Effects of UV Irradiation on the Particle Growth in Low Pressure Silane Plasmas

Summary form only given. The effects of UV irradiation on the particle growth were studied in low pressure capacitively-coupled silane plasmas. The growing speed of the particles increased when UV was irradiated on the plasmas. The particle growth was monitored two dimensionally by the laser light scattering method. The particles grew about 100 nm in diameter and dragged out toward the chamber wall by the ion drag force. The growth and disappearance process of the particles were faster in the discharge with the UV irradiation than that without the UV irradiation. The experiments were performed with various discharge conditions; the operating RF power range of 50 -100 W and the pressure range of 30 -100 m-Torr. For example, at 80 mTorr and 70 W, the particles grew up to approximately 70 nm in time about 3 seconds faster with the UV irradiation than the case without the UV irradiation. This result is attributed to the particle coagulation mechanism. The particle growth speed increases when the positive ion density increases in the silane plasmas. The photoemission from the initially-formed several nm size particles is responsible for particles having positive charges, which results in the increase of the particle growth speed. These results were also confirmed by the SEM photographs.