The written description specifically notes some unsuccessful attempts to cure this problem
in TiN films. One was characterized as successfully reducing the resistivity but resulting in TiN films
with undesirable contaminants. Application 09/128,143, Specification, p. 3, ll. 2-15.
The section of the written description titled “Summary of the Invention,” states that the
inventors discovered that post treating films with an inert plasma while biasing the substrate will
improve film resistivity and stability:
We have found that a post treatment of films formed via chemical vapor
deposition by exposure of the deposited film to an inert plasma while biasing
the substrate, results in more stable films. In particular, titanium nitride films
formed by chemical vapor deposition from a metallo-organo titanium
compound are modified to improve the resistivity and stability of the films.
Application 09/128,143, Specification, p. 3, l. 20 - p. 4, l. 2 (emphasis added). In the “Detailed
Description of the Invention” the 143 Specification describes post treating the film “[i]n accordance
to the process of the present invention” by subjecting the TiN film to an inert plasma containing “high
energy ions, obtained by applying a DC bias voltage to the substrate:”
In accordance with the process of the present invention, films of titanium
nitride are post treated with an inert plasma containing high energy ions,
obtained by applying a DC bias voltage to the substrate. Only a low power
RF level need be applied, i.e., sufficient power to form a plasma from a
precursor gas, and a voltage of about 100 to 1000 volts applied to the
substrate. For example, a voltage of about 400 volts while applying only 100
watts of RF power to form a plasma is quite sufficient to produce high energy
ions and to passivate or densify a titanium nitride film so that it remains stable
over time.
Application 09/128,143, Specification, p. 7, l. 20 - p. 8, l. 5 (emphasis added). The 143 Specification
expresses the theory that the improved results are due to densification of the film by bombardment
with high energy ions resulting from the voltage bias applied during the plasma treatment:
We believe that biasing the substrate in the plasma bombards the surface with
high energy ions that densify the film, and in turn reduce the absorption of
oxygen by the film after exposure to atmosphere.
Application 09/128,143, Specification, p. 4, ll. 2-6 (emphasis added). The 143 Specification
reiterates the belief that bombardment with high energy ions causes film densification:
Although the exact mechanism of the present invention is not known, we
believe the high energy ion bombardment of the films on a biased substrate
densifies the films.
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