Professor Dipankar Roy Studies Electrochemical-Mechanical Planarization (ECMP) of Metals

CAMP Professor Dipankar Roy is studying experimental and theoretical aspects of electrochemical-mechanical planarization (ECMP), an emerging new extension of CMP. It offers a realistic approach to low down-pressure planarization of interconnect structures containing porous, fragile low-k dielectrics. ECMP utilizes electrochemical surface reactions for material removal in conjunction with mechanical polishing performed at less than 1 psi pressure in completely or nearly abrasive-free electrolytes. Roy’s group is testing the efficiency of ECMP for planarization of copper (used as lines and vias for interconnects), tantalum (used as diffusion-barriers in integrated circuits), ruthenium (a promising material for diffusion barriers and electrodes in random access memory cells) and silver (a possible wiring metal). A main focus of Professor Roy’s current research in this area is to develop efficient slurry-electrolytes using carefully designed combinations of charge carriers, complexing agents, corrosion inhibitors and oxidizers. This work is funded by Intel Corporation through SRC, and part of the project is conducted in collaboration with CAMP Director S.V. Babu. A complete list of publications on ECMP by Professor Roy’s group can be found at: http://www.clarkson.edu/~samoy/pub.htm. For further information about Professor Roy’s research, please call him at 315-268-6676 or send e-mail to samoy@clarkson.edu.

Pulsed Laser-Based Nanoparticle Removal for Semiconductor Surface Cleaning and Nanoadhesion Measurements

Professor Cetin Cetinkaya and his group have been conducting analytical, computational and experimental work in the area of laser-based particle removal and noncontact nanoadhesion measurements. There is an immense need in various industries for dry removal of micro/nano-particles from substrates and trenches. Professor Cetinkaya’s group has developed a novel dry cleaning method to remove micron and submicron particles. The new technique, based on laser-induced plasma shock waves, is a noncontact method and the removal efficiency is an order of magnitude higher than the traditional laser cleaning methods. Recent experiments have proved that a latex particle with a diameter of 60 nm and larger particles can be removed from silicon surfaces. The dry laser cleaning method is being used to remove micron and submicron particles from varying substrates as well as from micro-holes and semiconductor trenches. The new cleaning method has demonstrated a great potential in the area of nanoparticle removal. Various applications of this technology are being investigated by Professor Cetinkaya’s group.

Modeling of the Chemical-Mechanical Polishing Process

Professor Ahmadi and his group have developed mechanical wear models for the chemical-mechanical polishing process. The work shows the importance of abrasive particles and wafer surface hardness, and the double layer forces on the removal rate. Their analysis includes the influence of abrasive particle adhesion to the surface of the wafer and the variation of surface hardness due to the presence of slurry. In addition Professor Ahmadi and his students are studying the effect of abrasive particle shapes, slurry pH, and colloidal forces on the removal rate.

Professor R. Shankar Subramanian is working on various aspects of modeling of chemical mechanical polishing. He is interested in predicting overall removal rates and in the process by which mechanical removal of material occurs at the microscopic level. The issues are the role of the mechanical properties such as the relative hardness of the wafer, abrasive particle, and the pad, the role of asperities on the pad, and the coupling of the chemistry to the mechanical removal process.

Professor Subramanian is collaborating with Professor John McLaughlin on the motion of a liquid drop on a solid surface because of the action of wettability gradients. Such motion can be important in a variety of applications such as the removal of debris in ink jet printing, and in moving drops from one place to another in microfluidic devices. He also is performing research on the role of colloidal particles adsorbed at the surface of a bubble or drop in arresting dissolution.

Reactive Pad for Metal CMP

Professor Yuzhuo Li and his group are investigating the use of a reactive pad for metal CMP. With the integration of fragile low k dielectric materials, it is critical to conduct metal CMP operations at low down force without introducing new defects and/or scarifying throughput. While intensive efforts have been made over the past several years on new polishing strategies (abrasive free, fixed abrasives, soft abrasives, chemical softlanding, ECMP, etc), there has been limited progress on making pads an active participant in controlling the chemical reactions on the film to be polished. Although pads that can release certain chemicals and conduct electricity have been studied, in many people’s minds, a pad serves solely as a mechanical partner during the CMP operation. CAMP Professor Yuzhuo Li, working with Dr. Stuart Hellring of PPG, has been instigating a new concept that brings the abrasive free CMP strategy and functional abrasive surface together to yield a new generation of pads for metal CMP. It can be viewed as a natural extension of the smart particle technology and abrasive free concept to the pad. The research team also includes CAMP Professor Devon Shipp and his postdoctoral research associate Tianxi Zhang.

Figure 1. Commonly seen dishing and erosion in copper CMP.

Figure 2. Edge over Erosion (EOE) in copper CMP for arrays containing small features and high metal density.


Investigation of Edge over Erosion in Copper CMP using Conventional and Mipox Pads

One of the most challenging issues in copper CMP today is how to properly identify, fundamentally understand, adequately model, and effectively combat new types of defects associated with the reduction of feature size and integration of low k materials. The Edge over Erosion (EOE) is an excellent example, which is being studied by CAMP Professor Yuzhuo Li and his group.

While commonly seen dishing and erosion as shown in Figure 1 have been intensively investigated, edge over erosion is new and much more difficult to identify its presence, its source, and an effective solution to reduce it. As shown in Figure 2, whereas conventional erosion is a localized thinning of the dielectric, EOE is a defect that is where the erosion is higher at the edge of the recessed region in a feature when compared to the center (Figure 2). It is observed that EOE is increasingly severe when the feature size is small (< 120 nm) and pattern density is high (>35%).



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