Douglas S. McKenzie

CD changes of 193-nm resists during SEM measurement

CD linewidth change during SEM inspection has been one of the issues encountered in the introduction of 193 nm resists. As a general tendency, the methacrylate resists exhibit faster line width reduction than the cycloolefin- maleic anhydride (COMA) systems; however, other resist components as well as CD SEM settings paly an important role. Based on the exposure time vs. CD loss, the line width slimming (LSW) is found to proceed in three steps, which are assigned as: 1) chemical change of outer resist layer, 2) evaporation of volatiles and 3) bulk chain scission or deprotection. Countermeasures for CD degradation are proposed form both the formulation and process sides. A calculation of e-beam penetration depth suggests that deprotection, chain scission and other reactions occur in the first 20-40nm, and these reaction rates combined with thermal effects determine LWS. The CD SEM measurement method has been improved to minimize e-beam exposure and to spread out the thermal load over a larger period of time. An optimized formulation exhibits less than 0.2% LWS per measurement with the improved CD measurement program.

E-beam curing effects on the etch and CD-SEM stability of 193-nm resists

Electron beam (e-beam) curing techniques are known to improve etch and CD-SEM stability of 248 and 193nm resists. The effects of three different e-beam curing processes (standard, LT and ESC) on the methacrylate and hybrid type 193nm resists were studied with respect to resin chemistry changes, resist film shrinkage, pattern profiles, etch rates, and CD SEM stability. Both methacrylate and hybrid type 193nm resists lose carbonyl groups from the resins, with possibly a reduction in the free volume leading to improved etch resistance/selectivity. Methacrylate resist films shrink ca. 22-24% and hybrid resist films shrink ca. 23-27%. The LT process shrinks the least compared to the ESC and standard process. The ESC and LT processes were found to stabilize the patterns uniformly compared to the standard process. Etch rate, selectivity and resist surface roughness after etch of both methacrylate and hybrid resists were improved using the e-beam curing process. E-beam curing drastically reduces the CD SEM shrinkage (from ca. 15% to 2- 5%); however, considerable shrinkage occurs during the curing process itself.

Performance of imide and methide onium PAGs in 193-nm resist formulations

The performance of a new class of photoacid generators (PAGs) made from the onium salts of bis(perfluoroalkylsulfonyl)imide and tris(perfluoroalkylsulfonyl)methide anions were studied in 193nm formulations. The lithographic properties such as sensitivity, resolution, pattern profiles, footing, I-D bias and PEB sensitivity were investigated in methacrylate and COMA/methacrylate hybrid type matrix resins. In general the iodonium PAGs were about three times slower than the sulfonium PAGs. Methide and imide PAGs possessing similar fluoroalkylgroups showed comparable performance in terms of exposure latitude, I-D bias. And PEB sensitivity. Compared to the reference PAG, the profiles exhibited T-tops and sum. Among the new PAGs studied bis(perfluorobutanesulfonyl)imide exhibited close performance to that of the reference PAG except for the scum. Details on the exposure results of these PAGs in both methacrylate type and COMA/methacrylate hybrid type polymer based 193nm resist formulations are provided.

Low-polydispersity novolak resins for i-line resists

Low polydispersity novolak resins were prepared in a sequential process where low molecular weight (Mw) oligomers were first synthesized in a preliminary stp followed by a second condensation with preformed bis-hydroxymethyl derivatives of phenolic starting materials. Resins prepared in this way were found to have polydispersities comparable to that of fractionated resins made in the standard resin synthetic process. The sequential process afforded higher yields of usable resins since no low Mw fractions were isolated and discarded. In several instances, unique bis- hydroxymethyl phenol monomers or monomer/dimmer mixtures were prepared for use in making the low dispersity resins. These compounds were further condensed with the products of the initially prepared low Mw resins in a second acid catalyzed condensation.

PEB sensitivity studies of ArF resist

In an effort to develop a production-worthy 193-resist, it is important to understand the critical factors that impacts the CD variation during a routine photo lithographic process. A comprehensive investigation was done on factors affecting PEB sensitivity in ArF resist system. The areas of interest are polymer components, PAGs, bases, and photo lithographic process. In order to understand effects of the PAGs on PEB sensitivity, a number of PAGs possessing different types of cations and anions were investigated. Sulfonium type cations and acids with longer alkyl chains were found to be effective in reducing the PEB sensitivity. Influence of lithography process conditions was also studied on the PEB sensitivity. Increasing the soft bake (SB) temperature and decreasing the post exposure bake (PEB) temperature reduced the PEB sensitivity but mostly at the expense of line-edge roughness (LER). This paper presents our findings of the critical factors affecting PEB sensitivity and describes improved lithographic results of an optimized experimental formulation. In addition, delay effects after coating, soft bake, exposure, and post exposure bake (PEB) were also investigated and these results are included.

Novel hybrid copolymers of cycloolefin/maleic anhydride (COMA)/methacrylate for 193-nm resist compositions

A novel process for the preparation of hybrid copolymers based on cycloolefin-maleic anhydride and methacrylate (COMA/Methacrylate) monomers has been developed. A variety of copolymers have been synthesized form t-butylnorbonene carboxylate (BNC), hydroxyethylnorbornene carboxylate (HNC), and norbornene carboxylic acid (NC) with different types of methacrylate monomers such as 2-methyl-2-adamantyl- methacrylate(MAdMA), mevalonic lactone methacrylate(MLMA) and maleic anhydride (MA). The effect of the different types of monomers and the ratios of monomers in the copolymer on lithographic performance has been studied. Lithographic evaluation of some of these polymers has shown resolution down to 80nm for semi and fully isolated lines using conventional 193nm illumination and standard development conditions. This paper will report the chemistry of the hybrid polymer platforms and the progress of our effort to develop 193 resist for semi-dense and isolated line applications.

PEB sensitivity studies of ArF resists: II. Polymer and solvent effects

Keeping post exposure bake (PEB) sensitivity low has become one of the most crucial factors for implementing the 193nm resist process into mass production. In a previous report, we have demonstrated that the nature of the photo acid generator (PAG) has a strong effect on the PEB sensitivity of 193 resists. Based on our findings, we decided to extend our studies to the other important resist components, such as polymers prepared with various monomer compositions, and casting solvents. Also, in an effort to investigate whether PEB sensitivity can be reduced by process optimization, the influence of soft bake and post exposure bake conditions was studied. This paper describes our new findings on some of the important factors that affect the PEB sensitivity of 193 resists.

Illumination, acid diffusion, and process optimization considerations for 193-nm contact hole resists

We have studied 193 nm contact hole resists in view of resist components, process conditions and optical settings. Sidewall roughness was improved by optimizing photoacid generators. Side lobes were eliminated by applying higher post exposure bake temperature or modification of polymers. The influence of optical settings, types of masks and mask bias was discussed with simulation and lithographic results and guidelines for better resolution and iso-dense bias were proposed. The optimized formulation, AZAX1050P has a high resolution combined with a large depth of focus and an iso- dense overlap window (130 nm(NA=0.63) DOF 0.38micrometers Exposure latitude 10%).

High-performance 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 (BTCDC), and 5-[2-trifluoromethyl-2,1,1-trifluoro-2-hydroxypropyl]-2- norbornene (F1) with different types of methacrylate monomers and maleic anhydride (MA). The effect of the monomers and the ratio of monomers in the copolymer on lithographic performance and etch rate has been studied. Lithographic evaluation of some of these polymers has shown resolution down to 80 nm using conventional 193 nm illumination and standard development conditions, particularly for semi and fully isolated lines. This paper will report the chemistry of the polymer platform and relative advantages of having certain monomers in terms of lithographic performance and line edge roughness.

Continuous metal removal technique for resist resins

Modern resists require very pure raw materials to insure highest quality images. Many methods have been developed to reduce metals in resins used to make photoresists. Extractive washing techniques and ion exchange methods have been the predominant methods used to reduce metal levels for these critical raw materials. This has been especially important for the novolak resins because of the generally poor quality of the starting materials used to make them and by the nature of the resin isolation steps traditionally used. Both of the commonly used cleaning methods are time consuming and are predominantly batch processes. Based upon techniques developed to efficiently fractionate resins, we have developed a technique for the rapid, continuous reduction of metal contaminants in film forming resin solutions by an extractive method using a double inlet liquid/liquid centrifuge.