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TITLE: Process-Induced Damage or Antenna Rules
During manufacture, the gate oxide may become damaged when
exposed polysilicon and metal structures collect charge from the
processing environment (e.g., reactive ion etch) and develop
potentials sufficiently large to cause Fowler-Nordheim current to
flow through the thin oxide. This process-induced damage is
generally referred to as "antenna rules". Given the known process
charge fluence, a figure of exposed conductor area to transistor
gate area ratio is determined which guarantees time-dependent
dielectric breakdown reliability requirements for the fabricator.
Failure to consider antenna rules in a design may lead to either
reduced transistor performance or to total failure if the antenna
rules are seriously violated.
There are layout techniques to help deal with antenna ratio
rules. For example, if a design uses a large array of clocked
devices connected to a single clock source via a metal1 clock
distribution structure then a "cut and link" method can be used
to moderate the antenna rule effects. In this method, the metal1
distribution structure is divided up into pieces of metal1
connected to gate structures such that the antenna rule is
obeyed. Short links from metal1 to metal2 then back to metal1
connect the clock distribution structure in a way that it
prevents the total area of the clock distribution structure from
being connected to gate poly structures during metal1 etch.
Specific numbers for the antenna ratio rules are contained in
design rules for each fabricator. MOSIS customers can obtain this
information by accessing: MOSIS Rules
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