The progressively decreasing feature size of the circuit components has tremendously increased the need for the global surface planarization of the various thin film layers that constitute the integrated circuit (IC). Global planarization, being one of the major solutions to meet the demands of the industry, needs to be achieved following the most efficient polishing procedure. Chemical mechanical polishing (CMP) is the planarization method that has been selected by the semiconductor industry today. CMP, an ancient process used for glass polishing, was adopted first as a microelectronic fabrication process by IBM in the 80 s for SiO2 polishing. To achieve efficient planarization at miniaturized device dimensions, there is a need for a better understanding of the physics, chemistry and the complex interplay of tribo-mechanical phenomena occurring at the interface of the pad and wafer in presence of the fluid slurry medium. In spite of the fact that CMP research has grown by leaps and bounds, there are some teething problems associated with CMP process such as delamination, microscratches, dishing, erosion, corrosion, inefficient post-CMP clean, etc.; research on which is still developing. The fundamental understanding of the CMP is highly necessary to characterize, optimize and model the process. The CMP process is ready to make a positive impact on 30% of the US$ 135 billion global semiconductor market. This paper presents an overview of CMP process in general, the science and mechanism of polishing, different metal and dielectric CMP processes. The impact of consumables on the CMP process, post-CMP cleaning, modeling of different CMP processes as well as the future trends are also discussed.

Chemical mechanical planarization for microelectronics applications

The special mechanical properties of nanoparticles allow for novel applications in many fields, e.g., surface engineering, tribology and nanomanufacturing/nanofabrication. In this review, the basic physics of the relevant interfacial forces to nanoparticles and the main measuring techniques are briefly introduced first. Then, the theories and important results of the mechanical properties between nanoparticles or the nanoparticles acting on a surface, e.g., hardness, elastic modulus, adhesion and friction, as well as movement laws are surveyed. Afterwards, several of the main applications of nanoparticles as a result of their special mechanical properties, including lubricant additives, nanoparticles in nanomanufacturing and nanoparticle reinforced composite coating, are introduced. A brief summary and the future outlook are also given in the final part. (Some figures may appear in colour only in the online journal)

https://iopscience.iop.org/article/10.1088/0022-3727/47/1/013001/pdf

Mechanical properties of nanoparticles: basics and applications

Energy absorption capability of nanocomposites: A review

Evaluations of the effective material properties of carbon nanotube-based composites using a nanoscale representative volume element

3. FEOL Applications: Device Level 180 3.1. Shallow Trench Isolation (STI) CMP 180 3.2. Replacement Metal Gate CMP 184 3.3. Poly-Si CMP for FinFET Devices 186 4. MOL Applications: Contact Level 187 4.1. Tungsten CMP 187 5. BEOL Applications: Multilevel Interconnects 188 5.1. Copper Interconnect Technology 188 5.2. CMP Challenges in Cu Interconnects 189 5.2.1. Low-k and Ultralow-k Material Challenges 189 5.2.2. Integration Challenges 190 5.2.3. CMP Process Challenges 191 5.3. Copper Planarizarion Process 191 5.4. Ta/TaN Liner CMP Process 193 6. CMP Process-Induced Defects 194 6.1. Defects in FEOL CMP 194 6.2. Defects in MOL Tungsten CMP 195 6.3. Defects in Cu BEOL CMP 195 6.3.1. Corrosion of Copper 196 6.3.2. Scratches 196 6.3.3. Dishing, Erosion, and Trenching 196 6.3.4. Mechanical Damage 197 6.3.5. Other Defects 197 7. Models of CMP Processes 198 7.1. Models Based on Contact Mechanics 198 7.2. CMP Process Models 199 8. Alternative CMP Processes 200 9. Concluding Remarks 201 10. Acknowledgments 201 11. References 201

Chemical mechanical planarization: slurry chemistry, materials, and mechanisms.

The abrasion mechanism in solid-solid contact mode of the chemical mechanical polishing (CMP) process is investigated in detail. Based on assumptions of plastic contact over wafer-abrasive and pad-abrasive interfaces, the normal distribution of abrasive size and an assumed periodic roughness of pad surface, a novel model is developed for material removal in CMP. The basic model is MRR=/spl rho//sub w/NVol/sub removed/, where /spl rho//sub w/ is the density of wafer N the number of active abrasives, and Vol/sub removed/ the volume of material removed by a single abrasive. The model proposed integrates process parameters including pressure and velocity and other important input parameters including the wafer hardness, pad hardness, pad roughness, abrasive size, and abrasive geometry into the same formulation to predict the material removal rate (MRR). An interface between the chemical effect and mechanical effect has been constructed through a fitting parameter H/sub w/ a "dynamical" hardness value of the wafer surface, in the model. It reflects the influences of chemicals on the mechanical material removal. The fluid effect in the current model is attributed to the number of active abrasives. It is found that the nonlinear down pressure dependence of material removal rate is related to a probability density function of the abrasive size and the elastic deformation of the pad. Compared with experimental results, the model accurately predicts MRR. With further verification of the model, a better understanding of the fundamental mechanism involved in material removal in the CMP process, particularly different roles played by the consumables and their interactions, can be obtained.

Material removal mechanism in chemical mechanical polishing: theory and modeling

The use of smooth post-ECP topography (instead of final chip topography) as an objective during dummy filling enables a computationally efficient model-based dummy filling solution for copper while maintaining solution quality. A layout can be divided into tiles and the “case” of each tile identified. Exemplary cases can include conformal fill, over fill, super fill, or super/over fill (if the ECP model cannot distinguish between super and over fill cases). One or more undesired tile cases can be converted to a desired tile case. Then, a height difference between tiles can be minimized. Dummy features can be inserted in the layout to perform the conversion and to minimize the height difference between tiles. Minimizing the CMP-effective density difference between tiles with ECP considerations can be performed to further improve planarization.

Dummy filling technique for improved planarization of chip surface topography

Recently, a comprehensive model has been developed by Luo and Dornfeld ("Material removal mechanism in chemical mechanical polishing: theory and modeling", IEEE Trans. Semiconduct. Manufact., vol. 14, pp. 112-133, May 2001) to explain the material removal mechanism in chemical mechanical planarization (CMP). Based on the model, the abrasive size distribution influences the material removal from two aspects, one, the number of active abrasives, and the other, the size of the active abrasives. In this paper, experimental evidence supporting this view of abrasive size effects is discussed. A detailed model of wafer-abrasive-pad contact is developed to explain how and where abrasive size distributions come into the comprehensive material removal model. A material removal rate formulation as a function of abrasive size distribution is proposed and verified. In the future, the application of the model to the CMP process optimization, for example, improving the nonuniformity, or obtaining minimum surface scratching and preferred material removal rate by changing abrasive size distribution, may be attempted.

Effects of abrasive size distribution in chemical mechanical planarization: modeling and verification

In this paper, the boundary element method (BEM) based on elasticity theory is developed for two-dimensional (2-D) thin structures with the thickness to length ratio in the micro (10−6) or nano (10−9) scales. An efficient analytical method is developed to deal with the nearly-singular integrals in the boundary integral equation (BIE) for 2-D thin structures. The nearly-singular integrals, which are line integrals for 2-D problems and arise when two boundary curves are close to each other, are transformed into function evaluations at the two end points of the element of integration. In addition, a new nonlinear coordinate transformation is developed for nearly weakly-singular integrals to further increase the numerical accuracy. For the test problems studied, very promising results are obtained when the thickness to length ratio is in the orders of 10−6 to 10−9, which is sufficient for modeling most thin structures in the micro- or nano-scales. The developed method can be applied readily to model layered coatings, thin films or other layered structures to analyze contact stresses, interfacial cracks, thermal effects and nonlinear deformations.

Analysis of two-dimensional thin structures (from micro- to nano-scales) using the boundary element method

A material removal rate (MRR) model as a function of abrasive weight concentration has been proposed for chemical mechanical planarization/polishing (CMP) by extending a material removal model developed earlier in 2001 and 2002. With an increase of the weight concentration of abrasives, three regions of material removal exist: a chemically dominant and rapid increasing region, a mechanically dominant linear region, and a mechanically dominant saturation region. A detailed model is proposed to explain that the transition from the first to the second region is due to a transition from a wafer surface covered with a single soft material to a surface covered with both soft and hard materials. The slope of the linear region is a function of abrasive size distribution, and the saturation removal rate is a function of abrasive size distribution and wafer-pad contact area. The model can help to clarify the roles of chemicals, wafer-pad contact area, and abrasive size distribution in CMP.

Material removal regions in chemical mechanical planarization for submicron integrated circuit fabrication: coupling effects of slurry chemicals, abrasive size distribution,and wafer-pad contact area

Jianfeng Luo

Papers

Material removal mechanism in chemical mechanical polishing: theory and modeling

Dummy filling technique for improved planarization of chip surface topography

Effects of abrasive size distribution in chemical mechanical planarization: modeling and verification

Analysis of two-dimensional thin structures (from micro- to nano-scales) using the boundary element method

Material removal regions in chemical mechanical planarization for submicron integrated circuit fabrication: coupling effects of slurry chemicals, abrasive size distribution,and wafer-pad contact area