Specific Process Knowledge/Lithography/Strip

Strip Comparison Table

Equipment		Plasma Asher 1	Plasma Asher 1	III-V Plasma Asher	Rough Acetone Strip	Fine Acetone Strip
Purpose		All purposes	clean wafers only, no metal	III-V materials only
Performance	Minimum feature size
	Exposure light/filters/spectrum
	Exposure mode
Process parameter range	Positive Process
	Negative Process
Substrates	Batch size	1 small samples 1 50 mm wafers 1 100 mm wafers 1 150 mm wafers	1 50 mm wafers 1 100 mm wafers 25 150 mm wafers with automatic handling	1 small samples 1 50 mm wafers 1 100 mm wafers 1 150 mm wafers
	Allowed materials	Si and silicon oxide, silicon nitride Quartz, pyrex	Si and silicon oxide, silicon nitride Quartz, pyrex	III-V compounds

Plasma Asher 1

The PlasmaAsher1 is placed in Cleanroom 3.

The Plasma Asher1( 300 auto load model) can be used for the following process:

• Photoresist stripping
• Surface cleaning after storage
• Surface cleaning after processes using oil pump or diffusion pump vacuum
• Surface cleaning as part of photolithography after wet developing of lacquer structures prior to wet or plasma etching
• Stripping of photoresist layers after etching, including after being exposed to high temperatures as after implantation, ion etching, sputter etching, RIE
• Removal of organic passivating layers and masks
• Etching of glass and ceramic
• Etching of SiO$_{2}$, Si$_{3}$N$_{4}$, Si
• Removal of polyimide layers

The machine can be used for almost every materials, but if you have any doubt about your materials are compatible with the plasma process it is better to ask photolithography group at Danchip.

Overview of typical processes

	Photoresist stripping	Surface treatment of plastic, ceramic and metal	Ashing of organic material
Process pressure	0.8- 1.0mbar	0.5- 1.0mbar	0.8-1.5mbar
Process gases	O2, N2	O$_{2}$, CF$_{4}$, N$_{2}$ or their mixtures	O2
Process power	600-1000W	150-300W	1000W or less for heat- sensitive materials
Process time	5-60min, depending of photoresist thickness	a few seconds to a few minutes	Between 0.5 and 20 hours, depending on the material
Batch size	1-10 wafers at a time	1 wafer at a time	1 wafer at a time, use a container: Petri dish, evaporating dish weighing dish, beaker, etc.
Size of substrate	2"-6"	2"-6"	2"-6"
Allowed materials	All	All	All

A typical process time for stripping of 1.5 µm AZ5214e resist is 15-25 min and for stripping of 9.5 µm AZ4562 resist is 20-35 min with the process parameters: 210ml O$_{2}$/min or mixture of 210ml O$_{2}$/min and 70ml N$_{2}$/min, power 1000W.

Plasma Asher 2

Plasma asher for removing AZ resist on 6" wafers: positioned in cleanroom ? (class 10 yellow room)

The Plasma Asher 2 is the same as Plasma Asher 1 but has another loading system which is more convenient for batch loading of 6inch substrates.

In this machine, only O2 and N2 gases are used for processes (in PlasmaAsher1, CF4 is used as well).

The typical process parameters when operating the equipment:

• Photeresist stripping

Pressure: 0.8 - 1.0 mbar

Gas: O2

Power: 600 - 1000 watts

Time: 5 -30 min., depending on photoresist type and thickness

A typical process time for stripping of 1.5 um AZ5214e resist is 25 min for 6 wafers load in a boat, recipe 1.

A Descum process in manuel mode:O2:70, N2:70, power:150W, time:10min Be sure to wait for cooling if the mashine has been used at 1000W right before. At a load at 2 Fused silicawafers resist removed 0.01-01,5um

The other materials have not been tested yet.

Rough Acetone Strip

Acetone bath "rough" for removing most of the resist

Acetone bath "fine" for removing the rest of the resist incl. ultrasound

This acetone strip is only for wafers without metal and SU-8.

There are two acetone bath: one rough for stripping the most of the resist from the surface and one fine with a ultrasound for cleaning the resists remains.

Here are the main rules for acetone strip use:

• Place the wafers in a wafer holder and put them in the first bath for 2-5 min, this time is depending how much resist you have on the surface.
• After the rough strip place your wafers directly in the final bath, switch on for the ultra sound and strip them for 2-3 min.
• Rinse your wafers for 4-5 min. in running water after stripping .

Lift-off wet bench

Acetone lift-off: positioned in cleanroom 3

This bench is only for wafers with metal!

Here are the main rules for lift-off bench use:

• Place the wafers in a dedicated wafer holder.
• Put the holder in the acetone and start the ultrasound. The strip off time is depending of resist thickness.
• Rinse your wafers for 4-5 min. in running water after stripping.

Find more info about the lift-off process here: Specific Process Knowledge/Photolithography/AZ5214E standard resist - reverse process

Overview of acetone benches

	Acetone strip	Lift-off
General description	wet stripping of resist	lift-off process
Chemical solution	CH3COCH3	CH3COCH3
Process temperature	20 oC	20 oC
Batch size	1-25 wafers at a time	1-25 wafer at a time
Size of substrate	4" wafers	4" wafers
Allowed materials	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride	All metals