Brigham Young University
SOP
Standard Operating Procedure
Microelectromechanical Systems (MEMS) Oxide Chemical Release
For Multi-User MEMS Processes (MUMPs)
Principal Investigator: Dr. Larry Howell
Primary Contact: Dr. Larry Howell
Secondary Contact: Dr. Brian Jensen
422-2625
422-6030
Lab #: 486
Building: Clyde
Contents
Description of Work and Scope of SOP
Precautions
General Notes
Prequalifications
Required Equipment, Safety Equipment & Personal Protective
Equipment (PPE)
Procedure / Steps Needed To Complete Work Safely
Waste Disposal Procedures
Chemicals Used
Mixtures & Ratios
Chemical Spill / Release Procedures
Appendix: Lab Layout
Completed By: Jeff Anderson
Edited By: Gary Johns
Approved By:
Page
2
2
2
2
2
3
4
5
5
5
6
Description of Work and Scope of SOP
This SOP addresses the work performed to chemically etch the sacrificial oxide layers of MEMS dies. The die
comes shipped with the devices being suspended in oxide, which must be etched away to free the mechanisms and
enable device movement. The die is bathed in a series of chemical baths to remove photoresist and etch away
sacrificial layers. One of these chemicals is Hydrofluoric Acid, which is lethal in small amounts and shows
delayed symptoms. This SOP also addresses removal of waste chemicals, cleaning of equipment, and handling of
a released die. This applies to all professors, undergraduate and graduate students, and lab personnel.
PRECAUTIONS:
 SPLASH PROOF SAFETY GOGGLES MUST BE WORN AT ALL TIMES WHILE WORKING IN THE LAB
 HF IS LETHAL IN SMALL AMOUNTS AND SHOWS DELAYED SYMPTOMS
 ACID GEAR MUST BE WORN WHILE HANDLING HF AND EXTREME CAUTION MUST BE USED
 CHECK ACID GLOVES FOR HOLES PRIOR TO USE
GENERAL NOTES
 WHEN MOVING A DIE FROM ONE LIQUID TO ANOTHER, DO SO QUICKLY AND SAFELY WHILE MAINTAINING A
PUDDLE OF LIQUID ON THE DIE.
 BEAKERS MUST BE LABELED ACCORDING TO THE CHEMICAL(S) THEY CONTAIN. EMPTY LABELED BEAKERS
ARE LOCATED IN DR. HOWELL’S CUBBY NEXT TO THE WET BENCH (SEE LAB LAYOUT IN APPENDIX)
 WHEN POSSIBLE PLEASE PREPARE FOR EACH STEP PRIOR TO PERFORMING A MEMS CHEMICAL OXIDE
RELEASE. MUCH OF THE CLEANUP CAN BE DONE WHEN SOAKING A DIE.
 DEPTH MEASUREMENTS FOR CHEMICALS IN THE BEAKERS CAN BE APPROXIMATED. THE CHEMICAL
SHOULD COVER THE DIE.
Prequalifications
Before proceeding, all workers planning to perform a MEMS chemical oxide release must:
 Read and understand the cleanroom acid safety training and demonstrate knowledge through passing a
written test (Contact Phil Brown for test, 422-4344);
 Read and understand the cleanroom solvent safety training and demonstrate knowledge through passing a
written test (Contact Phil Brown for test, 422-4344);
 Complete Hydrofluoric Acid (HF) training (Schedule with Bryant Brown (422-2789) or Kerry Smith
(422-2943) of Risk Management and Safety); and
 Read and understand this SOP prior to beginning experiment.
Required Equipment, Safety Equipment & Personal Protective Equipment (PPE)
The following items are located in Dr. Howell’s cubby next to wet bench unless otherwise stated:
 Teflon (PTFE) die grippers
 Plastic Beakers (Use 50 mL beakers for one die, or 250 mL beakers for 2 or 3 dies)
o Acetone Beaker
o 2 Isopropyl Alcohol Beakers
o 2 Deionized (DI) Water Beakers
o HF Beaker
Note: Beakers are already labeled - please do not remove the labels.
 Oven (see Lab Layout in Appendix)
 Stainless Steel Wafer Tweezers
 Stainless Steel Tweezers
 Timer
 Silicon wafer
 Gel Pak
Standard Cleanroom PPE
 Full bunnysuit
 Shoe covers
2




Latex Gloves
Splash-proof safety goggles
Paper snood
Closed toe, closed heel, full leather shoes (tennis or other athletic shoes not acceptable)
Note: Shoes must be immediately removed and discarded if splashed with HF.
Acid Gear to be worn while working with HF (located next to the acid bench):
 Full length Acid Apron
 Full face shield
 North Brand Natural Rubber Gloves 18 mils thick, double length
Procedures / Steps Needed To Complete Work Safely
A. Put on the Standard Cleanroom PPE (It must be worn at all times during the MEMS oxide release)
B. Gather required equipment and prepare for release
a. Gather required equipment to wet bench. Steps B through D are performed at the wet bench
(See Lab Layout in Appendix)
b. Prior to use, prepare the following beakers and equipment according to following chart:
Equipment Preparation
Acetone Beaker
Isopropyl Alcohol
Beakers
Deionized Water (DI)
Beakers
(Plastic?) HF Beaker
PTFE Die Grippers,
tweezers, wafer tweezers
c.
Rinse with methanol. Let evaporate or
swish with a little acetone before use.
Rinse with methanol. Let evaporate or
swish with a little isopropyl alcohol.
Rinse with methanol. Let evaporate or
swish with a little water before use.
Rinse with water. Blow dry with house
nitrogen.
Rinse in methanol. Let evaporate or blow
dry with house nitrogen.
Use tweezers to remove die from package and grip die with PTFE Die Grippers (Die will stay in
grippers until otherwise noted). Note: Hold Die Grippers on side to avoid applying a force
strong enough to release the die from the grippers.
C. Removing photoresist
a. Fill Acetone Beaker with Acetone (found in Solvents Cabinet) to a depth of 0.5 to 1 inch.
b. Soak die for 25 minutes in acetone to remove photoresist- mild agitation will help remove the
photoresist thoroughly.
D. Preparation rinse for release
a. Fill Isopropyl Alcohol Beaker with isopropyl alcohol (found in Solvents Cabinet) to a depth of
0.5 to 1 inch.
b. Soak die for 2 minutes in isopropyl alcohol.
c. Fill one DI water Beaker with DI water (from hose on wet bench) to a depth of 0.5 to 1 inch.
d. Soak die for 5 minutes in DI water.
E. Put on Acid Gear (See “Required Equipment, Safety Equipment and PPE” section.)
F.
Move equipment to acid bench (see Lab Layout in Appendix)
a. Move DI water beaker (with the die still submerged) to the acid bench.
b. Move empty HF Beaker and empty DI water beaker to the acid bench.
G.
HF Release
a. Fill second DI water Beaker with DI water (from hose on wet bench) to a depth of 0.5 to 1 inch.
3
b.
c.
At the acids bench, fill HF Beaker with 48% HF (located in Acid Cabinet) to a depth of 0.5 to 1
inch.
At the acids bench, soak the die for 2.0 to 2.5 minutes in HF with occasional gentle agitation.
H. Final Rinse
a. At the acids bench, move die to second DI Water Beaker. Let soak die for 10 minutes. Note: It
is critical to leave a small puddle of HF on the die when moving it between the HF Beaker and
the DI Water Beaker. Don’t let it dry off.
b. Bring waste HF container to the acid bench, dispose of used HF (see waste disposal procedures),
clean HF beaker as prescribed in Equipment Cleanup Chart, and remove Acid Gear.
c. Return to wet bench with DI water and die.
d. Fill second Isopropyl Alcohol Beaker with isopropyl alcohol to a depth of 0.5 to 1 inch.
e. At the wet bench, soak die for 5 minutes in isopropyl alcohol.
I.
Bake to reduce stiction and adhesion effects
a. Remove the die from the die grippers placing it on a silicon wafer.
b. Place the silicon wafer, with die, into the oven (see Lab Layout in Appendix) using the wafer
tweezers. Bake for 10-15 minutes at approximately 110°C. Note: This does not guarantee a
stiction free release, but it should minimize the problem.
c. Remove the die and wafer from the oven using wafer tweezers, and place the die and wafer on
the table beside the oven until it has cooled to room temperature.
J.
Cleanup
a. Properly dispose of all remaining used chemicals in designated waste containers (see waste
disposal procedures). Solvent and Acid waste containers can be found in the Solvent Cabinet
and Acid Cabinet, respectively.
b. Carefully place released MEMS die on Gel-Pak.
c. Clean and put away equipment. Beakers and the specified equipment should be rinsed as
follows, prior to being put away:
Equipment Cleanup
Acetone Beaker
Isopropyl Alcohol
Beaker
DI Water Beakers
HF Beaker
PTFE Die Grippers,
tweezers, wafer tweezers
d.
e.
Rinse with water, follow with methanol.
Air-dry right side up on paper towel.
Rinse with water, follow with methanol.
Air-dry right side up on paper towel.
Rinse with water, follow with methanol.
Air-dry right side up on paper towel.
Rinse under running water for several
minutes. Blow dry with house nitrogen.
Rinse in Methanol. Let evaporate or blow
dry with house nitrogen.
Beakers should be returned to the Platicware shelf in Dr. Howell’s cubby. Other tools should be
returned to the Tools shelf in Dr. Howell’s cubby.
The Wet bench and Acid bench must be cleaned (see Chemical Spill/Release Procedures). NO
DROPS OF HF SHOULD BE LEFT ON THE ACID BENCH.
Waste Disposal Procedures:
Properly dispose of all used chemicals in designated waste containers. Waste containers are labeled and located
within secondary containment inside the acid and flammable liquids (solvent) chemical cabinets. (Note: the
flammable liquids cabinet has built in secondary containment, and the plastic tub(s) inside the acids cabinet
constitutes secondary containment.) Waste HF should be stored in a clearly labeled plastic container inside of a
plastic secondary container isolated from the other wastes. When waste bottles are full, place the container in the
plastic tray just inside the cleanroom door and contact Chemicals Management (422-6156) to have them collect
the chemical waste.
4
Chemicals Used:
**Lab Workers Must Review All Applicable MSDS When Being Trained**
The following list of chemicals does not take the place of the required MSDS, which provide information
regarding signs and symptoms of exposure, exposure limits, physical appearance, etc.
Notes: NFPA Ratings and CAS Numbers Can Be Found on most MSDS, and NFPA ratings range from 0 (minimal) to 4 (severe).
Health
Flammability
Reactivity
Acetone
CAS
67-64-1
Starting
Concentration
100%
Isopropyl Alcohol
67-63-0
88%
Hydrofluoric Acid
7664-39-3
48%
Chemical Name
NFPA
Ratings
1
3
0
1
4
3
0
Other Hazards
Carcinogen, Skin Absorption, etc.
0
1
Causes sever burns with delayed
symptoms- absorbs through skin
and binds calcium in body. Fatal
in small quantities.
67-56-1
100%
1
3
0
Methanol
Note: HMIS or Saf-T-Data ratings may be substituted for NFPA ratings, when NFPA ratings do not exist. N = Not
Determined
Mixtures and Ratios:
Acetone- 100%
Isopropyl Alcohol- 88%
Hydrofluoric Acid- 48%
Methanol- 100%
Chemical Spill / Release Procedures:
Berkshire Lab towels (wipers) can be used to absorb spilled Acetone, Isopropyl Alcohol, and Methanol, which
may be cleaned up while wearing
 Latex gloves
 Splash-proof safety goggles
 Bunnysuit
In case of small spills (10 mL or less) of dilute HF (see Lab Layout for location of HF spill kit):
1. Apply calcium chloride (CaCl2) to spill. The solution should turn milky white as the calcium binds with
the fluoride (creating CaF2), leaving hydrochloric acid (HCl).
2. The HCl should be neutralized with baking soda (sodium bicarbonate) and then cleaned up. (After being
neutralized the solution is not dangerous and can be disposed of down the sink).
In case of larger spills (10 mL or more), call university police by dialing 911 from a campus phone.
While performing cleanup, place contaminated absorbent materials in a plastic bag that can be sealed to be liquid
tight, for waste pick-up. Contact Chemicals Management (422-6156) to have the waste removed.
Contact with HF – For large exposure, greater than 1 square inch (or unknown) call 911. Rinse affected area for 5
minutes and, if contact was with skin quickly apply calcium gluconate. If possible, the person who has been
exposed should self administer calcium gluconate. If splashed on clothes, remove and shower for 5 minutes
before applying calcium gluconate. Give emergency HF card to paramedics. If 911 was not called, take
emergency HF card with you to Utah Valley Hospital ER. (See Lab Layout)
5
Appendix: Lab Layout
Shower
Calcium
Gluconate and
HF card
Acid Gear
Acid Bench
Acids Cabinet
Use this oven
Solvent Cabinet
Wet Bench
HF Spill kit
Inside lab
Lab door
door
Dr. Howell’s
Cubby
MSDS
Next to lab
entrance door
6