Specific Process Knowledge/Etch/DRIE-Pegasus/System-description: Difference between revisions
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--[[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 | === A few words about RF matching in general === | ||
(This section contains material from the Dry Etch TPT lecture) | (This section contains material from the Dry Etch TPT lecture) | ||
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<!-- The fact that the plasma generated in the chamber by the coil induces a electronic current flowing in a loop (with an associate inductance) within itself that couples to the inductance of the coil making it vary over time - this is another reason for introducing the so-called matching network as illustrated above.--> | <!-- The fact that the plasma generated in the chamber by the coil induces a electronic current flowing in a loop (with an associate inductance) within itself that couples to the inductance of the coil making it vary over time - this is another reason for introducing the so-called matching network as illustrated above.--> | ||
The matching unit consists of two tunable capacitors and an impedance matching network. The network measures the impedance of the circuit and automatically changes the capacitances of the capacitors (called Load and Tune) in order to match the 50 ohm impedance. The changing of the active area inside the capacitor is done by rotating the shaft as illustrated above. | The matching unit consists of two tunable capacitors and an impedance matching network. The network measures the impedance of the circuit and automatically changes the capacitances of the capacitors (called Load and Tune) in order to match the 50 ohm impedance. The changing of the active area inside the capacitor is done by rotating the shaft as illustrated above. It is unrealistic to achieved perfect matching (zero reflected power) so some minimum value (always less than 10 % of the input power) is found. | ||
This is, however, by no means a simple matter and the setpoints of Load and Tune (always measured as percentages of full capacitance) must be chosen wisely or the RF matching will fail. Therefore, if the setpoints for Load and Tune in a recipe are wrong - the process will fail and most likely abort. | |||
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 the matching network ensures that the impedance matching is still preserved. | |||
=== Why RF matching is extremely important in the Bosch process === | |||
In the continuous processes (that means fixed parameters that do not change during the process) that are used in most dry etch tools the action of the impedance matching network is mostly seen in the beginning of the process when the plasma stabilizes. Once stabilized and a minimum reflected power has been established, the capacitors usually needs only minor adjustments. Below is a datalog of an oxygen cleaning process running with: | |||
* 100 sccm O2 | |||
* 1200 W coil power | |||
* 20 W platen power | |||
* Automatic matching | |||
showing the values of the Load and Tune positions. The only process parameter that changes is the pressure - along the X axis one can see the different pressure settings. | |||
[[File:RF matching 2.jpg|600px]] | |||