Thomas I. Wallow

Dissolution/swelling behavior of cycloolefin polymers in aqueous base

Polycycloolefins prepared by addition polymerization of norbornene derivatives are quite different from hydroxystyrene-based polymers in terms of their interaction with aqueous base. Their dissolution kinetics monitored on a quartz crystal microbalance is not a smooth function of the ratio of the polar to nonpolar functionalities in polymer but abruptly changes from very fast dissolution to massive swelling within a narrow range of composition. The maximum swelling is a function of thickness and the entire film thickness can swell in a few seconds at > 3,000 angstroms/sec or at immeasurably fast rates. The initial concentration of a pendant carboxylic acid in polymer has to be selected to minimize swelling and the concentration of an acid-labile group to induce fast dissolution in the exposed area. Furthermore, swelling which occurs in the partially- exposed regions must be minimized by incorporating a third monomer unit or by adding a dissolution modifying agent (DMA) such as t-butyl cholate. However, the function of DMA which is also acid-labile is quite complex; depending on the matrix polymer composition and its dissolution/swelling behavior, DMA could function as a swelling suppressor or promoter and a carboxylic acid generated by acidolysis of DMA as a dissolution or swelling promoter. Photochemically generated sulfonic acid could also affect the dissolution/swelling behavior. Base hydrolysis of anhydride during development is controlled by the polarity (carboxylic acid concentration) in polymer film, which has been demonstrated in an unequivocal fashion by IR spectroscopy under the condition strongly mimicking the development process and thus could boost development contrast but could hurt performance as well. Thus, incorporation of carboxylic acid in the form of methacrylic acid, for example, in radical copolymerization of norbornene with maleic anhydride must be handled carefully as it would increase the susceptibility of the anhydride hydrolysis and could introduce heterogeneity in the polymer as methacrylic acid is rapidly consumed, producing a terpolymer containing a different molar concentration of norbornene and maleic anhydride (a proof against the commonly believed charge transfer polymerization mechanism).

193-nm single-layer resist materials: total consideration of design, physical properties, and lithographic performances on all major alicyclic platform chemistries

The objective of this report will be to clarify the maturity of the current 193 SLR materials. We are going to report on all major platform chemistries, i.e.,(meth) acrylate system, ROMP system, cyclic olefin addition system, cyclic olefin/maleic anhydride system, vinyl ether/maleic anhydride system, and cyclyzed system at the same time. We are going to discuss maturity of each platform from several viewpoints such as polymerization process, physical properties of the resins, lithographic performances of the resists, and process latitude of the resists including etch performances. We are also referring to several critical issues such as etch resistance, surface roughness after etch, line slimming, etc. Three major platform chemistries, (meth)acrylate, COMA, and addition, are selected in order to cover the whole spectra of layer requirements. Those three systems respectively show characteristics lithographic performances.

Design and development of high-performance 193-nm positive resist based on functionalized poly(cyclicolefins)

One of the major factors that seem to limit the development of practically useful 193nm resist materials has been their low reactive-ion-etch (RIE) resistance. In this paper, we have shown convincingly that the RIE stability of poly(cyclicolefins) is superior to that of the alternating copolymers such as poly(norbornene-anhydride), and poly(acrylates). We have also shown that a high performance 193nm resist can be developed from functionalized poly(norbornenes) using appropriate formulation and process optimizations.

Design of an etch-resistant cyclic olefin photoresist

In the quest for a high performance 193 nm photoresist with robust plasma etching resistance equivalent to or better than the DUV resists of today, we have focused on the use of cyclic olefin polymers. In this paper, we will discuss monomer synthesis, polymerization approaches, polymer properties and early lithographic results of 193 nm photoresists formulated from cyclic olefin polymeric materials made from a metal-catalyzed addition polymerization process. The goal of this work is to produce a 193 nm photoresist with excellent imaging performance and etch resistance exceeding DUV resists, and in fact approaching novolak-based photoresists.

Characterization of the polymer-developer interface in 193-nm photoresist polymers and formulations during dissolution

Investigations of the dissolution behavior of the IBM V2 193 nm methacrylate photoresist polymer and its formulations using the recently developed impedance quartz-crystal microbalance methodology unequivocally confirm the presence of an interfacial gel layer during dissolution. All aspects of V2 dissolution behavior are strong functions of resist formulation, developer concentration, and resist film thermal history. The dissolution process is characterized by (a) a complex gel layer evolution regime; (b) a steady-state dissolution regime; and (c) a final gel layer decay regime upon depletion of solid resist film. The gel layer evolution regime exhibits a linear increase in mass and development of a lossy film component (interfacial gel) associated with developer uptake. The transition from this regime to the steady-state dissolution regime is accompanied by reproducible correlated excursions in frequency shift and film resistance measurements. The steady-state dissolution regime exhibits a linear decrease in mass and fairly constant gel-layer; upon depletion of the solid resist film, the gel layer decays. Absolute and relative metrics for phenomena occurring in these regimes can be extracted from the dissolution data and are useful for analyzing the influences of formulation components on dissolution and gelation behaviors. Formulation components explored include a photoacid generator, bis(t-butylphenyliodonium) perfluorobutanesulfonate, and common dissolution modifiers, t-butyl lithocholate and lithocholic acid. Film thermal history impacts dissolution phenomena strongly and appears to reflect both polymer annealing and residual solvent evaporation effects.

Approaches to etch-resistant 193-nm photoresists: performance and prospects

We have investigated three substantially different routes to 193nm single layer resists. This paper will attempt to shed light on the strengths and weaknesses of each approach. Design principles, polymer synthesis and properties, and resist properties will be discussed for the three main branches of 193nm resists.

Progress toward developing high-performance 193-nm single-layer positive resist based on functionalized poly(norbornenes)

In this paper, we have shown the progress we have made in improving reactive-ion-etch stability and lithographic performance of IBM 193 nm resist materials. Using selectively functionalized cyclicolefins, we have developed 193 nm resists with etch stability and post-etch surface roughness comparable to those of the matured, state-of-the-art DUV resists. Furthermore, we have also demonstrated dramatically improvement in dense line (100 nm 1:1 L/S) and semi-dense line (< 100 nm 1:2, 1:3 L/S) resolution using resolution enhancement techniques such as alternate phase shift mask.

Lithographic characteristics of 193-nm resists imaged at 193 and 248 nm

During the past few years an intensive effort has been made to develop 193 nm photoresists for the next generation of DUV lithography tools. The early portion of this effort was focused on the development of photoresist polymers that are transparent at 193 nm. Since the polyacrylic materials developed for 193 nm lithography were not highly reactive ion etch (RIE) resistant, recent 193 nm resist polymer efforts have focused on both optical transparency and RIE etch resistance. Most of these polymers developed for 139 nm lithography are highly transparent at 248 nm. This dual transparency produces the option of developing a resist that is backward compatible, i.e. imagable at both 193 nm and 248 nm. This paper will investigate the lithographic characteristics of resists initially developed for use at 193 nm, but imaged at both 193 nm and 248 nm. Various resist families will be compared, and aspects such as absorbance effects and PROLITHH/2TM simulations will be taken into consideration.

193-nm negative resist based on acid-catalyzed elimination of polar molecules

Development of 193-nm negative resists that meet the stringent performance requirements of sub-100 nm resolution with conventional 0.26 N TMAH developer has proven to be a significant challenge. Most of the systems that are currently under development are based on cross-linking mechanisms. They commonly suffer from image distortion caused by micro-bridging. An alternative approach is to look at polarity switch mechanisms. We have investigated the acid-catalyzed elimination of polar molecules as one such mechanism which may provide a pathway to develop negative resists that do not suffer from micro-bridging.

Molecular weight tailoring in methacrylate 193-nm photoresists

Understanding and control of molecular weight-dependent properties of 193 nm photoresist polymers has received only limited attention to date. Many physical and thermal properties of polymers in general and novolak- and poly(hydroxystyrene)-based systems in particular are molecular weight dependent. Since these properties markedly influence photoresist behavior, a more detailed understanding of molecular weight effects in 193 nm polymers would be valuable. In this communication, we present a survey of some of the interplays between molecular weight, thermal properties, dissolution behavior, and lithographic performance of methacrylate-based 193 nm polymers. More specifically, this presentation comprises a discussion of discontinuities in thermal properties surrounding the polymer critical entanglement molecular weight in methacrylate 193 nm polymers including the IBM Version 2 and Version 3 platforms. Tg vs. molecular weight curves for both platforms are in good agreement with predictions of the Gibbs-DiMarzio model and reveal that Mcrit is ca. 8,000 for these systems. Lithographic characterization at, below, and above this molecular weight reveals failure due to fraying and line collapse at low molecular weight, failure due to excessive bottom scumming at high molecular weight, and best performance at or near Mcrit.