The next generation tool for Dummy Filling

Very deep sub-micron technologies require that process related issues are taken into account during design. Starting with 130nm processes, a Chemical Mechanical Polishing (CMP) step has been adopted in the manufacturing process to flatten wafer surface between each metal layer. Designers have to insert “dummy tiles” into empty areas of their design to help flatten the surface for each metal layer, since metal density variations badly impact the CMP process.

This step, called metal filling or wafer planarization, is necessary for most advanced processes to increase the foundry yield. While non uniform feature density causes CMP to over-polish empty area, and under-polish dense areas, resulting in degraded performance, the insertion of dummy tiles ensures a uniform pattern repartition over the chips and wafers, thus an increased factory yield. These additional polygons, though electrically inactive, may add parasitic effects, which must be taken into account early in the design process to ensure correct behavior and timing of the chip.

GTstyle – Hybrid Metal Fill Engine

GTstyle is a metal fill engine dedicated to the 90nm processes and below, which combines the power and efficiency of a model-based approach with the simplicity of a rule based tool. GTstyle does not require a fully qualified process model, but delivers major yield improvement by ensuring that process targets for density and roughness are met throughout the design.

GTstyle unique features accommodate complex metal filling rules, while keeping a strict compatibility with Design Rule Checkers (DRCs) checks. GTstyle usually generates between 50 to 85% less dummy tiles than pure rule based engines, and keeps dummy tiles as far as possible from active geometries, dramatically reducing parasitics and impact on timing.

GTstyle is ideally suited for processes, where uniform density and minimum file size are desirable. It is easy to use but offers complex inter-layer and geometry spacing options, and its metal filling specific engine offers advanced features not available to multi-purpose DRC tools, such as custom fill shapes, dummy stacking and grounding, and uniform distribution along non-orthogonal grids.

Key benefits

Maximize CMP yield with highly accurate tile insertion based on local measurements of density and roughness, and their variation over large areas,
Minimize parasitic effects by limiting the number of inserted tiles, and positioning them away form critical active geometries,
Easy setup, as it does not require a fully qualified process model from the foundry,
Take into account impact of dummy tile insertion early in the design process, thanks to fast computation,
Compatible with existing DRC flows.

Main features

Accurate Density and Roughness Analysis

GTstyle accurately analyses the 3-D topology of the chip and accurately computes local density and roughness values, as well as variations of density and roughness across the chip and at the boundaries, since those variations may cause yield degradation. It compares those values to process-specific targets provided by the foundry. A patented insertion algorithm determines the minimum number of tiles to be inserted in order to achieve density, roughness, and gradient limits.

Keep Away Function

Inserting dummies in a chip creates parasitics that adversely affect the circuit behavior and performance. GTstyle enables the user to define a “keep away” distance between inserted tiles and active geometries. In areas, where density targets allow for metal fills to be placed far from active nets, a reduction of 90% of parasitic capacitance has been observed.

It is also possible to specifically increase the spacing around critical nets, provided by any 3rd party extractor, to meet hard to reach timing specifications.

Uniform Dummy Distribution

Traditional placement of dummies along a grid parallel to the device geometries may result in unbalanced parasitic effects along different nets, some nets being much closer than others to the inserted tiles. GTstyle supports non orthogonal grids to avoid this problem.

Insert any Type of Dummies

GTstyle metal fill engine is very flexible. It supports full layer filling, as well as the insertion of any user-defined dummy. Dummy tiles can be any shape, they can even be complex elements such as stacked vias, diodes to ground, etc...

In order to better achieve density target, GTstyle can concatenate dummies to create bigger metal filling patterns. And to minimize the impact of floating capacitances, GTstyle enables dummy grounding to build an efficient shielding: interconnect cells may be inserted between contiguous dummies, dummies can be stacked, and it is easy to insert dummy stripes, since GTstyle manages the antenna effect.

High Performance and Low Memory Usage

GTstyle has been optimized in terms of speed, memory, and disk usage. This allows designers to perform metal filling early in the design process and take into account the possible induced parasitic effects.

GTstyle is able to manage the largest databases since it directly operates on zipped or compressed files. Special optimizations in the filling algorithm have been developed to minimize the size of the generated GDSII or OASIS databases.

User Interface

GTstyle offers an intuitive Graphical User Interface to define the insertion rules specific to the project and to perform the insertion step. It is also avaiable through the command line making it fully scriptable and enabling automatic processing and easy inclusion in an existing flow.

Patented filling algorithm

At the heart of GTstyle is a patented filling algorithm, which calculates the minimum of tiles to be inserted in zones while keeping given density, roughness and gradient limits. As opposed to other metal-fill tools, GTstyle is highly flexible and can be used for any process.

GTstyle performance

GTstyle has been optimized in terms of speed, memory and disk usage. This allows designers to perform the metal-fill early in their design process, and take into account the possible induced parasitic effects.

GTstyle is able to manage the largest databases, since it directly operates on zipped or compressed files. Special optimizations in the filling algorithm have been developed in order to minimize the size of the generated GDSII/OASIS databases.

GTstyle is 10x faster than a classical DRC tool.

Supported platforms

SUN Sparc Stations, 32 and 64 bits, Solaris 2.5 and + HP HPUX 11.x x86 PC Linux RedHat 3 and + x86-64 PC Linux RedHat 3 and + ItaniumII Linux RedHat 3 and +