Copper interconnects electrodeposition

It may be considered a fortunate coincidence that this book is published at the time of the introduction of copper interconnection technology in the microelectronics industry. In 1998 the major electronic manufacturers of integrated circuits (ICs) are switching from aluminum conductors produced by physical methods (evaporation) to copper conductors manufactured by electrochemical methods (electrodeposition). This revolutionary change from physical to electrochemical techniques in the production of microconductors on silicon is bound to generate an increased interest and an urgent need for familiarity with the fundamentals of electrochemical deposition. This book should be of great help in this crucial time. 

One major recent advance in silicon-based semiconductor industry is the development of copper interconnects on chips. This new technology replaces the traditional aluminum or aluminum alloy (e.g. Al—Cu) conductors produced by physical vapor deposition (PVD) with copper conductors manufactured by electrodeposition. Copper has been replacing aluminum since 1999 owing to its low bulk electrical... 

The damascene copper interconnects are produced by electrodeposition of copper onto PVD Cu seed layer. The electrodeposition of copper layer is carried out to fill in vias and trenches and consequently to form the metal interconnects. The bottom-up fill of copper in fine via holes as schematically presented in Fig. 4 has successfully been demonstrated by Wang et al.37 using the electroless deposition process. 

Electrodeposition is a liquid-phase analog of plasma-enhanced CVD, used especially in the formation of copper interconnects. This method employs electrochemical voltages instead of surface temperature to control the growth characteristics. It is however more difficult to model and predict than CVD, because of solvation effects and the relative dearth of experimental methods to examine individual elementary steps in the key reactions. ... 

Copper interconnection via electrochemical means has received increasing attention. Currently the most acceptable method is based on electrodeposition of copper on top of a copper seed layer which has previously been deposited by CVD or sputtering method 1 . 

Electrodeposition has been used since the beginning of the century to form high-quality, mostly metallic, thin films car bumpers, decorative plating, metal contacts, and so on. It has recently been shown that high-quality copper interconnects for ultra-large scale integration (ULSI) chips... 

Copper electrodeposition on Au(111) Copper is an interesting metal and has been widely investigated in electrodeposition studies from aqueous solutions. There are numerous publications in the literature on this topic. Furthermore, technical processes to produce Cu interconnects on microchips have been established in aqueous solutions. In general, the quality of the deposits is strongly influenced by the bath composition. On the nanometer scale, one finds different superstmctures in the underpotential deposition regime if different counter-ions are used in the solutions. A co-adsorption between the metal atoms and the anions has been reported. In the underpotential regime, before the bulk deposition begins, one Cu mono-layer forms on Au(lll) [66]. 

Manufacture of Printed Wiring Boards. Printed wiring boards, or printed circuit boards, are usually thin flat panels than contain one or multiple layers of thin copper patterns that interconnect the various electronic components (e.g. integrated circuit chips, connectors, resistors) that are attached to the boards. These panels are present in almost every consumer electronic product and automobile sold today. The various photopolymer products used to manufacture the printed wiring boards include film resists, electroless plating resists (23), liquid resists, electrodeposited resists (24), solder masks (25), laser exposed photoresists (26), flexible photoimageable permanent coatings (27) and polyimide interlayer insulator films (28). Another new use of photopolymer chemistry is the selective formation of conductive patterns in polymers (29). 

A production process has recently been implemented by IBM. The aim was to reduce the electrical resistance of the interconnects in their chip to about one-third of the values attainable using aluminum and at the same time increasing the resistance against electromigration. This was made possible by employing electrodeposition of copper in a Damascene method. The manufacturing sequence is presented in Figure 17.11. 

Most processes in which control of events at the molecular scale is important have only one or two manipulated variables available during processing. For example, the applied potential is the only manipulated variable during the electrodeposition of copper to form an interconnect. A challenge for constructing predictive models for such systems is how to excite the dynamics during model identification experiments when so few manipulated variables are available. 

The multiscale systems approach is directly applicable to problems in nanotechnology, molecular nanotechnology and molecular manufacturing. The key ideas have been illustrated with examples from two processes of importance to the semiconductor industry the electrodeposition of copper to form on-chip interconnects and junction formation in metal oxide semiconductor field effect transistors. 

Andricacos, P.C. (1999) Copper on-Chip Interconnections - A Breakthrough in Electrodeposition to Make Better Chips. 

Andricacos, P.C. Copper on-chip interconnections a breakthrough in electrodeposition to make better chips. Interface (Electrochem. Soc.) 1999, 5, 33-48. 

Recently, copper plating has found an important new application in metallizing interconnects on semiconductor wafers3. Here, a specially designed and dedicated tool is used to plate well-defined disk-shaped silicon wafers. A very uniform copper layer must be electrodeposited with excellent gap-fill properties onto a resistive seed layer through contacts along the circumference of the wafer. The new process poses numerous critical challenges ... 

Copper is an important metal and has been widely investigated in electrodeposition studies from aqueous solutions. Numerous publications exist in the literature on this topic. Furthermore, technical processes have been established in aqueous solutions to make Cu interconnects on microchips. In general, the quality of the... 

Kim J-H, Kim R-H, H-Sang K (2008) Preparation of copper foam with 3-dimensionally interconnected spherical pore network by electrodeposition. Electrochem Commun... 

Copper Electrochemical Technology The mauufacture of complex microstructures for on-chip interconnects requires multiple layers of metallization. Copper electrochemical technology was introduced by IBM in 1999 and is now used widely as a basic chip fabrication process. The process depends critically on the action of solution additives that influence growth patterns during electrodeposition. 

---