On a chip the size of a fingernail, there are billions of transistors densely packed, and the circuit lines connecting them are only a few nanometers wideThis is about one ten thousandth of the diameter of a hair strand. Such a precise structure is achieved not through manual carving or mechanical polishing, but through a magical material called photoresist. As a core material with technological barriers in semiconductor manufacturing, photoresist can be regarded as the "bridge" between chip design and manufacturing. Its resolution directly determines the precision and accuracy of the pattern, which in turn affects the performance and production yield of the chip. Today, let's step into the world of photoresist and uncover its mysterious veil in chip manufacturing.

What exactly is photoresist?

Photoresist, also known as photoresist, is a mixed liquid material that is sensitive to light. It can undergo chemical reactions through illumination, thereby achieving the transfer of graphics from the mask to the substrate (such as a silicon wafer). You can imagine it as a special kind of“Electronic adhesive”But it's not used to stick things, it's used to“drawing”of

In the process of chip manufacturing, photoresist is uniformly coated on the surface of the silicon wafer. It is then irradiated with light sources such as ultraviolet and electron beams to cause chemical changes in the exposed area. After development treatment, it can be deposited on the silicon wafer“painting”Produce extremely intricate circuit patterns，It is a core material in semiconductor manufacturing.

Composition and classification of photoresist

Photoresist is not a simple adhesive, but a precise chemical mixture typically composed of four parts:

According to the changes in solubility after photochemical reactions, we can simply divide photoresists into two categories: positive photoresists and negative photoresists.

Positive photoresist:The exposed area undergoes photochemical reactions, making it easier to dissolve in the developing solution. After development, the exposed area is dissolved, leaving the pattern of the non exposed area.

Negative photoresist:The exposed area undergoes cross-linking reaction, making it difficult to dissolve in the developing solution. After development, the non exposed area is dissolved, leaving the pattern of the exposed area.

How does photoresist work?

The working process of photoresist can be roughly divided into the following steps:

Coating: Spin coat the photoresist evenly on the surface of the silicon wafer to form a thin film with uniform thickness.

Pre drying: By heating, the solvent in the adhesive film is removed to make it denser.

Exposure: Using specific wavelengths of light (such as ultraviolet light, deep ultraviolet light, extreme ultraviolet light, etc.) to irradiate the photoresist through a mask. The photoresist in the illuminated area will undergo a chemical reaction.

Development: Using a developer solution to process silicon wafers, depending on the type of photoresist, the irradiated area (positive photoresist) or non irradiated area (negative photoresist) will be dissolved and removed, thereby transferring the pattern on the mask onto the photoresist.

Hard film: Further heating treatment to enhance the adhesion and corrosion resistance of the remaining photoresist.

Etching or implantation: Using patterned photoresist as a protective layer, etching or ion implantation is performed on the underlying material, ultimately transferring the pattern to the functional material layer.

Remove photoresist: After completing the graphic transfer, remove the remaining photoresist.

This series of steps may seem simple, but each step requires high precision and cleanliness. A small chip often goes through dozens or even hundreds of photolithography cycles.

How to evaluate photoresistGood or bad?

The performance of photoresist plays a decisive role in the accuracy, yield, and reliability of chips. The industry usually focuses on multiple core parameters, which can be summarized into three core dimensions:Check accuracy, firmness, and toleranceThis is also a reflection of the core competitiveness of photoresist technology.

1. 看精度

Resolution: It determines the minimum line width that photoresist can achieve and is the core indicator of accuracy.

Exposure characteristics (light source)/exposure/DOF）Affects the imaging quality of the pattern and determines the suitable process nodes. The larger the lithography window, the better the performance stability.

Depth to width ratio: reflects the ability of graphic structure and affects the implementation of high-precision structures.

2. Look firm

Adhesion: determines the photoresist on the wafer (inorganic layer)/The adhesion stability on the metal layer, whether too high or too low, can affect the quality of the graphics.

3. See tolerance

Chemical resistance/etch resistance/Temperature resistance: determines the photoresist in dry process/Stability during wet etching, injection, electroplating, chemical plating, high temperature and other processes.