Ramil-Marcelo L. Mercado

A novel approach to developer-soluble anti-reflective coatings for 248-nm lithography

A novel approach to developer-soluble bottom anti-reflective coatings (BARCs) for 248-nm lithography was demonstrated. The BARC formulations are photosensitive, dye-filled systems incorporated with a polymer binder. The films are generated by thermally crosslinking the polymer matrix, and are then photochemically decrosslinked in order to render them soluble in developer solutions. The BARCs are compatible with solvents commonly used in the industry. Easy modification of the films with regard to optical properties for potential use with various substrates was also demonstrated. The BARCs exhibit anisotropic development in aqueous tetramethylammonium hydroxide (TMAH) solutions subsequent to simulated photoresist application, exposure, and post-exposure bake.

Resist double patterning on BARCs and spin-on multilayer materials

Many approaches to double patterning have been devised, of which most have been designed to reduce the number of process steps. The litho-freeze-litho-etch process (LFLE) is one such technique that eliminates the first etch step from the standard litho-etch litho-etch (LELE) process. The resist freeze material chemically modifies the patterned photoresist, as well as potentially the layer beneath, which may result in a performance change at the second lithography step. Another approach, litho-process-litho-etch (LPLE) does not involve the use of a chemical freeze material, instead relying on a thermal treatment to remove excess solvent from the polymer and differential energy of activation between two resists to create a double-patterned image. Finally, double patterning using negative-tone development of a positiveacting photoresist is another approach in consideration. In this paper, we present the results of several double-patterning processes on organic bottom anti-reflective coatings (BARCs) and spin-on multilayer stacks consisting of a silicon hardmask on top of a carbon underlayer. Pattern profiles of the first and second lithography steps are compared.

Improving the performance of light-sensitive developer-soluble anti-reflective coatings by using adamantyl terpolymers

In a search for improved resolution and processing latitude for a family of light-sensitive developer-soluble bottom antireflective coatings (BARCs), the structure of the binder terpolymer was altered by incorporating acid-cleavable adamantyl methacrylates. Contrast curves and 193-nm microlithography were then used as tools in developing a novel developer-soluble adamantyl BARC which does not include a photoacid generator (PAG) or quencher, but instead depends on acid diffusing from the exposed resist for development. This formulation eliminates concern about PAG or quencher leaching out of the BARC during application of the photoresist. Resolution for a resist A and the new BARC was 150-nm L/S (1:1) for both 38-nm and 54- to 55-nm BARC thicknesses. Resolution and line shape were comparable to that of the non-adamantyl control BARC with same resist at 55-nm BARC thickness, with both BARCs giving some undercutting using an AmphibianTM XIS interferometer for the 193-nm exposures. Light-sensitive adamantyl BARCs that do require inclusion of a PAG for optimum lithography with resist A are also described in this paper. The series of developer-soluble adamantyl BARCs were solution and spin-bowl compatible. The 193-nm optical parameters (n and k) for all adamantyl BARCs were 1.7 and 0.5-0.6, respectively.

Advantages of BARC and photoresist matching for 193-nm photosensitive BARC applications

As the semiconductor industry approaches smaller and smaller features, applications that previously used top antireflective coatings have now begun using developer-soluble bottom anti-reflective coatings (BARCs). However, there are several drawbacks to a wholly developer-soluble system, mainly because many of these systems exhibit isotropic development, which makes through-pitch and topography performance unsatisfactory. To solve this problem, we have developed several photosensitive BARC (PS BARC) systems that achieve anisotropic development. One issue with the PS BARC, as with traditional dry BARCs, is resist compatibility. This effect is compounded with the photosensitive nature of our materials. The acid diffusion and quenching nature of the resists has been shown to have a significant effect on the performance of the acid-sensitive PS BARC. Some resists contain a highly diffusive acid that travels to the PS BARC during the post-exposure bake and aids in clearance. Others show the opposite effect, and the same PS BARC formulation is not able to clear completely. To address the lack of compatibility and to further improve the PS BARC, we have developed a solution that properly matches PS BARC and photoresist performance.

Acid-degradable hyperbranched polymer and its application in bottom anti-reflective coatings

A photosensitive developer-soluble bottom anti-reflective coating (DBARC) system is described for KrF and ArF lithographic applications. The system contains an acid-degradable branched polymer that is self-crosslinked into a polymeric film after spin coating and baking at high temperature, rendering a solvent-insoluble coating. The DBARC coating is tunable in terms having the appropriate light absorption (k value) and thickness for desirable reflection control. After the exposure of the resist, the DBARC layer decrosslinks into developer-soluble small molecules in the presence of photoacid generator (PAG). Thus the DBARC layer is removed simultaneously with the photoresist in the development process, instead of being etched away in a plasma-etching chamber in the case of traditional BARC layers. The etch budget is significantly improved so that a thin resist can be used for better resolution. Alternatively, the etch step can be omitted in the case of the formation of layers that may be damaged by exposure to plasma.

Photoresist-induced development behavior in DBARCs

Developer-soluble bottom anti-reflective coating (DBARC) BSI.W09008 has provided promising lithography results with five different 193-nm photoresists, with the accomplishments including 120-nm L/S (1:1) and 130-nm L/S through-pitch (i.e., 1:1, 1:3, and isolated line). This DBARC is not inherently light sensitive and depends on diffusing photoacid from the exposed photoresist for development. With undercutting being an issue for the PAG-less DBARC with some resists, the shapes of 130-nm lines (both dense and isolated) were improved by either a) incorporating a small amount of a base additive in the BSI.W09008 formulation or b) altering the structure of the DBARCs binder polymer. With selected photoresist(s) and/or resist processing conditions, either photoacid diffusion or photoacid activity is inadequate to give DBARC clearance and BSI.W09008 performs more as a dry BARC. The post-development residue obtained from BSI.W09008 on a silicon substrate is much less dependent on the initial DBARC film thickness and the exposure dose than for earlier-generation photosensitive (PS)-DBARC BSI.W07327A, using the same photoresist. BSI.W09008 also gives less post-development residue than BSI.W07327A using the same resist on a silicon nitride substrate at exposure doses of 14-25 mJ/cm2.

Dual-layer dye-filled developer-soluble BARCs for 193-nm lithography

A family of dye-filled developer-soluble bottom anti-reflective coatings (BARCs) has been developed for use in 193-nm microlithography. This new dye-filled chemical platform easily provides products covering a wide range of optical properties. The light-sensitive and positive-working BARCs use a transparent polymeric binder and a polymeric dye in a thermally crosslinking formulation, with the cured products then being photochemically decrosslinked prior to development. The cured BARC films are imaged and removed with developer in the same steps as the covering photoresist. Two dye-filled BARCs with differing optical properties were developed via a series of DOEs and then used as a dual-layer BARC stack. Lithography with this BARC stack, using a 193-nm resist, gave 150-nm L/S (1:1). A 193-nm dual-layer BARC stack (gradient optical properties) from the well-established dye-attached family of light-sensitive BARCs also gave 150-nm L/S (1:1) with the same resist. However, the latter provided much improved line shape with no scumming. The targeted application for light-sensitive dual-layer BARCs is high-numerical aperture (NA) immersion lithography where a single-layer BARC will not afford the requisite reflection control.