Effects of Electrochemistry on Surface Roughness during Chemical-Mechanical Polishing of Copper

Kulkarni, Milind V.; Baker, M. O.; Greisen, D. A.; Ng, Dedy; Griffin, Richard; Liang, Hong

doi:10.1007/s11249-006-9134-4

Cited by 15 publications

(12 citation statements)

References 20 publications

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“…Results are discussed later. We have in the past reported effects of friction on oxidation of Cu during polishing [18][19][20][21] Figure 2. ͑Color online͒ ͑a͒ Friction coefficient of the tantalum sample in different electrolytes.…”

Section: Resultsmentioning

confidence: 99%

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Oxidation of Tantalum with Mechanical Force

Kar

Wang

Liang

2008

Electrochem. Solid-State Lett.

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Mechanical forces can be used to trigger chemical reactions through activating bonds and to direct the course of such reactions in organic materials, particularly in polymers ͓Nature, 446, 381 ͑2007͒; Nature, 446, 423 ͑2007͔͒. In inorganic materials, the small molecules present significant challenges in directing the reaction kinetics. Using an in situ electrochemical-mechanical technique, we have generated oxides of tantalum with the assistance of mechanical forces in the tangential direction. Using this approach, we were able to control the amount of mechanical and electrical energy in a designed chemical environment. Meta-stable oxides, TaO and Ta 2 O, have been formed with mechanical forces.Industrial processes such as polishing and planarization utilize mechanical forces to make smooth surfaces. 1 In different chemical environments, mechanical forces can result in unique chemical reactions. 2-10 Among those reactions, mechanical-force-related metal oxidation is not found in the chemistry textbook. The metal oxide has emerged as important since the invention of computers. 11 Understanding fundamental issues of metal oxides, such as metalinsulator transition, would enable us to design photovoltaic devices, gas sensors, microelectronics, and corrosion-protection devices. 12, 13 We assemble a system that is able to generate, monitor, and evaluate oxidation states of metals in situ through an electrochemical-mechanical approach. The system is similar to what has been used for tribo-corrosion study. 14,15 The observation of controlled oxidation enables us to study the kinetics of the process. ExperimentalMaterials.-The tantalum sample disk was obtained from Goodfellow and was 99.99 wt % pure. We choose tantalum in this study because it was a nonreactive metal in air, water, strong acids, or alkaline solutions. Usually, the tantalum forms a passive layer of Ta 2 O 5 . 16 Before the experiments, the sample was cleaned with acetone, isopropanol, and deionized water after touch-polishing with 800-1200 grit sand papers. Hydrogen peroxide 35 wt % was obtained from Sigma Aldrich. The state of oxidation is our target of analysis due to mechanical and electrochemical reactions.Test apparatus.-The system setup is shown in Fig. 1, consisting of samples and electrodes. The insert on the right of Fig. 1 illustrates the interface of the test sample and its rubbing partner, a polymeric polishing pad. Sliding direction is shown with arrows. The sliding speed, down force, and electrolyte can be varied as desired. This technique enables us to quantify the amount of input mechanical energy with controlled electrical potential and pH values. Figure 1 shows a three-electrode system that is employed to perform the galvanostatic three-electrode electrochemical reactions. There is a potentiostat, a polymer shaft ͑1͒, test sample ͑2͒, reference electrode ͑3͒, counter electrode ͑4͒, and a polymer pad ͑5͒. The workpiece is tantalum. The shaft is connected to the tantalum that slides against the polymer pad at a desired speed under a fixed a...

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Section: Resultsmentioning

confidence: 99%

“…Details about this technique have been reported elsewhere. 19 The oxide thickness of the sample prepared through pure mechanical polishing was about 250 nm, while that of electrochemical-mechanical polishing was around 215 nm. It has been reported that the thickness of the native oxide of Ta is 2-3 nm.…”

Section: C14mentioning

confidence: 96%

Oxidation of Tantalum with Mechanical Force

Kar

Wang

Liang

2008

Electrochem. Solid-State Lett.

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“…The high friction distribution in region 1 is correlated with the Ra ͑surface roughness͒ value in a later section. Region 2 (pH [6][7][8][9][10][11][12][13][14].-Region 2 displays the alkaline pH and impressed anodic potential. Based on static etching experiments, we found that the dissolution of copper eventually stops at pH 6 or above.…”

Section: Resultsmentioning

confidence: 99%

Friction and Wear-Mode Comparison in Copper Electrochemical Mechanical Polishing

Sen

Gao

et al. 2008

J. Electrochem. Soc.

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This paper investigates friction and wear mechanisms of copper electrochemical mechanical polishing ͑ECMP͒ in pH and potential parameters as illustrated in the Pourbaix diagram. Three approaches were used in this study. First, a unique experimental setup was designed to investigate the effects of pH and electropotential on planarization. Second, the friction was measured in situ during polishing and used as a monitoring process. Third, the worn areas correlated with the frictional behavior of post-chemical mechanical polishing samples were characterized to study ECMP removal mechanisms. Results showed that friction maps can be generated in conjunction with the equilibrium Pourbaix diagram. This map is helpful in monitoring the removal rate and wear during copper ECMP. These findings can be used as guidance in ECMP process design and optimization.In the last two decades, chemical mechanical polishing ͑CMP͒ has emerged as a standard planarization process in semiconductor industries to fabricate integrated circuits. 1 The low-cost operation has been introduced to silicon, aluminum, tungsten, copper, shallow trench isolation, low-k, and micro/nanoelectromechanical systems. [2][3][4][5] Material removal studies of CMP have been conducted intensively in the past. These studies evaluate the effects of pH, 6,7 slurry chemistry ͑oxidizers, 6-9 complexing agents, 10,11 corrosion inhibitors, 12,13 and abrasives͒ 14-16 on planarization, and vary polishing parameters ͑rotating speed, downforce, 17 and hydrodynamic flow͒ 18,19 to observe the removal rate and generate removal-rate models based on mechanical and chemical approaches. 20-23 Overall, these studies have focused on indirect investigation of CMP, which often present challenging issues to study the removal mechanism due to the complexity of slurry chemistries. These findings also show there is a need to create a simple system in order to monitor and evaluate the removal mechanism of CMP.Planarization in CMP is achieved through rubbing a substrate through a pad in the presence of abrasive slurries. The friction force produced affects the quality of the surface finish. Our prior work has shown that CMP is a polishing technique and operates based on tribochemical principles. 15,24,25 The removal mechanisms involve mechanical abrasion by abrasives and pad, chemical wear, dissolution, and surface passivation due to slurry chemistry. 6,7 Friction plays an important role during polishing. To obtain a better understanding of CMP, we propose to "diagram" the effects of CMP in terms of its frictional behavior. In the present work, we developed a laboratory setup to be able to measure the friction coefficient in situ during polishing. Subsequently, we used an electrochemical approach to conduct copper CMP for pH and potential parameters on the equilibrium Pourbaix diagram. ExperimentalMaterials.-Copper wafers used in this study were electroplated on commercially available 8 in. diameter silicon substrates. The samples were cut into sizes of 3 ϫ 2 cm and were glued to a polishing ...

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“…The balance of thickness between oxidation and pad sweeping is, surface (108). If compounds were to form in the metal surface, electrochemical measurements, such as voltammetry can be used to detect them in situ.…”

Section: Kinetics Of Film Formationmentioning

confidence: 99%

Interfacial Forces in Chemical-Mechanical Polishing

Liang

2009

Advanced Tribology

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The demand for microelectronic device miniaturization requires new concepts and technology improvement in the integrated circuits fabrication. In last two decades, Chemical-Mechanical Polishing (CMP) has emerged as the process of choice for planarization. The process takes place at the interface of a substrate, a polishing pad, and an abrasive containing slurry. This synergetic process involves several forces in multilength scales and multi-mechanisms. This research contributes fundamental understanding of surface and interface sciences of microelectronic materials with three major objectives. In order to extend the industrial impact of this research, the chemical-mechanical polishing (CMP) is used as a model system for this study. The first objective of this research is to investigate the interfacial forces in the CMP system. For the first time, the interfacial forces are discussed systematically and comparatively so that key forces in CMP can be pinpointed. The second objective of this research is to understand the basic principles of lubrication, i.e., fluid drag force that can be used to monitor, evaluate, and optimize CMP processes. New parameters were introduced to include the change of material properties during CMP. Using the experimental results, a new equation was developed to understand the principle of lubrication behind the CMP. The third objective is to study the synergy of those interfacial forces with electrochemistry. The electro-chemical-mechanical polishing (ECMP) of copper was studied. Experiments were conducted on the tribometer in combination with a potentiostat. Friction coefficient was used to monitor the polishing process and correlated with the wear behavior of post-CMP samples. Surface characterization was performed using AFM, SEM, and XPS techniques. Results from experiments were used to generate a new wear model, which provided insight from CMP iv mechanisms. The ECMP is currently the newest technique used in the semiconductor industries. This research is expected to contribute to the CMP technology and improve its process performance. This dissertation consists of six chapters. The first chapter covers the introduction and background information of surface forces and CMP. The motivation and objectives are discussed in the second chapter. The three major objectives which include approaches and expected results are covered in the next three chapters. Finally chapter VI summarizes the major discovery in this research and provides some recommendations for future work. v DEDICATION To my mother, for her unconditional love, affection and support. vi ACKNOWLEDGEMENTS First and foremost, I would like to express my deepest gratitude to my academic advisor, Dr. Hong Liang. She taught me how to become a good researcher and provided an independent environment to assist my growth. She also gave me countless supports and encouragements during my last four years of study at Texas A&M University. I also want to thank her for her great patience and invaluable directions in the preparation of this dis...

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Effects of Electrochemistry on Surface Roughness during Chemical-Mechanical Polishing of Copper

Cited by 15 publications

References 20 publications

Oxidation of Tantalum with Mechanical Force

Oxidation of Tantalum with Mechanical Force

Friction and Wear-Mode Comparison in Copper Electrochemical Mechanical Polishing

Interfacial Forces in Chemical-Mechanical Polishing

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