Paper SE-TuM1
Temperature Effect on the Glancing Angle Deposition of Si Nanostructures

Tuesday, October 16, 2007, 8:00 am, Room 617

It is well-known that combining a glancing angle deposition (GLAD) process with suitable substrate rotation offers the ability to grow nanostructures with various shapes, including spirals, screws or vertical posts. When depositing on bare substrates, different growth phenomena are often encountered: Starting of as single fibers at the substrate, adjacent structures will merge together at a certain stage of growth. Also, dying out of structures due to a competitive growth of neighboured structures, and a broadening of the structures diameter with increasing structure height is often observed. However, for most applications, well-aligned, non-merged structures with comparable diameters are needed. Therefore, it is important to understand the influence of the deposition parameters on the nano-scaled structures in order to be able to control their growth. Here, the effect of the substrate temperature T_S on the growth of different Si nanostructures is studied. An ion-beam induced GLAD process was used to grow Si nanostructures at different substrate rotational velocities and at different substrate temperatures T_S ranging from room temperature (RT) up to 360°C, while all other deposition parameters where held constant. Due to the different rotational velocities, spirals, screws and vertical posts could be deposited. Analyzing the structures by means of scanning electron microscopy , it is found that T_S strongly influences the morphology of the grown structures. For the spirals and the screws, T_S effects the critical structure height h_crit at which the single fibers start merging together. From RT to T_S = 300°C, h_crit is increased with increasing T_S from h_crit(RT) = 150nm to h_crit(300°C) = 350nm (for the spiral structures), thus giving the possibility to grow spirals consisting of single fibers without merging together over a larger thickness range. However, it was found that increasing the temperature over T_S = 300°C results in a sudden drop of the critical height h_crit (360°C) = 130nm. Moreover, the total structure height was found to be dependent on T_S as well, indicating a change of the film density. For the posts, it was found that T_S influences the total number of posts and the inter-post-distance as well as the total structure height , showing a change of the film density as found for the spirals and screws.