Sung Koo Lee

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.

Quencher gradient resist process for low k process

To accomplish minimizing feature size to sub 70nm, new light sources for photolithography are emerging, such as F2(157nm), and EUV(13nm). However there are many problems that should be solved for real device production. So extension of ArF(193nm) is necessary until the maturity of new lithography technique will be prepared. In this paper, we tested the feasibility of quencher gradient resist process (QGRP) to low k process. To compare with normal patterning process, QGRP needs additional step, over-coating. But this over-coating material differs from the normal over-coating materials in that over-coating material of QGRP has acid quencher sources. After the exposure, these quencher materials diffuse into the photoresist and quench excess acid that causes a sloped resist profile. As a result, vertical profile pattern can be obtained with QGRP. Using this QGRP, 70nm process, of which k value is 0.27, is possible with 0.75NA ArF scanner. For contact hole pattern, we could get direct 70nm C/H with QGRP. The exposure latitude of 70nm contact hole was improved more than 50% in case of QGRP compared with normal process. In addition, QGRP is applicable for immersion lithography.

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.

Investigation of systematic CD distribution error on intrafield

As feature size shrinks, better critical dimension uniformity (CDU) is highly demanded in aspects of device characteristics. Intra field CDU is one of main contributor in total CD variation budget. Especially systematic CD distribution in shot, bank and MAT boundary should be strongly considered to minimize repeated error to guarantee high yield even though it is not prominent in overall CDU value. In this paper, we investigated the several factors to affect systematic CD distribution error on intra field. First of all, localized mask CD variation caused by electron-beam scattering over local region, development loading and etch loading effect directly printed in wafer. Appropriate mask fabrication suppress CD variation at boundary region. Secondly, chemical flare effect is expected to make CD gradient at boundary region. Photo acid concentration change by sub-resolution assist feature (SRAF) can reduce the CD gradient. We demonstrated SRAF size dependency in positive tone develop (PTD) and negative tone develop (NTD) case. Thirdly, out-of-field stray light (OOFSL) due to adjacent exposed field causes CD gradient at field boundary. Exposure dose reduction is expected as a solution in this case. Even though we perfectly control CDU at boundary region after mask patterning, other process issues such as etch and CMP loading effect also make worse the CD distribution at boundary region. Through the consideration of above factors, we optimized systematic CD distribution error at boundary region before etch. Furthermore we compared several techniques to compensate post-etch systematic CD distribution.

Reflection control for immersion lithography: a single organic antireflectant over high-reflective substrates for double patterning

When patterning critical layers at hyper NA, a multilayer antireflectant system is required in order to control complex reflectivity resulting from various incident angles. Multilayer antireflectants typically consist of an organic antireflectant and inorganic substrates. However, there are still some applications which need a single organic antireflectant over high reflective substrates. A 2P2E application in double patterning is one of them. Even though the pitch for double patterning is relatively loose, the reflectivity control is still challenging in terms of profiles and overall process window. The optical constants and thickness of antireflectants should be well optimized depending on applications. We have investigated several organic antireflectants for a single antireflectant over high reflective substrates. The organic films differ in terms of n, k, thickness to cover both the 1st minimum and the 2nd minimum applications. The overall patterning performance including profiles and process window has been evaluated. ASML 1900i was used to perform lithography. Simulation was performed using ProlithTM software.

Correlation between polymer platform of ArF photoresist and defect in the track nozzle of manufacturing process line

As the minimum feature size of electronic devices continues to shrink, the industry is moving from wavelength of 248-nm KrF excimer laser sources to shorter wavelength of 193-nrn ArF excimer laser and ArF immersion to achieve required higher resolution. As minimum feature sizes are reduced, the ability to minimize defects is getting more important, because they have a close connection with yield. With the replacement of laser source, 248-nm with 193-nm, the platform of polymer was also converted from phenolic polymer into acrylic polymer. With this platform changes unexpected various defect problems had been occurred. Although KrF process causes not much of defect, ArF process causes more serious defect problems. One of those major defect source is solidification of polymer in track nozzle. The solidified polymer at track nozzle needs to be removed periodically, unless it causes significant throughput loss in mass production. The amount of this type of defect relies on physical properties of polymer platform such as hydrophilicity, solubility or structural rigidity. The hydrophilic phenol based KrF polymer shows minor defects, contrarily hydrophobic acryl based ArF polymer causes serious defects. The solidification of acrylate type polymer was caused by poor solubility. In order to improve solubility, olefinic moieties such as norbornylene, norbornyl devertives and opened maleic anhydride monomers were adopted in acrylate polymer. Those inserted olefins and opened maleic anhydride in acrylic polymer changed overall structure such as rigid helix structure into flexible structure. With the increase of solubility, particle defect was dramatically reduced. Conclusively, insertion of cycloolefin and opened maleic anhydride moiety releases rigid acrylic structure and it improves solubility. As solubility improves, crystallization at nozzle has been decreased and the particle defect is reduced. Moreover this flexible structure allows the resist reflow at the moderate temperature which is one of the resolution enhancement techniques.

Cycloolefin copolymer containing hindered hydroxyl group for 193nm photoresist

The basic requirements for polymer design rule in photoresist are as following. The performances of the photoresist relate to transmittance, adhesion on BARC material, dry etch resistance and process margin as a function of the exposure tool. However, it is very difficult for us to find the polymer that has good performance for 193 nm ArF photoresist, because it has many limitations as target feature size of photoresist become smaller. One of the most important properties in it is adhesion. Researchers usually introduce functional group, as an adhesion promoter, such as carboxylic acid group, hydroxyl group and lactone group at the side chain of the polymer. Carboxylic acid group represents the highest adhesive property, but it has poor dark erosion because of affinity with developer, 2.38 wt% TMAH solution. Lactone group has a limit for introduction as a functional group because it can cause low dry etch resistance and pattern slope. On the other hand, in case of primary alcohol, the hydroxyl group occurs cross-link with carbonyl unit of a neighboring unit. We have recently synthesized cycloolefin copolymer, which has a secondary hindered alcohol in its side chain. And they showed good performances in adhesion, resolution, PED stability, processing window, dry etch resistance, and good pattern profile in both L/S and C/H pattern profile. In this paper we will discuss the properties and the evaluation results.