An Introduction to Polysilicon Micromaching

1. An Introduction to Polysilicon Micromaching Robert W. Johnstone www.sfu.ca/~rjohnsto/ www.sfu.ca/immr/

2. Personal Information • Robert W. Johnstone • Graduate Student at Simon Fraser University • School of Engineering Science • Simon Fraser University • 8888 University Drive, Burnaby, BC • Canada V5A 1S6 • Tel: (604) 291-4971 • Fax (604) 291-4951 An Introduction to Polysilicon Micromachining

3. Outline • Introduction • Fabrication • MEMS Technology • Sensors • Actuators • Packaging Issues and Integration • MUMPs Examples • Design Issues • Evaluations and Questions An Introduction to Polysilicon Micromachining

4. Introduction An Introduction to Polysilicon Micromachining

5. Introduction: Terminology • Micromachining • Microfabrication • Microelectromechanical Systems (MEMS) • Microsystems Technology (MST) An Introduction to Polysilicon Micromachining

6. Introduction Microfabrication Micromachining Bulk Micromachining LIGA Process Microelectronics Surface Micromachining Raised Structures An Introduction to Polysilicon Micromachining

7. Introduction: Features of MEMS • Miniature mechanical systems • Batch fabrication approach • Utilizes microelectronic manufacturing base • Common technology for sensors, actuators and systems An Introduction to Polysilicon Micromachining

8. Introduction: Why Miniaturize? • System Integration • Avoid assembly of discrete components • Better reliability • Lower costs • Better Performance • Better Response • Smaller devices have less inertia, less thermal mass, less capacitance, etc. • Increased Reliability • Mass decreases faster than structural strength An Introduction to Polysilicon Micromachining

9. Traditional Hundreds of components Manual/semi automated assembly Plenty of solder joints Sensitive to shock and vibration Future Single chip No assembly Minimal solder joints Batch fabrication Insensitive to shock & vibration Introduction: Systems-on-a-Chip An Introduction to Polysilicon Micromachining

10. Hard disk drive heads Inkjet print heads Heart pacemakers In vitro diagnostics Hearing aids Pressure sensors Chemical sensors Infrared imagers Accelerometers Gyroscopes Machine monitoring Micro fluidics Magnetoresistive sensors Microspectrometers Micro optical systems Military systems Introduction: Growth Prediction Technologies experiencing growth. An Introduction to Polysilicon Micromachining

11. Introduction: Growth Prediction MEMS Device Revenues Source: SEMI MEMS use in existing systems Source: MST News An Introduction to Polysilicon Micromachining

12. Introduction: Applications Relevant Examples • Telecommunication relies on routing optical signals • Present systems use large and centralized networks • A low cost optical switch can revolutionize telecommunications technology • MEMS enables practical, low cost micro-mirrors An Introduction to Polysilicon Micromachining

13. Introduction: Applications Inertial Measurement • MEMS enables low cost chips that can monitor motion and position • Enables integration of inertial measurement in systems not possible with traditional technology • Applications in air bags, skid control, machine tools, sports equipment etc An Introduction to Polysilicon Micromachining

14. Introduction: Applications Micro Fluidics • Ink jet printing • mTAS – Micro Total Analysis System (chemical analysis) • Environmental monitoring: Detection of pollutants and pathogens • Biomedical devices: heart/lung and kidney Dialysis machine, dosing systems etc • DNA analysis systems for diagnostic, therapeutic • And forensic studies An Introduction to Polysilicon Micromachining

15. Introduction: Applications Development Strategy • Strategy #1 • Build the best one possible to meet the most stringent requirements • Strategy #2 • Build them cheap and worry about performance later An Introduction to Polysilicon Micromachining

16. Introduction: Applications Industry’s Interest in MEMS • New products in old fabs • Seamless integration into existing fabrication plants • Minimal additional investment • Risk is low • Logical next step An Introduction to Polysilicon Micromachining

17. Introduction: Major Challenge Technology Standards • Application specific technologies • Differently tuned technology for different devices/applications • Presently low synergy or cooperation in formulating a common technology An Introduction to Polysilicon Micromachining

18. Fabrication An Introduction to Polysilicon Micromachining

19. Fabrication: Technology • Basic fabrications processes based on IC technology An Introduction to Polysilicon Micromachining

20. IC technology Bipolar CMOS BiCMOS MEMS related technology Bulk micromachining Surface micromachining LIGA, LIGA-like Micro EDM 3D stereo lithography Laser micromachining Focused ion beam milling Fabrication: Spectrum An Introduction to Polysilicon Micromachining

21. Fabrication: Basic Processes Silicon Processing • Lithography • Oxidation • Diffusion • Thin film deposition • CVD process • Thermal evaporation • Sputtering An Introduction to Polysilicon Micromachining

22. Fabrication: Lithography Lithography is the process of transferring a pattern from a mask to a photoresist using a photographic tool (mask aligner), and to the silicon substrate using etching techniques. PATTERN TRANSFER An Introduction to Polysilicon Micromachining

23. Fabrication: Lithography • Coat the wafer with an adherent and etch-resistant photoresist • Selectively remove the resist to leave the desired pattern by exposure and development steps • Etch to transfer the mask pattern to the underlying material • Remove (strip) the photoresist and clean the wafer An Introduction to Polysilicon Micromachining

24. Fabrication: Lithography Mask Pattern UV Light Transparent region Opaque region Photomask Photoresist Oxide Silicon substrate An Introduction to Polysilicon Micromachining

25. Fabrication: Lithography Positive Photoresist Silicon substrate Expose and develop Silicon substrate Strip resist Silicon substrate Etch oxide An Introduction to Polysilicon Micromachining

26. Fabrication: Lithography Negative Photoresist Silicon substrate Expose and develop Silicon substrate Strip resist Silicon substrate Etch oxide An Introduction to Polysilicon Micromachining

27. Fabrication: Lithography Subtractive vs. Additive Pattern Transfer Film Mask Mask After lithography Film Etch After mask removal An Introduction to Polysilicon Micromachining

28. Fabrication: Lithography Spin Coating of Photoresist Dispense resist Spin Spin complete PR Spinner An Introduction to Polysilicon Micromachining

29. Fabrication: Lithography Types of Lithographic Tools An Introduction to Polysilicon Micromachining

30. Wafer and mask out-of-contact during alignment Wafer and mask in-contact during exposure Fabrication: Lithography Contact Printing An Introduction to Polysilicon Micromachining

31. Fabrication: Lithography Projection Printing (using Wafer Stepper) An Introduction to Polysilicon Micromachining

32. Thermal oxidation is a high temperature process used to grow a continuous layer of high-quality silicon dioxide on silicon substrate Dry oxidation: oxidizing species is oxygen Wet oxidation: oxidizing species is water vapour Fabrication: Oxidation An Introduction to Polysilicon Micromachining

33. Fabrication: Oxidation After oxidation Oxidation process An Introduction to Polysilicon Micromachining

34. Fabrication: Oxidation Dry Oxidation Rate Ref: Fundamentals of Silicon Integrated Device Technology An Introduction to Polysilicon Micromachining

35. Fabrication: Oxidation Wet Oxidation Rate Ref: Fundamentals of Silicon Integrated Device Technology An Introduction to Polysilicon Micromachining

36. Fabrication: Oxidation Oxidation Through a Window in the Oxide Oxidation complete Oxidation process Oxide removed An Introduction to Polysilicon Micromachining

37. Fabrication: Oxidation Local Oxidation Silicon nitride deposition Oxidation complete Oxidation Silicon nitride removed An Introduction to Polysilicon Micromachining

38. Film Thickness (Microns) Color and Comments Film Thickness (Microns) Color and Comments 0.05 Tan 0.60 Carnation pink 0.07 Brown 0.58 Light orange or yellow to pink borderline 0.10 Dark violet to red violet 0.57 Yellow to "yellowish" (At times it appears to be light creamy gray or metallic) 0.12 Royal blue 0.56 Green yellow 0.15 Light blue to metallic blue 0.54 Yellow green 0.1 Metallic to very light yellow green 0.52 Green (broad) 0.20 Light gold or yellow - slightly metallic 0.50 Blue green 0.22 Gold with slight yellow orange 0.49 Blue 0.25 Orange to melon 0.48 Blue violet 0.27 Red violet 0.47 Violet 0.30 Blue to violet blue 0.46 Red violet 0.31 Blue 0.44 Violet red 0.32 Blue to blue green 0.42 Carnation pink 0.34 Light green 0.41 Light orange 0.35 Green to yellow green 0.39 Yellow 0.36 Yellow green 0.37 Green yellow Fabrication: Oxidation Oxide Layer Color Chart Silicon Processing for the VLSI Era: Volume 1- Process Technology An Introduction to Polysilicon Micromachining

39. Fabrication: Diffusion • Diffusion is a process by which atoms of impurities (eg., B, P, As, Sb) move into solid silicon as a result of the presence of a concentration gradient and high temperatures. An Introduction to Polysilicon Micromachining

40. Fabrication: Diffusion Diffusion Through an Oxide Window An Introduction to Polysilicon Micromachining

41. Fabrication: Diffusion Diffusion Profiles Diffusion from unlimited source Diffusion from limited source Diffusion from concentration step An Introduction to Polysilicon Micromachining

42. Fabrication: Diffusion Resistivity of Diffused Layers in Silicon Irvines’s Curves An Introduction to Polysilicon Micromachining

43. Fabrication: Diffusion Oxidation/Diffusion Furnace Separate furnaces for oxidation and diffusion processes An Introduction to Polysilicon Micromachining

44. Fabrication: Thin Film Deposition • Chemical Vapor Deposition (CVD) Processes • Physical Vapor Deposition (PVD) Processes • Thermal evaporation • Sputtering An Introduction to Polysilicon Micromachining

45. Fabrication: Thin Film Deposition CVD is the formation of a solid film on a substrate by the reaction of vapour phase chemicals which are decomposed or reacted on or near the substrate. An Introduction to Polysilicon Micromachining

46. Reaction Energy Thermal Photons Electrons Processes APCVD – Atmospheric pressure CVD LPCVD – Low pressure CVD PECVD – Plasma enhanced CVD Fabrication: Thin Film Deposition Reaction Types Heterogeneous reaction Chemical reaction takes place Very close to the surface Good quality films Homogeneous reaction Chemical reaction takes place In the gas phase Poor quality films An Introduction to Polysilicon Micromachining

47. Fabrication: Thin Film Deposition Deposition Conditions An Introduction to Polysilicon Micromachining

48. Fabrication: Thin Film Deposition Crystallographic Forms Deposition condition and reaction chemistry determine the crystalline nature of the film An Introduction to Polysilicon Micromachining

49. Fabrication: Thin Film Deposition APCVD • Atmospheric pressure chemical vapor deposition • Large volume of carrier gases needed • Poor step coverage • Low throughput • Primarily used for LTO Process gases An Introduction to Polysilicon Micromachining

50. Fabrication: Thin Film Deposition LPCVD • Low-pressure chemical vapor deposition • Reaction rate limited operation • Operates at 0.1 to 1Torr pressure • Good quality films • Conformal coverage • Typically used for HTO, Poly-silicon, some metal films and nitride An Introduction to Polysilicon Micromachining