HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory MICRO NANO AND SYSTEMS RESEARCH GROUP Microfabrication Introduction to Micro System Technology Lecture 2 Quan Zhou MICRO NANO AND SYSTEMS RESEARCH GROUP Microfabrication and Micromachining Methods MICRO NANO AND SYSTEMS RESEARCH GROUP Silicon Micromachining Material deposition methods Ö Bulk micromachining Ö Micromolding Ö Surface micromachining Ö Electroplating LIGA technique Ö Micro stereo lithography Material removal methods Ö Laser-assisted chemical vapor Ö Excimer laser micromachining deposition Ö Ion beam milling Ö Localized electrochemical deposition Ö Micro electro-discharge machining Ö Micro Ultrasonic machining Ö Diamond milling Ö Plasma beam machining Ö Electron beam machining Ö Dry etching MICRO NANO AND SYSTEMS RESEARCH GROUP Ö Soft Lithography Table of Contents, Slide 2 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Materials MICRO NANO AND SYSTEMS RESEARCH GROUP Silicon Metal Glass Ö Au, Pt, Al, Ti, Ni Ceramics Active materials: Polymers Ö Piezoelectric Ö Thick resist lithography Ö SMA (e.g. NiTi) – PMMA, SU-8, AZ4562, AZ9260, Ma- Ö MSM P 100 Ö EMFi Ö Surface polymer micromachining Ö Magneto/electrostrictive materials – Polyimide, Parylene, Electro- depositable photoresists, Ö Active polymers Conductive polymers Ö Soft lithography – PDMS MICRO NANO AND SYSTEMS RESEARCH GROUP Ö Micromolding – PMMA, PC, PS, COC, PP Table of Contents, Slide 3 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Properties of Silicon MICRO NANO AND SYSTEMS RESEARCH GROUP Have the same time good electric and mechanical properties Ö the elasticity of silicon is comparable to that of steel Ö stiffer than steel due to its low density Ö Some silicon compounds, have excellent physical and chemical properties for surface micromachining. – silicon nitride – silicon dioxide Ö Can be used for sensor and MICRO NANO AND SYSTEMS RESEARCH GROUP actuator Ö Integrated MEMS on single chip Ö Low cost, high reliability Table of Contents, Slide 4 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Silicon Fabrication Techniques MICRO NANO AND SYSTEMS RESEARCH GROUP Layer techniques BulkBulk micromachining micromachining Doping Lithography SurfaceSurface micromachining micromachining Etching MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 5 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Layer Techniques MICRO NANO AND SYSTEMS RESEARCH GROUP Purpose Ö Produce and structure layers of materials in the micro and nanometer range Methods Ö Thin film techniques Ö Deposition from the liquid phase Ö Thick film techniques MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 6 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Thin Film Techniques MICRO NANO AND SYSTEMS RESEARCH GROUP Thickness of a few nm to a few µm For generation of function layer and structuring the chip Deposition processes Ö Thermal deposition Ö Physical layer deposition – vapor deposition – sputtering process Ö Chemical layer deposition – chemical vapor deposition (CVD) – Plasma Enhanced CVD (PECVD) MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 7 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Deposition from the Liquid Phase MICRO NANO AND SYSTEMS RESEARCH GROUP Galvanic techniques Ö can deposit various kind of metal Ö high aspect ratio Ö Used for LIGA Catalytic method Ö allow only the deposition of metals Spin-coating method Ö Used for phtosensitive coating MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 8 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory High-Aspect-Ratio Photolithography MICRO NANO AND SYSTEMS RESEARCH GROUP MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 9 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Doping MICRO NANO AND SYSTEMS RESEARCH GROUP Doping atoms are introduced to a silicon substrate in a defined way so that n or p conducting layers are formed. Ö Determine the electric properties Ö Improve mechanical properties such as wear and corrosion, as etching stop barrier – boron, phosphorus Doping methods used in MST Ö Diffusion methods – Process in a furnace – doping profile only on the surface Ö Ion implantation MICRO NANO AND SYSTEMS RESEARCH GROUP – the ion can penetrate up to few micrometers Table of Contents, Slide 10 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Diffusion Doping MICRO NANO AND SYSTEMS RESEARCH GROUP Expose to Dopant Dopant Successfully Implanted Remove Oxide Layer Feature Successfully Created MICRO NANO AND SYSTEMS RESEARCH GROUP Add Oxide Layer to Continue Table of Contents, Slide 11 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Lithography MICRO NANO AND SYSTEMS RESEARCH GROUP Used for preparing the substrate of a wafer for the subsequent processing stage. Elements Ö Light source – light, X-ray, electron or ion beams – Ultraviolet (UV) light with a wavelength of 250-450 nm is used for silicon process Ö Mask – a chromium pattern on a light- transparent substrate (glass). Ö Resist MICRO NANO AND SYSTEMS RESEARCH GROUP – sensitive to the light source, about 1 µm thick, applied on the silicon wafer or another deposition layer – positive and negative resist Table of Contents, Slide 12 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Three Lithography Methods MICRO NANO AND SYSTEMS RESEARCH GROUP Contact lithography Ö resolution 1 µm or high Ö high mechanical load, easily damaged Proximity lithography Ö air gap 20-50 µm, reduced wear Ö resolution is limited to 2 µm Projection lithography Ö using a reducing high resolution lens (5:1 - 10:1) Ö resolution of 0.5 m Ö expansive MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 13 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Preparation of Substrate MICRO NANO AND SYSTEMS RESEARCH GROUP Select Silicon Substrate Add Oxide Layer Add Photoresist Layer Select Pattern Mask MICRO NANO AND SYSTEMS RESEARCH GROUP Ready for Exposure Table of Contents, Slide 14 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Exposure of the Photoresist MICRO NANO AND SYSTEMS RESEARCH GROUP Expose to Ultraviolet Light Exposed Photoresist is Hardened MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 15 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Patterning of the Photoresist MICRO NANO AND SYSTEMS RESEARCH GROUP Prepare for Etching Expose to Photoresist Solvent Remove Unhardened Photoresist MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 16 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Etching of the Oxide Layer MICRO NANO AND SYSTEMS RESEARCH GROUP Expose to Hydrofluoric Acid Remove Exposed Oxide Remove Hardened Photoresist MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 17 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory More in Lithography MICRO NANO AND SYSTEMS RESEARCH GROUP Aspect ratio Ö 1-2 using UV lithography Ö 6-8 with special techniques Gray-tone lithography Ö raster-screen photomask Electro-optical methods Ö “write” point by point with a electron or ion beam Ö no mask needed Ö time-consuming X-ray lithography Ö small wavelength (1 nm), MICRO NANO AND SYSTEMS RESEARCH GROUP structure precision can be 0.2 µm. Table of Contents, Slide 18 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Example: A Microstructure Made using Gray-Tone Lithography MICRO NANO AND SYSTEMS RESEARCH GROUP MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 19 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Etching Techniques MICRO NANO AND SYSTEMS RESEARCH GROUP To remove the exposed (unexposed) areas of the photo resist from the wafer and the respective deposited layers. Ö Wet Etching Ö Dry Etching MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 20 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Wet Etching MICRO NANO AND SYSTEMS RESEARCH GROUP Dipping the substrate into an etching bath or spraying it with etching solution. Etching solution Ö acidic or alkaline Two types (based on structure of the material or the etching solution) Ö Isotropic etching Ö Anisotropic etching MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 21 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Isotropic Etching MICRO NANO AND SYSTEMS RESEARCH GROUP Etching is isotropic if the material is amorphous or polycrystalline Attack the material at the same rate in all directions Ö Formation of cavities with rounded off edges Ö The resist is under cut Ö Limited for deep forming, not suitable for cavity width smaller than 2-3 µm. Used for many applications in surface micromachining MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 22 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Anisotropic Etching MICRO NANO AND SYSTEMS RESEARCH GROUP Single-crystal silicon can be anisotropically etched The etching speed is dependent on the crystal’s orientation Etching solution Ö KOH Ö NaOH Ö EDP (ethylene diamine pyrocatechol). Resist Ö Silicon dioxide Ö Silicon nitride MICRO NANO AND SYSTEMS RESEARCH GROUP Table of Contents, Slide 23 HELSINKI UNIVERSITY OF TECHNOLOGY Control Engineering Laboratory Basic Structures can be Produced in Silicon MICRO NANO AND SYSTEMS RESEARCH GROUP MICRO NANO AND SYSTEMS RESEARCH GROUP a) (110) silicon;