I. Equipment description
The ESI 3511 is a downstream remote microwave plasma system: the process chamber is located downstream away from where a plasma of O2/N2 or N2/5%H2 is created.
Flowing down to the process chamber, the reactive mixture is no longer electrically active and it contains only molecules and atoms in the ground electronic state (“afterglow”). The single atoms present in this region are at metastable state, hence highly chemically reactive, and are used to burn organics off the surface. Charged species bombardment conditions are found only in the plasma-generation region, so no damage to the sample surface is created in the process chamber.
The process is assisted with the sample sitting on a heated platen for improved ash rate and a heat lamp is used for better uniformity.
Main applications are:
- High rate photoresist removal with low damage
- Surface cleaning before subsequent processes
Characteristics of the tool are:
- frequency: 2.45 GHz
- power: up to 1200W
- O2 5’000sccm
- N2 500sccm
- N2/5%H2 2’000sccm
- Platen temperature up to 300°C
- Heat lamp 1kW
- Cassette loader for 25 wafers, 100mm
II. Standard process
Resist ashing at 250°C, 900W, 1200mT O2/N2.
Fixed time (max 150sec) or with optical End-Point-Detection.
4.4um/min on positive photoresist.
Hotplate temperature stabilization rates:
- Heating rate (active, thermal resistors): ~15°C/min.
- Cooling rate (passive, local air convection): ~3.5°C/min.