Progress in Spin-on Hard Mask Materials for Advanced Lithography

Abstract

Hard masks used in lithography processes play a vital role in pattern transfer to the desired substrate. Hard mask materials can be categorized into organic and inorganic types. Examples of organic type hard masks include amorphous carbon, organo siloxane based materials with reflection control properties. These organic hard masks are deposited either by CVD process or spin-on processes. SiN, SiON and TiN are some examples of inorganic type hard masks and typically these hard masks are deposited through CVD process. In either type, key requirement is etch resistance to either oxygen rich plasma or halogen rich plasma depending on the substrate to be etched away. However, in the advanced lithography processes, in addition to good etch resistance, they also need to possess good wet removability, fill capability in high aspect ratio contacts and trenches. In this paper, we discuss the advances made in the spin-on organic and inorganic hard masks. The spin-on option provides high throughput and several alternate material options compared to CVD option. Spin-on carbon (SOC) is a high carbon containing polymer solution and as a coating material, the polymers need to be soluble in organic solvent and insoluble after curing for coating upper layer materials. Recent progress made in good filling, low outgas, high thermal stability and planarization properties required for double and quadruple patterning is presented. Similarly, novel spin-on type inorganic formulations providing Ti, W, and Zr oxide hard masks with high etch selectivity, wet removal capability and good shelf-life stability are described. These novel AZ ® Spin-on MHM formulations can be used in several new applications and can potentially replace any metal, metal oxide, metal nitride or silicon-containing hard mask films currently deposited using CVD process in the semiconductor manufacturing process.

Planarization of topography with spin-on carbon hard mask

“…Previously, synthesis and performance of high carbon content polymers for advanced SOC were reported, and pattern transfer of resist into substrate down to CD 40nm were demonstrated without pattern deformation or wiggling [1,2]. Figure 1 compares planarization of topography by single coat-etch and multiple coat processes.…”

“…High thermal stability is necessary to avoid outgas contamination during vacuum process without temperature restriction [1,2]. As the CD size decreases in the advanced nodes such as 2Xnm and beyond along with multiple patterning technology, hard masks with good planarization and filling properties are needed to control the CD uniformity.…”

Spin-on Metal Oxides and Their Applications for Next Generation Lithography

“…Future generation of lithography processes require hard masks with higher resistance to plasma etch and materials that can be easily wet stripped after pattern transfer process to prevent dry etch damage to the substrate underneath [4,5]. Previously we reported that AZ® Spin-on metal hard mask (MHM) materials are useful for generating metal oxide containing underlayers [4][5][6][7][8][9]. The materials demonstrated good long term shelf life and pot-life stability.…”

“…The underlayer coating is strippable in chemical solutions after curing of the film to form metal oxide. The specially designed underlayers can be used to significantly improve photosensitivity of EUV photoresist performance [8,10]. The metal oxide films have excellent dry etch resistance and/or good gap fill performances so that they can be used as a hard mask to replace silicon underlayers in processes, such as trilayer or image reversal processes [4,5].…”

Unique Characteristics of Metal-containing Film

“…A more pragmatic approach is spin-on metals or metal oxides of interest are commonly generated by a sol-gel process, where the precursor solution is applied by spin-coating and heated to high temperatures [1,2]. The sol-gel process is terminated with ligands to provide metal oxide nanoparticles [3,4].…”