Positron lifetime and coincidence Doppler broadening (CDB) measurements using a positron beam have been applied to the study on the defects in Si(100) implanted with 1x10(15) Ar(+)/cm(2) at 100 keV. Not only an amorphous phase is induced by Ar(+) irradiation of Si, but the defects extend beyond the predicted depth. Annealing at 700degreesC leads to transformation into crystalline phase and increase of the peak due to Ar-related defects is observed around 10x10(-3) m(0)C in the CDB ratio curve, indicating that the number of Ar atoms involved in the complexes increases. The crystallization accompanies formation of V-Ar complexes with six vacant sites on average, and these complexes are found to be stable even above 800degreesC. It has been proved that positrons are very useful probes to study the chemical state of vacancy-inert gas atom complexes and the initial stage on their evolution.