Robert Lang

Graded spin-on organic bottom antireflective coating for high NA lithography

Immersion lithography for the 32nm node and beyond requires advanced methods to control 193 nm radiation reflected at the resist/BARC interface, due to the high incident angles that are verified under high numerical aperture (NA) imaging conditions. Swing curve effects are exacerbated in the high NA regime, especially when highly reflective substrates are used, and lead to critical dimension (CD) control problems. BARC reflectivity control is also particularly critical when underlying surface topography is present in buried layers due to potential reflective notching problems. In this work, a graded spin-on organic BARC was developed to enable appropriate reflectivity control under those conditions. The graded BARC consists of two optically distinct polymers that are completely miscible in the casting solution. Upon film coating and post-apply baking, the two polymers vertically phase-separate to form an optically graded layer. Different characterization techniques have been applied to the study of the distribution of graded BARC components to reveal the internal and surface composition of the optically graded film, which includes Variable Angle Spectroscopic Ellipsometry (VASE) and Secondary Ion Mass Spectroscopy (SIMS). Also, optical constant optimization, substrate compatibility, patterning defectivity and etch feasibility for graded BARC layers are described. Superior 193 nm lithographic performance and reflectivity control of graded BARC beyond 1.20 NA compared to conventional BARCs is also demonstrated.

Current developments of a high-performance CA resist for mask-making application

The mask fabrication industry is slowly migrating to chemically amplified (CA) resists to take the advantages of their high contrast, resolution, and sensitivity. During this migration process, the industry has encountered several problems associated with CA resists such as baking homogeneity of thick mask plates on hot plates, footing on Cr masks, and storage stability of mask blanks. In addressing these issues, we have adopted a low Ea CA resist platform to overcome the bake latitude issue. The resist formulation has been reformulated to reduce the footing and a new package method has been introduced to extend the storage of the blanks. In addition, we will also discuss our studies on two major areas, such as sensitivity and etch resistance, which we think is extremely important for E-beam resists in the future. The mask industry started with 248nm DUV CA resist systems and then found out that there was a need for even higher sensitivity resist systems to address the throughput issue. In our early study, we have observed that by simply increasing photoacid generator loading in the resist formulation we were able to increase the sensitivity, but there was a significant reduction in the dose latitude. After studying the dissolution and inhibition properties of different PAGs, we have been able to optimize PAG and base loading in combination with proper choice of PAGs to achieve high sensitivity and large dose latitude. The new resist formulation exhibits a large dose latitude of 38% for 100 nm l/s images with high sensitivity of 4.4μC/cm2 at 100 kV. Due to the electron scattering effect and the image collapse issues with thicker resists, thinner imaging layer is desirable. Sufficient etch selectivity is needed to compensate the insufficient resist thickness. Therefore, there is a need to develop a high Cl2/O2 RIE (used in Cr etch process) etch resistant resist system for mask making. We have reported earlier that a resist formulation based on blending KRS-XE with SSQ polymer has resolved 50nm l/s resist images with etch rate 20% better than conventional novolak I-line resist systems. Since then, we have investigated a few new SSQ polymers and found some lithographic improvement in this new blending systems due to better compatibility of the SSQ polymer to the KRS-XE.

Highly etch-selective spin-on bottom antireflective coating for use in 193-nm lithography and beyond

Extending 193nm lithography to well below 100nm resolution will depend on high NA tooling coupled with thin resist processing. Semiconductor manufacturing uses BARCs (Bottom Antireflective Coating) based on organic spin coatable polymers, to improve the resolution by absorbing light that otherwise will be reflected back into the resist. However, the use of organic BARCs for patterning sub 100nm features will be limited due to poor etch selectivity to the photo resist. IBM has developed a new class of polymers that can function as planarizing BARCs. These materials show an etch selectivity to the photo resist in excess of 3:1 in fluorocarbon based ARC-open RIE chemistry. The hardmask properties of these materials for oxide open are equivalent to typical resists. Furthermore these materials can be implemented like organic ARCs and are stripped in resist strips available in manufacturing. Basic materials characterization data, optical tunability, lithographic performance with different resists, process window data, and complete integration schemes will be presented.

A New High Performance CA Resist for E-beam Lithography

Three major lithographic applications have emerged for electron beam exposure tools: optical mask fabrication, direct writing for device fabrication, and more recently projection e-beam printing. The traditional mask making process uses poly(butenesulfone) resist. A wet etch process was adopted to generate patterns on chrome. Recently, shrinking dimensions, optical proximity correction features, and the complexity of phase shift masks have forced the industry to a chrome dry etch process. ZEP, a poly(methyl α-chloroacrylate-co-α-methylstyrene) based resist, has been well accepted for most of the >180 nm device mask making. The acceptance of ZEP comes in spite of its low contrast, marginal etch resistance, organic solvent development, and concerns of resist heating associated with its high dose requirements. These issues have spawned interest in using chemically amplified resist (CAR) systems for direct write and mask making applications. We have developed a high contrast resist based on ketal protecting groups, KRS-XE, which is robust against airborne contamination and can be used for all forms of e-beam exposure in both chrome mask and silicon processing. This high contrast resist is processed with aqueous base developer and has a wide bake latitude. The development of KRS-XE has provided the capability of fabricating chrome masks for future generation (

Extending the performance of KRS-XE for high-throughput electron-beam lithography for advanced mask making

The performance of KRS-XE, a low activation energy, chemically amplified resist designed specifically for mask making with electron beam lithography, has been extended in terms of its sensitivity, coated-film stability and etch resistance. By careful manipulation of resist composition, high sensitivity formulations have been generated that will allow exposure doses of less than 10 mC/cm2 with 50 keV electron beam tools. This sensitivity enhancement has been achieved without sacrificing the robust process latitude previously reported for this resist. The performance of this resist can be maintained, even in coated film form, for prolonged periods of time by careful packaging of the coated films. Additionally, formulations with etch resistance versus chlorine/oxygen plasma in excess of that of novolak-based resists have been generated by the incorporation of organometallic additives. The combination of these improvements leads to resist formulations that will allow the high resolution and throughput that is demanded for state-of-the art mask making applications.

High-performance e-beam resist coupling excellent dry etch resistance and sub-100-nm resolution for advanced mask making

Recently, there is a significant interest in using CA resists for electron beam (E-beam) mask making application. CA resists provide superior lithographic performance in comparison to traditional non CA E-beam resists in particular high contrast, resolution, and sensitivity. However, most current CA resists exhibit very large sensitivity to PAB and/or PEB temperatures resulting in significant impact on CD. In addition, image collapse issues associated with high aspect ratio patterning as well as electron scattering effects in low KeV tools necessitate thinner resists. Therefore, there is a need to have a high etch resistant resist system which can withstand the demanding chrome etch process. Previously, we reported on the KRS-XE resist which exhibits dry etch resistance comparable to the best deep UV resist and excellent lithographic performance and bake latitudes. No PEB is needed for this resist. In this paper, we report on an advanced KRS-XE resist formulation which exhibits dry etch resistance surpassing the industry standard, novolak, in the chrome etch process. This new resist also exhibits excellent lithographic performance - 50nm lines/space delineated and requires no PEB. This paper will highlight the lithographic and etch performance of this new resist.

Applicaton of blends and side chain Si-O copolymers as high-etch-resistant sub-100-nm e-beam resists

Recently, there is significant interest in using chemically amplified (CA) resists for electron beam (E-Beam) applications including mask making, direct write, and projection printing. CA resists provide superior lithographic performance in comparison to traditional non CA E-beam resists in particular high contrast, resolution, and sensitivity. Due to the electron scattering effect and the image collapse problem, thinner imaging layer is desirable. Sufficient etch selectivity is needed to compensate reduced resist thickness. Therefore, there is a need to have a high etch resistant resist system which can survive Cr etch (Cl2/O2RIE etchant) process in mask making. For device making, the thin film bilayer approach needs a resist that can withstand O2 etch for image transfer to the underlayer. We have found Si-O containing polymer has the etch characteristics for both applications. In the first approach, using a blend of KRS-XE and silsesquioxane polymer, we have been able to resolve resist images down to 50nm with etch rate 20% slower than conventional novolak I- line resist systems. In the second approach, we have investigated the copolymer of vinyl phenol and acrylate siloxy silane systems. Superior litho performance and etch properties have been observed. In this presentation, we will discuss the chemistry, the miscibility in blends, etch characteristics and lithographic performance of these resist systems.

Enhancement of KRS-XE for 50 keV Advanced Mask Making Applications

KRS-XE, a high performance chemically amplified photoresist designed specifically for e-beam mask making applications, has been enhanced to achieve reduced “footing” on chrome oxide surfaces while still maintaining the original lithographic characteristics that make KRS-XE a promising mask making candidate. These attributes include high resolution, superior bake latitudes, high vacuum stability, coated shelf life of greater than 2 months, and, most notably, the absence of a post exposure bake. In conjunction with the footing reduction the requisite sensitivity requirement of <10uC/cm2 with 50 keV exposure tools has been achieved while retaining the robust process latitude previously reported for this resist. Through a careful study of the photoresist formulation components a route to the ultra-high sensitivity of <2.5uC/cm2 at 50 keV has been elucidated which will further enhance throughput, decrease heating effects, and potentially be a suitable resist for e-beam projection lithography (EPL).