BioMEMSLecture 7 and 8

8/13/2019 BioMEMSLecture 7 and 8

http://slidepdf.com/reader/full/biomemslecture-7-and-8 1/27

Biomicroelectromechanical systems

Lecture 7 and 8

Shantanu Bhattacharya



Review of previous lecture

•Photolithography

•Plasma definitions.•Types of plasma

systems.



Magnetically enhanced plasma

Ref :Boumans, P.W.J.M., Inductively coupled plasmaemission spectroscopy, Interscience publication, New York

Another type of

plasma is enhanced

magnetically. Theplasma used in our

case the ICP or

inductively coupled

plasma is also

enhanced

magnetically. A streamof gas in led into the

plasma chamber.




e-

+

Inlet

gas

Outletgas


A Tesla coil placed on

the top of the chamber is

activated to cause anelectrical discharge. This

discharge causes some

gas atoms to dissociate

and come to excited

states and also generate

ions and electrons.




e-

+

Inlet

gas

Outletgas

B

R= m v

q B

m= Particle mass

v= Particle velocity

q= particle charge

B= magnetic field




Outer Gas

Inner Gas

ICP Matching

Network ICP Coil

View PortWindow

ChamberBlock

Helium Coolant Inlet

Vacuum Port

Chuck

ProcessGas Inlet

RIE Matching

Network

Trion Inductively coupled plasma systemThe inner and outer gas

streams mix inside the

chamber

1. Ref: Service and warranty manual ,TrionTechnologies

The figure on the left shows a schematic of the gas piping that leads the process gasesinto the chamber. Two streams of gases are injected. One is the inner stream that is the

main process gas. The secondary stream shot at an angle is mainly used to produce

turbulence in the plasma chamber as the molecules in the secondary stream have

higher velocities and are directed an an angle.The plasma is produced in the same way

as mentioned in the previous slides. The addition in this case is the application of an RF

Bias which drives the plasma to the substrate.



MEMS materials

• Silicon and microelectronic materials• Glass, Quartz

• Polymers

– Poly (dimethylsiloxane) (PDMS)

– Poly (methyl methacrylate) (PMMA)

– Teflon, etc.

• Biological Entities

– Cells, Proteins, DNA – Frontier of BioMEMS !



Some Fabrication Methods for soft materials

• Soft Lithography – Replication and molding

– Micro-contact printing

– Micro-molding in capillaries

– Micro-transfer molding

– Solvent assisted micro-molding

– Dip Pen Lithography

• Compression Molding

– Hot Embossing

– Injection Molding

• Inkjet Printing

Evan et. al., 2007, NC

state at Chapel Hill



Replication and Molding



Micro contact printing

Ink the PDMS structure with

molecules (alkylthiols,

proteins, DNA, etc.)

• Transfer the layer throughphysical contact in a gold

layer (optimize time)

• Inking is performed via

covalent binding onsubstrate

• Can be performed on flat

surface or curved surface



Capillary moulding (Used for micropatterning)

SU8- Thick –ve

resist

UV exposure

SU8- Thick –ve

resist

Master Mold

SU8- Thick –ve

resist

PDMS soft mold

release

Thermosetting resin

paste

Coating the paste

Capillary infiltration

Ribs for PDP (release the mold)

•Create a master and replicate a polymer layer to

create capillaries.

•Spin coat the resin to be patterned

•Contact the polymer replica for the resin to go in the

capillary.

•Usually have a thermosetting component and so the

replica can be released to obtain the ribs.



Dip Pen Lithography

AFM Tip used to ‘write’ molecules

• Being commercialized by Nanoink,

Inc.

• SAMs, DNA, Proteins, etc.

• Serial (need array of cantilevers for

parallel writing)

• Continuous source of molecules –microfluidics .



Compression Molding

•Take a patterned hard substrate that can

withstand heat and pressure without much

deformation.

•Press this over a spun on thermoplastic

polymer layer, heat the ensemble and

release it.

Cavity

Barrel

Hopper Hydraulic

screw drive

and gearing

Clamping

unit

Heater bands Screw

Features down to 0.1um

deep and 0.6um wide (for

CD-R)

l h h



Nano imprint lithographyImprint mold with

10nm diameter

pillars

10nm diameter hole

imprinted in PMMA

10nm diameter metal

dots

• Nano-scale extension of hotembossing

• Need a nano-scale master mold

• Added to ITRS Roadmap



Plasma assisted etching

•Etching is an act of engraving by means of which, an agent eats away lines or

surfaces left unprotected in different substrate.

•The extent of undercut is given as etch anisotropy (A).

Rv

Rl A 1

Where, Rl= Lateral etch, Rv= Vertical etch

If A=1, lateral etch iszero, Etch is perfectly

anisotropic

Photoresist

If A<1, lateral etchexists

103 101 10-1 10-3 10-5

High-pressure

plasma etching

Reactive ion

etchingIon Milling

Pressure (torr)

Different plasma etching regimes

1. Ref: Morgan, R.A., Plasma Etching in semiconductor

fabrication Elsevier Amsterdam 1985.



Steps for Plasma etching

+

e-

e-

e-

e-

+

+

+

+

*

*

*

*

*

Cation

Electron

High energy

species

1. Ref: Boley Forrest I., Plasmas –

laboratory and cosmic,D. Van Nostrand Company, Inc., Priceton, New Jersey.




+

e-

e-

e-

e-

+

+

+

+

*

*

*

*

*

*

1. Ref: Boley Forrest I., Plasmas – laboratory and cosmic,

D. Van Nostrand Company, Inc., Priceton, New Jersey.




+

e-

e-

e-

e-

+

+

+

+

*

*

*

*

*

*

Chemical

reaction

1. Ref: Campbell, Stephen A., Science of microelectronic

fabrication, Oxford University Press, New York, 1996




+

e-

e-

e-

e-

+

+

+

+

*

*

*

*

*

*

Reaction

products

Outlet

1. Ref: Campbell, Stephen A., Science of microelectronic

fabrication, Oxford University Press, New York, 1996



Results: Fabrication Methodology Develo ped

Si

CH3

CH3

O

UV

Si

CH2OOH

CH3

OO2

-CH2O

Si

.

CH3

O OH+

.

Si

OH

CH3

O

Si

CH3

CH3

OSi

CH3

CH3

O

UV

Si

CH2OOH

CH3

OO2

-CH2O

Si

.

CH3

OSi

.

CH3

O OH+

.

Si

OH

CH3

O

Change of

PDMS

surface on

exposureto Oxygen

Plasma

Hydrophilic

groups

109o

Untreated PDMS

20o

Treated PDMS

Ref:Surface wettability studies in PDMS and glass and its correlation with bond strength, S.Bhattacharya, A. Datta, J.Berg and S. Gangopadhyay, JMEMS, Vol. 14, No.3, pp.590-597



Bond Strength Measurement

Blister Size 3mm

PEEK1 tubing

Steel tube

(23 gauge)

Epoxy

Schematic of blister

Plan view

Elevation

1 Poly Eukaryotic

Ether Ketone

Testing of bond

strength using

compressed air

PDMS-PDMSblister after

testing

Glass-PDMSblister after

testing



Effect on PDMS surface of Plasma exposure

Surface transformations on exposure to Oxygen plasma

Si

CH3

CH3

O

UV

Si

CH2OOH

CH3

OO2

-CH2O

Si

.

CH3

O OH+

.

Si

OH

CH3

O

Si

CH3

CH3

OSi

CH3

CH3

O

UV

Si

CH2OOH

CH3

OO2

-CH2O

Si

.

CH3

OSi

.

CH3

O OH+

.

Si

OH

CH3

O

Si

CH3

CH3

O

UV

O2

Si

.

CH3

O

+

.

Si

OOH

CH3

O

CH3

O2 -OH

.

Si

.

CH3

O

Si

.

CH3

O

+

O

Si

CH3

O Si

CH3

O

O O

Si

CH3

CH3

OSi

CH3

CH3

O

UV

O2

Si

.

CH3

OSi

.

CH3

O

+

.

Si

OOH

CH3

O

CH3

O2 -OH

.

Si

.

CH3

O

Si

.

CH3

OSi

.

CH3

O

+

O

Si

CH3

O Si

CH3

O

O O

Scheme1

Scheme2

1. Ref: Hillborg H., Gedde U.W., IEEE transactions ondielectrics and electrical insulation, Vol. 6 No. 5,

October 1999.



Surface cracking and oozing out of Oligomeric chains

Thin Silica

Layer

PDMS

Bulk

Cracks on the

Silica Layer

Short chain oligomers

coming up from the bulk

PDMS

Uncracked protective silica

layer

Cracked due to

harsher

treatments

1. Ref: Plasma treatment of Poly (dimethyl) silaxane, Owen M.J., Smith P.J.,

Journal of adhesion science and technology, Vol.8, No. 10, pp. 1063-1075, 1994

ff b h



Differences between various etch regimes

S.N. High PressureEtching Ion Milling Reactive Ion Etching

1 Mean free path of

the species is much

less than chamber

size

Mean free path is

comparable to

chamber size because

of low pressures

Moderate mean free

path of the species.

2 The plasma is used to

start and stop

chemical reactions

The plasma is used to

abrade the substrate

by sputtering out

material

Processing is

primarily chemical

transformation of the

surface

3 Ion impact energy is

low .

Ion impact energy is

high

Moderate impact

energy

4 The plasma is

homogeneous and

isotropic

It has a high

directionality.

The degree of

anisotropy is higher

1. Ref: Spitzer Lyman, Jr., Physics of fully ionized gases,

BioMEMSLecture 7 and 8

Documents

Transcript of BioMEMSLecture 7 and 8