Tema 8. Tecnología y Fabricación de CIs

TEMA 8 Tecnología y fabricación de CIs G. Fabricación de dispositivos http://jas.eng.buffalo.edu/education/fab/pn/diodeframe.html http://jas.eng.buffalo.edu/education/fab/nmos/nmos.html 1

I. Fabricación de un transistor MOSFET MOSFET Tipo N L = longitud del canal W = anchura del canal 2

1. The device fabrication steps are shown for n-channel Metal-Oxide-Semiconductor (MOS) Field Effect Transistor (FET). All photolithography processes are shown by means of animation. The steps shown here are the most detailed and serve as basis for the next few applets showing the device fabrication. 3

2. For NMOS process, the starting material is a P-type lightly doped, <100>-oriented, polished silicon wafer. The first step is to form the SiO 2 layer (0.5-1um thick) by thermal oxidation. The oxidation temperature is generally in the range of 900-1200 degree C, and the typical gas flow rate is about 1cm/s. Primera etapa: formación de las islas de fuente y drenador 4

3. Following oxidation, several drops of positive Photoresist are dropped on the wafer. The wafer is spun at about 3000rpm to be uniformly spread out. After the spinning step, the wafer is given a pre-exposure baking (80-100 degree C) to remove the solvent from the PR film and improve adhesion to the substrate. Primera etapa: formación de las islas de fuente y drenador Primer proceso fotolitográfico (I) 5

4. Third step is to define the active area (Drain and Source regions) by photolithography. The PR layer not covered by the mask undergoes a chemical change by UV light and is removed by the spraying the wafer with the developing solution. The final remaining PR is a copy of the pattern on the mask. Finally, the wafer is rinsed and spin-dried, and then baked again so that the PR can resist the strong acid used to etch the exposed oxide layer. Primera etapa: formación de las islas de fuente y drenador Primer proceso fotolitográfico (II) 6

5. For SiO 2 etching, HydroFluoric(HF) acid is usually used because it attacks oxide, but not silicon or PR. Therefore, the HydroFluoric(HF) acid etches away the oxide in the openings in the PR, and stops at the silicon surface. Primera etapa: formación de las islas de fuente y drenador Primer proceso fotolitográfico (III) 7

6. After SiO2 etching: PR is stripped by using either a solvent (Aceton) or a plasma oxidation, leaving behind an insulator pattern that is the same as the opaque image on the mask. Primera etapa: formación de las islas de fuente y drenador Primer proceso fotolitográfico (IV) 8

7. Next, a two-step diffusion process is used to form drain and source regions: A Phosphorus predeposition is first formed under a Constant-Surface-Concentration Condition(CSCC) Is followed by a drive-in diffusion under a Constant-Total-Dopant Condition(CTDC). Finally, a thin layer of Phosphosilicate Glass on the wafer is removed by HF. Primera etapa: formación de las islas de fuente y drenador 9

8. After the forming the drain and source regions, additional oxide layer is grown from thermal oxidation as before. IMPORTANT: The Phosphorus spreads out by diffusion during this furnace operation, but the concentration are still much higher than that of the substrate doping. Segunda etapa: formación del óxido de campo 10

9. The second photolithography process is done to remove the oxide, defining a gate region. The same procedure (PR Drop ->Spinning ->Pre-Baking ->Mask Alignment->UV Exposure -> PR Developing -> Rinsing and Drying -> Post-Baking -> Oxide Etching) as in Lithography #1 is used. TERCERA etapa: definición de la región de puerta (GATE) Segundo proceso fotolitográfico (I) 11

10. The second photolithography process is done to remove the oxide, defining a gate region. IDEM. TERCERA etapa: definición de la región de puerta (GATE) Segundo proceso fotolitográfico (II) 12

11. The second photolithography process is done to remove the oxide, defining a gate region. IDEM TERCERA etapa: definición de la región de puerta (GATE) Segundo proceso fotolitográfico (III) 13

12. The second photolithography process is done to remove the oxide, defining a gate region. IDEM. TERCERA etapa: definición de la región de puerta (GATE) Segundo proceso fotolitográfico (IV) 14

13. After the second photolithography, a very thin gate oxide layer (a few hundred angstroms) is grown by thermal oxidation. CUARTA etapa: Crecimiento del óxido nativo de puerta (GATE) 15

14. The third photolithography process is done to remove the oxide, defining contact holes for the Source and Drain contacts. The same procedure(pr Drop -> Spinning -> Pre-Baking ->Mask Alignment ->UV Exposure -> PR Developing -> Rinsing and Drying -> Post-Baking -> Oxide etching) as in lithography #1 is used. Quinta etapa: definición de contactos de fuente y drenador Tercer proceso fotolitográfico (I) 16

15. The third photolithography process is done to remove the oxide, defining contact holes for the Source and Drain contacts. IDEM Quinta etapa: definición de contactos de fuente y drenador Tercer proceso fotolitográfico (II) 17

16. The third photolithography process is done to remove the oxide, defining contact holes for the Source and Drain contacts. IDEM Quinta etapa: definición de contactos de fuente y drenador Tercer proceso fotolitográfico (III) 18

17. The third photolithography process is done to remove the oxide, defining contact holes for the Source and Drain contacts. IDEM Quinta etapa: definición de contactos de fuente y drenador Tercer proceso fotolitográfico (IV) 19

18. A metal such as Aluminum is then evaporated on the whole substrate surface (a few thousand angstrom thick) under high-vacuum condition. This method is attractive because it is simple and inexpensive and produces no ionizing radiation. The Al layer will form electrical contacts later. SEXTA etapa: deposición de aluminio 20

19. The final lithography process is done to remove the Al-layer, defining a contact pattern. The same procedure( PR Drop -> Spinning -> Pre-Baking ->Mask Alignment ->UV Exposure ->PR Developing->Rinsing and Drying->Post-Baking ->Aluminum Etching) as in lithography #1 is used. Séptima etapa: Definición exacta de contactos en puerta, fuente y drenador Cuarto proceso fotolitográfico (I) 21

20. The final lithography process is done to remove the Al-layer, defining a contact pattern. IDEM Séptima etapa: Definición exacta de contactos en puerta, fuente y drenador Cuarto proceso fotolitográfico (II) 22

21. The final lithography process is done to remove the Al-layer, defining a contact pattern. IDEM Séptima etapa: Definición exacta de contactos en puerta, fuente y drenador Cuarto proceso fotolitográfico (III) 23

22. Fabricación de dispositivo MOSFET completada. 24