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Solar Cell and NMOS Transistor Process EE290G Joey Greenspun.

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Presentation on theme: "Solar Cell and NMOS Transistor Process EE290G Joey Greenspun."— Presentation transcript:

1 Solar Cell and NMOS Transistor Process EE290G Joey Greenspun

2 An SOI Process For Fabrication of Solar Cells, Transistors and Electrostatic Actuators Power, computation, actuation Process geared towards creation of microrobots Two processes Metal gate NMOS + Solar 25 V beak down voltages 11% efficient Poly gate CMOS + Solar 50 V break down voltages 14% efficient Bellew, Hollar, Pister Transducers ‘03 400x400 um 2 Solar Cell 2 Stage NMOS Buffer Inchworm Clutch

3 Considerations for Solar + Transistor Process Power microrobot actuators Inchworm needs ~50V V oc for Si is ~.5V Controlled by SCµM GPIOS currently 3.3V Transistors must have appropriate V t 0.5V

4 Simulated Solar Cell 1.ISO - Etch isolation 2.Grow oxide liner 3.Deposit Nitride 4.Deposit Poly 5.CMP 6.NPLUS Implant 7.NMINUS Implant 8.PPLUS Implant 9.Dopant activation 10.CONT etch 11.METAL, Al liftoff Process Steps

5 Isolation 40 um SOI wafer Boron doped to 10 -15 Grow wet oxide (protect Si) Pattern with ISO, STS-OX (Oxide RIE), STS2 (DRIE) 1.ISO - Etch isolation 2.Grow oxide liner 3.Deposit Nitride 4.Deposit Poly 5.CMP 6.NPLUS Implant 7.NMINUS Implant 8.PPLUS Implant 9.Dopant activation 10.CONT etch 11.METAL, Al liftoff Process Steps 2um Line/Space Design Rule

6 Isolation Oxide for clean interface Nitride for dielectric strength, and robustness to HF Poly deposits quickly, and much lower stress than Si x N y 1.ISO - Etch isolation 2.Grow oxide liner 3.Deposit Nitride 4.Deposit Poly 5.CMP 6.NPLUS Implant 7.NMINUS Implant 8.PPLUS Implant 9.Dopant activation 10.CONT etch 11.METAL, Al liftoff Process Steps

7 Chemical Mechanical Polishing Alternative to CMP: Blanket plasma etch, stopping on the nitride Hot phosphoric acid to remove nitride Hydrofluoric acid to remove protective wet oxide 1.ISO - Etch isolation 2.Grow oxide liner 3.Deposit Nitride 4.Deposit Poly 5.CMP 6.NPLUS Implant 7.NMINUS Implant 8.PPLUS Implant 9.Dopant activation 10.CONT etch 11.METAL, Al liftoff Process Steps

8 Inplants Solar Cell on the left NMOS on the right 1.ISO - Etch isolation 2.Grow oxide liner 3.Deposit Nitride 4.Deposit Poly 5.CMP 6.NPLUS Implant 7.NMINUS Implant 8.PPLUS Implant 9.Dopant activation 10.CONT etch 11.METAL, Al liftoff Process Steps 2um Line/Space Design Rule

9 Dopant Drive in and Activation Drive in and activate dopants Choose oxide thickness for AR coating and gate dielectric Solar Cell on the left NMOS on the right 1.ISO - Etch isolation 2.Grow oxide liner 3.Deposit Nitride 4.Deposit Poly 5.CMP 6.NPLUS Implant 7.NMINUS Implant 8.PPLUS Implant 9.Dopant activation 10.CONT etch 11.METAL, Al liftoff Process Steps

10 Contacts Etch contact holes in oxide Solar Cell on the left NMOS on the right 1.ISO - Etch isolation 2.Grow oxide liner 3.Deposit Nitride 4.Deposit Poly 5.CMP 6.NPLUS Implant 7.NMINUS Implant 8.PPLUS Implant 9.Dopant activation 10.CONT etch 11.METAL, Al liftoff Process Steps 2um Line/Space Design Rule

11 Metalization Aluminum liftoff (gates might be hard) Alternative, sputter and etch metal Solar Cell on the left NMOS on the right 1.ISO - Etch isolation 2.Grow oxide liner 3.Deposit Nitride 4.Deposit Poly 5.CMP 6.NPLUS Implant 7.NMINUS Implant 8.PPLUS Implant 9.Dopant activation 10.CONT etch 11.METAL, Al liftoff Process Steps 2um Line/Space Design Rule

12 Metalization Aluminum liftoff (gates might be hard) Alternative, sputter and etch metal Solar Cell on the left NMOS on the right 1.ISO - Etch isolation 2.Grow oxide liner 3.Deposit Nitride 4.Deposit Poly 5.CMP 6.NPLUS Implant 7.NMINUS Implant 8.PPLUS Implant 9.Dopant activation 10.CONT etch 11.METAL, Al liftoff Process Steps 2um Line/Space Design Rule

13 MEMS Optional DRIE to pattern MEMS structures AR coating will be etched during MEMS release Switch to Nitride? Germanium protection possible, but process intensive 1.ISO - Etch isolation 2.Grow oxide liner 3.Deposit Nitride 4.Deposit Poly 5.CMP 6.NPLUS Implant 7.NMINUS Implant 8.PPLUS Implant 9.Dopant activation 10.CONT etch 11.METAL, Al liftoff 12. MEMS Process Steps 2um Line/Space Design Rule

14 Preliminary Simulation Results 200x200 um 2 Solar Cell Simulation V oc =.63 V FF = 82.7% Efficiency = 10.0% Colby’s 200x200 um 2 Solar Cell V oc =.64 V FF = 64.4% Efficiency = ~8%

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