Consumables for Advanced Shallow Trench Isolation STI

One of the main motivations for the development of the STI process is to eliminate the bird s beak phenomenon. With STI, the field oxide is well embedded into the Si and is clearly distinctive from the active-area regions. It allows very narrow active-area pitches and a higher device-packing density. 

Microelectronic Applications of Chemical Mechanical Planarization, Edited by Yuzhuo Li Copyright 2008 John Wiley Sons, Inc. 

FIGURE 13.1 Illustrations of the various processing steps for local oxidation of silicon and shallow trench isolation (from Ref. 7). 

As shown in Fig. 13.1, a CMP step is required in the STI process. There are two possible approaches to implementing the CMP step STI—direct and indirect. In a direct STI process, the CMP process is applied directly on a wafer right after the trench oxide deposition (Fig. 13.1). The CMP process removes the overburden oxide as well as the topography created during trench oxide deposition over the features with various pattern densities across the dies and the wafer. For some slurries, especially the conventional oxide slurries, these topographies are a challenge. To overcome this difficulty, a pre-CMP step is sometimes implemented in which a reverse mask is applied onto the film and the oxide in the raised area is preferentially etched. After the etching step, the 

CMP step is used to planarize and remove overburden oxide. This is also called indirect STI process. The requirements for direct-polish STI CMP processes include minimal within-die (WID) oxide and nitrite ranges, limited nitride loss, limited oxide dishing, low defectivity, and excellent nonuniformity, both within wafer (WIW) and wafer to wafer (WTW) [8]. 

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J. Schlueter, I. Kim, F. J. Krupa, The Effect of Consumables in the Development of Advanced Shallow Trench Isolation (STI) CMP Processes, Proceedings of Chemical-Mechanical Planarization for ULSI Multilevel Interconnection Conference (CMP-MIC), 1999, pp.336-339... 

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