Sol Gel Spin Coating Process

Spin-coating is used for many applications where relatively flat substrates or objects are coated with a thin layer of material. In spin-coating, Figure 1, the material, in the form of a stable sol, to be made into coating is deposited onto the substrate surface and spun off to leave a uniform layer. There are four key stages in the sol-gel spin-coating process, Figure 2 [3]:

(1) Stage 1: This step involves the deposition of the sol onto the substrate surface, Figure 2. This can be done using a nozzle that pours the sol out, or the sol could also be sprayed onto the surface. Usually this dispense stage provides a substantial excess of coating solution (sol) compared to the amount that will ultimately be retained in the final coating. For many solutions, it is often beneficial to dispense the sol through a submicron-sized filter to eliminate particles that could lead to flaws.

(2) Stage 2: This step involves aggressive fluid expulsion from the substrate surface by the rotational motion, Figure 2. In this step, the substrate is accelerated up to its final desired rotational speed. Because of the initial depth of the fluid on the wafer surface, spiral vortices may briefly be present during the early stage of substrate rotation, as a result of the twisting motion caused by the inertia exerted by the top of the fluid layer. As the substrate below rotates faster and faster, eventually, the fluid thickness difference f

Figure 1. Schematic of the sol-gel spin-coating process.

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