Utah-94-721002-System-Manual.pdf - 第157页
System Manual = lñÑçêÇ=fåëíêìãÉåíë=mä~ëã~= qÉÅÜåçäçÖó= mä~ëã~ä~Ä PKOKNMKO= i~ëÉê=áåíÉêÑÉêçãÉíêó= RF Process Chamber Laser Camera Signal Tim e PC Process chamber • In-situ etch rate monitoring • Endpoint does not require …
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(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.
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Gases with a low vapour pressure (e.g. SiCl4, BCl3) 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 heated jacket) 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.
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Endpoint
Light
o/p
Monochromator
Light
o/p
RF
Reactive
s
p
ecies
Etch by-
products
PC
Etch time
Process chamber
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)
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RF
Process Chamber
Laser
Camera
Signal
Tim
e
PC
Process chamber
• 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.
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A laser interferometer (LI) 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)
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mä~ëã~ä~Ä= lñÑçêÇ=fåëíêìãÉåíë=mä~ëã~=qÉÅÜåçäçÖó= System Manual
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Material etched Gas species
detected
Wavelength
nm
Rise/fall at endpoint
Si F 704 Rise
Si SiF 440, 777 Fall
Si SiCl 287 Fall
SiO2 F 704 Rise
SiO2 CO 483 Fall
Resist, polyimide O 843 Rise
Resist, polyimide CO 483 Fall
Resist, polyimide OH 309 Fall
Resist, polyimide H 656 Fall
Si3N4 N2 337 Fall
Si3N4 CN 387 Fall
Si3N4 N 674 Fall
W F 704 Rise
Al Al 391, 394, 396 Fall
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Signal
Time
% level
Normalisation
time
Endpoint
closed time
(no false
endpoint can
be found)
Endpoint
capture
time
Signal crosses its
endpoint threshold level.
Endpoint capture timer
started.
END of
process
Overetch
time
Endpoint trace – (signal, falling)
Normalisation
level
Threshold
level
Time
% level
Signal
Normalisation
time
Endpoint
closed time
(no false
endpoint can
be found)
Endpoint
capture
time
Signal crosses its
endpoint threshold level.
Endpoint capture timer
started.
END of
process
Overetch
time
Endpoint trace – (signal, falling)
Normalisation
level
Threshold
level
Process Information (Information contained in this document is confidential)
Issue 1: December 03 Page 16 of 30 Printed: 08 January 2006 09:37