Disintegration of TiSi2 on narrow poly-Si lines at high temperatures

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Abstract
The thermal stability of TiSi2/poly-Si structures with narrow lines has been studied as a function of the dopants introduced into the poly-Si (i.e. boron or arsenic) in the temperature range from 700 °C to 950 °C. The silicide layer was formed by rapid thermal processing (RTP) in nitrogen via a solid–solid reaction between titanium and poly-Si. The integrity, upon heat treatment, of the TiSi2 film on large areas was investigated by Rutherford backscattering spectroscopy (RBS) analysis, plan-view scanning electron microscopy (SEM), and cross-sectional SEM studies. Electrical information about the thermal stability of the bilayer was obtained from sheet resistance measurements on Van der Pauw structures in combination with linewidth measurements of bridge resistors with a nominal width between 0.8 and 1.5 μm. To provide for statistical variation about one hundred measurements were collected for each linewidth and temperature setting. The results clearly show that the thermal stability of the bilayer is a function of the amount and type of dopants in the polysilicon, favoring the use of high levels of arsenic. Moreover, the thermal stability was observed to be affected by the linewidth, since at the temperature for onset of degradation (above 900 °C), narrow lines were found to disintegrate at a much higher rate than wider ones. Cross-sectional SEM and TEM micrographs of the polycide lines clearly reveal the TiSi2/poly-Si interface to suffer from bowing. The effect was observed to be more pronounced on narrow undoped and boron-doped polycide lines. Both the narrow line disintegration and the bowing effect of polycide structures can have important implications for submicron very large scale integrated (VLSI) technologies.

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