The Effect of Slurry Properties on the CMP Removal Rate of Boron Doped Polysilicon

Abstract

Doped polysilicon is used as a via fill material for through silicon via technology. Boron doping is used to reduce the polysilicon resistivity but boron doping significantly decreases the polish removal rate. Here the influence of slurry characteristics, chemistry and abrasive properties, on the chemical mechanical polishing of heavily boron-doped polysilicon is investigated. The effect of slurry pH on silica abrasive size and colloidal stability is examined as well as the influence of these effects on the polish rate. The optimum abrasive concentration is ∼6 wt% and higher concentrations did not improve the polish rate due to the saturation of slurry particles on the wafer surface. Smaller abrasive particles, with 10 times higher surface area per unit weight improved the polish rate ∼20%. Finally, polish conditions with mechanical and chemical dominance are compared.Integrated circuit fabrication includes many depostion manufacturing steps which leave undesired topographies on wafer surfaces. These include copper electroplate for damascene copper interconnects and Si chemical vapor deposition (CVD) for through silicon via (TSV) fill. 1,2 These technologies have been enabled by the use of chemical mechanical polish (CMP) which has high removal rate and the ability to planarize and minimize damage of the polished surface. 3,4 During the CMP process a rotating wafer is pushed (with down force F) into a polymeric rotating pad while slurry is spread over the pad to provide chemistry and abrasives to the wafer surface. The polished surface quality and the polish rate depend strongly on the polish properties such as polish pressure, velocity and the slurry chemistry and abrasives which are specific to the type of material being polished. The presence of oxidizers is essential to improve the polish behavior for metals while for semiconductors an etchant is used to weaken the wafer surface chemical bonds. 3,5 The pH of the solution, chemical additives and abrasive shape, type and size are some of the slurry factors which can influence the polish rate significantly.Doped polysilicon is used as both a p-type and n-type semiconductor in field effect transistors and as a fill material for TSV used for the front end of line and 3D packaging processes. 6 CMP is an enabling IC fabrication process and the CMP of doped polysilicon has been studied. 7-9 Improving the polish rate of doped polysilicon can significantly improve the manufacturing cost and time. Enhancement of polish rate can be achieved by optimizing the polish properties such as pressure, flow rate and velocity, as has been shown in our prior publications. 10,11 Polish rate can also be improved by enhancing the slurry chemistry and by understanding the basic properties of the slurry.Pietsch et al. studied the influence of slurry pH and found that the maximum etch and polish rate of single crystal silicon (n-type Si (100) and (111) wafers with 150 cm resistivity) occurs at pH∼11. 8,[12][13][14] They showed that the presence of hydroxyl anions plays a major role in th...

A Polishing Processes Optimization Method for Ring-Pendulum Double-Sided Polisher

“…Moreover, the convergence rate of surface error for elements improved from 37.59% to 44.44%. Pirayesh et al [14] examined the influence of slurry pH on the size of silica abrasives and their colloidal stability, and how these factors ultimately impacted the polish rate. Their findings provided strong evidence supporting the significant effects of slurry pH, abrasive concentration, and grain size on the polish rate.…”

Chemical-Mechanical Impact of Nanoparticles and pH Effect of the Slurry on the CMP of the Selective Layer Surfaces

“…X-ray photoelectron spectroscopy (XPS) is an important surface analytical tool that can be used to identify compounds formed on the metal surface due to the action of chemicals present in the CMP slurry. In the literature, there are numerous studies on similar topics [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] applied to the copper CMP of integrated circuits. It is worth mentioning that the present study intends to extend to other fields, namely to surfaces coated through selective transfer (the surfaces of the selective layer) in the friction process, considering the slurry pH (important for removal through CMP of the selective layer) [7,[22][23][24][25][26], H 2 O 2 (the most common oxidant) [27][28][29][30][31][32][33], size [21,[28][29][30][31], and concentration [12,21,34] of nanoparticles used in the CMP slurry.…”