CMOS non-metal (nitride and oxide
strip) wet bench:
The Nitride Etch wet bench is to be used for etching or stripping nitride from
silicon wafers, performing clean processing on SiN4 or SiO2 substrates which
cannot be processed at another wet bench. Glass, GaAs, or wafers with metal
cannot be used in the nitride bath.
Performance of the tool:
What the tool can do?
Bath 1- Piranha 9:1 H2SO4:H2O2
Bath 2- Nitride etching 85% Orthophosphoric acid
Bath 3 -BOE (buffer oxide etch) for oxide etching
Bath4 - 50:1 HF
Dump rinsing
Drying
System overview:
This wet bench is equipped with quartz bath for orthophosphoric acid (nitride
etching) with temperature controller and nitride etch controller.
Quartz bath for piranha cleaning with temperature controller
Polypropylene bath for BOE (buffered oxide etching) which drain to HF waste
collection system
Polypropylene bath for dilute HF which drain into HF waste collection system
Dump rinse and spin-rinse dryer for 2”, 3”, 4”and 6” wafers
Quick dump rinser (QDR):
Bench is fitted with a QDR, the purpose of which is to rapidly wash the surface of
the water and leave the wafer in a clean condition.
How to use:
 At rest the QDR will be partly full of water when the lid is opened and
wafers are placed inside close the lid and press the start button, this water
will dump and the bath rapidly fills using the top sprays and the bottom fill.
 When full the water flow will stop and the unit will dump its contents.
 A new cycle of filling will commence, the number of cycles can be set on
the dump cycle counter.
 After completion of the cycle the light will flash and warning sound will be
audible until the wafers are removed.
Spinner:
The bench is fitted with a spinner suitable for drying a single wafer and a holder
that will accept wafers of 2”-6”.
How to operate the spinner:
 N2 fault indicates that there is no nitrogen pressure.
 The heater fault indicates that there is an over temperature situation with the
heater.
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The process timer will stop the spinner after the pre-set time has elapsed.
Lift the lid
Insert the wafer
Close the lid
Turn safety cam such that flat faces the front
Press start/stop switch(spinner will run for pre-set time and nitrogen purge
will be on)
 End of cycle/dry complete light will illuminate, the spinner start stop will
flash and there will be an audible alarm.
Chemical hazards:
Sulphuric acid, hydrogen peroxide, orthophosphoric acid, BOE and hydrofluoric
acid are used at this wet bench. You must read the Material Safety Data Sheets for
these chemicals and understand safe chemical handling procedures before working
at this bench.
The primary hazard classification for the chemical mixtures used at this bench are:
For 90% sulphuric/peroxide - Corrosive, oxidizer, air/water reactive.
For 50:1 HF - Corrosive, toxic.
For 13:1 BOE- corrosive, toxic.
For 85% orthophosphoric acid- corrosive
Chemical frequency:
Bath 1: Piranha 9:1:H2SO4:H2O2 fill the tank with 5400ml of H2SO4 and add
600ml of H2O2 this fills the bath till red line once it indicates low level spike with
H2O2.
Bath 2: Nitride etch Check the log before you begin to see when the chemicals
were last changed. The frequency of the change on these baths is dependent on the
usage. Recommended changes are posted on the log sheet. A decrease in etch rate
indicates the bath needs to be changed. Fill in any changes of chemicals you make
on the log sheet.
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The hot pot must be below 50 °C to be drained.
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Rinse the hot pot out well and fill it up once with DI water before adding
new chemicals.
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Remember to turn off the 'aspirate' button before adding chemicals to the
bath.
Bath 3 BOE - once a month
Bath 4: Oxide etch 50:1: DI: HF this bath does not have any level indicator, the
bath is filled according to the ratio.
How to fill the tank:
To fill orthophosphoric bath:
 The orthophosphoric bath is filled with orthophosophoric acid (no ratio) till
the “Red line” (liquid level) present inside the bath it takes 2 bottles of
phosphoric acid (2.5L).
 The solution is maintained at 160 °C
 The DI water drip light will turn on automatically based on the
temperature of the bath (starting at about 100°C). No need to make
any adjustments to it.
 Be very careful removing the cassette from the hot phosphoric bath.
The high temperature, 160 °C, causes the Teflon to expand, making
the cassette and handle feel 'loose'.
 Wafers go directly from the hot phosphoric bath into the dump rinser.
 Photoresist should not go into the bath; the chemistry will destroy the
resist, causing contamination of the bath.
 Selectivity of nitride to Silicon and Silicon Dioxide is very good.
Controllers:
• The wet bench is fitted with temperature controllers and the timers.
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Users are allowed to set temperature values and process duration.
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Do not alter anything other than temperature and process duration.
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This bench has nitride-etch controller, here the users are allowed only to set
the process duration.
Nitride Etch Controller:
The STATUS LED display panel has the following indicators;
Normal- the controller is in normal operating mode. All parameter
conditions have been met.
Hold- the controller is in standby condition. The TIMER will display HOLD
alternating with the current timer count. Various alarm conditions will put
the controller in hold state. HOLD is exited by pushing the HOLD (on-off)
button on the Power panel. When in the hold state the power to the bath
heaters and DI H2O drippers is denied. If the timer was on at the onset of
the hold condition it will continue to count. It may not be started if
controller is on hold state.
Setup- the controller is in setup mode. This mode allows for selected
parameter values and limits to be entered. Lab users should not have need
to change any parameter except time (described later in this document). If
you think you want to change any parameters or that are set incorrectly,
please see one of the technicians responsible for the wet bench.
Alarm- indicates the controller or process has gone outside the pre-set
tolerances. There will be another LED lit to show which parameter has
drifted. Alarm status mode will go off when the tolerance is back to normal.
Heat- shows that power to the heating portion of the bath is on. As the
bath reaches temperature, the LED will be lit only a fraction of the time. At
temp it should light about every 10 seconds.
DI H2O-indicates the dripper is adding DI water to the bath. You should
check to make sure the flow meter indicates water is flowing at least once
during you process.
The ALARM LED display panel has the following indicators;
System- the controller has a problem with the software which has been
detected by the diagnostic routines. The unit may need to be re-powered or
commands need re-entering.
Sensor- indicates that the process temp or redundant over-temp sensor is
either open, shorted or not connected. Heater input is stopped and the
temperature flashes in the process temperature display alternating with
"SN".
Redundant High Temp- indicates that the redundant over-temp
thermocouple has sensed the bath temperature to be over 10 degrees above
the set point. When the bath has returned to normal temperature the
controller has to be turned back on by pressing the "PWR (on-off)" button
and the "HOLD (on-off)" key. Essentially, the system has shut off and must
be re-started.
Hi-Acid Concentration- alarms anytime the concentration of acid raises
the boiling point of the solution to other than the process set point. Two °C
above the set temperature of 155 ± 0.7 °C, the system will add DI
water. When it alarms several actions are initiated; the dripper adds water
to the bath as the controller increases the bath temp seeking the boiling
point. If the boiling point is not attained within five minutes, the
controller will place the bath into HOLD status shutting off the dripper and
heater. When this alarm is activated the process display will read "HI" with
the sensed bath temp. DI water drip: 4 - 5 (do NOT change it!).
Low-Temperature ("L TEMP") - If the bath temperature drops below the
set point once it has risen to it during warm-up the LED will activate. The
bath temp and "LO" will alternately flash in the temperature display. No
other controller functions will be triggered.
Liquid-level ("LIQ LEVEL") - both high and low liquid conditions are
monitor and if sensed heater and dripper activity are suspended until the
condition is rectified. The process display will flash the "LL" symbol
alternating with the bath temp.
POWER KEYS segment contains the following membrane keys and their
functions;
PWR (on-off) and HOLD (on-off) keys- in the case of a power outage or
emergency power off at the wetbench, the controller will remain off (all
display black) until the PWR key is pressed. Once pressed the system goes
into HOLD status, i.e., power is denied to the heaters and the DI dripper.
Pushing the HOLD key will activate full controller functions. A second
pressing of the HOLD key will but the system back into HOLD status.
Pressing the PWR key a second time will return the system to a dormant
condition.
The usual stand-by mode of the wetbench is HOLD status (because the
interlock is on the liquid level sensor), hence HOLD must be pressed in order
to activate the heaters and dripper.
ADJ DRIP key- will only work for the period of time it is depressed. It adds
DI water to the bath via the dripper. Generally, lab users will not need to
use it unless to verify that the dripper system works when there is doubt
about it. Adjustments to the DI water flow are made by SNF staff.
ALARM SILEN key- turns off audible alarms (du...) and will stop any alarm
prompts which are flashing in the temperature window. Any alarm LED's
which are lit will remain lit. The audible alarms will not turn back on to
signal any conditions which have already been announced.
SETUP keys are used for programming the controller (so the average user
should not have to adjust them) and have the following functions;
POLL PARAM key enters the controller into program mode. It steps
through the various parameters and displays their values in the temp and
time alpha-numeric windows. Below is the key to the parameter code. All
changes, except for time, are made by staff only.