Introduction to MR Inspection: Emerging Applications to Reduce Media Cost Per Disk By Michael E. Boyd

1. Introduction to MR Inspection
**********************
Emerging Applications
to
Reduce Media Cost Per Disk
Michael E. Boyd
1

2. Areal Density and Impact on Media Test
14 1997 Forecasted 95 mm Disk Pricing 1
0 .9
12
0 .8
10 0 .7
8 0 .6
T e s t T im e
0 .5$ P e r D is k
(M in /D is k )
6 0 .4
4 0 .3
Test Time Growth 0 .2
2
0 .1
0 0
97 98 99 00
COST PRODUCTIVITY FACTORS
 Increasing areal density creates test  Yields
time dilemma  Test methodology
 Budget for test roughly fixed  Equipment throughput and cost
– 15-20 % of media cost  Equipment utilization
 Continued pressure on disk pricing
2

3. Test Requirements
Drive Requirements
Magnetics
Defects
Glide
Technology Driven Cost Driven
Scratches
TA’s TPI vs % Coverage
Shallow Defects
Consumables
Low Glide
Contamination
Test Strategy
3

4. Test Challenges
 Future Test strategies of media makers
diverge:
 Parallelism in Test
 More magnetics testing, less single bit defect testing
 More emphasis on disk mechanics (glide and TA’s)
 Optical Glide
 Optical Certification
 Optically assisted testing
 Discrete Testers
4

5. Possible New Additions to Final Test
 Optical Testing:
 Traditional focus has been to replace glide or
certification testing
 Optical systems for glide have had an issue with
sensitivity vs. throughput
 Optical systems can find magnetic defects, however
over-rejection is the problem
 MR Glide:
 Scanning with MR drive head on an erased disk
 Best sensor for detecting contact thermal asperities,
non-contact bump/pit thermal signals, and scratches
 Has not been utilized in production testing
5

6. Defining Optical, Certification, PZT, & MR Glide Signals
Optical Signals, are
Bright Field
from Specular Light,
&
Dark Field
from Scattered Light.
Optical Signals Cert. Missing Pulse Signal
MR Glide Signal, is
Magnetic Signal
from the Defect’s Edges,
&
Mass Spin-Valve Signal.
Non-contact MR Glide Signal PZT Glide Signal
6

7. Signal Characterstics from Reference 10m x 10m ~1.25 in Bump Defect
AFM Microgaph
Optical Signals Non-contact MR Glide
Bright & Dark Field
Contact PZT Glide
7

8. Signal Characterstics from Reference 10m x 10m ~2 in Pit Defect
AFM Micrograph
Optical Signals Non-contact MR Glide
Bright & Dark Field
Non-contact PZT Glide
8

9. Based on Defects Presented
Bump/Pit Signal Polarity to Type &
Defect Signal Amplitude to Size Dependence
Signal Bump/Pit Signal Defect Signal
Type Polarity to Type Amplitude to Size
Optical Bright Field Yes Yes
Optical Dark Field No Yes
PZT Glide ? ?
MR Glide Yes Yes
9

10. PS5100 Signal vs MR Glide Signal on Scratch Defect
PS5100 Microscope Image ~2.5m Width
PS5100 Optical Signal Non-contact MR Glide Signal
10

11. PS5100 Signal vs MR Glide Signal on Polishing Defect
PS5100 Microscope Image ~40m x 30m
PS5100 Optical Signal Non-contact MR Glide Signal
11

12. PS5100 Signal vs MR Glide Signal on Bump Like Binary P.D.
PS5100 Microscope Image ~40m x 20m
PS5100 Optical Signal Non-contact MR Glide Signal
12

13. PS5100 Signal vs MR Glide Signal on Head Slap
PS5100 Microscope Image ~ 30m x 10m
PS5100 Optical Signal Contact MR Glide Signal
13

14. Based on Defects Presented
PS5100 Error Signal Characteristics vs
MR Glide Error Signal Characteristics
Defect PS5100 MR Glide
Type Error Signal Error Signal
Scratch Dark Field Only Magnetic Only
P.D. Bright Field Only Thermal Only
Head Slap Bright & Dark Field Thermal Asperity
Binary P.D. Bright Field Only Thermal Only
14

15. Typical Test Cycle
10-25 seconds 10-20 seconds 20-35 seconds 120-150 seconds
Burnish Optical Scan Glide Certify
• Mechanical Process • Pre-glide screen • Using PZT or AE Heads • Defect Testing
• Removes Surface • Saves heads • Verify surface asperities • Defects below specified
Asperities • Increases are below set limits size and count
Throughput • Typically one event fails
disk • Parametrics within
set ranges
• OD, MD, ID
• Every disk or sample
15

16. MG250 Missing Pulse Errors vs PS5100 Bright
and Dark Field Errors
16

17. MG250 Missing Pulse Errors vs MR Glide Errors
17

18. Correlation of Cert. Missing Pulse Errors
to PS5100 and MR Glide
Error Type Correlation
MR Glide Very Good (~85%)
PS5100 Good (~70%)
With Proper Adjustment
of Error Detection Thresholds
Overkill and Underkill is Minimized
18

19. MG250 Certification Errors vs. EPS Errors
19

20. Possible Test Sequence
Grade 1 PZT Glide Only
Pass disks
Optical Test Grade 2
and/or MR Glide PZT Glide Ceritify by Zone
Pass Disks
Fail Disks
20

21. One Estimate of Savings
Yield Time Savings Savings/Disk
Grade 1 15% 135 sec 20 sec
Grade 2 80% 15 sec 12 sec
Grade 3 5% 165 sec 8 sec
Total Savings 40 sec
21

22. Conclusions
 Correlation studies suggest that there is to sizeable
under and over-rejection to have Optical or MR glide
replace traditional glide and certification testing
 If over-rejection is minimized valuable yield and
throughput benefits can be obtained with appropriate
sequential testing
 These tests should also improve isolation of critical
defects such as scratches, TA’s, and shallow defects
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