Boron Nitride E-Beam Crucibles

Overview of Crucible Liners and E-Beam Evaporation Best Practices

Crucible liners play a pivotal role in e-beam evaporation, directly impacting material deposition and process efficiency. MetalsTek offers a range of crucible liners with custom sizes available to suit diverse operational needs.

Insulating Crucibles: Why They Are Not Ideal

Electrically insulating crucibles are generally unsuitable for e-beam evaporation due to their inability to manage electron flow during the process.

Electron Accumulation:
When electrons bombard the material in an insulating crucible liner, they cannot discharge to the ground. This causes charge buildup on the material.
- Beam Deflection: As the charge accumulates, it starts deflecting the e-beam, disrupting deposition.
- Recommendation: MetalsTek advises using electrically conductive crucible liners for all metal depositions. Conductive liners enable electrons to flow seamlessly through the material, into the crucible liner, and finally to the hearth, preventing beam deflection and ensuring a stable process.

Common Causes of Crucible Breakage

Proper handling and parameter settings are essential to prevent crucible damage during e-beam evaporation. Two common causes of breakage are incorrect ramp/soak settings and abrupt power shutdowns.

1. Mismanaged Ramp/Soak Settings

E-beam evaporation processes typically involve two ramp/soak power levels to gradually heat materials to deposition temperature. Errors in these settings can lead to significant problems:

Transition to PID Control: Once the material reaches deposition temperature, power control transitions from the ramp/soak levels to a PID loop. This loop manages the e-gun power supply and quartz crystal controller to maintain the desired deposition rate.
- Unstable Power Oscillations: If ramp2/soak2 settings are far from the required power level for deposition (e.g., 1 Ångström/sec), the PID loop struggles to stabilize. Wild power swings (+90% to 0%) can occur, rapidly liquefying and condensing the material, which stresses the crucible and causes cracks.
- Solution: Ensure that ramp2/soak2 levels are as close as possible to the power needed for the desired deposition rate. This minimizes PID loop adjustments, reducing the risk of rapid phase changes.

2. Abrupt Power Shutdowns

Improper handling of the power supply after deposition is another common cause of crucible damage:

Rapid Cooling Stress: Turning off the power supply suddenly or using an insufficient ramp-down period causes the melt to solidify rapidly. This rapid solidification creates mechanical stress on the crucible liner, leading to cracks or breakage.
- Preventive Measure: Implement a gradual power ramp-down to allow the melt to cool evenly, reducing stress and prolonging crucible life.

Boron Nitride Crucibles for E-Beam Sources