As a rule, any impurity will increase the resistivity of a pure
metal. Bombardment of metallic targets in a reactive gas such as oxygen,
nitrogen or methane will generally increase resistivity. Tantalum nitride
is probably the prime illustration of the ability to tailor film properties.
By altering the deposition conditions, either resistor or capacitor films
may be routinely deposited. The effect of nitrogen on the and TCR of
tantalum films, shown in Figure 7.5 is widely known[7.2]. The resistivity
curve in Figure 7. 5 includes a plateau and levels out at about
with a TCR in order of -75 ppm/°C. The exact shape and displacement
of both TCR and resistivity will shift depending on a number of
deposition factors, such as substrate temperature, pumping speed, gas
ratios and internal sputtering configuration. Reactive sputtering has also
been used to deposit ruthenium dioxide resistors, which are usually
screened. Jia et. al.,[7.3] deposited resistive films with controlled
resistivity and TCR by varying deposition temperature and oxygen
partial pressure.