INTEGRATED CIRCUITS. Dr. Esam Yosry. Lec . #6. Lithography. Introduction Lithography Photolithography Photoresist Process Types of Photoresist Photomask Clean Rooms. Introduction ( Chip Fabrication Cycle). Introduction ( Processes). Oxidation Diffusion Ion Implantation Deposition
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Photolithography is the heart of integrated circuit processing. It is the method used to transfer the individual circuit design knowledge onto the silicon wafer.
Probably one half of the wafer fabrication costs go into obtaining proper photolithography.
The basic elements consist of:
Silicon Wafer with Silicon Dioxide
To be etched
Apply photo resist
Apply Ultraviolet Light
Decreasing feature size require the use of shorter λ
Etch Silicon Dioxide
This flow chart shows the typical process used for VLSI Lithography.
1.Substrate Cleaning and Preparation
The goal of coating is to apply a uniform, defect free film of photoresist over The entire wafer. Spin Coating is used for VLSI
Before spin After spin
PR Wafer PR
The Soft-Baked is used to:
Typical process Temp is 90-100°C
To produce the desired photochemical effects in the shortest time possible.
Time is important because:
However, short times usually mean lower resolution.
Exposure to UV light chemically changes the resist
Development removes the unwanted photoresist.
etched on the wafer
surface is drawn on
Photolithography must be carried out in a clean room otherwise dust particles causing fabrication errors.
The total number of dust particle are controlled with temp and humidity.
Clean rooms standards:
Class 100 < 100 pp ft3 (0.5µ)
Class 10 < 10 ppft3 (0.5µ)
Class 1 < 1 ppft3 (0.5µ)
Many thanks to Prof. Hany Fikry and Prof WaelFikry for their useful materials that help me to prepare this presentation.