Clement Anyadiegwu

New spin-on metal hardmask materials for lithography processes

Since the critical dimensions in integrated circuit (IC) device fabrication continue to shrink below 32 nm, multilayer stacks with alternating etch selectivities are required for successful pattern transfer from the exposed photoresist to the substrate. Inorganic resist underlayer materials are used as hard masks in reactive ion etching (RIE) with oxidative gases. The conventional silicon hardmask has demonstrated good reflectivity control and reasonable etch selectivity. However, some issues such as the rework of trilayer stacks and cleaning of oxide residue by wet chemistry are challenging problems for manufacturability. The present work reveals novel spin-on underlayer materials containing significant amounts of metal oxides in the film after baking at normal processing conditions. Such an inorganic metal hardmask (MHM) has excellent etch selectivity in plasma etch processes of the trilayer stack. The composition has good long term shelf life and pot life stability based on solution LPC analysis and wafer defect studies, respectively. The material absorbs DUV wavelengths and can be used as a spin-on inorganic or hybrid antireflective coating to control substrate reflectivity under DUV exposure of photoresist. Some of these metal-containing materials can be used as an underlayer in EUV lithography to significantly enhance photospeed. Specific metal hard masks are also developed for via or trench filling applications in IRT processes. The materials have shown good coating and lithography performance with a film thicknesses as low as 10 nm under ArF dry or immersion conditions. In addition, the metal oxide films or residues can be partially or completely removed by using various wet-etching solutions at ambient temperature.

Reworkable Spin-on Trilayer Materials: Optimization of Rework Process and Solutions for Manufacturability

Trilayer stacks with alternating etch selectivity were developed and extensively investigated for high NA immersion lithography at 32nm node and beyond. The conveyance of pattern transfer function from photoresist to Si-containing bottom anti-reflective coating (Si-BARC) and carbonrich underlayer hard-mask (UL) elegantly solved the small etch budget issue for ultra-thin photoresists in immersion lithography. However, due to the hybrid nature of Si-BARC, many different behaviors were observed in comparison to conventional BARC. Lithographic performance, stability, and reworkability were among the most challenging issues for trilayer scheme. Despite of the rapid improvement in lithographic performance and stability of trilayer materials reported by several papers, the rework and cleaning of trilayer materials by wet chemistry remained a challenging problem for manufacturability. The dual function requirement of reflection control and pattern transfer (i.e. hard-masking) for spin-on Si-BARC mandates hybrid materials. Si-BARC containing both organic moiety and inorganic backbone were extensively studied and demonstrated excellent performance. However, the hybrid nature of Si-BARC necessitates the revisit of different wet chemistries and process adjustment is essential to achieve desirable results. In addition, the similarity in chemical structures between Si-BARC and low-κ dielectrics demands subtle rework differentiation by wet chemistry from a chemistry point of view. In our development, we strived to identify rework solutions for trilayer materials in both front-end-of-line (FEOL) and back-end-of-line (BEOL) applications. Rework solutions including diluted HF, Piranha, and low-κ compatible strippers were extensively investigated. The optimization of solution mixture ratios and processing conditions was systematically studied. Thorough defect inspection after rework was performed to ensure the readiness for manufacturability. Extensive Piranha rework study on stack wafers and monitor wafers were carried out and excellent results are reported.

Development of spin-on-carbon hard mask for advanced node

Spin-on-carbon (SOC) hard mask is useful for multilayer lithography process because of its high etch resistance, low cost of ownership, low defectivity, high alignment accuracy, good gap filling and planarization for topography. SOC is a high carbon containing polymer solution and as a coating material, the polymers need to be soluble in organic solvent and insoluble after curing for coating upper layer materials. High carbon content (>80%) of SOC is very important for good etch resistance. As the semiconductor industry is moving to 2X nm node and beyond, further improvement of SOC properties mentioned above is required to achieve higher resolution. We synthesized a series of novel monomers and high carbon polymers applicable for SOC applications of advanced nodes. The optimized SOC was a PGMEA based formulation, had high carbon content 90%, excellent filling/leveling properties, and adequate etching properties applicable to trilayer process. The SOC successfully transferred patterns from resist into substrate and the SOC patterns did not show deformation or wiggling down to CD 40nm. This paper describes some of the SOC polymer chemistry and the performance of an optimized SOC formulation.

Some non-resist component contributions to LER and LWR in 193-nm lithography

Improvement of line edge roughness (LER) and line width roughness (LWR) is required for integration of semiconductor devices. This paper describes various process factors affecting LER/LWR of 193 nm resists such as mask layout (bright field/dark field), pitches, optical settings, substrates, film thickness, baking temperature and development condition. The origins of line roughness are discussed in view of aerial image contrast, transmittance of resists and pattern profiles. Bright field mask exhibited lower LER/LWR values than dark field mask, LER/LWR deteriorated as larger pitches and illumination condition affected roughness and these results are explained using normalized image log-slope (NILS). BARC dependence of line roughness is explained by pattern profile difference due to interactions between resist and BARC and in some cases BARC reflectivity. Contributions of film thickness, SB & PEB temperature and development condition to line roughness are also reported.

Study of the Effect of Amine Additives on LWR and LER

We will give an account of our investigation on structure property relationships of amines with regards to line width roughness (LWR) and line edge roughness (LER) of a 193 nm alicyclic-acrylate resist. Specifically, we have looked at basicity, molar volume and logD as factors which may have an influence of roughness of 80 nm 1:1 L/S features. For relatively hydrophobic amines (Log D > -1), the lower the hydrophilicity at acidic pH the greater the LER and LWR becomes. Specifically, in this range of Log D, more hydrophobic larger amines, with higher basicity, tend to give worse L/S feature roughness. For amines which are more hydrophilic, the relationship becomes more complex with some amines giving a lower LER while others do not. This appears to be predicated on a delicate balance between basicity, hydrophilicy and size.

Novel diamantane polymer platform for enhanced etch resistance

The dominant current 193 nm photoresist platform is based on adamantane derivatives. This paper reports on the use of derivatives of diamantane, the next higher homolog of adamantane, in the diamondoid series, as monomers in photoresists. Due to their low Ohnishi number and incremental structural parameter (ISP), such molecules are expected to enhance dry etch stability when incorporated into polymers for resist applications. Starting from the diamantane parent, cleavable and non-cleavable acrylate/methacrylate derivatives of diamantane were obtained using similar chemical steps as for adamantane derivatization. This paper reports on the lithographic and etch performance obtained with a number of diamantane-containing monomers, such as 9-hydroxy-4-diamantyl methacrylate (HDiMA), 2-ethyl-2- diamantyl methacrylate (EDiMA), and 2-methyl-2-diamantyl methacrylate (MDiMA). The etch advantage, dry and wet lithographic performance of some of the polymers obtained from these diamantane-containing polymers are discussed.

Versatility in lithographic performance of advanced 193 nm contact hole resist

This paper introduces high performing contact hole resist targeting 65 nm node and below IC applications. Both 80 nm and 100 nm contact hole performance are evaluated under optimized condition by ProlithTM simulations and the advantage of the shrinking technique (RELACSTM) is discussed for 65 nm node. The functionality of 193 nm polymers and the influence of resist components on lithographic performance are described with experimental design. The optimized resist, AZ® AX2050P is versatile in lithographic performance with large process window, excellent resist profile, good contact circularity and sidewall roughness. Its unusual PEB sensitivity property, resist pattern thermal flow behavior and performance with RELACSTM material are also reported. AZ® AXTM2050P has a high resolution combined with a large depth of focus and an iso-dense overlap window with RELACSTM R602 [85 nm CD (NA 0.85) DOF 0.30 μm @ Exposure latitude 8%].

193-nm resist composition using hybrid copolymers of cycloolefin/maleic anhydride (COMA)/methacrylate

A high performance 193 nm resist has been developed from a novel hybrid copolymer based on a cycloolefin-maleic anhydride and methacrylate (COMA/Methacrylate) polymer system. A variety of copolymers have been synthesized from t-butyl norbornene carboxylate (BNC), t-butyl tetracyclo[4.4.0.1. 2,617,10] dodec-8-ene-3-carboxylate (TCDBC), t-butoxycarbonylmethyl tetracyclo[4.4.0.1.2,617,10]dodec-8-ene-3-carboxylate (BTCDC), and 5-[2-trifluoromethyl-1,1,1-trifluoro-2-hydroxypropyl]-2-norbornene (F1) and maleic anhydride (MA). The effect of the monomers and the ratio of monomers in the copolymer on lithographic performance studied. This paper will report the chemistry of the polymer platform and relative advantages and disadvantages of having certain monomers in terms of lithographic performance and line edge roughness, and post exposure bake sensitivity.