Closing the smoothness and uniformity gap in area fill synthesis

Abstract

Control of variability in the back end of the line, and hence in interconnect performance as well, has become extremely difficult with the introduction of new materials such as copper and low-k dielectrics. Uniformity of chemical-mechanical planarization (CMP) requires the addition of area fill geometries into the layout, in order to smoothen the variation of feature densities across the die. Our work addresses the following smoothness gap in the recent literature on area fill synthesis. (1) The very first paper on the filling problem (Kahng et al., ISPD98 [7]) noted that there is potentially a large difference between the optimum window densities in fixed dissections vs. when all possible windows in the layout are considered.(2) Despite this observation, all filling methods since 1998 minimize and evaluate density variation only with respect to a fixed dissection. This paper gives the first evaluation of existing filling algorithms with respect to "gridless" ("floating-window") mode, according to both the effective and spatial density models. Our experiments indicate surprising advantages of Monte-Carlo and greedy strategies over "optimal" linear programming (LP) based methods. Second, we suggest new, more relevant methods of measuring a local uniformity based on Lipschitz conditions, and empirically demonstrate that Monte-Carlo methods are inherently better than LP with respect to the new criteria. Finally, we propose new LPbased filling methods that are directly driven by the new criteria, and show that these methods indeed help close the "smoothness gap".

Simultaneous flare level and flare variation minimization with dummification in EUVL

“…Although dummification may be limited to design rules and layout constraints, it has been shown that dummification can simultaneously reduce intra-chip flare level and flare variation in EUVL for the process with a clear-field mask, and thus may greatly simplify the flare compensation methodology with global CD resizing [10]. There are many existing dummy fill algorithms for improving ChemicalMechanical Polishing (CMP) quality [3,4,7,18,6]. The objectives of these algorithms mainly focus on density variation minimization or density gradient minimization for a layout.…”

EUV and e-beam manufacturability

“…Dummification (dummy fill) is one of flare mitigation strategies that has the ability to simultaneously reduce flare level and variation, which could greatly simplify the global CD resizing process [19,30]. Existing dummification algorithms designed for Chemical Mechanical Polishing (CMP), whose objective is to achieve maximum pattern density uniformity, are not suitable for EUV flare mitigation [6,7,8,9,39]. As illustrated in Figure 3(a) from [10], a uniform pattern density distribution still incurs large flare variation.…”

Recent research development in physical design for manufacturability

“…Chen and Chang [4] presented the first multilevel, full chip gridless detailed router considering the OPC effects. The router can handle non-unifonn wire widths and consider routability and OPC simultaneously.…”

“…Chen et al [4] highlighted the importance of the smoothness gap. For the dummy metal insertion methods based on the discretization, the lack of considering density variation across the die would result in a smoothness gap.…”