BACKGROUND

Field

The present disclosure generally relates to methods and apparatuses for processing a substrate, and more specifically to methods and apparatuses for enhancing photoresist profile control.

Description of the Related Art

Integrated circuits have evolved into complex devices that can include millions of components (e.g., transistors, capacitors, and resistors) on a single chip. Photolithography may be used to form components on a chip. Generally the process of photolithography involves a few basic stages. Initially, a photoresist layer is formed on a substrate. The photoresist layer may be formed by, for example, spin-coating. The photoresist layer may include a resist resin and a photoacid generator. The photoacid generator, upon exposure to electromagnetic radiation in a subsequent exposure stage, alters the solubility of the photoresist in the development process. Excess solvent may be removed in a pre-exposure bake process.

In the exposure stage, a photomask or reticle may be used to selectively expose certain regions of a photoresist layer disposed on the substrate to electromagnetic radiation. Other exposure methods may be maskless exposure methods. The electromagnetic radiation may have any suitable wavelength, such as a wavelength in the extreme ultra violet region. The electromagnetic radiation may be from any suitable source, such as, for example, a 193 nm ArF laser, an electron beam, an ion beam, or other source. Exposure to the electromagnetic radiation may decompose the photoacid generator, which generates acid and results in a latent acid image in the resist resin. After exposure, the substrate may be heated in a post-exposure bake process. During the post-exposure bake process, the acid generated by the photoacid generator reacts with the resist resin in the photoresist layer, changing the solubility of the resist of the photoresist layer during the subsequent development process.

After the post-exposure bake, the substrate, and, particularly, the photoresist layer may be developed and rinsed. After development and rinsing, a patterned photoresist layer is then formed on the substrate, as shown inFIG. 1.FIG. 1depicts an exemplary orthogonal sectional view of the substrate100having a patterned photoresist layer104disposed on a target material102to be etched. Openings106are defined between the patterned photoresist layer104, after the development and rinse processes, exposing the underlying target material102for etching to transfer features onto the target material102. However, inaccurate control or low resolution of the lithography exposure process may not retain critical dimensions of the photoresist layer104, resulting in an unacceptable line width roughness108. Furthermore, during the exposure process, acid (as shown inFIG. 1) generated from the photoacid generator may randomly diffuse to any region, including the regions protected under the mask unintended to be diffused, thus creating undesired wiggling or roughness profile150at the edge or interface of the patterned photoresist layer104interfaced with the openings106. Large line width roughness108and undesired wiggling profile150of the photoresist layer104may result in inaccurate feature transfer to the target material102, thus, eventually leading to device failure and yield loss.

Therefore, there is a need for a method and an apparatus to control line width roughness and enhance resolution as well as dose sensitivity so as to obtain a patterned photoresist layer with desired critical dimensions.

SUMMARY

Embodiments of the present disclosure include methods for efficient control of distribution and diffusion of acid from a photoacid generator in a photoresist layer during a post-exposure baking process so as to improve the lithography process window, such as the range for depth of focus. The methods can enhance and enlarge the depth of focus process window during a lithography process.

In one embodiment, a method of processing a substrate includes applying a photoresist layer comprising a photoacid generator on a material layer disposed on a substrate, exposing a first portion of the photoresist layer unprotected by a photomask to light radiation in a lithographic exposure process, providing a thermal energy to the photoresist layer in a post-exposure baking process, applying an electric field or a magnetic field while performing the post-exposure baking process, and dynamically changing a frequency of the electric field as generated while providing the thermal energy to the photoresist layer.

In another embodiment, a method of processing a substrate includes applying a photoresist layer on a substrate, exposing a first portion of the photoresist layer unprotected by a photomask to light radiation in a lithographic exposure process, performing a post-exposure baking process on the photoresist layer, and changing a drifting direction of a photoacid generator vertically in the photoresist layer while providing the thermal energy to the photoresist layer.

In yet another embodiment, a device structure includes a material layer disposed on a substrate, and a plurality of openings formed in the material layer, wherein the openings formed across the substrate have a corner angle between about 85 degrees and 95 degrees.

