Thermodynamics in Chip Processing

Terry Ring

Silicon Wafers

Chip Feature Scaling

Moore’s Law

• please see http://developer.intel.com/update/archive/issue2/focus.htm

What is a semiconductor?

• Conductor– Metal

• Insulator– Ceramic (oxides)

• Semiconductor– Diamond– Silicon– Germanium– Gallium Arsenide– Host of others

Intrinsic Silicon

• Silicon has four valence electrons. When a group of Silicon atoms bond together to produce a pure lattice structure, the material is referred to as Intrinsic Silicon.

Si

Si

Si

Si

Si

Si

Si

Si

Si

Silicon Doping

• This pure silicon configuration (intrinsic silicon) is a poor conductor because none of its electrons are available to serve as carriers of electric charge.

• The fabrication of integrated circuits requires that the substrate (the wafer surface) be somewhat conductive.

• This process is known as doping. Boron (B), Phosphorus (P), and Arsenic (As) are the most common dopant atoms used in the industry.

3

LiLithium

6.941

11

NaSodium

22.99

19

KPotassium

39.10

37

RbRubidium

85.47

55

CsCesium

132.9

87

FrxFrancium

(223)

4

BeBeryllium

9.012

12

MgMagnesium

24.31

20

CaCalcium

40.08

38

SrStrontium

1.008

56

BaBarium

137.3

88

Raxradium

226.0

21

ScScandium

44.96

39

YYttrium

88.91

57

LaLanthanum

138.9

89

AcxActinium

(227)

22

TiTitanium

47.90

40

ZrZirconium

91.22

72

HfHafnium

178.5

104

Unqx(261) 105

Unpx(262)

73

TaTantalium

180.9

41

NbNiobium

92.91

23

VVanadium

50.94 24

CrChromium

52.00

42

MoMolybdenum

95.94

74

WTungsten

183.9

106

Unhx(263) 107

Unsx(262)

75

ReRhenium

186.2

43

TcxTechnetium

98.91

25

MnManganese

54.94 26

FeIron

55.85

44

RuRuthenium

101.1

76

OsOsmium

190.2

108

Unox(265) 109

Unex(266)

77

IrIridium

192.2

45

RhRhodium

102.9

27

CoCobalt

58.93 28

NiNickel

58.71

46

PdPalladium

106.4

78

PtPlatinum

195.1 79

AuGold

197.0

47

AgSilver

107.9

29

CuCopper

63.55 30

ZnZinc

65.37

48

CdCadmium

112.4

80

HgMercury

200.6 81

TlThallium

204.4

49

InIndium

114.8

31

GaGallium

69.72

13

AlAluminum

26.98

5

BBoron

10.81 6

CCarbon

12.01

14

SiSilicon

28.09

32

GeGermanium

72.59

50

SnTin

118.7

82

PbLead

207.2 83

BiBismuth

209.0

51

SbAntimony

121.8

33

AsArsenic

74.92

15

PPhosphorous

30.97

7

NNitrogen

14.01 8

OOxygen

16.00

16

SSulfur

32.06

34

SeSelenium

78.96

52

TeTellurium

127.6

84

PoxPolonium

(210) 85

AtxAstatine

(210)

53

IIodine

126.0

35

BrBromine

79.90

17

ClChlorine

35.45

9

FFluorine

19.00 10

NeNeon

20.18

2

HeHelium

4.003

18

ArArgon

39.95

36

KrKrypton

83.80

54

XeXenon

131.1

86

RnxRadon

(222)

(1)*I A

(2)II A

(3)III B

(4)IV B

(5)V B

(12)II B

(11)I B

(7)VII B

(6)VI B

(13)III A

(14)IV A

(15)V A

(16)VI A

(17)VII A

(18)NobleGases

VIII B(10)(8) (9)

1

HHydrogen

1.008

58

CeCerium

140.1

90

ThxThorium

232.0

59

PrPraseodymium

140.9

91

PaxProtactinium

231.0

60

NdNeodymium

144.2

92

UxUranium

238.0

61

PmxPromethium

(147)

93

NpxNeptunium

237.0

62

SmSamarium

150.4

94

PuxPlutonium

(244)

63

EuEuropium

152.0

95

AmxAmericium

(243) 96

CmxCurium

(247)

64

GdGadolinium

157.3 65

TbTerbium

158.9

97

BkxBerkelium

(247) 98

CfxCalifornium

(251)

66

DyDysprosium

162.5

99

EsxEinsteinium

(254)

67

HoHolmium

164.9

100

FmxFermium

(257)

68

ErErbium

167.3

101

MdxMendelevium

(258)

69

TmThulium

168.9

102

NoxNobelium

(255) 103

LrxLawrencium

(256)

70

YbYtterbium

173.0 71

LuLutetium

175.0

Lanthanides

Actinides

1

HHydrogen

1.008

RepresentativeElements

TransitionElements

Inner-TransitionElements

NobleGases

Atomic Number

Name of Element

Aymbol of Element

Atomic Weight

x: All isotopes are radioactive.

( ) Indicates mass number of isotope with longest known half-life.

* Number in ( ) heading each column represents the group designation recommended by the ACS Committee on Nomenclature.

The Periodic Table of Elements

1

2

3

4

5

6

7

Period

Dopant Chemistry

• By looking at the Periodic Table, we can determine the number of electrons that Boron and Phosphorus have in their outer orbit.

B P

Si Si Si

Si Si Si

Si P Si

N-Type

P

P-Type

Si Si Si

Si Si Si

Si B Si

B

One Die or Chip

Anatomy of a Anatomy of a Memory ChipMemory Chip

Building Blocks of Building Blocks of

the DRAM memory the DRAM memory

cellcell

READ+

WRITE-_

Basic DRAM memory cell - Basic DRAM memory cell - 1T1T

C olum n or B itline

Ro

w o

r W

ord

line

Capacitor

Transistor

DRAM memory ArrayDRAM memory Array

MOSFET-Gate, Source, Drain Metal-Oxide-Semiconductor-Field-Effect-Transistors

• A MOSFET is composed of three main components; a gate, a source, and a drain. The gate is a physical structure built on the wafer surface to control the opening and closing of a source-to-drain channel. To create this structure, a metal and oxide layer are formed on a semiconductor surface (MOS). The source and drain regions are just highly doped, shallow pockets in the wafer surface next to the gate.

The Transistor(continued)

• Doing the dishes requires that we access a

Source (or reservoir) of water.

• Channel (or pipe) connects the reservoir to the

sink. Don’t want a continuous flow of water to

our drain (or sink). . .

• Need a gate (or valve) to block the water flow.

ReservoirWater

Channel

Gate

Source

Drain

Sink

ClosedGate Reservoir

Water

Gate

Source

Drain

Sink

OpenGate External

Energy(voltage)

Lithography

• Light passes thru die mask

• Light imaged on wafer

• Stepper to new die location

• Re-imageWafer with Photoresist

Mask

Light Source

ReductionLens

MS&E vs ChE

• How is a Materials Science and Engineering Education Different from Chemical Engineering Education?– Focus on Solids Processing

• What Crystal Structure

– Higher Purity Materials– Impurities Control Properties

• Semiconductors• Grain Boundaries

– Where atoms are in structure determines properties

Where Thermodynamics Comes into Chip Processing

• Evaporation Rate during Spin Coating• Evaporation Rate during Photoresist Drying• Metal Physical Deposition• Chemical Vapor Deposition

– Feed of TEOS– Rxn of TEOS

• Etching - SiF4 vapor pressure

• CMP Solution Equilibria– Dissolution/Precipitation

Lithography

• Light passes thru die mask

• Light imaged on wafer

• Stepper to new die location

• Re-imageWafer with Photoresist

Mask

Light Source

ReductionLens

PhotoLythography

PhotoResist UV light=193 nm 80 nm Line

Photoresist -Sales $1.2 billion/yr. in 2001

• Resins– phenol-formaldehyde, I-line

• Solvents• Photosensitive compounds

– Polymethylmethacrylate or poly acrylic acid = 638 nm RED LIGHT

– diazonaphthoquinone• Hg lamp, = 365 nm, I-line

– o-nitrobenzyl esters – acid generators• Deep UV, = 248 nm, KrF laser

– Cycloolefin-maleic anhydride copolymer– Poly hydroxystyrene

=193 nm gives lines 100 nm = 157 nm F laser

• Additives

Photoresist

• Spin Coat wafer

• Dry solvent out of film

• Expose to Light

• Develop

• Quench development

• Dissolve resist (+) or developed resist (-)

Spin Coating

• Cylindrical Coordinates– Navier-Stokes– Continuity

Newtonian Fluid-non-evaporating

2/1

22

322

32

0

22

2

3

41)(

)0(..

3

1

)(3

),(@0

0@0

.'.

thhth

solution

hthCB

hrrr

qrrrt

h

thdzvq

trhaz

v

zv

sCB

rz

v

oo

o

h

r

r

r

r

If hois a constant film is uniformFor thin films, h -1 t-1/2

Evaporation Model - Heuristic Model

• CN non-volatile, CV volatile

• e = evaporation rate of volatile component

– ei = kMA(Psolvent-I - 0)• q = flow rate

Evaporation Rate

• What is Psolvent-i in a mixture?

– Other solvents and non-volatile components

• fil = fi

v equilibrium condition

– fiv =yiP

– fil = γ i xi Pi

sat

– ln γ i =GiE/(RT)

Vapor Pressure of 2 solvent mix

• P =Σ γ i xi Pisat = γ 1 x1 P1

sat + γ 2 x2 P2sat

• y1 =P1/P= γ 1 x1 P1sat /(γ 1 x1 P1

sat + γ 2 x2 P2sat )

• Pisat obtained from Normal Boiling Point & Heat of

vaporization (Claperon Equation)

• Eqs 12.10 a Margules equation, GE/(x1x2RT)=A21X1+A12X2 1 x1 T exp 1 x1 2 A12 2 A21 A12 x1

Tln Psat d

d

HV T( )

Rg T2

2 x2 T exp 1 x2 2 A21 2 A12 A21 x2

See MathCad Example

• Vapor Pressure of Solvent Mix.mcd

• Binary Solvent Mixture

• Ternary mixture of Solvent plus Non-volatile Resin

Next StepDissolve Edge of Photoresist

• So that no sticking of wafer to surfaces takes place– Wafers are stored in a rack on edge

• So that no dust or debris attaches to wafers

Wafer with Photoresist

How would you set up this problem?

• fil = fi

s equilibrium condition– fi

s = γsi zi fs

i

– fil = γl

i xi fli same a previous example of solvent mix

– ln γl i =GiE/(RT) same a previous example of solvent mix

• γli xi fl

i = zi γsi fs

i

• γli xi = zi γs

i Ψi Chapter 14

• Ψi = exp{(ΔHisl/R)[(1/Tm) - (1/T)]} Chapter 14

• ΔHisl =Heat of fusion, Tm melting temperature

• zi γsi=1 for ideal solid (misicible)

• zi= mole fraction of mix in solid

Break

• Second lecture is next

• What did we learn

• Calculate the partial pressure– Used to calculate the evaporation rate of a

component of a solvent mixture

• Calculate the solubility of a solid in a solvent mixture

Lecture 2

• Metal Deposition on the wafer– Wires to connect the transistors and

capacitors • To each other• To outside world

– 2 Mb memory chip has– > 1 km of wire– 8 layers of wiring on top

Deposition Methods

• Growth of an oxidation layer• Spin on Layer• Chemical Vapor Deposition (CVD)

– Heat = decomposition T of gasses– Plasma enhanced CVD (lower T process)

• Physical Deposition– Vapor Deposition– Sputtering

Physical Vapor Deposition

• Evaporation from Crystal (metal)

• Deposition on Wall

Physical Deposition Reactor

• Wafers in Carriage (Quartz)

• Carrier Gasses enter• Pumped out via

vacuum system• Furnace

– Metal evaporated– Sublimation

• No liquid phase

Vacuum

Furnace

Chamber at lower Temp

P

V

s l v

Deposition Rate

• Ratei = Km A {Pi(TF) - Pi(TC)}

• What is the sublimation partial pressure of metal as a function of temperature?

• fiv = fi

s equilibrium condition

– fis = γs

i zi fsi= γs

i zi Pisat exp[VMi(P - Pi

sat)/(RT)]» Poynting Factor

– fiv =yiP

Metal Saturation Pressure

• Sublimation Vapor Pressure– Claperon Equation

• ΔHS is the heat of sublimation

• ΔHS = ΔHF + ΔHV

– solid to liquid then liquid to vapor

Tln Psat d

d

HS T( )

Z Rg T2

MathCad File

• Sublimation Vapor Pressure of Alloy.mcd