ISSM 2012
Electrochemical Induced
Pitting Defects at Gate
Oxide Patterning
Jungtae Park
Sr. Engineer of Defect Analysis Team
Samsung Electronics Co., LTD
YE-O-055
jtpark@samsung.com
ISSM 2012
1G-Number
Yield Loss Mechanism in
Leading-Edge Fabs
Root cause of yield loss in leading-edge fabs:
Physical Defects
• Pits
• Scratches
• Particles • Bridging
Defect
Found
No
Defect
Found
Non-Visual Defects
Residues
Charge
• Organic
• Surface
• Metallic
• Trapped
Up to 30% of yield loss in today’s fabs are not traceable to physical
defects, and the root cause for these yield issues are due to NVDs.
ISSM 2012
2G-Number
Yield Loss Mechanism in
Leading-Edge Fabs
ChemetriQ® Inspection System uses a
scanning surface potential difference
technique to detect changes in materials
and/or charge on the wafer surface
ChemetriQ Data
Charge Map
Radial
Charge
Profile
Defect Map / KLARF
Image &
Threshold
Analysis
0
-500
Charge Value (mV)
-1000
-1500
-2000
-2500
-3000
-3500
-4000
-4500
-5000
-150.0
-100.0
-50.0
0.0
50.0
100.0
150.0
Radial Position (mm)
Reference: K. Höppner, et al; Advanced Semiconductor Manufacturing Conference;
Novel In-Line Inspection Method for Non-Visual Defects and Charging, (2009)
ISSM 2012
3G-Number
Physical Defect Detected
with BF Inspection
Process flow
Resist coat
• Post etch and clean inspection (ACI)
• BF inspection detected physical defects
Exposure
• Defects primarily located on edge side
Develop
• SEM review highlighted Si pitting defects
ADI Inspection
LAL Oxide Etch
Pitting Defect
Resist Strip &
Wet Clean
ACI Inspection
ISSM 2012
BF Defect Map
SEM Image
4G-Number
Pitting Defect Correlates
to End of Line Yield

Defect maps showed strong correlation to
end of line yield – but no tool commonality

Only difference was p-Type pitting on left
side of wafer, n-Type pitting on top of wafer

Conclusion is that the defect was a process
induced defect – but which process?
p-Type
n-Type
BF Defect Maps – Multiple Lots, Multiple Process Tools
ISSM 2012
5G-Number
Correlating ADI Charge to
ACI Pitting Defects
p-Type
ChemetriQ
Charge Map (ADI)
ChemetriQ
Defect Map (ADI)
BF Inspection
Defect Map (ACI)
SEM Review
Image (ACI)
> +4.0V
charge results
in high risk of
p-Type pitting
n-Type
Pitting Defect
< -2.5V
charge results
in high risk of
n-Type pitting
Pitting Defect
ISSM 2012
6G-Number
--------
Physical Model
++++
+
resist
p
1 n
silicon
+ +
+ - +
a - -- --+
resist
c
1.
Resist charge induced at ADI
causes carrier redistribution
2.
Immersion of the wafer in a
wet chemistry causes:
a) Charged regions to become
neutralized by liquid
b) Current flow in substrate as
carriers redistribute
c) Etch in presence of current
begins pore formation
++++
+
i
b
2
+ resist
-
+
+
+ - +
3.
3
ISSM 2012
Once carriers redistributed,
no more current flows and
pore formation stops
7G-Number
Modeled Potential
at Equilibrium
N
Simulation Results

We simulated carrier flow in junction
under influence of applied potential

Added a 0.01V bias to the N-Si surface
and modeled the carrier distribution

The bias was then removed (simulating
charge removal in the liquid)

A 1.19mA current flow was induced
across the junction

Assuming a pore size of ~100nm
P
Potential w/ 0.01V at
N-silicon surface
N
P
N carrier conc.
(mol/m3) w/ 0.01V
P carrier conc.
(mol/m3) w/ 0.01V
– This represents ~30mA/cm2
– vs. 2mA/cm2 required for pore formation

ISSM 2012
Current duration proportional to
junction resistance / capacitance (~1ms)
8G-Number
Precursor NVDs can lead
to  Physical Defects
Resist
+ + + +
+ + + +
+ + + +
+ + + +
Substrate
Resist
Coat
Expose
& Develop
LAL Oxide
Etch
Resist Strip
& Wet Clean
Resist Charging
ACI Inspect
(Pitting Defect)
Pitting Defects
Precursor NVDs
A physical defect may be caused by an NVD at a previous
process, which may be multiple steps back in the process flow
ISSM 2012
9G-Number
Conclusion

Resist charge (NVD) can lead to pitting
defects on the Si due to an electrochemical
ER effect – referred to as a Precursor NVD

This defect can occur on both p-type
devices with (+) resist charge as well as
n-type devices with ( ̶ ) resist charge

This is consistent with an accelerated
electrochemical etch of Si due to etch in
presence of a current supplied by carrier
redistribution in charged resist regions.
ISSM 2012
10
G-Number