| Chemical mechanical polishing(CMP) has emerged to be most promising because it can provide the planarity necessary to build multilevel interconnect schemes.In the CMP process, a rotating wafer is pressed against a rotating pad while slurry including abrasive particles and chemical additives flows between the wafer surface and polishing pad.It synergizes the abrasive particles and chemicals in slurry.Despite its crucial importance in the microelectronic industry,many aspects of the CMP process remain unclear and ambiguous. Understanding of the fundamental of CMP material removal mechanism may offer insights into the control and optimization of the polishing process.In addition,as device size is shrinking and integration level of IC chip is increasing,a detailed quantitative model for material removal rate in CMP,is required for meeting the strict planarization requirements in the manufacturing the future generation Ultra Large Scale Integration(ULSI) chips.In this study,the paper firstly proposes a material removal mechanism at molecular scale. And then this molecular scale removal mechanism has got wide support form many aspects such as large contact deformation of pad/particle,the effect of adhesion force on the indentation depth of particle into wafer surface,the order-of-magnitude calculation of material removal on the basis of chemical kinetics and transport phenomena under the wafer surface defect condition,and the nano-scale experiments carried out by atomic force microscope(AFM),nano-mechanical testing system tribo-indenter(NTS) and spectroscopic ellipsometry(SE).Thirdly,with the consideration of the pad/particle large deformation,a new mathematical model is presented based on the molecular scale removal mechanism, probability statistics and micro contact mechanics.In order to interpret the influence of the abrasive particle size,concentration,oxidizer concentration and chemical mechanical synergy on material removal,another comprehensive model is proposed resting on the energy equilibrium knowledge in relation to the mechanical removal energy and chemical binding energy.Furthermore,the paper also reports another model being incorporation of the fresh wafer surface atoms removal.Finally,this dissertation also develops a novel mathematical model to systematically govern the combinational effects of oxidizer,complexing agent and inhibitor on polishing rate in CMP of copper.A more likely scenario for the process of the molecular scale removal mechanism has three steps:(ⅰ) chemical actions covert strongly the fresh wafer surface atoms/molecules into reacted molecular species;(ⅱ) mechanical actions deliver the energy that removes the weakly bonded reacted molecular species;(ⅲ) the slurry fluid washes the wafer surface,and the fresh surface sites are exposed,which is subsequently etched and removed.This molecular scale removal mechanism is verified form experimental and theoretical study.On one extreme, a mathematical model with the consideration of particle/pad large deformation states that the indentation depth of particle into wafer surface is at molecular scale or less.The effect of the adhesion force is also addressed,which strongly shows that the adhesion force can significantly influence the load force of particle/wafer.This model also predicts that the indentation depth of a particle into wafer surface considering the adhesion force is 2 or 4 times than that of no adhesion force.However,the magnitude of the indentation depth is still on the order of molecular scale.In the following,order-of magnitude calculations are used to support this new mechanism.And a closed-form equation supported by published experimental data is derived of the material removal rate in terms of the molecular removal mechanism.The results show that the material removal mechanism of SiO2 and W can be explained by the molecular scale removal mechanism.In another magnitude analysis,the growth rate and diffusion thickness of the oxide layer are quantitatively evaluated.The calculation reports that the diffusion depth for case of Si wafer is on the order of 1.0×10-3 nm, indicating the CMP material is removed at molecular scale.On the other extreme,a series of experiments was conducted to investigate the mechanism of CMP material removal in this research.Wear behavior between a single slurry particle and the wafer surface using AFM was proposed.The scratch depth under real CMP conduction is of an order of 1.0×10-11m determined on the basis of the linear regression mechanism.The SE tool was used to study the relationship between the thickness of oxidized layer and chemical action time.Since real CMP chemical action time is of an order of 1.0×10-8s,the thickness of the oxidized layer is of an order of 1.0×10-13m evaluated by theoretical model based on the experiment data.In addition,the indentation depth of a single particle into the wafer surface was investigated using NTS with 70 nN force.The indentation depth is of an order of 1.0×10-11 m on the basis of the linear regression mechanism.Nowadays,the abrasive particle size provided by Cabot Company is around 10nm.In addition,few abrasive grooves are found in high-quality-finished polishing wafer surface.The combined calculations and experimental results indicate that the CMP material is removed at molecular scale.No conclusive results have been proposed for the influence of the abrasive particle size on material removal during the CMP process.In this study,a mathematical model as a function of abrasive size and surface oxidizer concentration is presented for CMP.The influence in relation to the binding energy of the reacted molecules to the substrate is incorporated into the analysis so as to clarify the disputes on the variable experimental trends on particle size.It is shown that the mechanical energy and removal cohesive energy couple with the particle size, and being a cause of the non-linear size-removal rate relation.Furthermore,it also shows a nonlinear dependence of removal rate on removal cohesive energy.The model predictions are presented in graphical form and show good agreement with the published experimental data. Finally,variations of material removal rate with pressure,pad/wafer relative velocity,and wafer surface hardness,as well as pad characteristics are addressed.The present study also proposes a non-continuum statistic model for CMP material removal rate by a slurry particle, which considers the direct removal rate of the un-reacted surface sites.It is shown that higher chemical effects would not lead to a proportional increase of the removal rate.As chemical-mechanical synergetic effects are optimal,the removal rate is extremum.The predicted material removal rates follow trends similar to those shown by the experimental observations published previously.At last,the copper CMP is still a challenging subject for developing ICs.The paper presents a novel mathematical model that systematically describes the role of oxidizer,complexing agent and inhibitor on the material removal in CMP of copper.The physical basis of the model is the steady-state oxidation reaction and etched removal in additional to mechanical removal.It is shown that the complexing agent concentration-removal relation follows a trend similar to that observed from the effects of oxidizer on Cu-removal in CMP.The model prediction trends show qualitatively good agreement with the published experimental data. The governing equation of copper removal provides an important starting point for delineating the copper CMP process in addition to its underlying theoretical foundation.
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