We studied structure formation by deposition of hydrogen-saturated Si clusters Si6H13+ and Si8H19+ on Si (111)-(7X7) surfaces using the deposition system of cluster ions equipped with a scanning tunneling microscope (STM) for surface observation, The system uses a quadrupole ion trap as a mass-selective source of cluster ion beams and delivers to the substrate a beam of Si6H13+ focused to 2 mm diameter with a current of similar to 100 pA for the cluster kinetic energy on impact with the surface >5 eV. It was observed that when these clusters are deposited with suitable kinetic energy, i.e., similar to2 eV/Si atom, the impact energy makes the clusters mobile on the surface, leading to self-formation of cluster-agglomerated structures at step edges and along domain boundaries of (7X7) phases. Intentional manipulation of the deposited clusters is also possible using the STM tip; the clusters can be accumulated to the tip position by applying bias voltage larger than 3 V.