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SJSU EE 225A - 4-Mask Process

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1Process Documentation for 4-Mask NMOS ProcessD. W. ParentSJSU2Background• This NMOS process is based on:–AL Gate– Non self aligned structure• Covers most microelectronic manufacturing processes– Photolithography– Diffusion– Oxide Growth (Wet and Dry)–Etch– Metal deposition3About the Process• Process Design– To be robust with positive VT • Thin oxide transistors– VT 1-2 volts depending on the fixed oxide charge– ~400-550Å thick gate oxide• Parasitic Field Oxide transistors – VT 15-18 volts depending on the fixed oxide charge– ~4000-5000Å thick gate oxide• Maximum tolerable registration error ±4μm• Can handle large power supply• No ESD protection4Other uses for the Process• To provide an environment where students can design fabricate and test ICs in one semester (EE122/124).– Utilize the existing EE/MatE129 lab– Real world device physics examples (EE128)– Statistical information can be shared (EE102, EE/MatE167)!– Can be used as a research/MEMS platform• Can unify curriculum!• See all aspects of a product design5Semi Custom IC design• The most expensive and time consuming layers are pre-processed– S/D diffusion, Gate oxide, contact, and metalization• Circuits are made by wiring together the pre laid out transistors.• One mask is made and PL done on wafers.• Since the wafers are predone the turn around time is very short.• Since the transistors are pre laid out design time is reduced!6SOGS/D DiffusionField OxideCM1ResistorPass-through7MOSFETWLBGateM1S/D DiffusionField OxideCS/D Diffusion8Modeling the MOSFET9VT010VT short channel11VT• VT changes with VSBThis will cause trouble later.12Mobility• Mobility changes with electric field– The constant KNP, is never constant– We use an average13λ• This is due to the channel length narrowing.– The reversed biased diode’s depletion region gets bigger with VDS, and thus the length of the channel gets smaller, and thus the ID goes up.14What does the circuit design engineer control?• How big W and L are.• How the wires are connected.– This does not sound like much is it is a lot.15What does the process design engineer control?•Tox•Na• Junction Depth• Qi (kind of)16Major Process Steps• CLean1•Screen Oxide•Implant•Well drive• Field Oxide• S/D PL and Etch• SOG Deposition• S/D Diffusion•SOG Strip17Major Process Steps• Gate PL, etch• Gate Clean• Gate Oxide• Contact PL, etch and PR strip• Metalize• Metal PL, etch and strip• Anneal• Test18Clean 1Step Step Name Process Detail 1 Process Detail 2 Time Process Detail 3 Process Detail 4DATE & Operator intialClean 1Estimated time= 61 minutes1 PiranhaBath Temp 110oCH2SO4 (75%) + H2O2 (25%) 5Use Diffusion CLean Bench Use Proper PPE 2 Dump Rinse 5 3BOE DIP Bath Temp ~20oC 20:1 BOE 2Use Diffusion CLean Bench Use Proper PPE 4 Dump Rinse 5 5 PiranhaBath Temp 110oCH2SO4 (75%) + H2O2 (25%) 5Use Diffusion CLean Bench Use Proper PPE 6 Dump Rinse 5 7BOE DIP Bath Temp ~20oC 20:1 BOE 2Use Diffusion CLean Bench Use Proper PPE 8 Dump Rinse 5 9 RCA Bath Temp 70oC HCl:H2O2:H2O 1:1:6 10Use Diffusion CLean Bench Use Proper PPE 10 Dump Rinse 5 11 BOE DIP Bath Temp ~20oC 20:1 BOE 2Use Diffusion CLean Bench Use Proper PPE 12 Dump Rinse 5 13 Spin Rinse Dry Turn on N2 5 Use correct SRD 14Take out Wafers Turn off N2 Dot in, H out 019Clean 1•Piranha– removes organics and grows a thin layer of oxide around particles on the surface of the wafer•BOE– removes oxide and the particles that were trapped• RCA– Remove light metal ions20Screen OxideStep Step Name Process Detail 1 Process Detail 2 Time Process Detail 3 Process Detail 4DATE & Operator intialScreen OxideEstimated time= 115 minutes1 Load 900oC N2:4SLM 10Shiny side of wafer facing into furnace, every other slot, order, 2 dummies-5 device-2 dummiesPush Quartz boat until last wafer is past ceramic ring. 2 Push 900oC N2:4SLM 15 Use quartz rod 3Ramp900oC to 1100oC N2:4SLM 15Cap on, Restrictor on, Door open 4 Stabilize 1100oC N2:4SLM 5Cap on, Restrictor on, Door open 5 Soak 1100oC O2:10SLM 30Cap on, Restrictor on, Door open 6 Purge 1100oC N2:10SLM 10Cap on, Restrictor on, Door open 7 Pull 1100oC N2:4SLM 20 Use quartz rod 8Cool Room TempTransfer wafers to cool quartz boats 10 Turn of gas flows Ramp furnace back down21Screen Oxide• Scatters the implanted ions so they are more evenly distributed in the wafer22Screen Oxide23ImplantStep Step Name Process Detail 1 Process Detail 2 Time Process Detail 3 Process Detail 4DATE & Operator intialPWELL ImplantEstimated time= 15 minutes 1 Inspect Blue color 10 2Implant (Inovian) Species=B11 E=100keV 5 dose=8e13 Tilt=724Implant25Well DriveStep Step Name Process Detail 1 Process Detail 2 Time Process Detail 3 Process Detail 4DATE & Operator intialWell Drive Estimated time= 310 minutes1 Load 900oC N2:4SLM 10Shiny side of wafer facing into furnace, every other slot, order, 2 dummies-5 device-2 dummiesPush Quartz boat until last wafer is past ceramic ring. 2 Push 900oC N2:4SLM 15 Use quartz rod 3Ramp900oC to 1100oC N2:4SLM 15Cap on, Restrictor on, Door open 4 Soak 1100oC N2:4SLM 240Cap on, Restrictor on, Door open 5 Pull 1100oC N2:4SLM 20 Use quartz rod 6Cool Room TempTransfer wafers to cool quartz boats 10 Turn of gas flows Ramp furnace back down26Well Drive• Brings the surface concentration of the boron down to values that will produce positive VT.27Well Drive28Pre Oxide OxideStep Step Name Process Detail 1 Process Detail 2 Time Process Detail 3 Process Detail 4DATE & Operator intialPre OXIDE CLEANEstimated time= 10Bath Temp 110oC H2SO4 (75%) + H2O2 (25%) 5Use Diffusion CLean Bench Use Proper PPE 0 5 029Pre Oxide Clean• Removes any organics that were put on the wafer during handling.30Field OxidationStep Step Name Process Detail 1 Process Detail 2 Time Process Detail 3 Process Detail 4DATE & Operator intialField OxideEstimated time= 115 minutes1 Load 900oC N2:4SLM 10Shiny side of wafer facing into furnace, every other slot, order, 2 dummies-5 device-2 dummiesPush Quartz boat until last wafer is past ceramic ring. 2 Push 900oC N2:4SLM 15 Use quartz rod 3Ramp900oC to 1100oC N2:4SLM 15Cap on, Restrictor on, Door open 4 Stabilize 1100oC N2:4SLM 5Cap on, Restrictor on, Door open 5 Soak 1100oC 4SLM Wet 60Cap on, Restrictor on, Door open7mL HCL at T=95°C (#8)Ensure N2 is flowing if light is on and H2O is boiling 6 Purge


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