Si-Hyeung Lee

Study of machine to machine overlay error for sub-60-nm memory devices

According to the 2007 international technology roadmap for semiconductors, the overlay budget of 60nm memory devices is 11.3nm. To meet such a tight requirement, each overlay error budget should be controlled carefully. It turns out that scanner contributions due to machine to machine overlay (MMO) error are nearly half of the total overlay error budget. In a conventional way, overlay errors are corrected by ten linear terms: offset x and y, wafer rotation x and y, wafer magnification x and y, shot rotation x and y, and shot magnification x and y. Especially for the shot correction, average correction values are applied commonly for all shots. MMO cannot be compensated by only linear correction to meet such a tight specification any longer. In this article, a grid matching strategy through per-shot-correction (PSC) is investigated so that scanner contributions are minimized. In PSC, shot correction is implemented for each shot with different correction parameter values. By matching wafer grids from machin...

Synthesis of Silicon-Containing Photoresists for ArF Excimer Laser Lithography

Two new positive-type photoresists which are terpolymers of methyl methacrylate (MMA), 1,3-bis(trimethylsilyl)isopropyl methacrylate (BPMA) and either methacrylic acid (MAA) or maleic anhydride (MA) have been synthesized for ArF excimer laser lithography. Terpolymers have a silicon containing acid labile protecting group which can be deprotected by photo acid generator (PAG). Terpolymers have a good thermal stability up to 140°C and the glass transition temperature (Tg) of poly(MMAx-BPMAy-MAz) was 119°C. The minimum feature resolution with 0.17 µm L/S pattern was achieved with poly(MMA5.9-BPMA2.1-MAA2.0) by using an ArF exposure system with 17 mJ/cm2 energy dose.

Realization of sub-80-nm small-space patterning in ArF photolithography

In optical lithography, small space patterning is the most difficult task. The direct small-space patterning is not good enough with resolution enhancement technique (RET) in sub-80 nm level. Two sequential processes normally achieve the small space. Once the pattern is forming a larger pattern normally, and then makes them shrink to fit to the designed size by additional process. Usually resist thermal flow process has been used to obtain small space as additional process, which has several process issues such as flow amount control of isolated and dense small contacts, uniformity degradation and bowing profile. In order to solve these issues, we introduced the resolution enhancement lithography assisted by chemical shrink (RELACS) and shrink assist film for enhancement resolution (SAFIER) process in ArF lithography. In this paper, the RELACS and SAFIER process are compared with the resist thermal flow process for sub-80 nm space using ArF exposure tool. With the application of this process, we confirmed the improvement of in-wafer uniformity and the successful implementation of sub-80nm small space patterning regardless of pitch size and pattern arrangement.

Advanced RELACS (resolution enhancment of lithography by assist of chemical shrink) material for 193-nm lithography

The controllability of iso-dense bias generated by 193nm lithography was intensively studied with novel RELACS material. The shrinkage, shrinkage linearity, and shrinkage bias were considerably relied on MB temperature. It is the most powerful technology that changing of mixing bake (MB) temperature can control iso-dense bias. Furthermore, AZ Exp.R600 has several attractive advantages, which are able to improve LWS, LER, sidewall roughness of contact holes, surface roughness, and side lobe. Moreover, we have successfully developed a novel RELACS material to be applied for the patterning of sub-70nm contact hole.

Novel polymers for 193-nm single-layer resist based on cycloolefin polymers

A series of new cycloaliphatic olefin monomers protected by alicyclic hydrocarbon groups were synthesized. New polymers of cycloaliphatic olefins and cycloolefin-maleic anhydride (COMA) systems were also designed and prepared using the new monomers for 193 nm resist applications. These polymers were synthesized by free radical polymerization technique, utilizing azobisisobutyronitrile (AIBN) or di-t-butyl peroxide initiators. The cycloolefin polymers synthesized by free radical polymerization method were not good for ArF lithography because of their poor transparency at 193 nm, although they showed a good dry etch resistance. However, the new COMA polymers had good transparency at 193 nm and had an etch rate in CF4 mixture plasma of approximate 1.0 times that of DUV resists. Using ArF exposure tools (NA equals 0.6, (sigma) equals 0.7), 130 nm line/space patterns were resolved. Using Off-Axis illumination, 100 nm line/space patterns were resolved.

Stability Studies on Polymer Dispersed Liquid Crystal Films

Abstract Polymer Dispersed Liquid Crystal(PDLC) is a class of electroscattering materials exhibiting very promising properties for display device applications. For the last few years, the electrooptical properties of PDLC have improved drastically to use projection device with high brightness. We have studied stability of PDLC films which formed by ultraviolet initiated photopolymerization and liquid crystal phase separation. We evaluated several stability items in PDLC films such as running and environment test, accelerated life time at low and elevated temperature, voltage holding ratio(VHR) variations according to UV exposing time and temperature.

Novel methodology of employing scatterometry to assess optical proximity correction test pattern

While optical lithography is being pushed to its limits, there is a general concern as to which metrology tool is more suitable for inspection of new generation devices. Scatterometry is one of the few types of metrology that has true in-situ potential for deep submicron critical dimension and profile analysis. Physical metrology is the key element in maintaining adequate and affordable process latitude in lithography processing. Accurate metrology is needed for characterizing and monitoring the processing states, such as exposure, focus, post-exposure bake (PEB), critical dimension (CD) resolution, and uniformity. In addition, scatterometry is a good candidate tool to obtain data necessary to perform model-based optical proximity correction (OPC). However, it is unknown as to current scatterometry provides necessary sensitivity to yield results acceptable for OPC usage. In this paper, we have utilized scatterometry to measure test patterns used in a model-based OPC and performed OPC on DRAM bitline core and periphery adjoining region then, its results are compared to those model-based OPC performed using data obtained from CD-SEM and V-SEM. In doing so, we have attempted to obtain an ideal model which provides best performance in context of OPC. Furthermore, we have discussed 1-D and 2-D types of test patterns that are acceptable for OPC purpose and provided the verification results for each model using commercially available software.

Adaptability and validity of thin organic bottom anti-reflective coating (BARC) to sub-90-nm patterning in ArF lithography

The introduction of ArF lithography in device manufacturing has been studied with a low k1-factor. There are a number of issues that must be resolved to ensure the successful implementation of this technology. Such issues include the reduction in resist thickness and organic bottom anti-reflective coating (BARC) due to the characteristics of ArF resist with lower etch resistance in comparison with that of KrF. Requirements of a suitable high-performance of thin organic BARC material include chemical reactions with sub-layer, simulation for the minimization of reflectance, faster etch rate, and compatibility with resist. The optimum refractive index (n) and the extinction coefficient (k) of thin organic BARC are simulated to match the optical properties of substrates. These values are satisfied with the reflectance less than 2% at 1st minimum. In the case of SiN sub-layer with acid absorption capability, it is confirmed that the chemical reaction with thin organic BARC has an effect on line edge roughness (LER) and pattern profile. Also, the degree of these effects is dependent upon the acidity of thin organic BARC. In this paper, it is shown that the application of thin organic BARC to sub-90nm patterning in ArF lithography is very feasible and adaptable in the view of lithographic and etch performance.

What an antishrinkage coating method can surmount among stumbling block of ArF resists

ArF resist systems have some serious stumbling block related to etch selectivity, pattern collapse, and pattern slimming during CD-SEM measurement. Among these problems, when exposed to electron beam, the linewidth reduction of resist features is the main topic in our study. Since the pattern slimming may result in accuracy error of measurement and potential device reliability issues due to permanent deformation, any method to improve this undesired phenomenon should be found. In this paper, the anti-shrinkage coating approach as a method to improve pattern slimming during SEM measurement will be described. The Anti-Shrinkage Coating (ASC) material consists of anti-shrinking water-soluble polymers and other additives (e.g. cross-linker). The ASC method is a chemical attaching process that includes simple coating, mixing, baking, and rinse steps with DI water, applied after conventional photolithography. The ASC method results that the pattern shrinkage during SEM measurement is reduced less than a half of the resist alone. Additionally, the employment of the ASC method gives rise to improve pattern fidelity and LER, which are serious problems in ArF lithography. Finally, we expect that the ASC method can contribute to form the critical small space patterns.

Anti-shrinkage coating approach as a solution provider to ArF resists

Summary form only given. The authors present an anti-shrinkage coating (ASC) approach as a solution provider to improve the shrinkage of ArF resists during critical dimension (CD) measurement. Aqueous ASC material consists of anti-shrinking water-soluble polymers and other additives (e.g. cross-linker) and is coated and baked on the developed wafer and rinsed by deionised water. ASC was applied to two 193 nm resist systems and the shrinkages are about 7-8 nm after 50 measurements in the same SEM conditions as for measuring KrF resists. The line shrinkage of the ASC was improved by 70% compared to that of the ArF resist. In addition, the pattern fidelity and LER, which are serious problems for ArF resists, were also improved by the ASC process.