INTRODUCTION

Purpose: makes structures by transferring a pattern from a mask to a film

How:

• using light sensitive photoresist and controlled exposure to light through a mask
• in photolithography, light modifies the solubility of the photoresist in the exposed areas
• the photoresist will protect the film against further etching only in the unexposed areas

Lithography determines:

• feature resolution
• overlay accuracy between two patterns on top of each other

In fabricating smaller structures, the lithography has the main role. Lithography is the step that limits the dimension of the features in the film. In the next pages it will be discussed how smaller paterns (even smaller than the light wavelength) can be obtained.

Below is a picture of a mask aligner. It can be observed the dark chuck where the wafer is placed during exposure. The white chuck on the right side is the chuck that transports the wafer to the exposure site. On the left part of the picture the mask support is shown (rectangle with a circular hole). After the mask is placed in the support, they are placed on the metalic frame closed to the wafer chuck. A microscope is used to align the pattern on the mask to the pattern on the wafer. The picture captured can be observed on the right screen. The lamp used for exposure is situated on top of the microscope (the microscope is retracted during exposure).