[Figure 2] There are two kinds of PR (Photo Resist). Using Positive PR, the parts not exposed to light remain after development. On the other hand, with Negative PR, only the parts exposed to light remain after development.
After the patterning step is a step of cutting the material, called “etching”. Etching (cutting) is carried out on the whole area at the same time. The PR remaining after development keeps the underlying material from being cut away, and allows the desired sketch to be produced.
That was a brief explanation of the basic role and principles of the photolithography process. It would appear that photolithography is a rather simple process that involves little more than shining light through a mask. So why is it that the advancement of photolithography technology is garnering such attention from the semiconductor industry?
2. Why the need for advancement in photolithography?
Scaling processes down – that is, producing semiconductors using even smaller transistors – involves overcoming many limitations. One of the hurdles involves photolithography. Then, what kinds of obstacles do we face in photolithography?
A. Light diffraction and interference hindering patterning
Diffraction is a property in which light spreads out when passing through a narrow slit, while interference is a property in which two light waves meet and reinforce or cancel each other out. These are currently the two biggest obstacles to the patterning process in photolithography.
As shown in Figure , light has a diffracting property, and cannot move in a straight line when passing through a narrow slit. Instead, it propagates as a fan-shaped wave radiating from the slit. The diffraction pattern tends to be broader if the slit is narrow or or wavelength is long.