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aix-ccs

Aixtron MOCVD for III-N semiconductors: InN, GaN, AlN, InGaN, InAlN, AlGaN, InGaAlN.

 

SNF MOCVD lab capability introduction

 

Aix-ccs is a vertical metal organic chemical vapor deposition (MOCVD) system from Aixtron. It is a III-N system with a vertical closed coupled showerhead reactor, installed with a 1 by 4-inch susceptor and a 3 by 2-inch susceptor. It is categorized as contaminated tool in general but is a clean MOCVD so only accepts clean substrates. The system has been well calibrated for 4-inch wafer, while pieces and 2-inch wafer are possible on request.

 

Picture and Location

 aix-ccs

Shown above is the aix-ccs 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 GaN is grown (diagram courtesy of Aixtron).

 

  GaN growth schematics

 

Process Capabilities

Cleanliness Standard

MOCVD is classified as Gold contamination level in general sense, however, it also has its own classification. Aix-ccs is kept as “clean MOCVD” for now to prevent any foreign element contamination and maintain the high growth quality. Only clean substrates from clean benches are allowed in this system. 

The aix-ccs processes take place with a chamber temperature up to 1200C. 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
  6. Samples small enough (<=1cm) to fall into the exhaust line
  7. No metals
  8. Other III-V semiconductors like GaAs and InP

 

Performance of the Tool

What the Tool CAN do

  1. Deposit III-N films (single crystal, polycrystal), heterostructures and nanowires
  2. P-type and n-type doping
  3. Tightly controlled thickness from sub-nm to several micron

 

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 dry 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 is kept in a nitrogen glovebox to isolate the reaction chamber from the working area. Not shown here are two cooling systems hooked up to the reactor and the dry pump, and to the showerhead, respectively. Aix-ccs utilizes a vertical reactor with two arrays of close coupled showerhead (for group III and group V inlet respectively), a quartz liner, and a graphite susceptor. Right now only 4-inch Si wafer is calibrated, but pieces and 2-inch wafer are also possible with the assist of a dummy wafer by careful control. Below shows the pictures of the reactor.

 

ccs susceptor showerhead

 

                             Reactor inner view                                                                              Showerhead (reactor lid)

 

Possible Materials

The table below shows the precursors and resulting compounds in this system. Ternary and quaternary compounds like AlGaN and InAlGaN are also within the capability of this system.

 

Precursors 

TMIn 

(Trimethyl Indium)

    TMGa 

    (Trimethyl Gallium)

    TMAl (Trimethyl Aluminum)

    -High flow

   TEG 

   (Triethyl Gallium)

     TMAl (Trimethyl Aluminum)-

     Low flow

NH3

InN

    GaN

    AlN

   InGaN

     InAlN

Cp2Mg (Bis-cyclopentadienyl magnesium)

P-type doping of above compounds

SiH4 (Silane)

N-type doping of 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: Hongyun So (hyso@stanford.edu)

 

Training to Become a Tool User

Becoming a 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, the precursor flow rate calculation, and the in-situ reflection/curvature monitor analysis 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 until cooling step
  4. No Food, No drink

 

Procedure (See User Manual for details):

  1. Enable in Badger (MOCVD /aix-ccs)
  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 AIXACT as Technician, and reset the alarm on AIXACT
  6. Pump/purge 3 times before opening loadlock, load samples to loadlock and pump/purge 3 times before loading to the glovebox
  7. Check the “Reactor Open Release” is ready, and then put on gloves and lab coat, push your hands into the glovebox slowly 
  8. Wear clean gloves before touching anything in the glovebox. While pressing the “SHOWERHEAD UNLOCK” yellow button, lift up the reactor lid carefully 
  9. Remove the blank dummy wafer, and load your sample with the vacuum wand
  10. Close the reactor lid carefully and slowly, check if the reactor close indicator is lit up and the DOR is pumped to 0 mbar. If not, try to push the lid a little bit
  11. Turn off the DOR valve and check the seal, then turn back on the DOR valve
  12. Open/edit your recipe
  13. Turn on bubbler manual valves. Fully open and turn ¼ turn back.
  14. Wait until the “Timer N2 Purge Active” finish (turns red) and bubbler temperature stabilized
  15. Start the process, record the run ID and recipe name
  16. ill out the log book for growth conditions
  17. Watch carefully during the run until the run is finished. Observe film reflection and curvature evolution by analyzing in-situ Epi-TT and Epi-curve monitors
  18. Close the bubbler valves and lock the cabinet
  19. Open the reactor, take out samples, and close thenreactor door carefully
  20. nload the sample through loadlock and pump/purge 3 times before opening loadlock. Pump/purge 3 times after unloading
  21. Bake the reactor (recipe: Bake_1100C) after each growth, and then brush the showerhead with the vaccum brush
  22. Disable from Badger
  23. Mute the alarm buzzer on AIXACT
  24. Login to AIXACT as viewer

 

Safety

  1. In the case of toxic gas alarm, leave the room immediately (press the emergency STOP if possible). Follow the emergency procedure.
  2. Other situations: put system to base state (or press stop process button) and report.
  3.  

Process Monitoring Results & General Data

Results based on 4" Si substrate

 

    Ref. No.

    Specification

    Achieved data

    1.      

    AlN LT/HT Buffer

     

    1.1.            

    Growth rate

    0.39um/hr

    1.2.            

    Thickness uniformity (on wafer)

    1.27%

    2.      

    Al0.5Ga0.5N

     

    2.1.            

    Growth rate

    0.6um/hr

    2.2.            

    Alloy uniformity (abs. value)

    ~1 to1.5%

    3.      

    Al0.2Ga0.8N

     

    3.1.            

    Growth rate

    0.6um/hr

    3.2.            

    Alloy uniformity (abs. value)

    ~1 to1.5%

    4.      

    Undoped GaN

     

    4.1.            

    Growth rate

    2.7um/hr

    4.2.            

    Thickness uniformity (on wafer) @ 1.5μm

    <3%

    4.3.            

    XRD (0002)

    570arcsec

    4.4.            

    XRD (0102)

    902arcsec

    4.5.            

    Background doping level (hall)

    below Hall detect limit

    5.      

    2 DEG HEMT structure

     

    5.1.            

    Sheet resistance uniformity @ ~400Ohm/square

    6%

    5.2.            

    2 DEG sheet resistance

    362 Ohm/square

    5.3.            

    2 DEG charge carrier concentration

    1.1x 1013 cm-2

    5.4.            

    2 DEG mobility @ > 4 x1012 cm-2

    1590 cm²/V

    5.5.            

    AlGaN barrier with 25% Al concentration

    Al concentration uniformity (abs. value)

    ~2%

    5.6.            

    Thickness uniformity (on wafer)

    <2%

     AlGaN-on-Si growth monitoring (AlGaN/AlN/Si)

    Al%                                                         PL mapping

     

                                                              Thickness mapping

    26.9%               26.9%AlGaN PL map 26.9%AlGaN thickness map

    38.2%               38.2%AlGaN PL 38.2%AlGaN thickness map

    46.3%               46.3%AlGaN PL map 46.3%AlGaN thickness map

    66%                  66%AlGaN PL map 66%AlGaN thickness map

    72.2%               72.2%AlGaN PL map

    77.9%               77.9%AlGaN PL map

    82.2%               82.2%AlGaN PL map

     

    For more PL results, see the PL mapping data

    AlGaN/GaN HEMT growth monitoring:

    See the Improve the performance of MOCVD grown GaN-on-Si HEMT structure

               MOCVD workshop presentations

    EE412 class reports:

    MOCVD Growth Calibration for GaN LED on Silicon
    Development of Thin Film Release of GaN using AlN and AlGaN Buffer Layers for MEMS Applications

    MOCVD Users Publications:

    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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