Design rule correction system and method

Details Design rule correction system and method Design rule correction system and method

1998-04-09

2001-02-13

Lintz, Paul R. (Department: 2768)

Computer-aided design and analysis of circuits and semiconductor

Nanotechnology related integrated circuit design

C716S030000, C716S030000, C716S030000, C716S030000, C716S030000, C716S030000

Reexamination Certificate

active

06189132

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to object layouts and, more particularly, to a system and method for correcting design rule violations for object layouts in very large scale integrated (VLSI) circuits.
2. Description of the Related Art
Semiconductor chip layout is subject to complex rules governing, among other things, geometry of shapes on process layers. These complex rules may include, for example, width requirements, spacing requirements, overlap requirements, etc. Compliance with these rules, called design rules, is important to chip functionality and manufacturability.
Many conventional processes used to create or alter layouts can introduce design rule violations. Manual layout, for example, inevitably introduces violations due to the difficulty of satisfying a large number of complex design rules by hand. These violations are generally corrected via tedious iterations between design rule checking tool runs and manual layout modifications.
Technology migration is another process which gives rise to a very large number of design rule violations. Migration is the process which transforms layouts in one technology to a layout in a technology with different design rules. The migration process begins with a simple scaling, using commercially available programs, and is sufficient to produce a design-rule-correct layout. In many cases, however, non-scalable differences in the design rules result in the introduction of design rules violations, which must again be corrected by hand by tedious manual iteration.
To date, the only automation technology available to assist in design rule violation correction is compaction. Compaction is a technique used to minimize the area of a layout while satisfying design rules. Design rule violation correction is accomplished as a side effect of the process. The prime objective of minimizing area can cause great disruption to the layout. Critical alignments, inter-net spacing, symmetries, power, performance, etc. can be easily lost in the process. Designers generally find this degree of disruption unacceptable. Though some of the critical features may be preserved by the addition of manual constraints. Adding these constraints is another tedious, error prone process. As a consequence of these limitations, compaction has not found wide use as a design rule correction aid.
Compaction is performed as follows. Compaction includes two steps. The first step includes constraint graph generation and the second includes constrained optimization. Conventional compaction modifies a layout in one direction at a time. For simplicity, compaction is described for a horizontal direction (or x direction in Cartesian coordinates) modification. The same method applies for a vertical direction (or y direction in Cartesian coordinates).
The linear constraints are established which represent the separation between layout elements required by design rules. A constraint based optimization is performed based on a selected objective function which is subject to the system of linear constraints. In conventional compaction, the objective function is a minimum sum of all X
i
, where X
i
is a variable representing the position of an element, subject to the system of linear constraints. Conventional compaction also includes aspects, for example wire length minimization. Further details of compaction are contained in an article by Liao et al. entitled “An Algorithm to Compact a VLSI Symbolic Layout with Mixed Constraints”, 20th Design Automation Conference, Miami Beach, Fla., June 1983, pp. 107-112 and an article by Lee et al. entitled “A Performance-Aimed Cell Compactor with Automatic Jogs”, IEEE Transaction on Computer Aided Design, VOL. 11, No. 12, December 1992, pp. 1495-1507.
Minimizing the sum of X
i
's has the effect of selecting the smallest value of X
i
for each edge in the design. This is equivalent to pushing all edges in the design as far to one side as possible which also minimizes area which is unacceptable. Together with a wire length objective, the conventional compaction produces more reasonable results. However, this global minimization often comes with unacceptable perturbation of the original layout.
Therefore, a need exists for a system and method for automatically correcting design rule violations with minimal disruption to the input layout. A further need exists for a system and method for automatically correcting design rule violations during technology migration.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method of modifying a layout of a plurality of objects in accordance with a plurality of predetermined criteria includes the following steps. A step of defining an objective function for measuring a location perturbation and a separation perturbation of the objects in the layout is included. Defining a linear system using linear constraints in terms of design rules and the objective function to describe separations between layout objects is also included. The linear system is solved to simultaneously remove violations of the design rules and shapes and positions of objects in the layout are modified in accordance with the solution of the linear system such that a total perturbation of the objects in the layout is minimized.
In alternate methods of modifying a layout, the step of weighting the location perturbation and the separation perturbation in accordance with predetermined criteria is included. The step of defining the objective function includes defining the objective function for the location perturbation equal to |X
i
−X
i
old
| where X
i
is a final location of object i and X
i
old
is an initial location of object i, and defining the objective function for the separation perturbation equal to |X
j
−X
i
−(X
j
old
−X
i
old
)| where X
j
is a final location of object j and X
j
old
is an initial location of object j. The step of defining the system of linear constraints may include the step of defining linear constraints of the form X
j
−X
i
≧d
ij
where X
j
is a final location of object j, X
i
is a final location of object i and d
ij
is a relative distance between i and j as defined by design rules. The objective function may be a non-linear function which may be transformed into a linear function by modifying the linear constraints.
The method of modifying the layout may further include the steps of modifying the linear constraints in accordance with user defined design requirements and introducing the design requirements into the linear system to be used to modify the shapes and positions of the objects.
When the layout includes violations, the step of determining a status of the violation may be included wherein the status is keep, remove or ignore the violation. When the status is keep the violation, the step of modifying a linear constraint in the linear system may be included. When linear constraint is of the form X
j
−X
i
≧d
ij
where X
j
is a final location of object j, X
i
is a final location of object i and d
ij
is a relative distance between i and j as defined by design rules, the step of modifying the linear constraint to X
j
−X
i
≧X
j
old
−X
i
old
where X
i
old
in an initial location of object i, and X
j
old
is an initial location of object j may be included. If the status is ignore the violation, the step of deleting a linear constraint that is violated may be included. If the status is remove the violation, the step of removing the violation by solving the linear system is performed. When the layout includes violations where no solution exists, the step of relaxing constraints in accordance with a penalty term to improve the layout may be included.
Another method for modifying a layout of a plurality of objects to ensure compliance with a plurality of predetermined rules and design requirements includes determining a weighted perturbation cost, creating a system of linear constraints in accordance with the design rules and the weighted perturbation co

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