Oxidation/Diffusion/Implantation

Question 1

How does Method/Temperature/Orientation affect Oxidation?

Answer 1

1) Method Dependence - Wet/Dry - Water has higher solubility.
2) Temperature Dependence - Higher temp - faster reaction - Arrhenius Relationship
3) Orientation Dependence - Influence LINEAR RATE CONSTANT

Question 2

How does Pressure/Dopant affect Oxidation?

Answer 2

1) Pressure Dependence - Higher pressure/faster reaction - (Oxidation rate is dependent on Co, which is depdent on partial pressure) Co = outside conc
2) Dopant Dependence - Boron moves from silicon into oxide - weakens bond structure - increases PARABOLIC
Phosphorous stays in silicon - increases LINEAR.

Question 3

Oxide Thickness measurement techniques (3)

Answer 3

1) Colour - White light passes through oxide and is reflected by silicon - interference enhances a particular wavelength
2) Ellipsometer - Polarisation of reflected monochromatic light is measured.
3) Step height - etch region

Question 4

Describe with the aid of a diagram the LOCOS process that is partially recessed.

Answer 4

TOSWOR
Thin Oxide + SiN
Wet Oxide
Remove

Question 5

Explain the term of Bird’s beak

Answer 5

Thick oxide under active device regions, gradually thinning to form a BIRD’S BEAK.z

Question 6

Which is diffusion co-efficient and material constant?

D = Do * exp(-Ea/kT)

Answer 6

D is diffusion co-efficient - dependent on conditions

Do is material constant.

Question 7

Drive-in can be treated as Limited-Source/Constant total dopant/Gaussian if?

Answer 7

DT_drive_in > DT_diffusion

Question 8

Impantation - Ion Implantation machine

Answer 8

Ion Source
Mass analyser
Accerlerator
Deflection
Controls
Wafer

Question 9

Where/how is wet oxidation used?

Answer 9

For thick oxides, >200nm.

Bubbling o2 through pure h2o in a hot flask

Question 10

Where/how is dry oxidation used?

Answer 10

thin oxides - higher quality.

Sodium contamination results in oxide - reduced by adding HCL

Question 11

Dry or wet has a zero initial oxidation depth

Answer 11

Wet oxidation is 0nm.

Xi = 25 nm for dry oxidation

Question 12

How do you calculate the linear/parabolic constants for oxidation?

Answer 12

Use Arrhenius relationship and Do/Ea values provided.

Question 13

Units for oxidation

Answer 13

Micrometres and hrs

Question 14

How to model an implant profile?

Answer 14

Dt product

Question 15

What is k constant for diffusion?

Answer 15

eV