Keun Do Ban

Top antireflective coating process for immersion lithography

To accomplish minimizing feature size to sub 60nm, new light sources for photolithography are emerging, such as F2(157nm), and EUV(13nm). However, these new lithographic technologies have many problems to be solved for real device production. In case of F2 lithography, pellicle issue makes it difficult to use of F2 source in mass production. In case of EUV, light source and mask fabrication issues must be solved for real device application. For these reasons, instead of new light sources, extension of dry ArF lithography has been studied for sub 70nm device production by using Resolution Enhancement Technology (RET) such as using high NA tools, off axis illumination, and phase shift mask. Recently, a new technology called ArF immersion lithography is emerging as a next generation lithography. The first problem of this technology is contamination issues that come from the dissolution of contaminants from the photoresist to the immersion liquid. The second is optical problem that comes from the using hyper NA system. To solve these two problems, we have developed top antireflective coating (TARC) material. This TARC material can be coated on resist without damage to the resist property. In addition to, this TARC material is easily developable by conventional 2.38 wt% TMAH solution. The reflective index of this TARC is adjusted to 1.55, so it can act as an antireflective material. To this TARC material for immersion, quencher gradient resist process (QGRP) was applied also. As a result, we could improve resolution and process margin. However, some of resists showed defects that were generated by this TARC material and QGRP. To solve this defect problem, we introduced buffer function to the TARC material. Thanks to this buffer function, we could minimize defects of resist pattern in immersion lithography.

Polymer Structure Modifications for Immersion Leaching Control

ArF Immersion lithography is the most promising technology for 45nm node and possibly beyond. However, serious issues in ArF immersion lithography for semiconductor mass production still exist. One of the issues is immersion specific defects, which are caused by photoresist component leaching and residual water droplets. In order to minimize immersion specific defects, preventing water penetration into the resist film is regarded as an important factor. Several research groups have reported that higher receding contact angle reduced defectivity. High receding contact angle of film surface prevent water penetration into the resist film due to the hydrophobic nature. Resist component leaching phenomenon also can be caused by the water penetration into the film, so hydrophobic resist can reduce leaching quantity. In this paper, to investigate chemical leaching from resist surface, we evaluated the leaching value of PAG anion and contact angles of various polymers according to their hydrophobicity. Hydrophilicity of a polymer was changed by the degree of hydrophobic group substitution to polymer chain. We measured receding contact angle with four different resists composed of water-repellent functiona group. Receding contact angle of resist surface increased as the portion of water-repellent functional group increased. Also, the leaching amount of PAG anion decreased as the receding contact angle of film surface increased. We expect that higher receding contact angle prevents chemical leaching from resist film by repelling water at the surface. We will report detailed results in this paper.

Modified polymer architecture for immersion lithography

In the past several years, ArF immersion lithography has been developed rapidly for practical applications. ArF immersion lithography is now researched actively and developed for the purpose of implementing the 45-nm technology node. For the device designs involved immersion lithography, line width roughness (LWR) and film wettability are very important criteria to control in the point of high resolution and defectivity. Free radical polymerization in the presence of thiocarbonylthio compounds of general structure Z-C(=S)S-R provides living polymers of predetermined molecular weight and narrow molecular weight distribution by a process of reversible addition-fragmentation chain transfer (RAFT). A rationale for selecting the most appropriate thiocarbonylthio compounds for a particular monomer type is presented with reference to the polymerization of methacrylates, styrenes, acrylates, acrylamides, and vinyl acetate. In this study, resist polymers with narrow polydispersity (PD) and controlled molecular structure were prepared using controlled radical polymerization techniques, such as RAFT polymerization. PD index of polymers showed between about 1.2 to 1.4 and in some instances, between about 1.1 to 1.2 or less. Additionally, each polymer chain has a RAFT end group. That is the resulting polymer contains a chain transfer agent (CTA) moiety at each terminal end of polymer backbone. It is possible that hydrophobic CTAs can be used to decrease the hydrophilicity of resist film.

Studies on leaching of photoresist components by water

Immersion lithography has drawn tons of interests as a potential solution for sub-65nm patterning. High refractive index liquid, which is filled in the gap between exposure lens and a photoresist, can improve a resolution through increased effective numerical aperture (NA) of the exposure system. Most attractive liquid for this purpose is water. Our works were conducted as a part of the basic study for immersion lithography and aimed for the verification of leached resist components by water. It was observed that leaching relies largely on the free volume of a polymer and anion size of photoacid generator (PAG). The larger free volume and the smaller anion, the larger T-top resist profile was generated. Additionally, effects of solvents, quenchers and polarity of the polymer were investigated. Detailed results will be reported in this paper.

Novel rinse process for reducing pattern collapse in 0.30-k1 ArF lithography

In-house rinse, HR31 has a strong point in terms of lithographic performance, defect, bubble, and metal impurity. The collapse behavior was quantified in terms of SMCD (Standing Minimum CD) in 80nm dense L/S ArF resist patterns. It contributed to enlarging process window by improving collapse (SMCD: 84→72nm), CD uniformity (12.3→9.3nm), and lithographic margin [EL (11.7→12.8%), and DOF (0.20→0.25µm)].

High-etch-rate ArF BARC composed of polyester

As the pattern size decreases, the thickness of resist also should be decreased owing to the pattern collapse problem. So the using of surfactant containing rinse material, instead of DI water, can be a solution to the collapse problem. The developing of Bottom Anti Reflective Coating (BARC) that has high etch rate will be helpful to the collapse issue because it enables low thickness resist process and pattern collapse will be decrease. In this paper, Polyacetal, polyacrylate and polyesters BARCs were evaluated. Polyacetal type BARC shows best coating property. Regardless of the topology, polyacetal type BARC shows good conformality. However, polyacrylate and polyesters show coating fail on the topology wafer. In terms of pattern collapse, polyacetal type BARC also shows best results. Among the three types of BARC, ArF BARC that is made by polyester resin shows highest etch rate after 2000ÅBRAC etch. However, when the etching target is 60nm, all BARCs have same etch rate. For the matching with line and space resist, all these three BARCs show good profile. However, polyester type BARC does not match with contact hole resist and could not define contact hole pattern.