Presenter: Prof. David Garmire Agenda Minutes 1. Administrivia10 2. Photoresist and Patterning10 3. Deposition of Material25 4. Etching of Material25 5. Process Flow10 Lecture based in part on Chapter 2 of Kovacs Microsensors & Microactuators Lecture 2: Micromachining Review

Administrivia Meetings will be held 11:30-12:45  I will bring snacks, you can pack your lunch  May take a short break midway through Lab has CoventorWare installed Myuh website has a link to EE-693I  Will have a separate website located at:   Keep track of readings  Copies of powerpoint presentations + homeworks will be kept here Please give me your addresses

Photoresist and Patterning Positive Resists  Area of resist exposed to light becomes soluble to developer Negative Resists  “” insoluble “” Standard photoresist recipes  Positive resists - I, G, H lines from a mercury lamp  Use a mixture of DNQ (Diazonaphthoquinone) and Novolac resin  Negative resist – SU-8  Epoxy based polymer

Photoresist and Patterning Contact printing vs. stepper printing H. Kirchauer, 1998 Substrate Quartz Chrome Photoresist Substrate Quartz Chrome

Photoresist and Patterning Limitations  High throughput but diffraction limits resolution of features Substrate Quartz Chrome Photoresist

Photoresist and Patterning Current research approaches  Deep UV  Decrease in photoresist sensitivity at <200 nm  Need flatter masks  Electron-beam exposure  Maskless photolithography  Surface plasmonics  Nanoimprinting As you go to smaller feature sizes  Speed of processing decreases  Yield also decreases

Deposition of Material Many ways to add material to your wafer Generally known as:  Surface processing and surface micromachining  As opposed to bulk micromachining Caveat  “Adding material” may be defined in the broad sense  E.g. surface diffusion to create oxide layer

Vapor-phase Deposition Techniques (not just limited to metals) Resistive (thermal) Evaporation  Operating principle: heat material in low pressure to vaporize it  Simple! Electron-Beam Evaporation  Operating principle: excited electrons (10 keV) impact material  Fast! Sputtering  Operating principle: excited ions (Ar + ) impact material  Works on dielectrics  Good step coverage, good control Chemical Vapor Deposition (CVD)  Laser-driven Deposition Epitaxial Growth

Vapor-phase Deposition (not just limited to metals)

Electrodeposition (liquid  solid) Often done for Ni and NiFe deposition  Production of micro magnets Advantages  Can be done at room temperature in a beaker  (Relatively) cheap  Requires agitation and proper current density  Avoid electrolysis of the water Pulsed Electroplating (PEP)  Evens out the deposition  Increases the grain size

Electroless Deposition Can be done with Gold, Nickel, etc…  Requires a reducing agent  For Gold: KBH 4 and dimenthylamine borane (DMAB) Advantages  No current supply! Operating principle  Chemical instability  Seed layer forms on exposed catalyst surface  Formation continues from seed layer

Epitaxial Growth Silane on silicon  SiH 4  Si(s) + 2 H 2 Silicon tetrachloride (SiCl 4 )  SiCl H 2  Si(s) + 4 HCl Current experiments on using it for encapsulation

Topography Effects

Future of Deposition Roll-to-roll stamping of material  Low cost and high throughput  Difficult to keep equipment clean Printed MEMS  Sinter nanoparticle droplets  Low cost, No material wasted  Difficult to control variation Biotic MEMS  Use cells to deposit material  Difficult to understand signaling  Difficult to use standard materials From Wikipedia

Etching of Material Many ways to subtract material from your wafer Approach breakdown: Wet (liquid-based) etching  Isotropic  Anisotropic Gas or plasma (vapor-phase) etching  Deep Reactive Ion Etching (DRIE)  XeF 2 etching  Laser milling

Isotropic Wet Etching Most common:  HNA (HF + HNO 3 (nitric acid) + CH 3 COOH (acetic acid))  Operating Principle  Injection of holes into the Si to form Si + or Si 2+  Attachment of OH - to the positive ions of silicon  Removal of the Si(OH) 2 2+ compounds (complex and dissolution) Key to successful isotropic etch SiO 2 mask No AgitationWith Agitation

Anisotropic Wet Etching Most common  KOH and other hydroxides of Alkali metals  Ammonium hydroxide (useful if integrating with CMOS) KOH etches along the (111) plane 400 times more slowly than the (100) plane.  Refer to Si ball for details on

Deep Reactive Ion Etching (DRIE) Highly anisotropic  Yields very vertical sidewalls Operating Principles  Uses a chamber containing a plasma  Flourine radicals etch the silicon  Radicals are produced from the SF 6 plasma  A polymer is used to coat the sidewalls and prevent later etching: C 2 ClF 5 (Freon) or (CF2) teflon polymer In addition, laser-assisted chemical etching can be used.

Process Flow Create a process traveler  Itemize each step in the process  Piece of equipment used  Recipe used  Mask used  Approximate time needed  Machine reservation, qualification, special instructions Helps to plan the thermal budget May start from a sketch  Iterate and modify as necessary Post-processing information

Process Flow Example (switch to Word)

Process Flow Process rules

Some Standard Foundry Processes PolyMUMPS  X-fab  TSMC  Dalsa Check out the guidelines (designer’s manuals)