Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B9/00—Combinations of apparatus for screening or sifting or for separating solids from solids using gas currents; General arrangement of plant, e.g. flow sheets
  • B07B9/02—Combinations of similar or different apparatus for separating solids from solids using gas currents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B55/00—Safety devices for grinding or polishing machines; Accessories fitted to grinding or polishing machines for keeping tools or parts of the machine in good working condition
  • B24B55/12—Devices for exhausting mist of oil or coolant; Devices for collecting or recovering materials resulting from grinding or polishing, e.g. of precious metals, precious stones, diamonds or the like
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28D—WORKING STONE OR STONE-LIKE MATERIALS
  • B28D5/00—Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor
  • B28D5/0058—Accessories specially adapted for use with machines for fine working of gems, jewels, crystals, e.g. of semiconductor material
  • B28D5/007—Use, recovery or regeneration of abrasive mediums
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working

Definitions

• the invention relates to a method and a system, for cleaning contaniinaied silicon carbide (SiC) particles, and in particular, the contaminated SiC particles are cleaned by removing fine grain particles adherin to the contaminated SiC particles after being used in suspension in a cutting medium for the cutting or sawing of silicon wafers for solar cells and electronic objects often, called spent sawing sludge.
• SiC contaniinaied silicon carbide
• particles of silicon carbide (SiC) of specific grit sizes such as FEPA classes F500, F60Q, and F8Q0, are dispersed in an organic liquid, thus forming a suspension, which is used as a cutting medium.
• the most common dispersing agents are organic glycolic liquids such as polyethylene glycol or di-propylene glycol.
• surfactants that reduce surface tensions are added to the suspension.
• the sawing is usually conducted by a wire saw to which a thin, hardened iron wire with, brass on the surface, cuts the silicon (Si) block into a series of thin wafers while the particies from the sawing are suspended in the SiC containing suspension, During the sawing process, the suspension becomes contaminated with Si from the Si block, iron (Fe) from the cutting wire, and SiC fines (i.e. fine particles) from the breaking down of abrasive grains.
• the Si wafers are used for the manufacture of electronic or microelectronic devices, or for the manufacture of solar cell panels for the production of electric power.
• SiC particles for sawing lies within a narrow grain size range, i.e. that there is little or minimal difference between the size of the largest and the smallest grains.
• the cutting suspension becomes so contaminated with SIC fines, Si and Fe particles that it has to be replaced by a new suspension.
• particle size distribution of SiC particles is shifted out of the desired narrow range.
• Another alternative is to bum the spent cutting suspension whereby the liquid phase is burnt along with the solid particles. While glycol is burned and reduced to carbon dioxide and water, the solid particles form a heavy metal containing ash that presents another environmental problem.
• SiC fines Si and Fe particles .may be removed and recovered from the suspension. Recycling of SiC particles also means a reduction in the total energy consumption in, for example, manufacturing solar cells processes. Recycling also means less environmental strain with respect to both the production of the SiC and with respect to the burning or deposition of the carbide containing suspension in special land fills due to a lack of cleaning processes.
• FEPA F500, f 600 and F800 microgrits are commonly used in the sawing of Si wafers and it is important that the grains of SiC conform to the . standard to obtain a good result.
• the conventional practice is to dilute the suspension of particles and polyethylene glycol or di- propylene glycol with large quantity of water and treat the suspension in settling vessels. In such process, it is desirable to make use of the fact that the SiC particles have larger diameters than the contaminants of SiC fines, Fe and Si.
• the settling process therefore has to be interrupted before finer particles of SiC fines.
• Si and Fe reach the settled phase of SiC with desired grain size.
• the settled particles of SiC obtained in the settling vessel are dried and screened according to known methods. Glycol based dispersing agents, highly diluted with water, are required to increase the settling velocity, which makes an economical and ecological recovery process for the dispersing agent difficult.
• the method may include feeding the contaminated SiC particles to a jet mill to obtain a dispersed powder.
• the system may include a jet mill
• the system may further include a classifier system.
• the classifier system may include more than one classifier.
• Fig. 2A shows the particle size distribution of the fine fraction from the first classifier of the system of Fig. 1.
• Fig. 2B shows the particle size distribution of the fine traction from the second classifier of the system of Fig. 1.
• Fig. 3A shows a SEM (1 OOOx magnification) of new SiC particles before cutting of silicon wafer.
• Fig. 3B shows a SEM (1 OOOx magnification) of contaminated SiC particles after cutting of silicon wafer.
• Fig, 3C shows a SE (1 OOOx magnification) of the cleaned SiC particles obtained by the present method.
• Fig. 4A sho ws a SEM (2000x magnification) of new SiC particles before cutting of silicon wafer.
• contaminated SiC particles are cleaned by removing fine grain particles adhering to the
• the method allows recovery of SiC of a narrow grain size range by removing from the SiC particles smaller particles such as, but not limited to, iron (Fe). silicon (Si) and SiC fines.
• the method and system can be applied cost-effectively on an industrial scale and at. the same time have minimal negative impacts on the environment.
• the smallest particles will be present as individual grains that may be separated from tire larger particles by a convenient choice of process parameters. With respect to these SiC particles, however, subsequent to the removal and recovery of the dispersing agent from the used suspension, the small particles will adhere to the larger, say F500, F600 or F800 SiC grains that are typically applied for sawing silicon wafers.
• SiC silicon carbide
• Used SiC containing suspensions from the sawing of silicon wafers are filtered according to prior art technology to separate the solid stream from the liquid stream.
• the solid stream is heated under agitation so that the contaminated SiC particles assume the form of a dry powder.
• the liquid stream is separately recovered according to a known technology.
• the jet mill ( 12) is operated at a rotor speed of about 800 to about 1,200 rpm.
• the rotor speed of the jet mill (12) may be set at 800 rpm, 900 rpm, 1 ,000 rpm, 1 ,100 rpm, or 1 ,200 rpm.
• the dispersed powder is then fed to a classifier system to obtain the cleaned SiC particles.
• the classifier system may include more than one classifier.
• Classifier is a form of centrifugal separation of the particles into coarse and fine fraction.
• the dispersed powder is fed to a classifier via the bottom and is carried towards a set of rotors at the top of the classifier. Fine powder passes through the rotors and exit the classifier via the top, while coarse powder leaves the classifier via the bottom. The fine fraction then passes
• the classifiers may be arranged such that the classifiers are.
• a first classifier (14) is positioned upstream of a second classifier (16), whic in turn is positioned upstream of a third classifier (18),
• Each classifier (14), (16), (18) produces a coarse fraction and a fine fraction, in the case where the classifiers are connected in series, each coarse fraction of an upstream classifier is fed to a downstream classifier and each fine fraction of a respective classifier is separated out from the classifier system.
• the coarse fraction from the first classifier (14) is fed to the second classifier (16).
• the coarse fraction from the second classifier (16) is fed to the third classifier (18).
• Fine fractious from the first classifier (14), the second classifier (16) and the third classifier (18) may be individually collected.
• fine fractions ' from the first classifier (14), the second classifier (16) and the third classifier (18) may be collectively collected.
• Fine fraction usually contain significant portion of coarse powder.
• the yield of the cleaned SiC particles obtained from the present method improves by at least 3 %, for example.
• at least one of the fine fractions is recycled back, to the jet mill (12).
• fine fraction from the third classifier (18) may be recycled back to the jet mill (12).
• fine fraction from the first classifier (14) or the second classifier (16) may be recycled hack to the jet mill (12).
• fine fractions from the second classifier (16) and the third classifier (18) may be collectively collected and recycled back to the jet mill (12).
• the fine fractions from the respective classifier (14), (16), (18) may be individually collected and separated out from the classifier system.
• the fine fractions may be sold as useful products. For example, fine fraction from the first classifier (14) is collected and sold under the trade name SiSiCar®50. Fine fraction, from the second classifier (16) is collected and sold under the trade nameSiSiCar®70.
• the coarse fraction of the last classifier i.e. the third classifier (18) of Fig. .1, contains the cleaned SiC particles.
• the second classifier (16) is operated at a rotor speed of about 2,100 to about 2,800 rpm.
• the rotor speed may be set at 2,100 rpm, 2,200 rpm, 2,300 rpm, 2,400 rpm, 2,500 rpm, 2,600 rpm, 2,700 rpm, or 2,800 rpm.
• [0O52J Fig. 2B shows the particle size distribution of the feed (Sample 4), fine fraction (Sample 5) and coarse fraction (Sample 6) from the second classifier of the system of Fig, 1.
• the third classifier (1 8) is operated at a rotor speed of about 2, 100 to about 2,800 rpm.
• the rotor speed may be set at 2,100 rpm, 2.200 rpm, 2,300 rpm, 2,400 rpm, 2,500 rpm, 2,600 rpm. 2,700 rpm, or 2,800 rpm.
• Fig, 2C shows the particle size distribution of the feed (Sample 6), fine fraction (Sample 7) and coarse fraction (Sample 8) from the third classifier of the system of Fig. 1.
• a system for cleaning contaminated silicon carbide (SiC) particles by removing fine grain particles adhering to the contaminated SiC particles is disclosed,
• the system may include a jet mill.
• the system may further include a classifier system.
• the classifier system may include more than one classifier.
• the classifiers may be arranged such that the classifiers are- connected in series.
• each classifier produces a coarse fraction and a fine fraction, whereby each coarse fraction of an upstream classifier may be fed to a downstream classifier and each fine fraction of a respective classifier may be separated out from the classifier system.
• Fig. 3 A shows a SEM (lOOOx magnrficaiion) of new SiC particles before cutting of silicon wafer.
• Fig. 3B shows a SEM (lOOOx magnification) of contaminated SiC particles after cutting of silicon wafer.
• Fig. 3C shows a SEM (lOOOx raagnitlcatioii) of the cleaned SiC panicles obtained by the present method.
• Fig, 4 A shows a SEM ⁇ 2000x magnification) of new SiC particles before cutting of silicon wafer.
• Fig. 4B shows a SEM (2000x magnification) of contaminated SiC particles after cutting of silicon wafer.
• Fig, 4C shows a SEM (2000x magnification) of the cleaned SiC particles obtained by the present method
• Some users employ silicon carbide manufactured in accordance with. FEPA F800 suspended in polyethylene glycol as the cutting medium. After usage, the suspension will be saturated with fine impurities that the particle size distribution would have shifted out of the desired narrow range.
• This powder is heavily laden with fine impurities.
• the first coarse fraction then enters the bottom of second Classifier and separates into a second fine and second coarse fraction at a rotor speed of 2,700 rpm.
• the cleaned silicon carbide particles are very well "de- dusted", that is, most of the fine impurities have been removed.
• the overall yield of the cleaned silicon carbide is about 73 %.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Carbon And Carbon Compounds (AREA)
• Processing Of Stones Or Stones Resemblance Materials (AREA)

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• 2013
  • 2013-10-24 CN CN201380080752.7A patent/CN105764620A/zh active Pending
  • 2013-10-24 WO PCT/IB2013/059593 patent/WO2015059521A1/en active Application Filing
  • 2013-10-24 SG SG11201603186PA patent/SG11201603186PA/en unknown
  • 2013-10-24 EP EP13824164.1A patent/EP3060357A1/de not_active Withdrawn
• 2014
  • 2014-10-23 TW TW103136566A patent/TW201516005A/zh unknown

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