Evaluation of Low Pressure MEMS Probes - Semiconductor Wafer ...

June 7-10, 2009
San Diego, CA
Evaluation of Low Pressure MEMS
Probes
Probelogic Inc
Scott Clegg, Krzysztof Dabrowiecki
Probelogic
Shoichi Asanuma
TOTO
Darren James
Rudolph Technologies

Outline
• Design Review
– Specifications
– Resultant Design
• Design Evaluation
– Force vs deflection
– Life Tests
–Scrub
• Conclusion
June 7 to 10, 2009
IEEE SW Test Workshop 2

Design Specification
• User replaceable
probes
• Compatible with
existing technology
• Reliable solution
• Chose a buckling
beam type design
• Precision ceramics
June 7 to 10, 2009
IEEE SW Test Workshop 3

Standard
Machinable Ceramics Review
Hole Shape: Critical for fine-pitch hole integrity and reliability
All Hole Diameters:
0.11mm
Hole
Pitch:
0.15mm
Hole Pitch:
0.13mm
Test Die
Finer grain
ceramic
June 7 to 10, 2009
IEEE SW Test Workshop 4

Polycrystalline Drill Bits – Precision Drilling
Flat tool prepared on the drilling machine
OD: 0.035mm
1.2
工 具 径 の 精 度 とばらつき ~ 径 の 分 布 ~
Distribution of Tool OD
Frequency 確 率 密 度 関 Function 数 f(x)
1.0
0.8
0.6
0.4
0.2
0.0
June 7 to 10, 2009
30 31 32 33 34 35 36 37 38 39 40
工 具 径 [μm ]
(um)
IEEE SW Test Workshop 5

Surface Roughness of Inner Hole Wall
Standard
Surface roughness
of hole inner wall
Test Die
Ra (um)
Test
Die
Std.
0.1059
0.4433
June 7 to 10, 2009
IEEE SW Test Workshop 6

Upper Die Measurements
June 7 to 10, 2009
IEEE SW Test Workshop 7

Lower Die Measurements
Mechanical drilling of machinable ceramic
June 7 to 10, 2009
IEEE SW Test Workshop 8

Buckling Beam Review
Probe Made from 2mil Wire
Probe fabricated from 2mil wire
BCF~2gm/mil
High Stress
Concentrations
Limit Force and
Overdrive
Coined from wire
Coined from a slender wire.
Bending in curved section
June 7 to 10, 2009
IEEE SW Test Workshop 9

Observations Regarding
Standard Buckling Beam Probes
• Spring rate of probe is driven by
– Length and offset of coined section
– Width of coined section
• Stress concentrations
– Transitions
– Micro-hole constraints
• Pitch Limitation
– Wire size
– Cross-sectional length of coined section
June 7 to 10, 2009
IEEE SW Test Workshop 10

MEMs Probe Design
• Design Constraints
– Multiple layer photolithographic & plating process
– Minimize layer count
– Maximum stress less than ½ ultimate strength at
greater than 5mil OD
– Minimize cross-section for fine pitch applications
June 7 to 10, 2009
IEEE SW Test Workshop 11

• Long slender probe
–Three layers
• Fine pitch (less than
60um)
• Lower production costs
– Stress concentration
• Limits spring rate
–Low BCF
• 1.0 to 1.5 gm from 50um
to 75um OD
• Maximum 2.0 gm
Final Design
June 7 to 10, 2009
IEEE SW Test Workshop 12

Probe Tip Contact Force
No overdrive
2.5 mils overdrive
June 7 to 10, 2009
IEEE SW Test Workshop 13

Will Low Force Work?
• Build test vehicle
– Fully functional
– 60um pitch
• Evaluate
– Life time contact resistance
– Scrub
• Depth
• Alignment
June 7 to 10, 2009
IEEE SW Test Workshop 14

MEMs Probes
• Unique probe tip geometry
• Superior material properties
• Prime manufacturing tolerances
June 7 to 10, 2009
IEEE SW Test Workshop 15

Test Procedure
• Wafer scrub analysis
– Scrub wafer at 50um and 75um overdrive
– Measure scrub position and depth with
WaferWoRx 300
• CRES as a function of touch downs
– Measure test vehicle path resistance with PRVxII
– Scrub on wafer multiple times at 50um overdrive
– Periodically remeasure path resistance with
PRVxII
June 7 to 10, 2009
IEEE SW Test Workshop 16

Wafer Scrub Analysis
• Scrub wafer at 50um
and 75um OD
• Use WaferWoRx 300
system
– Measure scrub depth
profiles
– Measure scrub position
June 7 to 10, 2009
IEEE SW Test Workshop 17

Wafer Scrub Analysis
June 7 to 10, 2009
IEEE SW Test Workshop 18

Wafer Scrub Analysis
June 7 to 10, 2009
IEEE SW Test Workshop 19

Wafer Scrub Analysis
June 7 to 10, 2009
IEEE SW Test Workshop 20

Wafer Scrub Analysis
June 7 to 10, 2009
IEEE SW Test Workshop 21

Wafer Scrub Analysis
June 7 to 10, 2009
IEEE SW Test Workshop 22

Summary of Readings
• Scrub depth – 0.18um ± 0.03um (one sigma)
• Scrub length – 15um ± 7um (one sigma)
• Scrub width – 12um ± 4um (one sigma)
• Scrub alignment – 7um ± 4um (one sigma)
Comments:
All measurements at 75um OD
Probe tip width 8um
Rejected alignment outliers
June 7 to 10, 2009
IEEE SW Test Workshop 23

Life Testing: CRES
June 7 to 10, 2009
IEEE SW Test Workshop 24

Conclusion
• Design constraints led to low force probe
design with maximum force of ~2gm
• Probe penetrates wafer .18um for 75um OD
yielding good wafer contact
• Small probe tip contact with hard plated metal
yields low, consistent, and stable CRES
• Path resistance drops to less than 2 Ohms
when probing aluminum wafer
• New drill technology and machinable ceramic
material aids in improved alignment accuracy
June 7 to 10, 2009
IEEE SW Test Workshop 25

• Rod Doe
Acknowledgements
– Senior Engineer
– Rudolph Technologies
• Shoichi Asanuma
- TOTO Advanced Ceramics
• Additional data
regarding hard
ceramics will be
presented during
Wednesday morning
session
June 7 to 10, 2009
IEEE SW Test Workshop 26