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Chapter 8 Ion Implantation

Chapter 8 Ion Implantation. Hong Xiao, Ph. D. hxiao89@hotmail.com www2.austin.cc.tx.us/HongXiao/Book.htm. Objectives. List at least three commonly used dopants Identify three doped areas Describe the advantages of ion implantation Describe major components of an implanter

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Chapter 8 Ion Implantation

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  1. Chapter 8Ion Implantation Hong Xiao, Ph. D. hxiao89@hotmail.com www2.austin.cc.tx.us/HongXiao/Book.htm www2.austin.cc.tx.us/HongXiao/Book.htm

  2. Objectives • List at least three commonly used dopants • Identify three doped areas • Describe the advantages of ion implantation • Describe major components of an implanter • Explain the channeling effect • Relationship of ion range and ion energy • Explain the post-implantation annealing • Identify safety hazards www2.austin.cc.tx.us/HongXiao/Book.htm

  3. Ion Implantation • Introduction • Safety • Hardware • Processes • Summary www2.austin.cc.tx.us/HongXiao/Book.htm

  4. Materials Etch PR strip Test Metalization Wafers Photo-lithography Thermal Processes Dielectric deposition Packaging Masks Implant PR strip CMP Final Test Design Wafer Process Flow IC Fab www2.austin.cc.tx.us/HongXiao/Book.htm

  5. Introduction: Dope Semiconductor • What is Semiconductor? • Why semiconductor need to be doped? • What is n-type dopant? • What is p-type dopant? www2.austin.cc.tx.us/HongXiao/Book.htm

  6. Introduction • Dope semiconductor • Two way to dope • Diffusion • Ion implantation • Other application of ion implantation www2.austin.cc.tx.us/HongXiao/Book.htm

  7. Dope Semiconductor: Diffusion • Isotropic process • Can’t independently control dopant profile and dopant concentration • Replaced by ion implantation after its introduction in mid-1970s. www2.austin.cc.tx.us/HongXiao/Book.htm

  8. Dope Semiconductor: Diffusion • First used to dope semiconductor • Performed in high temperature furnace • Using silicon dioxide mask • Still used for dopant drive-in • R&D on ultra shallow junction formation. www2.austin.cc.tx.us/HongXiao/Book.htm

  9. Dopant Oxide Deposition Deposited Dopant Oxide SiO2 Si Substrate www2.austin.cc.tx.us/HongXiao/Book.htm

  10. Oxidation SiO2 Si Substrate www2.austin.cc.tx.us/HongXiao/Book.htm

  11. Drive-in SiO2 Doped junction Si Substrate www2.austin.cc.tx.us/HongXiao/Book.htm

  12. Strip and Clean SiO2 Doped junction Si Substrate www2.austin.cc.tx.us/HongXiao/Book.htm

  13. Dope Semiconductor: Ion Implantation • Used for atomic and nuclear research • Early idea introduced in 1950’s • Introduced to semiconductor manufacturing in mid-1970s. www2.austin.cc.tx.us/HongXiao/Book.htm

  14. Dope Semiconductor: Ion Implantation • Independently control dopant profile (ion energy) and dopant concentration (ion current times implantation time) • Anisotropic dopant profile • Easy to achieve high concentration dope of heavy dopant atom such as phosphorus and arsenic. www2.austin.cc.tx.us/HongXiao/Book.htm

  15. Misalignment of the Gate Gate Oxide Metal Gate Metal Gate p+ S/D p+ S/D n-Si n-Si Aligned Misaligned www2.austin.cc.tx.us/HongXiao/Book.htm

  16. Ion Implantation, Phosphorus P+ SiO2 Poly Si n+ n+ P-type Silicon www2.austin.cc.tx.us/HongXiao/Book.htm

  17. Comparison of Implantation and Diffusion Doped region SiO2 PR Si Si Junction depth Ion implantation Diffusion www2.austin.cc.tx.us/HongXiao/Book.htm

  18. Comparison of Implantation and Diffusion www2.austin.cc.tx.us/HongXiao/Book.htm

  19. Ion Implantation Control • Beam current and implantation time control dopant concentration • Ion energycontrols junction depth • Dopant profile is anisotropic www2.austin.cc.tx.us/HongXiao/Book.htm

  20. Applications of Ion Implantation www2.austin.cc.tx.us/HongXiao/Book.htm

  21. Other Applications • Oxygen implantation for silicon-on-insulator (SOI) device • Pre-amorphous silicon implantation on titanium film for better annealing • Pre-amorphous germanium implantation on silicon substrate for profile control • …... www2.austin.cc.tx.us/HongXiao/Book.htm

  22. Some Fact about Phosphorus www2.austin.cc.tx.us/HongXiao/Book.htm

  23. Some Fact about Arsenic www2.austin.cc.tx.us/HongXiao/Book.htm

  24. Some Fact about Boron www2.austin.cc.tx.us/HongXiao/Book.htm

  25. Stopping Mechanism • Ions penetrate into substrate • Collide with lattice atoms • Gradually lose their energy and stop • Two stop mechanisms www2.austin.cc.tx.us/HongXiao/Book.htm

  26. Two Stopping Mechanism • Nuclear stopping • Collision with nuclei of the lattice atoms • Scattered significantly • Causes crystal structure damage. • electronic stopping • Collision with electrons of the lattice atoms • Incident ion path is almost unchanged • Energy transfer is very small • Crystal structure damage is negligible www2.austin.cc.tx.us/HongXiao/Book.htm

  27. Stopping Mechanism • The total stopping power Stotal = Sn + Se • Sn: nuclear stopping, Se: electronic stopping • Low E, high A ion implantation: mainly nuclear stopping • High E, low A ion implantation, electronic stopping mechanism is more important www2.austin.cc.tx.us/HongXiao/Book.htm

  28. Stopping Mechanisms Ion Random Collisions (S=Sn+Se) Channeling (SSe) Back Scattering (SSn) www2.austin.cc.tx.us/HongXiao/Book.htm

  29. Stopping Power and Ion Velocity I II III Nuclear Stopping Stopping Power Electronic Stopping Ion Velocity www2.austin.cc.tx.us/HongXiao/Book.htm

  30. Ion Trajectory and Projected Range Vacuum Substrate Collision Ion Trajectory Ion Beam Projected Range Distance to the Surface www2.austin.cc.tx.us/HongXiao/Book.htm

  31. Ion Projection Range ln (Concentration) Projected Range Substrate Surface Depth from the Surface www2.austin.cc.tx.us/HongXiao/Book.htm

  32. Projected Range in Silicon 1.000 P B Projected Range (mm) 0.100 As Sb 0.010 10 100 1000 Implantation Energy (keV) www2.austin.cc.tx.us/HongXiao/Book.htm

  33. Barrier Thickness to Block 200 keV Ion Beam 1.20 1.00 B 0.80 0.60 P Mask Thickness (micron) 0.40 As 0.20 Sb 0.00 PR Si SiO2 Si3N4 Al www2.austin.cc.tx.us/HongXiao/Book.htm

  34. Implantation Processes: Channeling • If the incident angle is right, ion can travel long distance without collision with lattice atoms • It causes uncontrollable dopant profile Lots of collisions Very few collisions www2.austin.cc.tx.us/HongXiao/Book.htm

  35. Channeling Effect Lattice Atoms Channeling Ion Collisional Ion q Wafer Surface www2.austin.cc.tx.us/HongXiao/Book.htm

  36. Post-collision Channeling Collisional Channeling Collisional q Wafer Surface www2.austin.cc.tx.us/HongXiao/Book.htm

  37. Post-collision Channeling Collisional Channeling Collisional Dopant Concentration Distance from surface www2.austin.cc.tx.us/HongXiao/Book.htm

  38. Implantation Processes: Channeling • Ways to avoid channeling effect • Tilt wafer, 7° is most commonly used • Screen oxide • Pre-amorphous implantation, Germanium • Shadowing effect • Ion blocked by structures • Rotate wafer and post-implantation diffusion www2.austin.cc.tx.us/HongXiao/Book.htm

  39. Shadowing Effect Ion Beam Polysilicon Doped Region Substrate Shadowed Region www2.austin.cc.tx.us/HongXiao/Book.htm

  40. Shadowing Effect After Annealing and Diffusion Polysilicon Doped Region Substrate www2.austin.cc.tx.us/HongXiao/Book.htm

  41. Q & A • Why don’t people use channeling effect to create deep junction without high ion energy? • Ion beam is not perfectly parallel. Many ions will start to have a lot of nuclear collisions with lattice atoms after they penetrating into the substrate. Some ions can channel deep into the substrate, while many others are stopped as the normal Gaussian distribution. www2.austin.cc.tx.us/HongXiao/Book.htm

  42. Damage Process • Implanted ions transfer energy to lattice atoms • Atoms to break free • Freed atoms collide with other lattice atoms • Free more lattice atoms • Damage continues until all freed atoms stop • One energetic ion can cause thousands of displacements of lattice atoms www2.austin.cc.tx.us/HongXiao/Book.htm

  43. Lattice Damage With One Ion Light Ion Damaged Region Heavy Ion Single Crystal Silicon www2.austin.cc.tx.us/HongXiao/Book.htm

  44. Implantation Processes: Damage • Ion collides with lattice atoms and knock them out of lattice grid • Implant area on substrate becomes amorphous structure Before Implantation After Implantation www2.austin.cc.tx.us/HongXiao/Book.htm

  45. Implantation Processes: Anneal • Dopant atom must in single crystal structure and bond with four silicon atoms to be activated as donor (N-type) or acceptor (P-type) • Thermal energy from high temperature helps amorphous atoms to recover single crystal structure. www2.austin.cc.tx.us/HongXiao/Book.htm

  46. Thermal Annealing Lattice Atoms Dopant Atom www2.austin.cc.tx.us/HongXiao/Book.htm

  47. Thermal Annealing Lattice Atoms Dopant Atom www2.austin.cc.tx.us/HongXiao/Book.htm

  48. Thermal Annealing Lattice Atoms Dopant Atom www2.austin.cc.tx.us/HongXiao/Book.htm

  49. Thermal Annealing Lattice Atoms Dopant Atom www2.austin.cc.tx.us/HongXiao/Book.htm

  50. Thermal Annealing Lattice Atoms Dopant Atom www2.austin.cc.tx.us/HongXiao/Book.htm

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