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System Manual Oxford Instruments Plasma Technology Plasma lab 3.2.2 ICP operating parameter ranges For an ICP 180 or ICP 380 the typical process operating ranges are: Total gas flows == 10 to 200sccm. The maximum flow de…

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Plasma
lab
Oxford
Instruments
Plasma
Technology
System
Manual
3.2
3.2.1
HIE
processes
RIE
operating
parameter
ranges
For an
RIE
tool
the
typical process
operating
ranges are:
Total
gas
flows
= 10
to
150
sccm.
The
maximum
flow
depends on
type
of
pumps
fitted
to
the
system i.e.
their
maximum
flow
capacity,
their
pumping
performance, and
the
required
operating
pressure.
If
you
need
to
use a
low
pressure,
you
may have
to
limit
the
flow
rate
to
achieve this.
Pressure = 5
to
500mTorr.
Below
50mTorr,
the
plasma
may
not
strike easily (or
with
sufficient
stability)
for
certain gases and
power
levels,
so
you need
to
check this and adjust
the
process accordingly, since
operating
the
system
without
a plasma could cause damage. This
is
because
it
is
likely
to
cause a
high
reflected power,
or
dumping
of
power
into
the
matching
unit.
It
is
always essential
to
check
for
a plasma.
You can use
the
'low
pressure strike'
feature
in
the
software
to
allow
easier
striking
for
low
pressure
processes. For certain flow/pressure combinations,
the
pressure
controller
may have
difficulty
in
maintaining
a constant pressure,
therefore
this may also be a
determining
factor
in
the
flow/pressure
used.
RF
power
=
typically
20W
to
400W (or
up
to
1200W
for
RIE
System133
or
RIE
800 Plus). A plasma may
not
strike easily
for
low
power
levels
for
certain
gases.
You
will
need
to
check this and adjust
the
process
accordingly, since
operating
the
system
without
a plasma could cause damage.
It
is
always
important
to
have a cover
plate
(typically
quartz
or
graphite)
on
the
RIE
electrode
to
protect
it
from
sputter
etch
damage,
particularly
when
operating
with
high
RF
powers and
therefore
high
DC
biases.
Helium
pressure
(if
applicable) = 0
to
30Torr. Depends
on
the
cooling
efficiency
required
(some
processes
benefit
from
no
cooling) and
the
maximum
tolerable
helium
leakage.
Temperature
is
limited
by
the
operating
range
of
the
electrode
or
its heater/chiller,
depending
on
type
of
electrode
or
heater/chiller used.
NOTES:
(A) The system base pressure
will
be approaching
10-
6
Torr
when
measured using
the
Penning gauge.
However,
the
time
taken
to
reach this pressure
will
depend
on
whether
the
chamber has recently
been vented
to
atmosphere and
the
cleanliness
of
the
chamber walls.
If
the
process chamber /
electrodes are anodised,
the
time
will
increase
as
the
anodised surfaces
will
take
longer
to
outgas
compared
with
bare metal surfaces.
(B)
Operating
with
chlorine-based processes can cause damage
to
the
electrode unless
it
is
protected
with
a cover
plate
(or
dummy
wafer
in a
tool
with
wafer
clamping).
(C)
Operating
with
a
high
reflected
power
(>5%
of
forward
power)
is
not
advised,
as
this
will
cause
damage
to
the
matching
unit
or
RF
generator. To reduce
the
high
reflected power, adjust
the
process parameters
or
re-tune
the
matching
unit.
Process
Information
(Information
contained
in
this
document
is
confidential)
Issue
1:
December 03 Page 6
of
30 Printed: 08 January 2006 09:37
System
Manual
Oxford
Instruments
Plasma Technology
Plasma
lab
3.2.2
ICP
operating
parameter
ranges
For an
ICP
180
or
ICP
380
the
typical process
operating
ranges are:
Total
gas
flows
==
10
to
200sccm. The
maximum
flow
depends
on
type
of
turbo
pump, i.e. its maximum
flow
capacity, and
the
required
operating
pressure.
If
you
need
to
use a
low
pressure, you may have
to
limit
the
flow
rate
to
achieve this.
Pressure
==
1
to
60mTorr.
Below
5mTorr and above 20mTorr
the
plasma may
not
strike easily (or
with
sufficient
stability)
for
certain gases and
power
levels,
so
you
need
to
check this and adjust
the
process
accordingly, since
operating
the
system
without
a plasma
either
on
the
substrate electrode
or
in
the
ICP
tube
could cause damage. This
is
because
it
is
likely
to
cause a
high
reflected power,
or
dumping
of
power
into
matching
unit.
It
is
always essential
to
check
for
a plasma in
both
regions. You can use
the
'low
pressure strike'
feature
in
the
software
to
allow
easier
striking
for
low
pressure processes. For certain
flow/pressure combinations,
the
pressure
controller
may have
difficulty
in
maintaining
a constant
pressure,
therefore
this
may
also be a
determining
factor
in
the
flow/pressure used.
ICP
power
==
approximately
200W
to
2500W (or 4000W
for
ICP
380). The
minimum
power
level
will
be
dependent
on
how
easily
the
plasma strikes
for
certain gases. You
will
need
to
check this and adjust
process accordingly, since
operating
system
without
a plasma
either
on
the
substrate electrode
or
in
the
ICP
tube
could cause damage.
The
maximum
ICP
power
limit
is
set
by
the
power
rating
of
the
RF
generator. However, most processes
perform
well
with
only
moderate
ICP
power
levels. This also helps
to
avoid excessive substrate heating.
Substrate
electrode
RF
power
==
typically
5W
to
400W. A plasma
may
not
strike easily
for
low
power
levels
for
certain
gases.
You
will
need
to
check this and adjust
the
process accordingly, since
operating
the
system
without
a plasma
either
on
the
substrate electrode
or
in
the
ICP
tube
could cause damage.
Helium
pressure
==
0
to
30Torr. Depends
on
the
cooling
efficiency
required
(some processes
benefit
from
no
cooling) and
the
maximum
tolerable
helium
leakage.
Temperature
is
limited
by
the
operating
range
of
the
electrode
or
its heaterlchiller,
depending
on
type
of
electrode
or
heater/chiller used.
NOTES:
(A) The system base pressure
will
be
of
approaching
10-
6
Torr
or
better
when
measured using
the
Penning gauge. However,
the
time
taken
to
reach this pressure
will
depend
on
whether
the
chamber has recently been
vented
to
atmosphere and
the
cleanliness
of
the
chamber walls.
If
the
process chamber / electrodes are anodised,
the
time
will
increase
as
the
anodised surfaces
will
take
longer
to
outgas compared
with
bare metal surfaces.
(B)
Operating
with
chlorine
based processes can cause damage
to
the
electrode unless
it
is
protected
with
a
dummy
wafer.
(C)
Operating
with
a
high-reflected
power
(>5%
of
forward
power)
is
not
advised,
as
this
will
cause
damage
to
the
matching
unit
or
RF
generator.
To reduce
the
high-reflected
power,
adjust
the
process parameters
or
re-tune
the
matching
unit.
Process
Information
(Information
contained
in
this
document
is
confidential)
Printed: 08 January 2006 09:37 Page 7
of
30
Issue
1:
December 03
Plasmalab
Oxford
Instruments Plasma Technology
System
Manual
3.2.3
Low-pressure
strike
facility
"Low
pressure
strike"
is
a necessary
software
facility, since
for
low
pressure
RIE
or
ICP
processes,
the
concentration
of
free electrons being produced simply isn't
high
enough
to
start
and
maintain
the
ionisation 'chain reaction'
or
avalanche
which
is
required
to
initiate
the
plasma.
So
it
is
necessary
to
use
higher
pressures
during
the
first
few
seconds
of
the
process step. The
software
therefore
allows
the
operator
to
raise
the
pressure
briefly
at
the
start
of
the
plasma process
to
enable
the
plasma
to
strike.
This does
not
cause any problems
for
the
processes involved, because
the
time
taken
to
strike
the
plasma
at
the
higher
pressure
is
very short, and
will
be a very small percentage
of
the
total
process time.
3.2.4
DC
bias
With
any plasma etch system
it
is
important
to
remember
that
DC
bias readings can be affected by surface
coatings
on
the
lower
electrode. These can include:
(a)
Quartz
cover
plate
(or any
other
insulating cover
plate
material),
(b) Electrode surface anodisation,
(c)
Polymer coating
on
electrode surface
generated
by process,
(d)
Any
other
insulating coating generated by plasma.
In all
of
these
cases,
the
DC
bias reading
will
be inaccurate
due
to
the
lack
of
DC
contact
to
the
plasma.
Quite
often,
the
measured
DC
bias
will
be close
to
zero
if
there
is
a
complete
insulation
of
the
electrode
or
if
the
process conditions are such
that
there
is
minimal
contact
between
the
exposed areas
of
the
electrode and
the
plasma.
This
is
not
to
say
that
the
sheath
potential
(or
ion
energy) has actually reduced
to
zero; in
fact
it
has
not
changed
at
all
from
the
non-insulated
case.
It
is
simply
that
the
measurement
of
this value via
DC
bias
is
no
longer
possible.
It
is
also
quite
common in these
cases
for
the
DC
bias reading
to
vary sharply
throughout
the
run.
It
is
therefore
recommended
that
the
DC
bias
for
a
particular
process
condition
be measured
with
a bare
electrode (e.g.
prior
to
loading
the
quartz
cover plate). In load locked single
wafer
systems,
it
is
necessary
to
measure
the
DC
bias
without
a
wafer
loaded,
as
this
will
expose
the
central
wafer
lift
pin
to
provide
accurate
DC
bias measurement.
This
is
the
only
way
of
obtaining
a reliable/stable
DC
bias measurement.
If
the
electrode
is
anodised,
it
may also
be
necessary
to
ensure
that
the
wafer
lift
pin
is
exposed and clean
as
this
will
be
the
only
conductive
path
for
the
DC
bias measurement.
If
there
is
no
wafer
lift
pin (e.g.
RIE
80 Plus),
it
may be necessary
to
use
the
central locating pin
for
the
DC
bias measurement
or
even
to
scratch away a small area
of
anodisation.
If
it
is
suspected
that
there
has been
polymer
deposition
on
the
electrode,
it
may be necessary
to
clean
off
the
polymer
(with
an O
2
plasma
or
by
mechanical cleaning)
to
allow
an accurate measurement
of
the
DC
bias.
3.2.4.1
Electronegative
gas
mixtures
Strongly electronegative mixtures, such
as
SF
6
gas above 10
Pa
(70 mTorr), may give close-to-zero
DC
bias.
This
is
not
a
fault,
but
is
due
to
the
formation
of
negative ions in
the
plasma. A
DC
bias exists
only
because
of
the
difference
in
mobility
between
the
negative and positive charges in a
normal
plasma.
When
both
charge carriers are heavy ions,
the
plasma does
not
rectify
and
the
dc bias collapses.
Process
Information
(Information
contained
in
this
document
is
confidential)
Issue
1:
December 03 Page 8
of
30 Printed: 08 January 2006 09:37