Specific Process Knowledge/Lithography/Coaters/Spin Coater: Gamma UV processing: Difference between revisions

=General Process Information=

*Spin coating

*Soft baking

'''Features of Spin Coater: Gamma UV'''

*Cassette-to-cassette wafer handling

*Purging

*Cooling

The top and bottom heaters of the VPO module are typically set to 120°C. The wafer is baked under a low vacuum (~0.35 bar) in order to heat and dehydrate the wafer before HMDS application. The HMDS is injected into the process chamber using nitrogen as a carrier gas. 10 liters per minute of dry nitrogen is bubbled through liquid HMDS before flowing into the chamber. The injection lasts until ambient pressuer is reached in the chamber. After the reaction time, the chamber is purged using nitrogen. Finally, the wafer is cooled on the cool plate.

*Spin-off

*Backside rinse using PGMEA

The wafer is first centered on the spindle chuck and held in place by vacuum. If static dispense is specified in the process, the spindle remains static during the ensuing resist dispense. In the case of dynamic dispense, the spindle is accelerated to a low spin speed before the resist is dispensed. Using too high spin speed during dispense can cause surface wetting issues, while a too low spin speed causes the resist to flow onto the backside of the wafer. The resist is dispensed through the dispense arm, positioned over the center of the wafer. The resist pump administers a volume of resist which depends on the substrate size.

Dependent on the spin speeds used in the various steps of the spin coating, resist may creep over the edge of the wafer and onto the backside. Also, some resists tend to leave fine strings of resist protruding from the edge of the wafer, or folded onto the backside, an effect sometimes referred to as "cotton candy". This resist will contaminate the soft bake hotplate, and thus subsequent wafers with resist. In a backside rinse step, solvent administered through a nozzle to the backside of the wafer while spinning dissolves the resist and washes it away. After the rinse, a short spin dries the wafer before the soft bake. Backside rinse may be done as part of the spin-off step(s). During the backside rinse solvent inevitably creeps onto the front side of the wafer, and may remove the resist coating on the edge of the wafer. As an alternative to backside rinse, a wafer which is left dirty on the backside by the spin coat process may be soft baked in proximity in order to protect the hotplate from contamination. This leaves front side coating intact, but also leaves the backside dirty.

After spin coating, the solvent in the resist formulation must be evaporated in a baking step in order to solidify the resist. This soft bake can be carried out as a contact bake or a proximity bake. In a contact bake, the wafer is held in close contact to the hotplate surface while resting on shallow bumps only 150µm above the hotplate. In a proximity bake, the wafer is first moved into proximity, e.g. 1mm, of the hotplate surface, then held there (on the lift pins) for the duration of the bake. The hotplate temperatures of the baking modules of Spin Coater: Gamma UV are set at temperatures relevant to the resist used, typically 90-110°C. After baking, the wafer is cooled for 20 seconds on the cool plate.

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! QC Recipe:

! (2421) DCH 100mm nLOF 2020 2um HMDS  

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| Resist volume

!QC limits

!Spin Coater: Gamma UV - AZ nLOF 2020

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|Film thickness deviation from nominal

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{| {{table}}

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! QC Recipe:

! (3411) DCH 100mm 5214E 1.5um HMDS  

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| Resist volume

!QC limits

!Spin Coater: Gamma UV - AZ 5214E

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|Film thickness deviation from nominal

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==HMDS priming==

The standard HMDS priming process has been developed to mimic the behavior of the IMTEC Star2000 HMDS oven, which produces a contact angle of 81-82° on an oxidized silicon surface. The fast HMDS priming has been developed to have a process time of approximately one minute, in order to match the process time of typical coating and softbaking processes.

Test results:

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Test results:

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|taran

|4" wafer, no HMDS. 9 points on one wafer, exclusion zone 5mm

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==AZ nLOF 2020 coating==

*'''(2420) DCH 100mm nLOF 2020 2um'''

*'''(2620) DCH 150mm nLOF 2020 2um'''

*'''(2621) DCH 150mm nLOF 2020 2um HMDS'''

''Sequence names, process parameters, and test results (Sequence no. 3000-3999):''

*'''(3410) DCH 100mm 5214E 1.5um'''

*'''(3610) DCH 150mm 5214E 1.5um'''

*'''(3611) DCH 150mm 5214E 1.5um HMDS'''

|4" wafer. 9 points on one wafer, exclusion zone 5mm.

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==AZ "5206E" coating (syringe)==

Spin coating of AZ 5206E (AZ 5214E 1:1 by volume in PGMEA) dispensed from syringe on Spin Coater: Gamma UV is divided into three steps: HMDS priming, spin coating, and soft baking. The HMDS priming is equal to the ''HMDS fast'' process. The spin coating uses dynamic dispense of resist at 800? rpm, using a volume of 1.5 ml for 100 mm substrates. The dispense is followed by spin-off at a thickness dependent spin speed for 30 seconds. The thickness range is approximately 0.4-0.6µm. Soft baking is done at 90°C for 60s.