E-beam lithography on transparent substrates: challenges and results

Transcription

1 E-beam lithography on transparent substrates: challenges and results Thomas Händel

2 Outline Motivation Material properties Experimental samples, process and electron-beam lithography system Experimental steps and results Conclusion Acknowledgement Beams & More 2011 page 2

3 Motivation Suppliers view Large variety of transparent substrates for the semiconductor industry Among them are Quartz, Boron Nitride (BN), Gallium Nitride (GaN), Sapphire (Crystal of Al 2 O 3 ), Silicon Carbide (SiC) and others Check and ensure the functionality of the electron-beam lithography system from the automatic handling until the exposure of the substrates Requests from potential and existing customers Beams & More 2011 page 3

4 Motivation Customers view GaN material of choice for applications in high-power and high-frequency as well as optoelectronic devices Increased product development in the commercial market such as wireless infrastructure, cable television, satellite and power electronics* Development of high-performance GaN-on-SiC power transistors at NXP Semiconductors** Excellent thermal properties of SiC Higher operating temperatures High electron drift velocity and large electrical field breakdown of GaN Increase in extended frequency range, efficiency and power density performance Development of High Brightness Light-Emitting Diodes (HB LED s) at Optogan** Large band gap and stimulated emission at room-temperature Enhanced power efficiency and highest light intensity * Source: CS Europe, Frankfurt/Main, March 2011, ** Source: Compound Semiconductor Magazine, August/September 2011 Beams & More 2011 page 4

5 Outline Motivation Material properties Experimental samples, process and electron-beam lithography system Experimental steps and results Conclusion Acknowledgement Beams & More 2011 page 5

6 Material properties Si GaAs GaN SiC Density 1, g/cm Dielectric constant Refractive index 1, Opaque Opaque Transparent Transparent Linear thermal expansion, /K Resistivity 1, cm up to 10 5 up to 10 8 up to up to Thermal conductivity 1, W/cm K Young s module 1, GPa Current wafer size, mm up to 450 up to 150 up to 100 up to at 300K 2 infrared refractive index - Values vary depending on modification and source Beams & More 2011 page 6

7 Absorbed energy, ev/µm³ Material properties (Cont.) 1,E+06 1,E+05 1,E+04 1,E+03 1,E+02 1,E+01 1,E+00 1,E-01 1,E-02 Proximity function for 50keV electrons in 170nm PMMA 950k Monte Carlo Simulation GaN / SiC GaAs Si 1,E-03 0,01 0, Radius, µm Beams & More 2011 page 7

8 Material properties (Cont.) Back scattering on GaAs and GaN larger than on Si substrates Individual proximity correction function required for each substrate material Adaption of proximity correction is a default procedure in electron-beam lithography No special requirements on transparent substrates Beams & More 2011 page 8

9 Outline Motivation Material properties Experimental samples, process and electron-beam lithography system Experimental steps and results Conclusion Acknowledgement Beams & More 2011 page 9

10 Experimental samples Substrate number Material Diameter, mm Total thickness, mm #1 GaN on SiC #2 GaN on SiC #3 GaN on SiC #4 SiC Substrate #2 GaN 2mm Substrate #4 SiC 363mm SiC 400mm Beams & More 2011 page 10

11 Process Substrate #2 Au PMMA 950k GaN SiC Substrate #4 Au PMMA 950k 20nm 170nm 2mm 363mm 20nm 170nm Process steps 1. Coating: 170nm PMMA 950k, 180 C, 3min 2. Au evaporation (Anti-charging layer) 3. Exposure 4. Au removal 5. Development: MIBK:IPA=1:1 6. Rinse: IPA SiC 400mm Beams & More 2011 page 11

12 Vistec SB250 Series Cost-effective system for mask and wafer direct writing Electron beam shape VSB Acceleration voltage 50kV Current density up to 20A/cm² Maximum substrate size wafers up to 200mm masks up to 7 inch Stage travel range 210 x 210mm² Laser interferometer / 1024 Minimum feature size < 50nm 25nm (HSQ) Source: Ferdinand-Braun-Institut für Höchstfrequenztechnik, Berlin, Germany Beams & More 2011 page 12

13 Outline Motivation Material properties Experimental samples, process and electron-beam lithography system Experimental steps and results Conclusion Acknowledgement Beams & More 2011 page 13

14 Experimental steps 1. Check and ensure the functionality of a. Sensors to be used for substrate recognition and tracking b. Prealigner to be used for substrate alignment c. Fully automatic substrate handling d. Electrostatic chuck and height measurement e. Process f. Exposure 2. Inspection and measurement Beams & More 2011 page 14

15 CCD signal Substrate alignment Fully automated prealignment Second flat Main flat Encoder counts Alignment results Alignment offset 10µm Alignment angle 0.4mrad Beams & More 2011 page 15

16 Fully automated Shaped Beam Systems Example: SB250 Series 200mm platform Cassette-to-cassette Material handling for mask and wafer substrates Beams & More 2011 page 16

17 Electrostatic chuck and height measurement Planation of wafer surface Substrate #2 Substrate #4 Height mapping difference* between un-chucked and chucked wafer surface on * Each height mapping interpolated by a 4 degree polynomial electrostatic chuck Beams & More 2011 page 17

18 Exposure results Core and pad of gates Substrate #2 101nm 101nm 100nm core in 170nm PMMA 950k Beams & More 2011 page 18

19 Exposure results Direct Write Overlay Accuracy Pattern for first exposure run Cross Cross width 1.4mm Cross length 24mm Cross step 27mm Pattern for second exposure run Four Angles Width 1.4mm Distance to cross 2.6mm No alignment marks used during exposure Beams & More 2011 page 19

20 Exposure results Direct Write Overlay Accuracy Substrate #4 17nm 18nm No alignment marks used during exposure Beams & More 2011 page 20

21 Exposure results Direct Write Overlay Accuracy 76mm GaAs Wafer 15nm 13nm No alignment marks used during exposure Beams & More 2011 page 21

22 Exposure results Contact holes Substrate #2 102nm 100nm contact holes in 170nm PMMA 950k Beams & More 2011 page 22

23 Exposure results Resolution Substrate #2 Lines 50nm half pitch in 170nm PMMA 950k Beams & More 2011 page 23

24 Outline Motivation Material properties Experimental samples, process and electron-beam lithography system Experimental steps and results Conclusion Acknowledgement Beams & More 2011 page 24

25 Conclusion We demonstrated successfully the functionality for Vistec Shaped Beam Systems on transparent substrates Sensor adjustment for recognition of opaque and transparent materials Fully automated handling including substrate alignment Electrostatic chucking and height measurement Exposure performance in the same range as on GaAs substrates Beams & More 2011 page 25

26 Acknowledgement This presentation had never been done without the cooperation and support of my colleagues at GmbH. Special thanks to Monika Böttcher, Dr. Helder Alves and Thomas Keil Beams & More 2011 page 26

27 Thank you for your attention! Beams & More 2011 page 27