Cutting metallates of refractory metals

Details Cutting metallates of refractory metals Cutting metallates of refractory metals

1998-10-22

2003-06-03

Rose, Robert A. (Department: 3641)

Abrading

Abrading process

C451S053000, C125S013010

Statutory Invention Registration

active

H0002067

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to methods and apparatus for the saw cutting and other cutting of metallates of refractory metals including: niobates, tantalates, titanates, and more particularly crystals of lithium niobate and lithium tantalate and to fluids used for friction reduction, swarf removal and/or cooling in such processes (“lubricating fluids”).
Several Ta, Nb, Ti metallates have found significant usage as materials for manufacture of solid state power, signal translation, transducing and sensing devices, including usage as filters, resonators, delay lines, piezoelectric transducers. They are also useful in connection with the making of perskovite structure ceramics, including the so-called PMN types (e.g., lead-magnesium-niobate, with well-known substitutions for each such nominal component) useful for ferroelectric and dielectric properties.
The class of metallates involved here is glasslike materials available and usable in polycrystalline and single crystalline and in amorphous forms, usually grown or refined as single crystals by Czochralski process pulling and growth from a melt or Pfann zone refining process. The crystal boules or rods vary from a few cm to well over a foot in diameter. It is desirable for most usage purposes to cut them into wafer thin slices, with dimensional control, achieve very thin sections, avoid excessive kerf and swarf, suppress impurity pick-up, suppress surface wear and roughness, recycle swarf and avoid breakage or crystalline or mechanical structural flaws of the wafer to a high degree. Maintaining cutting tool life and precision, and control of lubricant waste and disposal are also important criteria.
The principal cutting method presently used for such materials is sawing using rotary metal blades with an edge coating composite of diamond particles in a polymeric or metal blade matrix (diamond saw), using water-soluble or emulsifible oils (in aqueous solutions or emulsions) as lubricants for cooling, removal of swarf and friction reduction. Sometimes water, per se or with minimal functional additives, is used as the lubricant. Generally a wafer thickness as low as 0.5 mm is achievable. Cutting is followed by deionized water rinsing of the wafers, and air drying, to further remove swarf and residual lubricant. Filtering is used to recover the swarf particles (often sub-micron sized) and the lubricant is recycled or disposed in an environmentally sound way, at a significant cost.
The objects of the present invention are to provide improved method, apparatus and lubricant systems and materials to enhance blade life and precision, enable greater speed of cutting, reduce swarf and other waste, reduce wear and roughness of the wafer surfaces, eliminate subsequent water rinsing, increase yields and/or reduce the thickness level regularly achievable with the metallate materials, particularly lithium niobates and tantalates, as well as reducing costs.
SUMMARY OF THE INVENTION
The objects of the invention are realized through method and apparatus employing a class of lubricants and systems for their utilization in the present context that can be recycled without complex or expensive reconstitution, cools more effectively than state of the art lubricants and enables closer control of the cutting. The invention can also be extended to other operations concerning the metallates including surface grinding and polishing, as well as the cutting of strips and dice from the wafer slices. It has been found that diamond blade wear can be reduced remarkably—to a degree that useful blade life is extended manyfold, that rpm, tool infeed rate and thereby speed of cutting can be increased.
The preferred processes and machines employ a lubricant comprising one or more of: (a) perfluorocarbon compounds (PFCs), including aliphatic perfluorocarbon compounds (&agr;-PFCs) having the general formula C
n
F
2n+2
, (b) perfluoromorpholines (PFMs) having the general formula C
n
F
2n+1
ON, (c) certain perfluoroamines (PFAs), (d) highly fluorinated amines (HFAs), (e) perfluoroethers and perfluropolyethers (PFEs and PFPEs), (f) hydrofluoro polyethers (HFPEs) and (g) highly fluorinated ethers (HFEs), and their respective polymerization products. Such compounds exhibit a very high degree of thermal and chemical stability due to the strength of the carbon-fluorine bond. PFCs are also characterized by extremely low surface tension, low viscosity, and high fluid density. They are clear, odorless, colorless fluids with boiling points from approximately 30° C. to approximately 300° C. (although the preferred boiling range for refractory metal matellate cutting is 30-200 C., and more preferably, as stated below, 50-150).
Fluorinated, inert liquids usable in accordance with the present invention can be one or a mixture of &agr;-PFC, PFM, PFA, HFA, PFE, PFPE, HFPE and HFE compounds having 5 to 18 carbon atoms or more and having a H:F ratio under 1:1. When any of these choices other than ethers are used, they preferably have a hydrogen content of less than 5% by weight, most preferably less than 1% by weight. When ethers are used, a hydrogen content of less than 2% is the most preferred.
These materials are preferably used in liquid phase and used alone (neat), but in some usages may usefully be mixed or emulsified with other functional or carrier liquids and/or mixed with particulate solids as pastes or waxes. They can also have useful solids suspended therein when used in liquid form.
Suitable fluorinated, inert liquids useful in this invention may include more particularly, for example, perfluoroalkanes or perfluorocycloalkanes, such as perfluoropentane, perfluorohexane, perfluoroheptane, perfluorooctane, perfluoro-1, 2-bis (trifluoro-methyl) hexafluorocyclobutane, perfluorotetradecahydro-phenathrene, and perfluorodecalin; perfluoroamines, such as perfluorotripropylamine, perfluorotributylamine, perfluorotriamylamine perflurotriethylamine, perfluoromorpholines, such as perfluoro-N-methylmorpholine, perfluoro-N-ethylmorpholine, and perfluoro-N-isopropylmorpholine, perfluorophenanthrene and perfluoroethers and perfluoropolyethers, such as perfluorobutyltetrahydrofuran, perfluorodibutylether, perfluorobutoxyethoxyformal, perfluorohexyl formal, and perfluorooctyl-formal, perfluro polyethers and the polymerization products of these classes.
The prefix “perfluoro” as used herein means that all, or essentially all, of the hydrogen atoms are replaced by fluorine atoms. Perfluorocarbon fluids originally were developed for use as heat-transfer fluids. They are currently used in heat-transfer, vapor phase soldering, and electronic testing applications and as solvents and cleaning agents and have also been described in connection with usage in certain shop operations such as: wire drawing, hot and cold bulk forrning, cutting and abrasion processes see, e.g., U.S. Pat. Nos. 5,676,005 (Oct. 14, 1997) and 5,743,120 (Apr. 28, 1998) and published PCT application WO097/35673 (published Oct. 2, 1997) of H. C. Starck, Inc. (Newton, Mass.), as well as the PCT published PCT applications of D. S. Milbrath et al. of 3M Co. (Minnesota Mining & Manufacturing Co., Inc., St. Paul, Minn.), WO9812286 and 9812287 published Mar. 26, 1998, based on U.S. applications Ser. No. 08/715,207 and 08/715,206 of Sep. 17, 1996.
The term “highly fluorinated” as used herein means having a H:F ratio under 1:1. Commercially available fluorinated, inert liquids useful in this invention include the PF-5062, HFE7100, HFE7200, FC-40 liquids (all available from 3M Company under the trade-name designations of “Fluorinert,” performance fluid or hydrofluorether as described in 3M's published PCT patent applications. Other perfluorocarbon liquids such as, HT-200, HT-230 and HT-270 (available from Montefluos Inc., Italy, under the tradename designation of “Galden”); Hostinert™ (Hoechst-Celanese); and Krytox brand K—101, 103, 105, 107 (DuPont) are also usable for purposes of the present invention.
Generally, fluorinated liquids of the invention should be selected for a 50-180° C

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