Abs. 604, 204th Meeting, © 2003 The Electrochemical Society, Inc.
Detection of Accelerator Breakdown Products in Copper Plating Baths 10
M. Pavlov, E. Shalyt, P. Bratin and D. M. Tench ECI Technology, Inc. 1 Madison Street, East Rutherford, NJ 07073
Ar (mC)
6 2.0 ppm MPS
4 1.0 ppm MPS 0.5 ppm MPS 1.0 ppm SPS VF UF
2
0 0
2
4
6
8
10
12
14
16
CVS Cycle Number
Fig. 1
Plot of Ar as a function of CVS cycle number for acid copper supporting electrolyte containing SPS, Viaform™ or Ultrafill™ additives, and various concentrations of MPS. 10 MPS Concentration 2.0 ppm
A (mC) r
8
1.0 ppm
6
0.5 ppm
4 0.25 ppm
2
0 0
0.2
0.4
0.6
0.8
1
Log (CVS Cycle Number)
Fig. 2
Plot of Ar vs. Log (cycle number) as a function of MPS concentration. 1 0 -1 -2
r
Slope of A vs. Log Cycle Number
Acid copper sulfate baths are employed in the "Damascene" process1 to electrodeposit Cu within fine trenches and vias in dielectric material on semiconductor chips. Two organic additives are required to provide bottom-up filling of the Damascene features. The "suppressor" additive, which is typically high-molecular-weight (MW) polyethylene glycol (PEG), adsorbs strongly on the Cu cathode surface, in the presence of chloride ion, to form a film that sharply increases the overpotential for Cu deposition. The "anti-suppressor" or “accelerator” additive counters the suppressive effect of the suppressor to provide the accelerated deposition within trenches and vias needed for bottom up filling. Close organic additive control needed for Damascene plating is provided by Cyclic Voltammetric Stripping (CVS) analysis, which involves alternate plating and stripping of Cu at a Pt rotating disk electrode. The additives are detected from the effect that they exert on the electrodeposition rate measured via the Cu stripping peak area (Ar). The accelerator concentration is typically determined by the linear approximation technique (LAT) or modified linear approximation technique (MLAT).2 During Damascene Cu plating, however, the accelerator species breaks down into species that may interfere with the electrodeposition process. These accelerator breakdown products must also be controlled if high quality Damascene deposits are to be consistently obtained. This paper describes a CVS method for detecting the mercaptopropanesulfonic acid (MPS) breakdown product of the bis(sodiumsulfopropyl)disulfide (SPS) additive that is widely used for Damascene copper plating. The method involves measurements of Ar on consecutive CVS cycles to detect the time-dependent effect of MPS in suppressing the copper deposition rate. CVS measurements were made using a Qualilab QL10® plating bath analyzer (ECI Technology, Inc.). The supporting electrolyte contained 157 g/L CuSO4 . 5 H2O, 10 g/L H2SO4, and 50 ppm chloride ion. The potential of the Pt rotating disk electrode (2500 rpm) was scanned at 100 mV/s between a positive limit of +1.575 V and a negative limit of -0.225 V vs. SSCE-M. During CVS measurements, the solution temperature was controlled at 25°C within +0.5°C. The effects of the commercial Viaform™ (Enthone Inc.) and Ultrafill™ (Shipley, Inc.) additives (at normal concentrations) were investigated. Figure 1 shows that Ar is constant for acid copper baths containing SPS, Viaform or Ultrafill additives but decreases monotonically with potential cycling in the presence of the MPS breakdown product. The MPS species apparently accumulates irreversibly on the Pt electrode surface and suppresses Cu deposition. Figure 2 shows that the decrease in Ar produced by MPS is exponential since a plot of Ar vs. Log (cycle number) is linear. As indicated by the standard curve shown in Fig. 3, the slope of such plots provides a measure of the MPS concentration.
8
-3 -4 -5
References: 1. P. C. Andricacos, Electrochem. Soc. Interface, p. 32, Spring 1999. 2. R. Gluzman, Proc. 70th Am. Electroplaters Soc. Tech. Conf., Sur/Fin, Indianapolis, IN (June 1983)
0
0.5
1
1.5
2
MPS Concentration (ppm)
Fig. 3
Dependence of slope of Fig. 2 plots on MPS concentration.