Micro-Fabrication Technology Lecture 3 PDF

2103570 Micro-Fabrication Technology Micro-Fabrication Lecture 3 : Deposition Process 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570 ...

2103570 Micro-Fabrication Technology Micro-Fabrication Lecture 3 : Deposition Process 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Outline Introduction of Deposition Physical Vapor Deposition  Evaporation  Sputtering Chemical Deposition  Chemical vapor deposition  Electro-Chemical deposition Lift-Off Process 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Fabrication Flow Multiple cycles Etching Photolithography Deposition Silicon Substrate Individual Packaging Package Final Test Inspection Dicing Die Seal 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Deposition 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Introduction Thin film deposition includes a list of technologies associated with growing layers of materials on a substrate with thickness from less than 1 nm to several microns. Applications of these technologies include in the fields of renewable energy, organic electronics, flat panel displays, optical, tribological, optical/magnetic storage and hard/decorative coatings. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Introduction 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Deposition Physical Methods Chemical Methods Evaporation Chemical Vapor Deposition Sputtering Electrochemical Deposition film substrate Applications Metallization (e.g. Al, Cr, Cu, Au) Dielectric materials (e.g. Al2O3,DLC) Si compounds (e.g. SiO2, Si3N4, Poly-Si) Alloys (e.g. NiTi) 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Deposition Process Deposition Physical methods Chemical methods Chemical Vapor Electrochemical Evaporation Sputtering Deposition Deposition Thermal DC LPCVD E-Beam RF PECVD Reactive Magnetron 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Physical Vapor Deposition 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Physical Methods Physical vapor deposition (PVD) is referred to any methods to deposit thin films by the condensation of a vaporized form of the material onto substrate surface. Vapor generation: Evaporation : boiling vapor of a molten metal Sputtering : bombard the target material with Ar ion substrate substrate film Ar+ Ar+ t t t material to be material to be deposited HEAT deposited Evaporation Sputtering 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation Evaporation consists in heating until evaporation of the material to be deposited under a vacuum environment. The material vapor finally condenses in form of thin film on the cold substrate surface and on the vacuum chamber walls. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation Vapor Pressure vs. Temperature 1 atmosphere = 760 torr = 1.013x105 Pa Vapor pressure curve for commonly evaporated materials 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation Evaporation Types Heating can be done by either resistive heating (Thermal Evaporation) or electron beam heating (E-beam Evaporation). material : material : Au, Al, Cr Electron beam Au, Al, Cr etc. Water-cooled resistive wire crucible Thermal Evaporation E-beam Evaporation 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation Thermal Evaporation the source material is placed in a crucible, which is heated by an resistive wire. Boats, crucibles, and filament source material : Au, Al, Cr etc. resistive wire Source materials 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation Thermal Evaporation Source: Kurt J. Lesker Company 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation E-beam Evaporation In e-beam evaporation, an electron beam is focused at the source material causing local heating and evaporation. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation Operating Procedure 1. Load the sample wafer and install target material inside chamber. 2. Pump down to ~ 10-5 to 10-6 torr. 3. Turn on the thickness monitor. 4. Turn on the evaporation power supply (either thermal or e-beam). 5. Open the shutter. 6. When the desired thickness is achieved, close the shutter, and turn off the power supply. 7. Vent the chamber and unload the sample wafer. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation Mean Free Path Defined as the average distance a molecule travel before colliding with another molecule (at a λ given pressure) Mean free path plays an important role on the step coverage!! Mean free path of air kT Mean free path  λ 2a 2 P k : Boltzmann constant (1.38 × 10-23 m2 kg s-2 K-1) T : temperature P : pressure 6 a : diameter of gas molecule 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation Shadowing effect The long mean free path in evaporation makes the deposition very directional. It causes shadowing effect. However, this feature is preferable for lift-off process. Shadow Source 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation Characteristics of Evaporation Utilizing high vacuum 10-5 to 10-6 torr to reduce the contaminations and the reactions of the deposited material with air. Very directional due to long mean free path. Shadow effect caused by the high directionality. Step coverage is not good. Can be used in Lift-off process. E-beam evaporation is more effective for high-temperature material deposition. Higher deposition rate compared to others. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering Sputtering concept Gas pressure ~1-10 mtorr Sputtering was achieved by accelerated inert ion (Ar+) in + substrate to bombard target (material to film be deposited). - - - - The target material is Ar+ - Ar+ - sputtered away in form of - vapor and deposited onto substrate placed on anode. - t - t t Better step coverage - material to be deposited because of shorter MFP. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering Type of sputtering DC sputtering : using DC bias for deposition of metals. RF sputtering : using AC bias at high frequency for deposition of dielectrics. Reactive sputtering : add reactive gas to deposit oxide or nitride film. Magnetron sputtering : use permanent magnet to increase the electron collision with Ar gas. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering DC Sputtering Gas pressure ~1-10 mtorr + substrate DC bias of a few kV is used film for ionization of Ar ion for metal deposition. - - - - Most common sputtering method Ar+ - Ar+ - - Material is released from the - t - source at much lower t t temperature than evaporation - material to be deposited 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering RF (Radio Frequency) Sputtering DC sputtering can not used for + substrate depositing dielectrics because film insulating target will cause positive charge build up on target during Ar+ bombarding which lower the - - - - voltage between electrodes. Ar+ - Ar+ - - Using AC bias at high frequency - t - (>1 MHz), heavy ions can not follow t t the switching, only electrons neutralize the positive charge - Insulator target buildup. ~ 13.59 MHz 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering RF (Radio Frequency) Sputtering + substrate substrate film + + + - + + + - target - - - + - - - + - - - - TIME -------> sputter deposition occurs when target Ar+ - Ar+ - is negative - - t - t t - Insulator target ~ 13.59 MHz 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering Reactive Sputtering Reactive gas such as O2 or + substrate N2 can be added into the SiO2 film chamber to produced oxide or nitride compounds such as SiO2, Si3N4, metal oxide. - - - - + O2 Ar+ - Ar+ - - t t t - Si 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering Magnetron Sputtering Magnets are used to increase the probability of electrons striking Ar. the ionization efficiency is increased significantly. Can be used with DC or RF Other reasons to use magnets:  Lower voltage needed to strike plasma.  Reduce wafer heating from electron bombardment.  Increased deposition rate 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering Sputtering concept Sputtering is preferred over evaporation in many applications due to a wider choice of materials to work with, better step coverage, and better adhesion to substrate. Composite materials can be deposited by co- sputtering or by sputtering from a single composite target. Sputtering target 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering Operating Procedure 1. Load the sample wafer and install target material inside chamber. 2. Pump down to ~ 10-5 to 10-6 torr. 3. Flow argon gas with pressure ~ 1-10 mtorr. 4. Turn on the thickness monitor. 5. Turn on the DC or RF power supply. 6. Ignite the plasma. 7. Open the shutter. 8. When the desired thickness is achieved, close the shutter, and turn off the power supply. 9. Vent the chamber and unload the sample wafer. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering Applications Sputtering is used to apply films in many products such as hard disks, compact disks, also to apply hard coatings such as TiN, TiC, TiAlN. Disks are formed by the process of sputtering multiple metallic films and a protective overcoat layer onto a highly planar, low defect glass substrate. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Sputtering Characteristics of Sputtering Utilizing low vacuum 1-10 mtorr as Argon gas is used during the process. Not directional due to shorter mean free path (~1 mm). Better step coverage than evaporation due to shorter MFP and larger target size. Alloys can be sputtered uniformly due to the bombardment mechanism. Better adhesion among other techniques. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Evaporation vs Sputtering Evaporation Sputtering Fast Thousand atomic layers per Slow Rate second (e.g. 0.5 µm/min One atomic layer per second for Al) Choice of materials Limited Almost unlimited Possibility of incorporating Better (no gas inclusions, Purity impurities (low-medium very high vacuum) vacuum range) Alloy compositions, Alloy composition can be Little or no control stochiometry tightly controlled Changes in source Easy Expensive material Uniformity Difficult Easy over large areas Capital Equipment Low cost More expensive Adhesion Often poor Excellent Shadowing effect Large Small 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Chemical Deposition 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Chemical Vapor Deposition Chemical Vapor Deposition (CVD) CVD is a chemical process used to produce high-purity, high- performance solid materials. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react at a hot surface (>300°C) to produce a desired film. wafers 350°C -500°C 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Chemical Vapor Deposition (c) (d) (e) 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Chemical Vapor Deposition Reaction Mechanisms 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Chemical Vapor Deposition Growth Rate vs Gas Flow Rate At a given temperature At high flow rates, the growth rate (deposition rate) reaches a maximum and then becomes independent of flow. The surface reaction rate dominates the deposition. (reaction rate limited deposition process). 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Chemical Vapor Deposition Growth rate vs Temperature At a given flow rate At high temperature (regime B), the reaction rate exceeds the rate at which the gas arrive at the surface. Therefore, the deposition is limited by the gas flow (mass transport limited deposition process). 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Chemical Vapor Deposition Step coverage is angle of arrival    Surface migration (diffusion) and MFP are important factors!!  A : Uniform coverage resulting from long MFP and rapid surface migration. B : Nonconformal step coverage for long MFP and no surface migration. C : Nonconformal step coverage for short MFP and no surface migration. 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Chemical Vapor Deposition Characteristics of CVD 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Low Pressure CVD (LPCVD) system works at vacuum (~0.1-1.0 torr), resulting in high diffusivity of reactants reaction rate limited wafers can be stacked closely without loosing uniformity as long as they have the same temperature temperature is well controlled around 600 – 800°C through the use of multiple heaters 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Plasma Enhanced CVD (PECVD) Use rf-induced plasma to transfer energy to reactant gases Low temperature process (< 300°C) For sample which can not sustain high temperature Film quality is worse compared to LPCVD 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Chemical Vapor Deposition Carbon Nanotube Growth Not only planar film, CVD is also used to grow carbon nanotube!! 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Chemical Vapor Deposition CNT Growing Conditions Hydrocarbon gases : C2H2 (acetylene), C2H4 (ethylene), CH4 (methane) Carrier gases: H2, Ar Temperature: 600-1000 °C Catalyst: Fe (Ni, Co) 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Electrochemical Deposition Electrochemical deposition (electroplating) is a process to deposit metal such as Ni, Cu, Au, Ag on conducting surface. When an electrical potential is applied between 2 electrodes in the liquid (electrolyte), a chemical redox process takes place resulting in the formation of a layer of material on the substrate. Anode Cathode Cl - Ni2+ NiCl2 solution Electroplating 2103570 Micro Fabrication Technology process of nickel www.mnems.eng.chula.ac.th/2103570  Electrochemical Deposition Process flow PR Conducting layer substrate 1. photolithography Ni Ni PR substrate substrate 2. Electrochemical deposition 3. PR removal 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Electrochemical Deposition Examples of electro-chemical deposition 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  Lift-off Process A process to pattern metallic films by allowing metal to adhere to the substrate where it is desired. Normally, this can be done by using evaporation technique due to the bad step coverage. 1. photolithography 2. Evaporation 3. PR removal 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570  The End 2103570 Micro Fabrication Technology www.mnems.eng.chula.ac.th/2103570