Question

Lithography often has to be done over underlying topography on a silicon chip. This can result in variations in the resist thickness as the underlying topography goes up and down. This can sometimes cause some parts of the photoresist image to be underexposed and/or other regions to be overexposed. Explain in terms of the chemistry of the resist exposure process why these underexposure and overexposure problems occur.

Answer 1

Underlying topography on a silicon chip can cause variations in resist thickness, resulting in underexposure or overexposure of certain parts of the photoresist image during lithography.

Step-by-step explanation:

Lithography involves exposing a resist material to light to create a pattern on a silicon chip. However, when there is underlying topography on the chip, there can be variations in the resist thickness due to the uneven surface. This can lead to underexposure or overexposure of certain areas of the resist image.

Underexposure occurs when the resist thickness is too thin, and the light does not interact with the resist molecules enough to create a strong reaction. As a result, the exposed area appears less developed. On the other hand, overexposure happens when the resist thickness is too thick, causing excessive interaction with the light and resulting in overdevelopment of the exposed area.

Ultimately, the variations in resist thickness caused by the underlying topography can affect the chemical reactions during resist exposure, leading to underexposure and overexposure in specific regions of the photoresist image.