Specific Process Knowledge/Lithography/Coaters/Spin Coater: RCD8 processing

Spin coating

The process of spin coating on Spin Coater: RCD8 consists of a selection of the following steps:

• Acceleration to a low spin speed if dynamic dispense is used
• Resist dispense
• Closing the Gyrset
• Resist spreading at low spin speed
• Spin-off
• Deceleration
• Opening Gyrset

The wafer is first centered on the chuck and held in place by vacuum (or pins in the case of the non-vacuum chuck). If static dispense is used, 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 may be dispensed manually, or automatically using the syringe dispense system on the media arm. After dispense, a short spin at low spin speed may be used in order to spread the resist over the wafer surface before spin-off.

The spin-off cycle determines the thickness of the resist coating. The thickness is primarily a function of the spin-off speed and the spin-off time, both following an inverse power-law (y=k*x^-a). The acceleration to the spin-off speed also influences the thickness, but the effect is dependent on previous steps. The spin-off is usually a simple spin at one speed, but it may be comprised of several steps at different spin speeds. After spin-off, the wafer is decelerated.

The coated thickness, t, as a function of the spin-off speed, w, follows an inverse power-law, t=k*w^-a. The constant, k, is a function of the resist viscosity and solid content, and the spin-off time. The exponent, a, is dependent on solvent evaporation, and is usually ~½. This means that from the thickness t₁ achieved at spin speed w₁, one can estimate the thickness t₂ at spin speed w₂ using the relation:
t₁*w₁² = t₂*w₂² => t₂ = t₁ * w₁²/w₂².
For SU-8, however, a is observed to be ~1 (probably due to the low solvent content and/or the formation of skin). In this case, the relation simply becomes:
t₁*w₁ = t₂*w₂ => t₂ = t₁ * w₁/w₂.

Automatic dispense

Automatic dispense on the Spin Coater: RCD8 is done using a Nordson EFD Performus VII pressurised cartridge dispense system. The syringe containing the resist is mounted on the media arm, and the resist is dispensed using a nitrogen pressure supplied by the control box. The dispense rate is controlled by the nitrogen pressure, while the dispense time, and thus the volume, is set in the recipe. The dispensed volume may be estimated by measuring the distance the syringe cap is displaced during a dispense, and calculating the corresponding volume using the diameter of the syringe (23 mm).

Observed dispense rates (uncertainty from measurements ~0.1 ml/s):

• SU-8 2075:
  • 0.2 ml/s @ 1.0 bar
  • 0.5 ml/s @ 2.0 bar
  • 0.7 ml/s @ 3.0 bar
• AZ 5214E:
  • 1.2 ml/s @ 0.1 bar
  • 2.4 ml/s @ 0.18 bar

Standard recipes

General

• 1 DCH Centering test

5s @ 100rpm; 5s @ 250rpm; 5s @ 500rpm.

• 1 DCH Chuck cleaning

10s @ 100rpm; 1s @ 0rpm; 10s @ -30rpm; 20s @ 1500rpm.

• 1 DCH Gyrset cleaning

Gyrset down; 10s @ 100rpm; 1s @ 0rpm; 10s @ -30rpm; 20s @ 1500rpm; Gyrset up.

• 1 DCH predispense

0.2s dispense at cup (arm position 0mm).

SU-8 2075

Spin curve for SU-8 2075

Spin curve for SU-8 2075 using Gyrset

Spin coating of SU-8 2075 on Spin Coater: RCD8 is...

Recipe names, process parameters, and test results:

• 1 DCH SU8 aut disp 100um

Spin-off: 30 s at 2100 rpm.

Substrate	Thickness	Uniformity (+/-)	Test date	Tester initials	Comments
Silicon with native oxide	100 µm	3.5%	14/4 2015	taran	5 points on one wafer, exclusion zone 15mm

• 1 DCH SU8 aut dsp Grst 100um

Spin-off: 30 s at 2000 rpm.

Substrate	Thickness	Uniformity (+/-)	Test date	Tester initials	Comments
Silicon with native oxide	99 µm	3.0%	15/4 2013	taran	5 points on one wafer, exclusion zone 15mm

AZ 4562

Spin curve for AZ 4562

Spin coating of AZ 4562 on Spin Coater: RCD8 using manual dispense is a very simple process. The wafer is accelerated at 1000rpm/s to the spin-off speed, spun for 30s, then decelerated at 1000rpm/s.

Recipe names, process parameters, and test results:

• 1 DCH 4562 man disp 10um

Spin-off: 30 s at 2000 rpm.

Substrate	Thickness	Uniformity (+/-)	Test date	Tester initials	Comments
Silicon with native oxide	9.92 µm	2.9%	29/4 2015	taran	9 points on one wafer, exclusion zone 5mm

AZ 5214E

Spin curve for AZ 5214E

Spin coating of AZ 5214E on Spin Coater: RCD8 using manual dispense is a very simple process. The wafer is accelerated at 1000rpm/s to the spin-off speed, spun for 30s, then decelerated at 1000rpm/s.

Recipe names, process parameters, and test results:

• 1 DCH 5214E man disp 1.5um

Spin-off: 30 s at 4700 rpm. OBS! Do not use with non-vacuum chuck!

Substrate	Thickness	Uniformity (+/-)	Test date	Tester initials	Comments
Silicon with native oxide	1.52 µm	0.3%	21/4 2015	taran	9 points on one wafer, exclusion zone 5mm

• 1 DCH 5214E man disp 2.2um

Spin-off: 30 s at 2100 rpm.

Substrate	Thickness	Uniformity (+/-)	Test date	Tester initials	Comments
Silicon with native oxide	2.19 µm	0.4%	22/4 2013	taran	9 points on one wafer, exclusion zone 5mm

AZ MiR 701

Spin curve for AZ 4562

Spin coating of AZ 4562 on Spin Coater: RCD8 using manual dispense is a very simple process. The wafer is accelerated at 1000rpm/s to the spin-off speed, spun for 30s, then decelerated at 1000rpm/s.

Recipe names, process parameters, and test results:

• 1 DCH 4562 man disp 10um

Spin-off: 30 s at 2000 rpm.

Substrate	Thickness	Uniformity (+/-)	Test date	Tester initials	Comments
Silicon with native oxide	9.92 µm	2.9%	29/4 2015	taran	9 points on one wafer, exclusion zone 5mm

AZ nLOF 2020

Spin curve for AZ 4562

Spin coating of AZ 4562 on Spin Coater: RCD8 using manual dispense is a very simple process. The wafer is accelerated at 1000rpm/s to the spin-off speed, spun for 30s, then decelerated at 1000rpm/s.

Recipe names, process parameters, and test results:

• 1 DCH 4562 man disp 10um

Spin-off: 30 s at 2000 rpm.

Substrate	Thickness	Uniformity (+/-)	Test date	Tester initials	Comments
Silicon with native oxide	9.92 µm	2.9%	29/4 2015	taran	9 points on one wafer, exclusion zone 5mm

Template recipes

Manual dispense

• 1 TMPLT man disp
• 1 TMPLT man disp spread
• 1 TMPLT man disp Gyrset
• 1 TMPLT man disp Gyrset sprd

Automatic dispense

• 1 TMPLT aut disp SU8
• 1 TMPLT aut disp SU8 Gyrset
• 1 TMPLT aut disp
• 1 TMPLT aut disp spread
• 1 TMPLT aut disp Gyrset
• 1 TMPLT aut disp Gyrset sprd