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aix200

Aixtron MOCVD for III-V and dilute nitride semiconductors: InAs, GaAs, AlAs, InP, GaP, AlP, InGaAs, AlGaAs, InGaP, InGaAsN, InPN, et al.

 

SNF MOCVD lab capability introduction

 

Aix200 is a horizontal metal organic chemical vapor deposition (MOCVD) system from Aixtron. It is a III-V-N system with the model of Aixtron 200/4. It is categorized as contaminated tool in general but divided into a "non-gold period" for the first couple of months after each reactor cleaning, and a "gold contaminated period" for extended experiments requirement in the next couple of months. The system can accommodate pieces, one 2-inch wafer, or one 4-inch wafer.

 

Picture and Location

 aix200

Shown above is the aix200 system. It is located in Allen Extension building 213XA.

 

Background

Metal Organic Chemical Vapor Deposition (MOCVD), or Metal Organic Vapor Phase Epitaxy (MOVPE), or Organo Metallic Vapor Phase Epitaxy (OMVPE), these are three expressions used interchangeably in the field for the same material growth technique. MOCVD is a flexible growth technique. It can accommodate both high crystal quality and high growth rate (up to more than 2um/h).

MOCVD utilizes metal organics and hydrides as precursors. The precursors are pyrolyzed in gas phase near the substrate, releasing alkyl radicals and hydrogen. The radicals are then adsorbed to substrate surface where the interface reaction occurred by which target materials are formed and deposited on the substrate while the alkyls are pumped out in gas. Below is a schematic example of how GaAs is grown. Note that we use tertiarybutylarsine (TBAs) instead of AsH3, and tertiarybutylphosphine (TBP) instead of PH3 for lower toxity and higher decomposition efficiency in this system (diagram from Applied Surface Science 159–160 (2000) 318–327).

 

GaAs growth

Process Capabilities

Cleanliness Standard

MOCVD is classified as Gold contamination level in general sense, however, it also has its own classification. Aix200 is kept as “clean MOCVD” in the first 1-2 months after each chamber cleaning, and then changed to “gold contaminated MOCVD” in the last couple of months before the next chamber cleaning. The reactor is cleaned every 4 months.

 

The aix200 processes take place with a chamber temperature up to 800C. To prevent contamination and ensure safety, the following materials are not allowed:

  1. Polymers
  2. Wet samples
  3. Any foreign material with low melting point (below or close to process temperature), or high vapor pressure 
  4. Plastic, including Teflon
  5. No particles except for a few used as catalysts in “gold contaminated” period 
  6. Samples small enough (<=5mm) to fall into the exhaust line 
  7. No metals except for some with low vapor pressure in “gold contaminated” period

 

Performance of the Tool

What the Tool CAN do

  1. Deposit III-V films (single crystal, polycrystal and quasi-amorphous), heterostructures, and nanowires
  2. Dilute nitride of III-V materials
  3. P-type and n-type doping
  4. Tightly controlled thickness from sub-nm to several micron
  5.  

The System

MOCVD is mainly composed of five parts: In the direction of gas flow, gases go through a gas blending unit, and then go in to reactor where precursors react on the heated susceptor. The unreacted gases and the by-products are then pumped out of the reactor by a pump (vacuum system), and the exhaust goes to a scrubber for abatement of toxic gases. All the four parts are controlled by an electrical control unit. The relationship is shown below (diagram courtesy of Aixtron):

     

    MOCVD structure

     

The reactor door is kept in a nitrogen glovebox to isolate the reaction chamber from the working area. Not shown here is a cooling system hooked up to the reactor and the glovebox. Aix200 utilizes a horizontal reactor with a quartz liner, a graphite susceptor, and a graphite disk. Depending on the disk geometry and with the assist of a dummy wafer, it can accommodate pieces, one 2-inch wafer, one 4-inch wafer, or a quarter 4-inch wafer. Below shows the pictures of the reactor.

     

    liner  susceptor

     

     

Possible Materials 

The table below shows the precursors and resulting compounds in this system. It is also capable of growing ternary and quaternary compounds like AlGaAs and InGaAsP.

      

    Precursors

    TMIn (Trimethyl Indium) TMGa (Trimethyl Gallium)                      TMAl (Trimethyl Aluminum)
    TBAs (Tertiary-Butyl Arsine) InAs GaAs AlAs
    TBP (Tertiary-Butyl Phosphine) InP GaP AlP
    UDMHy (unsymmetrical Dimethyl Hydrazine) Dilute nitride of above compounds
    DMZn (Dimethyl Zinc) P-type doping of all above compounds
    SiH4 (Silane) N-type doping of all above compounds

     

Contact List and How to Become a User

Contact List

The following people make up the Tool Quality Circle:

  • Process Staff: Xiaoqing Xu (steelxu@stanford.edu)
  • Maintenance:Ted Berg (tberg@stanford.edu), Ray Seymour (rseymour@stanford.edu), Jim Haydon (jhaydon@stanford.edu)
  • Super-Users: Antony Jan (antonyj@stanford.edu)

 

Training to Become a Tool User

Becoming an MOCVD user is a three stage process. There are two on-site training sessions with 2 hours each. In the first session, the trainer will go through all the operation procedures while in the second session the users are going to recall and show what have been learned. The recipe compilation and the precursor flow rate calculation will also be covered in the second training. The third session is a qualification session when the users need to run a deposition under the supervision of the trainer. It is recommended to shadow the experienced users on the tool first before taking training.

 

Operating Procedures

Basic Operation Instructions 

Rules:
  1. Qualified users only
  2. New users should be accompanied by an experienced user or the trainer for the first three experiments
  3. Do not leave the lab when running a recipe
  4. No Food, No drink

 

Procedure (See User Manual for details):
  1. Enable in Badger (MOCVD /aix200)
  2. Check the CL4 toxic gas monitor before entering the MOCVD room
  3. Follow the log book to do the pre-growth check
  4. Set the bubbler thermostats to the temperatures for growth
  5. Login to CACE as technician (username: P1, password: P1)
  6. Bake the reactor (recipe: BakeHT ) first if you need to do a delicate experiment
  7. Pump/purge 3 times before opening loadlock, load samples to loadlock and pump/purge 3 times before loading to the glovebox
  8. Check the “Reactor Gate Release” is ready and open the reactor gate carefully
  9. Change the sample disk (if necessary), load the dummy wafer (if necessary), and load sample. Wear clean gloves before touching the reactor inner parts
  10. Close the reactor gate carefully and slowly
  11. Click process pump and pump purge (IGS)
  12. Pump the Double O-Ring below 2 mbar and check the seal
  13. Open/edit your recipe (max power limited to 90%)
  14. Turn on bubbler manual valves and SiH4 valves (if necessary). Fully open and turn ¼ turn back.
  15. Wait until the “Timer N2 Purge Active” finish (turns red) and bubbler temperature stabilized
  16. Start the process, record the run ID and recipe name
  17. Fill out the log book for growth conditions
  18. Watch carefully during the run until the run is finished, click “OK&base”, and click ‘cooling’ to make sure it is in ‘on’ state
  19. Close the bubbler valves and SiH4 (if opened) and lock the cabinet
  20. Turn off the process pump and pump purge (IGS)
  21. Wait until reactor temperature below 65ºC and “Reactor Gate Release” is ready
  22. Open the reactor, take out samples, and close the reactor gate carefully
  23. Unload the sample through loadlock and pump/purge 3 times before opening loadlock. Pump/purge 3 times after unloading
  24. Pump DOR down before you leave and then turn off DOR valve, process pump and pump purge(IGS)
  25. Logout from CACE
  26. Disable from Badger

 

Safety
  • In the case of toxic gas alarm, leave the room immediately (press the emergency STOP if possible). Follow the emergency procedure.
  • Other situations: put system to base state (or press stop process button) and report.

 

Process Monitoring Results & General Data

  1. "Crystallinity, Surface Morphology, and Photoelectrochemical Effects in Conical InP and InN Nanowires Grown on Silicon" by Vijay Parameshwaran: http://pubs.acs.org/doi/abs/10.1021/acsami.6b05749
  2. "Electrochemical Reduction Properties of Extended Space Charge InGaP and GaP Epitaxial Layer" by Vijay Parameshwaran: http://jes.ecsdl.org/content/163/8/H714.short
  3. "Dilute phosphide nitride materials as photocathodes for electrochemical solar energy conversion" by Vijay Parameshwaran: http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1672513
  4. "GaAs buffer layer technique for vertical nanowire growth on Si substrate" by Xiaoqing Xu: http://scitation.aip.org/content/aip/journal/apl/104/8/10.1063/1.4866915
  5. "Engineering a Large Scale Indium Nanodot Array for Refractive Index Sensing" by Xiaoqing Xu: http://pubs.acs.org/doi/abs/10.1021/acsami.6b11413
  6. "Wafer-level MOCVD growth of AlGaN/GaN-on-Si HEMT structures with ultra-high room temperature 2DEG mobility" by Xiaoqing Xu: http://scitation.aip.org/content/aip/journal/adva/6/11/10.1063/1.4967816
  7. "Laser liftoff of gallium arsenide thin films" by Garrett Hayes: https://www.cambridge.org/core/journals/mrs-communications/article/laser-liftoff-of-gallium-arsenide-thin-films/F7084882EE6B1FD4CEBB9CCC0F0CDCA4
  8. "Optical Absorption Enhancement in Freestanding GaAs Thin Film Nanopyramid Arrays" by Dong Liang: http://onlinelibrary.wiley.com/doi/10.1002/aenm.201200022/full
  9. "Rapid Melt Growth of Single Crystal InGaAs on Si Substrates" by Xue Bai: https://www.hindawi.com/journals/amse/2016/7139085/
  10. "Low-resistance gateless high electron mobility transistors using three-dimensional inverted pyramidal AlGaN/GaN surfaces" by Hongyun So: http://scitation.aip.org/content/aip/journal/apl/108/1/10.1063/1.4939509
  11. "Interdigitated Pt-GaN Schottky interfaces for high-temperature soot-particulate sensing" by Hongyun So: http://www.sciencedirect.com/science/article/pii/S0169433216300393
  12. "Continuous V-Grooved AlGaN/GaN Surfaces for High-Temperature Ultraviolet Photodetectors" by Hongyun So: http://ieeexplore.ieee.org/document/7409926/
  13. "Rapid fabrication and packaging of AlGaN/GaN high-temperature ultraviolet photodetectors using direct wire bonding" by Hongyun So: http://iopscience.iop.org/article/10.1088/0022-3727/49/28/285109

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