The Location of Very Small Particles in Silane RF Discharges
K Rozsa, G Bano, Alan Gallagher
The size and location of silicon particles that grow in a pure silane, capacitively coupled rf discharge are measured by laser light scattering.The discharge conditions were similar to those typically used to produce amorphous silicon devices, except the temperature is 300 K. At earlydischarge time, when the particles are small ( D - 15 nm), they are located at the middle of the discharge. The larger ones that occur at laterdischarge times form a double layer nearer the electrodes. Surprisingly, the particles are not concentrated at the region of brightest dischargelight, which represents the distribution of high-energy electrons. Yet as expected, the distribution of film deposition on the electrodes fits radicaldiffusion with a source proportional to light intensity. It is also shown, by tilting the substrate, that a small gradient in plasma potential canhave a major effect on particle positions.