Specific Process Knowledge/Lithography/Strip/plasmaAsher04 processDevelopment

Process gas ratio for plasma asher 4 & 5

Ashing rate as function of gas mix ratio when processing a single 100 mm wafer and when processing a full boat with 25 wafers. The green area (~50% N₂) covers the optimum range for both situations.

The ashing rate is related to the gas mix, usually expressed as percentage of nitrogen of the total amount of gas. Process development tests found that a gas mix of 50% nitrogen gives the highest ashing rate for both processing single substrates and when processing a full boat with 25 substrates.

Please note that the ashing rate for a full boat is approximately ten times slower, than the processing time for a single substrate.

	Single substrate	Full boat
Test results	Highest ashing rate at 30-80% Nitrogen	Highest ashing rate at 50-70% Nitrogen
Wafers	1	25
Wafer size	100 mm	100 mm
Boat position	Center of chamber	Center of chamber
Test wafer position	Center of boat	Center of boat
Total gas flow rate	500 sccm	200 sccm
Gas mix ratio	Tested parameter	Tested parameter
Chamber pressure	1.25 mbar	1.3 mbar
Power	1000 W	1000 W
Test processing time	2 minutes	10 minutes
Test average temperature	43°C	47°C

Process chamber pressure for plasma asher 4 & 5

Ashing rate as function of chamber pressure when processing a single substrate and when processing a full boat with 25 substrates. The green area covers the optimum range (~1.3 mbar) for both situations.

The ashing rate is related to the chamber pressure during processing. Process development tests found that 1.3 mbar gives the highest ashing rate for both processing single substrates and when processing a full boat with 25 substrates.

Please note that the ashing rate for a full boat is approximately ten times slower, than the processing time for a single substrate.

	Single substrate	Full boat
Test results	Highest ashing rate at 1.3 mbar	Highest ashing rate at 1.4 mbar
Wafers	1	25
Wafer size	100 mm	100 mm
Boat position	Center of chamber	Center of chamber
Test wafer position	Center of boat	Center of boat
Total gas flow rate	150 sccm	200 sccm
Gas mix ratio	30% N2	50% N2
Chamber pressure	Tested parameter	Tested parameter
Power	1000 W	1000 W
Test processing time	2 minutes	10 minutes
Test average temperature	43°C	55°C

Process gas flow rate for plasma asher 4 & 5

Ashing rate as function of total gas flow when processing a single substrate and when processing a full boat with 25 wafers. The green area covers the optimum range (~200 sccm) for both situations.

The ashing rate is related to the total gas flow rate during processing. Process development tests found that 200 sccm gives the highest ashing rate for both processing single substrates and when processing a full boat with 25 substrates. The experiments indicate that the gas flow rate has only a minor impact on the ashing rate.

Please note that the ashing rate for a full boat is approximately ten times slower, than the processing time for a single substrate.

	Single substrate	Full boat
Test results	Highest ashing rate at 200 sccm	Highest ashing rate at 200 sccm
Wafers	1	25
Wafer size	100 mm	100 mm
Boat position	Center of chamber	Center of chamber
Test wafer position	Center of boat	Center of boat
Total gas flow rate	Tested parameter	Tested parameter
Gas mix ratio	30% N2	30% N2
Chamber pressure	1.3 mbar	1.3 mbar
Power	1000 W	1000 W
Test processing time	2 minutes	10 minutes
Test average temperature	43°C	47°C

Process power for plasma asher 4 & 5

Ashing rate as function of microwave power.

The ashing rate is related to the power used during processing. Higher power increases ashing rate.

	Single substrate
Test results	Ashing rate follows Power
Wafers	1
Wafer size	100 mm
Boat position	Center of chamber
Test wafer position	Center of boat
Total gas flow rate	200 sccm
Gas mix ratio	30% N2
Chamber pressure	1.3 mbar
Power	Tested parameter
Test processing time	2 minutes
Test average temperature	40°C

Process temperature for plasma asher 4 & 5

Ashing rate as function of temperature.

The ashing rate is related to the temperature during processing. Higher temperature increases ashing rate.

	Single substrate
Test results	Ashing rate follows temperature
Wafers	1
Wafer size	100 mm
Boat position	Center of chamber
Test wafer position	Center of boat
Total gas flow rate	200 sccm
Gas mix ratio	30% N2
Chamber pressure	1.3 mbar
Power	1000 W
Test processing time	2 minutes
Test average temperature	Tested parameter

Comparison of ashing rate between substrate sizes for plasma asher 4 & 5

Comparison of ashing rate with different substrate sizes. Process was done using a single substrate placed in the middle of the glass boat, which was placed in the center of the chamber.

The ashing rate is highest for 100 mm substrates, lower for 150 mm substrates and even lower for 200 mm substrates.

All substrate sizes follows the same pattern:

• Ashing rate increases with a higher percentage nitrogen in the gas mix
• Ashing rate increases with a higher chamber pressure
• The total gas flow has only little influence on the ashing rate, but slightly favors the lower flow rate of 200 sccm, similar to previous experiment results

Process parameter impact on ashing rate
Investigating the ashing rate using linear regression models on the process parameters, indicates that the gas mix and the chamber pressure has a significant impact on the ashing rate, while the gas flow has only little effect:

• 
  100 mm parameter impact
• 
  150 mm parameter impact
• 
  200 mm parameter impact