Oxford-100-Manual.pdf - 第156页
Plasmalab Oxford Instruments Plasma Technology System Manual (2) The helium setpoint should be set so that there is 1-2 mTorr chamber pressure with a wafer in place. This ensures that there is sufficient cooling. It is p…
System
Manual
(h)
Troubleshooting:
Oxford
Instruments
Plasma Technology
Plasma
lab
Check
the
backs
of
wafers
for
excessive
contamination,
scratching
or
curvature/bowing.
Vent
chamber and check electrode
for
particles, scratches,
or
erosion. Check
wafer
clamp
integrity
and
wafer
clamping
force
i.e. can
you
move
the
wafer
by
finger
pressure
when
clamped?
Compare results
with
blank
Si
if
possible.
If
blank
Si
is
OK,
there
is
a
problem
with
the
customer
wafers, i.e.
they
are
warped
or
too
flexible
or
too
thin
(thin
wafers may
require
reduced He
pressure
to
avoid
flexing
of
wafers),
or
the
clamp
ring
does
not
have
sufficient
clamping points
to
maintain
wafer
flatness.
Also check
that
the
measured He pressure
is
correct -
if
the
Helium pressure
gauge
is
faulty,
the
actual pressure could be
far
too
high. Typical CM
gauge
pressure
when
wafer
is
clamped and
helium
pressure
applied
(APC
fully
open and
no
other
gases
flowing)
is
in
the
range 0.3-2mT
for
the
range
of
Helium
pressures given above.
For
the
range
of
helium
pressures given previously: Typical CM
gauge
pressure
when
the
wafer
is
clamped and
the
helium
pressure
applied
(with
the
APC
fully
open and
no
other
gases
flowing)
is
in
the
range
0.3mTorr
to
2mTorr.
Checks
with
the
system
vented:
(1)
Ensure
that
the
electrode
is
very
flat
and clean (no bumps
or
grooves
eroded
into
it) and
that
the
back
of
the
wafer
is
clean and
smooth
(no resist
or
glue
or
anything
else
adhering
to
the
back),
and
is
mechanically
strong
so
that
it
does
not
buckle
or
bow.
(2)
Check
that
the
wafer
lift
star (or pins) retracts
fully
below
the
surface
of
the
electrode. This can be
checked
with
a
flat
edge placed
on
top
of
the
star -
if
it
wobbles
then
the
star
is
too
high.
If
the
star sticks
up
above
the
electrode,
the
helium
will
escape and
the
cooling efficiency
will
be
severely reduced (also, because
of
the
increased
gap
between
wafer
and electrode surface,
which
needs
to
be a
few
tens
of
microns
for
best cooling).
(3)
Check
that
the
clamping
ring
is
actually clamping
the
wafer
to
give
maximum
clamp force. Often,
there
can be a discrepancy
between
the
wafer
clamp
recess
height
and
the
wafer
thickness,
meaning
that
the
wafer
is
not
clamped and 'rattles'
about
inside
the
clamp ring. The clamping
force should
therefore
be adjusted
as
described in Section
6.
of
the
system manual.
You should
try
to
move
the
wafer
with
your
finger,
if
you
can
move
it
then
it
is
not
clamped
properly
and
you
may need
to
temporarily
modify
the
ring
by
adding
strips
of
PTFE
or
aluminium
foil
to
make
it
press
down
on
the
wafer.
(4)
The
wafer
should be placed centrally
in
the
clamp ring.
(5)
Press
down
on
the
wafer
in various places and
see
if
it
moves. This
will
indicate
that
the
wafer
is
not
sitting
down
flat
on
the
electrode. Try polishing
away
any bumps.
Checks
with
the
system
under
vacuum:
(1)
A
good
test
of
whether
the
wafer
is
being
clamped
properly
is
to
measure
the
helium
pressure in
the
chamber (measured on CM gauge)
both
with
and
without
a
wafer
in place
for
a variety
of
helium
pressure setpoints.
There should
be
a clear
difference
between
helium
pressure
with
and
without
wafer.
If
there
is
no
difference
then
it
indicates
that
there
is
a
helium
leak caused by incorrect clamping.
Process
Information
(Information
contained
in
this
document
is
confidential)
Printed: 08 January 2006 09:37 Page
13
of
30
Issue
1:
December
03
Plasmalab
Oxford
Instruments
Plasma
Technology
System
Manual
(2)
The
helium
setpoint
should be set
so
that
there
is
1-2 mTorr chamber pressure
with
a
wafer
in
place. This ensures
that
there
is
sufficient
cooling.
It
is
probably
best
to
work
at
as
high
a level
as
you
can
tolerate
if
there
is
any
doubt
over
cooling
efficiency.
3.2.9 Gases
with
low
vapour
pressure
Gases
with
a
low
vapour
pressure (e.g.
SiCI4,
BCI3)
present
unique
problems
for
the
gas supply system, e.g.
temperature
dependence
of
gas pressure, condensation
in
the
gas lines, and
low
line pressure.
To avoid
the
loss
of
line pressure
during
cold
weather,
it
is
recommended
that
gases
with
a
low
vapour
pressure are sited indoors, inside an extracted gas cabinet. However,
it
is
NOT recommended
to
deliberately
heat
the
gas cylinder (e.g. by using a
heatedjacket)
as
this
will
result
in
the
re-condensation
of
the
gas in
the
gas line
and/or
MFC,
since these areas are likely
to
be cooler
than
the
cylinder. The
presence
of
condensed gas
in
the
gas line
or
MFC
will
cause
loss
of
flow
or
severe pulsing
of
measured gas
flow.
Note
that
condensation problems can sometimes
be
observed even
without
direct
cylinder heating. This
is
usually
due
to
a
slight
temperature
difference
between
cylinder and
MFC.
In such
cases,
it
is
recommended
that
heating
tape
is
placed
around
the
MFC,
filter
and valve assembly
of
the
gas line
to
ensure
that
the
MFC
and
other
components are
kept
at
a
higher
temperature
than
the
gas cylinder. An
alternative
solution
would
be
to
use a
heated
MFC.
3.2.10
Endpoint
detection
techniques
3.2.10.1
Optical
emission
spectroscopy
Light
olp
Process
chamber
Reactive
species
Etch
time
Light
olp
Wavelength
•
Monitoring
of
reactive species
or
etch by-products provides
endpoint
signal.
•
Endpoint
relies
on
etch stop layer.
• Scanned
monochromator
allows
full
spectrum analysis.
Process
Information
(Information
contained
in
this
document
is
confidential)
Issue
1:
December 03 Page 14
of
30 Printed: 08 January 2006 09:37
System
Manual
Oxford
Instruments Plasma Technology
Plasma
lab
3.2.10.2
Laser
interferometry
PC
Signal
Process
Chamber
Process
chamber
Time
• In-situ etch
rate
monitoring
•
Endpoint
does
not
require
etch stop layer
•
Endpoint
can be chosen
anywhere
within
the
layer once etch
rate
has been established.
3.2.10.3
Comparison
of
OES
and
laser
endpoint
techniques
A laser
interferometer
(L1)
endpoint
system has
the
benefits
that
it
gives very precise measurement
of
etch
depth
in
the
etched layer
or
layers and can be used on very small pieces
of
wafer.
It
works
best
with
a
flat
transparent
layer (or stack
of
layers) on a reflective substrate.
It
can be used
to
determine
when
the
etch reaches an interface
between
differing
materials (by
detecting
a change
in
slope
of
the
laser reflectance signal
with
time),
or
can measure
the
etch
depth
when
partially
etching
through
a layer (by
counting
interference
ripples).
It
can also
often
be used
to
identify
multiple
interfaces
when
etching
through
different
layers in a
multi-
layer stack
of
materials
(through
the
changes in reflectance
of
the
materials in question).
The disadvantage
is
that
the
laser
spot
needs
to
be aligned every
time
to
a suitable measurement
point
on
the
wafer
(i.e. an etched area,
not
a masked area). Also,
it
only
measures a single
point.
so
any process
non-uniformity
will
result
in a range
of
etch depths across-wafer
or
across batch.
The optical emission spectroscopy
(OES)
system has
the
benefit
that
it
does
not
require
alignment
for
every run,
it
simply looks
at
optical emission
from
the
whole
plasma. This however, means
that
it
needs
larger
wafers
or
a larger etched area (>2cm
2
)
to
effectively
determine
endpoint.
The size
of
the
etched
area needed
for
good
OE
endpoint
is
also
dependent
on
the
materials being etched since
the
emission
lines
for
certain materials can be very
faint.
Also,
if
the
etch rate
of
the
material
is
low
then
the
concentration
of
its etch species
will
be
low.
OE
can
only
detect
a change in
the
strength
of
a
particular
emission line (or
group
of
emission lines),
so
can
only
detect
when
the
etch
passes
through
an interface
between
differing
materials.
OE
can give a
qualitative
idea
of
uniformity,
since
the
length
of
the
transition
of
the
signal
from
before
endpoint
to
after
endpoint
will
indicate
the
quality
of
the
etch
uniformity.
Also
the
endpoint
is
more
accurate
for
the
whole
(average)
of
the
wafer
rather
than
a single
point
on
the
wafer.
Process
Information
(Information
contained in this
document
is
confidential)
Printed: 08
January
2006 09:37 Page 15
of
30
Issue
1:
December 03