Process Guidelines rev. 1 (1063229), страница 3
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Pick a bottle that will not splash and spit acetone! Test it ahead of time-When the photoresist sets (no more interference patterns), position the bottle ofAcetone parallel to the wafer (the tip of the bottle is now perpendicular to thewafer). See Fig. 5.-Start a flow of acetone off the edge of the wafer and slowly turn the streamtowards the wafer edge. Remove a band of resist reaching in 3-5 mm from thewafer’s edge. Then, slowly turn the stream out away from the wafer edge.
Allowthe spin to finish.-If the spin cycle ends before edge bead removal, hit start again and performEBR. Allow 10 sec. for the acetone to dry, then hit STOP.16Basic Photoresist Processing TechniquesFigure 8: Edge bead removal-EBR must be performed if you are using a CNTech hotplate.-Press VACUUM to release your wafer. Use a wafer handler or tweezers toremove your wafer from the chuck. Move immediately to the hotplates for Postapply bake (PAB). See Section 4.2 Baking a Wafer.- When you are done, replace the aluminum foil on the shield and drain pan.
Thisprevents resist contamination for the next user, due to evaporating solvents, andalso contributes to general cleanliness of the spinner.- If your photoresist surface does not look uniform:1. Does the surface have particles on it?a. A particle will leave a wake behind it. Is there a spot on your waferthat appears to have a wake that widens as you move away fromthe particle?b. Also, consider the location of the particle. If it does not interferewith any exposure regions or regions of interest, then you do nothave to re-coat your wafer.c.
Did you blow out your pipette with the nitrogen gun? The pipettemight have loose pieces of flashing (a result of the molding processof the plastic) inside.17Basic Photoresist Processing Techniquesd. Did you follow decanting photoresist instructions from Part 1:Preparing Photoresist? Is your resist contaminated with particles?e. Was the surface of your wafer clean? If you continually getparticles in the same region after spinning, your wafer may have aparticle or spot on it. Try a new wafer.2.
Are there regions on your coated wafer where the resist looks “ghostly”or less opaque than the rest of the wafer?a. This is likely due to a solubility difference between the solvent usedin the photoresist and the resist itself. It results in a slightly thinnerregion of resist. If it is in a region of interest, you may want to recoat your wafer.3. Are there spots were the resist did not coat or adhere to the wafer?a. Did you apply enough resist to your wafer to adequately coat it?b. Did you apply HMDS to your wafer? If not, see Part 2: PreparingSamples for PR Coating.c.
Did the acetone splash/spit as you were making your edge beadremoval?- If you need to recoat your wafer, start a spin on the wafer and apply acetone.After the acetone has spun off, apply isopropanol (IPA) for the final clean. Allowthe IPA to spin off (notice the interference pattern changing and ending).Examine your wafer. Reapply resist if you are satisfied with the cleaningprocess.- Once you are satisfied with your spin, proceed to the post-applied bake (PAB)process.18Basic Photoresist Processing Techniques4.2 Baking a Wafer-Post Applied Bake (PAB):- PAB removes most of the remaining solvent from the photoresist film.- PAB time and temperature affect the selectivity of the developer betweenexposed and unexposed regions of the PR.
Other influences include adhesion,sensitivity, and dimensional control of the photoresist.- Thus, varying PAB temperatures and time will affect clearing dose, contrast, andfilm thickness. Make sure you understand these affects when choosing astarting point. See Appendix ? for more information.1. Select the hotplate vacuum surface diameter for your wafer size (See Part 3 forspecific hotplate operations).2. Using a pair of wafer tweezers with your right hand, position your wafer abovethe hotplate chuck, centering between the appropriate pin holes for your wafersize.
See Fig. 5.Center waferbetween thesepin holesFigure 9: Center your wafer between the pin holes. Each pin hole pair corresponds to a wafer size.3. This next step requires good coordination. While holding the wafer above thehotplate with your right hand, use your left hand to hold a timer (set to your baketime) and depress the vacuum toggle switch. Press start on the timer at thesame time you depress the vacuum and lower the wafer onto the hotplate chuck.Bake time variation has a critical effect on photoresist performance; following thesame procedures every time will produce the most reproducible results. See Fig.6.19Basic Photoresist Processing TechniquesFigure 10: How to position your hands.4. As time nears completion, position yourself in the same manner above.
You willdisengage the vacuum switch at the same time engaging the nitrogen switch astime expires. This will produce a nitrogen “pillow” where the wafer will floatabove the chuck. Quickly capture the wafer with your tweezers. The wafer willoften float across the entire chuck surface, so be prepared.5. Immediately place your wafer on the stainless steel hood surface and allow yourwafer to cool. Doing this set reproducibly will help ensure the tight processcontrols required by Chemically Amplified Resists (CARs).6. Measure your film thickness using the Alfa Step or FilmMetrics tool (SeeAppendix).20Basic Photoresist Processing Techniques3.3 Lab-Line Ultra-Clean 100 Oven (3490M): This oven is currently not inservice!Figure 11: Ultra-Clean Oven located in the back corner of the Process Cleanroom.- The Lab-Line Ultra-Clean Oven has an operating range from slightly aboveambient to +250°C.
It is designed with an air circulation system that forcesheated air up the chamber walls and draws that air toward the center forrecirculation and reheating to ensure uniformity.- Use the sign-up sheet Velcro-ed on the front of the oven. List the date, yourname, photoresist used, and time needed.- The temperature is set by using the thumb wheels (#5 in Fig. 7) located at thebottom of the oven. (See below for details)- Different programming cycles can also be set on the Lab-Line Oven. Forexample: (Note: To activate timing functions, turn the Time Mode switch ON)21Basic Photoresist Processing Techniqueso Auto/Manual Timing Switch (Switch #9 below)-For Auto Start, the timingcycle will begin only when the oven temperature exactly matches thetemperature set point.
If the oven temperature changes after timingbegins (i.e. if the door is opened), the timer will continue to time to the endof the cycle without interruption. For Manual Start, the timing cycle willbegin the instant the Time Mode Switch is turned on (#6 in Fig. 7). AGreen LED will light next to your selection.o Control/Stop Heating (Switch #10)- This switch allows you to specify thefunction to be performed AFTER the timing cycle has been completed.For Control Heating, the oven will continue to maintain the temperatureafter the timing cycle is completed.
The timer alarm is activated and thetime readout will hold its current value. This selection is preferred forapplications where several timed batches will be put in one after another.For Stop Heating, the oven will stop heating and start to cool down afterthe timing cycle is completed. Power to the heaters is cut off at the end ofthe timing cycle. The blower continues circulating air, however, until thepower switch is turned off. Choose this selection for applications where along, gradual cool-down is required.o Count Up/Count Down (Switch #11)- For Count Up, the timer will start at00.0 and count up to the set point.
A time reading during the timing cyclewill show time elapsed. For Count Down, the timer will start from the setpoint and count down to 00.0. A time reading during the timing will showTime Remaining. When the timing cycle is completed, the timer stops andthe slowly beeping, medium-pitched alarm sounds (if the Timer Alarmswitch is on).o Hours/Minutes (Switch #12)-Hopefully, this switch is self-explanatory.22Basic Photoresist Processing TechniquesFigure 12: Schematic of Ultra 100 Oven's Control Panel- Since the Lab-Line oven is designed with an air circulation system, cleanlinessplays a factor in the ultimate outcome of your prepared wafer surface. Anyphotoresist particles that are present in the oven may be deposited onto theresist surface as it bakes.
To ensure cleanliness during your baking cycle, use acan of compressed air to blow out the oven before inserting your wafers.- In addition, be sure that the quartz wafer boat you are using is clean. Use thehigh pressure nitrogen gun to blow off any resist particles. Some quartz waferboats are used for mask fabrication, where an edge-bead removal process is notused, and the grooves within the boat will gradually accumulate PR. Therefore,each time a wafer is placed within the groove, particles are formed.23Basic Photoresist Processing Techniques3.4 Solitec 5110-CT Resist Spinner:Figure 13: Solitec Resist Spinner- The Solitec Resist Spinner is the most popular spinner used in the CNTechcleanroom.
It has a spin speed range from 50-10,000 RPM and will hold up to a9” diameter wafer. Different process sequences can be pre-programmed toallow different acceleration, spread speed, and spin speed cycles.- Several different vacuum and non-vacuum wafer chucks are available for useand reside in the plastic bin above the spinner. For membrane and maskchucks, see Janice Eddington or Quinn Leonard for more information.- Use the wafer centering handler to center your wafer. Do not try to center thewafer yourself or you will sacrifice the uniformity of your resist.- Make sure you have turned on the vacuum and nitrogen supplies, located on thelower front panel of the spinner, before you begin.
Failure to do this will result inan error message from the spinner (MOTOR PURGE button will light).- Replace the aluminum foil on the shield and drain pan once you are done. Thisprevents resist contamination for the next user, due to evaporating solvents, andalso contributes to general cleanliness of the spinner.- For complete operating procedures, see Part 4: Coating Samples.24Basic Photoresist Processing TechniquesPart 5: Exposure ToolsGeneral Comments:Listed below is a brief overview of the different exposure stations available at CNTech.Contact the staff member listed for further information as well as instrument training.5.1 E-beam:JEOL JBX-5D2-U E-beam Lithography SystemContact: Scott Dhuey (dhuey@nanotech.wisc.edu)The electron beam microfabricator provides an exposure method for various researchinitiatives at the Center for NanoTechnology. It allows direct write of patterns in photoresiston silicon wafers for the purposes of testing resist sensitivity and characteristics or patterngeneration for other purposes.
It also provides a medium for patterning of optical and X-raymasks. In addition to providing unaffiliated users with access to an advanced lithographytool, the e-beam provides students with experience in advanced lithography tools.Specifications:- 50KeV Electron Beam- LaB 6 Current Source- 2 MHz Pattern Generator- Variable field size25Basic Photoresist Processing Techniques--Low and high resolution modes10mm working distance for high resolution modeNo height mapCurrent Range - 10pA to 10 mABeam size ~ 10 nm for small current125 mm (~5”) stage travel with 1/120 interferometerBest resolution: 50 nm nested lines in 200 nm resist (Hank Smith et al.) 70 nm nested lines in 150 nm resist (JPL) 75 nm nested lines in 350 nm UV3Down to 30 nm in 150 nm resist-problems with repeatabilityPattern code fully accessible-custom modificationSubstrates:- 3-5” Si wafers- SiNH membranes- 4-5” Quartz masksField Sizes:- Low Resolution Mode 100 mm working distance: 800 microns- High Resolution Mode 10 mm working distance: 80 microns and smallerResist Dose Requirements:UV series ~30 mC/cm2Apex E ~12 mC/cm2Sal-605 ~12 mC/cm2PMMA ~600 mC/cm2-26Basic Photoresist Processing Techniques5.2 ES-1 Beamline:ES-1 General Purpose BeamlineContact: Quinn Leonard (quinn@nanotech.wisc.edu)-Length: 9.6 mAcceptance: 9.2 mradConfiguration: (2) 13 µm Be; 64 cm HeScanning: NoFlux Constant (800 MeV) Calculated: 0.55 mW/cm mA27Basic Photoresist Processing TechniquesMeasured: 0.55 mW/cm mA-E peak:- 800 MeV: 1523 eV 1 GeV: 1727 eVImage Dimensions: Horizontal: 50 mm Vertical (FWHM): 5 mm5.3 ES-5 Beamline:Suss XRS200/2M (Black Stepper)Contact: Quinn Leonard (quinn@nanotech.wisc.edu)The 2M is the Center's workhorse and is used for photoresist characterization, deviceprototyping and general lithography studies.
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