Appeal 2007-2035
Application 09/848,846
resulting from the presence or absence of a halo implant, we fail to see how
such a technique would result in three or more threshold voltages for three
different devices. Nor has the Examiner explained on this record how this
can be achieved.
In our view, using the claimed technique to conduct halo implants
using a common mask to impart to at least three different devices three
different threshold voltages goes well beyond mere duplication of parts. The
claimed invention uses a common mask for three different devices to vary
the degree of masking which dictates the resulting halo implant. In short,
the type of mask dictates the type of halo implant. The particular type of
halo implant that is formed, in turn, dictates the resulting threshold voltage
for that particular device. That is the essence of the claimed invention.
As shown in Figure 6 of the present application, partial masking
(partial exposure) for transistor 26 results in only one halo region 41.
Complete masking (no exposure) for transistor 26a results in no halo region
at all. But no masking (full exposure) for transistor 26b results in two halo
regions 41. As a result, transistor 26b has the highest threshold voltage and
transistor 26a has the lowest threshold voltage. The threshold voltage of
transistor 26 is between that of the other transistors. See Specification 9, l. 1
- 10, l. 16.
To render the claimed invention obvious over Lowrey, the skilled
artisan would have to recognize that the common mask (polysilicon 45)
could somehow be altered to provide at least three different exposure levels
that would result in at least three different types of halo implants for three or
more discrete devices respectively. Such an alteration of the structure of
Lowrey, in our view, simply strains reasonable limits and amounts to
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