Linear sweep voltammetry and chronoamperometry methods were used to measure limiting current in an industrial wafer-plating cell. Copper deposition in a dilute solution, under mass-transfer-limited conditions, is used to study the variation of the mass transfer boundary-layer thickness. It is shown that a shear-plate fluid agitation mechanism is capable of generating a thin ͑i.e., Ͻ10 m͒, spatially uniform and nonperiodic boundary layer across the entire wafer. It is anticipated that thin boundary layer deposition will prove to be beneficial in MEMS, flip-chip bumping, and WL-CSP applications.A thin, uniform, and stationary diffusion boundary layer is important in obtaining high-quality electrodeposits. Limiting current depends on thickness of the diffusion boundary layer for a given reactant concentration. Plating current is then usually set below onehalf of limiting current to obtain plated deposits acceptable for their appearance and uniformity. In cases where operating current is set to greater than one-half of limiting current, the effects of mass transfer typically impact the morphology of the deposit, and rough growth is often observed. Moreover, control of limiting current density and diffusion boundary layer thickness becomes even more important when the subject is the plating of metal alloys. In alloy deposition, cell potential is set such that one metal is deposited at its diffusion limiting current. Thus, uniformity of the diffusion boundary layer significantly influences composition of the final plated alloy, and its material properties.The reciprocating paddle cell is a known practical method for depositing alloy films on wafer substrates. It has been shown that the diffusion boundary layer's thickness profile, in a paddle-arm cell, may be periodic in nature due to the wake trailing the paddle. 1 It has also been shown that paddle distance from the cathode has a greater impact on deposition uniformity than does paddle speed. 2 The primary electrochemical technique for measurement of the mass transfer boundary-layer thickness is determination of limiting current. At limiting current, concentration of reacting species is virtually zero over the entire electrode surface. Limiting current measurements are usually carried out in a traditional three-electrode cell, using a potentiostat. Techniques for determining limiting current and mass-transfer coefficient correlation, for a variety of different electrode geometries and fluid flow conditions in laboratory experimental cells, were reviewed by Selman and Tobias. 3 However, only limited methods have been available to characterize the mass transfer boundary layer in industrial wafer plating cells, due to their complicated cell geometries and limited accesses for probes. It is difficult to install a standard reference electrode in an industrial wafer plating cell. Moreover, a potentiostat is not usually available in a typical wafer fabrication facility. These problems are barriers to transferring experimental results obtained from bench-or beaker-scale test...

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Economical manufacturing of electroplated copper pillars requires maximizing the deposition rate while achieving the coplanarity, flatness, and morphology required by the overall packaging process. Various aspects of the deposition are influenced by the resist pattern and the deposition rate. Experimental comparison of several different commercial copper chemistries is provided for copper pillars fabricated in 120 micron thick dry film resist with features sizes from 60 to 120 microns diameter. Feature height co-planarity and pillar top surface shape are analyzed versus feature size and pitch for a range of deposition rates.

Solders based on tin-lead alloys are used extensively in semiconductor packaging. Electrodeposition is a favored solder- application process in flip-chip packaging because it provides superior thickness control and is easily scaled down to small pitch sizes. However, industrial processing and consumer use of lead-bearing products is a recognized public-health hazard, and the international trend toward regulation is driving demand for lead-free alternatives such as the Sn/Ag eutectic. Direct alloy deposition and stack deposition have been used to produce Sn/Ag bumps. Electrocodeposition, in which metallic or dielectric particles suspended in the plating bath are incorporated into a metal electrodeposit is potentially more economical. In this study, electrocodeposition of silver particles with tin was used to generate Sn/Ag composites and alloys.

The demand for higher functionality in smaller form-factor electronic devices continues to grow. This growth is enabled in large part by wafer-scale packaging technologies for 2-D, 2.5-D, and 3-D integration. Solder bump, copper pillar, and TSV processes are key enablers for advanced packaging. Sacrificial polymer materials such as photoresist and polyimides are used for patterning and/or passivation steps [1,2]. Typical challenges in removing these materials include long process times, short bath life, corrosion, sludge formation, and filter clogging. This paper presents a novel tool design that addresses these issues by a high rate of hydrodynamic agitation that maintains a thin boundary layer at the wafer surface. The outcome is quick removal and breakdown of the sacrificial layer, independent of pitch and without all the negative side effects.