Spray resists available to date (AZ 4999) are designed for extreme topologies, which means that even vertical silicon trench sidewalls can be covered with resist. These excellent features however come at a price: The surface of these resist is very rough and reflective film thickness measurements are not possible without post-treatment. In addition, a pronounced formation of “bumps” is observed. These resist dries so fast that a major part of the drops is already dried upon deposition on the substrate.
Small bumps are thus formed on the resist surface which interfere with many subsequent processes. The use of the highly volatile acetone can in addition lead to gas formation in the resist line of the spray coater which also impairs a uniform coating of the substrate. Spray resist of the Allresist were therefore optimized further with modified resist samples and the Süss spray coater “Gamma Altaspray”. These experiments were conducted using etched silicon wafers with slope angles of 54 ° (depth 300 – 400 µm). The solvent composition was successively changed towards a less volatile solvent, and acetone was completely omitted. This resulted in the fabrication of significantly improved surfaces which also allowed performing reflective film thickness measurements. The tendency to form bumps was considerably lower, but nevertheless a complete and sufficient coating of wafer topologies was achieved. At film thicknesses of 3 – 5 µm, a resolution of 1 – 2 µm was obtained.
Good resist surface with complete covering of all topologies – positive resist SX AR-P 1250/25.2
Resolution assay of negative resist SX AR-N 2250/1.1 film thickness 5 µm, high sensitivity
Allresist now offers a series of positive and negative resists which are suitable for different topologies and plane substrates.
Vertical trenches: AR-P 1210 (pos.); AR-N 2210 (neg.)
Etched 54 ° slopes: AR-P 1220 (pos.); AR-N 2220 (neg.)
Plane wafers: AR-P 1230 (pos.); AR-N 2230 (neg.)
These systems can, due to the different drying features of each system, much faster be adjusted to the specific demands of spray coaters from other manufacturers.