SU-8 Shrinkage

ByKelly McNabb

Goal: Measure SU-8 shrinkage that have gone through various soft and hard bake conditions

To measure the shrinkage, the SU-8 scaffolds needed to be lifted off, but there was some issues. Originally, the SU-8 was spincoated onto an oxide layer, which would be etched away using BOE. The SU-8 had appeared to be disintegrating due to the long exposure time to BOE. I switched over to the XeF2 which was safer for the SU-8. I was able to lift off six of the eight conditions.  The ones that I could not lift off are 65° C 10 min/ 125° C 2.5 min/ 200° C 2.5 min and 65° C 10 min/ 125° C 2.5 min/ 120° C 2.5 min. The 65° C 10 min/ 95° C 2.5 min/ 200° C 2.5 min and 65° C 10 min/ 95° C 2.5 min/ 120° C 2.5 min was hard to liftoff.

 

 10x  20x  40x
65° C 1 min/ 125° C 2.5 min/ 200° C 2.5 min  10x_2  20x_1  40x_2
65° C 1 min/ 125° C 2.5 min/ 120° C 2.5 min  2_10x_2 2_20x_2  2_40x_2
65° C 1 min/ 95° C 2.5 min/ 200° C 2.5 min  5_10x_2  2_20x_2  2_40x_2
65° C 1 min/ 95° C 2.5 min/ 120° C 2.5 min  6_10x_2  6_20x_1  6_40x_2
65° C 10 min/ 95° C 2.5 min/ 200° C 2.5 min  7_10x  7_20x  7_40x
65° C 10 min/ 95° C 2.5 min/ 120° C 2.5 min  8_10x_2  8_20x_1  8_40x_1

I measured the width and height of the liftoff scaffolds and compared it to the scaffolds on the wafers.

Condition Scaffold Wafer
Width (µm) Height (µm) Width (µm) Height (µm) Width Strain % Height Strain %
65° C 1 min/ 125° C 2.5 min/ 200° C 2.5 min 221 110.5 223 111 0.90 0.45
65° C 1 min/ 125° C 2.5 min/ 120° C 2.5 min 221 110.5 223 111 0.90 0.45
65° C 10 min/ 125° C 2.5 min/ 200° C 2.5 min N/A N/A 222 111
65° C 10 min/ 125° C 2.5 min/ 120° C 2.5 min N/A N/A 222 112
65° C 1 min/ 95° C 2.5 min/ 200° C 2.5 min 223 111 223 111 0 0
65° C 1 min/ 95° C 2.5 min/ 120° C 2.5 min 222 110.5 222 111 0 0.45
65° C 10 min/ 95° C 2.5 min/ 200° C 2.5 min 222 111 222 111 0 0
65° C 10 min/ 95° C 2.5 min/ 120° C 2.5 min 222 111 222 111 0 0

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