Plasma source ion implantation using high-power pulsed RF plasma

Abstract

In plasma source ion implantation of molecular gases such as nitrogen, oxygen, etc., the ratio of atomic and molecular ionic species is very important from the standpoint of implanted ion energy. Hence, it is very beneficial to produce more atomic ion species rather than molecular ones to achieve deep implant profiles. The high RF power has been known to be an efficient way to produce atomic ion species along with high ionization rate of molecular gases. A large-scale plasma source ion implantation system has been built, in which a high-power pulsed RF amplifier and a water-cooled internal antenna were used to produce high-density inductively coupled RF plasma. The pulsed RF amplifier, aiming at the higher generation rate of atomic ion species, was constructed based on a 4CX5000A RF tetrode and turned out to give output of up to 50 kW PEP and 2 kW average at 13.56 MHz. The 4CX5000A RF tetrode tube was series-connected with an RF MOSFET to form an electron tube-MOSFET cascode circuit. The Ar plasma density at 30 kW pulsed RF power was measured to reach 7.5×10 11/cm 3 at 0.13 Pa (1 mTorr) of Ar pressure. The pulsed RF amplifier was used to produce an inductively coupled N 2 plasma and plasma source ion implantation was performed on Si using a hard-tube type HV pulse modulator at 55 kV of implantation voltage. The Auger depth profile results showed that the pulsed high-power RF plasma was more advantageous in plasma source ion implantation to achieve a deeper ion implantation, which was resulted from the increased atomic ion species compared to the continuous wave (CW) mode operation.