A week in the life of an MBE operator: A case study: Analysis

Faebian Bastiman

Keeping a journal of your weeks activities may seem like an monumental effort, but personal i found the experience very insightful. It enabled me to realise where I have been spending my time, wasting my time and what needs more attention. Let’s summarise the individual days: Monday, Tuesday, Wednesday, Thursday, Friday.

Firstly working in a clean room is thirsty work; it is in fact similar to spending that day on an airplane. You can expect your body to require an extra litre of water compared to office work. Failure to realise this and keep your fluids topped up can lead to dehydration and a string of related problems.

The next thing we notice is that the days comprise routine tasks. Every day is based around:

  1. Drinking water
  2. System checks
  3. Growing sample 1
  4. Growing sample 2
  5. Transferring samples
  6. Loading/unloading samples
  7. Updating paper work
  8. Preparing samples for characterisation
  9. Planning next samples
  10. Analysising and summerising recent samples (includes preparing results for publications)
  11. Software and system development

System checks are essential. The pumps, gauges, vacuum and fluxes should be checked daily. Auto logging and flux collection could be utilised to speed up the whole process. This would be particularly useful for the flux checking, which currently consumes just over an hour in the morning, and would be longer when checking more sources. Automatically running these checks at 0700, and having the system ready at 0850 to start growing the first sample would allow 3 samples a day.

This work was performed on a Oxford (VG) V80 system circa 2003. The sample transfer is manual (sadly) but not too cumbersome. Of course the sister system (the V90) possesses automatic sample transfer, pump down/vent and batching. In this particular case that would save us around an hour a day. This particular project requires constant RHEED analysis and so batching will not free up that much of our time either. In order to really save time on the sample transfer we would need: auto transfer and auto RHEED capture (jpg). In that  way we could run 24/7. The current throughput peaks around 0.25 samples per hour, 2 samples a day. With automation we could get 0.5 samples per hour, 12 samples a day… however, this is an absolute maximum. Honestly after growing 12 samples in one day, one would require the next day to do the analysis.

Note that preparing to present result at a weekly meeting was perhaps the most useful exercise of the week. The detailed analysis enabled new insights (and in fact led to a publication) that would otherwise have been missed. There  is a tendency to analyse productivity on throughput rather than worth. Sitting down and looking at what you have is certainly worth it. The advantage of automation is therefore to free up time for analysis. Note that the analysis was actually performed post work on a Wednesday evening in this particular week. That is a feature that is all too common. Let’s try to get ourselves down to a productive 40 hour week.

10 samples in a 40 hour week from a lone operator is about all you can expect from a manual machine. Having two growers on that manual machine could enable 20 samples in 80 hours, but  then forces the growers to endure the “unsociable” hours of shift work with no compensation. If you would like more than 10 samples a week consider buying an automatic machine. Automation enables working smarter, not harder. A lone grower can easily grow 60 samples in a 40 hour week, feeding multiple projects. Or, alternatively, 5 growers could grow 12 samples a day and share the automatic system for one day a week each. This also enables the grower to do his/her own characterisation and analysis. The “samples” I mention are characterisation test structures and are typically only 1-3 hours each. Should you require 8-12 um thick pins or DBRs you can of course only grow 2 samples a day by MBE. MBE is limited to around 1-2 um/h, and strictly the best quality growth seems to be at 0.57um/h (for some reason).

Typically, a research topic will require anywhere form 5 to 30 samples per publication. That is around 1 to 3 weeks of growth, plus a whole week of analysis. Running an MBE  system at a 2 sample per day pace may seem unproductive at first glance, but if you take the care and effort to ensure every sample contributes to the topic (i.e is logical, systematic and provides a valuable data point) then the result is 12 peer reviewed journal publications a year, which in is in fact very productive indeed.

Updating paperwork is also essential and should be performed meticulously. A growth sheet, run log and maintainence/problem log are mandatory. The growth sheets needs  enough information for any one to be able to repeat the growth recipe with no prior knowledge. The run log is a chronological list of samples grown, with some fundamental growth parameters, characterisation parameters and importantly the final resting place of the wafer (which will hopefully be a wafer drawer close to hand). The maintenace/problem log simply tracks anything and everything out of the ordinary with regard to the system’s operation, it then represents a list of things to repair or improve in the next maintenance and development cycle.

Characterisation and growth are intimate friends. The best growth experiences of my life involve working in a grower-characteriser pair with another researcher. One person grows the samples, one person characterises the samples, the two discuss the results and plan the next samples. One produces growth papers, the other characterisation/device papers. Both share the publications (first author, second author switching) and everybody wins.

Finally we have system development. No system is perfect, not even a brand new system that you personally specified (though admittedly that should be close to perfect). There will always be additions and improvements. Technology is always advancing and that includes all aspects of MBE software and hardware. Perhaps I “shake my fist at the heavens” more than most during my MBE operating day, but noticing the parts to improve and actually spending the time to improve them are essential. The system should be working for us and not the other way around. If your system does not do what you want to, change it. If you do not know how  to, ask. I would be delighted to discuss improvements and implementation thereof with you.

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A week in the life of an MBE operator: A case study: Friday

Faebian Bastiman

Friday

0850: Day starts: Drink 1L of water to hydrate body and counteract dehydration caused by long term exposure to dry, cool air conditioned laboratory.

0855: System checks. Inspected the ion gauge pressures, the status of all pumps and LN2 level. Inserted MIG into beam path in preparation for BEP flux measurements.

0856: Outgas Ga. Executed a program in the Ga cell’s PID controller than ramps up to 975°C in 30 minutes, holds for 30 minutes and then ramps down to 950°C and holds.

0900: As flux check. As shutter and valve were opened. Fluxes were taken at several valve positions consistent with previous days. Fluxes are recorded in the “flux check record” tab of the log spread sheet.

0926: As flux check completed. Gathered flux values were compared with legacy data for continuity checks. As shutter is closed and background As4 is pumped from the system. Vacuum recovery progresses prior to Ga flux check.

0940: Ga flux check. Ga shutter was opened for 60 seconds and the flux was recorded, averaged over 10 seconds. The shutter was then closed, the background flux was sampled, subtracted and the “flux check record” tab of the log spread sheet was updated. Current flux value is compared to legacy data for continuity.

1000: Sample 1: Start. Transferred sample from outgas stage to growth chamber and manually began recipe.

1010: Sample 2 Outgas. Transferred sample 2  from FEL to outgas stage and executed outgas program in PID controller.

1020: Paperwork.

1210: Sample 1: Complete. Transferred sample from growth chamber to FEL.

1215: Lunch and consumption of another litre of water.

1245: Software test. Wrote and executed a test recipe to observe the functionality of the new software. Made notes and suggested improvements/modifications/extensions.

1530: Sample load/unload. The sample in the FEL (grown today) was removed and placed in a labelled box. One new Si(111) substrate was mounted and the FEL pumped down manually and the degas cycle started . The intention to implement “automatic FEL pump down and degas” was reaffirmed whilst shaking a fist at the heavens. Sample was cleaved and passed to a colleague for SEM analysis.

1600: Update log. Sample locations were updated on the “locations” tab of the log spread sheet to reflect new sample locations and status.

1610: Day ends (early Friday finish). Drink another litre of water. Go home.

Total 6.33 hours. Growth: 1 samples. Samples/hour: 0.16

A week in the life of an MBE operator: A case study: Thursday

Faebian Bastiman

Thursday

0850: Day starts: Drink 1L of water to hydrate body and counteract dehydration caused by long term exposure to dry, cool air conditioned laboratory.

0900: Confer with colleague. Discussed recent results with a colleague and outline strategy for samples to grow today.

0915: System checks. Inspected the ion gauge pressures, the status of all pumps and LN2 level. Inserted MIG into beam path in preparation for BEP flux measurements.

0916: Outgas Ga. Executed a program in the Ga cell’s PID controller than ramps up to 975°C in 30 minutes, holds for 30 minutes and then ramps down to 950°C and holds.

0920: As flux check. As shutter and valve were opened. Fluxes were taken at several valve positions consistent with previous days. Fluxes are recorded in the “flux check record” tab of the log spread sheet.

0946: As flux check completed. Gathered flux values were compared with legacy data for continuity checks. As shutter is closed and background As4 is pumped from the system. Vacuum recovery progresses prior to Ga flux check.

1000: Ga flux check. Ga shutter was opened for 60 seconds and the flux was recorded, averaged over 10 seconds. The shutter was then closed, the background flux was sampled, subtracted and the “flux check record” tab of the log spread sheet was updated. Current flux value is compared to legacy data for continuity.

1010: Sample 1: Start. Transferred sample from outgas stage to growth chamber and manually began recipe. Notice that yesterday’s “development” of the control software has resulted in the substrate rotation behaving very strangely! Disabled lift motor just in case. Contacted technician.

1020: Sample 2 Outgas. Transferred sample 2  from FEL to outgas stage and executed outgas program in PID controller.

1030: Paperwork.

1230: Sample 1: Complete. Transferred sample from growth chamber to FEL.

1240: Lunch and consumption of another litre of water.

1245: Technician investigates substrate rotation issue. The technician investigated the virtual interface communication and investigated the rotation issue. The fault was not found. The rotation will be operated manually (with the virtual interface deactiveated).

1515: Sample 2: Start. Transferred sample from outgas stage to growth chamber and manually began recipe.

1600: Platen 5. Received platen 5 back from etching. Loaded a Ta plate in preparation for outgas.

1610: Platen cleaning with P50 dry abrasive sheet. Most of material removed whilst plate was dry. WOrk was performed in a fume cupboard and a face mask was needed as there was much dust. Clean ok.

1655: Sample 2: Complete. Transferred sample from growth chamber to FEL.

1700: Technician investigates substrate rotation issue (2). The technician continued to investigate the substrate rotation issue and rectified the communications problem. The virtual interface can be utilised once more.

1730: Disperse NWs for TEM. As outlined below.

  1. Cleave a small piece of wafer
  2. Place 5ml of IPA in a lidded container
  3. Insert piece of wafer
  4. Scratch the surface with tweezers to snap many NWs
  5. Place small glass bowl in ultra sonic bath
  6. Add small amount of water to the bowl
  7. Carefully place the lidded container in the bowl
  8. Ultra sonic for 5 minutes, then…
  9. Place a TEM grid on a piece of filter paper
  10. Check TEM grid is the correct way up in the microscope
  11. Use a pipette to remove  a small amount of fluid from the lidded container
  12. Carefully wet the TEM grid from the solution in the pipette
  13. Place filter paper and TEM grid on the hot plate
  14. Repeat wetting 5 – 8 times, leaving to try between each step
  15. Remove filter paper and TEM grid from hot plate
  16. Using vacuum tweezers (carefully) place TEM grid on a glass slide
  17. Check NWs are on the TEM grid with optical microscope
  18. Place TEM grid in a small box (blue lid)
  19. Store in desiccator

1830 Sample load/unload. The two samples in the FEL (grown today) were removed and placed in labelled boxes. Two new Si(111) substrates were mounted along with Platen 5 (fitted with a Ta disc) and the FEL pumped down manually and the degas cycle started . The intention to implement “automatic FEL pump down and degas” was reaffirmed whilst shaking a fist at the heavens. Samples were passed to a colleague for SEM analysis.

1900: Update log. Sample locations were updated on the “locations” tab of the log spread sheet to reflect new sample locations and status.

1910: Day ends. Drink another litre of water. Go home.

Total 10.33 hours. Growth: 2 samples. Samples/hour: 0.19

A week in the life of an MBE operator: A case study: Wednesday

Faebian Bastiman

Wednesday

0850: Day starts: Drink 1L of water to hydrate body and counteract dehydration caused by long term exposure to dry, cool air conditioned laboratory.

0855: System checks. Inspected the ion gauge pressures, the status of all pumps and LN2 level. Inserted MIG into beam path in preparation for BEP flux measurements.

0856: Outgas Ga. Executed a program in the Ga cell’s PID controller than ramps up to 975°C in 30 minutes, holds for 30 minutes and then ramps down to 950°C and holds.

0900: As flux check. As shutter and valve were opened. Fluxes were taken at several valve positions consistent with previous days. Fluxes are recorded in the “flux check record” tab of the log spread sheet.

0915: As flux check completed. Gathered flux values were compared with legacy data for continuity checks. As shutter is closed and background As4 is pumped from the system. Vacuum recovery progresses prior to Ga flux check.

0920: Ga flux check. Ga shutter was opened for 60 seconds and the flux was recorded, averaged over 10 seconds. The shutter was then closed, the background flux was sampled, subtracted and the “flux check record” tab of the log spread sheet was updated. Current flux value is compared to legacy data for continuity.

0930: Colleague absent. In the absence of a colleague to discuss the strategy, the next sample was planned based my analysis of previous samples.

1000: Sample 1: Start. Transferred sample from outgas stage to growth chamber and manually began recipe.

1010: Sample 2 Outgas.

1020: Paperwork.

1155: Sample 1: Complete.

1200: Lunch and consumption of another litre of water.

1230: Sample 2: Start. Transferred sample from outgas stage to growth chamber and manually began recipe.

1420: Sample 2: Complete

1430: Sample 3: Considered. Theoretically a third sample could now be grown, however that would consume the same intended to grow first tomorrow. Incurring a 2 hour penalty and making it difficult to grow 2 samples tomorrow at the established 0.25 sample/hour rate. In order to avoid this problem another sample holder (platen) is required, making a total of 4. Two spare platens have been abrasively cleaned and are waiting etching, rinsing, baking and outgassing. The current platen 1 needs removing and cleaning as RHEED access is currently restricted.

1431: Paperwork

1500: Sample load/unload. The two samples in the FEL (grown today) were removed and placed in labelled boxes. Two new Si(111) substrates were mounted and the FEL pumped down manually and the degas cycle started . The intention to implement “automatic FEL pump down and degas” was reaffirmed whilst shaking a fist at the heavens. Samples were passed to a colleague for SEM analysis.

1525: Update log. Sample locations were updated on the “locations” tab of the log spread sheet to reflect new sample locations and status.

1530: Paperwork

1700: Day (almost) ends. Drink another litre of water. Go home.

1930: Analysis and presentation. Started preparing power point presentation slides for tomorrow’s weekly meeting. Analysis and comparison of results was very valuable. I noticed a new trend I had not seen before.

2130: Day (really) ends. Analysis and Presentation complete.

Total 10 hours. Growth: 2 samples. Samples/hour: 0.2.

A week in the life of an MBE operator: A case study: Tuesday

Faebian Bastiman

Tuesday

0850: Day starts: Drank 1L of water to hydrate body and counteract dehydration caused by long term exposure to dry, cool air conditioned laboratory.

0855: System checks. Inspected the ion gauge pressures, the status of all pumps and LN2 level. Inserted MIG into beam path in preparation for BEP flux measurements.

0856: Outgas Ga. Executed a program in the Ga cell’s PID controller than ramps up to 975°C in 30 minutes, holds for 30 minutes and then ramps down to 950°C and holds.

0900: Sample load/unload. The two samples in the FEL (grown yesterday) were removed and placed in labelled boxes. Two new Si(111) substrates were mounted and the FEL pumped down manually and the degas cycle started . The intention to implement “automatic FEL pump down and degas” was reaffirmed whilst shaking a fist at the heavens. Samples were passed to a colleague for SEM analysis.

0920: Update log. Sample locations were updated on the “locations” tab of the log spread sheet to reflect new sample locations and status.

0930: As flux check. As shutter and valve were opened. Fluxes were taken at several valve positions consistent with previous days. Fluxes were recorded in the “flux check record” tab of the log spread sheet.

0945: As flux check completed. Gathered flux values were compared with legacy data for continuity checks. As shutter was closed and background As4 was pumped from the system. Vacuum recovery progressed prior to Ga flux check.

0950: Ga flux check. Ga shutter was opened for 60 seconds and the flux was recorded, averaged over 10 seconds. The shutter was then closed, the background flux was sampled, subtracted and the “flux check record” tab of the log spread sheet was updated. Current flux value was compared to legacy data for continuity.

1000: Sample 1: Start. Transferred sample from outgas stage to growth chamber and manually began recipe. Sample growth sheet was created.

1020: Confer with colleague. Discussed recent results with a colleague and outline strategy for samples to grow today.

1030: Paperwork.

1110: Platen cleaning P50 dry abrasive sheet.  Cleaned worked ok but glue was water soluble and grit came away from cloth. Will need to order wet and dry P60 ASAP.

1145: Sample 2 Outgas. Transferred sample2  from FEL to outgas stage and executed outgas program in PID controller.

 

1200: Sample 1: Complete. Transferred sample from growth chamber to FEL. Transferred sample 2 from outgas stage to growth chamber. Transferred new sample from FEL to outgas stage and executed outgas program in PID controller.

1230: Sample 2: Start. Manually began sample 2 recipe. Initial step is oxide conditioning, which takes 45 minutes including the temperature ramp from 100°C to 700°C. Sample growth sheet was created.

1240: Lunch and consumption of another litre of water.

1350: Paperwork

1530 Sample 2: End. After cooling, sample 2 was transferred from the growth chamber to the FEL.

1600 Sample load/unload. Both sample 1 and sample 2 were removed and placed in labelled boxes. Two new Si(111) substrates were mounted and the FEL pumped down manually and the degas cycle started . The intention to implement “automatic FEL pump down and degas” was reaffirmed whilst shaking a fist at the heavens. Samples were passed to a colleague for SEM analysis.

1615: Paperwork. Growth sheets were double checked. Run log was updated. All files were backed up to online server. Paper lab book was updated.

1700: Day ends. Drink another litre of water. Go home.

Total 8 hours. Growth: 2 samples. Samples/hour: 0.25.

A week in the life of an MBE operator: A case study: Monday

Faebian Bastiman

Monday

0740: Day starts: Drank 1L of water to hydrate body and counteract dehydration caused by long term exposure to dry, cool air conditioned laboratory.

0745: System checks. Inspected the ion gauge pressures, the status of all pumps and LN2 level. Inserted MIG into beam path in preparation for BEP flux measurements.

0746: Outgas Ga. Executed a program in the Ga cell’s PID controller than ramps up to 975°C in 30 minutes, holds for 30 minutes and then ramps down to 950°C and holds. NB: The growth schedule for this week is more GaAs NW samples grown on Si(111) wafers. Only a single Ga cell is needed for this purpose.

0748: Preparation chamber LN2. Opened the preparation chamber’s LN2 solenoid and cooled the TSP pumps housing in preparation for the sample outgas. The manual fill was observed with a critical eye. The intention to implement “automatic LN2 fill of preparation chamber” was reaffirmed whilst shaking a fist at the heavens.

0750: Outgas sample. One of the two samples loaded last Friday evening was moved to the outgas stage in the preparation chamber. The outgas program was executed in PID controller: Ramp from 50°C to 400°C in 24 minutes, hold for 1 hour, ramp down to 100°C and hold.

0800: Update log. Sample locations were updated on the “locations” tab of the log spread sheet to reflect the new sample locations and status.

0810: As flux check. As shutter and valve were opened. Fluxes were taken at several valve positions consistent with previous days. Fluxes are recorded in the “flux check record” tab of the log spread sheet.

0850: As flux check completed. Gathered flux values were compared with legacy data from the log spread sheet for continuity checks. 40 minutes of the day were consumed simply checking the As flux, plus another few minutes spent daydreaming about an automatic flux checking software extension. The intention to implement “automatic flux checking” was reaffirmed whilst shaking fist at the heavens. As shutter is closed and background As4 is pumped from the system. Vacuum recovery progresses prior to Ga flux check.

0900: Ga flux check. Ga shutter was opened for 60 seconds and the flux was recorded, averaged over 10 seconds. The shutter was then closed, the background flux was sampled, subtracted and the “flux check record” tab of the log spread sheet was updated. Current flux value is compared to legacy data for continuity.

0910: RHEED. Retracted MIG. Turn RHEED gun on and set to standby value in preparation for growth. Inspected outgas program for sample 1: 45 minutes remain. Top up preparation chamber’s LN2.

0930: Confer with colleague. Discussed recent results with a colleague and outline strategy for samples to grow today.

0940: Paperwork.

1010: Sample 1: Start. Transferred sample from outgas stage to growth chamber and manually began recipe. Lament the current lack of recipe execution software. Attempt to transfer the second sample to the outgas stage failed due to misalignment of cassette inside FEL. Shake fist. Seal FEL, vent, dismount cassette. Used the opportunity to load a new sample and dismount the Ta outgas plate. Reload cassette and double check alignment. Pump down and degas FEL. Cost of misalignment: 4 hours. However loading the second sample means a total of 3 samples can be grown today if I work 12 hours…

1215: Sample 1: End. Sample 1 complete. Left sample to cool to 100°C in preparation for transfer.

1220: Lunch time… and consumption of another litre of water.

1245: Paperwork

1315: Sample load/unload. Removed sample  1 from the growth chamber and place it in FEL. First sample from FEL was placed it in outgas stage. Second sample from FEL was placed in the storage cassette. Vented FEL, removed sample 1 and reloaded platen with new wafer. Pump down FEL and begin degas. Gave sample 1 to colleague for SEM analysis.

1330: Paperwork.

1500: Sample 2 start. With sample 2 (finally) outgassed, it was transferred to the growth chamber and the recipe started. Sample 3 was then transferred to the outgas stage and the standard outgas recipe was executed.

1515: Platen cleaning with wet and dry abrasive sheet. Abrasive sheet was too fine, retry tomorrow.

1700: Sample reshuffle. With the outgas of sample 3 complete, it was moved to the storage cassette. The newly degassed sample was moved from the FEL to the outgas stage in preparation for an outgas at the end of the day, and hence growth tomorrow.

1720: Sample 2 end. Sample 2 was left to cool for 30 minutes and was then transported into the FEL pending removal tomorrow morning. Sample 3 was transferred to the growth chamber. The outgas was performed on the new sample for tomorrow.

1750: Sample 3 start. The growth of sample 3 was started.

1800: Paperwork. Growth sheets were double checked. Run log was updated. All files were backed up to online server. Paper lab book was updated.

1930: Sample 3 end. After growth, sample 3 was transferred to the FEL pending removal (along with sample 2) tomorrow.

1940: Day ends. Drink another litre of water. Go home.

Total 12 hours. Growth: 3 samples. Samples/hour: 0.25.