Incident ion dose evolution of damaged layer thickness in Si substrate exposed to Ar and He plasmas

The effect of ion flux on the formation of a damaged layer in a Si substrate was investigated in detail. An inductively coupled plasma source was used to control the flux (Γ_ion) and energy (E_ion) of incident ions. The progressive behavior of the total damaged layer thickness (D_dam) estimated by spectroscopic ellipsometry primarily depends on the total ion dose (D_ion = Γ_ion x t_pr, where t_pr is the process time) and E_ion. The evolution of D_dam then saturates and becomes independent of D_ion. The characteristic total ion dose (D_dam) is defined, which distinguishes the progressive and saturation phases. Experimental results suggest that D_dam is estimated to be in the range from 1 x 10¹⁶ to 3 x 10¹⁶ cm^-2, regardless of Ar and He plasmas in the present study. This D_ion-dependent behavior was also confirmed by transmission electron microscopy and capacitance-voltage measurements. The interface thickness d_IL of the damaged layer was found to be independent of D_ion. This result confirms that d_IL can be used as a measure of the E_ion-dependent plasma-induced damage (PID) for in-line monitoring. The present D_ion dependence can be implemented in the conventional PID range theory, particularly, in the designs of high-density plasma sources. (author)