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Chapter 2

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Chapter 2

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  1. Chapter 2 ManufacturingProcess and CMOS Circuit Layout 1st rev. : March 7, 2003 2nd rev. : April 10, 2003

  2. CMOS Process

  3. A Modern CMOS Process Dual-Well Trench-Isolated CMOS Process

  4. The Manufacturing Process For a great tour through the IC manufacturing process and its different steps, check

  5. Patterning of SiO2 Chemical or plasma etch Si-substrate Hardened resist SiO 2 (a) Silicon base material Si-substrate Photoresist SiO 2 (d) After development and etching of resist, chemical or plasma etch of SiO 2 Si-substrate Hardened resist (b) After oxidation and deposition SiO of negative photoresist 2 Si-substrate UV-light Patterned (e) After etching optical mask Exposed resist SiO 2 Si-substrate Si-substrate (f) Final result after removal of resist (c) Stepper exposure

  6. Photo-Lithographic Process optical mask oxidation photoresist photoresist coating removal (ashing) stepper exposure Typical operations in a single photolithographic cycle (from [Fullman]). photoresist development acid etch process spin, rinse, dry step

  7. Recurring Process Steps • Diffusion and Ion Implantation: change dopant concentration of some parts of the material. • Deposition: Silicon Nitride Si3N4 (CVD, chemical vapor deposition, Polysilicon (polycrystalline silicon), Aluminum • Etching: Si2O (acid), Plasma etching (dry etching) • Planarization: Chemical-mechanical planarization (CMP) on top of Si2O before deposition of an extra metal layer.

  8. Define active areas Etch and fill trenches Implant well regions Deposit and pattern polysilicon layer Implant source and drain regions and substrate contacts Create contact and via windows Deposit and pattern metal layers CMOS Process at a Glance

  9. p-epi (a) Base material: p+ substrate with p-epi layer + p Si N 3 4 SiO (b) After deposition of gate-oxide and 2 p-epi sacrificial nitride (acts as a buffer layer) + p (c) After plasma etch of insulating trenches using the inverse of the active area mask p + CMOS Process Walk-Through

  10. SiO 2 (d) After trench filling, CMP planarization, and removal of sacrificial nitride n (e) After n-well and V adjust implants Tp p (f) After p-well and V adjust implants Tn CMOS Process Walk-Through

  11. poly(silicon) (g) After polysilicon deposition and etch n + + p (h) After n + source/drain and p + source/drain implants. These steps also dope the polysilicon. SiO 2 (i) After deposition of SiO 2 insulator and contact hole etch. CMOS Process Walk-Through

  12. Al (j) After deposition and patterning of first Al layer. Al SiO 2 (k) After deposition of SiO 2 insulator, etching of via’s, deposition and patterning of second layer of Al. CMOS Process Walk-Through

  13. Advanced Metallization

  14. Advanced Metallization

  15. Design Rules

  16. 3D Perspective Polysilicon Aluminum

  17. Circuit Under Design

  18. Its Layout View

  19. Layer Color Representation Well (p,n) Yellow Active Area (n+,p+) Green Select (p+,n+) Green Polysilicon Red Metal1 Blue Metal2 Magenta Contact To Poly Black Contact To Diffusion Black Via Black CMOS Process Layers

  20. Layers in 0.25 mm CMOS process

  21. CMOS Inverter Layout

  22. V DD 3 Out In 1 GND Stick diagram of inverter Sticks Diagram • Dimensionless layout entities • Only topology is important • Final layout generated by “compaction” program

  23. Design Rules • Interface between designer and process engineer • Guidelines for constructing process masks • Unit dimension: Minimum line width • scalable design rules: lambda parameter • absolute dimensions (micron rules)

  24. Intra-Layer Design Rules 4 Metal2 3

  25. Transistor Rules (DRC)

  26. Vias and Contacts

  27. Select Layer

  28. Layout Editor (Cadence, Magic,..)

  29. Design Rule Checker (on-line check) poly_not_fet to all_diff minimum spacing = 0.14 um.

  30. CMOS Layout ofComplexe Gate:From Chapter 6 Slides and Insert D Designing CombinationalLogic Circuits March 28, 2003

  31. Example Gate: NAND

  32. Example Gate: NOR

  33. B A C D Complex CMOS Gate OUT = D + A • (B + C) A D B C

  34. Constructing a Complex Gate OUT = D + A • (B + C)

  35. V V DD DD Stick Diagrams Contains no dimensions Represents relative positions of transistors Inverter NAND2 Out Out In A B GND GND

  36. X PUN C i VDD X B A j A PDN B GND C Stick Diagrams Logic Graph A j C B X = C • (A + B) C i A B PUN: Pull-up Network, PDN: Pull-down Network

  37. A C B A B C VDD VDD X X GND GND Two Versions of C • (A + B) Two Strips Line of Diffusions One Strip Line of Diffusions

  38. Consistent Euler Path (Insert D of textbook) X C i VDD X B A j A B C GND

  39. OAI22 Logic Graph X PUN A C D C B D VDD X X = (A+B)•(C+D) C D B A A B PDN A GND B C D

  40. Example: x = ab+cd Euler Paths For both PUD and PDN

  41. Cell Design • Standard Cells (gate collection) • General purpose logic • Can be synthesized • Same height, varying width • Datapath Cells • For regular, structured designs (arithmetic) • Includes some wiring in the cell • Fixed height and width

  42. Standard Cell Layout Methodology – 1980s VDD Routing channel VDD signals GND

  43. Standard Cell Layout Methodology – 1990s Mirrored Cell No Routing channels VDD VDD M2 M3 GND GND Mirrored Cell

  44. V DD Standard Cells N Well Cell height 12 metal tracks Metal track is approx. 3 + 3 Pitch = repetitive distance between objects Cell height is “12 pitch” Out In 2 Rails ~10 GND Cell boundary

  45. V V DD DD Standard Cells With minimaldiffusionrouting With silicided diffusion Out In Out In GND GND

  46. V DD Standard Cells 2-input NAND gate A B Out GND

  47. CMOS Fabrication and Layout • See the supplement data in Web! •