Melinda Chen
Update 0
Accomplishments
Read through sputtering documentation and project primers
Read through required textbook chapters and 'Filling in the Gaps' resources
Met with project partner Katie to go through project goals and potential avenues forward
Walked through state of current sputter chamber with team leads
Roadblocks
No major blocks so far
Plans
Literature review of current characterization techniques
Meet with Katie to draft project proposal and timeline
Update 1 (1/19-1/26)
Accomplishments
Drafted project proposal and timeline
Researched thin film characterization techniques
Submitted requests for training on XRR (with Professor Sokalski) and AFM
Compiled existing sputtering chamber setups from online sources into spreadsheet
Performed sputtering trials using Aluminum target + practiced tuning pressure using Argon flow rate and vacuum strength to maintain stable plasma
Roadblocks
Priority is figuring out why the sputtering current is so low + how to tune sputtering parameters to improve power
Plans
Get trained on XRR next Thursday
Continue literature review
Sputtering trials with Aluminum target --> Try sparking using high flow rate to create dense plasma then lowering pressure to increase amount of sputtered particles that reach the substrate
Responses
From Jay
For the progress update, be sure to link to the document(s) that show evidence of your progress. this week that would be a link to you project proposal
For roadblocks, this is an opportunity to request help, or clarify what you need from us to keep moving forward. I would argue training on certain equipment to be roadblock for you.
For plans, there should be more detail in how you're going to proceed, or link to your working doc that demonstrates your plans in more detail. For example, link what literature you plan to read first, this helps me guide your research. What do you want to learn form theses trials? why is it useful in working towards the end goal. For example you could discuss the methodology for DC al sputtering and how that informs the development of reactive DC AL2O3 sputtering. Being specific helps me evaluate if your plans for the week will actually end up being productive. Based on Fridays session, ik that you have more specific well justified plans, so be sure to articulate them here, or better yet, direct me to a document that articulates your plans.
Update 2 (1/20-2/2)
Accomplishments
Met with Professor Sokalski to discuss XRR
Assisted chamber modifications for RF sputtering
RF Sputtering trial with Aluminum target
learned how to use RF sputtering equipment and fundamentals behind impedance matching
Chamber bias literature review
Completed AFM online training and reached out to MCF contact for in-person training
Roadblocks
Main roadblock is still sputtering chamber not working - will continue to look into specific reasons why target seems completely unscathed after a few hours of being near plasma
Some of the RF sputtering electronics are cooked
Plans
AFM in-person training
Continue sputtering chamber debugging - both literature review and in-person tests
Ideally also XRR in-person training, depends on how fast MCF contact responds.
Responses
make sure to link working notes, and updated project tracker
Good job finalizing choice of XRR for characterization
Update 3 (2/2-2/9)
Accomplishments
Completed XRR training with Besty
Completed AFM training
Contacted Andrew to ask about correct AFM tips
Helped perform sputtering tests on Thursday and Saturday to try to debug chamber
Roadblocks
Sputtering chamber still not working - blocking capacitor seems like promising solution
Plans
Perform sputtering test with Aluminum Oxide/Insulating material to test blocking capacitor theory
Perform XRR on sample similar to expected sputtering chamber output
Start writing SOPs + Drawing out schematic of characterization pipeline
Responses
From Jay
Good job completing both AFM and XRR training, good job helping with sputter chamber debugging.
As discussed in person, RF sputtering test wont be fruitful until we implement a blocking capacitor. So I would prioritize XRR practice on oxide and evaporated Al samples.
DC Al sputter tests may still be interesting this week.
Please make sure to links to working docs, and an updated github project tracker.
Update 4 (2/9-2/16)
Accomplishments
Created Aluminum thin layer samples using the thermal evaporation chamber
Attempted XRR on samples
Seemed to be unsuccessful - potentially issues with surface roughness, or sample size.
Helped perform sputtering tests on Thursday with the blocking capacitor to try to debug chamber
Placed order for AFM tips - turns out Joel has some
Roadblocks
Sputtering chamber still not working : (
Plans
Perform XRR on thermally grown oxide -> hopefully better surface roughness and larger sample size will result in visible results
Track down AFM tips and try to perform AFM on thermally evaporated Al samples to get rough idea of surface roughness
Continue literature review/researching potential causes for sputtering chamber not working.
Responses - Jay
Given the chamber roadblocks, I think continuing to workout XRR with thermal oxide and sanity checking the evaporated Al samples with AFM techniques makes sense.
Rahim and I are working on upping the Vp-p of th rf supply in hopes that low Vp-p has been the issue. If this doesnt work, we will start doing reactive DC with V1 chamber.
Update 5 (2/16-2/23)
Accomplishments
Performed XRR on thermally grown oxide (see image below)
Scan provided reasonable outputs with visible peaks
Peaks were shallower than typical XRR data --> not crippling issue for thickness characterization but good thing to look into to see if we can improve the test setup
Cleaved thermally evaporated sample from a few weeks back and mounted in epoxy + polished for SEM and EDS
Goal was to identify if SEM was a viable alternative for characterizing thicknesses that are slightly too high for XRR
Was able to identify aluminum layer with EDS but extremely difficult to focus image
Also very difficult to capture images due to extremely high amount of drift at the level of magnification
Ultimately, characterizing thicknesses less than a micron without serious drift using the undergrad lab SEM will be difficult, thicknesses above 5 microns should be reasonable though
Roadblocks
Sputtering chamber still not working : (
Plans
Continue literature review/researching potential causes for sputtering chamber not working.
Performing AFM on thermally grown oxide to see if surface roughness is a contributing factor to shallow XRR peaks
More detailed plan for CV testing now that both Katie and I have done the probing lab
Response - Jay
lmk if u need help with the DC cheater plug issue.
Rahim and I have been working to setup an old donated sputtering RF power supply. We tried to use it in the past but the associated matching network was broken, so it couldn't strike any plasma. Now we are retrying it, buy using our 300W antenna tuner as the matching network. This should be ready sometime his week, ideally tn (Tuesday). The idea is that this power supply will have much higher Vp-p. This will help us determine if the chamber is the problem or the the low Vp-p on our radio power supply is the problem. Regardless, this may let you start doing RF process dev soon.
SEM image is very intersting. unfortunate that the feaure sizes we care about are a bit outside teh benchtop SEM resolution. However, based on your results. The benchtop SEM may be useful for some of Marta's work, ty!
Update 6 (2/23-3/1)
Accomplishments
Remade cheater plug + Re-attempted DC sputtering trials
Was able to get the power to 10W using high pressure (100 sccm, ~200 mtorr) but still no sputtering observed
Changing the chamber configuration (i.e. number of teflon layers + adding in a smaller radius teflon spacer next to the target to prevent shorting) drastically changed quality of plasma confinement
RF sputtering trial with power supply from the MCF
Power supply was able to provide reasonable forward voltage (although impedance matching was a bit difficult), however no sputtering was observed
Plasma confinement was poor in this trial as well, with the plasma mostly consolidated near the edge of the target.
Literature Review for CV testing/electrical properties
Found a couple of papers on CV testing setups for semiconductor oxides (linked in literature review spreadsheet)
Notably, Sarah Brown's Cornell thesis has some good background information on electrical properties as well as a very interesting setup they used for probing capacitance across a sample:
Currently reading up on Mott-Schottky analysis theory to better understand if/how we can pull oxide properties out of it
Performed AFM on thermally grown oxide with the goal of getting surface roughness and correlating that information to XRR results from last week
AFM is hard to do
Ended up getting an image but lots of artifacts - ran out of time so will have to go back and tune gains + amplitude setpoint to get a cleaner image
Roadblocks
Sputtering chamber still not working : (
Plans
RF sputtering trial using MCF's matching network
Should be able to read out DC bias with it attached which will at least give us some info on if the DC bias buildup is the issue
Basically:
Good DC Bias readout + sputtering --> Our RF power setup has an issue
Good DC Bias readout + no sputtering --> Our sputtering geometry has an issue (MFP potentially too low)
No DC Bias readout --> (cry?) and check grounding/connectivity
Re-do AFM, focusing on tuning gains to get clearer image
Reach out to Matt to ask for samples of different reference thicknesses to run XRR on + practice analysis
Continue CV testing literature review, come up with plan to fabricate electrode array
Update 7 (3/9-3/16)
Accomplishments
Attempted to set up RF power supply and matching network provided by MCF to run sputtering trials
power --> RFX-600 --> ATX-600 --> matching network (large yellow box) --> output (verified by Matt)
RFX-600 turns on, but ATX-600 does not turn on
Substituting in a different ATX unit did not appear to change anything
Joined Chamber Build for a day to make parts for Sputter V2, worked on drill-pressing holes in a steel plate and sacriligeously cutting through a heat sink
Roadblocks
Sputtering chamber still not working : (
Waiting on AFM tips (have been ordered) since the last batch was apparently all broken
X-ray lab closed between March 17 - March 21
Plans
Since XRR development and sputtering trials are both gated next week, main focus will be on getting practice with CV testing pipeline
Fabricate chip using thermally grown oxide w/MOScap fabublox procedure
Ideally also run gauntlet of tests on chip if no roadblocks in fabrication
Arrange meeting with Katie + mentors/instructors to discuss project direction since most process development tasks (figuring out sputtering chamber parameters, times, pressures etc... ) are gated by chamber development
Continue to help out with available chamber build + power supply tasks
Response - Jay
Recap of meeting 3/17
Next steps are to assess the viability of reactive Al evaporations, and/or cycles of Al evaporation followed by oxidation.
Overall good job helping out with setting up rf supply and moving chamber build forward
Update 8 (3/9-3/16)
Accomplishments
Set up temporary goals w/Jay and Katie given that sputtering chamber is in an uncertain state
Looking into reactive aluminum evaporation/alternative ways to make an aluminum oxide layer that don't involve
Justification: Will allow us to proceed w/ironing out characterization methods and help set the groundwork for DC reactive sputtering by figuring out reasonable pressures/times
Literature review of both reactive evaporative aluminum and plasma oxidation techniques
Main takeaways from literature review:
Potential options:
Plasma oxidation: Was difficult to find data on low-temperature oxidation of Aluminum. Out of the two closest papers, one opted to do "atmosphere-pressure plasma oxidation" with heating, while the other was performed in a Dielectric-Barrier-Discharge reactor. Seems like temperature is a much more important factor than pressure, anything below 550K (some sources say 550C, will need to hand-calc check which one it is) will max out at 1-2nm oxides.
Two mechanisms of oxidation: Cabrera-Mott (initial oxidation) --> Wagner (only relevant for high temp, slow growth after initial oxidation)
Potential strategy I think might work not mentioned in papers: Cycles of evaporation + oxygen flowing in
Since the worry with flowing O2 into the evaporator is that the temp required to evaporate Al at higher pressures is not reachable, we can maybe cycle Al evaporation --> O2 flow (still at elevated temp?) --> pump back down to low pressure --> Al evaporation
Attempted to figure out how low the vacuum can pump w/oxygen flowing in
MFC seems to be broken unfortunately
Roadblocks
Sputtering chamber still not working : (
Waiting on AFM tips (have been ordered) since the last batch was apparently all broken
X-ray lab closed between March 17 - March 21
MFC potentially broken
Plans
Evaporate Al chip on Polysilicon, run through the plasma etcher at highest possible O2 pressure (based on literature, 0.5 torr should be enough to see something)
Not a lot of hope for this if the temperature is not sufficiently high
If MFC gets fixed, try the Al evaporation --> O2 flow cycle mentioned above
Continue lit review on reactive Al
Also contact Jason to talk about potentially just annealing in tube furnace
Continue to help out with available chamber build + power supply tasks
Update 9 (3/23-3/30)
Accomplishments
Completed preliminary aluminum evaporation trials w/oxygen flowing in
Have well-fitted relationship between oxygen MFC SCCM settings and chamber pressure
Conducted 3 aluminum evaporation trials:
Initial trial w/oxygen showed promising results due to visibily different color of evaporated material.
Additional trials to figure out the maximum O2 pressure possible while still being able to evaporate were difficult due to QCM readings
However based on what pressure the QCM stopped behaving weirdly (i.e. extreme amounts of oscillation) for, around 7.5 sccm might be the limit
Resistivity is slightly higher than base aluminum, but not "insulating"
Sample preparation for "oxide" capacitor
Evaporated base layer, will do the oxide and top surface on Monday
Reserved XRR for next tuesday for evaporated "oxide" density characterization
Roadblocks
Sputtering chamber still not working : (
QCM unreliability w/reactive evaporation --> will need to find other ways of characterizing rate
Plans
Create a capacitor to test electrical properties + pure oxide evaporated for density characterization via XRR
Base layer of aluminum is already evaporated
Monday procedure:
Mask off half the chip w/nonstick size of tape
1 evaporation cycle with oxygen (for both chips)
Remove the XRR chip
1 evaporation cycle with normal aluminum
Test the capacitor
XRR to probe density of evaporated chip
Evaporation + low temperatre annealing trial for densification of the oxide layer
Continue to help out with available chamber build + power supply tasks
Update 10 (3/30 - 4/6)
Accomplishments
Completed fabricating capacitor test sample using reactive aluminum evaporation strategy. Process is as follows:
Deposited aluminum pads on 2 samples, masked off half the samples with polyamide tape
deposited (potential) oxide on both samples as well as extra sample for XRR thickness characterization
removed XRR sample
deposited top aluminum electrode on the un-masked portion
Performed XRR on evaporated sample, "oxide" was 16 nm thick and had noticeable density shift compared to the thermally grown silicon oxide sample
Roadblocks
NOT THE SPUTTERING CHAMBER WOOHOO
QCM unreliability with unknown material
Plans
Full send on sputtering trials now that the chamber is working
Thickness characterization
Power characterization
XRR + AFM
Capacitor using evaporation chamber masking technique
Update 11 (4/6 - 4/13)
Accomplishments
Attempted AFM on masked Al-evaporated chips to determine layer depth
Was able to image the transition from silicon subtrate to Al layer but still had imaging artifacts/streaking
Imaging only the Al portion for surface roughness yielded heavily aliased results - potentially small pinholes (smaller than AFM tip)
Compiled slides for second presentation/demo
Conducted first sputtering trial with new chamber, used temperature tracking stickers to determine if magnets are getting too hot
Sputtered aluminum at 100W
magnetic field clearly less strong compared to previous trials
Lots of small "sparks" on the substrate plate during the trial
All four temperature stickers changed color --> sputtering process is cycling the magnets above recommended temperature
Created 3D printed magnet aligning rig
Attempted to change the configuration of magnets in the sputtering chamber to be on the outside to allow for more effective cooling
Ran into a lot of issues w/fitting things under the aluminum casing and getting the magnets to stay still
Roadblocks
Magnets weakening with sputtering temperature --> parameters will likely change over time
Plans
Perform XRR on aluminum oxide chip that Jay sputtered
Run tests at lower powers w/temperature tracking stickers on both the outside and inside of chamber to see:
If it is possible to stay below temperature with lower power
If there is a significant temperature difference between the plate inside and outside the chamber --> if not, might be worth looking into cooling the plate, not just moving the magnets outside
Full send on sputtering trials now that the chamber is working
Thickness characterization
Power characterization
XRR + AFM
Capacitor using evaporation chamber masking technique
Response
Thank you for bearing with me and helping out on the sputter magnetron changes.
I endorse the plans to perform do rate testing on Al and Al2O3 using XRR for thickness measurement.
After rate tests are finished, lets discuss prioritizinng surface roughness vs composition characterization. I'm leaning towards composition, since that may inform design changes related to the steel retaining ring.
and Just for record: at the time of this response, weve returned to the original magnetron design sine we confirmed that magnet temp is at least below 180C.
Finally, I copy and pasted update 9 into this merge bc it was having conflicts. So I'm just gonna deny the march 30th PR.
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