Jeanette M. Roberts

Novel anionic photoacid generators (PAGs) and corresponding PAG bound polymers for sub-50 nm EUV lithography

A new series of anionic photoacid generators (PAGs) and corresponding polymers were prepared. The thermostability of PAG bound polymers was superior to that of PAG blend polymers. PAG incorporated into the polymer main chain showed improved resolution when compared with the PAG blend polymers. This was demonstrated by extreme ultraviolet lithography (EUVL) results: the fluorine PAG bound polymer resist gave 45 nm (1 : 1), 35 nm (1 : 2), 30 nm (1 : 3) and 20 nm (1 : 4) Line/Space as well as the 50 nm (1 : 1) elbow pattern.

Novel polymeric anionic photoacid generators (PAGs) and corresponding polymers for 193 nm lithography

A series of new anionic PAGs, as well as PAG-bound polymers designed for use in 193 nm photoresist materials, have been synthesized and characterized. These novel materials provide optical transparency at 193 nm and also good etch resistance. PAG incorporated resists and PAG blended resists were exposed at a wavelength of 193 nm using an ASML 5500/950B optical lithography system with 0.63 NA. Exposed wafers were evaluated using SEM. The fluorine substituted PAG bound polymer and PAG blend resist provided a 110 nm (220 nm pitch) line/space at 11.5, 13.0 mJ cm−2, and 80 nm isolated features at 3 and 1 mJ cm−2, respectively. The LER (3σ) results showed that the fluorinated PAG bound polymer has LER values of 6.7 and 6.8 nm for isolated 80 nm and dense 110 nm lines, respectively, while the fluorinated PAG blend resist has LER values of 8.6 and 8.9 nm. The improvement may be due to the direct bonding of PAG into the polymer main-chain, which provides a more uniform distribution, thereby controlling acid diffusion and allowing a higher loading of PAG than the blend sample. The fluorine-free PAG bound or blend resists showed lower photospeed compared to photoresists based on fluorine-substituted PAGs.

Characterization and modeling of line width roughness (LWR)

Control of Line Width Roughness (LWR) is one of the biggest challenges of next generation lithographies. However, control necessitates accurate definition and characterization schemes. In this paper, a new definition of LWR is proposed with the benefit of being independent on the resist line length used in the measurement. The definition corresponds to the sigma value of LWR for infinite resist-line-length, but it can be measured using any finite line length. It is based on an appropriate combination of LWR and CD metrology. As the line length (gate width) decreases the LWR is being partitioned between the sigma of LWR for finite lengths and the CD variation. This partitioning is controlled by the correlation length and the roughness exponent. A protocol for LWR characterization is described using these three parameters. Furthermore, LWR modeling using methods for generating lines similar to the experimental ones is investigated. The aim is to control LWR deliberately for better input to device simulators and solving characterization problems. An algorithm based on the convolution method is shown to reproduce reliably the roughness characteristics of real lines. This algorithm needs as input a triplet of parameters similar to those defined above for LWR characterization.

One small step: world's first integrated EUVL process line

The Intel lithography roadmap calls for Extreme Ultraviolet Lithography (EUVL) to be used for the 32 nm node. With the installation of the EUV Micro-Exposure Tool (MET) complete, Intel now has the worlds first integrated EUVL process line including the first commercial EUV exposure tool. This process line will be used to develop the EUV technology, including mask and resist, and to investigate issues such as defect printability. It also provides a test-bed to discover and resolve problems associated with using this novel technology in a fab (not lab) environment. Over 22,000 fields have been exposed, the discharge-produced plasma light source has operated for 50,000,000 pulses, 8 masks have been fabricated, and 8 resists have been characterized. The MET combines high resolution capability with Intels advanced processing facilities to prepare EUVL for high-volume manufacturing (HVM). In this paper we review the MET installation and facilities, novel capabilities of the linked track, data on optics quality and modeled tool capability, and the MET mask fabrication process. We present data on tool performance including printing 45 nm 1/2 pitch lines with 160 nm depth of focus and 27 nm isolated lines. We show tool accuracy and repeatability data, and discuss issues uncovered during installation and use.

Novel anionic photoacid generator (PAGs) and photoresist for sub-50-nm patterning by EUVL and EBL

A new series of anionic photoacid generators (PAGs), and corresponding polymers were prepared. The thermostability of PAG bound polymers was superior to PAG blend polymers. PAG incorporated into the polymer main chain showed improved resolution when compared with the PAG blend polymers. This was demonstrated by Extreme Ultraviolet lithography (EUVL) results: the fluorine PAG bound polymer resist gave 45 nm (1:1), 35 nm (1:2), 30 nm (1:3) and 20 nm (1:4) Line/Space as well as the 50 nm (1:1),30 nm (1:2) elbow patterns.

Synthesis and Properties of New Anionic Photoacid Generators Bound Polymer Resists for e-beam and EUV lithography

A new series of methacrylate substituted benzene sulfonic photoacid generators (PAGs) and a perfluoro alkanesulfonic PAG, bound polymeric resists based on hydroxystyrene (HS) and 2-ethyl-2-adamantyl methacrylate (EA) were prepared and characterized. The acid yield of these PAG bound polymer resists was among the range of 54-81% under deep ultraviolet exposure (254 nm) that agrees well with the electron withdrawing effect of the substituents on the PAG anion for enhancing acid generation efficiency. The intrinsic lithography performance of these polymer-bound PAG resists showed sub-50 nm half-pitch resolution and < 5 nm LER (3σ).

Polymer matrix effects on acid generation

We have measured the acid generation efficiency with EUV exposure of a PAG in different polymer matrixes representing the main classes of resist polymers as well as some previously described fluoropolymers for lithographic applications. The polymer matrix was found to have a significant effect on the acid generation efficiency of the PAG studied. A linear relationship exists between the absorbance of the resist and the acid generation efficiency. A second inverse relationship exists between Dill C and aromatic content of the resist polymer. It was shown that polymer sensitization is important for acid generation with EUV exposure and the Dill C parameter can be increased by up to five times with highly absorbing non-aromatic polymers, such as non-aromatic fluoropolymers, over an ESCAP polymer. The increase in the Dill C value will lead to an up to five fold increase in resist sensitivity. It is our expectation that these insights into the nature of polymer matrix effects on acid generation could lead to increased sensitivity for EUV resists.

Contributions to innate material roughness in resist

A method has been developed to probe the Innate Material Roughness (IMR) of resist materials. We have applied this to EUV and 248 nm resists to deconvolute the material contributions to roughness: 1) the polymer alone, 2) interaction between the polymer, photoacid generator (PAG), base quencher, and photolysis byproducts, 3) the effects of exposure, and 4) development. We studied ESCAP based resists (with more limited data on APEX polymers), an iodonium nonaflate PAG, a tetabutyl ammonium hydroxide (TBAH) base quencher, and standard tetramethylammonium hydroxide (TMAH) development.

Incorporation of ionic photoacid generator (PAG) and base quencher into the resist polymer main chain for sub-50 nm resolution patterning

Previous research has shown that polymer-bound PAG resists exhibit improved lithographic performance in both 193 nm and extreme ultraviolet lithography (EUVL) applications as compared to their more traditional blended PAG analogs. The further incorporation of base directly into the resist polymer backbone is a potential route for improving the resist performance and processing window. In this work, a new series of chemically amplified resists (CARs) that incorporate both PAG and base quencher functional groups into the polymer main chain are reported. The lithographic performance of these materials was investigated using electron-beam lithography (EBL). The polymer-bound PAG cation resist showed higher photospeed than the polymer-bound PAG anion resists. Base quencher incorporation slightly decreased the photospeed but improved the resolution in the case of resists with the polymer-bound PAG cation and pyridine base. Base quencher incorporation showed no improvement on the lithographic performance of polymer-bound PAG anion resists.

Molecular glass photoresists containing photoacid generator functionality: a route to a single-molecule photoresist

A single molecule photoresist composed of tris(4-(tert-butoxycarbonyloxy)-3,5-dimethylphenyl) sulfonium hexafluoroantimonate (TAS-tBoc) was successfully synthesized and characterized. The synthesized triarylsulfonium was found to perform comparably to a commercial triphenylsulfonium triflate photoacid generator (PAG) when used purely as a PAG in blended molecular glass resist. TAS-tBoc formed excellent amorphous films when spin-coated out of solution. When exposed to 248 nm UV radiation, TAS-tBoc showed a sensitivity of 4 mJ/cm2 and a contrast ratio between 6 and 15, depending on development conditions. Its etch rate under standard silicon dioxide etch conditions was 0.87 as standardized to that of tBoc-PHOST in the same RIE plasma conditions. The outgassing level of the resist under EUV exposure was determined to be 1.08 x 1013 molecules/cm2, well below the maximum outgassing cutoff that is considered acceptable for EUV imaging. When imaged by e-beam, TAS-tBoc showed a relatively high dose-to-clear of 150 &mgr;C/cm2 as compared to conventional chemically amplified photoresists. Lines down to 50 nm wide with aspect ratios of 2.5:1 were imaged using e-beam. These lines exhibited an LER of only 3.96 nm, significantly better than the typical LER for polymeric chemically amplified resist, even when imaged using e-beam, and also one of the lowest values reported for molecular glass materials in general.