The formulation of slurries for chemical–mechanical planarization (CMP) is currently considered more of an art than a science, due to the lack of understanding of the wafer, slurry, and pad interactions involved. Several factors, including the large number of input variables for slurries and the synergistic interplay among input variables and output parameters, further complicate our ability to understand CMP phenomena. This article provides a fundamental basis for the choice of chemical additives and particles needed for present-day and next-generation slurry design. The effect of these components on nanoscale and microscale interaction phenomena is investigated. Methodologies are suggested for the development of next-generation slurries required to overcome CMP challenges related to defectivity and the surface topography of soft materials such as Low-κ dielectrics and copper.
Understanding the pH and down pressure effects is critical in elucidating the chemical and mechanical mechanisms in chemical mechanical polishing ͑CMP͒. This paper describes the variation in polishing rate by nonagglomerated silicon dioxide particles. The repulsive interaction force, solubility of amorphous silica, and total contact area at the pad-particles-wafer interface are important factors in determining polishing performance. In situ friction force measurements are used to detect the variation of interfacial contact during polishing. Surface finishes and interaction force of silica/silica were investigated using atomic force microscopy.Chemical mechanical polishing ͑CMP͒ is the process to remove excessive topographic variations and to achieve global and local planarization in microelectronic device fabrication. 1,2 The miniaturization of microelectronic devices has augmented the roles of CMP in the semiconductor industry. CMP is a complex process achieved by the synergistic interactions of the mechanical abrasion and chemical reaction at the pad-particles-wafer interface. 3 In mechanical abrasion, the removal of material and planarization results from the direct contact of the wafer against particles embedded in the pad. 4,5 For chemical reaction, chemical environments are responsible for the physical and mechanical properties of top surface thin layer in dielectric and metal CMP. 6-8 The desired performances ͑i.e., global planarization, good surface finish, and high removal rate͒ of CMP are dominated significantly by the synergistic interaction coming from mechanical abrasion and chemical interaction. 9 To yield a desired CMP performance, one must understand the chemical and mechanical mechanism involved in the polishing process.CMP of dielectric silica has long been an important step for planarization in multilayer interconnects. The polishing mechanism of dielectric silica has been investigated to achieve a desired CMP performance. The mechanism controlling CMP is manifested in the contact response at the pad-particles-wafer interface and physical properties at the surface and near-surface level. Especially, the physical properties of near surface layer of silicon dioxide are significantly dependent on the slurry condition. Tomozawa et al. 10 noted that the decrease in microhardness of silica glass with water content is due to the diffusion of water into the surface of silica glass. Hammond and Ravitz 11 reported that fracture strength of silica decreases with water because surface free energy is lowered by the increase of the amount of water content. Nevot and Croce 12 have examined the existence of the near surface of silica having lower density than of the bulk using grazing X-ray reflection. Trogolo and Rajan 7 revealed the evidence of physically modified near surface thin layer of silica produced at pH 10.5 using transmission electron microscopy ͑TEM͒. The effect of pH on the polishing rate of silica by colloidal silica has been investigated. 13 Polishing rate remained constant for рpH 11, but bega...
Copper contamination during dilute HF (DHF) cleaning is one of the critical issues in silicon semiconductor device manufacturing. In this paper, copper outplating from DHF solution onto silicon surfaces was studied with transmission electron microscopy. It was found that copper ions preferentially deposited only at the amorphous silicon regions. A sharp circular boundary between the copper deposited and undeposited areas was obtained which was found to correspond to the amorphous‐crystalline transition in the substrate. The deposited copper particles were face centered cubic polycrystalline structure with particle size ranging from 5 to 60 nm. Similar Cu deposition patterns were also found on other samples with scanning electron microscopy. The pattern formation of copper deposition was attributed to the preferential nucleation of copper in the amorphous regions. © 2000 The Electrochemical Society. All rights reserved.
This paper reports on characterization of the surface coverage of particles by in-situ lateral friction force measurement during chemical mechanical polishing. The lateral friction force apparatus was made to operate close to real CMP conditions. For these experiments a sapphire wafer of constant surface roughness was used. For both 2psi and 4psi down force we observed increase in lateral friction forces with increasing solid loading. The lateral friction forces have been found to be significantly dependent on the contact area at the wafer-pad-slurry interface, thus showing that in-situ dynamic friction force changes in the surface coverage of particles. From these results, we conclude that the enhancement of frictional force is due to increased contact area at the wafer-pad-slurry interfaces. The lateral friction force measurement can provide an understanding of wafer-pad-slurry interactions.
Chronoamperometry was used to investigate the reaction/passivation kinetics and thickness of the chemically modified surface layer on the copper during chemical mechanical polishing (CMP). The result showed that the reaction/passivation kinetics and the thickness of the chemically modified surface layer are strongly dependent on the chemistry of CMP slurry in the chemical aspect of CMP and play critical keys in the selection of the chemistry and its concentration. BTA and H2O2 enhanced the passivation kinetics, resulting in thinner layer on the copper surface. In addition, the reaction kinetics increased as pH decreased.
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