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Deposit Thickness Distribution by Sj8eTJ

VIEWS: 5 PAGES: 15

									   Modeling The Deposit Thickness
Distribution in Copper Electroplating of
 Semiconductor Wafer Interconnects
     Eugene Malyshev 1, Uziel Landau 2,
                   and
            Sergey Chivilikhin 1
                     1 L-Chem,
                             Inc
                Beachwood, OH 44122
                         and
        2 Department of Chemical Engineering,

           Case Western Reserve University,
                 Cleveland OH 44106
          AIChE Annual Meeting,San Fransisco, CA.
Objectives


• Analyze the effects of the different process
  parameters
• Provide a convenient (for non-expert users) &
  comprehensive tool for:
   Cell Design
   Scale-up
   Process Optimization
 Issues in Design
Deposit-
• Deposit thickness uniformity (+/- ~3% across the
 wafer)
• Minimal edge exclusion (<5 mm)
• Deposit texture/appearance
• Good gap-fill
• Extreme electrical/mechanical/chemical properties
Process-
• Stable
• Controllable
• Scalable
 Parameters Analyzed


• Cell Configuration (Dimensions, Edge gap, Shields)
• Flow (Rotation and Convective Flow)
• Seed Layer Thickness
• Electrolyte Composition
   Acid Concentration (Conductivity)
   Reactant Concentration (Mass-Transport)
   Additives (Kinetics/Polarization Curve)
• Operating Parameters: Current/Voltage
Cell “Generic” configuration

  Base Case: r = 100 mm, gap =10 mm
             i = 20 mA/cm2, K= 0.55 S/cm,
             seed thickness = 1000A
             rotation = 60 rpm
             impinging flow = 4 gpm
         60 rpm
HOLDER            WAFER                            HOLDER   WAFER      GAP
                            GAP

               100 mm
                                                             10 mm
                   10 mm
                             150 mm




                                                            Seed thickness

                                      Applied Voltage
 DISTRIBUTED FLOW = 4 gpm




                   ANODE
Flow effects
         Rotating Disk vs. Combined Flow




       Flow Map:                               Flow Map:
       Modified Design                         Base Case




                   0.0090
       Delta, cm




                   0.0075                      Base case


                   0.0060   Modified

                                            Levich eqn.
                   0.0045
                        0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
                                           r/R
Numerical comparison with analytical model

                      Model system: rotating disk,
                      r = 7 mm, Cb = 0.28 mole/L, D = 6.7*10-6 cm2/s
                      0.04
       Delta, cm

                      0.03               Cell-Design
                      0.02
                                                  Levich eqn.
                      0.01

                      0.00
                             0   1   2   3    4    5   6    7    8   9   10   11

                                             1/2 [rad/sec]1/2
       i lim, A/cm2




                      0.30
                                     Levich eqn.
                      0.20

                      0.10
                                                           Cell-Design
                      0.00
                             0   1   2   3    4    5   6    7    8   9   10   11

                                             1/2 [rad/sec]1/2
Effect of edge-gap

             Wafer r = 100 mm
             Simulated gaps: 5 mm, 10 mm, and 15 mm;
             Cb = 0.28 mole/L, D = 6.7*10-6;
             Impinging flow = 4 gpm

                   0.090
    i lim, A/cm2




                                                                    5 mm
                   0.070
                                                                    50 mm
                   0.050                                            100 mm
                                                                    150 mm
                   0.030
                           0   1   2   3   4   5   6   7   8   9   10
                                   Radial coordinate, cm
Resistive substrate effect
HOLDER                                                                    HOLDER       WAFER      GAP
                                 WAFER    GAP


                             100 mm
                                                                                        10 mm
                                  10 mm




                                              150 mm
                                                                                       Seed thickness

                                                           Applied Voltage
 DISTRIBUTED FLOW = 4 gpm


                                                           Seed thicknesses = 500, 1000 and 2000 Å.
                                                           iaverage = 10 and 40 mA/cm2. Wafer r = 100 mm.
                                  ANODE
                                                           Rotation = 60 rpm. Impinging flow = 4 gpm.
                                                           Cb= 0.28 mol/L, k = 0.55 S/cm, D = 6.7*10—6cm2/s.
     Current, A/cm2




                      0.08
                                                                                               500 Å
                                                                 iaverage = 40     mA/cm2      1000 Å
                      0.06                                                                     2000 Å
                                    no seed resistance
                      0.04
                                                                    iaverage = 10 mA/cm2       500 Å
                      0.02         no seed resistance                                          1000 Å
                                                                                               2000 Å
                      0.00
                             0     1      2            3   4    5     6      7     8    9   10
                                              Radial coordinate, cm
       Effect of edge-gap
                                60 rpm
                     HOLDER                WAFER



 i = 20 mA/cm2
 gap = variable                                                               Gap
 seed = 1000 A
                        DISTRIBUTED FLOW = 4 gpm




                                           ANODE

Deposit,   Gap = 0 mm           Deposit,    Gap = 10 mm          Deposit,     Gap = 50 mm
[micron]                        [micron]                         [micron]
 2.5                             2.5                               2.5
 2.0                             2.0                               2.0
 1.5                             1.5                               1.5
            150 sec                           150 sec                       180 sec
 1.0                             1.0                               1.0
 0.5                             0.5                               0.5
 0.0                             0.0                               0.0
       0 1 2 3 4 5 6 7 8 9 10          0 1 2 3 4 5 6 7 8 9 10            0 1 2 3 4 5 6 7 8 9 10
        Radial coordinate, cm            Radial coordinate, cm            Radial coordinate, cm

             1-3 time steps = 20 sec, 4-7 time steps = 30 sec
         Shield design




                 60 rpm                              60 rpm                               60 rpm
       HOLDER                              HOLDER                            HOLDER




         WAFER                               WAFER                             WAFER


         DISTRIBUTED FLOW = 4 gpm              DISTRIBUTED FLOW gpm
                                           DISTRIBUTED FLOW==44 gpm          DISTRIBUTED FLOW = 4 gpm



                       ANODE                              ANODE                                    ANODE

i, A/cm2                            i, A/cm2                          i, A/cm2
0.05                                0.05                              0.05
0.04                                0.04                              0.04      10% variation
0.03                                0.03                              0.03
0.02                                0.02                              0.02
0.01                                0.01                              0.01
0.00                                0.00                              0.00
       0 1 2 3 4 5 6 7 8 9 10              0 1 2 3 4 5 6 7 8 9 10            0 1 2 3 4 5 6 7 8 9 10
         Radial coordinate, cm               Radial coordinate, cm              Radial coordinate, cm
 200 mm wafer vs. 300 mm wafer
          60 rpm                       Seed thickness = 1000 Å.
HOLDER             WAFER
                             GAP       Cb= 0.28 mol/L, k = 0.55 S/cm, D = 6.7*10—6cm2/s.
                                                                                200 mm wafer
                100 mm
                                                             2.25




                                           Deposit, micron
                    10 mm                                    2.00       deposit(r/R=1) / deposit(r/R=0) =   1.646    180 sec
                                                             1.75                                                    150 sec




                              150 mm
                                                             1.50                                                    120 sec
                                                             1.25
                                                                                                                     90 sec
                                                             1.00
 DISTRIBUTED FLOW = 4 gpm                                    0.75                                                    60 sec
                                                             0.50                                                    40 sec
                                                             0.25                                                    20 sec
                                                             0.00
                                                                    0         0.2      0.4       0.6        0.8     1 r/R


                                                                                300 mm wafer
                150 mm                     Deposit, micron   2.25                                                    180 sec
                                                             2.00       deposit(r/R=1) / deposit (r/R=0) = 1.847
                    10 mm                                    1.75                                                    150 sec
                                                             1.50                                                    120 sec
                              150 mm




                                                             1.25                                                    90 sec
                                                             1.00                                                    60 sec
  DISTRIBUTED FLOW = 9 gpm                                   0.75                                                    40 sec
                                                             0.50                                                    20 sec
                                                             0.25
                                                             0.00
                                                                    0         0.2      0.4       0.6        0.8     1 r/R
             Electrolyte conductivity (pH)
                                                  200 mm wafer
Deposit,                                                         Deposit,
[micron]               k = 0.55 S/cm                             [micron]               k = 0.055 S/cm
 4.0                                                              4.0
 3.5       iaverage = 20 mA/cm2                                   3.5       iaverage = 20 mA/cm2
                                                                                                                       180 sec
 3.0       seedth = 1000 A                                        3.0       seedth = 1000 A
                                                                                                                       150 sec
 2.5                                                              2.5
                                                    180 sec                                                            120 sec
 2.0                                                              2.0
                                                    150 sec                                                            90 sec
 1.5                                                120 sec       1.5
 1.0                                                90 sec        1.0                                                  60 sec
                                                    60 sec                                                             40 sec
 0.5                                                40 sec        0.5                                                  20 sec
                                                    20 sec
 0.0                                                              0.0
       0         0.2      0.4         0.6   0.8    1                    0         0.2      0.4         0.6   0.8   1
                                r/R                                                              r/R

                                                  300 mm wafer
Deposit,                                                         Deposit,
[micron]               k = 0.55 S/cm                             [micron]               k = 0.055 S/cm
 4.0                                                              4.0
 3.5       iaverage = 20 mA/cm2                                   3.5       iaverage = 20 mA/cm2                       180 sec
 3.0       seedth = 1000 A                                        3.0       seedth = 1000 A                            150 sec
 2.5                                                              2.5                                                  120 sec
                                                       180 sec
 2.0                                                              2.0                                                  90 sec
                                                       150 sec
 1.5                                                   120 sec    1.5
                                                                                                                       60 sec
 1.0                                                   90 sec
                                                       60 sec
                                                                  1.0                                                  40 sec
 0.5                                                   40 sec     0.5                                                  20 sec
                                                       20 sec
 0.0                                                              0.0
       0         0.2      0.4         0.6   0.8    1 r/R                0         0.2      0.4         0.6   0.8   1 r/R

               High (normal) acidity                                                     Low acidity
Additives effect


 Current density,
      [A/cm2]
        0.043
        0.038
                         Pure copper sulfate
        0.033
                    (0.5 M, pH = 2, no additives )
        0.028
        0.023
                          With additives *
        0.018
        0.013
                0       0.2     0.4       0.6    0.8   1
                                    r/R
  * - Plating from copper sulfate in the presence of 70 ppm Cl - ,
     50 ppm SPS and 200 ppm Polyethylene glycol [‘PEG’] -
     (molecular weight = 4000 )
  Conclusions
• The effects of the various process parameters have
  been simulated
• The simulated results are in general agreement with
  observations. Some Specifics:
   • A proper shield design at the wafer edge significantly
     enhances uniformity
   • Electrode rotation has a larger effect than the convective
     flow (in the practiced range)
   • Wafer plating (macroscopic scale) does not typically operate
     under mass transport control
   • The edge-gap has a major effect on the flow and the
     current density near the wafer edge
   • The resistive seed effect is noticed mostly at higher current
     densities (~40 mA/cm2)
   • Scaling to 300 mm enhances the non-uniformity effects,
     unless compensating measures are taken,.

								
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