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Approved by Principal Investigator________________________Date:________________ Approved by Super User: _____________________________Date:________________

Standard Operating Procedure BNC Acid Etching in the Sinks

Version 2010 June 16 I. Purpose

This Standard Operating Procedure (SOP) outlines requirements to be considered by an authorized user of Acid Handling and Use within the BNC sinks as well as describes the normal operation of the sinks and any hazards that may be encountered during normal operation. Finally, the SOP explains how to minimize any hazards and how to respond in an emergency situation. This document is to be reviewed one year from the date of approval or as conditions warrant, whichever is the shorter time period.

II. Personnel

A. Authorized Personnel

a. Complete Environment, Health & Safety (EH&S) training class.

: The acid use in the sink may be performed only by authorized personnel who are fully cognizant of all safety issues involved in the operation of both sink and material. These personnel are to ensure that the sink is only operated in the manner laid out in this document. To become an authorized user, one must:

b. Take the baseline BNC Safety Orientation presentation c. Read and fully understand the SOP d. Receive training on acid and sink use by an authorized Super User and

User. e. Sign the authorized user sheet to affirm that the above steps have been

completed.

B. Unauthorized personnel

: No unauthorized personnel may enter the BNC clean room facility unless accompanied by an authorized user. All visitors must be briefed on proper safety protocol and must wear appropriate protective eyewear located on the premises.

III. Hazards A. Electrical Hazards: electrical shock or electrocution could result from direct

contact with sink electrical power. Do not disconnect the sink electrical power lines. Use normal precautions with external house (110VAC) connections on and behind the sink.

Standard Operating Procedure – BNC Acid Etching in the Sinks 2

B. Hot Plate Usage on Sinks

C.

: the hot plates should be grounded (three wire plugs, green lead) and hotplates should never be sitting on or placed on liquids. All plates being used must be carefully and clearly labeled (user name, date and time, application). Offending hotplates will be removed and confiscated regardless of importance, user, or owner. Pressure Hazards

E.

: Pressurized house gases and water are used with the sink. Do not disconnect or tamper with water, gas, and vacuum lines behind the sink. Contact lab management for information.

Wastelines

: Wet chemical waste is associated with the sink. The waste is associated with water rinse in the drains, chemical siphons in the sinks to remove primary acid loads, and solid material such as wipes, empty bottles, and chemical residue. Proper waste disposal procedures outlined in the EH&S guidelines should be followed.

IV. Hazard Controls A. Electrical

1) Enclosures for protection against the house voltages of the power may only be removed after the power has been unplugged from the outlets or turned off at the respective electrical power panels and after following the safety procedures outlined in the safety and operations manual provided by the manufacturer.

2) Only qualified personnel may perform all internal maintenance to the sinks

and more than one user must be present when performing said maintenance.

3) Every portion of the electrical system should be assumed to be at dangerous voltage level.

C.

1. Enclosures for protection against valves and internal gas plumbing may only be removed after the system has been turned off; water and gases have been valve off and relieved of line pressure.

Chemical and Pressure

2. Only qualified personnel may perform all internal maintenance to the sinks

and more than one user must be present when performing said maintenance.

D. Other1. Proper eye protection must be worn at all times in the clean room and while

operating in the sink. Consult EH&S guidelines on the use of Personal Protective Equipment.


V. Normal Operation A. Inspect all water, electrical, gas, and vacuum connections for damage and

connectivity. B. Complete the “check-in” log and log ALL problems encountered. Report to lab

management any known offenders. C. Ensure that the sink work area is clean and hazard free. D. Gloves are required. E. Remove any unlabelled containers. F. Remove any unlabelled equipment. G. Rinse and wipe off work space surfaces to ensure hazard free working area. H. Use of Corrosives in the sink.

a. Full clean room attire is required. b. Adherence to EH&S guidelines are required (face shield, rubber apron,

rubber gloves on top of latex gloves, proper footwear). c. Proper transport and containment of corrosives. d. Proper labware.

I. Use of respective corrosives. a. Follow proper recipe protocols established by manufacturer, lab protocols,

or safety guidelines. See Appendix for references on corrosives or examples in following section for usage.

b. Careful controlled experiments with only necessary volumes. c. Document everything.

J.

Example: Silicon Oxide Etch Process

Objective: To remove the areas of silicon dioxides unprotected by photoresist and expose the silicon underneath.

a.

1. This operation should be started within 30 minutes of the completion of the hard bake of the photoresist.

Preparation and Precaution:

2. Use Buffered Oxide Etch (BOE) solution (6 parts 40% NH4F and 1 part 49% HF).

3. Always use plastic or Teflon beakers and graduated cylinders for etchants containing HF; HF WILL ETCH GLASS!

4. Know the oxide thickness on your substrate. Use profilometer to measure.

b. 1. Clean the substrate or wafer surface by rinsing with DI water; hold the

sample with Teflon tweezers.

Procedure:


2. Before beginning the etching, calculate the time needed to etch through the oxide of the known thickness using the known etch rate of the BOE solution; the etch rate at room temperature is ~700 A/min.

3. Use a stop watch to time the etching process. 4. Etch the wafer for about half of the estimated time. Remove your sample

and rinse with DI H20. 5. If the silicon dioxide has not been completely etched away, you will

observe a film of the DI water wetting or sheeting across the whole surface of the wafer. If the layer of SiO2 has been etched off, the DI water will not adhere to the back, except for a few isolated drops, and the wafer will appear dry and dull gray. This happens because SiO2 is hydrophilic as opposed to silicon which is hydrophobic. Observe the backside of the wafer to confirm this effect for a few seconds.

6. If the oxide is not thoroughly etched or removed, immerse the substrate or

the wafer back into the BOE solution. Etch for an additional 30 seconds. Recheck back of wafer as mentioned in step 5 after the substrate has been rinsed with DI water.

7. Repeat step 6 until SiO2 is completely etched and removed. 8. If you are unsure of your ability with the above method or you are

performing a critical step in your process and cannot tolerate much over etch, then use the method below. This should prevent any over etching and damage to the Si substrate surface.

a. Remove the substrate or the wafer from the BOE solution and rinse the

wafer for two minutes in running DI water.

b. Dry the wafer with an N2 gun.

c. Check the color of the oxide under a light microscope using incident white light. The oxide thickness can be estimated from an oxide color chart; dark or light tan color indicates about 700 angstroms of oxide remain.


d. Etch in BOE solution for 30 seconds.

e. Repeat a through d until you observe the following:

1. Dark tan or light tan color. In this case about 700Å remain to be

etched. Continue etching for 55 seconds and proceed to step 10.

2. White color. This indicates that silicon has shown up. Etch for 30 seconds and proceed to step 10.

NOTE: A very thin oxide layer is invisible since the last few hundred Angstroms of oxide do not show any color. Over etch the oxide approximately 20 seconds longer.

10. After the exposed positions of SiO2 have been etched, rinse the wafer in

running DI water for five minutes.

11. Dry the wafer with an N2 gun.

12. As a final check, view the etched areas of the wafer under the microscope, you should not see oxide, which has colors, but instead silicon, which appears rather white under a high-power microscope with vertically incident white light.

K.

Example: Piranha (Sulfuric Peroxide) Etch Process

Piranha Procedure adapted from Materials Science Division / Molecular Foundry

Lawrence Berkeley National Laboratory

(1) Background of Piranha Etch

Acidic Piranha Etch (or simply Piranha) is a mixture of two reactive chemicals in varying ratios that is chosen by the individual preparing the Piranha Etch. The two components are concentrated sulfuric acid (usually 98% concentration and CAS # 7664-93-1) and hydrogen peroxide (typically 30% concentration and CAS # 7722-84-1). These chemicals by themselves represents both chemical and health hazards to potential users; this is also true for other laboratory personnel who may be in the vicinity where these


solutions are being prepared, actively used or stored as hazardous waste. Acidic Piranha, also referred to as peroxydisulfuric acid or Caro’s acid, must always be regarded as capable of causing great bodily harm in multiple ways, particularly at elevated temperatures. Piranha solutions are colorless to slightly yellow (depending on amount of sulfur trioxide dissolved in the sulfuric acid) when freshly prepared, but may turn characteristic colors when contaminated with hydrated metal ions. Piranha is unstable and decomposes with the evolution of oxygen, sulfur trioxide and water. Acidic Piranha etches can be made in a variety of sulfuric-to-peroxide ratios, although the most typical ratio is 3 parts of sulfuric acid to 1 part 30% hydrogen peroxide (3:1). An additional type of acidic Piranha can be made by slowly dissolving solid ammonium persulfate in hot concentrated sulfuric acid at between 80-125oC; both types of acidic Piranha should only be used in open (unpressurized) Pyrex containers.

Piranha, in all acidic mixture proportions and types is self-reactive, volatile, corrosive, oxidative and exothermal in nature. Piranha etch is always prepared from its components and cannot be purchased as a separate entity, due to its extreme reactivity and relatively short usage life. It is a very powerful oxidizer that can cause organic materials to ignite spontaneously, as well as cause severe burns to mucous membranes that are slow to heal. It is an excellent solvent for many metals, their salts and an effective glass cleaner for the removal of organic contaminants.

Piranha is often used with a hot plate to maintain a specific elevated temperature after the initial heat of reaction has dissipated. Heating Piranha increases the solution’s reactivity and consequently the dangers associated with its use. Human exposure potential is also increased and made more severe. Thus, the risk management of Piranha is very critical to its safe use and subsequent disposal at BNC. Care must be exercised so that Piranha etches will pose a minimum/negligible risk to hazardous waste operations and personnel. Waste Piranha etches are usually stored in glass containers having a special plastic safety containment coating on their exterior surface. Plastic or PolyPro containers can be used with secondary containment if glass containers are not available.

(2) Designated Use Areas & Proper User Attire


Piranha Etch in the clean room must always be used and stored in compatible containers located either within a fume hood or secondary contained beneath the sink. Use areas should be free of exposed metals, have water rinse capabilities for dilution of small spills, and be free of paper or other organic materials. The following attire will help minimize the risk of harm by acidic Piranha Etch to laboratory workers: A. Closed toed non-mesh upper shoes must be worn when working with Piranha solutions, regardless of its temperature. B. No exposed jewelry, including necklaces, rings, metallic bracelets or hair bands should be worn at any time. C. Contact lenses can be worn safely underneath the chemical safety goggles. D. Long sleeved shirt and full length pants (no shorts) are highly recommended for all lab personnel.

(3) Potential Hazards & Examples

The following hazards are present whenever Piranha is being used or stored prior to waste disposal: A. Mixing hazards – Piranha solutions must always be generated in containers that are capable of safely sustaining temperatures of at least 240oC. B. Oxidation of organic materials – Piranha is a powerful oxidizer that will destroy organic materials rapidly, often with liberation of large amounts of heat and the distinct possibility of a fire. C. Pressurization of a closed or partially closed container – due to its ongoing reactivity, Piranha will evolve gaseous materials (primarily oxygen) that can pressurize a container where no pressure relief is possible (i.e., a closed bottle, regardless of the bottle’s materials of construction). D. Self-heating potential – when freshly mixed, sulfuric acid and hydrogen peroxide are exothermic and can self-heat to as much as 195oC. Be sure any container you are planning to use can sustain such extreme heat. Do not use any container that is damaged or cracked to contain Piranha solutions. E. Corrosivity – Piranha fumes, particularly at elevated temperatures will attack most common items. F. Reactivity – Piranha will react with most metals with the liberation of flammable hydrogen gas and enough heat to promote ignition


(remembering that it already contains an oxidizer!); do not use any metal accessories in direct contact with Piranha solutions. G. Slip Hazards – Piranha solutions that spill over their container can cause the container surface to become slippery when handled with a gloved human hand. H. Flammability – Although it is not considered a flammable liquid per se, Piranha promotes and supports combustion in the presence of organic materials such as clothing, paper or oils. Thus, do not use Piranha inside a hood where these combustible materials are either present or could be introduced at a later time during Piranha’s use. I. Inhalation - At its typical usage temperatures, the vigorous Piranha reaction produces extremely corrosive vapors that are an inhalation hazard; this becomes worse as the temperature of the vapors increases.

(4) Personal Protective Equipment (PPE)

Based on the multiple hazards associated with Piranha Etch solutions, the following PPE items are required to be used and/or worn when you are preparing, using, transferring or manipulating any Piranha solutions: A. Barrier between the solution and your face: At all times the direct path between the solution and your face must be obstructed by a transparent, protective barrier. To meet this requirement we recommend you use either a face-shield, or vertical hood sashes or an appropriately lowered horizontal hood sash. B. Safety goggles : Chemical safety goggles (vented) are required in addition to the barrier. C. Lab Apron: at least knee length and/or within 18 inches of the floor and the bottom of apron D. Covered hands and arms: To meet this requirement we suggest you use appropriate gloves (e.g., neoprene or polyvinyl chloride), as well as arm-guards or a lab coat. E. Safety/blast shield (recommended) – to be placed between user and an open Piranha container whenever it is being heated or exhibiting signs of an active reaction taking place (bubbling, frothing, boiling, etc.) This recommendation is particularly encouraged if you are etching away significant organics/resists, as opposed to merely cleaning glass. F. Eyewash – required within a maximum of 10 seconds travel distance from the work location within the same lab area.


G. Safety Shower – required to be present in a lab whenever a corrosive material is in use.

(5) Engineering/Ventilation Controls The following engineering and ventilation controls must be observed whenever Piranha solutions are being prepared, used or stored prior to waste disposal: A. Always use Piranha inside a fume hood that is operating properly (minimum of 100 lfpm). B. Use inside a fume hood with the sash at minimum height to optimize its draw and minimize both the liquid and vapor exposure potential to users. C. Do not place any solid objects in front of fume hood draw points that will compromise the designed operation of the fume hood. D. Do not store incompatible materials or equipment inside a fume hood where Piranha etch is either being prepared or used; incompatible materials include organic liquids, paper or cloth products, or bare metals that could come into contacts with emitted Piranha vapors. E. A hot plate with stir capability that incorporates over-temperature protection to prevent etchant overheating and subsequent boil-over should be used for conducting Piranha usage operations.

(6) Equipment, Materials and Supplies

The following items are important for the minimization of risk during preparation, use, and subsequent waste storage of acidic Piranha Etch preparations: A. Sulfuric acid (CAS 7664-93-9) B. Hydrogen Peroxide (CAS 7722-84-1); purchased not more than 30% concentration in water C. Combination hot plate and stirrer D. Teflon-coated stir bar E. Pyrex, Teflon or quartz container for preparing and using acidic Piranha etch F. Non-Mercury glass thermometer – capable of measuring temperature of at least 240oC.

(7) Personal Decontamination


Recommendations for minimizing harm to yourself if you become exposed to either Piranha Etch liquid or vapors: A. Know where the nearest safety shower and eyewash is located in your lab B. If you become exposed to acidic Piranha etch solution or vapors, remove appropriate D. Have a lab partner dial 2-3073 to summon the assistance or 9-911 after hours.

Example of Piranha Recipe

1. This recipe is for cleaning small (2 cm square) pieces of glass or silicon. 2. In a 250ml Teflon beaker add 15ml of 30% hydrogen peroxide. 3. Slowly add 45ml of concentrated sulfuric acid. The solution will start to

boil and foam after a few seconds delay. Add sulfuric acid slowly enough that the solution does not boil over the edge of the container. The solution can be stirred with Teflon tweezers or stir bar on combination

4. stir/hotplate. It is normal for the solution to evolve large bubbles that pop

at the surface. 5. Slowly add substrates one at a time with Teflon tweezers. Give time after

each substrate addition for solution to quit foaming. 6. Remove samples and rinse by depositing in a beaker of water. 7. Once the piranha has cooled to < 30°C slowly add waste to Piranha waste

container. If your waste container does not have a pressure release cap then do not tighten the cap and let your safety office know immediately.

8. Check rinse beaker of water for acidity that may require waste disposal. If

needed use a different waste container than Piranha waste.

L. Example: Glass Etching for Borofloat (Pyrex) Glass adapted from Mathies Lab.


1. Etching with 49% HF: Make sure to fill the container with enough acid to entirely cover the cassette and wafers, and gently agitate throughout etch. The rinse container should also be filled with an adequate volume of rinse water.

2. Etching with 1:1:2 HF:HCl:H2O or 5:1 buffered HF: Make sure to fill the container with enough acid to entirely cover the cassette and wafers, and gently agitate throughout etch. The rinse container should also be filled with an adequate volume of rinse water.

3. If a thick photoresist (e.g. AZ4620), add 0.2% surfactant (3M Novec 4200 Electronic Surfactant) into the buffered HF.

4. The etch rate for Borofloat glass is: A. 49% HF = 5-7 um/min B. 5:1 buffered HF = 2-3 um/hr C. 1:1:2 HF:HCl:H20 = too slow to measure

5. HF can be used for a few times until the etching rate goes below 5um/min.

M. Clean up. a. Remove all corrosives from the sink area. b. Clean and decontaminate all sink surfaces. c. Clean and remove if necessary all lab ware not associated with the sink. d. If any chemical material must remain in the sinks or work surface area,

follow all EH&S and lab safety guidelines by proper labeling. All offenders will be severely disciplined.

N. Shutdown. 1. All sink faucets OFF. 2. All gases off. 3. Sink must be drained with no standing liquids in the sink. Report

all drain obstructions to lab management. 4. All electrical devices turned off (with the exception of continuing

experiments, of which all proper labeling procedures must be followed). Offenders will have equipment confiscated.

VI. Emergency Procedures

A. Sink accidents: Notify lab management and PI immediately.

B. Power outage: If there is a power outage, turn off all water to avoid a hazardous situation when power is restored. If there is an emergency, leave laboratory


immediately and either return after emergency to shut down sink or contact lab management.


Appendix A. Authorized Users: I have read and understood the Standard Operating Procedures for BNC Acid Etching in the Sinks.

Name (print) Signature Date PI or Super

User Initial


Appendix B – In case of medical emergencies, consult lab safety protocol or lab safety plan. In the event of a sink accident, follow the procedure below:

1. Ensure that the sink is shut off per Normal Operation.

2. Provide for the safety of the personnel (first aid, evacuation, etc.) as needed.

3. Obtain medical assistance for anyone who may be injured. UC Optometry Clinic (Normal Hours) 642-2020 UC Optometry Clinic (24 Hour Emergencies) 642-0992 University Health Services (Emergency) 642-3188 Ambulance (urgent medical care) 9-911

4. If there is a fire, pull the alarm, and contact the fire department by calling 9-911. Do not fight the fire unless it is very small and you have been trained in fire fighting techniques.

5. Inform the Office of Environment Health, & Safety (EH&S) as soon as possible. 6. During normal working hours, call the following:

EH&S Office 642-3073 BNC Safety Officer 666-3356 EH&S Health & Safety Manager 642-3073 After normal working hours, call 642-6760 to contact the UC Police Department who can contact the above using their emergency call list.

7. Inform (PI NAME) and the BNC safety officer (BNC Management) as soon as possible. If there is an injury, (PI NAME) will need to submit a report of injury to the Worker’s Compensation Office.

8 After the incident, do not resume use of the aligner system until the BNC lab

manager and EH&S has reviewed the incident and approved the resumption of research.


Appendix C –References The following articles are attached as references: 1. Source: www.microchemicals.eu/technical_information (Etching with HF) 2. Williams and Muller, Etch Rates for Micromachining Processing – Part I 3. Williams and Muller, Etch Rates for Micromachining Processing – Part II 4. Stanford Nanofab Wet Etch Rates for Nonferrous metals

http://www.microchemicals.eu/technical_information�


WET ETCH RATES (ESTIMATED) for NON-METALS NOTE: Temperature and use of solution can change the etch rate (Please report any gross deviations of etch rate.)

*Etch rates are in angstroms per minute

6:1 Buff

HF 20:1 Buff HF

50:1 HF 10:1 HF Hot Phos. H2O2 Al etch Pad

Etch Freckle

Etch

Th Ox 910 300 50 280 <10 --- <10 385 73 LTO Undens 2900 740 300(a) 920 <10 --- <10 2370 459

4% Undens 4340 1000 350 2000 16 --- <10 4278 2530

8% Undens 6000 1650 600 3300 30 --- <10 5561 2970

LTO Dens 1400 400 87 715 <10 --- <10 642 91

4% Dens 1625 490 90 1460 <10 --- --- 1560 1355

8% Dens 2900 725 290 1500 <10 --- <10 3120 2385

Std Nitride <10 <10 <10 36 35 --- --- * 43

L Stress Nitride

<10 <10 <10 40 32 --- --- ** 148

Undope Poly --- --- --- --- <10 --- <10 --- 265

*For the Nitride wafers, when a 1600A stress sample was used 68A were stripped off in the first minute and 4A after that. However, when a 300A sample was used, 8A were removed in the first minute and each additional minute thereafter.

**Low Stress Nitride in Pad etch 337A in the first minute and 4A thereafter.

***Hot Phosphorus was 152C

****Aluminum Etch was 40C

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