1

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

2

Project Goal and Solution

Main Goal: Reduce transducer RMS roughness from 10 Å to 2 ÅProject Solution: Chemical Mechanical Processing /

Nanogrinding

3

On the advanced lapping process in the precision finishing of thin-film magneticrecording heads for rigid disc drives, Jiang, 2003

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

4

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.

6

Material Science and Engineering, Zantye, 2004

7

Fine LappingFixed versus Free Abrasive

Ultraprecision Polishing GMR Harddisk Magnetic Head, Zhong, 2006

8

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

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, 2006

11

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

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 magneticrecording heads for rigid disc drives, Jiang, 2003

14

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% 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

16