Kinetic on Copper Damascene and Cuprous Concentration Computation in with Cl- and SPS
Acceleration effect of Copper Damascene has been discussed by variety of researchers. West, Moffat and Dow have proposed a curvature enhanced effect, which SPS (bis(sodiumsulfopropyl) disulfide) adsorbs at the curvature and transforms cupric to cuprous (1). Tan’s experiment contradicts to this cupric to cuprous transformation by SPS (2). Even the PDSA (1,3-propanedisulfonic acid), without thiol groups at the both end, shows acceleration with the presence of chloride. Kondo’s recently proposed Cu(I)thiolate acceleration model (3). The role of SPS and Cl- is in the Fig. 2 and has been modeled by Broekmann (7). Cl- ions absorb on copper surface (4) and reduce SPS to form MPS (mercaptopropylsulfonic acid) by the electron bridge mechanism (5). This reaction occur allover copper surface. MPS is oxidized to SPS and reacts with cupric ions to reduce to cuprous and form Cu(I)thiolate. According to K. Kondo, Cu(I)thiolate complexes accumulate inside the almost reaching the TSV bottom vortex for the V-shape TSV. And these Cu(I)thiolate complexes recirculating inside the vortex preferentially release cuprous ions to via bottom.
Kinetic of reaction with the present of Cl- and Cl-+SPS were investigate at 25±0.2°C, and various parameters: WE potential, CuSO4, Cl-, SPS concentration. WE potential was -250mV vs. SCE, at this potential cathodic current dominated anodic current. Data of CVS and BE measurement using platinum RDE at 10rpm was used in simulation of Copper Damascene on TME (through mask electrode). Kinetic parameters were calculated from experiment and simulation using Comsol software to determine reaction rate constant of electrode surface reactions, which were catalyzed by Cl- and Cl-+SPS.
The copper deposition process was considered to occur in three pathways (Fig. 1). Pathway 1 was without Cl- and SPS, pathway 1, 2 were with Cl- presence, pathways 1, 2, 3 were both Cl-, SPS presence. The presence of Cl- and SPS was assumed that effected only on first step, the formation of cuprous and determination of overall reaction rate. Ratio of area covering by Cl- was fitted a logarithm model aCl = 0.0652*ln([Cl-]) + 0.7784, and that of SPS was fitted the Langmuir model aSPS=58.55*[SPS]/(1+58.55*[SPS]. Our result showed that with the present of Cl- and Cl-+ SPS overall reaction rate constant increased 1.66, and 2.07 times, respectively. Simulation the reaction on a TME showed that cuprous cation concentration was high at the bottom of TME and reduced when move to the bulk. The cuprous concentration profiled was used for estimation of reaction rate constants of pathway 2, and 3. The smaller reaction constant from Cu(I)thiolate to cuprous if compared to the cupric to cuprous is a critical factor to proof the Fig. 2 model properness (7).
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