CHE 309: CRE CVD

Lecture-1

Module: CVD

Contents

I. Introduction CVD

II. Plasma

III. Vacuum Technology

IV. Plasma CVD technology

V. CVD etching process

I. Introduction to CVD

1. CVD(Chemical vapor deposition)

2. CVD Reaction

3. CVD Reactors

4. PECVD, laser CVD, MOCVD

5. CVD

1. CVD (Chemical Vapor Deposition)

- CVD is a technique to deposit an extensive variety of thin film materials.

- Uses chemically reacting vapors to synthesize or deposit a film.

- Energy to cause bond breaking⦁ Thermal (usually)⦁ Photons (UV, laser, …)⦁ Dischange (plasma, )

- a CVD system … a chemical reactor with accessories.

- CVD Reaction Type

- CVD Application

• Micro electronics / VLSI- insulators : SiO2, PSG, BPSG, Si3N4, ∙ ∙ ∙- poly silicon : gate, shallow junction contact capacitor electrode- silicides : WSiX – gate, ∙ ∙ ∙- refractory : W

• Hard and Wear Resistant coationgs : Boron, Borides, Carbies, Nitrides

• Optical Fiber

• Composite

- Strengths & Weaknesses of CVD

• Various film formation- elements : Al, As, B, Bi, C, Cr, Co, Cu, Ge, Ag, Hf,

Pb, Mo, Ni, Nb, Os, Pd, Rh, Re, Ru, Si, Ta, Sn, W, U

- compounds : nitrides, oxides, silicides, borides, carbides, GaAs, ∙ ∙ ∙

- various composition

• Deposition rate : reasonable, controllable

• Lower impurities- purity, development of contamination prevention technology

- makes IC surface smooth

• Good step coverage

• High reaction temperature- mono crystal- poly crystal

• Complicated

WeaknessesStrengths

2. CVD Reaction

- Reaction Path of CVD

• Homogeneous / Heterogeneous reaction

• Diffusion – molecular (multi component)- thermal- surface

• Adsorption / Desorption

- Reaction Rate of CVD (deposition rate / film growth rate)

• Nucleation (gas phase)

= 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑓𝑖𝑛𝑒 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠

𝑑𝑒𝑝𝑙𝑒𝑡𝑖𝑜𝑛 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠

- Morphology vs Temp. supersaturation

Nucleation on Film Surface ∙ ∙ ∙ surface dependent∙ Selective deposition

Example : W (two step deposit)

- CVD Reaction Mechanism

• Complicated, lag behind applications.• In complexity, similar to combustion and heterogeneous catalysis.• but behind about 20 years

Example

Homogeneous nucleation ∙ ∙ ∙ formation of nucleifor fine particles

3. CVD Reactors

- PressureAPCVD (Atmospheric Pressure) ∙ ∙ ∙ ~ 1atmLPCVD (Low Pressure) ∙ ∙ ∙ ~ < 1torr

- Heating methodresistant heating

reactor inside ∙ ∙ ∙ substrate onlyreactor outside ∙ ∙ ∙ furnace type

RF HeatingLamp Heating

- Hot wall / Cold wallHot wall ∙ ∙ ∙ Substrate T < wall TCold wall ∙ ∙ ∙ >

- Form of reactor according to direction of gas flowvertical / horizontalbarrelpancake

- Reaction AssistPECVD (Plasma Enhanced)PACVD (Plasma Assisted)光 CVD ∙ ∙ ∙ laser, UV

- Batch vs Continuous ( In Line )

- Continuous CVD

- CVD Reactors

(Heating method)(Shape of reactor)(Pressure / Method)

- Epitaxial CVD

Epitaxy of Si ∙ ∙ ∙ most demanding ① Air pressure- high T, clean, ∙ ∙ ∙ ② LP.

(Heating method) (Form) (Pressure)

- Comparison of APCVD Reactors

* General Trend : increasing USE of LPCVD at the expense of APCVD

- Comparison of LPCVD Reactors

No homogeneous reaction!

- Single Wafer CVD

① Automation is easy② A favorable side is uniform material③ When the wafer size is 8’’, it’s good

Strengths

- Experimental CVD Reactors∙ to decouple fluid mechanics from chemical reation∙ One dimentional flow ∙ ∙ ∙ desirable

3. PECVD, laser CVD, MOCVD

(1) PECVD

Plasma : 50kHz ~ 40MHz6~600 Pa

non – equilibrium plasma ∙ ∙ ∙ kTe : 1~10eVkTi : ~0.04eV

chemical bond : ~ several eV

Application : passivation film (IC) : SiNX, PSG, SiO2, a-SiH

Advantages : low Temperature CVD : many research subjects

Disadvantages : Unfavorable for automation, lange wafer, contamination, damage

<Form of PECVD>

(2) Laser CVD

- Thermal CVD : exp[-Ea/kT]Ea : ~1~2eVkT : 0.62eV(at 700℃)

much of input energy is consumed for heating

- Plasma CVD

Laser : UV, visible, IRFilm : Si, C, Al, Zn, Cd, Ni, Fe, W, Ti

TiC, Cu, CoD

- Laser CVDPressure : 15~200PaTemp. : 50~300℃

- Applicationspecialized spot repairdirect – write deposition of fine lines.excimer laser : high net deposition rates over a relatively lange areagood for “proto type”, mask

- Problemslasers have notoriously low reliability.

(high maintenance cost)requires higher power and lange beam aperture lases for acceptable throughput

(3) MOCVD (Metal – Organic CVD)

- OMCVD (Organometallic CVD)

1968 : growth of GaAs at 1atm with Group Ⅲ metal organic+

Group V hilides

- MOCVD Reaction System

TMG : trimethyl gallium

TMA : trimethyl aluminum

DEZ : diethyl Zn. (dopant)

• Fundamental understanding of MOCVD ∙ ∙ ∙ not completelyunderstood

• Purity of starting materials (organometallic hydrides) is important

• Handling of hazardous materials

• Growth of Ⅱ-Ⅵ / Ⅲ-Ⅴ / Ⅳ-Ⅵcompounds semiconductor for high performance devices.- Vapor Phase Epitaxy (VPE)- Liquid Phase Epitaxy (LPE)- Molecular Beam Epitaxy (MBE)

• Advantages : Simpler than VPE by chemical transport methodBetter control of reactants feedingsharp doping profileepitaxy on insulator ∙ ∙ ∙ possibleease of change in starting material ∙ ∙ ∙ various films

COMPETITON

5. CVD

- CVD ∙ ∙ ∙ main feature : versatility for synthesizingboth simple and highly complex compounds

- Fundamental Principles of CVD ∙ ∙ ∙ interdisciplinaryreaction chemistrythermodynamicskineticscrystallographysolid state physicsreactor engineering

- Market of CVD equipments ∙ ∙ ∙ growing 19% / year1987 : ~ $300 million U.S.A. > Japan > Worldwide

- Research Topics

MOCVD ∙ ∙ ∙ compound semiconductor

Reactor : lange diameter wafer (uniformity)high throughput.

VLSI : shrinking line widthnew materiallower contamination

fast film growth : particle precipitation aided CVD

wear Resistant coating

new material