2.1 PLANAR PROCESS

The silicon planar process of fabrication includes the following steps:

1. Silicon Wafer (Substrate) Preparation

2. Epitaxial Growth

3. Oxidation

4. Photolithography

5. Diffusion

6. Ion Implantation

7. Isolation

8. Metallization

9. Packaging

The individual steps are explained in brief.

1. Silicon Wafer Preparation. The basic material required for making the substrate, i.e. silicon, is cut into thin sheets, or wafers. This step includes the substeps like crystal growth, doping, slicing into wafers, and polishing and cleaning the wafer.

   
   Figure 2.1: Silicon wafer preparation.

2. Epitaxial Growth. 'Epi' in Greek means 'upon' and 'teinon' in Greek means 'arranged.'

   A small layer of silicon is grown over the substrate.

   
   Figure 2.2: Epitaxial growth.

   Note	The thickness and other dimensions of the IC will be in mils.

   where

   
   

3. Oxidation. Here an oxide layer is grown over the epitaxial layer. The SiO ₂ layer formed by oxidation prevents diffusion of almost all impurities.

   After oxidations the structure has 3 layers, i.e. the substrate, the epitaxial layer, and the oxide layer.

   
   Figure 2.3: Oxidation.

4. Photolithography. The purpose of this step is to remove portions of the SiO ₂ layer so diffusion can occur in selected areas.

   The structure before applying the photolithography process is shown in Figure 2.4.

   
   Figure 2.4: Input structure for photolithography.

   The photolithography process involves many steps which are described in detail below.

   The first step is to make a photoresist layer above the oxide layer.

   
   Figure 2.5: Structure with photoresist layer.

   The second step is to make masks, the locations of...