RF Power Supply and Matching Box
5. Operation
59
Warning
High voltage is present in the matching box. Never put your hand into the matching box when
energized. Even if not energized, the coil and variable capacitors in the matching box may retain a
charge. You may get an electric shock or die by contact with high voltages, so when touching the
coil or variable capacitors inside the matching box, discharge the electricity to ground with a
grounding rod before touching them.
5-3-2. Matching adjustment
①
Turn on RF and increase Pf until 70% to 80% of the maximum reflected power.
When not discharging:
Turn off RF and change the gas pressure and the number of short circuits for the coil inside the
matching box so that discharging can begin.
②
When set up for a weak amount of discharge, turn the TUNE or MATCH variable capacitors to
intensify the discharge (so that Pr decreases). Generally, moving a variable capacitor to increase
VPP voltage makes discharging easier.
③
Because of the tendency for Pr to decrease, see
"Table 5-2 Relationship between the tendency for
Pr to decrease and coil short circuits
" and increase or decrease the number of coil short circuits or
add a fixed capacitor.
Reference
The air core coil and variable capacitors will oxidize if touched with bare hands. Wear gloves when
you must touch them.
Symptom
Cause
Corrective action
Can match at the minimum value
of the MATCH variable capacitor.
Insufficient coil (L) short circuits (L is
too large)
Short coil across 2 or 3 more
turns.
Can match at the maximum value
of the MATCH variable capacitor.
Excessive coil (L) short circuits (L is
too small)
Decrease the number of turns of
coil short circuits.
Can match at the minimum value
of the TUNE variable capacitor.
Because the load has large R
component of load impedance (Easily
occurs with a small-area load)
Add a capacitor in parallel with
load.
Can match at the maximum value
of the TUNE variable capacitor.
Because the load has small R
component of load impedance (Easily
occurs with a large-area load)
Add a capacitor in parallel with
TUNE variable capacitor.
The Pr minimum point for both the
TUNE, MATCH variable capacitors
is between 0% and 100% but a little
Pr remains.
Because the coaxial cable length is
inadequate
Try changing the coaxial cable
length by about
±
1 m.
Figure 5-5 Basic matching circuit
Table 5-2 Relationship between the tendency for Pr to decrease and coil short circuits