PolyMUMPs process

8/12/2019 PolyMUMPs process

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Introduction to MEMS Design &

Micromachining

Chapter 1(Three Layer PolySi Surface Micromachining Process)

Reference:PolyMUMPs Design Book Version 11.0

Dr Shafaat Ahmed

HEC Foreign Professor

Center for Advanced Studies in Engineering,

Islamabad, Pakistan


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1 Basic Micromachining Steps

Wafer

Deposition/

Growth Lithography Etch

MEMS

Chips

Steps in fabrication cycle

Basic steps: Deposition/Growth, Lithography, Etch

Other steps: doping, bonding, annealing,

Integrated Circuits and MEMS steps Identical

Process complexity/yield related to central loop

Reference: Chapter 8 from Hsus book


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2 Micromachining Classifications

Bulk Micromachining

Surface MicromachiningLIGA (X-ray lithography, electro-deposition, and molding)


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2.1 Bulk Micromachining

Bulk micromachining is a process based on etchingwells in the silicon, glass or any other substrate,leaving suspended structures by anisotropic andselective etching.

Deposit thin films on substrate and pattern themlithographically, Selectively etch away a portion ofthe substrate to form a free standing 3-Dmicrostructures bound by a cavity

Typically wet etching and relatively less expensiveequipment

Anisotropic etchants: KOH, EDP (Ethylene-Diamine-Pyrocatechol), TMAH (Tetra-Methyl AmmoniumHydroxide)

Isotropic Etchants:

HF (nitric and acetic acids, difficult to work with),

XeF2, BrF3(gas phase, gentle)

Echants demonstrate different etch rates in differentcrystal directions

etch rate is slowest, and fastest

Fastest:slowest can be more than 400:1

Etch stops: p+ silicon, p-n junction

Etch mask: SiO2, Si3N4

Issues with IC compatibility


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2.1 Bulk Micromachining

CMOS compatible Bulk Micromachining Supported CAN-MEMS post-process from 1997-1999 MITEL1.5, Supported since 1995. Last Run in August 2001

Presently some universities have the post-processing capability

Deposition of Pt and Si3N4layer on Bonding pads of CMOS Mitel1.5

Back side etching maskWafer Front Side Opening


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2.1 ProtolyneTM Technology from

Micralyne

Low cost proto-typing technology on glass

substrate for microfluidic applications. Design of Microchannels Courtesy ofRichard Oleschuck,

Queens University

Glass

Substrate

Bottom Plate

Etch

Holes=1.5 mmDeposit Mask

Pattern Mask

Litghography

Etch Channels in

Glass Substrate

Remove

Mask Layer

Etch Holes on

Top Plate= 2 mm

Etch Holes on Top

Glass Plate= 2 mm


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2.1 Bulk Micromachining- Examples

SEM photo of an etched cavity plus

an oxide arrow: (rectangulargeometry in (100) plane of Si wafer

Piezo resistive flow sensor fabricated by

anisotropic wet chemical etc. Slantedetched side walls (111) plane orientation

CMOS compatible bulk micromachining

suspended inductor


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Deposit thin films on substrate and pattern them lithographically, Selectivelyetch away one or more intermediate thin films to release a free standing 3-D onthe top of the substrate.

This leaves the wafer untouched, but add/remove layers above the wafersurface

2.2 Surface Micromachining


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2.2 Surface Micromachining Issues

Gear Train, Courtesy of Ash Parameswaran, Simon Fraser

University

CMOS compatible release etchant (HF) which does not attack Si

High temperature annealing to remove residual stresses from PolySi. DamageIC metalization

Release layer provides electrical isolation between electrostatic device elements

Typically Plasma etched and relatively expensive equipment


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2.2 Surface Micromachining Materials

Structural Sacrificial Etchant

PolySilicon Silicon Dioxide HF

Silicon Dioxide PolySilicon XeF2

Aluminium Photoresist O2Plasma

Photoresist Aluminium Al etch

Aluminium Single Crystal

Silicon

EDP, TMAH, XeF2

Poly-SiGe Poly-SiGe DI water


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3. Poly-Multi User MEMS Processes (Poly-MUMPs)

MUMPs: A Surface

Micromachining Process

3 Poly silicon layers

1 metal layer

2 Oxide Layers

1 Silicon Nitride layer

Multi ProjectWafer

More information on MUMPS:

http://www.memscap.com/

Ref: PolyMUMPs Design Book
http://www.memscap.com/http://www.memscap.com/


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3.1 PolyMUMPs Process Overview


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3.1 Step-by-step development of PolyMUMPs Process Layers


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4.1 MEMS Development in PolyMUMPs

Provides access to standard and reliable technology

to develop MEMS structures at reasonable cost

Process has fixed set of rules: material. Layer

thickness, gaps.

Designer has to converge his design to PolyMUMPs.

Keep in mind, dont expect PolyMUMPs to fulfill your

design requirements

Multi Project

Wafer


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5.1 Some design developed in PolyMUMPs Process

Heat ctuator based microgrippers

Poly1 is used as structural layer for gripper and heat actuators Poly2 and Metal is used for interconnections Pads are used for electrical probing the heat actuators during testing Not necessary to use all layers


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5.1 Some design developed in PolyMUMPs Process

ccelerometer

Si Nitride is used to isolate the device from substratePoly0 is used as base electrodePoly1 is used as structural layer to make the proof mass and springsPoly2 combined with Poly1 to increase the thicknessEtch holes on Poly2 layer ensure fast removal of sacrificial layer

Pads are used for electrical probing during testing

4 1


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4.1 PolyMUMPs in L-Edit

Menu bar Standard toolbar

Locator

Status bar

Drawing toolbar

Layer

palette

Mouse

button bar

MEMS Pro toolbar

Place & route

toolbar

Verificationtoolbar

Editing

toolbar

3D model

toolbar

Layout Area

4 1 L P l tt


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4.1 Layer Palette

Layer Name

Layer Palette

Scrollbar

3 Parts: names, icons, scrollbar

Used to display & select activelayer.

Mouse button functions on

icons:

Left: select layer

Middle: hide/show layer

Right: hide/show/lock/unlock

individual or all layers.

Each step (deposit, etch,

mask) of PolyMUMPs processhere is represented by a

LAYER NAME with specific

color

4 2 S t T h l Fil


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4.2 Setup Technology File

L-Edit uses a 256-color palette.

Each file has its own colorpalette.

These are colors that can beused to represent objects in that

file. Click on the color/code on the

left to select the color to edit.

Color: displayed color

Code: a 4-bit binary code to

represent the color. Composition: RGB (red, green,

and blue) component of the color(0-255).

Setup> Palette L-Edit command)

color code composition

4 2 Set p Design Technolog


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4.2 Setup DesignTechnology

Specify Technology name.

Specify Technology units Microns

Millimeters

Centimeters

Mils

Inches Other

Specify relationshipbetween L-Edit internalunit(used for calculation)and Technology unit.

Rescaling options:

Maintain physical size ofobjects

Rescale the design

Technology Unit

4 2 Setup Layers


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4.2 SetupLayers

Setup > Layers (L-edit command)

Setup Layers Layers List


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Setup LayersLayers List

First 7 layers (Layout Gridthrough

Error Layer) are Special LayersforL-Edit system objects.

The rest are custom layout layers.

To edit a layer: select a layer from

the list box.

To add a layer: click Add layer.

To remove a layer: click Delete layer.

To rearrange layers: click

or

buttons.

Name of the highlighted layer can

be specified in the Layer namebox:

Documents

PolyMUMPs process