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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 spin speed w₂ needed to achieve thickness t₂ using the relation:
t₁*w₁^½ = t₂*w₂^½ => w₂ = w₁ * t₁²/t₂².
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 => w₂ = w₁ * t₁/t₂.

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 resist level 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
KMPR 1025:
- 0.4 ml/s @ 0.5 bar
- 0.7 ml/s @ 1.0 bar
SU-8 2010:
- 1.1 ml/s @ 0.1 bar*AZ 5214E:
- 1.2 ml/s @ 0.1 bar
- 2.4 ml/s @ 0.18 bar

Edge bead removal

The automatic dispense system may also be used to administer solvent at the edge of the wafer after spin coating in order to remove the edge bead. Edge bead removal, or EBR, is usually done using PGMEA. Due to the low viscosity of the solvent, and the relatively high pressure of the EFD control box, it is necessary to use at tip at the end of the syringe. The flow rate of the solvent is a function of the pressure and the size of the tip orifice. While the dispense rate scales roughly linearly with the pressure, it is an exponential function of the tip orifice.

Observed dispense rates of PGMEA (uncertainty from measurements ~0.1 ml/s) for different tip sizes:

Red (0.010"):
- 0.2 ml/s @ 0.1 bar
- 0.25 ml/s @ 0.2 bar
Purple (0.020"):
- 0.3 ml/s @ 0.1 bar
- 0.65 ml/s @ 0.2 bar
Pink (0.024"):
- 0.5? ml/s @ 0.1 bar (not verified)
Grey (0.047"):
- ~2.5 ml/s @ 0.1 bar

Recipes

Auxiliary recipes, and template recipes. For each case a list of the steps/parameters in the respective recipe.

Process recipes developed by Danchip are listed under Process results.

Auxiliary recipes

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).

Manual dispense templates

1 TMPLT man disp

Spin-off; deceleration.

1 TMPLT man disp spread

Spread step; spin-off; deceleration.

1 TMPLT man disp Gyrset

Gyrset down; spin-off; deceleration; Gyrset up.

1 TMPLT man disp Gyrset sprd

Gyrset down; spread step; spin-off; deceleration; Gyrset up.

Automatic dispense templates

1 TMPLT aut disp SU8

Dispense; SU-8 string breaking; spread step; spin-off; deceleration.

1 TMPLT aut disp SU8 Gyrset

Dispense; SU-8 string breaking; Gyrset down; spread step; spin-off; deceleration; Gyrset up.

1 TMPLT aut disp

Dispense; spin-off; deceleration.

1 TMPLT aut disp spread

Dispense; spread step; spin-off; deceleration.

1 TMPLT aut disp Gyrset

Dispense; Gyrset down; spin-off; deceleration; Gyrset up.

1 TMPLT aut disp Gyrset sprd

Dispense; Gyrset down; spread step; spin-off; deceleration; Gyrset up.

Processing results

SU-8 2075

Spin coating of SU-8 2075 on Spin Coater: RCD8 using automatic dispense consists of three process steps: static dispense, spread, and spin-off. In the static dispense step the media arm is moved to the center of the wafer, and resist is dispensed for 7s, yielding a volume of 3.5ml at 2.0 bar. After the dispense, the media arm is moved up and down in a series of steps designed to break the string of resist between the syringe and the wafer. In the spread step the wafer is accelerated to 700rpm at 50rpm/s, and spun for 25s. In the spin-off step the wafer is accelerated at 500rpm/s to the spin-off speed, spun for 30s, then decelerated at 1000rpm/s.
In the Gyrset version, the Gyrset is closed after the dispense step, and opened after the spin-off step.

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 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 Non-vacuum chuck

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 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 coating of AZ MiR 701 (29cps) 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 MiR 701 man disp 2um ¹⁾

Spin-off: 30 s at 2350 rpm.

Substrate	Thickness	Uniformity (+/-)	Test date	Tester initials	Comments
Silicon with native oxide	2.00 µm	1.8%	29/4 2015	taran	9 points on one wafer, exclusion zone 5mm Non-vacuum chuck

¹⁾ Not implemented yet.

AZ nLOF 2020

Spin coating of AZ nLOF 2020 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 nLOF 2020 man disp 2.3um ¹⁾

Spin-off: 30 s at 2500 rpm.

Substrate	Thickness	Uniformity (+/-)	Test date	Tester initials	Comments
Silicon with native oxide	2.30 µm	1.7%	29/4-2015	taran	9 points on one wafer, exclusion zone 5mm Non-vacuum chuck

¹⁾ Not implemented yet.

@@ Line 27: / Line 27: @@
 **0.7 ml/s @ 3.0 bar
 *'''KMPR 1025:'''
-**?? ml/s @ 0.5 bar
+**0.4 ml/s @ 0.5 bar
-**?? ml/s @ 1.0 bar
+**0.7 ml/s @ 1.0 bar
-**?? ml/s @ 2.0 bar
 *'''SU-8 2010:'''
 **1.1 ml/s @ 0.1 bar*'''AZ 5214E:'''