SPT_Midterm

NaturalLength? L/lambda big or small

big

To match mobility of n and p type

Width bigger or change channel number

SCE reason

when L is comparable to the depletion region of S/D, also when the gate’s control is weak

for natural length to decrease, oxide dielectric big or small, what K?

bigger, High K materal

Types of defects(generally)

Interstitial, Substituntioal, Vacancy, dislocation

how can we add strain to the S/D with defects

dislocation or stacking fault

What is XRD

X-Ray deflection, to see lattices orientation

Hall effect measurement?

n or p type, to see the dominant charge or carriers. 

Melting point higher, H or Cl 

Cl 

Class 100, particles number, temp, what flow

0.5 100; 5 1; 19.4-25 ; Laminar, bigger than 100 Turbulent

Standard Clean SPM?

H2SO4 H2O2 ; Heavy organic (contains metal), also leaves a thin film of oxide

Standard Clean APM RCA1, SC1

NH4OH H2O2 H2O; PARTICLES, oxidize organic molecules, metals. Particles: electric repulsion, oxidation. Too much NH4OH then surface roughness, too less Not efficient.

what is HF for

remove native oxide

Standard Clean HPM RCA2 SC2

HCL H2O2 H2O, metal ions, and akali ions. (except Cu)

Steps for Wafer Cleaning

Cleaning, Rinsing(Dilution), Drying(Spin or evaporation) Spin - IPA + Marangoni (surface tension)

Post Etch Clean is needed

Why do we need high resistivity for DI water

High resistivity means high resistivity to electrcial current, hence very few ions. over 18M \omega

What kind of Waste is PR, how to remove

organic, O2 plasma ashing.

is hydrophilic or hydrophobic easier to clean?

Hydrophilic, because droplets stick on to the surface, thus touching the particles. 

What is Cross link and dissociation in PR masking?

search it up if you dont know

what are the ways to remove SiO2

HF in vaccuum, or thermal Si + SIO2 → SiO

CZ and FZ method?

Crystal pulling, floating zone. (FZ: limited wafer size, uneven heat)

Epitaxy source for Si

SiH4 1000, SiH2Cl2 DCS 1100, SiHCl3 TCS 1100.

Epitaxy dopant source (insitu doping)

B2H6, AsH3, POCl3, BN

What does epitaxy use to purge, and why

H2, better hybrid formation, etch native oxide;  N2 might react with Si, which impacts a lot

Small chamber Heat capacity big or small

big

Crystal defects in Si

Point, dislocation, Gross

What is the process for SOI wafer, SIMOX and bonding wafers

look it up

how to increase mobility of e and h with stress

tensile electron, stress liner NMOS , compressed hole. SEG(selective epi+insitu doping) PMOS. 

SiO2: dielectric constant, gap, refractive index, VBD

3.9, 9, 1.462, 12MV

four defects charges in SiO2

Fixed, mobile, Oxide trapped, interface trapped.

Source of Wet and dry oxidation

H2O, O2

Why is wet oxidation faster than dry

Higher oxidant solubility, H-O faster diffusion

Oxidation growth speed of orientation 100 110 111

avaliable bonds more, growth speed faster. surface density more, faster as well.

Pressure and oxidation growth speed?

proportional, the C* (eq. concentration of oxidant at surface)

doping and oxidation?

Faster for both n and p type, boron weaken SI-O bond, more O2 free. phosphorus piles up, vacancies more

For Dry oxidation, horizontal or vertical, particle contamination?

vertical better, think air flow

Issue with wet oxidation? for boiler, bubbler, flush

Water is hard to control, use pyrogenic steam system which is all gas, but this has saftey concerns due to flamable H2 (explodes as well). OTS

What is Masking, Pad, Screen, Gate for

Pad is to relieve tensile stress, and for LOCOS/STI under Nitride mask. SCreen is to reduce ion channeling during doping

Characterization of oxide or film. Color chart, Reflectometry, Ellipsometry, CV test

Reflectometry is for thk, Ellipsometry for thin

Diffusion profiles?

Constant total dopant (limited), constant surface concentration

Process of thermal diffusion

SiO2 Hard mask ; Depo. dopant oxide: (POCl3+O2→P2O2+CL3) ; Cap oxide (P2O5 +Si → SiO2 + P) ; Drive in USED furnace anneal, oxidation, RTA(for USJ as well to drive in)

2 conditions for ion implantation

High T 1100; High ramp rate. Also needs post implant annealing

Common Silicide (Alloy annealing)

TiSi2 CoSi2 NiSi2. Lower rho than Si

Reflow: USG PSG BPSG, why use PSG?

Undoped silicon glass, Boron, Ph. , Lower temp to soften after doped. Ph grabs Na, used as PMD(pre metal dielectricS)

Explain SIMS

primary, seconadary, for different doping profiles and junction depth. wht

what is the source for oxidation?

N2 purge HCl, and O2 or H2OWhat

what is the draw back of LOCOS

Bird Beak