The Quantum-Nano Fabrication and Characterization Facility (QNFCF) is now pleased to offer user training and support for the new Angstrom Engineering indium evaporation system in the RAC1 Cleanroom. This deposition system is engineered to enable the fabrication of high aspect ratio indium bumps via thermal evaporation. A 28cc alumina crucible allows deposition of indium films up to 20 µm in one run with a deposition rate up to 100 Å/s. Rate control and deposited thickness are monitored with no interruption thanks to a multi-quartz crystal microbalance.
This system is equipped with a large cryopump, a recirculating chiller for substrate temperature control and a collimation plate. The Aeres computer interface enables automated pumping/venting and the construction of complex deposition recipes.
The system features:
- Ultimate base pressure of <1e-7 Torr
- Water-cooled chamber walls and mid-height shield/collimation plate
- Variable-height stage:
- Source to substrate distance between 583 mm (23’’) and 685 mm (27’’)
- 10 and 30 rpm rotation
- Temperature-controlled with recirculating fluid between -30 and 125°C (stage temperature between -25 and 115 °C).
- Generic sample holder for susbtrates up to 200 mm and two single-wafer holders for 100 mm and 150 mm wafers.
- Thermal evaporation source with 6 kVA transformer for deposition rate up to 100 Å/s
- 12 quartz monitor crystals in one sensor head for continuous and accurate deposition
- Source/substrate shutter
- Shuttered viewport
This new shared capability has been made available to the QNFCF community through support from CFI John Evans Leadership Fund project #42248, led by Dayan Ban.
Interested researchers are encouraged to send their new project inquiries to Taso Alkiviades.
Angstrom Indium deposition system
Application: In bump fabrication
Prior to acceptance of this system, the QNFCF team collaborated with Angstrom Engineering to conduct process testing on a similar Indium series thermal evaporation system. A series of line features in AZ nLOF 2070 negative tone photoresist to test the effect of various deposition conditions on the microstructure of the resulting indium film. Depositions were carried out with the following parameters:
| Wafer # | Stage Chiller Temperature (°C) | Indium deposition rate (Å/s) | Indium film thickness (µm) |
| 1 | -10 | 5 | 5 |
| 2 | -10 | 50 | 5 |
| 3 | -30 | 5 | 5 |
| 4 | -30 | 50 | 5 |
| 5 | -70* | 5 | 5 |
| 6 | -70* | 50 | 5 |
*NOTE: QNFCF's Angstrom deposition system has a -50°C lower temperature limit on the stage.
Line features were cleaved with a diamond pen and examined using the JEOL JSM 7200F Scanning Electron Microscope.
Indium film micrographs
Wafer 1, -10°C stage temperature, 5 Å/s deposition rate, 5 µm film thickness.
Wafer 2, -10°C stage temperature, 50 Å/s deposition rate, 5 µm film thickness.
Wafer 3, -30°C stage temperature, 5 Å/s deposition rate, 5 µm film thickness.
Wafer 1, -30°C stage temperature, 50 Å/s deposition rate, 5 µm film thickness.
Wafer 5, -70°C stage temperature, 5 Å/s deposition rate, 5 µm film thickness.
Wafer 6, -70°C stage temperature, 50 Å/s deposition rate, 5 µm film thickness.
Observations
Preliminary testing and observation appears to show that films deposited at lower stage temperatures and higher deposition rates appear to form smoother lines. We believe this is because adatom mobility is suppressed by these two variables (lower temperature and high dep rate), hindering adsorbed In atoms and clusters from migrating to their optimal low energy location and enhancing the shadowing effect of the photoresist.