FYS 2210 H-08 Department of Physics http://www.uio.no/studier/emner/matnat/fys/FYS2210/h08/ http://www.fys.uio.no/studier/kurs/fys2210/ Halvlederkomponenter LAB COMPENDIUM SCHOTTKY DIODE N-MOSFET V. Bobal and B.G. Svensson Content I Introduction ……………………………………………………………………………..2 I.1 Contact information ...........................................3 II General Remarks ………………………………………………………………….……3 II.1 Safety issues ......................................................3 II.2 How to write a lab report ...................................4 III Syllabus ……………………………..…………………………………………………5 IV Main Process Description of Semiconductor IV Devices…………………………………7 IV.1 Oxidation……………………………………..7 IV.2 Lithography…………………………………...8 IV.3 Etching………………………………………..9 IV.4 Ion Implantation……………………………..11 IV.5 Metallization………………………………....13 V Characterization……………………………………………………………………….14 V.1 Schottky diode………………………………...14 V.2 N-MOSFET…………………………………...16 VI Analysis…………………………………………………16 VI.1 Analysis of Schottky and N-MOSFET processing…………………………16 VI.2 Analysis of Schottky characterization…………………………………...…17 VI.3 Analysis of N-MOSFET characterization………………………………….18 VII Appendix…………………………………………………………………………….19 VII.1 Cleanrooms rules…………………………………….……………………19 VII.2 Cleanroom Authorization Schema……………………………………...…24 VII.3 Chemicals and gasses in the cleanroom………………………………..….25 VII.4 Schottky diode process flow……………………………………………….26 VII.5 NMOSFET process flow………………………………… ……………….27 VII.6 Schottky Laboratory Experiment………………………………………….29 VII.7 NMOSFET Laboratory Experiment……………………………………….33 VII.8 List of equipment………………………………………………………..…42 VII.9 Hierarchy of alignment marks of masks…………………………………...43 1 I. Introduction The Lab Compendium for course FYS2210 describes the process of Schottky diodes on n- type silicon and N-MOSFET on p-type silicon substrate [100]. The laboratory experiment concerns a short but effective way to introduce the process and equipment tools which are used in very large scale integration (VLSI) for manufacturing of integrated circuits. It consists of 5 units, each of which having a duration of about 4 hours. The lab will be performed in small groups which will be defined in the first unit. Each of the groups will have to deliver one common lab report ( see instructions in Subsection II.2 ). The final deadline for the delivery is one week after the last lab unit. The lab reports can either be handed in directly to one of the contact persons identified below or by placing them in one of their mail boxes at the Physics department. The course is held in the MiNaLab in Gaustadalleen, close to Forskningsparken. The MiNaLab (see Fig. I.1) has been opened in 2004 and is part of a national program on micro- and nanotechnology. A close collaboration between academia (UiO) and industry (SINTEF) is intended to cover the whole chain from education and basic research to development and industrial production. For that purpose, MiNaLab contains two clean rooms, one for SINTEF (800 m 2) with Norway's only independent complete silicon processing line for small-scale production of Si particle detectors, and one for UiO (400 m 2), providing equipment for basic semiconductor research and device processing. Figure I.1 MiNa-lab 2 I.1 Contact information To enter the building, a key card and code is needed. In general, these cards are not handed out to students. Therefore, it is very important that you show up IN TIME. If you are late for good reasons, inform one of the persons below. The lab can not be performed on an alternative date! The following persons are available during lectures and the lab course. Please inform one of them in cases of illness or other obstacles and do not hesitate to ask in case of a problem! Bengt Svensson 22852859/22857467 [email protected] Viktor Bobal 22852892 [email protected] II General Remarks II.1 Safety issues By definition, a laboratory course involves the active handling of samples, measurement equipment, and in a lot of cases, also chemicals by its attendees. The processes of semiconductor device manufacturing imply the direct contact to high-purity semiconductor samples (wafers), chemicals for cleaning and etching them, furnaces operating at temperatures higher than 1000 ˚C, photolithography equipment sensitive to ultraviolet light and the ultraviolet light for exposure, ultra-high vacuum equipment in metallization chambers and ion implanters, high electric fields and so on. Each of the involved steps needs to be understood for a fully safe and self-confident performance during the device fabrication. Therefore, it is very important that you as a lab course attendee • carefully read and understand the lab manual! • Ask, if something remains unclear to you! • Do not hesitate to tell if you feel unsafe with a specific required action! The lab course in a clean room requires some further measures beyond the ones typical for a normal measurement lab course. You will be required to wear special protection gear to minimize pollution in the clean room. 3 Everyone residing in the clean room must wear a laboratory suit, laboratory shoes and a laboratory hat (hair net), gloves. The protection gear will not allow you to wear other hats, open long hair, or jewelry on your hands. It is recommended wearing socks in your shoes! Clean-room shoes are not very comfortable without them, furthermore it is unhygienic. All chemical handling must be taken place on the wet benches. The top of the wet benches are equipped with exhaust hoods which are necessary if you work with acids and solvents. Security eyeglasses must be worn whenever handling chemicals. Where indicated a face mask must be worn. Before working with chemicals, put on respective safety gloves. Since you will handle chemicals, the use of contact lenses is not recommended and can even be dangerous. A spill might stick between your eye and the lens, and, hence, will not be washed away with an eye-shower. Wear glasses instead, on top of those goggles. Always add acid to water never in reverse order! Don’t mix solvents and acids! It is strictly forbidden to disarrange and/or mess up the clean room. Do not run or jump inside a clean room! The laboratory must be kept as clean and proper as possible. The wet bench must be cleaned and dried after use. The next user cannot distinguish between water and concentrated acids. Spilled solvents can react with peroxides and nitric acid. Do not interchange chemical labeled test tubes and bins. Inform the lab staff in advance if you have latex or other allergy! For all used chemicals, a detailed list of properties and potential hazards is available. The chemicals you will have to deal with are organic solvents, acids, in particular hydrofluoric acid, metal, photoresist, and highly purified water. So-called Material Safety Data Sheets (MSDS) provide information on potential hazards in connection with handling the respective chemical. (http://siri.org/msds/ II.2 How to write a lab report Believe it or not: a lab report is first and foremost for YOU! By writing it, you may recollect all your gathered knowledge, sort and analyze it. By putting it down, ideally, a significant thinking process will help you to understand! There are general purposes for attending a lab course, like, for instance, to explain if and why a well-known scientific law or rule is not valid and which additional considerations have to be made. At the end of the lab course, one lab report has to be handed in for each group working together. A typical lab report shall consist of: • A clear description of the performed experiment in each lab unit • The (handwritten) protocol sheet obtained during the experiments 4 • The analysis according to the requirements in the respective assignment. This includes a clear definition of all used constants, physical quantities, and equations • If the assignment requires further discussion and comparison, include that as the last part of the unit report • Answer all questions • Characterization presenting the measurement results and analysis of I-V curves of N- MOSFET’s and C-V curves of Schottky diodes • Conclusions, summarize the report. The lab reports have to be handed in one week after the last lab unit. III Syllabus Unit 1 Within this unit, the general rules for gowning procedures and behavior in a cleanroom are clarified. A strong focus is put on safety. For your record, the Clean Room Authorization Scheme which you will have to sign after this unit is included in its original form in the Appendix. Only authorized people are admitted to the clean room. You are made familiar with all chemicals used within the lab course, are informed about which equipment to use for different processes. You will gain knowledge about the diode and the transistor processes. The lab is completed with a guided tour through the cleanroom of SINTEF, where Si particle detectors are produced and the cleanroom of UiO where you will execute your lab experiment. 5 Unit 2 Preparation (including complete cleaning processes) of Schottky contacts on an n-type of Si wafer by electron-beam evaporation through a lithography process. The obtained Schottky diodes will be characterized with current- and capacitance-voltage measurements (see unit 3). Start N-MOSFET process • Cleaning • Oxidation (grow Field oxide) • Lithography (opening of Source and Drain) • Etching Schottky process • Lift off • Characterization (C-V; I-V) Unit 3 N-MOSFET • Implantation • Lithography (definition of Gate) • Etching Unit 4 • Oxidation (grow Gate oxide) • Lithography (remove oxide of the Source and Drain area) • Etching • Deposition of metal (Al) for contact Unit 5 • Lithography (Al contact area) • Etching (remove Al from the wafer surface except of Source, Drain and Gate areas) • Characterization (I-V) 6 IV. Main Process Description of Semiconductor Devices IV.1 Oxidation We grow silicon dioxide (field oxide) on the Silicon wafers to isolate devices (diodes, transistors) from one other. The second half of our N-MOSFET process we are going to grow a much thinner layer (100 nm compared with the field oxide thickness of 2000nm) of SiO 2 to form the gate oxide.