Hi,
I am trying to adopt an anisotropic silicon etch recipe to Oxford NGP80 RIE machine. The Original recipe has been optimised for a different machine (NEXTRAL 330 RIE parallel plate plasma reactor with 31 cm electrode). The original recipe uses RF power ~ 300W with getting a self bias of ~150V for certain gas flow and combination. Keeping the pressure and gas flow same how can I translate RF power with a machine (Oxford RIE) that has an electrode of 24 cm? Is there any model/equation that roughly gives the relation between RF power, self-bias and electrode size?
Thanks in advance.
Regards,
Salahuddin
Consider the electrode areas:
Let the ratio of the areas of the powered electrode A to that of the grounded electrode B, be r (< 1).
The time-averaged ion current to each electrode will be in the ratio of their areas, since the dc potential on both electrodes is the same (i.e. » ground potential).
Thus, if the ion–particle current to the grounded electrode is Io, the current to the powered electrode will be r.Io.
The net electric current due to the ions (assuming unit ion charge) is therefore (1 – r)Io, while the total number of ions leaving the system is (1 + r)Io.
For charge neutrality, the number of electrons leaving the system to the instantaneous anode (in any part of the cycle) must also be (1 + r)Io.
When the powered electrode has a positive voltage, all the electrons travel to this electrode. These electrons constitute a net electric current (1 + r)Io, so that the total current in the circuit due to both ions and electrons becomes approximately, (1 – r)Io + (1 + r)Io = 2Io.
Similarly, in the negative half cycle all the electrons travel to the grounded electrode and it can be seen that the net electric current in the circuit will now be (1 – r)Io – (1 + r)Io = – 2r.Io.
Taking an average of the currents in the two cycles gives the time-averaged dc current in the circuit as (1 – r)Io.
So: You have to consider the electrode (both power and ground electrode) area and their ratio. For older case (with 31 cm electrode) you have a self bias voltage ~ 150 V.
In new case, you have to calculate for 24 cm.
Both case consider the area of ground electrode separately.
Good luck!
Hi,
question is the result you are after. DC bias of -150 V is not so bad for RIE. Pressure has a big influence so why not change it? As for the RF questions, please read the book by Brian Chapman: "Glow Discharge processes"!
Heinrich
Dear Dr Sahu,
Thanks a lot for your answer and detailed explanation. I will calculate and try the process for our system.
Regards,
Salahuddin
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