C.1.
The section of the 143 Specification tilted “Background of the Invention” notes problems with
certain prior art CVD processes for making TiN films:
the resistivity of the titanium nitride film is high and unstable. Over time the
resistivity increases to such an extent that the film is no longer usable for
semiconductor devices.
Application 09/128,143, Specification, p. 2. l. 23 - p. 3, l. 1. More specifically the 143 Specification
says the properties of TiN films made according to the prior art contain undesirable amounts of
carbon which causes the resistivity to degrade when exposed to the atmosphere:
The titanium nitride obtained contains significant amounts of carbon, and the
resultant titanium nitride films are chemically reactive. Thus when the films
are exposed to air or other oxygen containing gas, oxygen is absorbed and the
films then contain both carbon and oxygen as impurities. Since the oxygen
absorption is uncontrolled, the stability of the films is impaired, which
adversely affects the resistivity of the film in particular, in addition to possibly
impairing the reliability of devices made from the films. After exposure to air,
the sheet resistivity of these titanium nitride films can increase to values of
about 10,000 :ohms-cm/sq up to about 100,000 :ohms-cm/sq, which is
highly undesirable when using the film as a barrier layer for conductive
contacts and vias.
Application 09/128,143, Specification, p. 7, ll. 4-17.
The 143 Specification notes that there is a need for a technique which will both reduce
resistivity and enhance the stability of CVD films:
Thus a method of treating a titanium nitride film deposited by chemical vapor
deposition that will modify the film to reduce its resistivity and improve its
stability is highly desirable.
Application 09/128,143, Specification, p. 3, ll. 16-19. The 143 Specification notes that for barrier
layer films stable sheet resistivities should be less than about 1000 :ohms-cm/sq:
For that application, stable sheet resistivities on the order of about 1000
:ohms-cm/sq or less are desired.
Application 09/128,143, Specification, p. 7, ll.17-19. The specification also notes that resistivity on
the order of 10,000 :ohms-cm and higher are unacceptable. Application 09/128,143, Specification,
p. 7, ll. 13-17.
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