufacturing operations at said facility, comprising: an evaporation source connected to receive a liquid HF source and to provide a flow of HF vapor therefrom; said flow of HF vapor being connected to pass through an ionic purifier unit which provides a recirculating volume of high-purity water, containing a high concentration of HF in contact with said flow of HF vapor, wherein said purifier exhausts a small amount of HF gas; and a dryer unit, connected to receive said flow of HF vapor from said purifier and to dry said HF vapor; and a piping connection which routes said vapor from said dryer to points of use in the semiconductor device fabrication facility.
  • a method for supplying a high-purity HF reagent to a workstation in a production line for the manufacture of a high-precision electronic component comprising: (a) drawing HF gas from a vapor space above hydrofluoric acid in an HF-containing reservoir; (b) passing said HF gas through a filtration membrane removing particles greater than 0.005 micron therefrom; (c) passing said HF gas thus filtered through a scrubber whereby said HF gas is contacted with an aqueous solution of HF in deionized water, wherein said scrubber exhausts a small amount of HF gas; and (d) recovering HF gas emerging from said scrubber and directing said HF gas to said workstation.
  • the source of gaseous HF for purification can be anhydrous HF. or alternatively can be a heated evaporator which evolves HF from 49% aqueous HF)
  • the disclosed innovative techniques are not strictly limited to manufacture of integrated circuits, but can also be applied to manufacturing discrete semiconductor components, such as optoelectronic and power devices.
  • the disclosed innovative techniques can also be adapted to manufacture of other technologies where integrated circuit manufacturing methods have been adopted, such as in thin-film magnetic heads and active-matrix liquid-crystal displays; but the primary application is in integrated circuit manufacturing, and applications of the disclosed techniques to other areas are secondary.
  • the primary embodiment is an on-site purification system.
  • the disclosed purification system can also be adapted to operate as a part of a manufacturing unit to produce ultra-high-purity chemicals for shipment; however, this alternative embodiment does not provide the advantages of on-site purification as discussed above.
  • Such applications encounter the inherent risks of handling ultra-high-purity chemicals, as discussed above; but for customers who require packaged chemicals (with the attendant handling), the disclosed innovations at least give a way to achieve an initial purity which is higher than that available by other techniques. Again, in such applications a dryer stage may also be used after the ionic purifier.
  • the primary embodiment is directed to providing ultrapure aqueous chemicals, which are most critical for semiconductor manufacturing.
  • the disclosed system and method embodiments can also be used for supply of purified gas streams. (In many cases, use of a dryer downstream from the purifier will be useful for this.)
  • piping for ultrapure chemical routing in semiconductor front ends may include in-line or pressure reservoirs.
  • references to "direct" piping in the claims do not preclude use of such reservoirs, but do preclude exposure to uncontrolled atmospheres.

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  • Cleaning Or Drying Semiconductors (AREA)

Abstract

La présente invention concerne un système de purification et de génération sur site d'acide fluorhydrique ultra-pur intégré à une installation de fabrication de dispositifs à semi-conducteurs. Une opération d'évaporation (éventuellement accompagnée d'une oxydation d'arsenic) est suivie par un passage en colonne de fractionnement permettant d'éliminer la plupart des autres impuretés, puis par un passage dans une colonne ionique de purification permettant de supprimer les contaminants non éliminés par la colonne de fractionnement, et le produit résultant étant ensuite envoyé dans le réservoir d'acide fluorhydrique (HFS).
EP96919223A 1995-06-05 1996-06-05 Fabrication sur site d'acide fluorhydrique ultra-pur destine au traitement des semi-conducteurs Withdrawn EP0833705A4 (fr)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
WOPCT/US95/07649 1995-06-05
PCT/US1995/007649 WO1996039358A1 (fr) 1995-06-05 1995-06-05 Purification de gaz ammoniac jusqu'au niveau requis pour son utilisation dans la fabrication de composants electroniques
US3871195P 1995-07-07 1995-07-07
US49941495A 1995-07-07 1995-07-07
US499414 1995-07-07
PCT/US1996/009554 WO1996041687A1 (fr) 1995-06-05 1996-06-05 Fabrication sur site d'acide fluorhydrique ultra-pur destine au traitement des semi-conducteurs

Publications (2)

Publication Number Publication Date
EP0833705A1 true EP0833705A1 (fr) 1998-04-08
EP0833705A4 EP0833705A4 (fr) 1999-12-15

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EP96919223A Withdrawn EP0833705A4 (fr) 1995-06-05 1996-06-05 Fabrication sur site d'acide fluorhydrique ultra-pur destine au traitement des semi-conducteurs

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EP (1) EP0833705A4 (fr)

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
No further relevant documents disclosed *
See also references of WO9641687A1 *

Also Published As

Publication number Publication date
EP0833705A4 (fr) 1999-12-15

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