Experimental investigation on mechanisms of silicon chemical mechanical polishing

Estragnat, E.; Tang, Guang Ping; Liang, Hong; Jahanmir, Said; Pei, P.; Martin, Jean Michel

doi:10.1007/s11664-004-0140-8

Cited by 55 publications

(28 citation statements)

References 16 publications

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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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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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“…The H 2 O 2 and deionized water forms an oxide layer rapidly. The oxide layer can be either Cu 2 O or Cu(OH) 2 . In presence of acetic acid, copper acetate [Cu(CH 3 COO) 2 ] can also be formed.…”

Section: Effects Of Ph On Cu Chemical-mechanical Polishingmentioning

confidence: 99%

“…CMP, originally a process used for glass polishing, was adopted first as a microelectronic fabrication process in the 1980s for SiO 2 polishing [2]. To achieve efficient planarization at miniaturized device dimensions, there is need for good understanding of the physics, chemistry, and the complex interplay of tribomechanical [2][3][4][5][6][7][8][9][10] phenomena. To date, problems associated with the CMP process still exist, such as delamination, microscratches, dishing, erosion, corrosion, and inefficient post-CMP cleaning.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2006

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In this research, we investigated the electrochemical behavior of copper (Cu) surfaces during chemical-mechanical polishing (CMP) with alumina containing slurries. The variation of pH and the percent of oxidizer were tested against impressed anodic and cathodic potentials. The polarization curves as well as potential and current values were measured in order to investigate the effects of electrochemical interactions during polishing. The polishing performance was evaluated through friction, wear, and surface quality. Surface characterization was conducted using an atomic force microscope. The areas scanned contained surfaces having different post-CMP surface chemistry. In such, the electrochemical, chemical, and mechanical action could be revealed and compared in situ and simultaneously. Research results showed that in acidic environment, the low pH dominated the surface roughness over oxidizer and anodic current. At high pH, however, oxidizer and anodic current played important roles. As a result, an optimized polishing condition was proposed.

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“…In previous research we found that hydrodynamic force is limited for effective cleaning. 14,17 Therefore, in this work we focus on the direct contact force in order to see the effectiveness of the particle removal. The effect of surfactant in reducing this contact force is discussed.…”

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confidence: 99%

Nanoparticle Removal Mechanisms during Post-CMP Cleaning

Huang

Jeng

et al. 2007

Electrochem. Solid-State Lett.

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In this research, the synergistic interaction of a brush, an adhered particle, and a wafer surface was evaluated during post chemical mechanical polishing ͑CMP͒. The approach includes theoretical analysis combined with experiments. A theoretical model was used to predict the particle/wafer contact area and contact force in order to identify the maximum tangential force required to remove particle agglomerates. Experiments are carried out to validate the analysis and to further study the removal mechanisms. This research suggests that a combined effort between a brush and surfactant would be effective in removing small particles during cleaning. For large particles, the mechanical force would be the dominating factor.Chemical mechanical polishing ͑CMP͒ was introduced as a method to planarize interlevel dielectrics ͑ILD͒ and damascene metal wiring for on-chip multilevel interconnects. As the size of microelectronic device decreases, planarization of both front and back end layers becomes crucial for interconnects smaller than 0.5 m. 1-3 CMP processes leave a large amount of contamination on the surface, such as residual particles, metallic contamination, and a damaged surface layer. Therefore, a cleaning process called post-CMP cleaning has become a standard manufacturing step. One of the major concerns on the CMP is the high level of residual particles. Depending on the type of CMP and the polishing conditions, these particles can be physically adsorbed on the surface or partially embedded in the substrate due to the mechanical pressure exerted by the polishing pad.It has been accepted that the van der Waals force plays an important role in the adhesion process. To overcome the adhesion force, the mechanical scrubbing from the brush or chemical loosening using solutions or additives is necessary. Chemical additives are used to control the electrostatic repulsion in order to prevent particle readhesion. This can be done by controlling the charges on the substrate and particles, which can be altered by modifying the solution pH or the addition of surfactant. The objective of using surfactant is that it can be used to modify the apparent charges on particles and on the substrate surface. Another important characteristic is that particles can be kept apart during the occupation of the organic surfactant molecules when attached to the particle.The post-CMP cleaning has become a standard process step for local and global planarization. Reports have been found in understanding the mechanisms. These include the basic cleaning principles, 4,5 the effect of hydrodynamic force, 6,7 modeling parameters to study the adhesion force, 8-13 studying the lubrication behavior and friction forces, 14 and using additives and different chemicals during cleaning. 15,16 These results, among others, have discussed the mechanical nature of surface material removal in a micrometerlength scale and larger. The abrasive particles used in CMP are in nanometers. Interesting questions arose when considered sizes become smaller. Thus, understandin...

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Experimental investigation on mechanisms of silicon chemical mechanical polishing

Cited by 55 publications

References 16 publications

Friction and Wear-Mode Comparison in Copper Electrochemical Mechanical Polishing

Friction and Wear-Mode Comparison in Copper Electrochemical Mechanical Polishing

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

Nanoparticle Removal Mechanisms during Post-CMP Cleaning

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