Specific Process Knowledge/Etch/DRIE-Pegasus/picoscope: Difference between revisions
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The processes A and D4 have fixed pressure settings. This means that when transitioning from one phase (with a certain gas flow, RF powers and pressure) to another phase at, say, the same total gas flow and RF powers but with lower pressure, the APC will open up more than what is required to reach the new pressure in order to arrive there faster. When the pressure reading passes the new setting, the valve will close. This feedback loop produces the pressure oscillations seen in plots above. | The processes A and D4 have fixed pressure settings. This means that when transitioning from one phase (with a certain gas flow, RF powers and pressure) to another phase at, say, the same total gas flow and RF powers but with lower pressure, the APC will open up more than what is required to reach the new pressure in order to arrive there faster. When the pressure reading passes the new setting, the valve will close. This feedback loop produces the pressure oscillations seen in plots above. | ||
To get rid of the oscillations we must change from the Fixed pressure mode must to Fixed APC mode. Here, this is no feedback loop: In the transition between phases, the different gas flows, RF powers and APC setting will produce a different pressure that reached a | To get rid of the oscillations we must change from the Fixed pressure mode must to Fixed APC mode. Here, this is no feedback loop: In the transition between phases, the different gas flows, RF powers and APC setting will produce a different pressure that is reached without any overshooting. The price one may have to pay is that the new pressure may be reached at a slower speed. Also, with a pressure setting defined in terms of APC percentage in the recipe, the actual pressures during the process itself will have to be noted manually. | ||