George M. Jordhamo

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).

IBM 193-nm bilayer resist: materials, lithographic performance, and optimization

193nm lithography will be the future technology for sub- 150nm resolution. As the dimensions get smaller, resist thickness is also needed to be reduced for better resolution and wider process window. Single layer 193nm resist, with thickness of less than 500nm, may not be able to satisfy some of the substrate etch requirement. With bilayer resist scheme, the thin resist offers the advantages of high resolution and good process window. The thick underlayer provides the etch resistance required for substrate etching. IBM has developed a silane substituted alternating copolymer based 193nm bilayer resist system and demonstrates sub-120nm resolution using Nikon 0.6NA stepper with Chrome on Glass (COG) mask. Lithographic performance and formulation optimizations of this 193nm bilayer resist as well as underlayer evaluation and some etch study will be discussed.

Deep-UV hardening of deep-UV resists

Deep UV (200 - 300 nm) or electron beam hardening has been used extensively to enhance the thermal flow resistance of i-line based diazoquinone-novolak resists. Since novolaks have Tg below 125 degrees Celsius, the images require stabilization for processing at elevated temperatures. The images of hardened resists are able to withstand elevated temperatures of greater than 150 degrees Celsius such as encountered in ion implantation or reactive ion etching. The next generation of positive resists are based on polyhydroxystyrene (PHS) either as a homopolymer with acid labile additives or as copolymer with acid labile groups. Since the Tg of PHS is above 130 degrees Celsius, the resists based on homopolymer have inherent stability to temperatures in the 150 - 200 degrees Celsius range. However, many formulations use copolymers with groups which lower the Tg to 100 - 150 degrees Celsius and thus the processing of unhardened images at elevated temperatures may cause distortion. We have investigated the photo/thermochemical stabilization of PHS by deep UV (200 - 300 nm radiation). Irradiation of films or in solution of PHS causes photoexcitation of the phenol portion of PHS inducing quinone formation and crosslinking. The reaction is aided by the presence of oxygen and heating. Exposure at elevated temperatures of 125 degrees Celsius reduces the dose to gel by 40% while exposure in air reduces the dose requirement by 50%. In the deep UV (240 - 260 nm) region the darkening reaction is due to quinone formation. ESCA studies of photolyzed PHS confirm the incorporation of oxygen into the backbone and into the aromatic ring of PHS. The presence of photoacid from PAG enhances the photocrosslinking of PHS up to 40%. Photostabilized images are able to withstand temperatures in excess of 200 degrees Celsius.

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.

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.

Selection of attenuated phase shift mask compatible contact hole resists for KrF optical lithography

Multiple contact hole resist samples from a variety of DUV resist suppliers, including both acetal and ESCAP chemistries are evaluated on an organic anti-reflective under layer (ARC) using an attenuated phase shift mask (APSM). One sample exhibited excellent surface inhibition and superior lithographic performance for patterning contact holes of 0.2 micrometers imaging size. For most of resists, the process windows are limited by unwanted sidelobe printing through focus. The sensitivity of sidelobe printing to focus can be attributed to lens aberrations. For the first time, we prose to use Depth-of-focus (DOF) loss PWLdof and Exposure latitude (EL) loss PWLel to characterize resists surface inhibition, as well discovered that DOF loss is a sensitive measure of surface inhibition. Similar lithographic performance is obtained from acetal and ESCAP based materials. The two ESCAP resists EB3 and EA2 have better oxide etch resistance than the acetal resist AC1. The top surface reticulation is observed on ESCAP resist EB3 and EA2 during the oxide etch, but not on the acetal resist AC1. 110 nm underexposed resolutions achieved with the resist EA4 at a mask size of 250 nm. Faster resists generally exhibit better resolution but have smaller process windows when side lobe printing is included as a criterion. Selection of a resist formulation for attenuated phase shift applications has to face a compromise between resolution, photospeed, process window and surface inhibition. Finally, ARC operational modes and optical properties had little effect on sidelobe printing, and optimization of PEB temperature is important in suppressing sidelobe printing.

Postmodification as a way to improve the lithographic performance of resist materials

Monomer components and composition of a resist polymer have large influence on its lithographic performance. Finding the right components and composition for a resist polymer involves laborious systematic synthesis of different polymers. On the other hand, post-modification offers a convenient way to incorporate desired functional groups into an existing polymer and hence improve its lithographic performance and mechanical properties. Using this method, different groups could be quickly tested and the results could direct the future design of new resist materials. Another advantage of this method is that functional groups which are sensitive to the polymerization condition could also be incorporated. In this paper, we demonstrated the feasibility of using the post-modification method. Through a simple esterification reaction in which the acid groups react with alkyl halides in the presence of 1,8- diazobicyclo[5.4.0]undec-7-ene(DBU) or trialkylamine, three different functional groups were incorporated into the existing Ibm Version 2 (V2) methacrylate polymer. The post- modification reaction gave high yield and it is possible to control the percentage of the acid groups modified by the initial feeding ratio fo the alkyl halide and the carboxylic acid. Depending on the structures of the added groups, the post-modified resist materials demonstrated improved lithographic performances such as better compatibility towards 0.26 N developer and better etch-resistance than the precursor materials. The synthesis, characterization and lithographic performance of the modified polymers are presented.

ArF resist for contact hole application

In building the cyclic olefin addition polymer as a potential platform for 193nm contact hole application, we have encountered an unusual bottlenecking or lipping profile. We have investigated the causes and possible cures of this lipping profile in contact hole printing. The lipping was found to be tool dependent, mask dependent as well as duty cycle dependent. Several treatments were evaluated in terms of their ability to reduce or eliminate the lipping profile. These included various flood exposures, pre wet during development, the use of additives in the resist formulation and various surfactants added to TMAH developer. Among them, the most effective way to eliminate the lip profile was found to be modification of the developer by the addition of surfactants. A proper surfactant was selected to provide better wetting for the resist which resulted in the elimination of the lip profile. In addition, resist formulation changes were also beneficial in reducing the lipping profile. This study will present the results of designed experiments which investigated several different treatments and the resultant impact on profile quality.

Dissolution behavior of novolak resins

Novolak and polyhydroxystyrene (PHS) constitute the film forming polymers of positive resists. Laser interferometry was used to study the dissolution and film morphology of spun cast films. PHS forms uniform films with polymer chains preferentially orientated. Novolak resins exhibit disruption of ordering throughout the depth of the film. Thicker (greater than 1 micrometer) films of novolak are more disordered. Casting solvents can also alter film morphology. Micron thick films of novolak resins, except for monodisperse fractions, show disruption of order, especially in layers at the vicinity of the substrate. Thicker novolak films exhibit more disorder due to solvent/surface tension gradients. PHS films of higher Tg are not sensitive to coating disruptions. The addition of surfactants eliminates global radial phase separation of diazoquinone and novolak and restores uniform orientation in plane of dissolution by neutralizing surface tension driven gradients.