Ceria-Based Slurries for Non-Prestonian Removal of Silicon Dioxide Films

Abstract

A slurry with a non-Prestonian dependence on the polishing pressure can help in minimizing dishing and erosion during shallow trench isolation chemical mechanical planarization. Here, we show that ceria-based slurries containing diallyldimethylammonium chloride (DADMAC) yield a non-Prestonian blanket film polish rate with a low threshold pressure (1-2 psi) when polishing plasma-enhanced chemical vapor (PECVD) tetraethylorthosilicate (TEOS) deposited oxide as well as thermal oxide films. The polishing mechanism of this non-Prestonian slurry was investigated by a series of experiments involving zeta potential measurements, thermogravimetric analysis (TGA) and UV-vis spectroscopy and it was shown that more DADMAC molecules are adsorbed on silica particles (as oxide film representatives) than on ceria particles and the binding strength between DADMAC and silica is much higher than that with ceria surface. Shallow trench isolation (STI) is an ubiquitous complimentary metal-oxide semiconductor isolation process technology. Deposition of an isolation stack that contains 3 to 10 nm thick 1,2 thermally grown pad oxide on top of a silicon substrate followed by the deposition of either plasma-enhanced chemical vapor deposition (PECVD) or low-pressure chemical vapor deposition (LPCVD) nitride layer (10 to 30 nm) 1 is the first step in the STI process. In the next step, active areas and isolation fields are determined by patterning the silicon nitride and silicon dioxide pad layers on the silicon substrate, followed by etching of trenches into the silicon substrate using the oxide/nitride stack as a mask. The trenches are then filled with oxide, employing high density plasma-enhanced chemical vapor deposition (PECVD) process using tetraethylorthosilicate (TEOS) as the source of silicon, because of its high gap-filling capacity. The deposited oxide not only fills the trenches but also generates an overfill, which needs to be removed. This is achieved through planarization of the oxide film topography by chemical mechanical planarization (CMP) using a slurry that produces a high oxide and very low nitride removal rates (RRs).In this STI process, major concerns include dishing within the oxide features resulting from over-polish as well as the erosion of the underlying nitride film and, in some cases, the details of the corner rounding near active areas. Therefore, optimization of the CMP process is crucial in order to achieve complete removal of the oxide on top of the nitride film with good planarity and uniformity and to avoid erosion and dishing during the CMP process. 3,4 One method that can be used to minimize dishing and erosion during STI CMP is to control the polishing performance by using a slurry that shows a non-Prestonian polishing behavior. Non-Prestonian behavior occurs when there is a non-linear relationship between applied polishing pressures and resulting polishing rates. Here we consider only the effect of pressure and not that of the rotational velocity on the blanket film polish rates.Several models were di...

AFM-Based Study of the Interaction Forces between Ceria, Silicon Dioxide and Polyurethane Pad during Non-Prestonian Polishing of Silicon Dioxide Films

“…The measured force-distance curves in DI water at pH 4 with and without DADMAC additive are correlated with the non-Prestionian oxide removal rate behavior reported in Ref. 7 along with the coefficient of friction (COF) values obtained during CMP.…”

“…The results obtained were used to explain the observed non-Prestonian oxide removal reported earlier in Ref. 7. The AFM force measurements showed that there is a repulsive interaction between the IC1000 pad and oxide film surface at pH 4 with and without DADMAC additive indicating that the interaction of these surfaces has minimum effect in oxide removal.…”

“…7, DADMAC creates an adsorbed layer on the oxide film which can presumably restrict the contact of ceria particles with the oxide film and, consequently, suppress the removal rates in low pressure zones. This is consistent with the AFM results shown in Figure 3 as the adhesion force between silica particles (representing an oxide film) and ceria-coated silicon substrate (representing ceria particles) vanished in the presence of DADMAC in the liquid medium.…”

“…These non-spherical ceria particles are the same as those that were used in Ref. 7 and several of our earlier publications cited there which include images of these ceria particles. Also, we do not repeat here many of the useful and necessary details that are well described in Ref.…”

Functional Paper-Based Platform for Rapid Capture and Detection of CeO2 Nanoparticles

“…Therefore, CeO 2 particles can be found in wastewaters from CMP polishing operations. 23 Six different waste samples were collected from a typical CMP process as follows. CGS/SiN and CGS/SiO 2 : 0.1 wt % ceria slurry with glycine and nicotinic acid used for silicon nitride (SiN) and silicon oxide (SiO 2 ) wafers polishing with measured pH values of 4.3 and 4.45, respectively.…”