vacuum systems outline • vacuum principles • vacuum …eng.utah.edu/~gale/mems/lecture 03 vacuum...

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Fundamentals of Micromachining Vacuum Systems Outline Vacuum principles Vacuum pumps Vacuum materials and components Vacuum instrumentation Vacuum systems Uses of Vacuum in Microfabrication Rough Vacuum High Vacuum Ultra-High Vacuum wafer chucks evaporation surface analysis load locks ion implantation molecular beam epitaxy (MBE) sputtering reactive ion etching (RIE) low pressure chemical vapor deposition (LPCVD) Units of Pressure Measurement 1 atmosphere = 760 mm Hg = 760 torr 760,000 millitorr or microns 29.9213 in. Hg 14.6959 psi 1.01325 bar 1013.25 millibar 101,325 pascals (Pa) 407.189 in. H 2 O 33.9324 ft. H 2 O 1 Pascal = 1 N/m 2 1 Torr = 1 mm Hg 1 micron = 1 µm Hg 760 mm Hg 33.93 ft H 2 O

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Page 1: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Fund

amen

tals

of

Mic

rom

achi

ning

Vac

uum

Sys

tem

s

Out

line

•V

acuu

m p

rinc

iple

s

•V

acuu

m p

umps

•V

acuu

m m

ater

ials

and

com

pone

nts

•V

acuu

m in

stru

men

tati

on

•V

acuu

m s

yste

ms

Use

s of

Vac

uum

in M

icro

fabr

icat

ion

Rou

gh V

acuu

mH

igh

Vac

uum

Ult

ra-H

igh

Vac

uum

waf

er c

huck

sev

apor

atio

nsu

rfac

e an

alys

islo

ad lo

cks

ion

impl

anta

tion

mol

ecul

ar b

eam

epit

axy

(MB

E)

sput

teri

ngre

acti

ve io

n et

chin

g(R

IE)

low

pre

ssur

e ch

emic

alva

por

depo

sitio

n(L

PCV

D)

Uni

ts o

f Pr

essu

re M

easu

rem

ent

•1

atm

osph

ere

=–

760

mm

Hg

= 7

60 to

rr

–76

0,00

0 m

illit

orr

or m

icro

ns

–29

.921

3 in

. Hg

–14

.695

9 ps

i

–1.

0132

5 ba

r

–10

13.2

5 m

illi

bar

–10

1,32

5 pa

scal

s (P

a)

–40

7.18

9 in

. H2O

–33

.932

4 ft

. H2O

1 P

asca

l = 1

N/m

2

1 T

orr

= 1

mm

Hg

1 m

icro

n =

1 µ

m H

g

760

mm

Hg

33.9

3 ft

H2O

Page 2: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Vac

uum

Ran

ges

•L

ow o

r R

ough

Vac

uum

(L

V)

–76

0 to

10-3

torr

•H

igh

Vac

uum

(H

V)

–10

-3 to

10-8

torr

•U

ltra

-Hig

h V

acuu

m (

UH

V)

–10

-8 to

10-1

2 to

rr

Part

ial P

ress

ures

of

Gas

es in

Air

at S

TP

Gas

Sym

bol

Vol

ume

Per

cent

Par

tial

Pre

ssur

e, T

orr

Nitr

ogen

N2

7859

3O

xyge

nO

221

159

Arg

onA

r0.

937.

1C

arbo

n D

ioxi

deC

O2

0.03

0.25

Neo

nN

e0.

0018

1.4

x 10

-2

Hel

ium

He

0.00

054.

0 x

10-3

Kry

pton

Kr

0.00

018.

7 x

10-4

Hyd

roge

nH

20.

0000

54.

0 x

10-4

Xen

onX

e0.

0000

087

6.6

x 10

-5

Wat

erH

2OV

aria

ble

5 to

50,

typ

.

Idea

l Gas

Law

- 1

•V

= v

olum

e of

enc

losu

re

•N

= n

umbe

r of

mol

ecul

es

•N

m =

num

ber

of m

oles

= N

/NA

•n

= p

arti

cle

dens

ity

= N

/V

•P

= p

ress

ure

•T

= a

bsol

ute

tem

pera

ture

•k B

= B

oltz

man

n’s

cons

tant

= 1

.381

x 1

0-23

J/K

•N

A =

Avo

gadr

o’s

num

ber

= 6

.022

x 1

023 p

arti

cles

/mol

e

•R

= G

as c

onst

ant =

NAk B

= 8

.315

J/m

ole-

K

Tnk

P

TN

kP

V

RT

NP

V

BB

m

===

Idea

l Gas

Law

- 2

•H

isto

rica

l Law

s:–

Boy

le’s

Law

: P

1V1

= P

2V2

at c

onst

ant

T

–C

harl

es’

Law

: V

1/T 1

= V

2/T 2

at c

onst

ant

P

–G

ay-L

ussa

c’s

Law

: V

= V

0(1

+ T

/273

)

Page 3: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Kin

etic

Gas

The

ory

•V

eloc

ity

of a

mol

ecul

e is

•M

ean

squa

re v

eloc

ity

is

•Pr

essu

re e

xert

ed o

n a

wal

l in

the

x-di

rect

ion

is

•If

vel

ocit

ies

for

all d

irec

tion

s ar

e di

stri

bute

d un

ifor

mly

,

•T

hus,

•E

ach

mol

ecul

ar D

OF

has

an a

vera

ge e

xcit

atio

n of

k BT

/2.

zv

yv

xv

vz

yx

ˆˆ

ˆ+

+=

r

22

22

zy

xv

vv

v+

+=

2 xx

vnm

P=

22

3xv

v=

Tnk

vnm

PB

==

231

Tk

vm

B23

221

=

Dis

trib

utio

n Fu

ncti

ons

- 1

•B

oltz

man

n’s

post

ulat

es f

or a

n id

eal g

as:

–T

he n

umbe

r of

mol

ecul

es w

ith x

-com

pone

nts

of v

eloc

ity

in th

era

nge

of v

x to

v x +

dv x

is p

ropo

rtio

nal t

o so

me

func

tion

φ o

f v x

2

only

:

–T

he d

istr

ibut

ion

func

tion

for

spe

ed v

mus

t be

the

prod

uct o

f th

ein

divi

dual

and

iden

tica

l dist

ribu

tion

fun

ctio

ns f

or e

ach

velo

city

com

pone

nt:

zz

vzy

yvy

xx

vxdv

vN

dNdv

vN

dNdv

vN

dN)

()

()

(2

22

φφ

φ=

==

zy

xz

yx

zy

xvz

vyvx

dvdv

dvv

vv

dvdv

dvv

N

dN)

()

()

()

(2

22

2,

φφ

ψ=

=

Dis

trib

utio

n Fu

ncti

ons

- 2

•A

mat

hem

atic

al s

olut

ion

to th

e ab

ove

equa

tion

s ha

s th

efo

rm o

f (A

and

vm a

re c

onst

ants

):

•N

orm

aliz

atio

n of

the

dist

ribu

tion

fun

ctio

ns:

22

/2)

(m

xv

vx

Ae

v−

Nv

NA

dvN

Ae

dNm

xv

vvx

mx

==

=∫

∫∞ ∞−

−∞ ∞−

2/

22

π2/1

2)

(−

=mv

m

Tk

vdv

ev

vdN

vN

vB

mv

v

m

vm

34

12

23/

03

4

0

22

22

==

==

−∞

∫∫

π2/1

2

=

m

Tk

vB

mdv

vdv

dvdv

zy

x2

4π= D

istr

ibut

ion

Func

tion

s -

3

•N

orm

aliz

ed d

istr

ibut

ion

func

tion

for

a s

ingl

e ve

loci

tyco

mpo

nent

(Gau

ssia

n):

•N

orm

aliz

ed d

istr

ibut

ion

func

tion

for

vel

ocit

y m

agni

tude

(Gau

ssia

n):

•N

orm

aliz

ed d

istr

ibut

ion

func

tion

for

a r

ando

mly

dir

ecte

dve

loci

ty (M

axw

elli

an):

=T

kmv

Tkm

vB

x

Bx

2ex

p2

)(

22/1

2

πφ

=T

kmv

Tkm

vB

B2

exp

2)

(2

2/3

2

πψ

Tkmv

vT

kmv

BB

2ex

p2

4)

(2

2

2/3

2

ππ

Page 4: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Impi

ngem

ent R

ates

•T

he n

umbe

r of

mol

ecul

es w

ith

a ve

loci

ty f

rom

v x to

vx +

dv x

is d

Nvx

= N

φ(v x

2 ) d

v x.

•A

= a

rea

unde

r co

nsid

erat

ion.

•O

nly

thos

e m

olec

ules

with

in s

trik

ing

dist

ance

v xdt

wil

l hit

the

wal

l aft

er d

t sec

onds

.

•T

he n

umbe

r of

mol

ecul

es w

ith

velo

citie

s fr

om v

x to

v x +

dv x

impi

ngin

g up

on th

e w

all p

er ti

me

dt is

()

PT

mk

mTk

VN

Adt

dNB

Bi

2/12/1

22

−=

π

2/1

0

2

2)

(

=

∫∞

mTk

dvv

vB

xx

φdt

dvv

Av

VNN

dx

xx

vx)

(2

=in

tegr

ate:

Gas

Flo

w -

1

•V

isco

us F

low

–oc

curs

for

pre

ssur

es g

reat

er th

an 1

0-2 to

rr

–ga

s m

olec

ules

con

stan

tly

coll

ide

wit

h on

e an

othe

r

–co

llis

ions

wit

h ea

ch o

ther

are

mor

e fr

eque

nt th

an w

all c

olli

sion

s

–ga

s be

have

s li

ke a

coh

eren

t, co

llec

tive

med

ium

; it a

cts

like

a f

luid

•Fr

ee M

olec

ular

Flo

w–

occu

rs f

or p

ress

ures

less

than

10-2

torr

–ga

s m

olec

ules

trav

el f

or la

rge

dist

ance

s be

twee

n co

llis

ions

–co

llis

ions

wit

h w

alls

are

mor

e fr

eque

nt th

an w

ith

each

oth

er

–ga

s m

olec

ules

fly

inde

pend

entl

y of

eac

h ot

her

Gas

Flo

w -

2

•Pi

pe o

f ra

dius

r a

nd le

ngth

l:

•V

isco

us F

low

–P

oise

uill

e’s

equa

tion:

•Fr

ee M

olec

ular

Flo

w–

Knu

dsen

’s e

quat

ion:

)(

8

32)

(1

2

2/13

12

PP

mTk

lrP

PC

QB

mol

=

−=

ππ

()

2 12 2

4

12

16)

(P

Pl

rP

PC

Qvi

s−

=−

π

2/1

2

2

=

ππσ

ηT

mk

fB

Page 5: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Mea

n Fr

ee P

ath

•M

FP is

the

aver

age

dist

ance

a g

as m

olec

ule

trav

els

befo

reco

llid

ing

with

ano

ther

gas

mol

ecul

e or

the

cont

aine

r w

alls

.

•σ

is th

e di

amet

er o

f th

e pa

rtic

les

•πσ

2 is

the

cros

s-se

ctio

nal a

rea

for

hard

-sph

ere

coll

isio

ns

Mea

n F

ree

Pat

h (c

m)

=5

x 10

-3 to

rr-c

m

Pre

ssur

e (t

orr)

22

MFP

22

πσπσ

P

Tk

N

VB

==

For

com

mon

gas

es, {

H2O

, He,

CO

2, C

H4,

Ar,

O2,

N2,

H2}

, at T

= 3

00 K

:

Gas

Thr

ough

put

•Q

= P

S

•P

= g

as p

ress

ure

in to

rr

•S

= p

umpi

ng o

r le

akin

g sp

eed

in li

ters

/sec

ond

(L/s

)

•Q

= g

as th

roug

hput

in

torr

-lite

rs/s

econ

d (t

orr-

L/s

)–

Thi

s is

the

quan

tity

of

gas

mov

ing

thro

ugh

an o

rifi

ce p

er u

nit t

ime.

•Q

is d

irec

tly

rela

ted

to th

e po

wer

nee

ded

to m

ove

the

gas:

–1

Wat

t = 7

.50

torr

-L/s

ec =

100

0 Pa

-L/s

ec

•C

= g

as c

ondu

ctan

ce in

lite

rs/s

econ

d (L

/s)

•Q

= C

(P2

- P

1)

Vac

uum

Pum

p Pr

essu

re R

ange

s

-12

-10

-8-6

-4-2

0+2

Pre

ssur

e in

Tor

r (u

nits

are

exp

onen

ts o

f ten

)

Ultr

a-H

igh

Vac

uum

Hig

h V

acuu

mR

ough

Vac

uum

VE

NT

UR

I PU

MP

RO

TA

RY

PIS

TO

N M

EC

HA

NIC

AL

PU

MP

DR

Y M

EC

HA

NIC

AL

PU

MP

RO

TA

RY

VA

NE

ME

CH

AN

ICA

L P

UM

PS

OR

PT

ION

PU

MP

BLO

WE

R/B

OO

ST

ER

PU

MP

LIQ

UID

NIT

RO

GE

N T

RA

PD

IFF

US

ION

PU

MP

CR

YO

PU

MP

TU

RB

OP

UM

PIO

N P

UM

PT

I SU

BLI

MA

TIO

N P

UM

P

Page 6: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Vac

uum

Pum

ps

•T

wo

fund

amen

tal t

ypes

:–

Con

cent

rati

on p

umps

•G

as e

nter

ing

the

inle

t is

com

pres

sed

and

expe

lled

out

an

outl

et

•C

an r

un c

onti

nuou

sly

–E

ntra

inm

ent p

umps

•G

as e

nter

ing

the

inle

t is

trap

ped

insi

de

•M

ust b

e re

gene

rate

d to

em

pty

the

trap

ped

gas

Rot

ary

Van

e M

echa

nica

l Pum

ps -

1

Inle

tO

utle

t

Ele

ctric

Mot

or

Fra

me

Gas

Bal

last

Val

ve

Oil-

Fill

ed P

ump

Bod

y

Oil

Fill

Oil

Dra

in

Oil

Sig

htG

lass

Rot

ary

Van

e M

echa

nica

l Pum

ps -

2

Firs

t Sta

geS

econ

d S

tage

Gas

Bal

last

Val

ve

Inte

rsta

ge R

elie

f Val

veD

isch

arge

Val

ve

Rot

ary

Van

e M

echa

nica

l Pum

ps -

3

•G

ases

are

rem

oved

by

com

pres

sing

them

sli

ghtl

y ab

ove

atm

osph

eric

pre

ssur

e an

d th

en f

orci

ng th

em th

roug

h a

chec

k va

lve.

•T

he r

otar

y va

ne m

odul

es a

re im

mer

sed

in a

n oi

l bath

.

•T

he p

urpo

se o

f th

e oi

l is t

o:–

cool

the

pum

p

–lu

bric

ate

the

rota

ry v

anes

–pr

ovid

e a

lip

seal

for

the

vane

s

–op

en th

e se

cond

sta

ge e

xhau

st v

alve

at l

ow in

let p

ress

ures

•T

hey

are

pow

ered

by

an e

lect

ric

mot

or:

–B

elt d

rive

: 25

0 to

400

rpm

–D

irec

t dri

ve:

1725

rpm

(m

ost c

omm

on ty

pe)

Page 7: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Rot

ary

Van

e M

echa

nica

l Pum

ps -

4

•Po

tent

ial P

robl

ems:

–O

il m

ust h

ave

low

vap

or p

ress

ure

to a

chie

ve d

esir

ed p

erfo

rman

ce•

Wat

er o

r di

rt o

r im

puri

ties

in th

e oi

l wil

l rai

se th

e va

por

pres

sure

–B

acks

trea

min

g of

oil

vap

or c

an o

ccur

at l

ow p

ress

ures

•T

his

can

be tr

appe

d in

a m

olec

ular

sie

ve f

ilte

r

•M

ost o

ften

res

pons

ible

for

the

oily

sm

ell i

n a

vacu

um c

ham

ber

–L

arge

gas

load

s ca

n fr

oth

the

oil a

nd p

reve

nt s

eali

ng•

Gas

bal

last

can

be

open

ed to

all

ow f

roth

to s

ettl

e

•R

ough

ing

valv

es s

houl

d be

ope

ned

slow

ly (

feat

here

d) to

pre

vent

this

–B

elts

can

bre

ak o

n be

lt-d

rive

pum

ps•

Dir

ect d

rive

pum

ps e

lim

inat

e th

is p

robl

em

Sorp

tion

Pum

ps -

1

Sorp

tion

Pum

ps -

2

Liqu

id N

itrog

en B

ath

Sty

rofo

am L

N2

Buc

ket

Blo

w-O

ut P

lug

Alu

min

um B

ody

with

Inte

rnal

Fin

s

Mol

ecul

ar S

ieve

Nec

k F

lang

e

Sorp

tion

Pum

ps -

3

•G

ases

are

pum

ped

by–

Cry

ocon

dens

atio

n: g

ases

fre

eze

into

sol

id p

hase

on

cold

sur

face

s

–C

ryos

orpt

ion:

gas

es a

re tr

appe

d in

a p

orou

s m

olec

ular

sie

ve

•V

esse

l is

cool

ed b

y im

mer

sion

in li

quid

nit

roge

n (L

N2)

whi

ch r

each

es -

196°

C, o

r 77

° K

.

•P

umpi

ng is

com

plet

ely

oil f

ree

and

has

no m

ovin

g pa

rts.

•E

ach

sorp

tion

pum

p re

quir

es a

bout

2-3

gal

lons

of

LN

2 an

dab

out 2

0 m

inut

es to

coo

l dow

n.

•Se

vera

l sor

ptio

n pu

mps

are

oft

en c

ombi

ned

on a

man

ifol

d.

•Pu

mps

mus

t be

rege

nera

ted

by h

eati

ng to

250

° C

for

30

min

s. to

mel

t fro

st a

nd d

egas

the

mol

ecul

ar s

ieve

mat

eria

l.

Page 8: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Ven

turi

Pum

ps -

1

Muf

fler

Low

Pre

ssur

eV

entu

riH

igh

Pre

ssur

eS

uppl

y A

ir

Low

Vac

uum

Suc

tion

Ven

turi

Pum

ps -

2

•B

erno

ulli’

s pr

inci

ple

is u

sed

to p

ull v

acuu

m f

rom

the

pinc

hed

mid

sect

ion

of a

flo

w r

estr

icti

on.

•T

ypic

ally

dri

ven

by 6

0 psi

cle

an d

ry a

ir.

•V

entu

ri p

umps

can

usu

ally

pum

p a

cham

ber

from

760

Tor

rto

60

Tor

r.

•C

ompl

etel

y oi

l fre

e an

d ha

s no

mov

ing

part

s.

•In

stan

t on

and

off.

•V

entu

ri p

umps

can

rem

ove

abou

t 90

% o

f th

e ai

r in

ach

ambe

r, g

reat

ly r

educ

ing

the

capa

city

req

uire

men

ts o

fot

her

pum

ps.

•D

raw

back

is th

eir

nois

e; th

ey u

sual

ly n

eed

a m

uffl

er.

Roo

ts B

low

ers

/ Boo

ster

Pum

ps -

1

Inle

t

Out

let

Roo

ts B

low

erB

oost

er P

ump

Rot

ary

Van

eM

echa

nica

lP

ump

Roo

ts B

low

ers

/ Boo

ster

Pum

ps -

2

Inle

t

Out

let

Fig

ure-

Eig

htLo

bed

Rot

ors

Page 9: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Roo

ts B

low

ers

/ Boo

ster

Pum

ps -

3

•Pr

ecis

ion

shap

ed r

otor

s m

ate

to h

ousi

ng a

nd to

eac

h ot

her

to w

ithi

n on

ly a

few

thou

sand

ths

of a

n in

ch.

•R

otor

s sp

in a

t 250

0 to

350

0 rp

m.

•G

ears

syn

chro

nize

the

roto

rs.

•It

is a

hig

h th

roug

hput

, low

com

pres

sion

pum

p th

at is

use

dfo

r m

ovin

g la

rge

gas

volu

mes

.

•M

ust b

e be

low

10

Tor

r to

oper

ate.

•“W

indm

ills”

at a

tmos

pher

ic p

ress

ure,

cre

atin

g m

uch

heat

.

•R

equi

res

a m

echa

nica

l for

elin

e pu

mp.

Dif

fusio

n Pu

mps

- 1

Inle

t

Out

let

Oil

Fill

and

Dra

inA

ssem

bly

Ele

ctric

al P

lug

Oil

Hea

ter

Eje

ctor

Arm

Wat

erC

oolin

gLi

nes

Dif

fusio

n Pu

mps

- 2

Inle

t

Out

let

Oil

Fill

and

Dra

inA

ssem

bly

Ele

ctric

al P

lug

Oil

Hea

ter

Eje

ctor

Arm

Wat

erC

oolin

gLi

nes

Mul

tista

ge J

etA

ssem

bly

Dif

fusio

n Pu

mps

- 3

•O

il is

vap

oriz

ed a

nd p

rope

lled

dow

nwar

d by

an

inte

rnal

boil

er a

nd m

ulti

stage

jet a

ssem

bly.

•O

il v

apor

rea

ches

spe

eds

of 7

50 m

ph o

r m

ore

(sup

erso

nic)

.

•O

il va

por

stre

ams

trap

and

com

pres

s ga

ses

into

bot

tom

of

pum

p, w

hich

are

then

eje

cted

out

into

the

fore

line

arm

.

•O

il v

apor

is c

onde

nsed

on

side

s of

pum

p bo

dy w

hich

are

wat

er c

oole

d.

•C

an o

nly

oper

ate

at p

ress

ures

of

100

mT

or

less

.

•A

mec

hani

cal f

orel

ine

pum

p is

req

uire

d fo

r op

erat

ion.

•M

ulti

stag

e je

t ass

embl

y is

des

igne

d to

fra

ctio

nate

the

oil,

usin

g li

ghte

r w

eigh

t fra

ctio

ns f

or h

ighe

r va

por

velo

citi

es.

•T

ypic

ally

300

- 2

800

L/s

pum

ping

spe

eds.

Page 10: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Dif

fusio

n Pu

mps

- 4

•Po

tent

ial P

robl

ems:

–B

acks

trea

min

g of

oil

vap

or c

an o

ccur

if f

orep

ress

ure

beco

mes

too

larg

e.•

Bac

kstr

eam

ing

occu

rs f

or p

ress

ures

of

1 to

10

mT

orr.

•C

old

cap

on to

p of

mul

tist

age

jet a

ssem

bly

help

s to

red

uce

this

.

•L

iqui

d ni

trog

en f

ille

d cry

otra

p al

so h

elps

to r

educ

e th

is.

•M

axim

um to

lera

ble f

orel

ine

pres

sure

(cr

itic

al fo

repr

essu

re)

mus

t not

be e

xcee

ded,

or

pum

p w

ill “

dum

p”

or “

blow

-out

”, s

endi

ng o

il u

p in

toth

e ch

ambe

r.

–P

ump

can

over

heat

if c

ooli

ng w

ater

fai

ls•

Mos

t pum

ps h

ave

a th

erm

al c

utou

t sw

itch.

–Pu

mpi

ng r

equi

res

low

vap

or p

ress

ure

oil

•W

ater

, dir

t, or

oth

er im

puri

ties

wil

l rai

se v

apor

pre

ssur

e.

•O

nly

spec

ial o

ils

are

suit

able

for

dif

fusi

on p

ump

use.

Dif

fusio

n Pu

mp

Oil

s

•D

iffu

sion

pum

p oi

ls h

ave

very

low

vap

or p

ress

ure.

•T

ypes

–H

ydro

carb

on o

ils

•A

piez

on A

, B, C

, Lit

ton

Oil

, Con

voil-

20

–S

ilic

one

oils

•D

C-7

04, D

C-7

05, I

nvoi

l 940

–P

olyp

heny

l eth

ers

•Sa

ntov

ac 5

, Con

vale

x 10

–Fa

tty

este

rs•

Oct

oil,

But

yl P

htha

late

, Am

oil,

Invo

il

–Fl

uoro

ethe

r po

lym

ers

•K

ryto

x, F

ombl

in

Liq

uid

Nit

roge

n T

raps

/ B

affl

es -

1

Inle

t

Out

let

Fill

Ven

t Chi

lled

Baf

fles

Liqu

id N

itrog

enR

eser

voir

Liq

uid

Nit

roge

n T

raps

/ B

affl

es -

2

•B

affl

es a

nd tr

aps

in th

e pu

mpi

ng li

nes

can

grea

tly

help

tore

duce

bac

kstr

eam

ing:

–lo

w p

ress

ures

in m

echa

nica

l rou

gh p

umps

(0.

1 to

1.0

Tor

r)

–hi

gh p

ress

ures

in d

iffu

sion

pum

ps (

1 to

100

mT

orr)

–m

ost i

mpo

rtan

t with

in th

e “c

ross

-ove

r” r

egio

n.

•L

N2

cryo

trap

s sh

ould

not

exp

erie

nce

air

pres

sure

abo

ve10

0 m

Tor

r, o

r th

ey w

ill f

rost

com

plet

ely

over

.

•R

esid

ual w

ater

in a

cry

otra

p ca

n be

fro

zen

and

caus

e tr

apto

bre

ak, c

ausi

ng c

atas

trop

hic

fail

ure

of v

acuu

m s

yste

m.

–B

low

out

any

wat

er v

apor

wit

h dr

y N

2 be

fore

fil

ling

wit

h L

N 2.

•L

N2

cryo

trap

s re

quir

e co

nsta

nt r

efil

ling

.–

Exp

ensi

ve, b

ut a

utof

ill v

alve

s ar

e av

aila

ble.

Page 11: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Dif

fusio

n Pu

mpe

d H

igh

Vac

uum

Bel

l Jar

Sys

tem

Tur

bom

olec

ular

Pum

ps -

1

Inle

t

For

elin

eE

lect

rical

Con

nect

ion

to C

ontr

olle

r

Rot

ors

Sta

tors

Sha

ft

Hig

h S

peed

Mot

or

Tur

bom

olec

ular

Pum

ps -

2

•V

ery

clea

n m

echa

nica

l com

pres

sion

pum

p

•U

se h

igh

spee

d ro

tati

on b

lade

s to

impa

rt v

eloc

ity

and

dire

ctio

n to

gas

mol

ecul

es

•9,

000

to 9

0,00

0 rp

m m

otor

spe

eds!

•20

to 6

0 bl

ades

per

dis

k

•10

to 4

0 co

mpr

essi

on s

tage

s pe

r pu

mp

•R

equi

res

a m

echa

nica

l for

elin

e pu

mp

•T

ypic

ally

100

to 8

00 L

/sec

pum

ping

spe

eds

•Id

eal f

or h

ydro

carb

on f

ree

appl

icat

ions

Tur

bom

olec

ular

Pum

ps -

3

•Pu

mpi

ng s

peed

is p

ropo

rtio

nal t

o th

e ro

tor

spee

d.

•T

he c

ompr

essi

on r

atio

of

the

turb

ine

esta

blis

hes

the

base

pres

sure

.

•T

he c

ompr

essi

on r

atio

is h

ighe

r fo

r hi

gher

mol

ecul

arw

eigh

ts:

–A

ppro

xim

atel

y: l

og10

K =

1.5

(M

)1/2

–Fo

r H

2, M

= 1

, so

K =

101.

5 =

30

= v

ery

smal

l

–Fo

r hy

droc

arbo

ns, M

= 1

00, s

o K

= 1

015 =

ver

y la

rge

•B

ase

pres

sure

is u

sual

ly li

mit

ed b

y H 2

.

Page 12: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Tur

bom

olec

ular

Pum

ps -

4

•Po

tent

ial P

robl

ems:

–V

ery

high

spe

ed r

otor

bla

des

have

clo

se-m

atin

g st

ator

bla

des.

•S

ligh

t im

bala

nces

can

cau

se v

ibra

tion

and

bea

ring

wea

r pr

oble

ms.

•Su

dden

bla

st o

f at

mos

pher

ic p

ress

ure

can

bend

the

blad

es d

own,

caus

ing

cata

stro

phic

fai

lure

, “cr

ashi

ng th

e pu

mp.

–L

ubri

cati

on o

f th

e hi

gh s

peed

rot

or is

an

engi

neer

ing

prob

lem

.•

Cir

cula

ting

oil

is m

ost r

elia

ble,

but

pum

p m

ust b

e ri

ght-

side

-up.

•G

reas

e-lu

bric

ated

bea

ring

s ar

e le

ss r

elia

ble,

but

all

ow p

ump

to b

epl

aced

at a

ny o

rien

tati

on.

–T

oo h

igh

of a

pre

ssur

e w

ill c

ause

aer

odyn

amic

lift

and

dra

g.•

A m

echa

nica

l for

elin

e pu

mp

mus

t be

used

•A

erod

ynam

ic li

ft c

an b

end

blad

es, c

ausi

ng c

atas

trop

hic

fail

ure.

Tur

bo P

umpe

d H

igh

Vac

uum

Bel

l Jar

Sys

tem

Cry

opum

ps -

1

Cry

opum

ps -

2

Inle

t

Reg

ener

atio

nF

orel

ine

Exp

ande

rM

otor

Hyd

roge

n V

apor

Bul

b T

herm

omet

er

1st S

tage

Cry

oarr

ay

2nd

Sta

ge C

ryoa

rray

Exp

ande

r M

odul

e

Rel

ief

Val

ve

Hel

ium

Lin

e C

onne

ctio

ns

Page 13: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Cry

opum

ps -

3

•U

se a

clo

sed-

loop

hel

ium

cry

ogen

ic r

efri

gera

tor.

•Pr

imar

y pa

rts

are:

–C

ompr

esso

r

–E

xpan

der

–C

old

Hea

d

•G

ases

are

pum

ped

by tw

o pr

oces

ses:

–C

ryoc

onde

nsat

ion

(H2O

, CO

2, N

2, O

2, A

r, s

olve

nt v

apor

s)•

Gas

es a

re c

onde

nsed

into

a s

olid

pha

se o

n cr

yoge

nica

lly

cool

edsu

rfac

es.

(The

y be

com

e fr

ost!

)

–C

ryos

orpt

ion

(H2,

He,

Ne)

•N

on-c

onde

nsab

le g

ases

are

ads

orbe

d on

to s

urfa

ces

of c

ryog

enic

ally

cool

ed p

orou

s m

edia

, usu

ally

act

ivat

ed c

harc

oal o

r zeo

lite

s.

•T

ypic

ally

100

- 1

000

L/s

pum

ping

spe

eds.

Cry

opum

ps -

4

•F

irst

sta

ge a

rray

ope

rate

s at

50

to 8

0 K

–P

rim

aril

y us

ed f

or p

umpi

ng w

ater

vapo

r an

d ca

rbon

dio

xide

.

•Se

cond

sta

ge a

rray

ope

rate

s at

10

to 2

0 K

–P

rim

aril

y us

ed f

or p

umpi

ng o

ther

con

dens

able

gas

es.

•A

ctiv

ated

cha

rcoa

l in

the

seco

nd s

tage

pro

vide

scr

yoso

rptio

n.–

Pri

mar

ily

used

for

pum

ping

oth

er n

on-c

onde

nsab

le g

ases

.

–C

harc

oal a

nd z

eoli

tes

have

abo

ut 8

000

ft2 /

cm3

of s

urfa

ce a

rea.

•C

ompl

etel

y oi

l fre

e op

erat

ion.

•C

an o

pera

te f

rom

any

ori

enta

tion

.

•V

ery

clea

n va

cuum

with

hig

h pu

mpi

ng s

peed

.

•V

ery

high

impu

lsiv

e pu

mpi

ng c

apac

ity.

Cry

opum

ps -

5

•Po

tent

ial P

robl

ems:

–M

ust b

e re

gene

rate

d to

ext

ract

the

trap

ped

gase

s•

Allo

w to

war

m to

roo

m te

mpe

ratu

re (

slow

), o

r

•U

se a

bui

lt-in

hea

ter

to w

arm

to 2

50 C

and

out

gas

(fas

t).

•R

egen

erat

ion

take

s th

e pu

mp

off-

line

for

sev

eral

hou

rs.

–R

egen

erat

ion

proc

ess

can

prod

uce

cons

ider

able

pre

ssur

e.•

Pum

ps h

ave

a sa

fety

pre

ssur

e re

lief

val

ve o

n th

e bu

cket

.

–M

ust b

e st

arte

d fr

om b

elow

100

mT

orr

•U

se a

mec

hani

cal r

ough

ing

pum

p

Cry

opum

p C

ompr

esso

r M

odul

e

Coa

lesc

er

Pow

er S

uppl

y

Ads

orbe

r

Com

pres

sor

Sur

geV

olum

e

Page 14: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Cry

o Pu

mpe

d H

igh

Vac

uum

Bel

l Jar

Sys

tem

Tita

nium

Sub

lim

ation

Pum

ps -

1

Pop

pet V

alve

Sum

p

Baf

fle

Tita

nium

Bal

l

LN2

Col

d T

rap

Tita

nium

Sub

lim

ation

Pum

ps -

2

•“T

SP”;

a ty

pe o

f “g

ette

r pu

mp”

•T

itani

um, w

hich

has

bee

n fr

eshl

y ev

apor

ated

ont

o th

e si

des

of a

sum

p, w

ill c

hem

ical

ly c

ombi

ne w

ith g

as m

olec

ules

.

•T

itani

um s

ubli

mes

fro

m a

hea

ted

sour

ce a

nd e

vapo

rate

s to

coat

the

wal

ls o

f th

e su

mp.

•T

ypes

of T

i sou

rces

:–

35 g

Ti-

ball

; 750

W o

pera

ting

, 200

W s

tand

by

–15

g m

ini-T

i-ba

ll; 3

80 W

ope

rati

ng, 9

5 W

sta

ndby

–4.

5 g

Ti f

ilam

ent;

380

W o

pera

ting,

zer

o st

andb

y

Typ

ical

pum

ping

spe

eds

for

fres

hly

coat

ed T

i sur

face

s (L

/sec

-in2 )

:

H

2N

2O

2C

OC

O2

H2O

20°C

:20

3060

6050

20

-190

°C:

6565

7070

6090

Non

-Eva

pora

ble

Get

ter

Pum

ps

•“N

EG

” pu

mps

.

•Z

r-V

-Fe

allo

y th

at i

s fo

rmed

into

a c

artr

idge

ove

r a

cons

tant

an s

trip

hea

ter.

•P

umps

all

of

the

tim

e, u

ntil

load

ed w

ith

gas

mol

ecul

es.

•R

egen

erat

ed b

y he

atin

g to

~35

0°C

for

30

min

s. to

deg

asth

e al

loy.

•V

ery

sim

ple

in c

onst

ruct

ion

and

oper

atio

n.

Page 15: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Ion

Pum

ps -

1

NS

exte

rnal

per

man

ent m

agne

t

pum

pbo

dy

titan

ium

cath

odes

mul

ticel

lcy

lindr

ical

anod

ear

ray

+Vpo

wer

supp

ly

cold

cath

ode

disc

harg

e

Dio

de Io

n P

ump

Ion

Pum

ps -

2

NS

exte

rnal

per

man

ent m

agne

t

pum

pbo

dy

titan

ium

cath

ode

grid

s

mul

ticel

lcy

lindr

ical

anod

ear

ray

--V

pow

ersu

pply

cold

cath

ode

disc

harg

e

Trio

de Io

n P

ump

Ion

Pum

ps -

3

•O

pera

tion

is b

ased

upo

n a

rare

fied

gas

ele

ctri

c di

scha

rge.

–H

igh

elec

tric

fie

ld c

an io

nize

a g

as m

olec

ule,

for

min

g a

free

elec

tron

and

a g

as io

n.

–F

ree

elec

tron

is c

olle

cted

by

the

anod

e, w

hile

gas

ion

is c

olle

cted

by th

e ca

thod

e.

–F

ast e

lect

rons

, acc

eler

ated

by

the

E-f

ield

, wil

l col

lide

wit

h an

dio

nize

oth

er g

as m

olec

ules

.

–A

coa

xial

mag

neti

c an

d el

ectr

ic f

ield

wil

l pro

duce

spi

ral o

rbit

s fo

rth

e fr

ee e

lect

rons

; the

larg

er p

aths

gre

atly

incr

ease

the

ioni

zati

on.

–H

ighe

r io

niza

tion

leve

ls w

ill s

usta

in a

cold

cat

hode

dis

char

ge.

–G

as io

ns a

ccel

erat

ed in

to th

e ca

thod

e ca

n st

ick

and

ther

efor

e be

pum

ped.

Ion

Pum

ps -

4

•C

atho

de p

late

s ar

e m

ade

of ti

tani

um (T

i).

•P

umpi

ng m

echa

nism

s:–

Inci

dent

gas

ions

may

be

impl

ante

d in

to th

e T

i cat

hode

pla

tes.

–In

cide

nt g

as io

ns m

ay s

putt

er T

i fro

m th

e ca

thod

e pl

ates

into

the

cyli

ndri

cal a

node

cel

ls, th

us p

rovi

ding

add

itio

nal g

ette

r pu

mpi

ng.

–H

2 is

dir

ectl

y ab

sorb

ed b

y th

e fr

esh T

i sur

face

s.

–G

as m

olec

ules

may

be

trap

ped

and

burr

ied

by s

putt

ered

Ti.

–E

lect

ric

disc

harg

e cr

acks

larg

er m

olec

ules

into

sm

alle

r on

es th

atar

e m

ore

read

ily

pum

ped.

•Io

n pu

mps

mus

t be

star

ted

at 1

0-5

torr

or

less

.

•In

term

edia

te p

umpi

ng is

usu

ally

pro

vide

d by

a s

orpt

ion

ora

cryo

pum

p.

Page 16: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Ion

Pum

ps -

5

•D

iode

pum

ps u

se a

Ti p

late

as

the

cath

ode.

•T

riod

e pu

mps

use

a T

i scr

een

as a

gri

d el

ectr

ode

and

the

pum

p bo

dy a

s th

e ca

thod

e.

•T

ypic

al tr

iode

pum

ps w

ill o

pera

te f

or ~

35,0

00 h

ours

(ab

out

4 ye

ars)

at a

n in

let p

ress

ure

of 1

0-6 to

rr o

f N

2.

•T

he io

n pu

mp

curr

ent i

s pr

opor

tiona

l to

the

gas

pres

sure

inth

e pu

mp,

so

this

can

be

used

as

a pr

essu

re g

auge

.

•A

ppen

dage

ion

pum

ps a

re o

ften

use

d to

sus

tain

hig

hva

cuum

in lo

ng s

ervi

ce d

evic

es s

uch

as m

icro

wav

e tu

bes.

Ion

/ Ti-

Sub.

Pum

ped

Ult

ra-H

igh

Vac

uum

Sys

tem

Vac

uum

Gau

ge P

ress

ure

Ran

ges

-12

-10

-8-6

-4-2

0+2

Pre

ssur

e in

Tor

r (u

nits

are

exp

onen

ts o

f ten

)

Ultr

a-H

igh

Vac

uum

Hig

h V

acuu

mR

ough

Vac

uum

BO

UR

DO

N G

AU

GE

TH

ER

MO

CO

UP

LE G

AU

GE

CO

NV

EC

TIO

N T

HE

RM

OC

OU

PLE

GA

UG

EP

IRA

NI G

AU

GE

CA

PA

CIT

AN

CE

MA

NO

ME

TE

R

CO

LD C

AT

HO

DE

GA

UG

EIO

NIZ

AT

ION

GA

UG

ER

ES

. NIT

RO

GE

N A

NA

LYZ

ER

RE

SID

UA

L G

AS

AN

ALY

ZE

R

Bou

rdon

Gau

ges

- 1

Gea

rB

ox

Exp

ansi

onT

ube

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Bou

rdon

Gau

ges

- 2

•M

echa

nica

l gas

pre

ssur

e fl

exes

the B

ourd

on tu

be a

ndca

uses

the

arc

to u

nwin

d, w

hich

thro

ugh

a se

ries

of

gear

san

d le

vers

mov

es a

nee

dle

on th

e ga

uge’

s fa

ce.

•It

is

com

plet

ely

inse

nsit

ive t

o th

e ch

emic

al c

ompo

sitio

n of

the

gas.

•It

can

be

used

for

mea

suri

ng p

osit

ive

pres

sure

and

vac

uum

.

•L

ower

sen

siti

vity

for

vac

uum

mea

sure

men

ts is

abo

ut 0

.1to

rr.

•G

auge

s ar

e pr

ecis

ion

inst

rum

ents

and

can

be

dam

aged

by

mec

hani

cal s

hock

.

Cap

acita

nce

Man

omet

ers

- 1

Met

alD

iaph

ragm

Sta

inle

ssS

teel

Bod

y

Cap

acito

rE

lect

rode

10 k

Hz

osci

llato

ran

d de

mod

ulat

or

Cap

acita

nce

Man

omet

ers

- 2

•M

echa

nica

l gas

pre

ssur

e de

form

s a

tens

ione

d m

etal

diap

hrag

m.

•A

n ai

r ga

p ca

paci

tor

is f

orm

ed b

etw

een

the

diap

hrag

m a

nda

set o

f fi

xed

elec

trod

es.

•T

he c

apac

itan

ce th

us v

arie

s w

ith

the

pres

sure

.

•T

he c

apac

itan

ce is

mea

sure

d by

a d

emod

ulat

ion

and

ampl

ifie

r ci

rcuit

that

mak

es a

10

kHz

osci

llat

or w

ith

the

diap

hrag

m c

apac

itor

.

•C

apac

itan

ce m

anom

eter

s ar

e ex

trem

ely

line

ar a

nd a

ccur

ate.

–T

ypic

ally

wit

hin

1% o

f fu

ll s

cale

.

•T

hey

are

inse

nsiti

ve to

the

chem

ical

com

posi

tion

of

the

gas.

Cap

acita

nce

Man

omet

ers

- 3

•C

an b

e us

ed to

mea

sure

pre

ssur

e in

all

mod

es:

–G

auge

–A

bsol

ute

–D

iffe

rent

ial

•A

sin

gle

capa

cita

nce

man

omet

er c

an o

nly

read

ove

r 3-

4de

cade

s of

pre

ssur

e.

•C

apac

itanc

e m

anom

eter

s ca

n be

con

stru

cted

to c

over

the

rang

e fr

om a

tmos

pher

ic p

ress

ure

dow

n to

~10

-5 to

rr b

yus

ing

diap

hrag

ms

of d

iffe

ring

stif

fnes

s.

•C

apac

itanc

e m

anom

eter

s ar

e of

ten

used

to a

ccur

atel

ym

easu

re p

ress

ure

in p

roce

ss r

eact

ors,

and

are

oft

en u

sed

infe

edba

ck c

ontr

ol lo

ops.

Page 18: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

The

rmoc

oupl

e G

auge

s -

1

Chr

omel

Alu

mel

K-t

ype

4-po

int

heat

er a

ndth

erm

ocou

ple

Sta

inle

ssS

teel

Can

The

rmoc

oupl

e G

auge

s -

2

•E

lect

ric

curr

ent p

asse

d th

roug

h a

fila

men

t hea

ts u

p th

efi

lam

ent t

o a

tem

pera

ture

that

dep

ends

upo

n ho

w f

ast t

hesu

rrou

ndin

g ga

s co

nduc

ts th

e he

at a

way

.

•T

he te

mpe

ratu

re is

mea

sure

d by

a th

erm

ocou

ple,

whi

ch is

part

of

the

fila

men

t ass

embl

y, a

nd th

e te

mpe

ratu

re r

eadi

ngis

con

vert

ed in

to a

n ap

prox

imat

e pr

essu

re o

n a

met

er.

•S

ince

dif

fere

nt g

ases

hav

e di

ffer

ent t

herm

al c

ondu

ctiv

ities

,th

erm

ocou

ple

gaug

es r

ead

diff

eren

tly

for

diff

eren

t gas

es.

•R

ead

from

abo

ut 1

to 1

000

mT

orr.

•V

ery

rugg

ed, r

elia

ble,

and

inex

pens

ive.

Pir

ani G

auge

s -

1

Sta

inle

ssS

teel

Can

Tun

gste

nR

esis

tive

Hea

ters

Pir

ani G

auge

s -

2

•S

imil

ar to

a T

C g

auge

, an

elec

tric

ally

hea

ted

fila

men

t tak

eson

a te

mpe

ratu

re th

at d

epen

ds u

pon

the

rate

of

heat

loss

toth

e su

rrou

ndin

g ga

s.

•T

he te

mpe

ratu

re o

f th

e fi

lam

ent i

s se

nsed

by

mea

suri

ng th

ech

ange

in th

e re

sist

ance

of

the

fila

men

t as

it is

hea

ted.

–Fo

r m

ost m

etal

s, th

e T

CR

is a

bout

+20

0 pp

m/°

C.

•P

iran

i gau

ges

requ

ire

a m

ore

soph

istic

ated

con

trol

ler,

but

are

mor

e ac

cura

te a

nd f

aste

r re

spon

ding

than

a T

C g

auge

.

•M

ost u

se a

Whe

atst

one

brid

ge c

ircu

it to

line

ariz

e th

efi

lam

ent a

gain

st a

com

pens

atin

g fi

lam

ent t

hat i

s he

ld a

tat

mos

pher

ic p

ress

ure.

•P

iran

i gau

ges

are

also

sen

siti

ve to

the

gas

com

posi

tion

.

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Hot

Fila

men

t Ion

izat

ion

Gau

ges

- 1

Gla

ssE

nvel

ope

Col

lect

or

Fila

men

tG

rid(0 V

)

(+25

V)

(+17

5 V

)

Hot

Fila

men

t Ion

izat

ion

Gau

ges

- 2

•A

lso

know

as

“Bay

erd-

Alp

ert”

gau

ges.

•E

lect

rons

are

ther

mio

nica

lly

emitt

ed f

rom

a h

ot f

ilam

ent

and

then

acc

eler

ated

by

a gr

id e

lect

rode

.

•T

he a

ccel

erat

ed e

lect

rons

wil

l ion

ize

any

gas

mol

ecul

es in

the

vici

nity

of t

he g

rid,

and

the

posi

tive

ly c

harg

ed g

as io

nw

ill c

ontr

ibut

e to

a c

urre

nt th

roug

h th

e co

llec

tor

elec

trod

e.

•I P

= I

E*S

*P, w

here

–I P

= p

ositi

ve io

n cu

rren

t thr

ough

col

lect

or e

lect

rode

–I E

= e

lect

ron

emis

sion

cur

rent

thro

ugh

fila

men

t

–S

= g

auge

sen

siti

vity

par

amet

er

–P

= g

as p

ress

ure

Hot

Fila

men

t Ion

izat

ion

Gau

ges

- 3

•T

he io

niza

tion

rat

e de

pend

s up

on th

e ga

s sp

ecie

s, s

o io

nga

uges

are

sen

sitiv

e to

the

gas

com

posi

tion.

•A

ccur

acy

is a

bout

10%

of

full

sca

le, w

hen

cali

brat

ed.

•Io

n ga

uges

can

wor

k fr

om 1

0-3 to

10-1

1 to

rr!

•L

ower

pre

ssur

e li

mit

is s

et b

y so

ft x

-ray

em

issi

on f

rom

elec

tron

s st

riki

ng th

e gr

id.

•H

ot f

ilam

ent r

equi

res

som

e pr

ecau

tions

:–

Exp

osur

e to

pre

ssur

es a

bove

10-3

torr

wil

l bur

n ou

t fil

amen

t.

–H

ot f

ilam

ent i

s an

igni

tion

sou

rce

whi

ch c

an tr

igge

r ex

plos

ions

inth

e pr

oces

s ch

ambe

r w

ith

com

bust

ible

gas

es.

Col

d C

atho

de I

oniz

atio

n G

auge

s -

1

NS

NS

Per

man

ent

Mag

net

Cat

hode

(-20

00 V

)

Sta

inle

ssS

teel

Bod

y(0

V)

Col

dC

atho

deD

isch

arge

Page 20: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Col

d C

atho

de I

oniz

atio

n G

auge

s -

2

•A

col

d ca

thod

e di

scha

rge

repl

aces

the

hot f

ilam

ent f

orpr

oduc

ing

ioni

zing

ele

ctro

ns.

•Io

nize

d ga

s m

olec

ules

are

col

lect

ed b

y th

e ne

gati

vely

char

ged

cath

ode,

and

the

elec

tric

cur

rent

is p

ropo

rtio

nal t

oth

e ga

s pr

essu

re.

•C

an o

pera

te f

rom

10-2

to 1

0-8 to

rr.

•M

ore

rugg

ed th

an a

hot

fil

amen

t ion

gau

ge, b

ut le

ssac

cura

te, t

ypic

ally

only

abo

ut 5

0% o

f fu

ll s

cale

.

•C

old

cath

ode

disc

harg

e is

sti

ll a

pot

enti

al s

ourc

e of

igni

tion

for

com

bust

ible

pro

cess

gas

es.

Cle

anli

ness

Ins

ide

a V

acuu

m C

ham

ber

•A

t 10-6

torr

:–

ther

e ar

e 4

x 10

4 m

olec

ules

/cm

3

–th

e m

ean

free

pat

h is

abo

ut 5

x 1

03 cm

–th

e im

ping

emen

t rat

e is

abo

ut 1

015 m

olec

ules

/cm

2 /se

c

•T

hus,

at 1

0-6 to

rr, a

mon

olay

er o

f m

olec

ules

wil

l dep

osit

on

any

surf

ace

in a

bout

1 s

econ

d.

•10

-6 to

rr i

s eq

uiva

lent

to a

pur

ity

of 1

ppb

!–

(Rel

ativ

e to

atm

osph

eric

pre

ssur

e at

~10

3 to

rr)

•T

he m

atte

r in

one

fin

gerp

rint

(1

cm x

1 c

m x

20 µ

m),

whe

nva

pori

zed,

wil

l pro

duce

a p

ress

ure

of 1

0-4 to

rr i

nsid

e a

10ft

3 va

cuum

cha

mbe

r!

•T

hus:

AL

WA

YS

WE

AR

GL

OV

ES!

!!

Vac

uum

Mat

eria

ls -

1

•St

ainl

ess

Stee

l–

Typ

e 30

4 SS

is m

ost c

omm

on.

•E

asy

to m

achi

ne.

•E

asy

to f

usio

n w

eld.

•C

oppe

r–

Use

Oxy

gen-

Fre

e H

igh-

Con

duct

ivit

y (O

FH

C)

allo

y.•

Use

d fo

r el

ectr

ical

con

duct

ors.

•C

eram

ics

–A

lum

ina (

Al 2

O3)

is v

ery

com

mon

.•

Use

d fo

r el

ectr

ical

insu

lato

rs.

•K

ovar

–(5

4% F

e, 2

9% N

i, 17

% C

o); u

sed

for

glas

s-to

-met

al s

eals

.

Vac

uum

Mat

eria

ls -

2

•E

last

omer

s–

Bun

a-N

•In

expe

nsiv

e, g

ood

to 8

0°C

, rat

her

impe

rmea

ble

to H

e.

–V

iton

•O

utga

sses

ver

y lit

tle,

goo

d to

150

°C.

–P

olyi

mid

e•

Goo

d to

200

°C, s

tiffe

r th

an o

ther

ela

stom

ers,

per

mea

ble

to H

2O v

apor

.

–S

ilic

ones

•C

an h

andl

e hi

gher

tem

pera

ture

s, b

ut v

ery

perm

eabl

e to

H2O

and

He.

–T

eflo

n•

Ver

y in

ert,

but e

xhib

its

cold

flo

w p

last

icit

y, m

akin

g it

a p

oor

seal

.

•V

ery

perm

eabl

e to

He,

goo

d to

150

°C.

Page 21: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Vac

uum

Joi

ning

Tec

hniq

ues

- 1

Inte

rnal

con

tinuo

us fu

sion

wel

ds a

re m

ost c

omm

only

use

d fo

r jo

inin

g tu

bing

,pi

pes,

and

cha

mbe

r po

rts.

For

sm

all b

ore

tubi

ng, e

xter

nal o

rbita

l wel

ding

mus

t pro

duce

com

plet

epe

netr

atio

n w

elds

.

Vac

uum

Joi

ning

Tec

hniq

ues

- 2

AS

A fl

ange

s ar

e a

com

mon

sta

ndar

d th

at u

ses

a ca

ptur

ed O

-rin

g to

pro

vide

sea

ling.

Vac

uum

Joi

ning

Tec

hniq

ues

- 3

KF

or

“Qui

ck-F

lang

es”

are

a co

mm

on s

tand

ard

for

roug

h or

hig

h va

cuum

plu

mbi

ng.

The

y ut

ilize

an

O-r

ing

supp

orte

d ag

ains

t fla

t fla

nges

with

an

inte

rnal

cen

terin

g rin

g.

Com

pres

sion

is s

uppl

ied

by a

tape

red

clam

p an

d w

ingn

ut.

No

tool

s ar

e ne

eded

.

Vac

uum

Joi

ning

Tec

hniq

ues

- 4

Met

al-s

eale

d, o

r “C

on-F

lat”

flang

es a

re u

sed

for

ultr

a-hi

gh v

acuu

m a

pplic

atio

ns w

here

elas

tom

er s

eale

d fla

nges

wou

ld b

e to

o le

aky.

A k

nife

edg

e on

eac

h fla

nge

bite

s in

to a

nd c

ompr

esse

s a

copp

er g

aske

t. T

he e

xtre

mel

yhi

gh p

ress

ure

of th

e kn

ife e

dge

caus

es th

e co

pper

to d

efor

m to

mat

ch th

e su

rfac

es o

f bot

hfla

nges

. T

hese

flan

ges

are

bake

able

up

to 3

50°C

.

Page 22: Vacuum Systems Outline • Vacuum principles • Vacuum …eng.utah.edu/~gale/mems/Lecture 03 Vacuum Systems.pdf · • Vacuum principles • Vacuum pumps • Vacuum materials and

Thi

ngs

to W

atch

for

in V

acuu

m S

yste

ms

•R

eal L

eaks

•V

irtu

al L

eaks

•W

ater

Lea

ks

•O

il C

onta

min

atio

n

•F

inge

r P

rint

s

•O

rgan

ic M

ater

ials

that

Out

gas