Biossensores - Introduction & Microfabrication Technologies - NOVA School of Science & Technology 2024 PDF

Biossensores Aula 1 Introduction & Microfabrication Technologies Hugo Águas - FCT-UNL 2024 1 Biossensores  General definition:  A Biosensor is an analytical device that combines a biological component with a physicochem...

Biossensores Aula 1 Introduction & Microfabrication Technologies Hugo Águas - FCT-UNL 2024 1 Biossensores  General definition:  A Biosensor is an analytical device that combines a biological component with a physicochemical transducer, used for the detection of an analyte  MEMS:  Micro-electro-mechanical-systems, are the devices that can integrate into a single platform, elements: sensors; actuators; processors.  Bio-MEMS http://upload.wikimedia.org/wikipedia/commons/thumb/8/8a/AutoFISH.jpg/220px-AutoFISH.jpg  Integration of biosensors with MEMS providing additional functionality 2 Bio-MEMS 3 MEMS – Micro Electro Mechanical Systems MEMS of Silicon => REVOLUTION Using silicon processing technology allows the manufacture of complex systems in a wafer of Si. Enable the development of smart products by integrating microelectronics, microsensors and microactuators: Sensor Microprocessor Actuators (eyes, ears, nose,....) (arms and legs) (brain) 4 MEMS – Micro Electro Mechanical Systems Micro-electro-mechanical systems (MEMS) are the integration of: Mechanics; Sensors; Actuators; Electronic usually manufactured on a common silicon substrate through Micromanufacturing technology. The electronic part is manufactured using the same processes used in the manufacture of integrated circuits. Micromechanical components are manufactured using compatible Micromaquination (micromachining" or Microfabrication technology that selectively removes parts of silicon or adds new layers to form mechanical devices and Electromechanical. 5 MEMS - Advantages In the MEMS, the distinction between complex mechanical systems and integrated electronic circuits is mitigated. Historically, sensors and actuators are the most expensive and least reliable parts of electronic macro sensor-actuator systems. MEMS allow these complex electromechanical systems to be built using the production techniques of the integrated circuits, reducing the cost of manufacture and increasing the reliability of sensors and actuators to levels similar to those of the Electronic. Devices that have superior performance and much lower manufacturing costs can be produced. 6  Bio-MEMS - Materials http://www2.imec.be/content/user/Image/Press_releases/235172.jpg  Silicon  Material conventionally used in microfabrication, taking advantage but the same technologies developed for microelectronics, being possible to manufacture microchannels, sensors, devices, etc.  Some disadvantages related to cost, bio incompatibility, lack of transparency, fragility. http://www.mems.hu/sites/all/libraries/research/polymer_photonics/photonics01.jpg  Polymers  Attractive materials due to ease of microfabrication, low cost, high transparency and resilience, bio compatibility. The most common polymers are PMMA; PDMS and SU-8. 7  Bio-MEMS - Materials Paper http://3278as3udzze1hdk0f2th5nf18c1.wpengine.netdna-cdn.com/wp-content/uploads/2010/06/paper1.jpg Paper has gained importance recently as support for microfluidic devices. It is a cheap material, easy to manipulate and standardize and due to its porosity can serve as particle and cell filter and as immobilization support. Fluids move by action of capillarity forces and is easily incinerable. 8 Why use Silicon? It has the advantage of the long experience gained in the production of Integrated Circuits It is available on the market in ultra pure form (9 nines) Their physical and chemical properties are very well known Electronic and mechanical parts can be integrated into a single It has exceptional mechanical and electrical properties: Very strong: Yield Strength: 7x109 N/m2 vs. aço 4.2x109 N/m2 Relatively light: Density: 2.3 g/cm3 vs. aço 7.9 g/cm3 Semiconductor Resistivity 0.5 mΩ-cm (Doped) a 230 kΩ-cm (Intrinsic) 9 10 MEMS – Micro Electro Mechanical Systems Example of an electric motor smaller than the diameter of a silicon-made human hair: 11 12 13 14 MEMS – Processing: There are only 3 basic operations for the manufacture of microstructures: Material deposition Definition / Transfer of Patterns Removal / Erosion 15 MEMS – Thin Film Deposition Processes A thin film can have between 1nm and 100 nm. The most common deposition techniques can be classified into two groups: Depositions that occur due to a Chemical reaction: Chemical Vapor Deposition (CVD) Electrodeposition Epitaxy Thermal Oxidation These processes explore the creation of solid films directly from liquid or gaseous chemical reactions with the substrate. The film is usually not the only reaction product. Sub products include gases, liquids or even solids. Depositions that occur due to a Physical reaction: Physical Vapor Deposition (PVD) Casting In these processes the deposited material is physically moved to the substrate, i.e. no chemical reaction occurs. 16 Chemical Vapor Deposition- CVD In this process the substrate is placed inside a reactor, to which gases are supplied. The fundamental principle of the process is the chemical reaction that occurs between the gases supplied. Reaction product is a solid material condensing on surfaces inside the reactor. Widely used, for example to deposit polycrystalline silicon; silicon oxide and silicon nitride 17 Chemical Vapor Deposition- CVD  The two most important CVD technologies for the manufacture of MEMS are LPCVD and PECVD:  Low Pressure CVD (LPCVD): This process produces films with very good uniformity and properties. The biggest problems of this process are the high deposition temperature (greater than 600ºC) and the relatively low deposition ratio. vídeo CVD 18 PECVD – Plasma Enhanced Chemical Vapor Deposition Plasma-assisted CVD (PECVD): Low temperature process (tipically 200ºC) due to the extra energy supplied to molecules by plasma. The quality of the films tends to be lower than that of processes that occur at higher temperatures. 19 CVD –Examples of synthesis reactions Polysilicon deposition: SiH3Cl → Si + H2 + HCl SiH4 → Si + 2 H2 Silicon oxide deposition: SiH4 + O2 → SiO2 + 2 H2 SiCl2H2 + 2 N2O → SiO2 + 2 N2 + 2 HCl Si(OC2H5)4 → SiO2 + byproducts Silicon nitride deposition: 3 SiH4 + 4 NH3 → Si3N4 + 12 H2 3 SiCl2H2 + 4 NH3 → Si3N4 + 6 HCl + 6 H2 20 Epitaxy This process is quite similar to that of CVD, however if the material is an ordered semiconductor (crystalline), it is possible to continue to build on the substrate, a film with the same crystallographic orientation of this. The most important epitaxy technology is VPE (Vapor Phase Epitaxy). In this process, gases are introduced in an induction-heated reactor, in which only the substrate is heated. The temperature of the substrate should be at least 50% of the melting temperature of the material to be deposited. Epitaxy also has the advantage of providing a high film deposition ratio and a high thickness (>100µm). 21 22 Thermal Oxidation Its most basic film formation technique. Classic process of oxidation of a wafer of Si. It consists simply of oxidation of the substrate surface in an oxygen-rich atmosphere. The temperature is high: 800ºC - 1100ºC. Part of the substrate is consumed. The film grows by diffusion from the oxygen to the substrate, causing the oxide to grow downwards. This process is naturally limited to materials that can be oxidized. 23 Electro-deposition Process restricted to electrically conductive materials. Electro Plating: Results from the application of an electrical potential between the substrate and a counterelectrode (platinum), generating a redox reaction that leads to the deposition of a film on the substrate. Electro-deposition is a suitable process for depositing metallic films such as copper, gold and nickel. 24 Physical Vapor Deposition - PVD PVD (physical vapor deposition) encompasses several deposition techniques, in which a material is released from a source and transferred to the substrate. The most important techniques are evaporation and sputtering. PVD encompasses standard technologies for metal deposition. It is more common than metal CVD, as it can be carried out with less process risks and cheaper. However, the quality of the films is usually lower than that of CVD and the covering of the surface is not as good. The choice between PVD methods to be used is in many cases arbitrary and depends on the technique currently available. 25  PVD - Evaporation The substrate is placed inside a vacuum chamber, in which the source of the material to be deposited is also placed. The material is then heated to its Evaporação por canhão de evaporation point. electrões Vacuum is necessary for evaporated molecules to move freely into the chamber and condense on the surface. The two most common evaporation techniques are evaporation by electron gun and resistive evaporation: In evaporation by electron gun, an electron beam is focused for the source of the material to evaporate, causing local fusion and evaporation of the material In resistive evaporation, a tungsten bar containing the evaporating material is electrically heated with a high current to make the material evaporate. It is mainly used for the deposition of Metals 26 PVD – Sputtering In Sputtering, the material is released from the target at a temperature far below the evaporation of the material. The substrate is placed in a vacuum chamber along with the target material and an inert gas (usually Air) is introduced at low pressure. Plasma is generated using an RF power source, causing gas ionization. Ions are accelerated against the target surface, breaking the bonds of target atoms in the form of steam and condensing on all surfaces, including the substrate. 27 PVD – Pulverização Catódica (Sputtering) 28 “Casting” – Spin Coating The material to be deposited is dissolved in liquid form, through a solvent. The material can be applied to the substrate by "spray" or "spinning". Once the solvent evaporated, a thin film of the material is on the substrate. This technique is particularly useful for polymeric materials, which can be easily dissolved in organic solvents, which is the common method of applying photoresist on substrates for photolithography. "Casting" is a simple technology that can be used for most polymers. The control of the thickness of the films depends exactly on the processing conditions, but can be carried out accurately. 29 “Casting” – Spin Coating 30 Definition / Transfer of Patterns - Lithography Lithography is the transfer of a pattern to a photosensitive material through selective exposure to a radiation source as a light. A photosensitive material is a material that alters its physical properties by exposure to a radiation source. If photosensitive material is selectively exposed to radiation through a mascara, the pattern is transferred to the material, since the properties of exposed and unexposed regions will differ. 31  Photolithography Photolithography is simply lithography using visible spectrum radiation. In photolithography the photosensitive material used is the photoresist. When the resist is exposed to radiation, its chemical resistance to the revealing solution changes. When it is placed in the developer after exposure, one of two regions (exposed or not exposed) is dissolved. If the exposed region is removed the resist is called by positive. If the unexposed region is removed the resist is called negative. 32  Transferência de Padrões Lithography is the main technique for transferring patterns in micromachination. The fotoresist does not have good mechanical properties to be machined, however it can serve to transfer yarn patterns in an economical way. The photoresist layer can be used as a temporary mascara for erosion of a sub layer, thus transferring the pattern to that layer. The photoresist can also be used as a sacrificial sublayer in a deposition. The reist is subsequently eroded and the material deposited on the resist is removed. This process is called a Lift-off. 33 Example of a Lift-off process 34 Example of an Erosion process (Etching) 35  Mask alignment To make devices, one must align the patterns of the various layers. The first pattern to be transferred should include a series of alignment marks, used as a reference for the later masks. When using several masks it is important to identify the mask number next to the marks to carry out their specific alignment. 36 Mask Alignment Alignment marks should not be arbitrarily placed on the substrate, because the mask aligner may have limited displacement and thus can only align the localized marks in a certain region of the substrate. This should take into account the type of mask aligner to be used before making the masks. ◼ Typically, two alignment marks are used to align the mask and substrate. ◼ An alignment mark is sufficient to align the direction of x and y, but two marks are required to align the rotation. 38  Exposure The exposure parameters required to achieve high accuracy in the transfer of patterns depends on the wavelength of the radiation and the dose required for the alteration of the photoresist. In the limits of the patterns, light is diffracted in several directions, so that if the image is exposed, the radiation dose received by the parts that should not receive radiation begins to be significant. This results in an erosion of the image along the limits. If the image is sub exposed, the default is not completely transferred. 39 Removal / Erosion - Etching In order to form a functional MEMS structure on a substrate, it is necessary to erode the previously deposited films and/or even the substrate itself. In general there are two classes of erosion processes: Wet erosion, where the material is dissolved by immersion in a chemical solution; Dry erosion, where the material is plucked or dissolved by reactive ions or by an erosive gas. 43 Wet Erosion This is the simplest erosion technology. Only one container with the solution appropriate to the dissolution of the material in question is required. On the other hand, the mascara material (e.g. fotoresist) must be resistant to the attack solution. Some materials such as silicon exhibit anisotropy to some chemicals, causing a different erosion rate according to the crystallographic direction. When erosion is isotropic, the material is also eroded under the mascara of the same distance as in depth. This is particularly undesirable when the size of the patterns is similar to the thickness of the film. In this case it is preferable to opt for dry erosion. 44 Dry Etching Dry erosion technology divides into two classes: Erosão de ião reactivo – RIE (reactive ion etching) Erosão por arranque – sputter etching 45 RIE – Reactive Ion Etching The substrate is placed inside a vacuum reactor, where specific gases are introduced and where a plasma is generated. Ions are accelerated against the material, reacting with this. On the other hand, if ions have enough energy they can pull the atoms out of the material without a chemical reaction. Changing the conditions of the process can further promote the chemical part of erosion, or more the physical part, altering the anisotropy of erosion, since physical erosion is more anisotropic than chemistry. The most used gases are Freon type (CF4; SF6; etc) 46 Sputter Etching e Vapor Phase Etching  Sputter etching is essentially equal to RIE without the contribution of the reactive part of the process. The process system is typically identical to that used for sputtering deposition.  Ar is used as erosion gas. 47 48 49 50 51 55 56 The Future...... 57