Albanova NanoFabLab Mask aligner

Mask aligner, Karl Süss model MJB3

Maximum mask size 100 mm (4 inch)
Maximum substrate size 63 mm (2.5 inch)

Mercury lamp

Life time about 600 hrs.
Nitrogen cooling is very important.
Lamp must be cool before restarting or you risk damage to the lamp.
Therefore wait about 30 min. before turning on after previous shut-off.
It is better to leave lamp on for several hours instead of turning off and on and off and on ...
The first exposure after turning on the lamp should be made without a wafer.

If the lamp bulb explodes...
it will fill the area around the system with toxic mercury vapour. This can cause severe neurological damage. EVACUATE THE LAB FOR AT LEAST 30 MINUTES! The maskaligner will also be seriously damaged.

Below is a typical mercury spectrum. In the mask aligner the i- h- and g-lines can be used. Currently only the g-line is used for exposure, this is optimum for S-1800 series photo-resist. To use the shorter wavelengths would give higher resolution but require the optics to be changed in the system.

Mercury lamp power supply

It can be operated at constant power or constant intensity
Constant instensity means better reproducibility
- CI1 refers to i-line, 365 nm
- CI2 refers to h-line, 405 nm, (Obsolete: always used in our system)
- CP refers to constant power operation, this is now more functional with our lamp, please use this mode.

In constant intensity (CI) mode, the controller monitors the lamp intensity with a sensor and controls the power supply in a feedback loop to keep the intensity constant.
We always us CI2 (405 nm) because the calibrating power meter we have is for this wavelength. I = 25 mW / cm².

Optics

WHAT IS NEW ?

Before	NOW
Turn on/off complete system, also nitrogen in service corridor	ONLY turn on/off N2 and air-switches on the maskaligner control unit
No vacuum -> no possibility of different exposure modes	Vacuum is available. Possibility to select exp. modes
Height adjustment while in contact	NEVER height adjustment in contact
The separation lever was never used	The separation lever MUST be used
Exposures in constant power mode	Exposures in constant intensity mode, higher repeatability

Switches for compressed air and nitrogen

On/Off switch

X-, Y- and theta adjustments. Only use the outer, thinner part of the adjustment screws for X and Y.
For theta you should use the thick, main part of the screw.

The "Contact Arm" is used to lift up the stage and sample to press against the mask.
The "Contact / Separation Lever" is used to switch between close contact
or small separation between sample and mask.

Exposure modes

Mode	How does it work?	Resolution	Comments
Vacuum Contact (HP)	Vacuum is made between the mask and the wafer prior to exposure	≅0.8 µm pitch	RISK OF BREAKING THE MASK
Standard (ST) Hard contact mode	During exposure the vacuum holding the substrate to the chuck is switched off and positive nitrogen pressure is used to press the substrate against the mask	≅1.5 µm pitch	RISK OF BREAKING THE MASK
Soft contact mode	The substrate is held to the mask only by mechanical pressure of chuck throughout the exposure. The vacuum holding the substrate to the chuck remains on	≅2 µm pitch	SAFE
Proximity contact	Exposures are made with a small gap between the mask and substrate. The gap is determined by height adjustment	Depends on separation	SAFE. It has to be adjusted manually.

Microscope

Splitfield	Left objective	Right objective
Half field of view from left obj., half from right obj.	Image only from left obj.	Image only from right obj.
Left shutter fully clockwise right shutter fully anti-clockwise	Left shutter halfway right shutter fully anti-clockwise	Left shutter fully clockwise right shutter halfway

Anders Liljeborg Nanostructure Physics, KTH.