Advanced resists for e-beam lithography: processing, exposure and characterization (Part II)

Transcription

1 Advanced resists for e-beam lithography: processing, exposure and characterization (Part II) Dra. Mariana Pojar de Melo Prof. Dr. Antonio Carlos Seabra Dep. Eng. de Sistemas Eletrônicos Escola Politécnica da USP M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/ Processing Steps for Lithography Substrate cleaning Dehydration Adhesion Promoter Resist Spinning Pre-bake Plasma Flash Development Post-exposure Exposure Etching Hard Deposition (Lift-off) M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 44

2 Plasma Flash O plasma for 5s Very tricky! Before After Seabra, A.C. Uso de Resistes Amplificados Quimicamente e Sililação em Litografia pro Feixe de Elétrons, Tese de Doutorado, Escola Politecnica da USP (1997.). M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/ Processing Steps for Lithography Substrate cleaning Dehydration Adhesion Promoter Resist Spinning Pre-bake Plasma Flash Development Post-exposure Exposure Etching Hard Deposition (Lift-off) M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 46

3 Hard (or post bake, HB or PB) Enhances profile stability during subsequent steps like plasma etching by careful thermal crosslinking M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/ Processing Steps for Lithography Substrate cleaning Dehydration Adhesion Promoter Resist Spinning Pre-bake Plasma Flash Development Post-exposure Exposure Etching Hard Deposition (Lift-off) M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 48

4 Transferring patterns to the sample Etching (wet or dry) Metal and resist deposition resist metal Depositions Lift-off resist resist 1 Direct write resist resist 1 Exposure resist metal Development 1 resist resist1 Resist development metal Development resist resist 1 wet Etching metal Dry metal Deposition metal Lift-off M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/ Reactive Etching ETCHING FLUX PRESSURE POWER/ RESISTS TONE GAS RATE OR (sccm) (mtorr) VOLTAGE SELECTIVITY PMMA positive CF W/ 00V 38nm/min C F W 30nm/min SF W 130nm/min ZEP-50 Positive CF W/ 00V 5.4nm/min C F W 0nm/min SF W 75nm/min HSQ Negative SiCl 4 /Ar 4/ W 11nm/min SF 6 /He 1.5/ W 9nm/min Calixarene Negative MC6AOAc CF W/ 00V 10nm/min Si CF W/ 00V 9nm/min SF 6 /He 1.5/ W 16nm/min SiO C F W 3nm/min M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 50

5 Lift-off using a Bilayer (ZEP50/PMGI) AFTER LIFT-OFF: For nanolithography, the production of highresolution objects requires a precise control of the undercut length. Cr line -90nm 90nm metal deposition ZEP-50 PMGI Cr line - 70nm Deyu et al., A ZEP 50-LOR bilayer Resist Lift-off Process by e- beam lithography for nanometer pattern Transfer, IIIE, 007. M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/ Proximity Effect Electron Scattering in the Substrate and Resists M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 5

6 Proximity Effect Can be modeled by a double Gaussian : 1 1 I( r) e (1 ) r r e M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/ May be a matrix of 50,000 x 50,000 points Proximity Effect Silicon and PMMA resist (thickness of 0,5 µm) = 0.75 (independent of beam energy) kev = 15 / 0 / 5 / 30 / 35 = 1.4 /. /.8 / 4.0 / 5.8 GaAs and PMMA resist (thickness of 0,5 µm) = 1.4 (independent of beam energy) kev = 15 / 0 / 5 / 30 / 35 = 0.7 / 1.0 / 1.3 / 1.8 /. M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 54

7 Proximity Effect Proximity Effect Parameters:,, M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/ Nano Proximity Effect Software Photonic crystal 0nm, pitch 700nm Images from Raith GMBh uncorrected M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 56

8 Nano Proximity Effect Software Finger structure 50 nm lines 50 nm gaps Images from Raith uncorrected M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/ Nano Proximity Effect Software Finger structure line scan results 50.1 nm 51.1 nm M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 58

9 Strategies to minimize the proximity effect Use thin resists Use thin s Adjust the acceleration voltage Divide the geometry into sub-structures with different doses M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/ Proximity Effect Beam Accel. Beam Diam. Voltage spot Current Substrate Resist (nm) (kv) size (pa) α (μm) β (μm) η (μm) Si / SiO PMMA 5 10 nm Si / SiO ZEP 50A (30nm) 5 10 nm spin valve / Si / SiO ZEP 50A (30nm) 5 10 nm Si HSQ (40nm) 10 nm 50 8 Si HSQ (40nm) 10 nm Si PMMA (10nm) 6, Si PMMA (10nm) Si PMMA (10nm) Si PMMA (10nm) Si PMMA (5nm) 6, Si PMMA (5nm) Si PMMA (5nm) Si PMMA (5nm) Si PMMA (45nm) 6, Si PMMA (45nm) Si ZEP 50A (30nm) M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 60

10 Recommendations SOme words about resists Clearly identifiy the process to be used after exposure Evaporation/Sputtering/... Etching (Wet/Dry) PMMA has high resolution (~10nm) Barely stands dry etching, it almost evaporates! Good only for wet etching or liftoff M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/ Recommendations Alignment Marks Must be visible under optical microscopes AND electron microscopes Crosses with about 80x80m dimension and arms of about 15m are great for our purposes Should be patterned in materials with different molecular weight compared to (gives good contrast in secondary electrons detection) or made like holes In In next level aligned M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 6