E-beam Resists

The term e-beam (electron beam) resist refers to a type of photoresist used in e-beam and deep ultraviolet applications. They can fabricate masks for highly integrated circuits, be involved in electron beam direct writing, and be used for multi-layer processing processes. E-beam resists work by changing the solubility of the resist in the developer, leaving the desired pattern on the resist surface. Currently, e-beam lithography using e-beam resists offers a promising alternative to UV lithography.

• E-beam lithography process flow

E-beam lithography is the process of directly drawing or projecting patterns onto a wafer coated with a photoresist with an E-beam. It has high resolution, a short production cycle, and easy pattern generation and modification. E-beam lithography is the most cost-effective option for manufacturing high-resolution graphics since it can achieve critical dimensions quickly and easily. The typical process flow in e-beam lithography is as follows: pre-baking, coating, soft-baking, exposure, post-baking, developing, and hardening. Fig. 1 illustrates a simple process flow in which e-beam resist plays an important role.

Fig. 1 A simple process flow in e-beam lithography (EBL) ^[1].

Classification of E-beam Resists

E-beam resist is a photoresist that sensitive to electrons, and the chemical properties of the exposed part change after scanning by e-beam because the resist undergoes molecular chain recombination. Therefore, the properties of e-beam resists are mainly affected by materials. According to the materials, e-beam resists can be classified as polymethylmethacrylate (PMMA) resists, dendritic resists, and molecular glass resists ^[2]. The first two are polymer-based resists.

• PMMA resist

E-beam lithography requires a photoresist with high sensitivity, high contrast, and anti-dry etching selectivity. The earliest developed e-beam resist applied PMMA as a resin system. The PMMA resist exhibits excellent resolution, strong adhesion, a mature and simple process with high stability, and low cost. Under e-beam irradiation, PMMA's main chain is broken to form low-molecular-weight polymers. However, PMMA has poor etching resistance and low sensitivity, so chemical amplification technology is generally used to compensate for PMMA shortages. Alternatively, adding electron-withdrawing groups to PMMA to prepare e-beam resists based on PMMA derivatives is also a suitable method.

Fig.2 Chemical structure of PMMA ^[1].

• Dendritic resist

In addition to PMMA, dendritic polymer is also a good choice for a polymer-based resist. A dendritic resist uses dendritic polymers, which are based on triphenyl skeletons connected by chemical bonds to other phenyl groups. This type of e-beam resist is generally a chemically amplified photoresist that is composed of dendritic polymers and PAGs, and can achieve a minimum line resolution of 100 nm. Fig. 3 shows two typical dendritic resists ^[3].

Fig.3 Typical dendritic resists for e-beam lithography ^[3].

• Molecular glass resist

Molecular glass resist is an amorphous small molecule compound that can form a uniform and dense amorphous film. It is one of the promising candidates for advanced lithography due to its advantages such as explicit molecular structure, low molecular weight, monodispersity, high thermal stability, high glass transition temperature, and amorphous state ^[4]. The e-beam resist based on the molecular glass system is better than polymer materials with too large molecular weights, wide molecular weight distributions, and chain entanglement for high resolution and low line edge roughness.

Alfa Chemistry has been researching photoresists for years and is committed to expanding their applications. We offer a wide range of positive and negative E-beam resists for E-beam lithography. Please click on the links at the top of the page for more details about our products. If you have any questions, please do not hesitate to contact us.

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