Timothy G. Adams

Hologram: liquid-crystal composites

We describe the formation and selected properties of composites made from DMP-128 transmission holograms and the nematic liquid crystal E7. Analysis of the liquid crystal structure in the composites by polarizing microscopy, refractive index measurements, and differential scanning calorimetry produced two primary observations. (1) Treatment of the interior surface of the porous holograms controls the nature of the liquid crystal alignment; both planar and homeotropic alignment is possible for the E7 composites. (2) Incorporation of E7 into DMP composites significantly reduces its degree of order compared to that for a standard nematic cell.

Organic antireflective coatings for 193-nm lithography

Organic anti-reflective coatings (ARCs) continue to play an important role in semiconductor manufacturing. These materials provide a convenient means of greatly reducing the resist photospeed swing and reflective notching. In this paper, we describe a novel class of ARC materials optimized for lithographic applications using 193 nm exposure tools. These ARCs are based upon polymers containing hydroxyl-alkyl methacrylate monomers for crosslinkable sites, styrene for a chromophore at 193 nm, and additional alkyl-methacrylate monomers as property modifiers. A glycouril crosslinker and a thermally-activated acidic catalyst provide a route to forming an impervious crosslinked film activate data high bake temperatures. ARC compositions can be adjusted to optimize the films real and imaginary refractive indices. Selection of optimal target indices for 193 nm lithographic processing through simulations is described. Potential chromophores for 193 nm were explored using ZNDO modeling. We show how these theoretical studies were combined with material selection criteria to yield a versatile organic anti-reflectant film, Shipley 193 G0 ARC. Lithographic process data indicates the materials is capable of supporting high resolution patterning, with the line features displaying a sharp resist/ARC interface with low line edge roughness. The resist Eo swing is successfully reduced from 43 percent to 6 percent.

Planarizing AR for DUV lithography

A systematic approach was taken in order to improve the planarity of a DUV anti reflectant (AR) utilized for various lithographic steps, particularly those involving a patterned transparent layer. These layers can occur in both front and back end processing. Two approaches were pursued to accomplish this. The first approach was to minimize the molecular weight of the AR polymer. Polymers with weight average molecular weights from 45,000 daltons to as low as 2,300 daltons were evaluated. The planarity of the AR improved significantly for polymers with Mws below 20,000 daltons. The second approach was to add plasticizers in order to reduce the glass transition temperature of the precrosslinked film. The addition of plasticizers to the AR was effective in increasing the planarity. One of the plasticizers contained a DUV chromophore used to maintain the required optical density of the AR. It was proven possible to make these changes while maintaining lithographic performance in both resist profiles and reflection control.

Complex triarylsulfonium salts as photoacid generators for deep-UV microlithography: synthesis, identification, and lithographic characterization of key individual components

Triarylsulfonium salts are among the most commonly used photoinitiators in the fields of radiation sensitive coatings and microlithography. In this paper, assorted sulfonium salts are evaluated as photoacid generators for DUV microlithography. The preparation of assorted triarylsulfonium salts from commercially available triarylsulfonium chloride is described. Analysis of this class of photoacid generators revealed that it comprises a mixture of triarylsulfonium cations. These materials are essentially complex mixtures derived from the various sulfonium cationic species which are present in the starting triarylsulfonium chloride. In order to better understand the unique properties of these photoacid generators, we focused on identifying the major triarylsulfonium cations present in the mixture. This paper describes the synthesis, identification and lithographic characterization of each of the components of this class of photoacid generators. The identity of each component was verified spectroscopically (1H and 13C NMR, IR and UV) and the compounds were also characterized by thermogravimetric analysis. The acid generating efficiency of each component was determined using tetrabromophenol blue as a spectrophotometric indicator dye. Lastly, full lithographic characterization of each component was performed and the results compared and contrasted with the triarylsulfonium mixtures.

Improved lithographic performance for resists based on polymers having a vinyl ether-maleic anhydride (VEMA) backbone

ArF lithography, in combination with chemically amplified resists, has been investigated as one of the most promising technologies for producing patterns below 100 nm. In considering the polymer matrix for 193 nm photoresist applications, factors such as sensitivity, transparency to 193 nm radiation, adhesion to substrate, dry etch resistance, ease of synthesis, and availability of monomers are very critical. In these respects, remarkable progress has been made in development of ArF resist material. Polymers of acrylic and methacrylic esters show good imaging performance at 193 nm, but have insufficient dry-etch resistance under oxide or nitride etch condition. On the other hand, cyclic olefin-maleic anhydride (COMA) alternating copolymers exhibit good dry etch resistance, but have poor resolution capability. We previously reported a new platform, based on a vinyl ether-maleic anhydride (VEMA) alternating polymer system, that demonstrated both good resolution and high dry etch resistance. In this paper, VEMA systems with improved lithographic performance are presented. The new platform (VEMA) showed good performance in resolution, depth of focus (DOF), iso-dense bias, and post-etch roughness. With conventional illumination (NA=0.6, sigma=0.7), 120 nm dense line/space patterns with 0.4 (mu) M DOF were resolved. And 90 nm L/S patterns 0.6 (mu) M DOF were resolved with off-axis illumination (NA=0.63). Another important factor to be considered for the dry-etch process is post-etch roughness. In the case of VEMA system a clean surface was observed after etch under oxide, nitride, and poly conditions. The VEMA resist system is regarded as one of the most production-worthy material for real device manufacture.

Manipulation of the thermal properties of positive DUV polymers

The thermal properties of the blocked polymers used in chemically amplified positive DUV photoresists are critical in determining ultimate resist performance as well as in the selection of processing parameters. Recently it has been shown that baking these resists at or above the glass transition temperature (Tg) significantly improves the delay stability of the resist. However in order to utilize this annealing concept two thermal properties, the Tg and the thermal decomposition temperature (Td), of the blocked polymer must be controlled.

DUV positive resist system designed for Micrascan use

The development of a new DUV positive resist, XP-9493, is reported. XP-9493 was designed for the Micrascan II exposure system. Its absorbance over the 245 - 252 nm wavelength range is 0.48/micrometers , substantially higher than that of APEX-E, which is approximately 0.2/micrometers . The dissolution selectivity, tan ((phi) ), of XP-9493, 7.7, is much higher than that of APEX-E, 4.1. Thus, XP-9493 is capable of higher resolution than APEX-E with better swing curve control. It is shown that the deprotection rate of this resist is proportional to the pKa of the photogenerated acid. This result leads to the prediction that protonation of the protected polymer may determine the rate of the deprotection reaction. Further study of the photospeed vs PEB temperature showed a two-tier activation energy for the deprotection reaction. At high PEB temperatures, >= 95 degree(s)C, the deprotection reaction is diffusion-limited, where the protonation step is rate limiting. The activation energy, Ea, under diffusion limited conditions is only 7.6 kJ/mole. At lower PEB temperatures, < 95 degree(s)C, the deprotection reaction is reaction-limited, where the deprotection of the protonated protected polymer is rate-limiting. Ea under these conditions is 26.3 kJ/mole. This behavior leads to lower linewidth shifts per unit PEB temperature change, (Delta) CD/(Delta) T, at the recommended process conditions. For XP-9493, (Delta) CD/(Delta) T is approximately 6 nm/ degree(s)C for 300 nm line/space pairs. XP- 9493 resolves 0.225 micrometers line/space pairs at 19 mJ, and 0.25 micrometers contact holes at 27 mJ. The 0.25 micrometers process window for XP-9493 is >= 1.0 micrometers depth-of-focus, with 25% exposure latitude on a MSII exposure tool.