Specific Process Knowledge/Etch/DRIE-Pegasus: Difference between revisions
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**the ion bombardment driven by the platen power ''first'' removes the passivation layer on the surfaces directly exposed to the ions (i.e. horizontal surfaces) | **the ion bombardment driven by the platen power ''first'' removes the passivation layer on the surfaces directly exposed to the ions (i.e. horizontal surfaces) | ||
**''then'' as the bottom of the structures are opened the etch of silicon itself starts. | **''then'' as the bottom of the structures are opened the etch of silicon itself starts. | ||
[[Image:boostdelay4b.jpg |400x400px|thumb| | |||
Here, it is clear that one can distinguish two phases of the etch cycle; one where the ion bombardment removes the polymer and one where the actual etching of silicon takes place. Considering what process conditions are favorable we realize that | Here, it is clear that one can distinguish two phases of the etch cycle; one where the ion bombardment removes the polymer and one where the actual etching of silicon takes place. Considering what process conditions are favorable we realize that | ||
#the ion bombardment requires a low pressure in order for the ions to have a long mean free path and hence good directionality. Also, a high platen power is required to drive the ion bombardment. | #the ion bombardment requires a low pressure in order for the ions to have a long mean free path and hence good directionality. Also, a high platen power is required to drive the ion bombardment. | ||
#a higher pressure during the etch increases the density of reactive species and hence the etch rate. Since a high platen power is no longer necessary to drive the ion bombardement, lowering it will reduce the impact on the masking material thus improving the selectivity. | #a higher pressure during the etch increases the density of reactive species and hence the etch rate. Since a high platen power is no longer necessary to drive the ion bombardement, lowering it will reduce the impact on the masking material thus improving the selectivity. | ||
The etch cycle may be split into three parts, Boost, Delay and Main, where process parameters such as pressure, gas flows or RF powers have different values.]] | |||
These conflicting demands are the same on the ASE. However, with hardware improvements on the DRIE-Pegasus such as | These conflicting demands are the same on the ASE. However, with hardware improvements on the DRIE-Pegasus such as | ||
*fast response digtal MFC's mounted on top of the process chamber itself to shorten the gas line | *fast response digtal MFC's mounted on top of the process chamber itself to shorten the gas line | ||