Sıra | DOSYA ADI | Format | Bağlantı |
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01. | Isotropic Etchingseoul Silicon Fusion | ppt | Sunumu İndir |
Transkript
Seoul National Univ. MAE Nano Fusion Technology Lab.Fundamentals of Multiscale FabricationLecture 3Multiscale fabrication II: Silicon bulk micromachiningKahp-Yang SuhAssociate ProfessorSNU MAEsky4u@snu.ac.krPaper reading: “Bulk Micromachining of Silicon”, Proceedings of The IEEE, GREGORY T. A. KOVACS, NADIM I. MALUF, AND KURT E. PETERSEN, Vol 86, No. 8, pp 1536-1551, 1998.
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krTitle: Fabrication techniques of convex corners in a (100)-silicon wafer using bulk micromachining: a review Author(s): Pal P, Sato K, Chandra SSource: JOURNAL OF MICROMECHANICS AND MICROENGINEERING Volume: 17 Issue: 10 Pages: R111-R133 Published: OCT 2007 Times Cited: 7Title: Micromachining for optical and optoelectronic systems Author(s): Wu MCSource: PROCEEDINGS OF THE IEEE Volume: 85 Issue: 11 Pages: 1833-1856 Published: NOV 1997 Times Cited: 181 Title: Silicon microstructuring technology Author(s): Lang WSource: MATERIALS SCIENCE & ENGINEERING R-REPORTS Volume: 17 Issue: 1 Pages: 1-55 Published: SEP 1996 Times Cited: 94 Title: Development of surface micromachining techniques compatible with on-chip electronics Author(s): French PJSource: JOURNAL OF MICROMECHANICS AND MICROENGINEERING Volume: 6 Issue: 2 Pages: 197-211 Published: JUN 1996 Times Cited: 25 Further readings (ISI web search)
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krMicromachining
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krSi Micromachining MethodsSFB: Silicon Fusion Bonding
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krBulk Micromachining
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krBenefits of Si bulk micromachining
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krhttp://www.saabmicrotech.se/node4084.aspEtching Process
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.kr• The purpose of bulk micromachining- Selectively remove significant amounts of silicon from a substrate- Broadly applied in the fabrication of micromachined sensors, actuators, and structures• Fabrication method: dry/wet etching- Undercut structures that are required to physically move- Form membranes on one side of a wafer- Make a variety of trenches, holes, or other structures Bulk Micromachining
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krFigure 1. Bulk silicon micromachining: (a) isotropic etching; (b) anisotropic etching; (c) Anisotropic etching with buried etch-stop layer; (d) dielectric membrane released by back-side bulk etching; (e) dopant dependent wet etching; (f) anisotropic dry etchingBulk Micromachining
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krTerminology:Etch Rate – How fast material is removedSelectivity – Ratio of etch rates of materials exposed to etchingAnisotropy – Degree of lateral etch to vertical etchWet Etching – chemical bathDry Etching – chemical / physical material removal using gas / vaporDry Etching Wet EtchingProduction-Line AutomationGood PoorCost chemicals Low HighSelectivity PoorCan be very goodSub-micron features Applicable Not ApplicableEtch RateSlow (0.1um/min)Fast (1 um/min)(Madou)Bulk Micromachining
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krSilicon Crystallography (1)
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krSilicon Crystallography (2)(see MEMS Open Courseware: Readings_Etc)
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.kr• Isotropic wet etching- Etching with chemical reaction etching in all directions a substrate- Induces etch reaction with silicon throughthe opening region agitation required: stirring, ultrasonic- Considering opening area to size of reaction bubble Bubble disturbs exchange of etchant Slow down etch rate- The most common isotropic wet silicon etchant: HNA HNA = HF + HNO3 + CH3COOH Reaction: 18HF + 4HNO3 + 3Si 2H2SiF6 + 4NO(g) + 8H2OIsotropic Wet Etching
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.kr• Anisotropic wet etching- Anisotropic etchants etch much faster in on direction than in another exposing the slowest etching crystal planes over time (111) planes have the slowest etch rate- Several solutions: Alkalic OH (KOH, NaOH) Tetramethylammonium hydroxide (THAH, (CH3)4NOH) Ethylenediamine pyrocatechol (EDP, NH2 (CH2)2 NH2+C6H4(OH)2)- Etching at concave corners on (100), stop at (111) intersections.Convex corners are under cutAnisotropic Wet Etching
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krExample of Anisotropic Wet Etching
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krAnisotropic Etching Mechanism
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.kr• Xenon Difluoride Etching (XeF2)- Non-plasma, isotropic dry etch process- Very high selectivity for Al, SiO2, Si3N4, PR- Reaction: 2XeF2 + Si 2Xe + SiF4- Etch rate: 1~ 3 m/min- Drawback: Rough surface reaction with water (HF) silicon fluoride polymer - Use of BF3 ~ much smooth surfaceDry Etching
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krExample of isotropic Dry Etching
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.kr• Plasma/Reactive Ion Etching (RIE)- Anisotropic dry etch process- Process in which chemical etching is accompanied by ion bombardment- Combination of physical and chemical etchingDry Etching
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krRIE principles
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.kr- Etch mask: PR (Photo Resist), Hard mask (SiO2, Al)- Selectivity = etch rate of etching material / etch rate of mask- Usually, standard PR (for CMOS) is not adequate for O2plasma etch, for which hard mask is required- Selectivity of silicon: AZ1512 Cl based etch (physical etch): <2 F based etch (chemical etch): <10(if O2 gas is inserted into the chamber, the selectivity would be smaller than 10)Mask materials for RIE
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.kr Reaction in RIE process (1)
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.kr Reaction in RIE process (2)
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krExample using BCl3
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.kr Reaction in RIE process (3)
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krExample using SF6
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krDeep reactive ion etching (DRIE)
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.kr- In wet etchants, the etch reactants come from a liquid source- In dry etchants, the etch reactants come from a gas or vapor phase source and are typically ionized Atom or ions from the gas are the reactive species that etch the exposed film- Selectivity: in general, dry etching has less selectivity than wet etching- Anisotropy: in general, dry etching has higher degree of anisotropy than wet etching- Etch rate: in general, dry etching has lower etch rate than wet etching- Etch control: dry etching is much easier to start and stop than wet etchingWet etching vs. Dry etching
Seoul National Univ. MAE Nano Fusion Technology Lab.http://nftl.snu.ac.krMEMS: Deposition + Lithography + Sacrificial Etching