In this paper we investigate fundamental resist properties to enhance resolution and focus margin for immersion
contact hole patterning. Basic chemistry factors have been used to manipulate the iso-focal region (the region of
smallest critical dimension variation through focus) of the photoresist and study the impact on resolution and focus
margin for small isolated contact holes. Acid diffusion length is one of the key factors investigated, which can be
controlled by polymer, PAG, quencher, bake temperature and bake time. The various criteria investigated for this study
were: focus and exposure latitude for dense L/S, dense C/H and semi-dense C/H. The effect of manipulating the acid diffusion of the photoresist on imaging small contact holes was verified using ultra-high NA immersion imaging at 1.35
We investigated the structure-property relationships of several polymer platforms containing hexafluoroisopropanol (HFIP) and tertiary alkyl ester functionalities in order to identify and develop fluorine-containing polymers suitable for 157nm lithography. We observed that the aqueous base solubility of homopolymers containing HFIP was highly dependent on the monomer structure, number of HFIP group per monomer unit, substituent on the alcohol and the polymer architecture. Copolymers of <i>tert</i>-butyl acrylate (TBA), <i>tert</i>-butyl 2-fluoroacrylate (TBFA) and <i>tert</i>-butyl 2-trifluoromethylacrylate (TBTFMA) with styrene hexafluoroisopropanol (STYHFIP) or norborene hexafluoro-isopropanol (NBHFIP) were also investigated to determine the effect of substitution at the acrylate α-position. Under the same ration of STYHFIP, the transparency of the co-polymers improved in the or der of CF<sub>3</sub>>F>H while the dry etch stability decreased in the order of CF<sub>3</sub>>F>H. When exposed to 157 nm radiation, photoresists of P(STYHFIP-TBA), P(STYHFIP-TBFA) and P(STYHFIP-TBTFMA) showed an increase in E<sub>0</sub> ni the order of H<F<CF<sub>3</sub>, but the difference was marginal. The PEB sensitivity was nearly identical for all three co-polymers suggesting that the nature of the substituent at the α-position of the acrylate monomer did not have a significant impact on the deprotection chemistry. The photospeed of P(NBHFIP-TBTFMA) was much slower than that of P(STYHFIP-TBTFMA) due to a slower dissolution rate of NBHFIP than that of STYHFIP and to the influence of the polymer matrix on the deprotection reaction.
A survey of fluorine-containing aromatic polymers, with and without base soluble functionality, was conducted to determine their potential utility in 157 nm lithography. The focus was toward the design and evaluation of fluorine- containing polymers that closely paralleled the ESCAP matrix resins now successfully used in 248 nm photoresists. New 4- hydroxytetrafluorostyrene (HTFS) based homo-, co- and ter- polymers were prepared and evaluated for their potential utility at 157 nm resists. Significant advances were made toward reducing absorbance with fluorine substitution and monomer variation. The polymers form good films, have acceptable thermal stability and show good dry etch resistance with promising potential in thin film resist applications. The synthesis and pertinent characteristics of the new polymer systems as well as preliminary oxide etch results on representative polymers are discussed.
A great deal of progress has been made in the design of single layer positive tone resists for 193 nm lithography. Commercial samples of such materials are now available from many vendors. The patterning of certain levels of devices profits from the use of negative tone resists. There have been several reports of work directed toward the design of negative tones resists for 193 nm exposure but, none have performed as well as the positive tone systems. Polymers with alicyclic structures in the backbone have emerged as excellent platforms from which to design positive tone resists for 193 nm exposure. We now report the adaptation of this class of polymers to the design of high performance negative tone 193 nm resists. New systems have been prepared that are based on a polarity switch mechanism for modulation of the dissolution rate. The systems are based on a polar, alicyclic polymer backbone that includes a monomer bearing a glycol pendant group that undergoes the acid catalyzed pinacol rearrangement upon exposure and bake to produce the corresponding less polar ketone. This monomer was copolymerized with maleic anhydride and a norbornene bearing a bis-trifluoromethylcarbinol. The rearrangement of the copolymer was monitored by FT-IR as a function of temperature. The synthesis of the norbornene monomers will be presented together with characterization of copolymers of these monomers with maleic anhydride. The lithographic performance of the new resist system will also be presented.
Top surface imaging (TSI) systems based on vapor phase silylation have been investigated for use at a variety of wavelengths. This approach to generating high aspect ratio, high resolution images held great promise particularly for 193 nm and EUV lithography applications. Several 193 nm TSI systems have been described that produce very high resolution (low k factor) images with wide process latitude. However, because of the line edge roughness associated with the final images, TSI systems have fallen from favor. In fact, top surface imaging and line edge roughness have become synonymous in the minds of most. Most of the 193 nm TSI systems are based on poly(p-hydroxystyrene) resins. These polymers have an unfortunate combination of properties that limit their utility in this application. These limiting properties include (1) High optical density (2) Poor silylation contrast (3) Low glass transition temperature of the silylated material. These shortcomings are related to inherent polymer characteristics and are responsible for the pronounced line edge roughness in the poly(p-hydroxystyrene) systems. We have synthesized certain alicyclic polymers that have higher transparency and higher glass transition temperatures. Using these polymers, we have demonstrated the ability to print high resolution features with very smooth sidewalls. This paper will describe the synthesis and characterization of the polymers and their application to top surface imaging at 193 nm. Additionally, it will describe the analysis that was used to tailor the processing and the polymer's physical properties to achieve optimum imaging.
This paper reports our work on a series of alicyclic polymer-based photoresist platforms designed for 193 nm lithography. The polymers described here were prepared from derivatives of norbornene and appropriate co-monomers by either free radical or ring opening metathesis polymerization methods. A variety of techniques were explored as a means of enhancing the lithographic, optical, dissolution, and mechanical properties of photoresists formulated from these alicyclic polymers. Recent studies designed to improve the lithographic performance of photoresists formulated with these materials are described.