Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Patent
1998-04-16
2000-04-18
Michalsky, Gerald A.
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
137 5, 137 88, 137 93, G05D 1113
Patent
active
060502835
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates generally to semiconductor processing, and particularly to mixing ultrapure liquid reagents with great accuracy.
The present inventors have developed a method for preparing ultra-high-purity liquid reagents (including aqueous HF, HCl, NH.sub.4 OH, NH.sub.4 F, and HNO.sub.3) in an on-site system located at the semiconductor wafer production site. In the example of aqueous ammonia, this is performed by: drawing ammonia vapor from a liquid ammonia reservoir, and scrubbing the filtered vapor with high-pH purified water (preferably ultrapure deionized water which has been allowed to equilibrate with the ammonia stream). This discovery permitted conversion of commercial grade ammonia to ammonia of sufficiently high purity for high-precision manufacturing without the need for conventional column distillation. 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 III 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 of ultrapurification 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. Details of such systems are described in copending U.S. application Ser. No. 08/179,001 filed Jan. 7, 1994, now U.S. Pat. No. 5,496,778, which is hereby incorporated by reference, and in copending provisional applications 60/023,358, 60/038,711 and 60/038,712 all filed Jul. 7, 1995. and all hereby incorporated by reference.
The present inventors have also developed systems for on-site purification of hydrogen peroxide, and details of such systems are described in copending U.S. provisional application 60/017,123 filed Jul. 7, 1995 which is hereby incorporated by reference.
BACKGROUND
One of the long-running technological shifts in semiconductor processing has been the changes (and attempted changes) between dry and wet processing. In dry processing, only gaseous or plasma-phase reactants come in contact with the wafer. In wet processing, a variety of liquid reagents are used for purposes such as etching silicon dioxide or removing native oxide layers, removing organic materials or trace organic contaminants, removing metals or trace organic contaminants, etching silicon nitride, etching silicon.
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.
The result of this is that purity of process chemicals at plasma etching is not as critical, since these steps are always followed by cleanup steps before high-temperature steps occur, and the cleanup steps can remove dangerous contaminants from the surface before high-temperature steps drive in these contaminants. However, purity of the liquid chemicals is much more critical, because t
REFERENCES:
patent: 4091834 (1978-05-01), Frigato
patent: 5522660 (1996-06-01), O'Dougherty et al.
Clark R. Scot
Hoffman Joe G.
Jones, Jr. Allen H.
Air Liquide America Corporation
Michalsky Gerald A.
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