Transcript Wafer Probing for 3D Chips

KGD Probing of TSVs at 40 um Array Pitch
Ken Smith, Peter Hanaway, Mike Jolley, Reed Gleason, Chris
Fournier, and Eric Strid
• 3D-TSV Probe Technology Goals
• MEMS probe tip evolution
• Contact performance
• TSV pad damage (or lack thereof)
• Conclusions
3D-TSV Probe Technology
Development Goals
• Scale array pitch to 40 um
• Reduce pad damage to allow prebond probe
• Decrease cost of test
– Simplified, high yield process
• Fundamental understanding and accurate
models of contact performance
Pyramid Probe Technology
• RF filters, switches
• Process monitors
(including M1 copper)
• RFSOC Multi-DUT
3D Probing Requires a New Cost Structure
DRAM
& Flash
4
2
COGS/
pin ($)
in 2012
Logic/SoC
1
0.50
0.25
0.12
0.06
3
6
12
25
50
100
200
400
800
Array Pitch (um)
Technology must be printed, repairable, scalable, compliant
1600
Scaling a Probe Card
•
•
•
•
Decrease XYZ dimensions by K
Same materials
Decrease Z motions by K
Force per tip decreases by K2; tip pressure constant
100 um pitch
~10 gm/tip
35 um pitch
~1 gm/tip
3D TSV Probe Card Architecture
• Pyramid Probe ST: Pads on membrane
– Routing limitation ~3-4 rows deep from DUT
pad perimeter
• Replaceable contact layer
PCB
PCB
Plunger
Wafer
Replaceable Contact Layer
• Tips are 5 um
square and 20
um tall
• 35 um pitch
array
• 24 x 48 tips
Contact resistance versus probing
force
• Single 12 um square tip
• Sn plated wafer 5 um thick
Contact resistance versus probing
force
• 6 um tip
• Force required is similar to 12 um tip
Force (gm•f ) vs. Deflection (um)
• 1gm•f /um tip design
• High durometer elastomer
Force (gm•f ) vs. Deflection (um)
• 0.1 gm•f tip design
• Low durometer elastomer
Pyramid Probe ST Routing
• Unique fine-pitch routing
• High-frequency performance similar to Pyramid Probes
• Example is memory array
• – 50 um x 40 um pad pitch
• – 40 x 6 pad array
Fully routed 6x40 array with 40-50 um pitch
Optical photograph of probe mark array
• Marks are exceptionally
uniform
• ~1 gram / contact for
low pad damage
Profilometer scan of probe mark array
• Maximum depth 100 nm
• Maximum berm 500 nm
Probe marks on ENIG TSV pad
• Exaggerated conditions: 10 TDs at 2.5 gf
• Navigation grid (50 x 40 um) shows 3 probe
marks on the 100 um diameter pad
Probe mark depth less than surface roughness (~200 nm)
Probe mark on ENIG pad
• ~3 x 7 um
• Exposed Ni ~50%
• Depends on surface grains
Probe mark uniformity: Profilometer scans
• Depth: Mean 68, Stdev 11
• Berm: Mean 363, Stdev 76
TDR traces on open and short
• <40 ps rise / fall times (100 ps / div)
• Limited by routing density in ST
Conclusions
• Practical probe cards are capable of 40 um
pitch and tip forces below 1 gm
• Pad damage at these low forces is extremely
small with scrub marks less than 100 nm
deep
• Lithographically printed probe cards enable a
scalability path to lower cost and finer pitches
• Probing the TSVs is not out of the question