Growth kinetics of Si on fullsheet, patterned and silicon-on-insulator substrates
Résumé
Using a reduced pressure-chemical vapor deposition cluster tool, we have studied the epitaxial growth of Si using either a silane or a dichlorosilane+hydrochloric acid chemistry on fullsheet, patterned and silicon-on-insulator (SOI) substrates. We have first of all developed a (''HF-last'' advanced wet cleaning+low thermal budget (775°C, 2 min) in situ H$_2$ bake) combination that yields atomically smooth, contamination free Si starting surfaces for both fullsheet and patterned wafers. We have then modeled the low temperature Si growth rate (silane or dichlorosilane+hydrochloric acid chemistry) on fullsheet wafers. A similar growth rate activation energy is found for both chemistries, i.e. $E_{GR}$~ 50 kcal mol$^{-1}$. The growth rate dependency on the Si precursor flow is vastly different, however. Fitting this dependency with a simple power law, a value of 0.36 is indeed associated to dichlorosilane, versus 0.92 for silane. The HCl etching rate is characterized by an activation energy $E_{ER}$~34 kcal mol$^{-1}$ , with a 0.52 power law dependency on the HCl flow. On patterned wafers, we have demonstrated that a deposited Si thickness limit (20 nm) exists at 775°C for high $F$(HCl)/$F$(SiH$_2$Cl$_2$) mass flow ratios. This limit disappears when (i) $F$(HCl)/$F$(SiH$_2$Cl$_2$) is reduced (ii) the growth temperature is increased to 800°C. Finally, we have highlighted the specifics of the growth on SOI wafers. A significant growth rate reduction (compared to bulk Si) has been evidenced on ultra-thin Si over-layer SOI wafers. It gets less and less pronounced as the buried oxide layer gets thinner and/or the Si over-layer thickness increases.
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