Specific Process Knowledge/Etch/DRIE-Pegasus/System-description: Difference between revisions
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== A closer look at the Bosch Process== | == A closer look at the Bosch Process== | ||
--[[User:jmli|jmli]] ([[User talk:jmli|talk]]) 15 May 2018 | --[[User:jmli|jmli]] ([[User talk:jmli|talk]]) 15 May 2018 | ||
=== A few words about RF matching - why it is important === | |||
The RF generators in a dry etch tool fac | |||
[[File:RF matching 1.jpg|700px]] | |||
RF generators in AC circuit with a load: | |||
One cannot just connect an RF generator to a coil, put a certain power through and expect a plasma generated absorb all energy. It is not possible: At RF frequencies even cables become inductors so circuits must be carefully constructed. Here, the coil of an ICP is shown but the RIE setup is equivalent. | |||
Most power RF generators are designed to transfer power into a 50 ohm load. This means that the circuit, in addition to the coil with some inductance and resistance, will also require tunable capacitors in order to produce a 50 ohm impedance. If the impedance is off, part of the power will be dissipated as Reflected Power for instance localized heating of RF cables due to standing waves. Therefore, the capacitances of the capacitors Load and Tune must be carefully chosen to minimize the reflected power. | |||
Effects of the plasma: | |||
Once a plasma has been ignited in the process chamber by the coil, an electron current will be induced in the conductive part of the plasma so as to oppose the RF magnetic field. As a result of the coupling between the coil and the plasma, the inductance of the coil changes. This, in turn, changes the impedance of the generator circuit and hence causes reflected power | |||
RF matching network: | |||
Therefore, in order to maintain the impedance matching, the two capacitances of the two capacitors, Load and Tune, need to change. This is taken care of by the RF matching network that will automatically detect changes in impedance and adjust the Load and Tune capacitors to ensure impedance matching. | |||