Utah-94-721002-System-Manual.pdf - 第160页
mä~ëã~ä~Ä = lñÑç êÇ=fåë íêìãÉåí ë=m ä~ë ã~=qÉÅÜåçäçÖó= System Manual PKP= mb`sa=éêçÅÉëëÉë= PKPKN= mb`sa=çéÉê~íáåÖ=é~ê~ãÉíÉê=ê~åÖÉë= For a PECVD tool the typical process o perating ranges are: Total gas flows = 150 to 300…
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Signal
Time
% level
Derivative
zero line
Derivative
+/- derivative
threshold
Normalisation
time
Endpoint
closed time
(no false
endpoint can
be found)
Endpoint
capture
time
Derivative crosses its
endpoint threshold level.
Endpoint capture timer
started.
END of
process
Overetch
time
Endpoint trace – (derivative, less than)
Time
% level
Derivative
zero line
Signal
Derivative
+/- derivative
threshold
Normalisation
time
Endpoint
closed time
(no false
endpoint can
be found)
Endpoint
capture
time
Derivative crosses its
endpoint threshold level.
Endpoint capture timer
started.
END of
process
Overetch
time
Time
% level
Derivative
zero line
Signal
Derivative
+/- derivative
threshold
Normalisation
time
Endpoint
closed time
(no false
endpoint can
be found)
Endpoint
capture
time
Derivative crosses its
endpoint threshold level.
Endpoint capture timer
started.
END of
process
Overetch
time
Endpoint trace – (derivative, less than)
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See the MKS OEM manual for details of gas correction factors. However, it is worth pointing out that for
certain gases (e.g. H2 or He) it is recommended that the MFC is calibrated for that particular gas, since
they have very different gas properties compared to other gases, and hence the errors on calibrations
factors is large.
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The gas emitted by a plasma etch process will be mostly made up of the input gases. However, there will
be a small but significant component of etch or plasma by-products (say up to ~10% in an RIE tool,
possibly more for ICP). The exact amounts will depend on process type and conditions. These can be any
combination of etch gas material and etched material.
For example:
Si + CF
4
= SiFx, CFx, F etc
SiO
2
+ CHF
3
= SiFx, COx, CFx, F, HF, CHx, SiOFx etc
Resist + O
2
= COx, O etc
As many of these by-products are toxic, it is a minimum requirement that these gases are exhausted in an
enclosed extraction system to the roof of the building - following health and safety regulations. In
addition to this, depending on local regulations, it may be necessary to have some form of gas scrubbing
before releasing these materials to the atmosphere.
Even if we were not running gases through the system, we would recommend that the system exhaust is
extracted correctly, since the pump exhaust will contain small droplets of pump oil which are in
themselves harmful to lung function.
Another important consideration is the gas absorbed in the pump oil. Since the exhaust gases contain HF
there will be a build up of HF in the pump oil. Therefore, it is important to use the correct protective
equipment when servicing the pump or changing pump oil, i.e. suitable gloves, protective clothing,
filtered facemask or breathing apparatus.
It is also worth remembering that when using O
2
processes the pump oil should be Fomblin oil and NOT
mineral oil to avoid risk of fire or explosive reaction between O
2
and mineral oil.
Process Information (Information contained in this document is confidential)
Printed: 08 January 2006 09:37 Page 17 of 30 Issue 1: December 03
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For a PECVD tool the typical process operating ranges are:
Total gas flows = 150 to 3000sccm. The maximum depends on the type of pumps 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 flow rate to achieve this.
Pressure = 200 to 2000mTorr. Below 300mTorr the plasma may not strike easily (or with sufficient
stability) for certain gases and power levels, so you need to check this and adjust 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 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 300W. A plasma may not strike easily for low power levels for certain gases.
You will need to check this and adjust process accordingly, since operating system without a plasma could
cause damage.
Temperature = room temperature to 400C (or up to 700C for a 700C stainless steel electrode). Film
quality/density will be worse at lower temperatures, therefore, it is recommended to operate at the
maximum temperature that the substrate will allow for best film properties.
The system base pressure for PECVD chambers is often measured simply by using the CM gauge, hence
base pressures are typically a few mTorr. The exact value is mainly determined by the offset of the CM
gauge zero (this is usually set slightly positive by a few mTorr to ensure a sensible reading, since a
negative offset will always read zero).
Operating with a high reflected power (>5% of forward power) is not advised as this will cause damage
to matching unit or generator. In such cases it will be necessary to adjust process parameters or re-tune
the matching unit.
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The uniformity of nitride films is usually worse for Low Frequency (LF) deposition since the LF is closer to
DC and hence is much more sensitive to the electrical conductance from electrode to plasma, and from
plasma through wafer and back to ground. So if the chamber and/or table are dirty then there is likely to
be more non-uniformity in the LF film.
It is recommended that when performing an LF
or mixed frequency deposition, that the customer should
do a brief conditioning of a few thousand angstroms, and then endeavor to keep that constant thickness
of film on the table under the wafer throughout the subsequent runs. This means putting dummy wafers
or Aluminum blanks over the unused wafer position to avoid a build up of film in the unused locations,
because it is known that these locations will give a very poor uniformity if this procedure is not carried
out.
If this does not cure the problem then it may be that the system needs a thorough clean, back to bare
Aluminum. Initially, using a plasma clean, but if that doesn't work, a bead-blast of the showerhead or the
table may be required.
It is
not recommended to use an IPA or water wipe-down of the chamber interior, - just an occasional dry
wipe-down, if necessary, to remove loose powder. This should only be done with the system stone cold (to
avoid melting/residues of clean room wipes on hot surfaces).
Process Information (Information contained in this document is confidential)
Issue 1: December 03 Page 18 of 30 Printed: 08 January 2006 09:37
System Manual= lñÑçêÇ=fåëíêìãÉåíë=mä~ëã~=qÉÅÜåçäçÖó= mä~ëã~ä~Ä
Another possible cause of non-uniformity is wafer material - GaAs is less conductive, so large GaAs wafers
show more non-uniformity, which can be counteracted to some degree by increasing the LF frequency,
but there is a trade-off with matching (i.e. reflected power is generally higher at higher frequency). (To
adjust the frequency, Press the Program button - adjust the Frequency - press the Program button again
to run at the new frequency).
For LF power, the PC should be setting (and the generator should be controlling) load power as this is the
power that actually reaches the plasma. The matching is often quite bad for LF, but this doesn't matter
too much as the LF generator increases its power output to compensate and to ensure that the power
delivered to the load (load power) is always as requested.
However, it is advisable to adjust the step-up transformer to minimize reflected power, to avoid
overheating of the LF generator, especially as the RFPP generators will switch themselves off
automatically if reflected power is above 40-50W for self-protection.
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Premature flaking of chamber wall / showerhead material can occur for a number of reasons:
1) For new systems the showerhead may need several deposition/clean cycles before it reaches its
best film adhesion performance. This can be improved by bead blasting the showerhead.
2) Temperature cycling of showerhead / chamber walls can cause flaking, therefore it is important
that chamber walls are set to a stable temperature, e.g. 60C, and that the showerhead cooling
water is flowing properly. It is also important that electrode temperature is maintained at a
constant value as this will also affect showerhead temperature.
3) The system should not be switched off overnight to save power. The system should be left
pumping with electrode maintained at deposition temperature at all times to avoid flaking.
4) Incomplete cleaning during a previous clean cycle can lead to premature flaking.
5) Wiping of chamber and or showerhead with water or IPA can leave residues which subsequently
causes early flake-off of films deposited.
6) Wiping of chamber walls / showerhead with clean room wipes while they are hot can also leave
behind residues which cause premature flaking.
7) Repeated venting of chamber will cause flaking. This one of the main reasons that for a PECVD 80
Plus or a PECVD 800 Plus, it is recommended to clean every 5-10 microns of film, whereas for a
load locked PECVD System 100 running high rate SiO
2
films, it is not necessary to clean as often.
8) Mixed deposition of oxide, nitride, and oxynitride films can cause increased stresses in deposited
films and hence premature flaking.
9) Changes to standard recipes can also cause increased stress and hence premature flaking.
For a PECVD System100 running high rate oxide we recommend plasma cleaning every 100microns for
best film repeatability. A dry wipe of showerhead and vacuum cleaning of any large particles may also be
required.
For a PECVD 80 Plus or PECVD 800 Plus, it is recommended to clean every 5-10microns of film. Plasma
cleaning may need to be carried out more often if mixing depositions or using a range of electrode
temperatures etc as listed above. A dry wipe of showerhead and vacuum cleaning of any large particles
may also be required.
Process Information (Information contained in this document is confidential)
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