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Increasing Resolution by Using Ultra-Short Irradiative Heating for the Post Exposure Bake of Photo Resists

IP.com Disclosure Number: IPCOM000124194D
Publication Date: 2005-Apr-11
Document File: 3 page(s) / 102K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that uses ultra-short anneals instead of conventional bake plate heating to control the diffusion length of the photo resist. Benefits include improving resolution and decreases line edge roughness.

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Increasing Resolution by Using Ultra-Short Irradiative Heating for the Post Exposure Bake of Photo Resists

Disclosed is a method that uses ultra-short anneals instead of conventional bake plate heating to control the diffusion length of the photo resist. Benefits include improving resolution and decreases line edge roughness.

Background

Semiconductor devices are formed by creating acid images in photo resist materials
(i.e. photolithography). These photo-generated acids diffuse during the post exposure bake (PEB) step. This results in the blurring of the latent acid-images. This PEB step is needed, however, to drive the catalytic chemistry within the photo resist. The PEB is currently done using bake plates which take a long time to reach the required temperature (~ 140oC) and also a long time to cool (i.e. several seconds at the minimum). In addition, this approach requires a long time to allow thermal energy to distribute in the system. The standard PEB time is approximately 90 seconds. During this time, the resulting acid diffusion significantly blurs the latent image, thereby limiting the resolving power of the lithographic process and affecting the resulting pattern profiles. 

Photo resist pattern profiles tend to be more conical (in the case of holes) or sloped (in the case of lines) when the acid diffusion length is long; this is due to an increased concentration at the top of the resist from the absorption of radiation (as a function of depth) and the diffusion of acid toward the air-to-photo resist interface. 

In addition, since acid diffusion is a random process, this may randomize the catalytic chemistry in the photo resist along the edge of the imaged feature. This results in line edge roughness and further degradation of the image quality.

Acid diffusion in photo resists is currently controlled and compensated for by increasing the size of the acid, adding bases to the photo resist, and controlling the architecture of the photo resist matrix polymer. The blur induced by the diffusion is compensated for by improving the resolution or the lithographic process by scaling either the wavelength (λ) or the numerical aperture (NA) of the lithography system, or both.  However, these approaches require resist formulation engineering and/or the purchase of new equipment.

General Description

The disclosed method uses a typical laser/flash anneal tool, as shown in Figure 1. The tool uses a CO2 laser t...