Chemical Mechanical Polishing of Dielectric Films Using Mixed Abrasive Slurries

Abstract

We report on the use of mixed abrasive slurries ͑MAS͒ containing alumina and ceria abrasives for chemical mechanical planarization ͑CMP͒ of silicon dioxide and silicon nitride films for shallow trench isolation applications, extending an earlier investigation of alumina/silica MAS for the CMP of copper and tantalum films. These slurries show a polish rate selectivity between oxide and nitride films that is as high as 65 and show an excellent surface quality even without additives. Analysis of dried slurry particles using transmission electron microscopy indicates formation of a sheath of smaller ceria particles around larger alumina particles. Possible explanations and supportive arguments for the improved performance of MAS during CMP are presented based on the particle-particle and particle-film interactions.Chemical mechanical planarization ͑CMP͒ is widely accepted as an effective technique for meeting current ͑2002͒ and near future planarization requirements of the semiconductor industry. 1 Damascene and dual-damascene processing, coupled with CMP, have successfully implemented copper ͑Cu͒ interconnects in integrated circuit ͑IC͒ fabrication, 2 leading to greatly reduced resistancecapacitance ͑RC͒ delays and superior chip performance. Another important application of CMP occurs in the use of shallow trench isolation ͑STI͒ for device isolation. STI offers better dimensional control ͑trench and width͒ and greater packing density 3,4 relative to the earlier isolation achieved by local oxidation of silicon ͑LOCOS͒. Better planarity is achieved due to the elimination of local encroachment of field oxide. 5 In STI, isolation trenches are plasma etched in the silicon substrate using a thin nitride mask layer, which simultaneously acts as a stop and a capping layer. The trenches are overfilled with chemical vapor deposited ͑CVD͒ oxide. 4 As in dualdamascene patterning, the overburden oxide is removed using CMP while removing as little of the nitride as possible. Finally, the nitride is etched using hot phosphoric acid and active devices are fabricated in the exposed silicon areas. It is critical to minimize microscratching, particulate adhesion, and overpolishing during STI CMP. 4 Introduction of a thin nitride film combined with a ceria-based, highly selective CMP process for overburden oxide removal can eliminate the need for overpolish. 6,7 These highly selective ceria-based slurries, however, can generate microscratches and hence performance must be improved further for an effective application to STI CMP.Thus, an important area of current research in CMP continues to be the development of slurries that can eliminate or minimize the problems associated with the conventional CMP process. 8,9 Typically, a slurry consists of two phases, namely, liquid and solid phases. Liquid phase consists primarily of deionized ͑DI͒ water with several additives like oxidizers, complexing agents, inhibiting agents, and surfactants. Solid phase is comprised of abrasives, which are usually inorganic oxides, e.g., alumina, silica, cer...

Colloid aspects of chemical–mechanical planarization

“…15), allowing for the manipulation of selectivity of the planarization process [76]. While the particles in these investigations were not uniform, it was evident that in most instances the smaller solid constituents were deposited on the larger cores [75,76].…”

“…Fig. 14 demonstrates that the mixed abrasives caused a significant increase in the removal rate and lesser roughness of silicon nitride, as compared to using each abrasive component separately [75].…”

“…While silica and alumina particles are commonly used for polishing copper and tungsten, silica and ceria are used to polish SiO 2 , poly-Si, Si 3 N 4 and perhaps low-k films [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Recently, composite abrasives in which core particles are coated or covered by a material of a different chemical composition, have also been investigated [24][25][26][27][28].…”

Investigation on Surface Hardening of Polyurethane Pads During Chemical Mechanical Polishing (CMP)

“…1,2 In most cases, a selected layer can be removed through the optimal design of slurries, which can include various kinds of abrasives and chemical components. [3][4][5] The various chemicals and abrasives in slurries can affect the interfacial surfaces that occur during the CMP process at different process temperatures. This effect can change the properties of the polishing pad and produce undesirable variation of the removal rate (RR) as well as within-wafer nonuniformity (WIWNU) throughout the pad lifetime.…”

Key Chemical Components in Metal CMP Slurries

“…The hardness of the alumina would still contribute toward the removal rate, and the surface coating with softer silica abrasives would prevent the surface defects. Hegde and coworkers [102,103] demonstrated this concept using the electrostatic interaction between the individual abrasives at a given operating pH.…”