| 13.2 Types of Design Rules |
The design rules primary address two issues:
1. The geometrical reproduction of features that can be reproduced by the mask-
making and lithographical process ,and
2. The interaction between different layers. |
| There are primarily two approaches in describing the design rules. |
1. Scalable Design Rules (e.g. SCMOS, λ-based design rules) :
In this approach, all rules are defined in terms of a single parameter λ. The rules are so chosen that a design can be easily
ported over a cross section of industrial process ,making the layout
portable .Scaling can be easily done by simply changing the value of
.
The key disadvantages of this approach are:
1. Linear scaling is possible only over a limited range of
dimensions.
2. Scalable design rules are conservative .This results in over
dimensioned and less dense design.
3. This rule is not used in real life. |
2. Absolute Design Rules (e.g. µ-based design rules ) :
In this approach, the design rules are expressed in absolute
dimensions (e.g. 0.75µm) and therefore can exploit the features of a
given process to a maximum degree. Here, scaling and porting is
more demanding, and has to be performed either manually or using
CAD tools .Also, these rules tend to be more complex especially for
deep submicron. |
The fundamental unity in the definition of a set of design rules is the minimum line
width .It stands for the minimum mask dimension that can be safely transferred to
the semiconductor material .Even for the same minimum dimension, design rules
tend to differ from company to company, and from process to process. Now, CAD
tools allow designs to migrate between compatible processes. |
| |
