Yuuichiro Yamazaki

Defect criticality index (DCI): a new methodology to significantly improve DOI sampling rate in a 45nm production environment

Increasing inspection sensitivity may be necessary for capturing the smaller defects of interest (DOI) dictated by reduced minimum design features. Unfortunately, higher inspection sensitivity can result in a greater percentage of non-DOI or nuisance defect types during inline monitoring in a mass production environment. Due to the time and effort required, review sampling is usually limited to 50 to 100 defects per wafer. Determining how to select and identify critical defect types under very low sampling rate conditions, so that more yield-relevant defect Paretos can be created after SEM review, has become very important. By associating GDS clip (design layout) information with every defect, and including defect attributes such as size and brightness, a new methodology called Defect Criticality Index (DCI) has demonstrated improved DOI sampling rates.

Investigation of factors causing difference between simulation and real SEM image

As the candidates of factors to consider for accurate Monte Carlo simulation of SEM images, (1) the difference of cross-section between an approximate shape for simple simulation and a real pattern shape, (2) the influence of native oxide growing on a pattern surface, and (3) the potential distribution above the target surface are proposed. Each influence on SEM signal is studied by means of experiments and simulations for a Si trench pattern as a motif. Among these factors, native oxide of about 1nm in thickness has a significant influence that increases SEM signals at the top edge and the slope. We have assumed and discussed models for the native oxide effect.

Maskless lithography: a low-energy electron-beam direct writing system with a common CP aperture and the recent progress

In order to realize SoC (System on a Chip) fabrication at low cost with quick-TAT (Turn-Around-Time) we have proposed a maskless lithography (ML2) strategy, a low-energy electron-beam direct writing (LEEBDW) system with a common character projection (CP) aperture. This paper presents a status report on our proof-of-concept (POC) system. We have developed a compact EB column consisting small electrostatic lenses and deflectors. The experimental results for our POC system indicated that the patterns corresponding to 50nm-node logic devices can be obtained with CP exposure at the incident energy of 5 keV. The technique to reduce the raw process time using a SEM function of LEEBDW system is also reported.

Development of EB inspection system EBeyeM for EUV mask

We are developing new electron beam inspection system, named EBeyeM, which features high speed and high resolution inspection for EUV mask. Because EBeyeM has the projection electron microscope technique, the scan time of EBeyeM is much faster than that of conventional SEM inspection system. We developed prototype of EBeyeM. The aim of prototype system is to prove the concept of EBeyeM and to estimate the specification of system for 2Xnm and 1Xnm EUV mask. In this paper, we describe outline of EBeyeM and performance results of the prototype system. This system has two inspection mode. One is particle inspection and the other is pattern defect inspection. As to the sensitivity of EBeyeM prototype system, the development target is 30nm for the particle inspection mode and 50nm for pattern defect inspection mode. The performance of this system was evaluated. We confirmed the particle inspection mode of the prototype system could detect 30nm PSL(Polystyrene Latex) and the sensitivity was much higher than conventional optical blank inspection system. And we confirmed that the pattern defect sensitivity of the prototype system was around 45nm. It was recognized that both particle inspection mode and pattern defect inspection mode met the development target. It was estimated by the performance results of the prototype system that the specification of EBeyeM would be able to achieve for 2Xnm EUV mask. As to 1Xnm EUV mask, we are considering tool concept to meet the specification.

Advanced lithography: wafer defect scattering analysis at DUV

Considerable effort is directed towards the development of next-generation lithography processes, addressing the need for transistor densification to meet Moores Law. The aggressive design rule shrinkage requires very tight process windows and induces various types of pattern failure with lithography process variations. Since the lithography process is critical in the wafer fabrication process, the requirements for high sensitivity defect detection in the lithography process becomes tighter as design rules shrink. Analysis of the root cause of the defects and of their interaction with various light sources and optics systems configurations for wafer inspection is essential for understanding the detection limits and requirements from advanced inspection systems targeting future lithography inspection applications. In this work, we present an analysis of wafer defects light scattering and detection for a variety of 3xnm design rule resist structures with various polarizations and optics configurations, at the visible, at UV and at DUV wavelengths. The analysis indicates on the defect scattering and inspection performance trends for a variety of resist structures and defect types, and shows that control of the polarization of the optical inspection system is critical for enhanced scattering and detection sensitivity. The analysis is performed also for the 2xnm and 1xnm design rules showing the advantages of polarized DUV illumination over unpolarized and visible illumination.

Experiment and simulation of charging effects in SEM

In semiconductor manufacturing, control of hotspots by optical proximity correction (OPC) requires accurate measurements of shapes and sizes of fabricated features. These measurements are carried out using CD-SEM. In order to measure 2D shapes, edges of features should be clearly defined in all directions. Positions of edges are often unclear because of charging. Depending on the SEM setup and the pattern under measurement, the effect of charging varies. The influence of measurement conditions can be simulated and optimized. A Monte Carlo electron-beam simulation tool was developed, which takes into account electron scattering and charging. CD-SEM imaging of SiO2 lines on Si were studied. In experiment, an effect of contrast tone reversal was found, when beam voltage was varied. The same effect was also found in simulations, where contrast reversal was similar to the experimental results. The time dependence of contrast variation was also studied. A good agreement between simulation and measurement was found. The simulation software proved reliable in predicting SEM images, which makes it an important tool to optimize settings of electron-beam tools. Based on such simulations, optimum conditions of SEM setup can be found.

Characterization of cross sectional profile of nanostructure line grating using small angle x-ray scattering

Grazing incidence small-angle x-ray scattering (GISAXS) is proposed as one of the candidates for characterizing cross section of nanostructure line grating pattern. GISAXS is expected as useful nondestructive tool for characterizing cross section. We developed GISAXS and evaluated the capability using the 4X nm resist line patterns and the 3X nm silicon gate line patterns. The GISAXS results are compared with TEM images to evaluate the reconstruction ability in cross section contour profile. The correlation is investigated between GISAXS and the reference tools such as CD-SEM and TEM in the values of CD, height and bottom corner radius. The static repeatability is also evaluated by performing measurement ten times. We report the results of GISAXS capability as cross sectional metrology tool in actual device of 4X and 3X generation.

SCATT: software to model scatterometry using the rigorous electromagnetic theory

Measurement of critical dimensions and vertical shape of features in semiconductor manufacturing is a critical task. Optical scatterometry proved capable of providing such measurements. In this paper, a software tool to model scatterometry was developed. Rigorous coupled wavelength analysis (RCWA) is used as a physical model. This software does not use fitting coefficients of any specific equipment and therefore is useful in understanding, analysis and optimization of measurements of specific patterns and potential sensitivity of methods and systems to process variation. Special attention was given to improve the accuracy and throughput of simulation; results of comparison to another software proved advantages of the developed software.

Hot Spot Management with Die-to-Database Wafer Inspection System

We constructed hot spot management flow with a die-to-database inspection system that is required for both hot spot extraction accuracy and short development turn-around-time (TAT) in low k1 lithography. The die-to-database inspection system, NGR-2100, has remarkable features for the full chip inspection within reasonable operating time. The system provided higher hot spot extraction accuracy than the conventional optical inspection tool. Also, hot spots extracted by the system could cover all killer hot spots extracted by electrical and physical analysis. In addition, the new hot spot extraction methodology employing the die-to-database inspection system is highly advantageous in that it shortens development TAT by two to four months. In the application to 65nm node CMOS, we verified yield improvement with the new hot spot management flow. Also, the die-to-database inspection system demonstrated excellent interlayer hot spot extraction from the viewpoint of LSI fabrication.

Time dependence of SEM signal due to charging: measurements and simulation using Monte Carlo software

CD-SEM measurement is the main measuring tool of critical dimensions (CD). CD-measurements involve systematic errors that depend on SEM set-up and the pattern. In addition to systematic errors, charging of a wafer plays an important role in CD-SEM and defect inspection tools. Charging dependence of secondary electron emission coefficient which is one of the major charging parameters, was studied. Timing characteristics were measured and then simulated using Monte Carlo model. The measurements and simulations were done for a multiple number of frames and for imaging of a contact hole using pre-charge of a large area. The results of simulation confirmed the measured results. The understanding of the effect helps in tuning the settings of CD-SEM.