Specific Process Knowledge/Lithography/Descum

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Plasma Asher 1

Plasma asher 1 was decommissioned 2024-12-02.

Information about decommissioned tool can be found here.

Plasma Asher 2

Plasma asher 2 was decommissioned 2024-12-02.

Information about decommissioned tool can be found here.

Plasma Asher 3: Descum

The user manual(s), quality control procedure(s) and results and contact information can be found in LabManager - requires login

Plasma Asher 3 is specifically used for controlled descum process after lithography. Please note that you only can process a single 100 mm wafer, or one small sample, at a time. The plasma asher is equipped with 2 gaslines: oxygen and nitrogen, but all standard processes use only oxygen (as recommended by Diener).

Ashing of AZ MiR701 resist:
You can use two different descum process developments: you can either change power settings or processing chamber pressure.

Testing different power settings:

Descum results for different power settings

Recipe settings:

• O2 flow: 5 sccm
• N2 flow: 0
• Pressure: 0.2 mbar
• Power: Varied

Experiment parameters:

FW/REV C2/C1 Power recipe 1 50/0 52/31 50% recipe 2 100/0 53/31 100% recipe 3 20/0 51/34 20%

Testing different pressure settings:

Descum results for different pressure settings

Recipe settings:

• O2 flow: varied
• N2 flow: 0
• Pressure: varied
• Power: V100% (100 W)

Experiment parameters:

FW/REV C2/C1 Oxygen Pressure recipe 1 100/0 53/31 5 0,2 recipe 2 100/0 37/38 45 0,8

Ashing of AZ5214E resist:

Descum results for different pressure settings

Recipe settings:

• O2 flow: varied
• N2 flow: 0
• Pressure: varied
• Power: V100% (100 W)

Experiment parameters:

FW/REV C2/C1 Oxygen Pressure recipe 1 100/0 53/31 17 0,4 recipe 2 100/0 37/39 45 0,8

Plasma Asher 4

Descum processing in plasma asher 4 & 5

Descum of AZ 5214E on 100 mm wafers. The descum process was tested for single substrates, as well as 3 substrates, placed vertically in the glass boat. For the 3 substrates only the center substrate was used for testing, the front and back wafers were used as dummy wafers.

When running multiple wafers, the first and last wafers should always be dummy wafers.

The user manual, risk assessment, and contact information can be found in LabManager - requires login

Typical descum parameters

• O₂: 100 sccm
• N₂: 100 sccm
• Pressure (DSC): 1.3 mbar
• Power: 200 W
• Chamber temperature at start: 30°C
• Time (single wafer): 5-10 minutes = 35-72 nm ashed
• Time (multiple wafers): 10-15 minutes = 40-80 nm ashed

Test setup	Single substrate	Center of 3 substrates
Test results	Ashing rate: 5.7 ±2.1 nm/min Non-uniformity: 0.6 ±0.4%	Ashing rate: 3.8 ±1.6 nm/min Non-uniformity: 0.4 ±0.2%
Wafers	1	3
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	200 sccm	200 sccm
Gas mix ratio	50% N2	50% N2
Chamber pressure	1.3 mbar	1.3 mbar
Power	200 W	200 W
Test processing time	Tested parameter	Tested parameter
Test average temperature	33°C	33°C

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Ashing amount and ashing rate when processing a single 100 mm wafer.

Single wafer ashing rate

Ashing time [min]:	1	2	5	10	15
Ashing amount [nm]:	5.2	6.2	35.1	72.3	87.1
Ashing rate [nm/min]:	5.2	3.1	7.0	7.2	5.8

Single wafer non-uniformity

Ashing time [min]:	1	2	5	10	15
Film thickness range, before descum [nm]:	11	12	10	11	9
Pre-ashing non-uniformity [%]:	0.37	0.40	0.33	0.37	0.30
Film thickness range, after descum [nm]:	10	10	12	19	33
Post-ashing non-uniformity [%]:	0.33	0.33	0.41	0.66	1.18

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Ashing amount and ashing rate when processing multiple 100 mm wafers. Test measured on the center of 3 wafers.

Multi wafer ashing rate

Ashing time [min]:	1	2	5	10	15
Ashing amount [nm]:	4.3	6.7	10.1	39.5	78.8
Ashing rate [nm/min]:	4.3	3.4	2.0	4.0	5.3

Multi wafer non-uniformity

Ashing time [min]:	1	2	5	10	15
Film thickness range, before descum [nm]:	11	13	11	12	14
Post-ashing non-uniformity [%]:	0.37	0.43	0.37	0.40	0.46
Film thickness range, after descum [nm]:	11	9	10	12	21
Post-ashing non-uniformity [%]:	0.37	0.30	0.33	0.41	0.74

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Comparison between single substrate processing and multi substrate processing
Processing a single substrate using the standard descum settings will provide users with a relatively controllable and uniform process. Adding dummy substrates in close proximity with the process substrate will reduce the ashing rate and improve the uniformity:

• 
  Ashing amount
• 
  Ashing rate
• 
  Non-uniformity

Plasma Asher 5

Plasma asher 5 is identical to plasma asher 4, see descum processing for plasma asher 4 [[1]].