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

Outline Project Goal Project Solution: CMP Overview Detailed Solution Other Considerations Summary 2

Project Goal and Solution Main Goal: Reduce transducer RMS roughness from 10 Å to 2 Å Project Solution: Chemical Mechanical Processing / Nanogrinding 3

Chemical Mechanical Planarization Overview Culmination of several smoothing processes Key components: – CMP Pad – Slurry – Process control: speed, pressure, etc. 4

Material Science and Engineering, Zantye,

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. 6

Material Science and Engineering, Zantye,

Fine Lapping Fixed versus Free Abrasive Ultraprecision Polishing GMR Harddisk Magnetic Head, Zhong,

Material Science and Engineering, Zantye,

Nanogrinding Plate Preparation – Tin-bismuth alloy (42% Sn, 58% Bi, Mohs) – Surface roughness – Spiral groove – Plate is “charged” by embedding diamonds 10

Plate Charging 50nm polycrystalline diamond spherical particles 6-hour+ charging times result in better planarity Ultra precision Polishing GMR Hard-disk Magnetic Head, Zhong,

Slurry Composition Ethylene glycol with 6% silica colloid (30% SiO 2, 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 12

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 13

Slurry pH (10) On the advanced lapping process in the precision finishing of thin-film magnetic recording heads for rigid disc drives, Jiang,

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 15

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% SiO 2, 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 NH 4 OH to achieve a pH of 10 16