INTEGRATED CIRCUITS – UNIT 5

CLASSIFICATION OF IC’s

• Monolithic IC

• Hybrid IC

INTEGRATED CIRCUITS

CHIP

INTEGRATED CIRCUIT

IC CHIP SIZE AND CIRCUIT COMPLEXITY

BASIC PLANAR PROCESSESMAIN STEPS USED TO FABRICATE AN IC :

1. Pure silicon is formed as INGOT and sliced into wafer.2. Fabrication of Integrated circuits on the wafer surface3. Wafer is cut into chips and is packaged.

THE PLANAR PROCESS

STEP 1: Silicon Wafer(Substrate) Preparation

STEP 2: Epitaxial Growth

STEP 3: Oxidation

STEP 4: Photolithography

STEP 5: Diffusion

STEP 6: Ion Implantation

STEP 7: Isolation Technique

STEP 8: Metallization

STEP 9: Assembly Processing and Packaging

Fabrication

Silicon Processing

Packaging

STEP 1: Silicon Wafer(Substrate) Preparation

Crystal Growth and doping – (Czochralski Crystal growth) Ingot trimming and grinding Ingot slicing – (Stainless steel saw blade with industrial

diamonds embedded in it) Wafer polishing and etching Wafer cleaning.

Czochralski Crystal Growth Process

Ingot slicing and Polishing

STEP 2: Epitaxial Growth (Extension of substrate crystal)

WHY EPITAXY? To enhance the performance of discrete bipolar transistorIt also offers a means of controlling the doping levels.It is generally oxygen and carbon free.

SiCl4+2H2 Si +4Hcl

STEP 3: Oxidation• SiO2 has the property of preventing diffusion

of almost all impurities through it. It serves very important purposes.

• SiO2 is an extremely hard protective coating and is unaffected by almost all reagents except hydrofluoric acid . Thus it stands against any contamination

Si +2H2O SiO2 + 2H2

LITHOGRAPHY

STEP 4: Photolithography

3

4

5

TYPES OF PHOTO RESISTpositive resist - the portion of the photoresist that is exposed to light becomes soluble to the photoresist developer. The portion of the photoresist that is unexposed remains insoluble to the photoresist developer.

 negative resist - the portion of the photoresist that is exposed to light becomes insoluble to the photoresist developer. The unexposed portion of the photoresist is dissolved by the photoresist developer.

DIFFERENCE b/w POSITIVE & NEGATIVE PHOTO RESIST

STEP 5 : DIFFUSION

STEP 6: ION IMPLANTATION

INDUSTRIAL SET UP FOR ION IMPLANTATION

ION IMPLANTATION SETUP