ME 645: MEMS: ME 645: MEMS: Design Fabrication Design Fabrication - - PDF document

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ME 645: MEMS: ME 645: MEMS: Design Fabrication Design Fabrication

Lecture 11_12_13: PolyMUMPS (Multi User MEMS process) + Flexure mechanisms for MEMS Comb drives

Design, Fabrication Design, Fabrication and Characterization and Characterization

P.S. Gandhi P.S. Gandhi Mechanical Engineering Mechanical Engineering IIT Bombay IIT Bombay

PRASANNA S GANDHI gandhi@me.iitb.ac.in PRASANNA S GANDHI gandhi@me.iitb.ac.in 1 1

Today Today

Pressure sensor: full

Pressure sensor: full fabrication fabrication

MUMPS

MUMPS

Details of

Details of PolyMUMPs PolyMUMPs process process

Design rules

Design rules

Ledit

Ledit software to develop your device by software to develop your device by

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Ledit

Ledit software to develop your device by software to develop your device by polyMUMPs polyMUMPs process process

Examples of the devices made by

Examples of the devices made by polyMUMPS polyMUMPS

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Pressure sensor Pressure sensor

Q:

Q: How do you conceive pressure sensor at How do you conceive pressure sensor at MEMS scale? MEMS scale?

Basic

Basic conceptual ideas conceptual ideas

Structure??

Structure??

Electromechanical

Electromechanical sensing element?? sensing element??

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Diaphragm subjected to differential pressure Piezoresistive sensing

Electromechanical Electromechanical sensing element?? sensing element??

Absolute Pressure Absolute Pressure Sensor Sensor

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Fabrication steps for a piezoresistive gauge or differential, bulk micromachined pressure sensor Insulator n-type epitaxial layer p-type substrate p-type diffusion Metal

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Silicon nitride

1: Deposit Insulator 2: Diffuse piezoresistors 3: Deposit and pattern material 4: Electrochemical etch of backside cavity

Glass

5: Anodic Glass bonding

Capacitive Capacitive Accelerometer Accelerometer

Bulk Micromachining Bulk Micromachining Silicon Mass Hinge

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1: Etch recess cavities in silicon 2: Deposit and pattern 3 masking layers; Anisotropic etch silicon 3: Remove first masking layer; Anisotropic etch silicon 4: Remove second masking layer ; Anisotropic etch silicon

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MUMPs Process MUMPs Process

Multi User MEMS process

Multi User MEMS process

Company MEMSCAP: offers PolyMUMPS,

Company MEMSCAP: offers PolyMUMPS, MetalMUMPS, and SOIMUMPS MetalMUMPS, and SOIMUMPS

Developed at BSAC (Berkeley Sensors and

Developed at BSAC (Berkeley Sensors and Actuators Center) in late 80’s Actuators Center) in late 80’s

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)

We will study PolyMUMPs a 3 level polysilicon

We will study PolyMUMPs a 3 level polysilicon micromachining process micromachining process

Cleaned Silicon Wafer

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Clean Silicon Wafer

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Doping of Phosphorous on silicon wafer Using Standard diffusion furnace using POCL3 as

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furnace using POCL3 as Dopant source Prevent charge feed through to substrate from electrostatic devices on the surface

Clean Silicon Wafer

Deposition of Silicon Nitride layer of thickness 600nm Using Standard LPCVD (Low Pressure Chemical

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(Low Pressure Chemical Vapor deposition) Acts as insulation layer

Clean Silicon Wafer Silicon Nitride layer

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Deposition of polysilicon film Thickness 500nm Using Standard LPCVD (Low Pressure Chemical

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(Low Pressure Chemical Vapor deposition)

Clean Silicon Wafer Silicon Nitride layer Poly0 layer

Deposition of Photo resist Thickness 500nm Spin Coating method

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer Photo resist layer

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Masking process Thickness 500nm Mask UV Source and Mask

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer Photoresist layer

Masking and Exposure with UV source followed by development of photoresist Mask photoresist Thickness 500nm

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer Photoresist layer

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Etching of poly0 layer Thickness 500nm Reactive Ion Etching (RIE)

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer

(RIE) After etching photoresist is stripped in solvent bath Deposition of PSG (Phosphosilicate Glass) layer Thickness 2 μm Thickness 2 μm LPCVD process is used to deposit PSG (1st Oxide

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide)

to deposit PSG (1st Oxide Layer) layer this is first sacrificial layer

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Lithographic patterning of DIMPLE Depth 750 nm Depth 750 nm Dimples Wafer is coated with photoresist and second

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide)

photoresist and second level (DIMPLE) is lithographically patterned. Dimples are reactive ion

• etched. After etching

photoresist is stripped Lithographic patterning of ANCHOR1 Dimples Anchor 1 Etch Wafer is coated with photoresist and second

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide)

photoresist and second level (ANCHOR1) is lithographically patterned. Anchor1 is reactive ion

• etched. After etching

photoresist is stripped

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Deposition of POLY1 Layer along with PSG hard mask PSG Mask

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide) Poly1 Layer

Lithographic patterning of POLY1 layer 2nd Oxide Layer Wafers are recoated with photoresist and third level

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide) Poly1 Layer 2nd Oxide layer

photoresist and third level (Poly1) is lithographically

• patterned. PSG is first

etched to create a hard mask and then poly1 is etched by RIE after etching photoresist and PSG mask are removed

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Deposition of 2nd

• xide layer

2nd Oxide Layer Second oxide layer 0.75 μm of PSG is deposited

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide) Poly1 Layer 2nd Oxide layer

μm of PSG is deposited

• n water. This layer is

patterned twice to allow contact to both poly1 and substrate layers. Lithographic patterning of P1_P2_Via Etch

P1-P2 Via Etch P1-P2 Via Etch

Wafer is coated with photoresist and fifth level

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide) Poly1 Layer 2nd Oxide layer

photoresist and fifth level (POLY1_POL2_VIA) is lithographically patterned. Unwanted second oxide is etched in RIE, stopping

• n POLY1 and

photoresist is stripped

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Lithographic patterning of using ANCHOR2 Etch

Anchor 2 Etch

Wafer is coated with photoresist and sixth level

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide) Poly1 Layer 2nd Oxide layer

photoresist and sixth level (ANCHOR2) is lithographically patterned. Second and first oxide are etched in RIE, stopping on either POLY0

• r Nitride and photoresist

is stripped Deposition of polysilicon and PSG hard mask dopping process process

PSG Mask

A 1.5 μm undoped polysilicon layer is

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide) Poly1 Layer 2nd Oxide layer Poly2 Layer

polysilicon layer is deposited followed by 200 nm PSG hard mask

• layer. The wafers are

annealed at 10500C for

• ne hr and dope the

polysilicon and reduce residual stress

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Lithographic patterning of POLY2 Wafer is coated with photoresist and seventh

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide) Poly1 Layer 2nd Oxide layer Poly2 Layer

photoresist and seventh level (POLY2) is lithographically patterned. PSG hard mask and Poly2 layers are etched in RIE, Deposition of Metal Layer

Metal Layer

Wafer is coated with photoresist and eighth

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide) Poly1 Layer 2nd Oxide layer Poly2 Layer Metal Layer

photoresist and eighth level (METAL) is lithographically patterned. Metal (gold with this adhesion layer) is deposited by lift off patterning.

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Releasing a structure

Metal Layer

The structure are released by immersing

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Clean Silicon Wafer Silicon Nitride layer Poly0 layer PSG layer (1st Oxide) Poly1 Layer 2nd Oxide layer Poly2 Layer Metal Layer

released by immersing the chip in 49 % HF

• solution. POLY! “rotor and

POLY2 “hub” are relesed.

MUMPs Process MUMPs Process

Software Ledit for developing your own

Software Ledit for developing your own designs: Demo designs: Demo

Some designs in the software

Some designs in the software

How they look like after fabrication!!

How they look like after fabrication!!

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PolyMUMPs PolyMUMPs Process: Process: Case study Case study

Design of an XY flexural

Design of an XY flexural nanostage nanostage: :

Need some fundamentals of flexure so

Need some fundamentals of flexure so will look that in details will look that in details

Concept of flexure mechanism

Concept of flexure mechanism

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Idea: to have motion without friction

Idea: to have motion without friction

Think how will you get such motion?

Think how will you get such motion?

Flexure Mechanism Flexure Mechanism

Advantages Advantages

No friction and hence no

No friction and hence no d t d t wear and tear wear and tear

Nanometric

Nanometric positioning positioning accuracy over wide range accuracy over wide range possible possible

Many different variations

Many different variations for the purpose of for the purpose of achieving both x and y achieving both x and y

Parasitic error

achieving both x and y achieving both x and y motions motions

Some of them shown here

Some of them shown here

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Poly MUMPs Designs: Poly MUMPs Designs: case study case study

XY t XY t

• XY stage

XY stage

• Mechanism with

Mechanism with decoupled decoupled motions in x and motions in x and y directions y directions

• Actuation using

Actuation using comb drives comb drives Fl l t Fl l t

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• Flexure also acts

Flexure also acts as guide to comb as guide to comb drives drives Q: How to design masks for realizing such a design

Design I Design I

Poly0 Poly1 Poly1-Poly2 via Poly2 Anchor1

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Metal

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MUMPs Designs MUMPs Designs

C b t t C b t t

• Comb actuators

Comb actuators by by PolyMUMPS PolyMUMPS

• Ackn

Ackn: University : University

• f Colorado,
• f Colorado,

Boulder. Boulder. Hrishikesh Hrishikesh Panchwagh Panchwagh

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Comb Drives Comb Drives

Electrostatic

Electrostatic actuators for MEMS actuators for MEMS

Analysis

Analysis

Applications

Applications

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Comb Drives: Comb Drives: actually fabricated actually fabricated

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Design need: Perfect Design need: Perfect linear guidance linear guidance

• What will happen if guide is not their

What will happen if guide is not their

• What will happen if guide is not their

What will happen if guide is not their

• r not designed properly?
• r not designed properly?

Guiding flexure mechanism

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Comb Drives: Comb Drives: Analysis Analysis

Basic equations for

Basic equations for

l

Basic equations for Basic equations for parallel plate parallel plate capacitor: capacitor:

w 2

2 1 CV E =

d

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2

2 1 V d Wl

r

ε ε = x E Fx ∂ ∂ − =

y x z

y E Fy ∂ ∂ − = z E Fz ∂ ∂ − =

Comb Drives: Comb Drives: Analysis Analysis

Based on these

Based on these Based on these Based on these fundamentals one can fundamentals one can easily derive equations easily derive equations for comb drive force for comb drive force

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y x z

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Comb Drives: Comb Drives: Applications Applications

Electrostatic

Electrostatic actuators for actuators for micromirrors micromirrors: example Out of plane : example Out of plane mirrors mirrors

Actuators to create rotary motion

Actuators to create rotary motion

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Widely used in sensors as well: New

Widely used in sensors as well: New concept to enhance the range of concept to enhance the range of sensing: How? sensing: How?

Enhancing Range: Enhancing Range: sensors with actuator sensors with actuator

Example: Measurement of

Example: Measurement of

Example: Measurement of

Example: Measurement of weight weight

What the sensitivity and

What the sensitivity and range of measurement range of measurement depend on?? depend on?? Think of a way to use Think of a way to use

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Think of a way to use

Think of a way to use actuator while measuring : actuator while measuring : Electromechanical system Electromechanical system

Similar concept can be applied very easily in MEMS based sensors: Example cantilever

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Thank You Thank You

PRASANNA S GANDHI gandhi@me.iitb.ac.in PRASANNA S GANDHI gandhi@me.iitb.ac.in 41 41