Negative-tone imaging (NTI) with EUV exposure has major advantages with respect to line-width roughness (LWR) and resolution due in part to polymer swelling and favorable dissolution mechanics. In NTI process, both resist and organic solvents play important roles in determining lithography performances. The present study describes novel chemically amplified resist materials based on NTI technology with EUV using specific organic solvents. Lithographic performances of NTI process were described in this paper under exposures using ASML NXE:3300 EUV scanner at imec. It is emphasized that 14 nm hp was nicely resolved under exposure dose of 37 mJ/cm 2 without any bridge and collapse, which are attributed to the low swelling character of NTI process. Although 13 nm hp resolution was potentially obtained, a pattern collapse still restricts its resolution in case coating resist film thickness is 40 nm. Dark mask limitation due mainly to mask defectivity issue makes NTI with EUV favorable approach for printing block mask to produce logic circuit. A good resolution of CD-X 21 nm/CD-Y 32 nm was obtained for block mask pattern using NTI with usable process window and dose of 49 mJ/cm 2 . Minimum resolution now reaches CD-X 17 nm / CD-Y 23 nm for the block. A 21 nm block mask resolution was not affected by exposure dose and explored toward low dose down to 18 mJ/cm 2 by reducing quencher loading. In addition, there was a negligible amount of increase in LCDU for isolated dot pattern when decreasing exposure dose from 66 mJ/cm 2 to 24 mJ/cm 2 . On the other hand, there appeared tradeoff relationship between LCDU and dose for dense dot pattern, indicating photon-shot noise restriction, but strong dependency on patterning features. Design to improve acid generation efficiency was described based on acid generation mechanism in traditional chemically amplified materials which contains photoacid generator (PAG) and polymer. Conventional EUV absorber which comprises of organic compounds is expected to have 1.6 times higher EUV absorption than polyhydroxystyrene based on calculation. However, observed value of acid amount was comparable or significantly worse than polyhydroxystyrene.

It is generally believed that the chemically amplified reaction between photo-generated acid catalyst and acid labile group of polymer during post-exposure bake (PEB) process plays a critical role for the reduction of line width roughness (LWR) in ArF lithography. In this work, we revealed experimentally how large the chemically amplified reaction affects LWR, and developed a new resist system with low LWR. Aerial image contrast dependence on LWR revealed that the innate LWR in a conventional ArF photoresist, which is independent of the aerial image contrast, was 5 nm. Surface roughness of a non-patterned resist film at half-exposed area, which was well correlated with LWR, was measured by AFM. The surface roughness increased from 1.7 nm to 10.8 nm during PEB process. The half-exposed area was baked and again dissolved into organic solution, and spin-coated on Si wafer, and then developed with 2.38 % TMAH solution. The recoated half-exposed resist film caused a 60 % reduction on the surface roughness. It revealed that uniform distribution of deblocked polymer was important factor for roughness reduction. HPLC analysis indicated that distribution of acidic group formulation in the polymer was gradually extended with increasing exposure dose. A Resist system that suppresses the chemically amplified reaction successfully reduced LWR from 6.5 nm to 4.8 nm.

Effects of a dissolution promoter (DP) on the lithographic behavior of DNQ-novolac resists were investigated. The key structure/property relationships of the DP in relation to other parameters of the resist components were identified.In this work, we observed; (1) A significant improvement in resolution and photospeed when the DP was appropriately used. (2) Improvements in resist profile to increase its steepness. (3) Novolac dispersivity was the key for obtaining a beneficial effect from DP incorporation into the resist matrix.(4) Molecular size of the DP influenced resist resolution. (5)The PEB process effectively acts to improve dissolution discrimination.The dissolution rate analysis indicated that the DP incorporation, when optimized, accelerated dissolution of exposed resist film while decreasing the dissolution rate of unexposed film. This results in resolution improvement by increasing the dissolution contrast. DP also enhanced the surface induction in the resist film dissolution, which resulted in improvement of the profile steepness.We are proposing a "selective dissolution model" to account for the influence of the DP to the resist dissolution. This model assumes a critical dissolution rate differentiation between the DP and the other components ,i .e. , a microscopically uneven dissolution of the resist film components at the dissolution front, which leads to the above unique dissolution behavior. PAC or DP diffusion in the resist film were found to be critical in obtaining the discussed DP effect in a real resist film.

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