Technology
An In-Depth Look
Figure A: LithoRoute Subsystems
Figure A shows that LithoRoute consists of three major subsystems, namely Global Route, Track Route and Detail Route. These three subsystems perform routing task at different granularity. The Global Route performs routing at the so-called GCELL level. The Track Route performs routing at the routing track level. The Detail Route performs routing at the finest level that can guarantee DRC clean.
In order to support large capacity designs, special techniques are deployed at all subsystems of the router.
- Global Route uses a multi-level data representation scheme. This representation is memory compact and efficient, enabling the Global Route to handle very large circuit at high speed. It also allows Global Route to run efficiently at incremental and iterative modes.
- Track Route divides problem into routing layers and each layer is further divided into lanes. The problem on each lane is solved independently. At each lane, the routing problem is formulated into a linear assignment problem, making it suitable for very large design with fast run time.
- Detail Route processes design in small partitions. The design is divided into many partitions. Each partition can be processed independently, making it suitable for very large design with fast run time.
At the heart of LithoRoute is a sophisticated data structures and flow control subsystem. The data structure employs a hybrid of grid models, where different grid models are used at different phases of the routing. This innovative arrangement improves run time, routability and usability of the system. The flow control unit contains the key know-how of the router to determine the routing strategy and detailed processing sequences required to finish all routes for the given design.
The input subsystem free the routing core from knowing details of the input including user design, design rules, technology rules, design constraints and model data. This model data is extracted from SPICE and lithography models provided by the foundry. The extraction is done offline to produce model data for the router.
The output system summarizes the routes and stores it to external OA database, which can then be used by other tools.
Buried deep inside the Detail Route is a rapid model calculator. Based on a patent-pending technology, the calculator quickly provides layout guidance for a given input geometry or routing pattern. This guidance is in turn used in a query function during the route searching step of the Detail Route. Figure B shows a conceptual diagram of a detail router utilizing such a model calculator. In addition to the usual tasks such as net ordering, cost calculation and constraints/rules check, the detail router performs additional query in search step to avoid “bad pattern” and guarantee layout to be litho-friendly with improved variability and yield.
Figure B: The Detail Route subsystem includes a model calculator.
Snapshot
An example of a layout produced by LithoRoute:
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