Thayer School of Engineering Winter 2008

ENGS 135–Thin Films and Microfabrication

The associated techniques of microfabrication and thin film deposition play an important role in modern science and engineering, with applications ranging from thin film optical coatings to microelectronics and microelectromechanical systems (MEMS). This course starts with theoretical and experimental background in the vapor deposition of thin films, and characterization of such films for optical, electrical, and mechanical applications. We next consider how such films can be patterned to form integrated systems of very small parts. We take a MEMS micromotor, a pressure sensor, and CMOS transistors as case studies. We then fill out the toolbox of microfabrication processing techniques with additional growth, deposition, doping, and etching techniques, and provide design experience using a microfabrication layout editor (L-Edit). We also compare top-down approaches (such as photolithographic patterning) to bottom-up approaches (such as self-assembling structures), and we consider the implication of scaling laws on effective microsystem design. The course will include field trips to industrial thin film and MEMS fabrication facilities.

Course assignments will include: reading, lab work and reports, two student paper/presentations, a layout design project, homework, and quizzes.

Prerequisite: ENGS 24 (Materials Science), equivalent, or consent of instructor.

Course Objectives:
At the end of this course, students may expect to
  1. Be able to specify vacuum system components suitable for vapor deposition, including both sputtering and thermal evaporation.
  2. Be able to relate deposition conditions to the microstructure and performance of a thin film.
  3. Be able to design simple anti-reflection and high reflectance coatings.
  4. Have a working knowledge of photolithography, etching, software design layout tools, and other microfabrication techniques.
  5. Be able to design and specify the fabrication process for a simple micromachine.
  6. Know the principles and processes involved in formation of a MOS transistor.
Following a short introduction by Gibson and Levey, the course will be taught in two sections; the first, on thin films and vacuum technology by Prof. Gibson and the second, on microfabrication by Prof. Levey.

Thin films & vacuum technology (Prof. Gibson)

This half of the course is designed to give you some theoretical and experimental background in vapor deposition of thin films, some simple patterning techniques, and the optical and electrical implications of material in thin film form. 

Assignments -
Weekly lab reports
Midterm paper  
Reading and weekly online quizzes
The Honor Principle
Quizzes: The quizzes will be open book and open notes, but there will be a time limit. You may not discuss the content of the quizzes with any other person until after the quiz is no longer available.
The paper requires you to pull together background information from a variety of sources, to use quotations and footnotes appropriately, and to write a bibliography. Please make sure that you do not fall into the trap of unwitting plagiarism. If you have doubts about what needs to be acknowledged, and how, please come and see one of us early enough in the writing process that we can avert problems. Please note that photocopied figures need to be referenced, and that any material drawn from the web must be acknowledged by the full URL. You are encouraged to utilize the expertise of the faculty, but all assistance should be footnoted and acknowledged.

Microfabrication (Prof. Levey)

The first half of the course concerns thin films, and stacks of such films of various thicknesses, i.e. a pattern in the vertical dimension. We now expand our design space to include patterning in lateral dimensions to create integrated systems of very small parts (ICs and MEMS). We motivate and organize discussion of the fabrication techniques required by looking at the steps required to make a surface micromachined motor, a MEMS pressure sensor, and a MOS transistor. 

Assignments-
Weekly Lab reports
Midterm paper presentation
Reading, quizzes, homework
Design Project

Outline of Microfabrication Section


Surface MEMS motor
Overview
CAD design/layout
Mask making
Wafer preparation (crystal growth covered with CMOS)
Chemical Vapor Deposition: nitride, oxide, doped oxide (PSG), and poly-silicon
Photolithography
Metal deposition by evaporation
Etching by RIE
Release and wet etching
Bulk MEMS diaphragm
Overview
Hard masks
Wet anisotropic etching, crystal orientation
Overview of related techniques (LIGA, deep RIE)
MOS Transistor
Overview
Silicon crystal growth, wafering, polishing
Wafer cleaning for microelectronics
Thermal oxidation (wet and dry)
Etching for microelectronics
Ion implantation
Passivation
Ohmic contacts

Other Techniques (Student Presentations)

TBA

INSTRUCTORS:

Ursula Gibson, 219c Cummings, 646-3243
Christopher Levey, 217e Cummings, 646-2071

TEXTBOOKS:

  1. Introduction to Microelectronic Fabrication, 2nd Edition, Richard C. Jaeger, Prentice hall, 2002.
  2. The Materials Science of Thin Films, Milton Ohring, Academic Press, 1992.