Specific Process Knowledge/Lithography/Coaters/Spin Coater: Gamma UV processing: Difference between revisions

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 The process of HMDS priming on Spin Coater: Gamma UV consists of five steps:
 *Dehydration
-*HMDS filling
+*HMDS injection
 *Reaction
 *Purging
 *Cooling
-'''UPDATE from here:''' The wafer is first baked in contact with the hotplate in order to heat the wafer to the hotplate temperature. The hotplates of the priming modules are set to 50°C. Then the wafer is baked under a low vacuum (~0.5 bar) in order to dehydrate the wafer before HMDS application. The HMDS is applied to the wafer using nitrogen as a carrier gas. 15 liters per minute of dry nitrogen is bubbled through liquid HMDS before flowing across the wafer surface. After the priming, the chamber is pump-purged twice, using a 7s pump to ~0.5 bar and a 10s nitrogen purge at 40 liters per minute. Finally, the wafer is cooled on the priming module coolplate.
+The top and bottom heaters of the VPO module are typically set to 120°C. The wafer is baked under a low vacuum (~0.35 bar) in order to heat and dehydrate the wafer before HMDS application. The HMDS is injected into the process chamber using nitrogen as a carrier gas. 10 liters per minute of dry nitrogen is bubbled through liquid HMDS before flowing into the chamber. The injection lasts until ambient pressuer is reached in the chamber. After the reaction time, the chamber is pump-purged using nitrogen. Finally, the wafer is cooled on the cool plate.
-The contact angle after HMDS priming is a function of the priming temperature, the priming time, and the surface condition of the wafer. Tests have shown the contact angle to decrease with increasing hotplate temperature, while it increases as a function of priming time at constant temperature. At a priming temperature of 50°C, the contact angle resulting from priming an oxidized silicon wafer for t = 30 - 300s may be approximated by
+The contact angle after HMDS priming is a function of the priming temperature, the priming time, and the surface condition of the wafer. The condition of the substrate surface is again a function of the substrate type, the substrate history, and the effectiveness of the dehydration step. Since the vapor pressure of water at the chamber temperature is much higher than the dehydration pressure, similarly the boiling point of water at the dehydration pressure is well below the chamber temperature, the dehydration can probably be considered to be quite effective. However, for thick oxides, transport effects may cause the 30s dehydration time to be insufficient to dehydrate the surface sufficiently.
-<math>\theta = 95 - 119.2 * t^{-0.51}</math>
-The condition of the substrate surface is again a function of the substrate type, the substrate history, and the vacuum baking temperature and time. Since the vapor pressure of water at 50°C (0.123 bar) is lower than the vacuum bake pressure of 0.5 bar, the degree of dehydration will be a function of the vacuum baking time. Thus, for thick oxides, the standard of 30s vacuum bake may not be enough to dehydrate the surface sufficiently.
 ==Spin coating==