MICROELECTRONIC SYSTEMS NEWS

FILENUMBER: 1147 BEGIN_KEYWORDS Process-Induced Damage Antenna Rules END_KEYWORDS DATE: November 2003 TITLE: Process-Induced Damage or Antenna Rules
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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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