LithoTalk

[Guest]

Hi,

I was wondering, what is the scientific reason for the negative edge profile (negative angle) for negative resists and positive edge angles for positive resists, respectively? I could not find a good answer in literature, just general remarks, that it has to do with the absorption.

Thanks,
Claudia

[admin]

Hi,

the reason is quite simple: The penetration depth of the incident light is typically only few µm, so the upper resist part gets a higher exposure dose than the substrate-near resist. Thus ...

1) In case of a positive resist, the upper resist part reveals a higher development rate, and

2) In case of a negative resist, the upper resist part has a higher degree of cross-linking, therefore a lower erosion rate in the developer.

Additionally, light scattering in the resist is more pronounced in the upper part of the resist due to the higher light intensity, and scattering also laterally exposes the resist where it should remain dark.

In case of positive resists, there is another reason for a positive profile: The dark erosion cannot be lowered below approx. 20-30 nm/min, and is often higher, so the upper part of the resist which is longer exposed to the developer shows a stronger erosion.

Maybe this makes is clear? If not, please let me know!

[Guest]

Hi,

thanks a lot for your explanation, this sounds logical to me.
Thanks!