Aromatic resins for underlayers

#The present invention relates generally to field of manufacturing electronic devices, and more specifically to the field of materials for use in semiconductor manufacture.

#It is well-known in lithographic processes that a resist pattern can collapse due to surface tension from the developer used if the resist pattern is too tall (high aspect ratio). Multilayer resist processes (such as three- and four-layer processes) have been devised which can address this issue of pattern collapse where a high aspect ratio is desired. Such multilayer processes use a resist top layer, one or more middle layers, and a bottom layer (or underlayer). In such multilayer resist processes, the top photoresist layer is imaged and developed in typical fashion to provide a resist pattern. The pattern is then transferred to the one or more middle layers, typically by etching. Each middle layer is selected such that a different etch process is used, such as different plasma etches. Finally, the pattern is transferred to the underlayer, typically by etching. Such middle layers may be composed of various materials while the underlayer materials are typically composed of high carbon content materials. The underlayer material is selected to provide desired antireflective properties, planarizing properties, as well as etch selectivity.

#Many attempts have been made to develop underlayer materials which possess desired antireflective properties and etch selectivity, and which are suitable for use with these multilayer processes. One feature of etch selectivity is the etch resistance of an organic material to plasma etches. It is generally desired in the industry to develop underlayer materials that have improved etch resistance as compared to conventional materials. Korean Pat. App. No. 2010080139 A discloses certain aromatic polymers formed from the self-condensation of pyrenol compounds in toluene (a non-polar solvent). Such aromatic polymers do not show desired etch selectivity, that is, etch resistance. U.S. Published Pat. App. No. 2010/0021830 discloses certain pyrene-containing aromatic polymers, but does not disclose polymers having certain fused aromatic ring moieties pendant from the polymer backbone. There remains a need for underlayer materials that possess desired antireflective properties and improved etch selectivity, particularly improved etch resistance to O2 and CF4 plasmas.

#A three-necked 50 mL round-bottom flask was equipped with a mechanical stirrer, a thermowell, and a condenser with a nitrogen inlet. The flask was charged with 1-pyrenol (5.0 g, 0.0229 mol), 2-naphthaldehyde (3.578 g, 0.0229 mol), and PGME (10 mL) and EtOH (7 mL). Stirring was then initiated and the reaction mixture was heated to 60° C. under nitrogen. A clear solution was obtained after 30 minutes and heating was removed at that time. HCl (3.0 mL, 37% in water) was added dropwise to the reaction mixture at 40° C. The reaction mixture was refluxed for 24 hours to give a thick, dark brown solution. The reaction mixture was cooled to room temperature and diluted with 10 mL PGME. The mixture was then added to 250 mL methanol to give a light grey precipitate. The precipitated resin was filtered, vacuum dried at 60 to 70° C. to give 4.3 g resin (Sample 1) as grey powder. Analysis by GPC: Mw=2321, polydispersity index (PDI)=1.24.

#The procedure of Example 1 was repeated and analysis of the resulting resin (Sample 2) by GPC provided the following: Mw=2231, PDI=1.33.

#A three-necked 50 mL round-bottom flask was equipped with a mechanical stirrer, a thermowell, and a condenser with a nitrogen inlet. The flask was charged with 1-pyrenol (4.0 g, 0.0183 mol), 2-naphthaldehyde (2.8624 g, 0.0183 mol), and toluene (24 mL). Stirring was then initiated and the reaction mixture was heated to 60° C. under nitrogen. A clear solution was obtained after 30 minutes and heating was removed at that time. Methanesulfonic acid (1.76 g, 0.0183 mol) was added dropwise to the reaction mixture at 40° C. The reaction mixture was heated at 100 to 110° C. for 12 hours to give a thick solution. The reaction mixture was then cooled to room temperature. The mixture was added to 250 mL methanol to give a grey precipitate. The precipitated resin was filtered, vacuum dried at 60 to 70° C. to give 3.6 g resin (Sample 3) as grey powder. Analysis by GPC: Mw=2697, PDI=1.6.