Twin well process

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1. Applied Electronics –PT Department of Electrical and Electronics Engineering PSG College of Tech nology Coimbatore - india Twin Tub Technology CMOS Process Pradeep Kumar.P

2. Twin well Process Provide separate optimization of the n-type and p-type transistors This means that transistor parameters such as threshold voltage, body effect and the channel transconductance of both types of transistors can be tuned independently n+ or p+ substrate, with a lightly doped epitaxial layer on top, forms the starting material for this technology. The n-well and pwell are formed on this epitaxial layer which forms the actual substrate. The dopant concentrations can be carefully optimized to produce the desired device characteristics because two independent doping steps are performed to create the well regions.

3. The starting material is either an n+ or p+ substrate with a lightly doped epitaxial layer, which is used for protection against latch up This process provides separately optimized wells, balanced performance n-transistors and p-transistors may be constructed Tub formation Thin-oxide construction Source and drain implantations Contact cut definition Metallization Twin well Process Continued…,

4. Twin well Process Steps Step1: N or p type substrate is taken Initially Step2: Epitaxial Layer Deposition, Lightly Doped Epitaxial Layer is Deposited above n+ or p+ Substrate. Electrical Properties of Layer is Fixed by Dopant and its Concentration. The Aim of This Step is to Deposite High-Purity Silicon Layer. Concentration of Dopant Distributed Throught the Layer Step3: Tub Formation n -well-Formation Protect certain region in this by using an oxide nitride mask Phosphorus implantation Form n-well Entire substrate to an oxidation process The oxide is going to be formed only over the n-well The rest of the portions are protected by the oxide nitride mask This n-well will also be driven deeper

5. Step4: p -well-Formation Protect certain region in this by using an oxide nitride mask Boron implantation Form p-well Entire substrate to an oxidation process Implant The p-well Step 5: Polysilicon Layer is Formed The Overall Surface Step 6: Polysilicon gates Are Formed for n-well and p-well by Using Photo-Etching Process Step 7: Using Blanket Implantation(Auto Aligning The Wells) Step 8: n+ Diffusion is Formed in n-well p+ Diffusion is Formed in p-well These Are Used For VDD and VSS Contacts(Substrate Formation)

6. Step9: Contact Cuts Are Defined In Both The Wells Step10: Metalization Process (Metal Contacts Are Created)

7. p- p-epitaxial p well N well p+ n+ gate oxide Al (Cu) tungsten SiO 2 SiO 2 TiSi 2 Dual-Well Trench-Isolated CMOS field oxide

8. Advantages of Twin Tub Method: Separate Optimized Wells Are Available Balanced Performance of N and P Transistors is Obtained( Speciality )

9. Advance Twin Tub Process

10. Thank You