n-MOS Fabrication Process

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N MOS Fabrication Process Yogesh Misra Mody Institute of Technology & Science (Deemed University) Faculty of Engineering & Technology Sikar [Raj.]

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (1) Pure Si single crystal Si-substrate Fig. (2) P-type impurity is lightly doped - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (3) SiO 2 Deposited over si surface Fig. (4) Photoresist is deposited over SiO 2 layer Thick SiO 2 (1 µm) Photoresist Thick SiO 2 (1 µm) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (5) Photoresist layer is exposed to UV Light through a mask Photoresist Thick SiO 2 (1 µm) UV Light Mask-1 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Mask-1 is used to expose the SiO 2 where S, D and G is to be formed.

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (6) Developer removes unpolymerised photoresist. It will cause no effect on Si surface Polymerised Photoresist Thick SiO 2 (1 µm) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (7) Etching [HF acid is used] will remove SiO2 layer which is in direct contact with etching solution Thick SiO 2 (1 µm) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (7) unpolymerised photoresist is also etched away [using H2SO4] Thick SiO 2 (1 µm) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (8) A thin layer of SiO 2 grown over the entire chip surface Thick SiO 2 (1 µm) Thin SiO 2 (0.1 µm) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (9) A thin layer of polysilicon is grown over the entire chip surface to form GATE Thick SiO 2 (1 µm) Thin SiO 2 (0.1 µm) Polysilicon layer (1 – 2 µm) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (10) A layer of photoresist is grown over polysilicon layer Thick SiO 2 (1 µm) Thin SiO 2 (0.1 µm) Polysilicon layer Photoresist - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (11) Photoresist is exposed to UV Light UV Light Mask-2 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Mask-2 is used to deposit Polysilicon to form gate.

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (12) Etching will remove that portion of Thin SiO2 which is not exposed to UV light Thick SiO 2 (1 µm) Thin SiO 2 (0.1 µm) Polysilicon - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (13) Polymerised photoresist is also stripped away Thick SiO 2 (1 µm) Thin SiO 2 (0.1 µm) Polysilicon used as GATE (1 – 2 µm) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

N-MOS Fabrication Process:

N-MOS Fabrication Process Fig. (14) n + Doping to form SOURCE and DRAIN - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO 2 (1 µm) Thin SiO 2 (0.1 µm) GATE - - - - - n+ - - - - - n+ SOURCE DRAIN

N-MOS Fabrication Process Step - Metallization:

N-MOS Fabrication Process Step - Metallization Fig. (15) A thick layer of SiO2 (1 µm) is again grown. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO 2 (1 µm) - - - - - n+ - - - - - n+ Thick SiO 2 (1 µm)

N-MOS Fabrication Process Step - Metallization:

N-MOS Fabrication Process Step - Metallization 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 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO 2 (1 µm) - - - - - n+ - - - - - n+ Thick SiO 2 (1 µm) Photoresist Mask-3 UV Light Mask-3 is used to make contact cuts for S, D and G.

N-MOS Fabrication Process Step - Metallization:

N-MOS Fabrication Process Step - Metallization Fig. (17) The region of photoresist which is not exposed by UV light will become soft. This unpolymerised photoresist and SiO 2 below it are etched away. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO 2 (1 µm) - - - - - n+ - - - - - n+ Thick SiO 2 (1 µm) Photoresist Mask-3

N-MOS Fabrication Process Step - Metallization:

N-MOS Fabrication Process Step - Metallization Fig. (18) The contact cuts are formed for S, D and G (hardened photoresist is stripped away). - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO 2 (1 µm) - - - - - n+ - - - - - n+ Thick SiO 2 (1 µm) Photoresist Mask-3

N-MOS Fabrication Process Step - Metallization:

N-MOS Fabrication Process Step - Metallization Fig. (19) Metal (aluminium) is deposited over the surface of whole chip (1 µm thickness). - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO 2 (1 µm) - - - - - n+ - - - - - n+ Thick SiO 2 (1 µm) Metal (1µm)

N-MOS Fabrication Process Step - Metallization:

N-MOS Fabrication Process Step - Metallization Fig. (20) Photoresist is deposited over the metal. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO 2 (1 µm) - - - - - n+ - - - - - n+ Thick SiO 2 (1 µm) Metal (1µm) Photoresist

N-MOS Fabrication Process Step - Metallization:

N-MOS Fabrication Process Step - Metallization Fig. (21) UV Light is passed through Mask-4 (with a aim of removing all metal other than metal in contact-cuts). - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO 2 (1 µm) - - - - - n+ - - - - - n+ Thick SiO 2 (1 µm) Metal (1µm) Photoresist UV Light Mask-4 Mask-4 is used to deposit metal in contact cuts of S, D and G.

N-MOS Fabrication Process Step - Metallization:

N-MOS Fabrication Process Step - Metallization Fig. (22) Photoresist and metal which is not exposed to UV light are etched away. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Thick SiO 2 (1 µm) - - - - - n+ - - - - - n+ Thick SiO 2 (1 µm) Metal (1µm) Photoresist Mask-4

N-MOS Fabrication Process Step - Metallization:

N-MOS Fabrication Process Step - Metallization Fig. (23) Final n-MOS Transistor - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - n+ - - - - - n+ SOURCE DRAIN GATE