What is the Junk growth, and why do it?

See Bravo MBE Junk Growth!

Echo MBE Junk Growth

ESW, 07/27/15 AMG, 07/30/21

Note: Must have 3” Si wafer loaded on trolley and in load chamber. The wafer is loaded with a backing wafer (Si preferred?). Must have run LC lamp bake as normal.

Note: Always check CAR and cracker motors for PID vibrations.

Note: specific Boron things?

Bake Si Wafer

1. Move Trolley into buffer chamber (after LC lamp bake)

2. Move Si wafer onto HTS. Watch out for Ta springs

3. Bake for 1 hour at 450 C

Growth Prep

1. End and save any RGA scans.

2. Start new RGA scan, to run during junk growth

3. Turn off Beam Flux

4. Make sure all cells are in auto

5. Wait for HTS to reach < 200 C

Transfer Wafer

1. Put substrate heater in manual mode.

2. Open gate valve between GC and BC

3. Open shutter between GC and BC

4. Confirm that CAR is aligned (Echo CAR alignment is fully manual). Transfer position is where grooves on controller are aligned. Check set screw.

5. Remove RHEED block

6. Transfer in Si wafer

7. No away bake

8. Manually rotate CAR to growth position (Black 2" line). Check set screws.

Junk Growth

1. Put substrate heater in auto, set substrate temp to 200 C.

2. Set As Sublimator output to ~30%, put in manual mode. This prevents interference with cracker when cracker temp and valve position are changed. If current output is significantly below 30% ,valve rehoming may be necessary.

3. Heat up sources (except dual dopant) to appropriate junk growth temperatures. Set wait times accordingly so all cells reach junk growth temperature simultaneously. Check cells with base/tip configuration to make sure base temperature stays below tip.

4. When reaching junk growth temperature, open As first. Junk growth with metallize without sufficient As overpressure.

5. Open As shutter

   1. Open As Valve to 250

   2. Set As Cracker temperature to 900.

   3. Never adjust cracker temperature with valve closed. Never open As valve with As shutter closed. Avoid adjusting cracker temperature other than junk growth.

6. Open other sources, except dual dopant, wait for 1 hour for outgassing

7. 30 minutes in, open Dual Dopant cell- dopants don't need to degas as long, and ramp up to junk growth temperature quickly.

   1. Dual Dopant shutter opens to Si, Si/Be shutter opens Bi in addition to Si. OK to open both shutters together.

Actuating Shutters

1. Rehome As valve at As Cracker temp 900 C

2. Open and close shutters a few times. Remember to close As Valve before closing As shutter

Closing Shutters

1. Close shutters except As

2. Open As Valve

3. Cool As Cracker to 850

4. Rehome As valve at 850 C

5. Close As Valve, then shutter

Source Turn off and Ending Growth

1. Cool shutters down to typical idling temperatures

2. Return As sublimator to auto mode

3. Put substrate heater in manual

4. Open gate valve, then shutter between BC and GC

5. Transfer out wafer. Note orientation (we want to check uniform deposition later)

6. Transfer in RHEED block

7. Close shutter, then gate valve. Put substrate heater in auto.

8. Stop RGA scan, and save.

9. Load/unload for standard quantum well growth if applicable.

Note: Debatable whether it is better to keep shutters open below 500 C, open throughout the heating up process, or open only after reaching the junk growth temperature