Sensitive evaluation of ion implantation using short wavelength laser induced photo-acoustic displacement

A highly sensitive photo-acoustic displacement (PAD) measurement method has been developed and applied to the monitoring of ion implantation in silicon. This technique is based on the measurement of small surface displacement by differential laser interferometer due to the absorption of YAG laser light (λ=532 nm). The PAD increased with the ion dose until the amorphous layer was formed. The definite correlation between PAD and ion dose were observed ranging from 1e9/cm ² to 1e15/cm² for boron, 5e8/cm² to 1e14/cm² for phosphor and 2e8/cm² to 1e13/cm² for arsenic ion implantation with the energy of 100 keV, respectively. Since the detection error was so small (0.13 picometers as standard deviation) that dose accuracy was confirmed to be very excellent (less than 0.4% :1e11/cm²-100 keV for boron). It was also found that the small dose variation (less than 0.2%) in middle dose region (1e13/cm²) with high energy phosphor implantation (2 MeV) was accurately detected by this technique