Chapter 6.22
Parylene Deposition System 2010 Labcoter 2
(parylene)
1.0 Title
Specialty Coating Systems Parylene Deposition System 2010
Labcoter 2
2.0 Purpose
The Parylene Deposition System Model 2010 is a vacuum system used for the sublimation and subsequent deposition of Parylene onto a silicon wafer (or other vacuum compatible substrate). Up to three 4-inch wafers, or one 6-inch wafer can be processed at one time. Only trained and approved users may use this machine.
Some desirable properties of the polymer Parylene
(poly-para-xylylene) are:
► Biocompatibility
► Truly
conformal material (pin-hole free at 25 nm thickness)
► Thin film
dielectric
► Excellent
moisture/chemical barrier properties
► High
mechanical strength
3.0 Scope
3.1
Deposition Process
The Parylene deposition process consists of three basic steps, all
done in the presence of a vacuum:
3.1.1
Vaporization - Heating solid Parylene dimer (di-para-xylylene) until it
sublimes into the gaseous state.
3.1.2
Pyrolysis - The heating and cleaving of the gaseous Parylene dimer into a
monomer (para-xylylene).
3.1.3
Polymerization - The formation of Parylene, as a polymer
(poly-para-xylylene), onto the substrate at room temperature.
3.2
Purpose of Equipment
The PDS 2010 consists of a series of tubes and chambers that
enable the Parylene deposition process to occur. The five main components of
the system are:
3.2.1
Vaporizer - This heats the Parylene dimer until it sublimes (vaporizes).
3.2.2
Pyrolysis Furnace - This further heats and cleaves the
gaseous Parylene dimer into monomer form.
3.2.3
Deposition Chamber - This is the chamber whereby Parylene is
deposited as a polymer onto the substrate.
3.2.4
Cold Trap - This is a cryogenic device that uses liquid nitrogen (LN) to
cool a steel thimble. The chilled thimble then condenses Parylene process
by-products and prevents contamination of the vacuum pump.
3.2.5
Vacuum Pump - This maintains vacuum to the system.
3.3
Materials
There are two types of Parylene dimer currently available for use in the PDS 2010: type N Parylene and type C Parylene. Type N is highly conformal, and deposits at the rate of approximately 0.75 microns per hour. Type C is less conformal than N, but deposits at a much higher rate of about 5 microns per hour. A third form of Parylene, type D, is not currently available for use in the PDS 2010. If you are interested in using type D for your application, consult Matt Wasilik for special process considerations.
4.0 Applicable
Documents
5.0 Definitions
& Process Terminology
5.1
Process Controls
Pre-operation of the PDS 2010 requires knowledge of the controls of the system. This section will describe the controls of the system.
5.1.1
Control Panel
5.1.1.1
Main Power - This button provides and removes
power to the system. When the button is depressed, power is provided to the
machine and the button is illuminated.
5.1.1.2
Emergency Stop - This is a rotary type button.
De-pressing it will remove power to the machine. Rotate the Emergency Stop
clockwise to release.
5.1.1.3
Furnace Temperature Controller - This
displays and controls the temperature of the pyrolysis furnace (units in
degrees Celsius).
5.1.1.4
Chamber Gauge Temperature Controller - This
displays and controls the temperature (in units of degrees Celsius) of the
vacuum gauge tube. The heating of this tube prevents the deposition chamber
pressure gauge from becoming coated with Parylene.
5.1.1.5
Vaporizer Temperature Controller - This
displays the vaporizer temperature (in units of degrees Celsius).
Note: The temperature of the vaporizer is
automatically adjusted by the controller by means of feedback to achieve the
set point chamber deposition pressure (see Section 11.1 -
System Schematics). The maximum vaporizer temp set point will not be
exceeded during the process deposition.
5.1.1.6
Vacuum Pressure Controller - This
displays the degree of vacuum in the system. The units are designated as vacuum
units, and correspond roughly to milli-Torr when in the range of 10-100.
Note: The set
point deposition pressure is regulated by means of a feedback signal to the
vaporizer temperature controller.
5.1.1.7
Alarm - This button enables the audio
alarm signal. It is illuminated only in the case of a system fault during a
deposition cycle. Depressing the button will deactivate the audio signal. If a
fault condition occurs the red light will illuminate and the system will
automatically shut down if the fault is not rectified within 5 minutes.
5.1.1.8
Process Start/Stop - Pressing this button
starts and stops a process run. A green light indicates that the process is
running. A blinking light indicates that the process is complete.
5.2
Changing Process Controller Set Points
Parylene Users are allowed to set the West 6100 controllers’ set points *only* as described below. Users are *not* allowed to change further settings within the controllers. Failure to adhere to these instructions may result in erratic machine performance. The set point values of the vaporizer, furnace, and vacuum West 6100 process controllers differ for Parylene N and C (see Section 5.3 for correct set point values). To change the set point values of these process controllers, perform the following steps:
5.2.1
Ensure that the West 6100 process controller is in the
Operator Mode (this is the default "running" state of the
controller).
5.2.2
Press the Function key (in lower right hand corner).
5.2.3
Adjust the set point value by pressing the Lower or Raise
keys.
5.2.4
Press the Function key to return to the Operator Mode.
5.3
Process Controller Set Points
5.3.1
Furnace Temperature Controller - The
furnace set point values are 690 for type C Parylene, and 650 for type N
Parylene.
5.3.2
Chamber Gauge Temperature Controller - The
chamber gauge set point value should ALWAYS be 135ºC.
5.3.3
Vaporizer Temperature Controller - The
vaporizer set point value for Parylene N is 160ºC. The vaporizer set point
value for Parylene C is 175ºC.
5.3.4
Vacuum Pressure Controller - The
base pressure of the system may change over time. Therefore, the vacuum set
point value for type C Parylene is 25 units above base pressure, and 55 units
above base pressure for type N.
6.0 Safety
7.0 Statistical/Process
Data
8.0 Available
Process, Gases, Process Notes
8.1
Adhesion Promoter
Silane A174 is used as an adhesion promoter for parylene on silicon substrates and other hydrophilic materials. It is kept in the solvent chemical cabinet in 432A.
8.1.1
In beaker, add 500ml IPA, 500 ml DI water, and 5 ml Silane
A174. If the mixture is to be used
immediately, stir continually for 5 min every 10 min for a period of 2 to 2.5
hours. Or else, leave the mixture
overnight.
8.1.2
Remove wafer from mixture and allow to air dry for 30 min.
8.1.3
Soak wafer in IPA for 5 min.
8.1.4
Test for hydrophobicity, and then dry wafer with N2 gun.
8.1.5
Vacuum bake in oven at 115ºC for 30 min.
Note: It has been found that parylene adhesion to
thin film aluminum works best when the aluminum is slightly porous.
9.0 Equipment
Operation
Surgical gloves are required to be worn when touching any component of the PDS 2010. Protective insulated gloves are required to be worn when handling the chilled thimble, or loading dimer into a "hot" vaporizer (dimer should NEVER be loaded when the vaporizer temperature is above 60ºC.)
9.1
Process Start Up
9.1.1
Ensure that the system is enabled on the wand and that the
main power is turned ON. The main power should normally be ON at all times.
9.1.2
Be sure to manually fill in all the required information on
the PDS 2010 login sheet.
9.1.3
Ensure that the system is satisfactorily clean (see Section 10.1 on system cleaning).
9.1.4
With the chamber lid removed, place the substrate into the
chamber fixture within the deposition chamber.
9.1.5
Ensure that the chamber lid gasket and the gasket-sealing
surface on the chamber are clean. Then place the chamber lid onto the chamber.
9.1.6
Ensure that the cold trap thimble, o-ring, and sealing
surface are clean. Then place the thimble into the cold trap housing. Be
careful not to nick the surface of the thimble while doing this, as even cracks
at the micron level can be detrimental to its performance.
9.1.7
Fashion a dimer boat out of aluminum foil using the
"boat form" tube. A new boat should be made for each run. Place the
dimer into one end of the boat.
9.1.8
Ensure that the vaporizer temperature has cooled below 60ºC.
Loading the vaporizer above this temperature could cause immediate vaporization
of the Parylene dimer, and consequent system degradation. Wear protective
gloves if the vaporizer is hot, and slide the boat containing the dimer into
the vaporizer. Ensure that the end of the boat containing the dimer is closest
to the vaporizer door.
9.1.9
Ensure that the vaporizer o-ring and sealing surfaces are
free from debris. Then close and lock the vaporizer door.
9.1.10 Ensure
that the process set point values are correct (see Section 5.3
on controller set points for
Parylene N and C).
9.1.11 Manually
hold the cold trap thimble in its upright position with the o-ring contacting
the sealing surface to ensure proper sealing. Then turn the vacuum switch to
the VACUUM position. The system pressure should begin decreasing immediately.
DO NOT use the HOLD position to test the system for leaks.
9.1.12 When the
pressure in the system reaches 200 vacuum units, fill the cold trap thimble
with LN and secure the lid. Note that a process should *NEVER* be run without
filling the cold trap to the top with LN. Note that long runs may require
refilling the cold trap with LN. Cold trap should essentially always be filled
with LN during a run. Failure to do this may result in severe pump damage.
9.1.13 If all
goes well, the system should achieve base pressure (0-10 vacuum units) within
about 2-5 minutes, and user may proceed with step (13) (out gassing of
substrate or photoresists could cause a longer pump-down time). If base
pressure is NOT achieved within this time, the system must be shut down and the
cause of the leak solved. DO NOT use the HOLD position to test the system for
leaks. Turn the vacuum switch to the VENT position and wait for the system
pressure to reach ambient. Once the cause of the leak is solved (residual
Parylene on the gasket and o-rings is a common cause of system leaks), user may
proceed with next step.
9.1.14 Once base
pressure is achieved, turn the furnace and chamber gauge switch to the ENABLE
position.
9.1.15 Turn the
vaporizer switch to the ENABLE position. The turntable within the deposition
chamber should begin rotating.
9.1.16 Press the
process start/stop button. The green light indicates that the process is
running. If all goes well, the vacuum gauge tube will begin to heat, followed
by the heating of the furnace, and finally the heating of the vaporizer.
9.1.17 After the
dimer has been deposited, the vaporizer will perform a several minute
"bake-out" to ensure vaporization of all the dimer.
9.2.1
Ensure that the green process-start/stop button is blinking.
This ensures that the dimer boat is empty, and that the deposition process is
complete.
9.2.2
De-press the process-start/stop button.
9.2.3
Turn the vacuum switch to the VENT position.
9.2.4
Wait for the pressure in the system to reach ambient.
9.2.5
Turn the furnace and chamber gauge switch to the DISABLE
position.
9.2.6
Turn the vaporizer switch to the DISABLE position. The
turntable within the deposition chamber should stop rotating.
9.2.7
After the system has vented, remove the cold trap thimble.
It is important to do this as soon as possible, as water from ambient will
begin to condense on the thimble, which in turn can enter the pump line.
Note: Residual
LN may be discarded by simply pouring onto the cement flooring.
Wear protective gloves when
removing the cold trap thimble from its housing. Place the thimble in the
cleaning fixture on the table, and secure it with the thumbscrews. DO NOT touch
the main shaft when removing as it will be very cold. Once it is secured in the
cleaning fixture, allow it to warm to room temperature before cleaning (see Section 10.1).
9.2.8
The substrate in the deposition chamber is now ready to be
removed. Use caution in lifting the deposition chamber lid. It can sometimes be
difficult to remove after a process run due to Parylene deposition around the
gasket. Also, waiting approximately 10 minutes after venting the chamber will
make lifting the lid easier.
Note: When removing wafers it is best to start from the BOTTOM shelf and move upwards. This is because when you remove the top wafer first, flakes of parylene come off of the backside as you pull it to unstick it from the metal holding shelf, and they fall onto the wafer below, they seem to stick pretty hard. Thus, starting from the bottom and moving up gives better surface cleanliness.
9.2.9 After removing the substrate, ensure that the substrate fixture is centered on the turntable. Replace the chamber lid, and leave the system in a VENTED state.
9.2.10 Disable the machine on the wand.
10.0 Troubleshooting
Guidelines
10.1 System Cleaning
The motivation for cleaning the system thoroughly before a process run will be the prevention of substrate contamination. An unclean system will have small flakes of Parylene and other contaminating particles that will lodge on the substrate during deposition. After cleaning, a release agent (2% microsoap solution) must be applied to all surfaces that will be coated with Parylene. This allows the coatings to be easily stripped later. It is also highly recommended that a vacuum cleaner be used to remove any possible contaminants in the general vicinity of the PDS 2010. The cleaner the system and environment, the less contamination there will be.
10.1.1 Cold Trap
Thimble
To ensure proper operation of the system, the cold trap thimble must be cleaned after each run.
10.1.1.1 Ensure that
after a process run, the cold trap thimble is secured to the cleaning fixture
on the table. The thimble must reach ROOM TEMPERATURE before cleaning.
Proceeding with cleaning before warming will damage the thimble.
10.1.1.2 Use a
plastic acrylic scraping tool to gently force the condensed Parylene off the
thimble. The majority of the condensed Parylene should strip off easily.
10.1.1.3 Use a
non-abrasive scotchbrite pad and 2% microsoap solution to scrub the remaining
film off the thimble.
10.1.1.4 Wipe the
thimble clean with a lint free cloth and microsoap solution.
10.1.1.5 Lastly,
gently place the clean, dry, room temperature thimble back inside the thimble
housing.
10.1.2 Deposition
Chamber
10.1.2.1 The inside
of the deposition chamber lid and viewing port will need to cleaned when the
coating becomes excessively heavy, blisters, or separates form the surface. DO
NOT attempt to clean very thin coatings, as they are difficult to remove.
Attempts to clean thin coatings may cause flaking dispersion and consequent
particle contamination within the system.
10.1.2.2 If the
coating on the chamber lid is thick, blistering, or separating from the
surface, carefully peel off the film. Films resulting from an accumulation of
several runs (approximately 80 grams of dimer) should peel off in their
entirety with ease. Thin films do not need to be removed. Furthermore, DO NOT
apply microsoap to a thin Parylene film that is NOT being removed. Doing so
will make removal of the film difficult at a later time.
10.1.2.3 After the
film is removed, wipe clean with a lint free cloth and microsoap solution. DO
NOT apply microsoap to the chamber gasket.
10.1.2.4 Use
isopropyl alcohol to clean residual Parylene off the chamber gasket.
10.1.3 Vaporizer
Tube
10.1.3.1 Use a
stainless steel flue brush to gently scrub the residual Parylene off the inside
of the vaporizer. A main source of substrate contamination is due to ash build
up in the vaporizer.
10.1.3.2 After
scrubbing, use a vacuum cleaner to remove the ash and dislodged material.
10.1.4 Pyrolysis
Furnace Tube
10.1.4.1 After a system
dimer throughput of 300-400 grams, a yellowish brittle deposit will form within
the pyrolysis tube. This deposit will be most prevalent near the inlet port of
the chamber base. Try separating the deposit with the plastic acrylic scraping
tool, and then peel it from the tube.
10.1.4.2 Use a
stainless steel flue brush to gently scrub the inside of the pyrolysis furnace
tube.
10.1.4.3 After
scrubbing, use a vacuum cleaner to remove any material, which may have fallen
down the pyrolysis tube and into the vaporizer (access via the vaporizer door).
10.1.5 Cold Trap
Thimble Housing
10.1.5.1 The
housing for the cold trap thimble will also need to be periodically stripped
and cleaned. Use a stainless steel flue brush to gently scrub the inside of the
housing. After scrubbing, use a vacuum cleaner to remove any dislodged material
in the housing.
10.1.6 Chamber
Ports, Inlet and Outlet
10.1.6.1 These
ports may also be gently scrubbed with a stainless steel flue brush when the
build up becomes excessive.
10.1.6.2 After
scrubbing, use a vacuum cleaner to remove any dislodged material.
11.0
Figures & Schematics
11.1
System Schematics
12.0
Appendices
12.1
Data Collection
Films < 2 microns were measured with the Nanoduv.
Films > 2 microns were measured with the
Nanospec, programs 52 and 53.
|
TYPE |
FURNACE |
CHAMBER
GAGE |
VAPORIZER |
VACUUM |
|
C |
690 |
135 |
175 |
25 |
|
N |
650 |
135 |
160 |
55 |
12.3 A-174 Silane Adhesion Promoter Application
Procedure
A-174 Silane is used to promote parylene adhesion to hydrophilic surfaces (such as silicon wafers), by making them hydrophobic. If your substrate is already hydrophobic, there is no need to use A-174 Silane. It is recommended for most electronic assemblies, such as printed circuit boards and hybrid circuits containing ceramics, metals and epoxy glass.
The recipe for the adhesion promoter is as follows:
500 ml IPA
+ 500 ml DI water + 5 ml A174
If you are planning to use the mixture soon, stir constantly
every 10min for 5min for a period of 2~2.5hrs. If you aren’t planning to use it
right away, leave it to stir overnight.
The following is the procedure for applying the adhesion
promoter to silicon wafers.
1. Leave
wafer in IPA @ room temp. for ~ 5-10 min, then water rinse for 10 min.
2. Put the
wafer in A174 + IPA + water mixture for 30 min.
3. Air-dry
the wafer for 30 min.
4. Put wafer
in IPA for 5 min
5. Test
whether the wafer is hydrophobic. If so, blow-dry the wafer.
6. Vacuum
bake in oven at 115ºC for 30 min.
Rev. 00 – 8/00, M. Wasilik
Rev. 01 – 3/03, E. Kim
Rev. 02 – 7/03, R. Prohaska
Rev. 03 – 8/04, E. Kim
Rev. 04 – 5/05, R. Hamilton
Rev. 05 - 10/06, M. Wasilik -
Added schematic with feedback block diagram; updated cold trap operation
instructions.