Abstract
Experiments comparing High-Density Plasma (HDP) CVD oxide for gap-fill with a PECVD oxide/plasma etch process show effects on hot carrier reliability, transistor matching, and transistor 1/f noise. We present results from wafers processed in a 0.35 micrometers CMOS technology with three levels of metal. The results indicate that the HDP process used for gap-fill significantly improves matching and noise characteristics of metal covered devices. Both n and p channel current mirrors show improved matching between metal an no metal coverage with the HDP process. The presence of a HDP oxide film in IMD stack can reduce the mean threshold voltage difference between metal and no metal covered n- MOSFETs from 45 mV to about 4 mV. Likewise, the total integrated noise over the frequency range of 10 Hz-100 kHz of metal covered n-MOSFET is improved by a factor of 1.25 by the HDP gap-fill process. However, the HDP process has resulted in significant degradation of the d.c. hot carrier reliability of n-MOSFETs. These effects may be explained by the large amounts of hydrogen incorporated in the back-end dielectric with the HDP process.
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