Wafer processing - IClean room environment

Semiconductor clean room:- controlled temperature (20ºC), air pressure, humidity (30%)- controlled airbone particulates- controlled vibration- controlled lighting

INESC:250 m2 Class 10 and 100 clean room250 m2 Class 10000 (grey area)

Class 100:<100 particles(>0.5m)/ft3

Wafer processing - IIresist coating

1- Vapor priming for improved resist adhesion to substrate

- Resist adhesion to Si wafers is poor- Dehydration bake to remove adsorbed water from the surface- surfactant to promote adhesion : HMDS (hexamethyldisilazane)

Vapor priming is better than spin coating with a liquid solution because lower contamination

~1 monolayer

Table II.6 – Vapor prime coating steps Step description

Conditions

Wafer dehydration and purge oxygen from the chamber

Vacuum, 10 Torr, 2 minutes N2 inlet (heated), 760 Torr, 3 min steps 3x

Priming Vacuum, 1 Torr, 3 minutes HMDS, 6 Torr, 5 minutes

Purge prime exhaust Vacuum, 4 Torr, 1 minute N2 inlet, 500 Torr, 2 minutes Vacuum, 4 Torr, 2 minutes

Return to atmosphere (backfill) N2 inlet, 3 minutes

2- Spinning resist and soft baking

Wafer processing - IIresist coating

SVG Resist coater and developer track:

Track system for spin coating of photoresist (1.2 to 2 m thick) and for development of post-exposed wafers.

(cassettes of 25 Si wafers 6 inch)

Requirements:Good control of thickness, uniformity, viscosity, particle contaminationTypical resist thickness: 0.6-2 m

Soft baking: remove solvents and stress and promote adhesion to wafer

Wafer processing - II

6 inch metallic holder

2 mm thick

1x1 inch squares

3 inch AlTiC wafers

6 inch Si wafer

tape

x-y- table

(a)

(b)

Coating and developing Exposure

(c)

6 inchSi wafers

Wafer processing - IIIexposure

Heidelberg Instruments Direct Write Laser Lithography System:

Direct write lithography system utilizing a HeCd laser (=442 nm (g-line) / write lens NA= 0.85) capable of critical dimensions down to 0.8 m. System works with mask designs in GDS2 format. 

INESC

Wafer processing - IVdevelopment

Positive resistsNegative resists

(INESC)

Solved in the exposed regions

Remain in the exposed regions

Selective dissolving of

resist

Resist profiles