Introduction. The successful implementation of copper electroplating in the metallization of chip...
1
Introduction. The successful implementation of copper electroplating in the metallization of chip interconnect structures derives from the use the electrolyte additives to affect the local deposition rate. The additives compounds added in copper plating solution to improve deposit properties are consumed on wafer surface and suppress the kinetics of Cu deposition. Since interior location of trenches and vias are less accessible to any additives, less suppression of the reaction kinetics occurs there, causing higher deposition rates and supperfilling of trenches and vias . Objectives of initial stage of copper electroplating study were: •Evaluation of copper electroplating features in commercial electrolytes used within electroplating process •Estimation of the effect of wafer density patterning (M1 and V1) on the electrochemical characteristics of copper electrodeposition. •Determination of the effect of additives additions (accelerator, suppressor and leveler) on electroplating parameters Two types of acid copper electrolytes were examined: 1- low copper content & high acidity (pH 0.7) 2- high copper content & low acidity (pH 1.9) Electrolyte 1 Copper 17 g/L Sulfuric acid 180 g/L Chloride 50 ppm Accelerator 2.3 ml/L Suppressor 8 ml/L Leveler 1.5 ml/L Electrolyte 2 Copper 40 g/L Sulfuric acid 10 g/L Chloride 50 ppm Accelerator 2.3 ml/L Suppressor 8 ml/L Leveler 1.5 ml/L Three types of Cu seeded wafers supplied by Tower/Motorolla were used as substrate: • Blanket wafer • Trench pattern (M1 step) • Via pattern (V1 step) M1 V1 Techniques & Methods: Electrochemical Tests: Potentiostatic measurements; Galvanostatic measurements. Surface Examination: SEM, HRSEM, EDS Current-Voltage characteristic of Cu deposition from additives free electrolytes 10 -4 10 -3 10 -2 -0.4 -0.3 -0.2 -0.1 0.0 0.1 1 m V /s B lanket V1 M1 P o te ntia l (V SCE ) C urrent (A /cm 2 ) Electrolyte 1 Electrolyt e 2 10 -4 10 -3 10 -2 -0.4 -0.3 -0.2 -0.1 0 .0 0 .1 1 m V /s B lanket V1 M1 P o te n tia l (V SCE ) C urren t (A /cm 2 ) The study of electrochemical characteristics of copper deposition was performed in 3-electrode electrochemical cell equipped with Pt counter electrode and saturated calomel reference electrode: Blanket wafer 10 -5 10 -4 10 -3 10 -2 -0.2 -0.1 0.0 Supp+Lev+Acc Supp+Lev Supp w ith ou t ad d itives P oten tial(V SCE ) C urrent(A /cm 2 ) 1 m V /sec The effect of additives on current-voltage profile of Cu in high acidic electrolyte. 0 100 200 300 400 500 -0.3 -0.2 -0.1 0.0 W ith o u t S up p re sso r 10m A /cm 2 S u p pre sso r: 2 m l 4 m l 6 m l 8 m l P o te n tia l (V S.C.E. ) T im e (sec) The effect of additives 0 100 200 300 -0.3 -0.2 -0.1 0.0 1 .5 m l/l 1 .0 m l/l 0 .5 m l/l WithoutLeveler 10m A /cm 2 P otential(V SCE ) T im e (sec) Leveler The effect of current density on Cu deposition characteristics in electrolyte 1 with additives M1 V1 Accelera tor SEM micrographs filled trenches and squares (face view ) Suppresso r 0 100 200 300 -0.08 -0.06 -0.04 2.3 m l/l 1.0 m l/l 0.5 m l/l W ith ou t A ccelerato r 10m A /cm 2 P o te n tia l (V SCE ) T im e (sec) Accelerato r embedded sludge localized area w/ missing Cu • Defects detectible under direct, e.g. visual, optic and SEM examination • Hidden defect: voids The effect of pattern density on Cu deposition characteristics 0 200 400 600 800 1000 0.00 0.02 0.04 2 m A /cm 2 B lanket M1 V1 P o te n tia l (V SCE ) T im e (sec) Electrolyte 1 without additives 0 200 400 600 -0 .2 5 -0 .2 0 -0 .1 5 -0 .1 0 -0 .0 5 4 2 10 m A /cm 2 1 m A /cm 2 P o te n tia l (V SCE ) T im e (sec) 0 200 400 600 -0.25 -0.20 -0.15 -0.10 -0.05 10 m A /cm 2 4 2 1 m A /cm 2 P o te n tia l (V SCE ) T im e (sec) Electrolyte 2 & 10 mA/cm2 1 min 2 min 1 min Filling features in additives containing Cu electrolytes 10 -5 10 -4 10 -3 10 -2 -0.2 -0.1 0.0 Supp A ccel P otential(V SCE ) C urrent(A /cm 2 ) Suppresso r Cu seed 2e - Cu 2+ • The effects of pattern density (M1 and V1) and additives on the electrochemical characteristics of Cu plating in high- and low-acidic electrolytes were determined • Current-voltage working windows for Cu-plating were defined. The current range of up to 10 mA/cm2 was established to be safe. The copper surface potential in this range remains above -0.28 V (SCE) , i.e. voids formation due to hydrogen evolution is avoided • It is possible to accurately control features’ filling in the current range established Conclusions: Electrolyte 2 &Blanket M1 and V1 wafers were presented by different pattern density and aspect ration. The combined action of the all three additives are provided inhibition of the Cu deposition reaction relative to additive free electrolyte, although an acceleration of the Cu deposition relative to the suppressor and suppressor&leveler additives electrolytes. Voltage/time curves in galvanostatic mode are shown the small shift in potential in the first few second of Cu electrodeposition onto blanket and patterned wafers from additives free electrolyte. These potential changes likely relate to initial nucleation and surface morphology changes. Voltage/time curves are presented more polarized values of voltages at initiation of Cu deposition for M1 and V1 patterned wafers in electrolyte with additives than in electrolyte without additives. This increase in cathodic potential is provided by suppression of Cu deposition by additives. After several seconds the cathodic potential is decreased and depolarization effect occurred over a longer period of time . This effect is increased with metal lines density and disappeared with increasing of current density. Patterned wafer specimen with M1 and F1 seed layer after copper electrodeposition from low acid electrolyte by current density 10mA/cm2 ,deposition time 1 ,2 minutes. • Swirl defects Single pit • Pits clusters Missing via • Embedded defects Localized protrusion defects (LPDs) Main electrochemical causes of defects : • Poor wetting of seed layer at the electroplating start • Particles trapped in trenches and vias (sludge) • Sporadic, localized growth due to organic additives Detectable Defects: Large molecules of suppressor adsorbs preferentially on the outside of trenches &vias and inhibits of Cu electrodeposition. Accelerator accumulated inside of trench and vias of smaller features and accelerated the deposition reaction at the bottom of trenches and vias.
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Transcript of Introduction. The successful implementation of copper electroplating in the metallization of chip...
Introduction.The successful implementation of copper electroplating in the metallization of chip interconnect structures derives from the use the electrolyte additives to affect the local deposition rate. The additives compounds added in copper plating solution to improve deposit properties are consumed on wafer surface and suppress the kinetics of Cu deposition.Since interior location of trenches and vias are less accessible to any additives, less suppression of the reaction kinetics occurs there, causing higher deposition rates and supperfilling of trenches and vias . Objectives of initial stage of copper electroplating study were: •Evaluation of copper electroplating features in commercial electrolytes used within electroplating process•Estimation of the effect of wafer density patterning (M1 and V1) on the electrochemical characteristics of copper electrodeposition.•Determination of the effect of additives additions (accelerator, suppressor and leveler) on electroplating parameters
Two types of acid copper electrolytes were examined:
1- low copper content & high acidity (pH 0.7) 2- high copper content & low acidity (pH 1.9)
Electrolyte 1 Copper 17 g/LSulfuric acid 180 g/LChloride 50 ppmAccelerator 2.3 ml/LSuppressor 8 ml/LLeveler 1.5 ml/L
Electrolyte 2 Copper 40 g/L Sulfuric acid 10 g/L Chloride 50 ppm Accelerator 2.3 ml/L Suppressor 8 ml/L Leveler 1.5 ml/L
Three types of Cu seeded wafers supplied by Tower/Motorolla were used as substrate:• Blanket wafer• Trench pattern (M1 step)• Via pattern (V1 step)
M1 V1
Techniques & Methods:Electrochemical Tests:Potentiostatic measurements;Galvanostatic measurements.
Surface Examination: SEM, HRSEM, EDS
Current-Voltage characteristic of Cu deposition from additives free
electrolytes
10-4 10-3 10-2
-0.4
-0.3
-0.2
-0.1
0.0
0.11 mV/s
Blanket V1 M1
Pote
ntia
l (V S
CE)
Current (A/cm2)
B B B
Electrolyte 1
Electrolyte 2
10-4 10-3 10-2
-0.4
-0.3
-0.2
-0.1
0.0
0.11 mV/s
Blanket V1 M1
Pote
ntial (
V SC
E)
Current (A/cm2)
B D F
The study of electrochemical characteristics of copper deposition was performed in 3-electrode electrochemical cell equipped with Pt counter electrode and saturated calomel reference electrode:
Blanket wafer
10-5 10-4 10-3 10-2
-0.2
-0.1
0.0
Supp+Lev+AccSupp+Lev
Supp
withoutadditives
without additives 8 ml/l Suppressor
B D F H
Pote
ntia
l (V S
CE)
Current (A/cm2)
1 mV/sec
Polarization curve for copper deposition from 17 g/l Cu+2electrolyte with suppessor
The effect of additives on current-voltage profile of Cu in
high acidic electrolyte.
0 100 200 300 400 500
-0.3
-0.2
-0.1
0.0Without Suppressor
B B B B B
Influence of suppersor on copper deposition from low acid electrolyte.10mA/cm2
Suppressor: 2 ml 4 ml 6 ml 8 ml
Po
ten
tia
l (V
S
.C.E
.)
Time (sec)
The effect of additives
0 100 200 300
-0.3
-0.2
-0.1
0.0
1.5 ml/l
1.0 ml/l
0.5 ml/l
Without Leveler
Leveling influence on copper deposition from low acid electrolyte
10mA/cm2
Leveler (ml/l) 0 0.5 1 1.5
Pote
ntial (V
S
CE)
Time (sec)
Leveler
The effect of current density on Cu deposition characteristics in electrolyte 1 with additives
M1
V1
Accelerator
SEM micrographs filled trenches and squares (face view )
Suppressor
0 100 200 300
-0.08
-0.06
-0.042.3 ml/l
1.0 ml/l
0.5 ml/l
Without Accelerator
10mA/cm2
Pote
ntial (V S
CE)
Time (sec)
Accelerator ( ml/l) 0 0.5 1 2.3
Accelerator
embedded sludge
localized area w/ missing Cu
• Defects detectible under direct, e.g. visual, optic and SEM examination
• Hidden defect: voids
The effect of pattern density on Cu deposition characteristics
0 200 400 600 800 1000
0.00
0.02
0.042 mA/cm2
Blanket M1 V1
Pote
ntial (V
S
CE)
Time (sec)
Electrolyte 1 without additives
0 200 400 600
-0.25
-0.20
-0.15
-0.10
-0.05
4
2
10 mA/cm2
1 mA/cm2
1 mA/cm2
2mA/cm2
4mA/cm2
10mA/cm2
Pote
ntial (V S
CE)
Time (sec)
17 g/l Cu+2 electrolyte with additivesV1 seed layer0 200 400 600
-0.25
-0.20
-0.15
-0.10
-0.05
10 mA/cm2
4
2
1 mA/cm2
1mA/cm2
2mA/cm2
4mA/cm2
10mA/cm2
1mA/cm2
2mA/cm2
4mA/cm2
10mA/cm2
Pote
ntial (V
S
CE)
Time (sec)
17 g/l Cu+2 electrolyte with additivesM1 seed layer
Electrolyte 2 & 10 mA/cm2
1 min
2 min
1 min
Filling features in additives containing Cu electrolytes
10-5 10-4 10-3 10-2
-0.2
-0.1
0.0
Supp
Accel without additives 8 ml/l Suppressor
D B ### ###
Pot
entia
l (V
SC
E)
Current (A/cm2)
1 mV/sec
Polarization curve for copper deposition from 17 g/l Cu+2electrolyte with suppessor
Suppressor
Cu seed
2e-
Cu2+
• The effects of pattern density (M1 and V1) and additives on the electrochemical characteristics of Cu plating in high- and low-acidic electrolytes were determined
• Current-voltage working windows for Cu-plating were defined. The current range of up to 10 mA/cm2 was established to be safe. The copper surface potential in this range remains above -0.28 V (SCE) , i.e. voids formation due to hydrogen evolution is avoided
• It is possible to accurately control features’ filling in the current range established
Conclusions:
Electrolyte 2 &Blanket
M1 and V1 wafers were presented by different pattern density and aspect ration.
The combined action of the all three additives are provided inhibition of the Cu deposition reaction relative to additive free electrolyte, although an acceleration of the Cu deposition relative to the suppressor and suppressor&leveler additives electrolytes.
Voltage/time curves in galvanostatic mode are shown the small shift in potential in the first few second of Cu electrodeposition onto blanket and patterned wafers from additives free electrolyte. These potential changes likely relate to initial nucleation and surface morphology changes.
Voltage/time curves are presented more polarized values of voltages at initiation of Cu deposition for M1 and V1 patterned wafers in electrolyte with additives than in electrolyte without additives. This increase in cathodic potential is provided by suppression of Cu deposition by additives. After several seconds the cathodic potential is decreased and depolarization effect occurred over a longer period of time . This effect is increased with metal lines density and disappeared with increasing of current density.
Patterned wafer specimen with M1 and F1 seed layer after copper electrodeposition from low acid electrolyte by current density 10mA/cm2 ,deposition time 1 ,2 minutes.
• Swirl defects Single pit• Pits clusters Missing via• Embedded defects Localized protrusion defects (LPDs)
Main electrochemical causes of defects :• Poor wetting of seed layer at the electroplating start• Particles trapped in trenches and vias (sludge)• Sporadic, localized growth due to organic additives
Detectable Defects:
Large molecules of suppressor adsorbs preferentially on the outside of trenches &vias and inhibits of Cu electrodeposition.
Accelerator accumulated inside of trench and vias of smaller features and accelerated the deposition reaction at the bottom of trenches and vias.
