Frieda Van Roey

Novel method for characterizing resist performance

The use of a single figure of merit to judge resist performance with respect to resolution, linewidth roughness LWR, and sensitivity is proposed and evaluated. Chemically amplified photoresists used in advanced lithography nodes need to fulfill stringent requirements for a considerable number of resist and process characteristics. Along with resolution, linewidth roughness and resist sensitivity are important examples where the specifications have become very tight. Previously, it has been shown that resolution, linewidth roughness, and resist sensitivity are fundamentally interdependent. Hence, when evaluating or optimizing resist performance, it is very important to take these three characteristics into consideration simultaneously. We propose to combine these characteristics into a single photoresist figure of merit KLUP. This figure of merit, which is determined from sizing dose, imaging wavelength, resist thickness, exposure latitude, acid diffusion length, linewidth roughness, and pitch, allows for a direct comparison of very different resist formulations independent of the exposure tool used. Thus, KLUP has great potential to assist in evaluating resist performance for the next lithography nodes, for both ArF and for EUV wavelengths.

EUV lithography program at IMEC

IMEC has started an EUV lithography research program based on ASMLs EUV full field scanner, the Alpha Demo Tool (ADT). Currently, the ADT is in the final phase of installation. The program focuses on three main projects: EUV resists, EUV reticles and assessment of the ADT performance. The intent of this program is to help improve and establish the necessary mask and resist infrastructure. In this paper, the status and the progress of the program is reviewed. In preparation for a resist process for the ADT, interference lithography has been used to track the progress of resist performance. Steady progress in resist development is seen, especially in terms of resolution, as some materials are now able to resolve 25nm HP. In its initial phase, the reticle project has concentrated on working with the mask and blank suppliers to assure timely availability of reticles for the ADT. An overview is given of the other reticle related activities, as well as first results of a defect printability study by simulation. In the ADT assessment project, simulation studies are reported aimed at the development of optical correction for flare and reticle shadowing effects. The impact of flare and shadowing effects are well understood and strategies for flare mitigation and shadowing effect correction are proposed.

Flare in extreme ultraviolet lithography: metrology, out-of-band radiation, fractal point-spread function, and flare map calibration

The critical role of flare in extreme ultraviolet (EUV) lithography is well known. In this work, the implementation of a robust flare metrology is discussed, and the proposed approach is qualified both in terms of precision and accuracy. The flare measurements are compared to full-chip simulations using a simplified single fractal point-spread function (PSF), and the parameters of the analytical PSF are optimized by comparing the simulation output to the experimental results. After flare map calibration, the matching of simulation and experiment in the flare range from 4 to 12% is quite good, clearly indicating an offset of about 3%. The origin of this offset is attributed to the presence of DUV light. An experimental estimate of the DUV component is found in good agreement with the predicted value.

Immersion specific defect mechanisms : Findings and recommendations for their control

Defectivity has been one of the largest unknowns in immersion lithography. It is critical to understand if there are any immersion specific defect modes, and if so, what their underlying mechanisms are. Through this understanding, any identified defect modes can be reduced or eliminated to help advance immersion lithography to high yield manufacturing. Since February 2005, an ASML XT:1250Di immersion scanner has been operational at IMEC. A joint program was established to understand immersion defectivity by bringing together expertise from IMEC, ASML, resist vendors, IC manufactures, TEL, and KLA-Tencor. This paper will cover the results from these efforts. The new immersion specific defect modes that will be discussed are air bubbles in the immersion fluid, water marks, wafer edge film peeling, and particle transport. As part of the effort to understand the parameters that drive these defects, IMEC has also developed novel techniques for characterizing resist leaching and water uptake. The findings of our investigations into each immersion specific defect mechanism and their influencing factors will be given in this paper, and an attempt will be made to provide recommendations for a process space to operate in to limit these defects.

Spectral analysis of line width roughness and its application to immersion lithography

Various approaches can be used to quantify line width rough- ness LWR. One of the most commonly used estimators of LWR is standard deviation . However, a substantial amount of information is ignored if only is measured. We use an automated approach to inves- tigate LWR, where standard deviation, correlation length, and power spectrum are measured online on critical dimension scanning electron microscopes. This methodology is used to monitor LWR, investigate the effect of LWR on critical dimension precision, and to benchmark new resists for immersion lithography. Our results indicate that online LWR metrology is a critical tool in a variety of applications, including but not restricted to process control.

193-nm contact photoresist reflow feasibility study

The patterning of very small contact hole features for the 130nm and 100nm device generations will be a difficult challenge for 193nm lithography. The depth of focus for small contacts is currently inadequate for a manufacturable process that includes both dense and isolated pitches. As higher NA 193nm scanners are not expected to improve focus margins considerably, other contact patterning methods are required which improve processing margins. In this work, we study the potential for contact photoresist reflow to be used with 193nm photoresists to increase process windows of small contact dimensions.

100-nm generation contact patterning by low temperature 193-nm resist reflow process

Contact lithography for the 100nm generation is a difficult challenge with current layer 193nm resist processes. The SIA roadmap lists the contact hole size for 100 nm lithography as 115 nm. Even with next generation very high NA (>0.7) 193nm exposure tools, early results indicate that these contact hole sizes can not be obtained with standard processing techniques. Therefore, we have investigated the feasibility of using resist reflow to obtain small contact hole sizes.

The need for LWR metrology standardization: the imec roughness protocol

As semiconductor technology keeps moving forward, undeterred by the many challenges ahead, one specific deliverable is capturing the attention of many experts in the field: Line Width Roughness (LWR) specifications are expected to be less than 2nm in the near term, and to drop below 1nm in just a few years. This is a daunting challenge and engineers throughout the industry are trying to meet these targets using every means at their disposal. However, although current efforts are surely admirable, we believe they are not enough. The fact is that a specification has a meaning only if there is an agreed methodology to verify if the criterion is met or not. Such a standardization is critical in any field of science and technology and the question that we need to ask ourselves today is whether we have a standardized LWR metrology or not. In other words, if a single reference sample were provided, would everyone measuring it get reasonably comparable results? We came to realize that this is not the case and that the observed spread in the results throughout the industry is quite large. In our opinion, this makes the comparison of LWR data among institutions, or to a specification, very difficult. In this paper, we report the spread of measured LWR data across the semiconductor industry. We investigate the impact of image acquisition, measurement algorithm, and frequency analysis parameters on LWR metrology. We review critically some of the International Technology Roadmap for Semiconductors (ITRS) metrology guidelines (such as measurement box length larger than 2μm and the need to correct for SEM noise). We compare the SEM roughness results to AFM measurements. Finally, we propose a standardized LWR measurement protocol - the imec Roughness Protocol (iRP) - intended to ensure that every time LWR measurements are compared (from various sources or to specifications), the comparison is sensible and sound. We deeply believe that the industry is at a point where it is imperative to guarantee that when talking about a critical parameter such like LWR, everyone speaks the same language, which is not currently the case.

Status 157-nm lithography development at IMEC

157nm lithography is currently considered as the main technology for the manufacturing of critical 65nm node layers and beyond. After a number of potential show stoppers of 157nm have been removed in the last three years, the final phase of development will now start based on the first full-field step and scan exposure systems, that will be inserted in the next 6 months. This paper describes the status and progress of the IMEC 157nm program, that is aiming to remove the remaining 157nm engineering challenges. Despite the fact that the first full field scanner (ASML Micrascan VII) will ship next month to IMEC, the investigation on a number of full-field issues already started. Results on reticle handling including vacuum ultra violet cleaning, on hard pellicle printing and on 157nm resist full field patterning are discussed in this paper.

Status of ArF lithography for the 130-nm technology node

Lithographers are preparing their processes for the 130nm node. About one year ago, first generation full field ArF step and scan systems have been introduced in a number of fabs. These systems have lenses with numerical apertures in the order of 0.6. At the same time, 0.7 NA KrF step and scan systems have been introduced as well. Also last year, KrF resists were shown to be much more mature than ArF resists.