1 U of M Materials Science Seagate Design Group Alan Bagwell Tony Lindert Loc Nguyen Greg Rayner Industrial Mentor: Dr. Vince Engelkes Faculty Advisor: Prof. C. Daniel Frisbie
Dec 30, 2015
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U of M Materials Science Seagate Design Group
Alan BagwellTony LindertLoc NguyenGreg Rayner
Industrial Mentor:Dr. Vince Engelkes
Faculty Advisor:Prof. C. Daniel Frisbie
Outline
• Project Goal• Project Solution: CMP Overview• Detailed Solution• Other Considerations• Summary
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Project Goal and Solution
Main Goal: Reduce transducer RMS roughness from 10 Å to 2 Å
Project Solution: Chemical Mechanical Processing / Nanogrinding
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Chemical Mechanical Planarization Overview
• Culmination of several smoothing processes
• Key components:– CMP Pad– Slurry– Process control:
speed, pressure, etc.http://www.icknowledge.com/misc_technology/CMP.pdf
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Material Science and Engineering, Zantye, 20045
Rough Lapping
• Goal: Bulk removal• Multi-step process
– Free Abrasive – Single crystal diamond (0.25+ micron particle size)– Zinc lapping plate– High speed and pressure for maximum removal
rate– High speed leads to a reduction in planarization.
Further lapping is required.
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Material Science and Engineering, Zantye, 2004
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Fine LappingFixed versus Free Abrasive
Ultraprecision Polishing GMR Harddisk Magnetic Head, Zhong, 2006
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Material Science and Engineering, Zantye, 2004 9
Nanogrinding
• Plate Preparation– Tin-bismuth alloy (42% Sn, 58% Bi, 1.5-2 Mohs)– Surface roughness– Spiral groove– Plate is “charged” by embedding diamonds
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Plate Charging
• 50nm polycrystalline diamond spherical particles
• 6-hour+ charging times result in better planarity
Ultra precision Polishing GMR Hard-disk Magnetic Head, Zhong, 2006
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Slurry Composition
• Ethylene glycol with 6% silica colloid (30% SiO2, 10 nm) to increase plate life and removal rate
• Chelating agent (Methionine) to dissolve metal ions
• Corrosion inhibitors: BTA, Standapol, or Triton• Polyoxyethylene ether as a surfactant to
increase wetting
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Slurry pH
• Slider consists of softer metals and harder AlTiC ceramic
• Picking the correct pH will increase the solubility of the ceramic and soften it
• This will allow both materials to abrade at similar rates
• At pH 11, copper in the GMR stack will corrode
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Slurry pH (10)
On the advanced lapping process in the precision finishing of thin-film magneticrecording heads for rigid disc drives, Jiang, 2003
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Other Considerations
• Plate Speed: 25 rpm• Nominal Pressure: 112 kPa• Slurry Flow: 1 mL every 30 seconds• Viscosity: 2.5 cP
– The viscosity can be increased by partially
replacing ethylene glycol with diethylene glycol
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Summary
• Fixed Abrasive Lapping– 50 nm polycrystalline spherical diamond particles
embedded in tin-bismuth grooved plate – Plate charging time of 8 hours
• Slurry Composition– Ethylene glycol with 6% colloidal silica (30% SiO2, 10 nm)– Standapol corrosion inhibitor– Polyoxyethylene ether surfactant– Diethylene glycol to raise viscosity to 2.5 cP– Chelating agent (Methionine) to dissolve metal ions– Organic pH regulators such as NH4OH to achieve a pH of 10
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