NanoDynamics and Clarkson Collaborate on Multiple Levels

cont. from page 7

Recently, NanoDynamics announced that it had completed a second round of financing, bringing its total to $16 million in just two years time. Blakely is enthusiastic about the company's prospects and the value of the many interactions that NanoDynamics and Clarkson have established. He made the following statements. "As an early-stage company, we have to use our resources effectively, and, over the years, I have always found Clarkson faculty and researchers to be particularly sensitive to the importance of the industrial relevance of our projects. I predicted to Vice Provost Babu and President Collins when I started NanoDynamics that we would be a major partner with Clarkson in the years to come and that has certainly been realized thus far. I look forward to many more years of fruitful collaboration with an ever-widening circle of faculty and students."

CAMP's Annual Technical Meeting 2004


Modeling of the Chemical-Mechanical Polishing Process

Professor Ahmadi and his group are developing models (based on mechanical contact theory) for the chemical-mechanical polishing process. The goal of their research is to provide a fundamental understanding of the parameters that control the effectiveness of CMP for surface planarization. Their current work focuses on the abrasive particle, wafer, and pad contact and the abrasive and adhesive wear mechanisms in the chemical-mechanical polishing process. They are developing a model for interactions of pad asperities with abrasive particles and the wafer. 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 from blanket wafers, and understanding the planarization process that occurs in the case of patterned wafers. Professor Subramanian also is interested in the process by which mechanical removal of material occurs at the microscopic level. Here, 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. He and doctoral student Qingjun Qin have been studying the mechanical removal of a polymer in a Struers Benchtop polisher using an alumina slurry. Experiments have been performed using IC-1000 pads, and the removal rate was measured as a function of the relative velocity, applied pressure, and particle concentration. The results clearly demonstrate the inadequacy of the Preston model in describing mechanical removal rates over a wide range of velocities.

Professor Subramanian is also working with doctoral student Qingjun Qin, on developing theoretical descriptions of polishing in an orbital polishing tool. (He is using a SpeedFam/IPEC 676 orbital tool.) In addition to his CMP research, Professor Subramanian is collaborating with Professor John McLaughlin (with support from NASA) 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 for medical and biological applications such as blood chemistry analysis, flow cytometry, polymerase chain reactions, and DNA screening. Information about this work is available at his web site (http://www.clarkson.edu/subramanian/solid.htm

Novel Pure Organic Particles for Copper CMP at Low Down Force

Professor Yuzhuo Li and his group are using novel, pure organic particles for metal CMP. With the integration of copper as interconnect and low k materials as dielectric, the CMP community is facing an ever increasing demand on reducing defectivity without scarifying production throughput. One such strategy is to significantly lower the polishing pressure to below 1 psi. Such a move has placed tremendous challenges to the tool manufacturers, consumable suppliers (especially the slurry vendors), and end-users. It is a challenge to maintain the high throughput (MRR and selectivity) at low down force without using harsh abrasives. Working with Kwok Tang at Dynea, CAMP Professor Yuzhuo Li and his graduate students Krishnayya Cheemalapati, Vivek R. Duvvuru, and Deenesh K. Bundi recently reported the use of novel pure organic particles for metal CMP. Unlike conventional abrasive particles such as silica and alumina, these unique particles are designed to specifically interact with the metal surface to be polished and to significantly modify the rheological behavior of the slurry. The obvious advantage of using such particles is the reduction of defects during CMP. The consequence of using such particles provides unsurpassed high selectivity in the removal rate for copper over barrier and dielectric materials due to their weak interaction with these particles. An added benefit for slurry that uses such particles is a CMP process conducted at a lower down force without compromising the throughput. Research results have been presented at CMP-MIC, SEMICON China, and Spring MRS meeting in 2004. The commercial potential of this technology has generated considerable attention from the leading semiconductor companies.

Mechanistic Investigation of the Post CMP Clean Process and of Organic Residue Removal

Professor Yuzhuo Li and his group are investigating the post CMP cleaning process. Effective cleaning of polished wafers is an integral and important part of the chemical mechanical polishing process. With the introduction of various low k dielectric materials and many potential integration schemes, the complexity of the polished surfaces increases rapidly. One must not only consider the co-existence of various materials on the polished wafer with vast different chemical and physical properties (such as surface functional groups, charge characteristics, and hydrophobicity), but should also carefully consider the dynamic nature of various components during polishing. More specifically, the introduction of polishing debris (at molecular and particulate levels) may have a significant impact on the mode of interactions among abrasive particles, chemical additives, and polished surfaces. Although significant effort has been placed on the interaction of the original abrasive particles and a perceived polished surface, the modification of abrasive particles by polishing debris has been largely ignored.

CAMP Professor Yuzhuo Li and his graduate students have recently conducted research to gain fundamental knowledge of the chemical interaction among abrasive particles and various additives under the influence of possible polishing debris. The surface adsorption behavior of the modified particles is then examined. Furthermore, the formation and removal mechanisms of certain organic residues were investigated. One of the major goals of this research is to provide some guidelines in designing an effective post CMP clean solution and process.


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