advances in disk metrology

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Advances in Disk Metrology

Robert Kertayasa Zeta Instruments March 2011

http://www.zeta-inst.com/




Agenda

• Introduction

• Technology

• Sample Results

• Other Applications

• Summary

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Introduction

Challenges in Data Storage Metrology





Cost of Data Storage is going DOWN! Yeah, we knew that!

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10 cents / GB

HDD is still ahead of the game compared to SSD. SSD is not a cost effective solution for the everyday user

Courtesy : Frys.Com website

How do we maintain our competitive edge over SSD while keeping up quality and reliability?

SSD drive not available

Data Storage Trends

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Fly height was 25nm in 1999 In 2011 it is ~ 2nm

Magnetic Spacing is decreasing as the areal density is increasing.

• Disk roughness 1Å Ra

• TPI (tracks per inch) is increasing

• Read write heads are flying lower than ever

• Higher percentage of the disk is being used to write data with the advent of ramp load / unload

• Data Zones are being pushed to the very edge of the hard disk surface

Challenges - Disk

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• Stylus profilers and interferometers have been traditionally used in disk metrology, to measure surface roughness, disk edge roll-off (dub-off)

• Defect inspection tools have been used to detect defects and bin them out by size

• New challenges

• Drive performance at the very edge of the disk is governed in part by the edge chamfer

profile – there is a urgent need for a chamfer metrology solution • Defects detected on the disk are channeled through a time consuming Failure Analysis

process, via optical microscope inspection, AFM and SEM. Given the short product life

cycles, there is a need to reduce the “time to defect resolution”

Challenges – Drive FA

• Modern disk drive have a lot of mission critical components that are beyond the measurement capability of the current metrology toolset

• Some examples

• Defects on the HGA

• Defects on the drive casing

• Ramp wear

• Lube pickup on read/write heads

• There is a need to create a Complete Metrology solution for the drive industry, that will help detect and measure defects that can measure from nanometers to millimeters

• complementary solution for high resolution instruments such as AFMs and SEMs

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Zeta Technology

Chamfer Metrology Solution





Zeta-CM 3D Imaging and Metrology Microscope for Data Storage Applications

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Disk Chamfer Measurement technique

On the Zeta-CM, disks can be tilted for optimal imaging of the chamfer. For example, a disk with a nominal 45°chamfer can be tilted to 45°. The chamfer will be in the horizontal plane for optimal 3D measurement. The Zeta-CM then scans the chamfer over a specified vertical range to generate a 3D image. Both OD and ID of the disk can be inspected with this technique.

Multiple slices are used to create the 3D view

q q Can be selected to optimize chamfer imaging

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Limitations of 2D Microscopy Typical Microscope Image from a µscope without 3D

Top view of the chamfer – 50X

Data Zone Chamfer Side Wall

When viewing the chamfer using a 2D microscope, one has to use a high powered objective. The chamfer goes out of focus as it rolls-off due to depth of focus (DOF) limitation. Engineers typically use 10X objectives for a higher DOF and wider field of view. However, it is not possible to get height or angle information using a small magnification.

470µm

35

0µ

m

Conventional “2D” Microscope cannot image the Chamfer


Disk Chamfer – Zeta-CM view

2D Microscope view Top view of the chamfer – 20X

Zeta 3D Image view After scanning the chamfer

On the Zeta-CM, a lower magnification can be used to capture a larger portion of the chamfer. In this case a 20X objective has been used.

1170 µm

88

0 µ

m

Ch

amfe

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Sid

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all

(no

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sib

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Dat

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Comparison of 3D metrology techniques


AFM STYLUS PROFILER ZETA INTERFEROMETERCONFOCAL

MICROSCOPE

Large vertical range > 1mm No Yes Yes Yes Yes

High Z resolution over the large range ~ sub-µm No Yes Yes Yes Yes

Very low reflectivity surface < 1% reflectivity Yes Yes Yes Yes Yes

Very high reflectivity surface > 90% reflectivity Yes Yes Yes Yes Yes

Very high roughness surface > 100µm Rpv No Yes, BUT! Yes No No

Large area imaging - single image > 200µm X 200µm No Yes, BUT! Yes Yes Yes

Large area imaging - stitching mm X mm No Yes, BUT! Yes Yes Yes

Speed of data acquisition < 1 min per scan No No Yes Yes Yes

True color imaging distinguish contaminants No No Yes No Sometimes

Cost of ownership LOW! No No Yes No No

Attribute

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Results Chamfer Metrology

Disk Drive Defects





Chamfer Image Comparison 3 different vendors

•Chamfer • Rough with some ridges

• Side wall • Rough

Vendor A Vendor C Vendor B

•Chamfer • Smooth

• Side wall • Slightly Rough

•Chamfer • Very rough with lots of

ridges

• Side wall • Smooth


Disk Chamfer – Analysis

Two measurement cursors for feature width and step height measurement. The roughness between the two cursors is also reported in a separate log.

Markers for feature angle and single point height and width information

Chamfer width = 195.13µm

Marker 1

Marker 2

Marker 3 Marker 4

Cu

rser

Pai

r 1

Cu

rser

Pai

r 2

Marker 1-2 angle = 43.5°

Marker 3-4 angle = 6.9°

Since the disk was rotated by 45°, actual slope of the chamfer is 51.9°


Chamfer Parameter Comparison 3 different vendors

Vendor A Vendor C Vendor B

Comparison of the multiple cross-sections across the chamfer and side wall allows the users to quantify the chamfer parameters.


Chamfer roughness and defects


70nm protrusion defect in the chamfer zone Contamination at the edge/chamfer

Drive & Disk Failure Analysis - Today


Current “Time To Defect Resolution” ~ Hours

Disk Defect Inspection - Minutes

Defect Inspection – Minutes

Re-scan and Scribe - Minutes

Optical Microscope Inspection

Manual process - Minutes

AFM or Stylus Profiler

Finding correct site – minutes

Scan – Minutes to Hours SEM

Sample Prep / Destructive process – Minutes

Defect Imaging – Minutes to Hours

Drive & Disk Failure Analysis with Zeta


“Time To Defect Resolution” with Zeta ~ Minutes for most defects

Disk Defect Inspection - Minutes

Defect Inspection – Minutes

Re-scan and Scribe - Minutes

Zeta Metrology Microscope – Seconds to Minutes

Auto or semi-automated process – seconds to minutes

Defect Metrology for most defects that are of the order of nanometers to microns

AFM or Stylus Profiler (As needed) – Minutes to Hours

Finding correct site – minutes

Scan – Minutes to Hours

SEM (As needed) – Minutes to Hours

Sample Prep / Destructive process – Minutes

Defect Imaging – Minutes to Hours

Chamfer Defects: Chip on Glass Substrate.


Image taken with regular microscope Zeta-CM image

Higher resolution with quantitative height information


Defect on the side wall of a disk 0.1 micron chip

20um


Lube Pickup on a Read-Write Head Automated analysis to quantify lube pickup


Note : This is an example of a custom application for the data storage industry

Read-Write Head Analysis Measurement of the dimensions and surface roughness


Read-Write Head Analysis Full head analysis using the interferometer option


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Summary

A new technology for next generation Defect Metrology





Summary – Part 1/2


Summary – Part 2/2


Zeta Technology Summary

• 3D Imaging AND Metrology in one compact package

• Cost effective metrology solution for a broad range of applications

• Handles very high roughness, very low reflectivity

• True color imaging

• Flexible and easy to use software

• Custom applications developed for customers as required

• Example : Diamond counts, area, volume on a CMP pad conditioning disk

• Largest vertical scan capability in its class (from µm to mm)

• Non-contact, no consumable costs

• Optional Film thickness, Nomarski and Interferometer make the Zeta-20 a very versatile and powerful metrology and imaging tool


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References

Where would be without the Internet?





References & Courtesy

• www.Frys.com

• “Disk Drive Contamination and Defect Sensitivity Trends”

• Thomas M. Coughlin, Coughlin Associates, www.tomcoughlin.com

• Ramp Load/Unload Technology in Hard Disk Drives (White Paper)

• Patricia Kim & Mike Suk, HGST

• Western Digital White Paper – “Fly Height Monitor Improves Hard Drive Reliability”

• http://hddscan.com/doc/HDD_from_inside.html


http://www.frys.com/

http://www.tomcoughlin.com/

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BACKUP





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Conventional Microscope (2D Only)

Zeta Images (2D & 3D)

• CCD Color Camera

• Digital camera to capture sample images and focus map data

• Zeta Optics Module

• Focus map signal generator

• High intensity white light LED to preserve sample color

• High efficiency optics design to optimize illumination

• Z-drive

• Precision mechanism for sub-micron vertical resolution

• Zeta Control Box

• FMM and Z-drive electronics controller

• XY Stage

• Convenient sample positioning

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Conventional microscopes have a very limited depth of focus. Test surfaces and features are clearly visible ONLY when they are

within the focal depth . The Zeta system scans a sample over a user specified vertical (or Z) range. At each Z position, it records the XY

location and the precise Z height of the pixels using the Zeta Optics Module. This

information is used to create a true color 3D image and a 2D composite image. The resulting image has a extended depth of focus so the entire surface is seen clearly. The Zeta 3D software

can be used to ascertain dimensional and roughness information

Zeta Technology


Note that the chamfer may have 2 discrete angles in some cases

Disk Chamfer Parameters

Data Zone Chamfer

Mean Chamfer Angle

Important Chamfer Parameters • Projected Chamfer Width

• Affects flying characteristics of the read write head at the disk edge. • Affects the available data zone closer to the disk edge. • Affects disk clamping at the ID and vibration / stability at run time

• Mean Chamfer Angle • Critical for proper handling of the substrate during the disk manufacturing

process. Affects the uniformity of the films deposited near the edge. • Chamfer Roughness & Finish

• Improper chamfer finish may leave residue or defects that will affect long term drive reliability


Current Measurement Methodology

Measurement Current Technique Challenges

Chamfer Width Measured using optical microscope and dark field illumination.

Limited field of view. Not automated. Manual process, not very repeatable.

Chamfer Angle

Measured using a Shadow Graph at some substrate manufacturers.

Shadow does not define the chamfer accurately. Only large variations in chamfer angle can be captured, finer variations cannot be captured.

Chamfer Roughness No method available at present. Measuring the roughness on a surface with a varying slope

Chamfer Defects

Visual inspection using microscope.

Very subjective, current methodology does not allow accurate sizing, binning or classification of the defects.

Roll-Off Disk inspection tool, Interferometer

Cannot correlate between tools. Cannot get accurate disk center and edge information. Not enough depth of field.

Zeta

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advances in disk metrology

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