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).

Process parameters
You can manipulate two different descum process development parameters: you can either change power or chamber pressure.

Power setting testing

Descum results for different power settings

Recipe settings:

• Resist: AZ MiR 701
• O2 flow: 5 sccm
• N2 flow: 0
• Pressure: 0.2 mbar
• Power: Varied

Experiment parameters

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

Pressure setting testing

Descum results for different pressure settings

Recipe settings:

• Resist: AZ MiR 701
• O2 flow: varied
• N2 flow: 0
• Pressure: varied
• Power: V100% (100 W)

Experiment parameters

	Forward/reverse	C2/C1	Oxygen	Pressure
recipe 1	100/0	52/31	5	0.2
recipe 2	100/0	37/38	45	0.8

Ashing of AZ 5214E resist

Descum results for different pressure settings

Recipe settings:

• Resist: AZ 5214E
• O2 flow: varied
• N2 flow: 0
• Pressure: varied
• Power: V100% (100 W)

Experiment parameters

	Forward/reverse	C2/C1	Oxygen	Pressure
recipe 1	100/0	52/31	17	0.4
recipe 2	100/0	37/39	45	0.8

Plasma Asher 4

Descum of AZ 5214E on 100 mm wafers. The descum process development was done for a single substrate, as well as 3 substrates (for decreased ashing rate and improved ashing uniformity). The substrates were 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. The wafers were placed in consecutive slots - when running multiple wafers in this way, 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
Tested with 1.5 µm AZ 5214E on 100 mm silicon substrate.

• O₂: 100 sccm
• N₂: 100 sccm
• Pressure (DSC): 1.3 mbar
• Power: 200 W
• Chamber temperature at start (with door closed): 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

Single wafer descum ashing rate and uniformity for plasma asher 4 & 5

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

Ashing amount and 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

Ashing non-uniformity

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

Multi wafer descum ashing rate and uniformity for plasma asher 4 & 5

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

Ashing amount and 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

Ashing non-uniformity

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

Comparison between single substrate processing and multi substrate processing for plasma asher 4 & 5

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 here.