www.scme-support.org
Microfabrication Process Course Using a Simple Pressure Sensor Design Matthias W. Pleil University of New Mexico,
[email protected] This material is based upon work supported by the National Science Foundation under Grant No. DUE 1700678 and the University of New Mexico
What are Microsystems (MEMS) • Microsystems, or Microelectromechanical Systems are the micro sensors and actuators are found in almost every modern electronic system. • MEMS are made in cleanrooms using processes akin to computer chip fabrication methods. • The fabrication of a simple micro pressure sensor device allows students to apply knowledge acquired across multiple disciplines and learn new critical skills in the fabrication of MEMS in a team environment.
• Sensor Type: • Inertial • • • •
• • • •
Accelerometer Gyroscope Magnetometer Combo Sensor
Pressure Microphone Environmental Optical • Microbolometer • Passive Infrared Sensor (PIR) and Thermopile
• Actuator Type: • Optical • Inkjet Head • Microfluidics
• Radio Frequency (RF) • Switch • Filter • Oscillator
Justification for Course Engineers and Technician students need to be knowledgeable of fabrication methods used in micro and nano fabrication technologies. Hands-on classes are critical for students wanting to succeed in the industrial environment. Students are generally not aware as to how micro devices are designed or made. Teaching in a cleanroom environment is also fun! TI DMD – 10x10um mirrors, 800k – 12M array
Course Description, Goals and Outcomes MicroElectroMechanical Systems (MEMS) are ubiquitous in all products and market segments that include electronic and sensing systems. Through hands-on labs and interactive lectures, the student can expect to be provided with an overview of MEMS fabrication methods, process optimization and characterization, applications, metrology, and design considerations found in surface and bulk micromachining technologies in a cleanroom environment.
Course Description, Goals and Outcomes The objective of this course is to provide the students with knowledge and skills needed to understand essential MEMS fabrication technologies through hands-on experience in the UNM MTTC Cleanroom. The overall manufacturing process of making MEMS devices will be covered and the individual process steps will be practiced in the cleanroom. Students will present characterization results with their teams and fabricate one or two MEMS devices. Problem solving, presentation, and collaboration skills will be enhanced while acquiring knowledge in a variety of fabrication tools and practices.
Course Description, Goals and Outcomes By the end of this course, students will be able to demonstrate microsystems process understanding, terminology, and interactions including but not limited to: MEMS Applications, Photolithography, Etching (Dry, Wet, Bulk…), Deposition (PVD, LPCVD, Sputter…), Metrology (SEM, Thin Film, critical dimensions), and materials properties. Students will also be able to demonstrate an understanding of MEMS device operation and design considerations required to make a successful product. Students will enhance their team working skills both in the cleanroom and outside of class to produce lab reports, presentations and project work.
Course Philosophy Work/Graduate Team environment – “Newbies” • Training on safety and equipment use • Work in small teams • Presentations to each other with Q&A – meeting with peers • Cross train students on equipment • Learn from each other • Let mistakes happen (labs are not scripted) • Respect cleanroom technicians (stressed – engineers can learn a lot) • Instructor is more of a mentor/manager – collaborative environment
Why a Pressure Sensor Device? • Electro Mechanical System • Simple two-mask process covering both bulk and surface micromachining principals • Process includes: • Deposition of Silicon Nitride and Gold/Chrome (LPCVD, PVD) • Photolithography – front/backside alignment, liftoff • Plasma Etching • Wet Anisotropic Etching
Wheatstone Bridge - topside
Etched Crystalline Silicon - backside
What’s covered? • Mechanical • Moving Membrane (stresses and strains)
• Electrical • Wheatstone Bridge – most used circuit in sensor technology
• Materials structure • Silicon Crystal – miller indices • Anisotropic wet etch • Simulation (ACES)
• MEMS History – “There’s Plenty of Room at the Bottom”
https://youtu.be/juf4d3sgOJw
What else is covered? • Metrology (measurement) • Thin Film Interference (Optical, Membrane deflection) • Film Thickness Step Height (Profilometer) • Microscope Critical Dimensions
• Characterization • Process Parameters Critical dimensions, thickness, etch rates….
• Students are trained on all of the process equipment, Cleanroom safety and protocols
Course Outline – Lecture • Overviews • • • •
MEMS Micromachining MEMS History Photolithography Deposition
• Pressure Sensor Process and Theory • Etch • Sputter • Probe
Course Outline – Lab • Cleanroom Safety and Protocols • Art Wafer • Photolithography Characterization I • Resources: • Equipment SOPs/Manuals • Metrology Mask Description
• Adjust SS, Exposure, resist type, dose to clear • Report out to teams
• Photolithography Characterization II • Team 1 - Exposure GAP and PEB • Team 2 - Develop Normality and Time
Course Outline – Lab • Deposition Lab • All students combined • Rainbow wafer & Etch Rate • Deposition Rate Experiment
• Entire class self organize to provide a single report
Pressure Sensor Process Labs Make sure you have a clean bake plate and chill plate - wipe down before starting - why?
• Background material • • • • • •
Pressure sensor process, storyboard Pressure sensor fabrication short animation Materials (photoresist, silicon, NiCr, KOH…) Process flow Frontside Coat map Etch Process (gasses, flows, MFC’s)
• Characterization Labs • Etch Rate Selectivity, gas flow rates, descum • Liftoff Process – Process flow, Ishikawa cause and effect, lessons learned
Frontside Coat HMDS Vapor Prime Coat
Bake
100C AZ9260 Chill
120C, 5min
5000rpm, 60sed
Backside Coat
Chill Second Time
Expose Develop 5min, Hard Contact AZ 400 1:4, 10min QDR 5X SRD Inpect
Cantilever Model Lab • Done in the classroom • Resonance Frequency Vs. • Length, width, thickness, mass added • Spring constant, Elastic Modulus
• Graph and analyze results • Extrapolate to the micro/nano scale – single cell detection
Sputter Lab • DC Vs RF sputter • NiCr thickness vs time • Uniformity of the resulting structures (thickness, resistance….)
Probe • Deflection Vs Pressure • Pressure Vs Resistance • Pressure Vs Gauge Voltage
Probe station at the MTTC includes out of plane interferometry
Student Examples
Crystalline Silicon Etch Simulation - ACES
Lithography Characterization
• Three Students did a poster and Pitch at the Engineering Expo • Won 2nd place!
Student Perceptions • All students felt the material was very or extremely relevant • Clarity of lectures was good to excellent • Amount of material presented - about right to much too much (OK, its a senior/grad course) • Instructor engagement - very to extremely engaging • Instructor knowledge - excellent • Compared to other courses: above average (1), top 20% (5) • Likely to recommend instructor and course? – all students 9-10 (scale of 10) - "promoters"
Student Feedback • Positive feedback overall. • Workload was considered to be about right or too much • All found the labs enjoyable: The most enjoying aspect of the course was the hands-on approach to the material presented. It was a better link to understanding of the science to making semiconductor devices rather than just pouring though theory with no real link to what actually happens in the work place. • Improvement opportunities – more labs, better structure, enforcement of due dates, make it a 4-5credit hr class, individual write-ups.
Student Feedback • Student opinion on added marketability – all said they will use this experience in their interviews – goes to confidence in understanding the material: I would describe the hands-on activities performed during the lab portions. How we actually observed these manufacturing processes directly and observed how variations that we controlled or not could impact the product outcome. • Skills, knowledge, confidence gaps filled – students felt more confident to run equipment, setup their own experiments and analize results. “…this course helped me how to follow the instructions and wor independently without any assistant and created my own recipes and studied the inferences.“ • Increased motivation on the topic? 5/6 students would consider looking into a career in Micro/Nano, one student is focused on automotive.
Improvement opportunities per students • Lab every other week (yeah, right) • Two processes instead of one (pressure sensor) – planning to add bimorph cantilever. • Enforce timelines, due dates. • Online Vs F2F (Lecture) • 4 preferred F2F, 2 prefer online (Perhaps I can record the lectures)
BiMorph Device -
No Cleanroom? Bring the cleanroom to the classroom • SCME has hands-on kits to teach the fabrication process steps • • • • • •
Anisotropic Etch (KOH or NaOH – need chemistry bench/hot plate) Liftoff (acetone, classroom) Pressure Sensor Process (classroom) Pressure Sensor Model kit (classroom – tables) Cantilever Model (classroom) Crystallography (classroom)
SCME Professional Development Opportunities for You! • Online short courses • Cleanroom Pressure Sensor 4-day short course • 40+ learning modules • YouTube channel – short lectures, animations www.scme-support.org
Interested in joining us? We support two MNT educator groups: 1. MNTeSIG – Micro Nano Tech education Special Interest Group • Meets every 2-3 months online • Face to Face meeting 1/yr as part of HI TEC Conference (High Impact Technology Education Conference) – next year in St. Louis • Member driven agenda • www.MNTeSIG.net – New Under Construction (give it a couple of weeks)
2. MNT ATMAE Focus Group (working on growing this into a division) Contact: Matthias Pleil –
[email protected] Cell: 505-363-3428 if you want to chat further
Abstract Advanced engineering and technology programs are under constant pressure to continually evolve and engage students. The MEMS (microsystems) industry continues to grow at 10-15% compounded annual growth rate (CAGR), fueling an every-increasing demand for additional technicians and engineers. Developing curricula to support these emerging technologies is timeconsuming and costly for engineering education departments. The Support Center for Microsystems Education (SCME), a National Science Foundation-funded Advanced Technological Education Center, (DUE #1700678) provides online short courses, training, mentoring, and handson educational materials targeting two-year technician, four-year engineering and microtechnology industry training programs. Since its inception in 2004 as a regional center, the SCME developed a fundamental pressure sensor design and set of manufacturing processes as a vehicle to develop supporting educational materials to provide an engaging, interactive way to learn how MEMS devices are used and made. In this paper, the author describes the adaptation of these materials into a special topics MEMS microfabrication course for graduate and undergraduate engineering students at the University of New Mexico utilizing the Manufacturing Training and Technology Center (MTTC) clean room facilities. Through hands-on clean room laboratories, students learn essential concepts of bulk and surface micromachining, photolithography process and characterization, thin film growth, deposition and measurement methods while practicing analysis, presentation and teamwork skills. The three-credit hour, semester long course requires students to spend 5hrs in the cleanroom plus 2hrs/week lecture, team presentation and discussion time in addition to work outside of class. Student work and initial perceptions will also be presented.
