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Final pptmos Final pptmos Presentation Transcript

  • N MOS Fabrication Process Sun Tiefeng: 2008054238 Bhuvan Adhikari 2009002702
  • INTRODUCTION Photolithography Etching NMOS Fabrication process • Gate • Source and Drain • Vias • Metal Contacts
  • Part 1 What is photolithography What is etchingPart 2 How photolithography and etching are used when we make MOSFET
  • What is photo-lithographyPhotolithography a process used in micro-fabrication to pattern parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photo-mask to a light- sensitive chemical "photo-resist", or simply "resist," on the substrate.
  • TYPES OF RESIST• Positive resiststhe resist is exposed with UVlight wherever the underlyingmaterial is to be removed.•Negative resists :the negative resist remains onthe surface wherever it isexposed
  • What is etchingTo produce circuit features, the resist patterns must be transferred into the underlying layers comprising the device.The pattern transfer is accomplish by an etching process that selectively removes unmasked portions of a layer
  • The two types of etching processesWet etch processescan lead to undercuttingresult in an isotropic etch profilethe vertical etch rate is equal tothe horizontal etch rate
  • The two types of etching processesDry etchingOne of the most widely usedUse plasma generated free radicalsRemove material only from the area dictated by photo-resist Provide the ability to control sidewall anisotropic pattern etching
  • N-MOS Fabrication Process Si-substrate Fig. (1) Pure Si single crystal ----------------------- ------------------------- -------------------------- -------------------------- Fig. (2) P-type impurity is lightly doped
  • N-MOS Fabrication Process Thick SiO2 (1 µm) ----------------------- ------------------------- -------------------------- --------------------------Fig. (3) SiO2 Deposited over si surface Photoresist Thick SiO2 (1 µm) ----------------------- ------------------------- -------------------------- -------------------------- Fig. (4) Photoresist is deposited over SiO2 layer
  • N-MOS Fabrication Process UV Light Mask-1 Photoresist Thick SiO2 (1 µm)------------------------------------------------------------------- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ----------------------------------- Mask-1 is used to expose the SiO2 where S, D and G is to be formed. Fig. (5) Photoresist layer is exposed to UV Light through a mask
  • N-MOS Fabrication Process Polymerised Photoresist----------------------------------------------------------------- Thick SiO2-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - (1 µm)---------------------------------- Fig. (6) Developer removes unpolymerised photoresist. It will cause no effect on Si surface
  • N-MOS Fabrication Process Thick SiO2 (1 µm)------------------------------------------------------------------- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ----------------------------------- Fig. (7) Etching [HF acid is used] will remove SiO2 layer which is in direct contact with etching solution
  • N-MOS Fabrication Process Thick SiO2 (1 µm)------------------------------------------------------------------- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ----------------------------------- Fig. (7) unpolymerised photoresist is also etched away [using H2SO4]
  • N-MOS Fabrication Process Thin SiO2 (0.1 µm) Thick SiO2 (1 µm)------------------------------------------------------------------- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -----------------------------------Fig. (8) A thin layer of SiO2 grown over the entire chip surface
  • N-MOS Fabrication Process Polysilicon layer (1 – 2 µm)----------------------------------------------------------------- Thin SiO2-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO2 (0.1 µm) (1 µm)----------------------------------Fig. (9) A thin layer of polysilicon is grown over the entire chip surface to form GATE
  • N-MOS Fabrication Process Photoresist Polysilicon layer------------------------------- Thin SiO2---------------------------------- (0.1 µm)-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO2---------------------------------- (1 µm)Fig. (10) A layer of photoresist is grown over polysilicon layer
  • N-MOS Fabrication Process UV Light Mask-2------------------------------------------------------------------- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ----------------------------------- Mask-2 is used to deposit Polysilicon to form gate. Fig. (11) Photoresist is exposed to UV Light
  • N-MOS Fabrication Process Polysilicon Thin SiO2 (0.1 µm) Thick SiO2 (1 µm)------------------------------------------------------------------- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -----------------------------------Fig. (12) Etching will remove that portion of Thin SiO2 which is not exposed to UV light
  • N-MOS Fabrication Process Polysilicon used as GATE (1 – 2 µm) Thin SiO2 (0.1 µm) Thick SiO2 (1 µm)------------------------------------------------------------------- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ----------------------------------- Fig. (13) Polymerised photoresist is also stripped away
  • N-MOS Fabrication Process GATE SOURCE DRAIN Thin SiO2 (0.1 µm) Thick SiO2 (1 µm)- - - - - - - - - - - - -- ---- - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - --- - - - - - - - - - - - - n+ - - - - - -n+ - - - - - - - - - - -- ------------------------------------ Fig. (14) n+ Doping to form SOURCE and DRAIN
  • N-MOS Fabrication Process Step - Metallization- - - - - - - - - - - - -- ---- - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - --- - - - - - - - - - - - - n+ - - - - - -n+ - - - - - - - - - - -- -- Thick SiO2 Thick SiO2 (1 µm) (1 µm)---------------------------------- Fig. (15) A thick layer of SiO2 (1 µm) is again grown.
  • N-MOS Fabrication Process Step - Metallization UV Light Mask-3 Mask-3 is used to make contact cuts for S, D and G. Photoresist - - - - - - - - - - - - -- ---- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - - -- - - - - - - - - - - - - n+ - - - - - -n+ - - - - - - - - - - -- -- Thick SiO2 Thick SiO2 (1 µm) (1 µm) ----------------------------------Fig. (16) Photoresist is grown over thick SiO 2. Selected areas of the poly GATE and SOURCE and DRAIN are exposed where contact cuts are to be made
  • N-MOS Fabrication Process Step - Metallization Mask-3 Photoresist - - - - - - - - - - - - -- ---- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - - -- - - - - - - - - - - - - n+ - - - - - -n+ - - - - - - - - - - -- -- Thick SiO2 Thick SiO2 (1 µm) (1 µm) ----------------------------------Fig. (17) The region of photoresist which is not exposed by UV light will become soft. This unpolymerised photoresist and SiO2 below it are etched away.
  • N-MOS Fabrication Process Step - Metallization Mask-3 Photoresist - - - - - - - - - - - - -- ---- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - - -- - - - - - - - - - - - - n+ - - - - - -n+ - - - - - - - - - - -- -- Thick SiO2 Thick SiO2 (1 µm) (1 µm) ----------------------------------Fig. (18) The contact cuts are formed for S, D and G (hardened photoresist is stripped away).
  • N-MOS Fabrication Process Step - Metallization Metal (1µm) - - - - - - - - - - - - -- ---- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - - -- - - - - - - - - - - - - n+ - - - - - -n+ - - - - - - - - - - -- -- Thick SiO2 Thick SiO2 (1 µm) (1 µm) ----------------------------------Fig. (19) Metal (aluminium) is deposited over the surface of whole chip (1 µm thickness).
  • N-MOS Fabrication Process Step - Metallization Photoresist Metal (1µm)- - - - - - - - - - - - -- ---- - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - --- - - - - - - - - - - - - n+ - - - - - -n+ - - - - - - - - - - -- -- Thick SiO2 Thick SiO2 (1 µm) (1 µm)---------------------------------- Fig. (20) Photoresist is deposited over the metal.
  • N-MOS Fabrication Process Step - Metallization UV Light Mask-4 Photoresist Metal (1µm) - - - - - - - - - - - - -- ---- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - - -- - - - - - - - - - - - - n+ - - - - - -n+ - - - - - - - - - - -- -- Thick SiO2 Thick SiO2 (1 µm) (1 µm) ---------------------------------- Mask-4 is used to deposit metal in contact cuts of S, D and G.Fig. (21) UV Light is passed through Mask-4 (with a aim of removing all metal other than metal in contact-cuts).
  • N-MOS Fabrication Process Step - Metallization Mask-4 Photoresist Metal (1µm) - - - - - - - - - - - - -- ---- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - - -- - - - - - - - - - - - - n+ - - - - - -n+ - - - - - - - - - - -- -- Thick SiO2 Thick SiO2 (1 µm) (1 µm) ----------------------------------Fig. (22) Photoresist and metal which is not exposed to UV light are etched away.
  • N-MOS Fabrication Process Step - Metallization SOURCE DRAIN GATE- - - - - - - - - - - - -- ---- - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - -- - - - - -- - - - - - - - - - - --- - - - - - - - - - - - - n+ - - - - - -n+ - - - - - - - - - - -- ------------------------------------ Fig. (23) Final n-MOS Transistor
  • THANK YOU