Oxford-100-Manual.pdf - 第155页
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, sc…
Plasma
lab
Oxford Instruments Plasma Technology
System Manual
3.2.8
Use
of
helium
backing
for
effective
process
temperature
control
3.2.8.1 Scope
For all systems
with
wafer
clamping and
helium
backing
for
wafer
temperature
control.
i.e. Plasmalab
System 100
with
ICP
65,
180 and 380 sources. Also, occasionally
RIE
133 systems and
RIE
80
Plus.
3.2.8.2
Purpose
It
is
important
to
ensure
that
the
helium
is
sealed adequately
behind
the
wafer.
If
the
helium
is
leaking
out
past
the
wafer
with
a
poor
seal against
the
table,
the
thermal
contact
to
the
temperature-controlled
table
will
be degraded. The
wafer
will
then
heat
up
more
than
expected and
the
process results may
suffer. For example, in
SiOz
etching
the
profile
may become
partially
isotropic and/or any photoresist
masking used may
burn
too
easily.
3.2.8.3
Simple
Method
to
check
Helium
backing
(a)
If
the
wafer
is
sealing
the
helium
effectively,
the
measured He
flow
will
be
less
than
that
when
no
wafer
is
present.
(b) Set a range
of
He pressures and
note
the
measured
helium
flows
with
no
wafer
loaded. (Set all
process
gases,
RF
and pressure
to
zero and
work
in
'manual'
mode.)
(c)
Load a
blank
Si
wafer
of
the
correct size
(if
the
system
is
a standard single
wafer
type) and
note
the
He
flows
for
the
same range
of
set He pressures.
(d) Load a typical customer
wafer
(e.g.
with
a
thick
SiOz
layer) and
note
the
He
flows
for
the
same
range
of
set He pressures.
If
a carrier
is
appropriate
for
the
system, use
that.
(e)
Fill results
in
the
following
table.
(If
you
do
not
have
the
capability
to
measure Helium
flow
then
measure CM
gauge
chamber pressure
with
APC
fully
open,
no
other
gases
flowing).
Set
Herrorr He flow/seem He flow/seem He flow/seem
No
wafer
Si
wafer
Customer
wafer
7
10
15
20
(f) The
larger
the
difference
between
'No
wafer'
and
'With
wafer'
flows,
the
better
the
seal.
'With
wafer'
values should be
less.
Pass
criteria are still being evaluated
but
a recent example
with
acceptable results
is
as
follows.
(g) Recent acceptable example:
Set
He
pressure
7Torr
10Torr
No
wafer
He
flow
4.2sccm
7.2sccm
With
wafer
He
flow*
<3.9sccm
<6.5sccm
*These
were
the
maximum
values observed (usually occurring
for
wafers
with
thick
SiOz
layers)
and
cooling
was
thought
to
be adequate because profiles
were
acceptable.
If
there
is
little
or
no
difference
between
the
'No
wafer'
and
'with
wafer'
flows,
then
the
seal
is
ineffective.
Process
Information
(Information
contained in this
document
is
confidential)
Issue
1:
December 03 Page 12
of
30 Printed: 08 January 2006 09:37
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