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INTRODUCTION TO SEMICONDUCTOR TECHNOLOGY

1 THE FABRICATION OF A SEMICONDUCTOR DEVICE

The manufacturing phase of an integrated circuit can be divided into two steps. The first,

wafer fabrication, is the extremely sophisticated and intricate process of manufacturing the

silicon chip. The second, assembly, is the highly precise and automated process of pack-

aging the die. Those two phases are commonly known as “Front-End” and “Back-End”. They

include two test steps: wafer probing and final test.

Figure 1. Manufacturing Flow Chart of an Integrated Circuit

1.1 WAFER FABRICATION (FRONT-END)

Identical integrated circuits, called die, are made on each wafer in a multi-step process. Each

step adds a new layer to the wafer or modifies the existing one. These layers form the ele-

ments of the individual electronic circuits.

The main steps for the fabrication of a die are summarized in the following table. Some of

them are repeated several times at different stages of the process. The order given here

doesn't reflect the real order of fabrication process.

PhotoMasking

This step shapes the different components. The principle is quite simple (see draw-

ing on next page). Resin is put down on the wafer which is then exposed to light

through a specific mask. The lighten part of the resin softens and is rinsed off with

solvents (developing step).

Etching

This operation removes a thin film material. There are two different methods: wet

(using a liquid or soluble compound) or dry (using a gaseous compound like oxygen

or chlorine).

Diffusion

This step is used to introduce dopants inside the material or to grow a thin oxide

layer onto the wafer. Wafers are inserted into a high temperature furnace (up to

1200 ° C) and doping gazes penetrate the silicon or react with it to grow a silicon

oxide layer.

Ionic

Implantation

It allows to introduce a dopant at a given depth into the material using a high energy

electron beam.

Metal

Deposition

It allows the realization of electrical connections between the different cells of the

integrated circuit and the outside. Two different methods are used to deposit the

metal: evaporation or sputtering.

"Front-End"

"Back-End"

WAFER

FABRICATION

ASSEMBLY

Wafer

Final

Test

Probing

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