Micro & nanofabrica,on

Transcription

1 Micro & nanofabrica,on

2 Photolitography : - contact - projec,on Electron Beam lithography (EBL) Nano imprint lithography Etching

3 Contact Photolithography Substrate (e.g. Silicon wafer) Photoresist spinning UV exposure (changes the chemistry of the resist so that it becomes soluble in the photoresist developer) Photomask (usually chromium on glass) in contact with resist Resist development Etching of substrate Photoresist removal Metal deposi,on Photoresist removal

4 Spinning photoresist hkps:// v=3m4wmyobxzy The thickness of photoresist on the substrate is determined by spinning speed

5 Contact Photolithography Substrate (e.g. Silicon wafer) Photoresist spinning UV exposure (changes the chemistry of the resist so that it becomes soluble in the photoresist developer) Photomask (usually chromium on glass) in contact with resist Resist development Etching of substrate Photoresist removal Metal deposi,on Photoresist removal

6 Contact Photolithography Resolu,on (smallest feature one can create) d 1µm Great for research labs (cheap) but not used in produc,on, mainly because: - the contact induces surface damage in both mask and substrate - Difficult to obtain an homogeneous light illumina,on for the big substrate areas used in industry (12 ).

7 Projec4on Photolithography Instead, projec,on photolithography is used in industry. The pakern size can be reduced compared to the size on the Cr mask and the pakern can be repeated many,mes on different loca,on on the substrate. It is an expensive process. The resolu,on is propor,onal to the light source wavelength λ.

8 Moore s law The number of transistors in an integrated circuit doubles every 2 years. S,ll valid today. Requires smaller and smaller transistors. ieee.org

9 Projec4on Photolithography The resolu,on is propor,onal to the light source wavelength λ. d = 0.61 λ n sinα = 0.61 λ NA To make smaller features: decrease the wavelength (e.g. use deep UV instead of UV). Limit: 193 nm (lower: glass not transparent) Improvement in op,cs (increase NA), exposure tricks, resists, etc nm node in nm node expected in 2017

10 Electron Beam lithography An electron beam is scanned on the surface

11 Electron Beam lithography Substrate (e.g. Silicon wafer) Electron beam resist Resolu,on 10 nm Electron beam exposure (serial process, similar to wri,ng) Resist development Then etch or metal deposi,on (same as for ager photolithography) Drawback: slow, expensive

12 1) Thermal-NIL Nano Imprint Lithography (NIL) Coat substrate with thermoplas,c polymer (= a polymer that is moldable above a specific temperature and solidifies upon cooling. ) Nanoimprint mold (usually in silicon, made using EBL and with an,s,cking coa,ng) Force Heat and Press Resolu,on 20 nm Cool down and separate Etch residual resist Then etch or metal deposi,on (same as for ager photolithography)

13 2) UV-NIL Nano Imprint Lithography (NIL) Deposit UV sensi,ve resist on the substrate Nanoimprint mold (usually in quartz, made using EBL and with an,s,cking coa,ng) UV Fill and expose Resolu,on 20 nm Separate Etch residual resist Then etch or metal deposi,on (same as for ager photolithography)

14 Nano Imprint Lithography (NIL) - Can pakern large areas - An imprint mold can be used thousands of,mes - Most of the cost is in the mold fabrica,on

15 Isotropic etch/anisotropic etch: Isotropic etch: etches at the same rate in all direc,on. Results in rounded etch profile. Usually wet etch (liquid) Δz=Δx Δz Δx

16 Isotropic etch/anisotropic etch: Anisotropic etch: etches at a different rate in z and x. Most ogen etches fast in z and slow in x. Results in deeper etch (see following exercises). Usually plasma (ion bombarding the substrate ver,cally) Example: Δz=10Δx Δx Δz

17 Top-down or bottom-up?

18 Before the lab visits! NANOWIRES

19 NANOWIRES: our specialty in Lund

20 Nanotrådar Ordnade rader av GaP nanoträd Nanotrådar odlade från ordnade rader med Au-partiklar definierade med elektronstrålelitografi

21 Neurons on GaP nanowire surfaces Scale bar 1 µm