cong nghe vi dien tu 1

7/28/2019 Cong Nghe Vi Dien Tu 1

1/146

1

BI GING MN HC

CNG NGH VI IN TCredits: 2

Prerequisites:- Semiconductor Devices

- Microelectronic Circuit Design

References

1. HONG H. LEE,Fundamentals of Microelectronics Processing. 3rd Ed., McGraw-Hill; USA; 1990.2. STEPHEN BROWN and ZVONKO VRANESIC, Fundamentals of Digital Logic with VHDL

Design, 3rd Ed., Mc.Graw-Hill, 2000.

3. SUNG-MO KANG and YUSUF LEBLEBICI, CMOS Digital Integrated Circuits Analysis andDesign. Mc.Graw-Hill, 2005.

4. DAN CLEIN, CMOS IC Layout, Newnes, 2000.5. DAVID A. HODGES, HORACE G. JACKSON, RESVE A. SALEH,Analysis and Design of Digital

Integrated Circuits in Deep Submicron Technology, Mc.Graw-Hill, 2003.

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CHNG 1. CSCNG NGH MCH TCH HP

1.1 Cac mach tch hpCac mach tch hp (IC) la cac mach in t c ch tao bi vic tao ra mt cach ng thi cac

phn t ring le nh transistor, diodes ... trn cung mt chip ban dn nho (in hnh la Si), cac phn t

c ni vi nhau nh cac vt liu kim loai c phu trn b mt cua chip. Cac vt liu kim loai ong

vai tro nh cac wireless wires. Y tng nay ln u tin c a ra bi Dummer nm 1952. Cac

mach tch hp u tin c phat minh bi Kilby, 1958.

Cac mach tch hp v c ban c chia thanh 2 loai chnh: analog (hay linear) va digital (hay

logic). Cac mach tch hp tng t hoc khuch ai hoc ap ng cac in ap bin i. Tiu biu la cac

mach khuch ai, timers, dao ng va cac mach iu khin in ap (voltage regulators). Cac mach s taora hoc ap ng cac tn hiu ch co hai mc in ap. Tiu biu la cac b vi x ly, cac b nh, va cac

microcomputer. Cac mach tch hp cung co th c phn loai theo cng ngh ch tao: monolithic hoc

hybrid. Trong khn kh giao trnh nay chung ta ch ngin cu loai th nht.

Quy m cua s tch hp cua cac mach tch hp trn s s Silicon a tng ln rt nhanh chong t

th h u tin c ch tao bi Texas Instruments nm 1960 vi tn goi SSI (Small Scale Integration)

n th h mi ULSI. Hin nay cng ngh CMOS vi minimum device dimension ( khoang cach gate to

gate)t ti c vai chuc nm (0.65, 0.45).

Khuynh hng chu ao trong vic giam nho kch thc linh kin trong cng ngh mach tch hp

la giam chi ph cho cung mt chc nng, giam tiu thu cng sut va nng cao tc cua linh kin. Mt

khuynh hng khac la vn tip tuc s dung cac a ban dn ln giam chi ph trn chip. Vi ca hai

khuynh hng trn, cng ngh x ly vi in t lun phai c cai tin.Cac cng ngh IC chu yu hin nay la cng ngh MOS va cng ngh BJT cho silicon va MES

cho gallium arsenide.

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1.2 Ban dn va cac hat taiSi n tinh th la vt liu c s cho cng ngh IC. Hnh 1-2a m ta mt planar view cua tinh th

Si vi cac in t cua lp ngoai cung (lp vo) trong cac lin kt cong hoa tri (covalent bond) gia cac

nguyn t ln cn. Mt cht ban dn co th c nh ngha nh la mt vt liu c dn in co th

iu khin c, trong khoang trung gian gia in mi va kim loai. Kha nng thay i dn cua Si

trong khoang nhiu bc co th c thc hin bi vic a vao mang tinh th Si cac nguyn t tap cht

hoa tr 3 nh Boron hoc hoa tr 5 nh Phosphorus, chung c goi la cac dopant hoc la cac tap cht

mong mun. Qua trnh nay goi la qua trnh pha tap hay doping. Cac ban dn sach c goi la ban dn

thun hay intrinsic, cac ban dn pha tap goi la extrinsic. Nu pha tap nhom 5 (chng han P) vao Si th

ngoai 4 in t lin kt cong hoa tr vi 4 in t lp vo cua cac nguyn t Si ln cn, in t th 5 cuanguyn t tap co lin kt long leo vi hat nhn va co th chuyn ng tng i d dang trong mang tinh

th Si. Dang ban dn nay c g la ban dn loai-n, va tap nhom 5 c goi la tap donor. Nu pha tap

nhom 3 (chng han B) vao Si th 3 in t lp vo cua nguyn t tap lin kt cong hoa tr vi cac in t

lp vo cua cac nguyn t Si ln cn do o co th coi lp vo cua nguyn t tap co 7 in t, va b trng

mt in t. V tr lin kt khuyt nay c goi la mt l trng (hole). Mt in t t nguyn t Si gn

o co th ri vao ch trng nay va l trng c xem nh chuyn di n v tr mi. Ban dn loai nay

c goi la ban dn loai -p, va tap nhom 3 c goi la tap acceptor. Cac in t va l trng khi dch

chuyn se mang theo chung cac in tch m va dng nn c goi la cac hat tai. Cac cht ban dn co

th dang nguyn t (nh Si, Ge) hoc hp phn. S in t trung bnh trn mt nguyn t thng bng

4, ngoai tr trng hp cac ban dn AV-BVI.

Mt ban dn thun thng la in mi tr khi no c kch thch nhit hoc quang. Nu kchthch u manh no co th tr thanh dn in. Cac mc nng lng kha d cua in t la ri rac va s kch

thch se lam cho cac in t co th nhay ln mc nng lng cao hn. V cht ban dn co th la in mi

hay dn in tuy thuc vao mc kch thch, nn co th coi no biu hin nh mt cht dn in nu

nng lng kch thch vt qua mt mc ngng nht nh, goi la energy barrier, ky hiu Eg (con c

goi la khe nng lng - energy gap). Khe nng lng thay i t 0.18 eV cho InSb ti 3.6 eV cho ZnS.

Cac vt dn nh kim loai khng co khe nng lng nn co th dn in khi co hoc khng co kch thch.

Cac cht cach in co khe nng lng ln n mc khng dn in ngay ca khi kch thch manh. Khi

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khng co kch thch tt ca cac in t cua ban dn chim cac mc nng lng thp trong cac trang thai

hoa tr. Mc du cac mc nng lng la gian oan nhng v co rt nhiu mc nn co th xem tp hp cac

trang thai cong hoa tr nh mt dai hay vung hoa tr (valence band). Mc nng lng cao nht cua vung

hoa tr ky hiu la Ev. Pha trn khe nng lng ( con goi la vung cm) la dai nng lng cua cac trang

thai dn, goi la vung dn. Mc nng lng thp nht cua vung dn ky hiu la Ec. Hnh 1-2a m ta cu

hnh cac mc nng lng cua mt ban dn thun 0oK. Khi ban dn thun c pha tap donor, cac in

t donor se chim cac mc nng lng gn di vung dn, vi mc nng lng thp nht trong cac mc

nay c goi la mc donor, ky hiu la Ed (hnh 1-2b). Khi ban dn thun c pha tap acceptor, cac l

trng se chim cac mc nng lng gn trn nh vung hoa tr, vi mc nng lng cao nht trong cac

mc nay c goi la mc acceptor, ky hiu la Ea (hnh 1-2c). Khi ban dn thun chu kch thch nhit,

mt s in t trong vung hoa tr b kch thch co th vt qua vung cm ln vung dn ng thi tao

ra mt s l trng tng ng vung hoa tr, va cac cp in t l trng (EHP - electron hole pair) c

tao ra. V cac mc donor trong ban dn loai -n rt gn vi vung dn nn cac kch thch nhe cung u

lam cho cac in t donor nhay ln vung dn, do o nng in t trong vong dn la rt ln ngay ca

nhit thp i vi vic hnh thanh cac EHP. Vi ban dn loai -p, v cac mc acceptor rt gn trn nh

vung hoa tr nn mt kch thch nhe co th lam cho cac in t trong vung hoa tr nhay ln chim cacmc acceptor va lai cac l trng trong vung hoa tr. Do o cac ban dn loai -p co th co nng l

trng ln ngay ca nhit thp.

Khi mt ban dn c pha tap loai-n hoc loai -p, mt trong hai loai hat tai se chim u th v

nng va c goi la hat tai c ban (hay majority carrier), loai hat tai con lai c goi la hat tai khng

c ban (hay minority carrier).

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1.3 Cac quan h c ban va dn inV chuyn ng cua cac hat tai tao ra s dn in, nn nng hat tai la ai lng c quan tm

hang u trong cng ngh IC. Vi ban dn thun, nng in t trong vung dn n bng nng l

trng trong vung hoa tr p:

n = p = ni (1.1)

trong o ni goi la nng hat tai ni cua ban dn thun trang thai cn bng (hay trang thai tnh).

Gia thit cac tap cht phn b ng nht. thoa man iu kin trung hoa in tch (trung hoa

tnh in) trong ban dn thun, cac in tch dng phai bng cac in tch m. Vi silicon, cac tap cht

hoc thiu hut hoc d tha mt in t so vi Si. V vy:

P + ND = n + NA (1.2)trong o, ND la nng cac nguyn t donor va NA la nng cac nguyn t acceptor . Phngtrnh

(1.2) con goi la iu kin trung hoa in tch khng gian, trong o a gia thit rng tt ca cac in t

donor va cac l trng acceptor u c kch thch hoan toan sao cho cac mc donor va acceptor u

hoan toan b chim bi cac in t. nhit phong, gia thit nay noi chung co th chp nhn c tr

khi pha tap qua manh (nng nguyn t tap cht > 1018 cm-3). Noi cach khac, ND co th c thay th

bi ND+ va NA bi NA-.

trang thai cn bng nhit:

pn = ni2 (1.3)

Quan h nay ung cho cac loai ban dn bt ky cn bng nhit.

Vi mt ban dn loai -n, nng in t nn co th nhn c khi thay (1.3) vao (1.2):

(1.4)( )[ ]

++= 21

224

2

1iADADn nNNNNn

Tng t cho ban dn loai -p:

(1.5)( )[ ]

++= 21

224

2

1iDADAp nNNNNp

6

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Nng hat tai ni cua Si la 4.5 x 1010 cm-3 27o C, cua GaAs la 9 x 106. ln cua nng tap cht

tng cong | ND - NA| noi chung ln hn rt nhiu so vi ni. V vy nng hat tai c ban co th c tnh

xp x t (1.4) va (1.5):

nn ND - NA (1.6)

pp NA - ND (1.7)

Nng hat tai khng c ban (thiu s) co th c tnh xp x t (1.6) , (1.7) va (1.3):

AD

in

NN

np

2

(1.8)

DA

ip

NNnn

2

(1.9)

trong o pn va la nng l trng trong ban dn n va np la nng in t trong ban dn p.

Xac sut f(E) mt trang thai in t vi mc nng lng E b chim bi mt in t c cho bi ham

xac sut Fermi-Dirac:

( ) kTEE FeEf

/1

1)(

+=

(1.10)

vi T la nhit tuyt i, k la hng s Boltzmann (8.62 x 10-5 eV/K = 1.38 x 10-23 J/K) va EF c goi

la mc Fermi. Mc Fermi chnh la th hoa hoc cua in t trong cht rn, va co th xem nh mc nng

lng ma tai o xac sut chim trang thai cua in t ung bng 1/2. th ham phn b xac sut

Fermi-Dirac cho cac nhit khac nhau c minh hoa hnh (1-3):

Hnh 1-3 phn b xac sut Fermi-Dirac

7

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T ham phn b xac sut Fermi-Dirac, s kha d cac in t trong ban dn co mc nng lng xac

nh co th c tnh t ham mt xac sut N(E). Nu s trang thai nng lng trn mt n v th tch

(hay mt trang thai) trong khoang nng lng dE la N(E)dE, th s in t trn mt n v th tch

(hay mt in t) trong vung dn, n, c cho bi:

dEENEfn

cE

)()(

= (1.11)

V nguyn tc N(E)co th c tnh t c hoc lng t va nguyn ly loai tr Pauli. Tuy nhin tin li

co th biu din cac in t phn b trong vung dn bi mt hiu dungcac trang thai Ncnh x tai

b vung dn Ec.Khi o nng in t trong vung dn co dang n gian:

N = Ncf(Ec) (1.12)

Trong oNcc cho bi:

2/3

2

22

=

h

kTmN n

c

(1.13)

=

GaAsfor)300/(107.4

for)300/(108.232/317

32/319

cmT

SicmT

trong o mn* la khi lng hiu dung cua in t khi tnh n anh hng cua mang tinh th ln c trng

cua in t va h la hng s Plank. Nu (Ec - Ef) ln hn mt vai ln kT (thng nhit phong kT =

0.026eV nn iu kin nay thoa man), thi phn b xac sut f(Ec) co th c tnh gn ung nh sau:

(1.14)( )

( ) kTEEkTEEc

fc

Fc

ee

Ef/

/1

1)(

+=

8

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Khi o (1.12) tr thanh:

(1.15)kTEE

c

fceNn/=

Tng t:

(1.16)kTEEv

vfeNp /=2/3

2

22

=

h

kTmN

p

v

Vi

=

GaAsfor)300/(107

for)300/(1004.132/318

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cmT

SicmT(1.17)

mp* la khi lng hiu dung cua l trng. Cac phng trnh (1.15) va (1.16) co hiu lc cho ca ban dn

thun va pha tap, ch thay EF bng EI cho trng hp ban dn thun.

Nu cac hat tai phn b u, mt dong in do s dch chuyn cua cac in t vi vn tc

trung bnh theo mt hng nao o (chng han hng x) la:nv

(1.18)nn

vqnJ =

Nu cac hat tai phn b khng u th con co thm thanh phn dong khuch tan:

(1.19)dx

dnqDvqnJ

nnn)(=

Trong oDla h s khuch tan cua hat tai. S hang th nht c goi la dong tri (drift), ty l vi

cng in trng Edo vn tc trung bnh cua cac hat tai ty l vi cng in trng Evi h s

ty l, c goi la linh ng:

sVEv ./cm; 2= (1.20)

Vi in t: ,vi l trng:Ev nn = Ev pp =

9

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linh ng cua hat tai phu thuc vao nng hat tai va vao nhit . Noi chung linh ng

cua in t ln hn linh ng cua l trng. Vi Si, nhit 20oC, n = 1900 cm2/(V.s) vap = 425

cm2/(V.s). Quan h (1.20) ung vi cng in trng khng qua ln (thng nho hn 0.2V/cm). Vi

in trng ln hn, linh ng tng chm theo cng in trng va tin ti gia tr bao hoa. Dong

in tng cng do ca hai loai hat tai la:

J =Jn + Jp (1.21)

T (1.19) d thy rng dn in:

= q(nn +pp) (1.22)

H s khuch tan trong (1.19) quan h vi linh ng theo h thc Einstein

(1.23)

q

kTD =

10

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1.4 Cac n v c s cua mach tch hpCac n v c s cua Si-based Ics la MOSFET va BJT, va cua GaAs-based ICs la MESFET. Mt

ng dung quan trong cua cac tip xuc pn trong ch tao IC la dung cach ly v in cho nhiu loai phn

t tch cc. Vi muc ch o cac tip xuc pn phai c ap t th phn cc ngc hoc bng khng.

ch nay chiu cao rao th se tng khi tng nng pha tap.

Cac transistor co th c dung nh cac phn t khuch ai hoc chuyn mach. Trong cu truc ba

lp cua BJT-transistor, lp base (lp gia) rt mong va c pha tap t hn so vi emitter va collector.

V vy mt dong base rt nho se gy ra mt dong emitter-collector ln hn nhiu. Mt BJT cach ly in

hnh dung cho cac mach tch hp c m ta hnh (1.2).

Hnh 1.2 Mt n v npn-BJT c ban dung cho IC.

V ca ba cc u phai trn b mt cua chip, nn dong collector phai chay qua mt ng dn co

in tr ln trong vt liu pha tap nhen. Mt phng phap chung giam in tr collector la dung mt

lp pha tap manh (n+) ngay bn di collector. Lp n+ nay c goi la lp ngm (buried layer). cach11

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ly n v BJT nay vi cac n v khac ngi ta dung lp p tao ra cac chuyn tip pn cach ly. Cac

BJT loai npn c dung nhiu v cng ngh ch tao n gian hn so vi pnp-BJT.

Transistor trng (FET) da trn cng ngh MOS chim u th trong cng ngh IC, c bit cho

cac IC logic. MOSFET co th la knh n hoc knh p tuy thuc vao hat tai cho s dn in la n hay p. V

linh ng cua in t cao hn nhiu so vi l trng nn MOSFET knh n c dung nhiu hn. Mt

lin hp co tnh lun chuyn cua NMOS va PMOS c goi la CMOS (complimentary MOS), hnh ( ).

Hnh 1.3 Cu hnh CMOS n gianDo kho khn trong cng ngh ch tao cu truc MOS cho GaAs nn MESFET la cu truc c s

cho IC trn c s GaAs. Tuy nhin cac MESFET-IC trn c s GaAs co tc cao, mt tch hp cao

va rng vung cm ln. Mt cu truc n gian cua MESFET trn c s GaAs c m ta hnh ().

MESFET hoat ng vi gate Schottky phn cc ngc va cac tip xuc Ohmic cho drain va source. la

GaAs ban in mi do pha tap thch hp, chng han Cl, sao cho mc Fermi c ghim gn gia vung

cm (do o in tr ln).12

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1.5 Mt s c s vt ly linh kin ban dn

Nng ht ti vt tri ti cc bvng in tch khng gian:

( ) 1/

0 ==kTqV

nenenn eppxpp

1/0 ==kTqV

pepepp ennxnn

13

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Phng trnh Shockley

AL

nqD

L

pqD

In

pen

p

nep

+= 0

( ) ( ) 2/12/1 , nnnppp DLDL ==

Di th phn cc ngc (C-B), dng ngc t n to p ch ph thuc

vo tc tim l trng p c iu khin bi chuyn tip pn (Emitter-

Base) phn cc thun.

Good pnp Transistor cn gn nh ton b l trng tim t Emitter

vo Base phi c gp vo Collector. Base cn mng sao cho

neutral length ca Base Wb nh hn nhiu so vi qung ng khuch tn

ca l trng (khng xy ra ti hp trong vng Base). ng thi dng in

14

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t t Base n Emitter phi nh hn nhiu so vi dng l trng t E n B.

Pha tp min B thp hn min E (p+n Emitter junction).

Cc i lng quyt nh tnh nng ca mt BJT: hiu sut tim

Emitter, h s truyn t dng, h s khuch i dng base-collector.

=

==

+

1

C

CCC

B

EpEpE

Ep

E

EpEn

Ep

I

I

I

I

I

I

I

I

I

I

II

I

Ch cn gii phng trnh trung ho cho min Base v cc dngc xc nh bi c trng ca ht ti trong 2 min chuyn

tip quanh Base.

Khi cc th phn cc ln v Emitter pha tp mnh th:

=

=

=

p

b

E

p

bC

p

bB

L

W

aI

L

WaI

L

WaI

coth

csch

2

tanh

1

1

1

15

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( )1,/

1 =

=kTqV

Bep

p

pp EB

E

E

epL

qAD

a

Lp l chiu di khuch tn trong min Base v pBe l nng l trng

cn bng trong min Base.

Ba yu t quan trng:- Th phn cc (s hng exp(qV/kT)

- Cc dng Emitter v Collectorc xc nh bi gradientnng ht ti khng cbn ti bin ca chuyn tip.

- Dng Base bng hiu dng Emitter v CollectorCu trc MIS: c bit quan trng cho digital ICs.

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c trng I-V:

( )

= 22

1

DDTG

in

D

VVVVL

ZCI

Z: chiu su ca knh, L: chiu di knh, Ci : in

dung lp cch in trn n v din tch, n linh

ng b mt ca in t.

18

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1.6 V du thit k BJTPhn nay se xem xet mt thit k cho vic ch tao mt BJT vi mt

lp ngm nh a noi ti phn trc. Tun t thit k va ch tao cha c

cp y. Hnh (1.6.1) la s cua mt n+pn+ BJT.

Cac thng s quan trong la h s khuch ai dong base-collector, ,

tn s cutoff, la tn s ng vi s suy giam cua h s khuch ai ac v n

v, tn s ct alpha, f, lin quan vi thi gian dch chuyn cua hat tai th

yu qua min base B, tng ng vi s suy giam 3 dB cua li so vi giatr cua no tn s thp:

f = 1/(2B)

va:

n

bB

D

W

2

=

19

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trong o la h s phu thuc vao mc pha tap (=2 cho base pha tap

ng nht), va vao in trng ap t.

Ngoai ra con co hai tiu chun cho s hoat ng bnh thng cua

transistor. Mt la th anh thung. Di iu kin phn cc ngc, co hai

nguyn nhn gy ra hin tng anh thung. Mt la tunnel do in trng

cam ng (thng gia hai min pha tap manh, hiu ng Zener). Hai la anh

thung thac lu, do cac cp in t-l trng c tao ra do cac hat tai c

gia tc bi in trng. Th anh thung (BV) thng lin quan vi h s

nhn collector nh sau:

[ ]nCBCB BVVM

o)/(1

1

=

Trong o n la hng s va (BV)Cbo la th anh thung h mach.

li dong c biu din bi:

T

E

En

En

Cn

Cn

C

E

C MI

I

I

I

I

I

I

I===

20

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Trong oT la h s vn chuyn base,

22

2/1

1sec

nbn

b

T

LWL

Wh

+

EB GG /1

1

+

Trong o Ln la quang ng khuch tan cua in t, s Gummel GB

c xac nh bi:

(1.6.1)

nB

Bo

base

B

nB

BD

qQdxxN

DG

/)(

1==

va GE c xac nh tng t cho emitter, QBo la in tch tip xuc cua

base. Du xp x ng vi iu kin Wb >> Ln.

[ ]nCBoCBbEB

BVVLWGG )/(2//

12 +

Nu gia thit co mt phn b Gauss cua nng tap cht (kt qua cua

u nhit), vi nng tai b mt la NBo th:

CBoB NDt

xxNN = )

4p(e

2

21

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Vi NC la nng tap collector (bn pha base cua chuyn tip

collector-base), khi o:

dxNdyedyeNDtq

Q

CB

EB

x

x

C

t

y

t

yBo

Bo

=

12

22

0

2/

0

2/

2/1

2

Vi

( ) 2/11 2Dtx

t EB=

( ) 2/12 2Dtx

t CB=

Trong o xEB va xCB la khoang cach t b mt ti mep cua cac min

emitter-base va collector-base tng ng. Khi o:

22

(1.6.2)

+=

q

WQxN

q

xQqBV bBoCBo

S

CBo22

)(2

11

Vi x1 = xepi - xBC

Cac phng trnh (1.6.1 v 1.6.2) dung xac nh cng ngh ch tao.

Vn co th c phat biu di dang: cho cac gia tr mong mun cua ,

fT, (BV)CBo, va RSB (tr khang sheet cua base), cn xac nh kch thc va

cach thc pha tap cho vic ch tao BJT nh hnh (1.6.1). Bai toan va li

giai c tom tt trong bangsau.

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24Lu thut toan cho bai toan

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ch tao:1.Chon mt gia tr tiu biu cua GE (5x1013 cm-4). Gia thit thoa

man (co th kim tra lai sau), tnh GB:

GB = GE/ = 5x1013/45 = 1.11x1012 cm-4s

Nng pha tap trung bnh base thng la 1017 cm-3.

T hnh 1-7 oc c DnB la 15 cm2/s. T (1.63) suy ra:

QBo/q = DnBGB = 1.67x1013 cm-2

T 1.57 va 1.58 vi = 4 va giai cho Wb

suy ra:

Wb = (DnB/2f)1/2 = 0.49 m25

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2.Gia thit chuyn tip base-collector nh x khoang 2 m tnh tb mt (xjC), th anh thung (BV)Cbo = 25 V, khi o dung hnh 1-24

tm ra:

Xepi - xB = x1 1.2 m

Nng pha tap collector ti a cho phep la NC = 8x1015 cm-3

Hnh 1-24

3.Kim tra th punch - through s dung (1.6.2): (BV)Cbo = 372 V. Vgia tr a chon la 25 V nn co th chuyn sang bc 4

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4.Vi qua trnh khuch tan nhit theo phn b Gauss, dung hnh 1-25 nhn c gia tr Nbo.

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Trong hnh 1-25, ng NB = 1016 cm-3 gn vi gia tr cua NC a tnh

t bc 2. Gia tr tm c la Nbo = 4x 108 cm-3. Gia thit qua trnh

khuch tan la 2 -step, chuyn tip xay ra khi

N(xj,t) = Nbo exp(-xjC2/4D2Bt2B) = NC

Hoc D2Bt2B = 1.6x10-9 cm2.

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5.By gi gia tr Qbo/q a tnh t trc co th c kim tra nh hnh1-26 cho rng cua vung in tch khng gian base - collector (xT)

va cac rng tng ng cua cac min pha tap manh (x1) va pha tap

nhe (x2). Nu gia tr tnh c nh hnh 1-26 ln hn gia tr a tnh

trc, th xjC phai tng va bc 4 c lp lai cho n khi iu kin

trn thoa man. Vi chuyn tip cha b ap t th phn cc th V

=0.7 V. Khi o :

rng toan b min in tch khng gian = 0.5 m

Pha base = 0.19 m

Pha collector = 0.31 m

Cac bin cua base tch cc, xCB va xEB la:

xCB = 2 - 0.19 = 1.81 m

xEB = xCB - Wb = 1.81 - 0.49 = 1.32 m

Dung 1.66 cho kt qua: Qbo/q = 5.3 x 1012 cm-2, Gia tr nay nhohn gia tr 1.67 x 1013 a nhn c t bc 1. Do o lp lai cac bc

4 va 5 cho cac gia tr:

xjC = 1.45 m

D2Bt2B = 7.85 x 10-10 cm2

Nbo = 6.5 x 1018 cm-3

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Cac gia tr nay cho kt qua Qbo/q = 1.66 x 1013 cm-2, rt gn vi gia tr

a tnh bc 1.

6.Chiu day lp epitaxi Wepi va xepi co th c tnh. T bc 2 co:Xepi - xBC = 1.2 m

Va xBC = xjC + rng pha collector cua chuyn tip B-C

= 1.45 + 0.31 = 1.76 m

Do o xepi = 1.2 + 1.76 = 2.96 m. Nu gia thit s phu trc cua lp

ngm vo lp epitaxi trong qua trnh epitaxi, th:

0.9Wepi = xepi + x2

vi x2 la chiu su thm nhp cua lp ngm vao lp epitaxi trong qua

trnh khuch tan cach ly. th nghim, t x2 = 2 m, khi o Wepi = 5.5

m. Gia thit in tr sheet khuch tan cach ly la 50 /, nng b mt

Nio(Nco) la 7 x 1018 cm-3 (t hnh 1-25). Dung gia tr nay cung vi phn b

Gauss co th tnh X2 = 2.44 m.

7.Gia tr tnh c cua x2 ln hn gia tr th (2m). iu nay chng tolp ngm qua gn chuyn tip B-C va do o bc 6 c lp lai.

Cac gia tr mi la:

Wepi = 6.4 m

Xepi = 3.1 m

Nio = 5.5 x 1018 cm-3

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8.V tr tnh t b mt cua chuyn tip emitter, xjE cn phai c xacnh. Phn base cua min B-E di th phn cc thun la xp x 0.1

m. Khi o:

XjE = xjC - xCB - Wb -0.1

= 1.45 - 0.19 - 0.49 - 0.1 = 0.67 m

Cui cung, nng tap tng cng tai xjE phai bng 0. iu nay ngu y

rng:

NE(xjE) = NB(xjE) - NC(xjE)

Hay NE = Nbo exp(-xjE2/4D2Bt2B) -NC = 1.55 x 1018 cm-3

Phng trnh nay co th dung quyt nh thu tuc pha tap.

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1.7 Cac giai oan chnh cua qui trnh ch tao vi in tHnh () m ta cac qua trnh c ban ca cng ngh ch tao IC, bao gm

qua trnh tinh ch vt liu, qua trnh moc tinh th va chun b cac wafertrn o IC c ch tao, qua trnh ch tao linh kin (IC), qua trnh ong

kin, lu gi va kim tra. Mt sau cua cac chip (die) c gn c hoc hoc

ni vi mi trng ga gi thch hp, thng la plastic hoc ceramic.

Cac wafer thng la cac a mong (chng han 0.5 mm vi Si) cua vt

liu n tinh th pha tap donor hoc acceptor. Yu cu sach cua tap va

d hoan hao cua cu truc tinh th la rt nghim ngt. Mt qui trnh x ly

tu biu c m ta hnh 1-28.

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Vt liu khiu co th la cat hoc mt khoang cht cua Si. Mt lo h

quang in nong chay c dung tao ra Silic co sach cp luyn kim

(metallurgical grade silicon, MGS), sach khoang 98%. Cac hat MGS

c a vao lo phan ng long vi mt kh tai cha hydrochloric acid

chuyn MGS thanh cac kh cha Si nh silane va chlorosilane. Cac kh

c tach va lam sach qua mt day cac b tach va chng ct. Co hai

phng phap chnh tao ra Si sach cp in t (electronic grade,

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EGS). Mt phng phap bao gm s phu Si t kh cha Si ln trn mt ng

Si nong (ng Si nong tao ra cac v tr kch c nguyn t ). ng Si ln rt

nhanh n ng knh 20 cm. Nu dung kh trichlorosilane, th phan ng

xay ra nh sau:

SiHCl3(gas) + H2(gas) Si(solid) + 3HCl(gas)

Phng phap th hai, co nhiu u im hn, s dung phan ng trong

b long. Trong o kh cha Si va cac hat mm Si tinh khit c nui. Si

EGS co cu truc a tinh th va cha tap cht co nng trong khoang ppm

(nho hn 20 ppm). Tip theo Si EGS se c cho nong chay nui thanh

thoi n tinh th.

Co 3 phng phap chnh nui thoi n tinh th t Si EGS. Phng

phap c s dung rng rai nht la ky thut Czochralski. Trong phng

phap nay, mt hat n tinh th mm nho c nhung trong EGS nong

chay, va tinh th mm se c keo gradual sao cho thoi n tinh th c

co ng knh 15 cm c hnh thanh t qua trnh lam ngui. Mt phng

phap khac la phng phap nong chay vung. Trong phng phap nay, mt

thoi Si t theo phng thng ng c lam nong chay cuc b t di ln

s dung lo cuc b quet t di ln (chng han lo vi song). Vung nong chay

c tai tinh th hoa nh cac tinh th mm. Phng phap th ba la phng

phap Bridgeman, c dung chu yu cho GaAs. Trong o vt liu a tinh

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th c lam nong chay doc theo mt thuyn hep, dai nh lo quet doc. Va

c lam ngui t mt pha co gn vi tinh th mm.

Qua trnh nui n tinh th co hai muc tiu. Mt la chuyn cu truc a

tinh th thanh cu truc n tinh th. Hai la loai bo cac tap cht khng mong

mun. Qua trnh nay xay ra mt phn cach rn - long. Trong qua trnh

nui n tinh th, cac tap cht co th c a vao tao ra n tinh th

ban dn loai n hoc p. Cac thoi ban dn se c ct thanh cac phin mong,

ng knh 0.5 mm (wafer). Mc du ch mt phn rt mong cua a ban

dn c dung tch hp linh kin, nhng day cua a bao am cho s

n nh c hoc cua IC.

So vi cng ngh ch tao wafer th cng ngh ch tao linh kin phat

trin nhanh hn nhiu. Mt s cng ngh co th tr thanh lac hu trc khi

c cng b. Tuy nhin nn tang va muc tiu cua chung co th cha thay

i.

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Hnh 1-29 m ta cac bc tun t cua qui trnhch tao IC. Khi cho

trc cac yu cu va cac chi tit ky thut cua mach th IC co th c thit

k di dang circuit layout vi cac chi tit v chiu rng, chiu su cua mi

mt n v c ban. Chng han vi mt MOSFet n gian, s b tr tng

th (layout) se c chuyn thanh cac s kh ln cho mi mt mc mt

na. Sau o cac s nay se c thu nho lai thu c mt na cui cung.

Vi cac mach VLSI, ngi thit k co th m ta mt cach in t toan b

layout cua mach. Sau o thit k c chuyn thanh dang s va c lu

tr trn bng t. Mt na co th bao gm nhiu mc khac nhau cho cac ch

tao khac nhau. Cac mt na c lam t cac vt liu nh chromium,

chromium oxide, hoc silicon.

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Bc tip theo la qua trnh quang khc (lithography), co th c lp

lai nhiu ln cho cac bc x ly tng ng vi cac mc mt na khac nhau.

Quang khc la qua trnh chuyn dang hnh hoc trn mt na vao b mt cuaSi wafer. Mi chu trnh quang khc thng bao gm s n mon qua cac ca

s m hoc vach cac dang nht nh cho bc tip theo, chng han nh phu

cac mang mong mun hay a tap cht vao cac vung a c m nh qua

trnh khuch tan hoc cy ion. Cac bc tiu biu cua qua trnh quang khcc m ta trong hnh 1-30. Cac mt na c dung m cac ca s qua

lp silicon dioxide sao cho tap cht di dang kh co th khuch tan qua

o. Mt lp can quang (photoresist, PR) t cac vt liu polymer nhay sang

c phu ln trn mt lp SiO2. Mt na c t n trn lp PR va cchiu tia cc tm. Cac ch l sang se b polymer hoa, con cac ch b th

khng. Cac vung khng b polymer hoa se b n mon bi acid BHF

(buffered-HF), l ra cac ca s cho qua trnh khuch tan. Cac wafer se

c t vao lo khuch tan co cha kh tai B2H6 hoc PH3 tao ra cacmin pha tap mong mun.

Cac bc x ly n v tiu bieu bao gm s phu mang epitaxi (n

tinh th) va mang khng epitaxi, s oxi hoa, cy ion va kim loai hoa (phu

kim loai). Qua trnh nay nhm muc tiu tao ra cac min tch cc va cach lychung vi nhau. Yu t chnh ay la s phn b tap cht va s m ta ro

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rang cua phn b tap cht. Cac wafer phai trai qua nhiu bc khac nhau

cua qua trnh x ly nhit cao nn co th dn ti s phn b lai tap cht.

Do o rt nhiu n lc a c thc hin ha thp nhit cua cac qua

trnh x ly.

Qua trnh ong kin mach IC bao gm vic gn chip (die) vao mt vt

liu ga nht nh, vic ni dy gia cac ng dnlinh kin vi ga va tao

hnh cho no. Cac vt liu ga thng la plastic, kim loai va gm.

Hnh 1-31 m ta qua trnh chi tit ch tao mt NMOS Si - gate IC t

cac wafer ban u n ong kin cho IC. Khi mt linh lin tng ln th

s chn cua IC tr thanh mt nhc im do kch thc b ga ln se lam

tn hao nhit ln. ng thi s chn cua IC nhiu cung lam tng tn hiu

nhiu. Bn canh o thi gian s dung (lifetime) cung la mt yu tto quan

trong trong vic thit k ga gi IC.

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CHNG 3. DESIGN AUTOMATION AND

VERIFICATION

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