Chapter 4.21
UVBAKE
Fusion M150PC
Photostabilizer System
(uvbake)
UVBAKE, Fusion M150PC
Photostabilizer System
After
reading this manual, the User should be able to describe all hazards associated
with the M150PC (Uvbake), give a brief description of the M150PC process and
theory of operation, and perform wafer/resist processing using this system.
The UVbake system uses both ultraviolet light and a heated chuck to respectively cross-link and harden patterned photoresist. The system may be used directly after developing the resist mask, and before dry-etching the substrate. Uvbake essentially replaces the conventional hard bake step prior to etching, and improves the selectivity of the resist greatly.
Uvbake irradiates ultraviolet (UV) light by means of an electrodeless, sealed bulb. High voltage DC power is converted to microwave energy by two magnetrons, which in turn produce a high-temperature plasma inside the bulb. This plasma then re-radiates the energy in the form of infrared, visible, and ultraviolet radiation. An optical reflector ensures a uniform distribution of energy over the plane of the substrate. The end result is a cross-linked resist with a much improved mask selectivity for subsequent dry-etch applications.
Fusion M150PC Maintenance Student Guide (original hardcopy located near machine)
5.1 Fusion
H-Mod Bulb – This
bulb is designed to produce very intense UV energy between 280 and 300 nm. This
corresponds to the absorption characteristics of the novolak resin used in most
positive photoresists.
5.2
Magnetrons – These components convert high
voltage electrical energy to RF (radio frequency) energy. This RF energy is
then transmitted through wave-guides and captured in the electrodeless H-Mod
bulb.
5.3
Faceted
Reflector – This
component is designed to provide diffused source of UV energy from the bulb to
the wafer surface in a three dimensional fashion. This way, vertical walls of
the resist receive the same amount of UV cure.
5.4
UV
Energy –
Ultraviolet energy (wavelengths 320 nm – 0.1 nm). Direct exposure of this type
of radiation is hazardous.
5.5
Blisters – The photoactive compound in resist will break down
and give off N2 gas after being exposed to UV energy. If the N2
is not allowed to escape before the bulk of the resist becomes cross-linked,
pockets of gas (blisters) will form. They will eventually “pop” and spew resist
debris in all directions, (therefore undesirable).
5.6
Reticulation – Wrinkling of the resist is also known as
reticulation. The common cause is when the surface has not been cured enough to
withstand the stress caused by the contracting bulk of the resist during
thermal ramp-up.
5.7
Pullback – This phenomenon results in the shrinking or
pinching in of the top portion of a resist pattern. The cause is the rapid
reduction in volume that takes place when a large quantity of solvent is
suddenly evaporated from the resist.
5.8
Pattern Flow – If the resist is heated above its glass transition
temperature, it will flow and become rounded. White light has been shown to
drastically reduce the glass transition temperature of resist.
5.9
Wet Edge – This refers to the degree of post-process resist
hardness at the wafer edges. The phenomenon is sometimes seen with thicker
resists. If the resist on the edges smears easily it should be wiped down with
a technicloth before further processing occurs. Alternatively, wafers with wet
edge may be further processed in uvbake with program O, which is essentially an
additional 3-minute hard bake.
6.1 Microwave Radiation – The User should be aware that the uvbake system
conforms to ANSI’s standard for exposure to microwave radiation. This standard
states that an individual should not be exposed continuously to microwave
radiation at average levels exceeding 5 mw/cm2 on a continuous basis
at 2.45 GHz. Uvbake incorporates RF detectors that shut the system down if a
peak level of 5 mw/cm2 should ever occur.
6.2
UV radiation – The User should also be aware that excessive
ultraviolet radiation can be dangerous to the eyes and skin. The uvbake system
incorporates several interlocks to prevent such direct exposure to UV
radiation. Some indirect UV light leakage may occur around the cover of the irradiator,
but exposure to this light poses no hazard.
6.3
Pinch Points – The User must be aware AT ALL TIMES of moving
parts of the uvbake system. These “danger” zones are labeled with red “Pinch Point”
signs. They are located at the cassette loading and receiving areas, and at the
robotic transfer armload and receive points. The User must exert caution at all
times such that a limb, finger, or article of clothing does not become trapped
or entangled.
6.4
High Voltage – The uvbake system operates at 4000 volts. The User
should never attempt to operate the system with any of the covers removed.
6.5
Ozone – The fusion H-MOD bulb generates ozone, which has a
characteristically pungent odor. During normal operation the ozone will be
removed through the exhaust port. If it is sensed that the exhaust port may not
be working correctly, the User should cease operation and report this fault.
6.6
Heat – The surface of the thermo-chuck may reach 250ºC
during normal operation. The surface temperature of the lamp will exceed 120ºF
during normal operation. There is NEVER a reason for the User to come into
contact with these components. Be aware however that a post-processed wafer may
still be hot!
7.0
Statistical/Process
Data
N/A
8.0
Available
Processes, Process Notes
Currently there are several recipes that have been characterized for specific applications. See the Appendix for details.
The UV / bake process is a
simple “one-stop-shop” stabilization treatment that replaces the conventional
resist hard bake step. Recipes will differ in parameters of course, but the
three basic segments of a process are:
8.1.1 Pre
Bake – While simultaneously heating
the resist, a low dose of UV energy breaks down the PAC (photoactive compound).
This also cross-links the resist enough to allow for a thermal ramp-up without
pattern degradation.
8.1.2 Ramp Up – The hot plate temperature is gradually increased
to a high temperature (program dependent). During this thermal ramp-up the
wafer is exposed to high intensity UV energy, and cross-linking occurs.
8.1.3 Post
Bake – For a more densely
cross-linked resist, a post-bake step is incurred in the recipe. The hot plate
remains at a high temperature for an extended time during this segment.
The default status of
uvbake’s LED screen should be Main Menu mode. In the Main Menu,
from top to bottom the options are:
8.2.1
Power Down – Turns power to the machine OFF. The default state
of the machine is with power ON, so this option should generally not be used.
8.2.2
Process Menu – Allows User to select and run processes.
8.2.3
Diagnostic Menu – Not available
8.2.4
Wafer Handling
Menu – Not available
8.2.5
Secs I
Parameters – Not available
8.2.6
Automatic Deck
Clearing – Selecting this option
will commence an automatic process that removes any derelict substrate from the
processing chuck.
At the bottom of the screen
in Main Menu mode, from left to right the options are:
8.2.7
Last – Selecting this will revert the screen to the
previously used option, whatever that may be.
8.2.8
Select – Selecting this key will execute the “highlighted”
operation to which the cursor arrow points.
8.2.9
Arrow Up – Allows cursor arrow to be moved up.
8.2.10 Arrow Down
– Allows cursor arrow to be moved down.
8.2.11 Stop –
Selecting this option stops all processing. It performs the same task as the
emergency stop button.
The Process Menu
allows the User to select and run processes. In the Process Menu, from
top to bottom the options are:
8.2.12 Main Menu
– Selecting this option will revert back to the Main Menu.
8.2.13 Select Process – Allows User to select one of 26 recipes (A-Z) for processing.
8.2.14 Define Process – Not available. Standard recipes have already been developed for use.
For assistance with the development of non-standard recipes consult uvbake
superuser.
8.2.15 Process Monitor – Not available
8.2.16 View Lamp Status – Selecting this option will
allow the User to view the bulb’s current state.
8.2.17 View Chuck Status – Selecting this option will allow the User to view the thermal chuck’s
current state.
8.2.18 View Cycle Status – Selecting this option will allow the User to view the current state
of the process cycle.
9.0 Equipment
Operation
To run a process using
uvbake perform the following steps:
9.1
From the Main Menu,
highlight and chose the Automatic Deck Clearing option using the arrow
keys and select button. This will remove any wafer inadvertently left in
the system.
9.2
Load the substrate(s)
to be processed into the load cassette, and place the cassette on the loading
block.
9.3
From the Main Menu,
highlight and chose Process Menu using the arrow keys and Select
button.
9.4
In the Process Menu,
chose the Select Process option. The User may then scroll through the
recipes using the arrow keys. The View Graph option may be selected for
a visual aid of the process. Press the Select key when the correct
recipe is found. A subsequent message will express which recipe has been
loaded, and then prompt the User to select the Resume key.
9.5
Next, selecting the Menu
option will place the screen back in the Process Menu. Select the View
Cycle Status option. This will bring up what is essentially a pre-process
menu. The Proc Mode option toggles among Cycle, Auto, and Batch
processing. Cycle should be selected when a single substrate is being
processed. Auto should be selected when more than one substrate is being
processed in sequence. Batch processing is not used.
9.6
Select the Cycle
Start (or Auto Start) key. Processing should begin by which the
substrate is moved to the thermal chuck via the robotic transfer load arm. The
User should note that once the Cycle Start (or Auto Start) key
has been selected, the Menu option transforms to the Disp option.
Selecting Disp allows the User to view the current process in a graphical
display format.
9.7
When the process is
complete, the robotic transfer receive arm will unload the substrate and place
it in the receiving cassette. The User may need to select the Stop
option to raise the cassettes after processing. Selecting Stop once
halts all processing. Selecting Stop again should bring up the Fusion
Semiconductor logo screen, and the option Proceed. Once Proceed
is selected, automatic deck clearing will occur and the machine will revert
back to the Main Menu.
10.0 Troubleshooting Guidelines
10.1 A wafer gets stuck inside
the chamber:
From the Main Menu, highlight and choose
the Automatic Deck Clearing option using the arrow keys and select
button. This will remove any wafer inadvertently left in the
system. An alternative is to select Stop twice. After the Fusion Semiconductor logo shows up, select Proceed. This will also remove any wafer inadvertently left in the system.
11.0 Figures & Schematics
N/A
Standard Uvbake Recipes
|
uvbake
program |
A |
TEMP |
TIME |
STEP |
LAMP |
TIME |
|
used
with svgcoat prog #s |
1,2 |
100 |
|
IDLE |
|
|
|
developed
for: |
lam3 |
100 |
5 |
1 |
FLASH |
0 |
|
|
|
200 |
50 |
2 |
OFF |
10 |
|
|
|
200 |
5 |
3 |
HIGH |
50 |
|
|
|
|
|
4 |
OFF |
0 |
|
RESULTS: |
|
blistering |
none |
reticulation |
None |
|
|
|
|
pullback |
none |
wet edge |
None |
|
|
|
|
reflow |
minimal |
Sel Al/PR |
2.2:1 |
|
|
|
|
|
|
|
|
|
|
uvbake
program |
B |
TEMP |
TIME |
STEP |
LAMP |
TIME |
|
used
with svgcoat prog #s |
|
50 |
|
IDLE |
|
|
|
developed
for: |
|
50 |
20 |
1 |
FLASH |
3 |
|
|
|
90 |
60 |
2 |
OFF |
60 |
|
|
|
100 |
90 |
3 |
FLASH |
5 |
|
|
|
100 |
60 |
4 |
OFF |
60 |
|
|
|
100 |
60 |
5 |
LOW |
20 |
|
|
|
100 |
80 |
6 |
HIGH |
60 |
|
|
|
100 |
0 |
7 |
OFF |
0 |
|
RESULTS: Not available |
|
blistering |
N/A |
reticulation |
N/A |
|
|
|
|
pullback |
N/A |
wet edge |
N/A |
|
|
|
|
reflow |
N/A |
Sel Al/PR |
N/A |
|
|
|