Allen Timko

Etching spin-on trilayer masks

Spin-on trilayer materials are increasingly being integrated in high density microfabrication that use high NA ArF lithography due to dwindling photoresist film thicknesses, lower integration cost and reduced complexity compared to analogous CVD stacks. To guide our development in spin-on trilayer materials we have established etch conditions on an ISM etcher for pattern transfer through trilayer hard masks. We report here a range of etch process variables and their impact on after-etch profiles and etch selectivity with AZ trilayer hard mask materials. Trilayer pattern transfer is demonstrated using 1st and 2nd minimum stacks with various pattern types. Etch recipes are then applied to blanket coated wafers to make comparisons between etch selectivities derived from patterned and blanket coated wafers.

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.

Spin-on trilayer approaches to high NA 193nm lithography

New challenges face ArF bottom antireflection coatings (BARCs) with the implementation of high NA lithography and the concurrent increase use of spin-on hard masks. To achieve superior reflectivity control with high NA at least two semi-transparent ARC layers, with distinct optical indices, are necessary to effectively lower substrate reflectivity through a full range of incident angles. To achieve successful pattern transfer, these layers in conjunction with the organic resist, should be stacked with an alternating elemental composition to amplify vertical resolution during etch. This will circumvent the inherent low etch resistance of ArF resist and the decreasing film thicknesses that accompanies increasing NA. Thus, incorporating hard mask properties and antireflection properties in the same two layer system facilitates pattern transfer as a whole rather than just enhancing lithography. As with any material expected to exhibit multiple roles there is a delicate balance between optimizing materials with respect to one of its roles while not impairing its other roles. We will discuss some of these conflicts and present Si-BARCs and carbon rich underlayers which aim to balance these conflicts. In this paper we will explore simulations aimed at finding the best film thicknesses and optical indices, etch rate selectivity, and lithographic performance of high silicon content and high carbon content BARC materials designed to meet the demands of both high NA lithography and trilayer processing.

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.

Spin-on trilayer scheme: enabling materials for extension of ArF immersion lithography to 32nm node and beyond

Trilayer stacks with alternating etch selectivity were developed and extensively investigated for high NA immersion lithography at 32nm node and beyond. This paper discusses the fundamental aspects of the Si-containing BARC (Si-BARC) materials with ultra-high silicon content and carbon-rich underlayers that we developed. Designing of materials at a molecular level is presented. It was demonstrated that this fundamental understanding assisted in achieving satisfactory shelf life and excellent coating defect results. Prolith® simulations using trilayer stacks showed superior reflectivity control for hyper-NA immersion lithography. The impact of high incident angles on substrate reflectivity was analyzed and this paper demonstrated that trilayer scheme provides wider process windows and is more tolerant to topography than conventional single layer BARC. Extensive resist compatibility investigation was conducted and the root causes for poor lithography results were investigated. Excellent 45nm dense lines performance employing the spin-on trilayer stack on a 1.2 NA immersion scanner is reported. In addition, pattern transfers were successfully carried out and the Si-BARC with high silicon content demonstrated outstanding masking property. In comparison to the theoretical %Si values, better correlation with etch selectivity was observed with experimental %Si. Furthermore, this paper addresses the wet rework of trilayer materials and results using Piranha rework are presented. Clean 12in wafers were obtained after reworking trilayer stacks, as evidenced by defect analysis.

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.

Performance of a dry 193nm resist under wet conditions

193 nm immersion lithography is rapidly moving towards industrial application, and an increasing number of tools are being installed worldwide, all of which will require immersion-capable photoresists to be available. At the same time, existing 193 nm processes are being ramped up using dry lithography. In this situation, it would be highly advantageous to have a single 193 nm resist that can be used under both dry and wet conditions, at least in the initial stages of 45nm node process development. It has been shown by a number of studies that the dominant (meth)acrylate platform of 193 nm dry lithography is in principle capable of being ported to immersion lithography, however, it has been an open question whether a single resist formulation can be optimized for dry and wet exposures simultaneously. For such a dry/wet crossover resist to be successful, it will need to make very few compromises in terms of performance. In particular, the resist should have similar LER/LWR, acceptable process window and controlled defects under wet and dry exposure conditions. Additionally, leaching should be at or below specifications, preferably without but at very least with the use of a top protective coat. In this paper, we will present the performance of resists under wet and dry conditions and report on the feasibility of such crossover resists. Available results so far indicate that it is possible to design such resists at least for L/S applications. Detailed data on lithographic performance under wet and dry conditions will be presented for a prototype dry/wet crossover L/S resist.