Yuri Uritsky

Development of Robust AFM Technique for Roughness and Morphology Characterization of Gate Stack Thin Films

Surface roughness and grain morphology are among the critical parameters to be monitored during IC wafer processing, because, with the shrinking device critical dimensions, such parameters become more influential in device performance and manufacturing yield. Among the surface roughness and morphology characterization tools, AFM (atomic force microscope) is unmatched in its combination of height profiling sensitivity and lateral resolution. However, the major problem with AFM is fast tip wear, the effects of which are greatest for thin films deposited in front‐end processing because of the minute surface feature sizes and high lateral resolution required for their imaging. To overcome this drawback, the major factors (tip oscillation amplitude and frequency) that influence the performance of AFM operated in the popular tapping mode were studied. The understanding of the effects of these factors allowed us to device a robust method to operate the AFM in a stable attractive tip‐to‐sample interaction regime ...

Wafer edge polishing process for defect reduction during immersion lithography

The objective of this study was to examine the defect reduction effect of the wafer edge polishing step on the immersion lithography process. The experimental wafers were processed through a typical front end of line device manufacturing process and half of the wafers were processed with the wafer edge polishing just prior to the immersion lithography process. The experimental wafers were then run through two immersion lithography experiments and the defect adders on these wafers were compared and analyzed. The experimental results indicated a strong effect of the edge polishing process on reducing the particle migration from the wafer edge region to the wafer surface during the immersion lithography process.

Depth-Resolved Composition and Chemistry of Ultra-Thin Films by Angle-Resolved X-Ray Photoelectron Spectroscopy

The capabilities of Angle Resolved X‐Ray Photoelectron Spectroscopy, ARXPS, to provide depth‐resolved elemental and chemical state composition for ultra‐thin films are evaluated for two important front end material situations, Silicon Oxynitride (10 to 40A thick) and As Ultra Low Energy (ULE) implant. We conclude that Maximum Entropy constrained model fits to the ARXPS data can provide reliable N depth distributions through the SiON films, in addition to chemistry information. Precise film thickness, and tool matching (N percentage and thickness) to a single angle XPS tool are also demonstrated. For the As implants, the as‐implanted As is too deep to be effectively dealt with using the Maximum Entropy constraint. A 3‐layer constrained model fit to the ARXPS proved successful, however, as demonstrated by comparison to detailed MEIS data on the same films. The broad As distribution, centered at ∼50A below the surface before anneal, sharpens and moves towards the surface, piling up right at the oxide overlay...

Locating defects on wafers for analysis by SEM/EDX, AFM, and other microanalysis techniques

Small-probe analytical tools (SEM/EDX, AFM, AES, TOF-SIMMS, XPS...) are essential for failure analysis in the semiconductor industry. One of the major challenges in this area is in locating the defect within the analytical tool so the defect can be analyzed. The problem is especially difficult for analysis of particles/defects on unpatterned wafers. We have eliminated this problem by developing a new technique called Mark-Assisted Defect Analysis (MADA). The instrument we developed to perform MADA has a robust defect locating capability, and the ability to place micro-sized laser marks in the vicinity of the defect. The marks serve as in-situ landmarks that direct subsequent analysis efforts to the defects location. MADA has enabled numerous analytical techniques to be employed which were previously not possible due to the difficulty in locating the defect within the analytical tool. Examples include the use of multiple analytical techniques for analysis of the same defect, AFM analysis of sub-half-micron particles on bare wafers, SEM/EDX analysis on defects that provide optical contrast but are nearly imperceptible by the SEM, and particle/defect analysis on unpatterned wafers using analytical tools that cannot accept full-wafer samples. In this paper we present an overveiw of the MADA technique and provide several examples of how the technique was employed to solve challenging defect analysis problems on unpatterned wafers.

On problems in obtaining root cause analysis of Al-based particles

Contamination in general and particle defects in particular are the major yield detractors in the semiconductor manufacturing. An efficient approach used in industry toward particle defect reduction is root cause analysis. This analysis aims to determine (using primarily a Scanning Electron Microscope with Energy Dispersive X-ray analysis (SEM/EDX)) a unique particle signature (composition and, in some cases, shape) to track down the particle culprit. If particles have the exact, unique chemical signature of one of the suspected parts (or process features) used in the processing chamber, this approach works remarkably well. If not, the application of additional, more sophisticated, chemistry sensitive analytical techniques is required to reach the root cause of the problem. In this study we utilized SEM/EDX, optical (Raman and Photoluminescence (PL)) and Auger electron spectroscopy (AES) and were able to determine the root cause of the two major particle classes formed in the Si-etch and Reactive Plasma C...

New sample preparation method for improved defect characterization yield on bare wafers

SEM-based defect characterization is a critical technology for wafer manufacturers and others using unpatterned wafers for process monitoring. One of the main drivers of this technology is the need to characterize increasingly smaller defects whose dimensions scale with the shrinking design rules of semiconductor devices. Light-scattering based inspection tools (e.g. KLA/Tencor 6200, SP1) are used to detect defects on the wafer surface and to output a file which contains the xy coordinates of defects relative to the wafers alignment features. The wafer and defect file are then transferred to the SEM review tool. The defect file is transformed into the coordinate system of the SEMs xy stage in two steps: first an approximate transformation is performed based on the wafers orientation on the SEMs stage, and then, after several defects have been located, a more accurate transformation is performed using two or more updated defect coordinates. Review of further defects then proceeds and may include high resolution imaging, cross sectioning, and chemical characterization by EDS. This above method can be tedious and somewhat unreliable. It depends largely on the accuracy of the defect file, which contains both systematic and random error. Searching is often required, and it is generally true that the smaller the defect, the more difficult it is to locate by SEM. In this paper, we will discuss the added value and drawbacks of employing a new sample preparation technique which uses precision surface marking and high accuracy defect mapping to minimize the difficulties of SEM-based defect review on unpatterned wafers.

Comprehensive characterization of micro arcing related particles

Particle identification to determine and eliminate root cause of contamination is a critical step in contamination/defect-free semiconductor manufacturing processes. Currently, a SEM equipped with EDX and a sophisticated navigation system is the most powerful tool in analyzing the chemical composition and morphology of individual sub micron particles on wafer surfaces to determine root cause (Integrated Particle Analysis System or PAS). Limitations of commercial instruments are low throughput and insufficient sensitivity and accuracy for compositional determination of sub 0.1 micron particles. This presentation overviews the types of navigational software enhancements that increase speed and accuracy, the importance of increased EDX sensitivity, and the use of AUGER, and Micro-Raman to assist in elucidating root cause of more complex sub micron particles. In one example Micro-Raman is used to differentiate Al{sub 2}O{sub 3} particles from anodized, oxidized aluminium or ceramic origins by identifying differences in trace impurities. Additionally an overview describing the use of a confocal laser microscope to rapidly identify differentiating characteristics of small and/or low profile defects collecting characteristic information is not possible by conventional analytical particle counting tools.

Low tip damage AFM technique development for nano structures characterization

Ambient dynamic mode (tapping mode or intermittent-contact mode) AFM imaging has been used extensively for the characterization of the topography of nano structures. However, the results are beset with artifacts, because hard tapping of the AFM tip on sample surface usually causes premature tip damage. Through careful study of the cantilever amplitude and phase signals as functions of tip-to-sample distance, principle of non-contact AFM operation was discovered to enable high resolution and low tip damage AFM image acquisition [1, 2]. However, current study discovers that the conventional way of acquiring amplitude and phase versus distance curves gives erroneous non-contact operating range, because the tip gets damaged during the data acquisition process. A new technique is developed to reliably map the operating parameters of an intact tip that ensures the AFM be operated with the correct non-contact settings. Two examples are given to illustrate the successful applications of this new technique. The first example involves the size characterization of polystyrene latex (PSL) nano particles used for light scattering tool calibration. The second example is the development of robust recipes for the measurement of the depth of phase-shift mask trenches.

Characterization of Barrier Layer Phase and Morphology As a Function of Differing Dielectric Substrate Conditions by AFM and Grazing Angle XRD

Tantalum (Ta) metal has emerged as one of the leading materials of choice for diffusion barrier applications in Cu‐damascene interconnects. For successful implementation, the microstructure, the electrical property and the surface roughness of the barrier layer have to be controlled. To satisfy such needs, atomic force microscopy (AFM) and X‐ray diffraction (XRD) techniques have been employed to monitor the surface roughness and crystal phase of the PVD Ta thin film deposited on low‐k dielectrics. XRD results show that the population of the two different Ta crystal phases, α and β, depends on substrate material, surface pretreatment prior to thin film deposition and deposition conditions. AFM results reveal that surface roughness of the thin barrier layer is mainly determined by the starting substrate surface roughness. Also, AFM surface imaging discovered that each Ta crystal phase possesses a unique surface morphology. Therefore, the population of the Ta crystal phases can be crudely quantified by perfo...

Full wafer particle defect characterization

The capabilities available for particle defect characterization on 200 mm and 300 mm wafers are discussed in relation to the original detection procedure (light scattering) and the ITRS requirements. A number of advanced characterization techniques (SEM/EDX, FIB, SAM, TOF-SIMS, Optical/Raman, AFM) are available in 300 mm configuration suitable for off-line characterization. Examples of use are presented. For on-line particle characterization (i.e. in the fab) only SEM/EDX has approached the stage of robustness, automation, and expert-free use needed for incorporation. It is beginning to replace optical as the particle review method.