trench effects in copper electroplating student: oleg gurinovich industry: novellus systems advisor:...
TRANSCRIPT
Trench Effects in Copper Electroplating
Student: Oleg Gurinovich Industry: Novellus SystemsAdvisor: Dr. Stacy Gleixner John Kelly, Jim Stimmell, Chiu ChiInstructor: Dr. Richard Chung TFI: Bill Gadson
Mate 198B Spring 2001
Research Objectives & Motivations
• Study variations in critical dimensions (CDs) of trenches during damascene process (lithography and etching steps)
• Study how variations in CDs affect electroplating performance by measuring electrical resistance of copper interconnects
• More companies switch to copper as a material choice for interconnects
• Strong correlation between to be filled feature size and electroplating bath chemistry
Why Use Copper and Electroplating?
• Interconnect lines density increase
• Need for more conductive and reliable material
• Relatively low cost of the process
• High speed of deposition
• High quality of the deposited film for well-optimized process
• Electroplated copper has good electromigration characteristics
Steps in Damascene Process
• Lithography
• Etching
• Diffusion Barrier Deposition (Ta, TiN, TaN)
• Seed Layer Deposition (Cu)
• Electroplating
• Chemical-mechanical Polishing
Electroplating Scheme
CuSO4+H
2O+H
2SO
4 + additives
Cathode (Wafer):
Cu2+ + e- = Cu+
Cu+ + e- = Cu0
Anode:
4OH-=O2+ 2H
2O + 4e-
2H 2O=O
2+ 2H+ +2e-
Electroplating Bath Additives
Brighteners
• accelerate Cu deposition at sites where present 4,5-dithiaoctane-1,8-disulphonic acid (SCH
2CH
2CH
2SO
3H)
2
Levelers
• adsorb at high-charge density sites organic compounds containing nitrogen Suppressing agents
• create uniform diffusion layer Example: polyethylene glycol, (C
2H
4O)
n
Experimental Procedure
• Measure width of 0.25 m trenches after lithography and etch steps to find variance in the trench width introduced by these two processes
• Measure electrical resistance of copper interconnects to find how actual trench size variations affect electroplated copper characteristics
Trench Width MeasurementsEquipment used: Top-down SEM, Hitachi-S6780
• Precision measurements were performed -random trench was selected -same trench was measured 25 times -SD was found 0.00273 m
Trench width distribution, lithography
0.23
0.24
0.25
0.26
0.27
0.28
0.29
0 2 4 6 8 10 12 14 16 1820 22 24 26 28 3032 34 36
Measurement point
Tre
nch
wid
th,
mic
ron
s
Series1
Trench width distribution, etching
0.15
0.16
0.17
0.18
0.19
0.2
0.21
0.22
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Measurement point
Tre
nch
wid
th,
mic
ron
s
Series1
Measurements Data
Width is distributed around mean value of 0.257 mNo significant trend
Trend is observed, central dies on the wafer have wider trenchesafter etching step
Trench Width After Etch Step
0.2380.240.2420.2440.2460.2480.250.2520.2540.256
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Measurement point
Tren
ch w
idth
, mic
rons
W1
W2
W3
W4
After-etching measurements
Discussions
• Lithography step doesn’t introduce special cause variation -data distribution does not show significant trend -mean value 0.257 m, SD is 0.0114 m
• Etching step does have special cause variation
-central area of the wafer is etched more than edges -account for this effect during electrical resistance measurements -mean trench width after etching 0.2454 m, SD is 0.00574
• Need to be aware of lithography defects while analyzing resistance data
Conclusions
• Etch step may affect electrical resistance of copper interconnects
• Based on the literature research, bath additives concentrations will affect trench fill capability
• Lithography step do not affect overall trench width distribution
• Measuring procedure (map) is developed