Dr. Ray J. Hoobler Profile

Dr. Ray J. Hoobler

Product Marketing Manager at KLA Corp

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Publications (6)

Proceedings Article | 12 May 2005 Paper

Models for reticle performance and comparison of direct measurement

Terrence Zavecz, Ray Hoobler

Proceedings Volume 5754, (2005) https://doi.org/10.1117/12.600235

KEYWORDS: Reticles, Semiconducting wafers, Photomasks, Metrology, Data modeling, Photoresist materials, Scanning electron microscopy, Performance modeling, Systems modeling, Image processing

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Proceedings Article | 20 August 2004 Paper

Photomask ADI, AEI, and QA measurements using normal incidence optical-CD metrology

Ebru Apak, T. Sarathy, William McGahan, Pablo Rovira, Ray Hoobler

Proceedings Volume 5446, (2004) https://doi.org/10.1117/12.557809

KEYWORDS: Photomasks, Reflectivity, Pellicles, Quartz, Photoresist materials, Data modeling, Metrology, Diffraction, Diffraction gratings, Critical dimension metrology

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Proceedings Article | 29 April 2004 Paper

Intra-wafer CDU characterization to determine process and focus contributions based on scatterometry metrology

Mircea Dusa, Richard Moerman, Bhanwar Singh, Paul Friedberg, Ray Hoobler, Terry Zavecs

Proceedings Volume 5378, (2004) https://doi.org/10.1117/12.543786

KEYWORDS: Semiconducting wafers, Critical dimension metrology, Lithography, Metrology, Error analysis, Scatterometry, Reticles, Photoresist processing, Statistical analysis, Finite element methods

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Current advanced lithography processes are based on a Critical Dimension (CD) budget of 10nm or less with errors caused by exposure tool, wafer substrate, wafer process, and reticle. As such, allowable CD variation across wafer becomes an important parameter to understand, control and minimize. Three sources of errors have an effect on CD Uniformity (CDU) budget, run-to-run (R2R), wafer-to-wafer (W2W) and intra-wafer. While R2R and W2W components are characterized and compensation conrol techniques were developed to minimize their contribution the intra-wafer component is more or less ignored with the consequence that its sources of errors have not been characterized and no compensation technique is available. In this paper, we propose an approach to analyze intra-wafer CD sources of variations identifying the non-random CDU behavior and connect this with disturbances caused by processing errors described by their wafer spatial coordinates. We defined a process error as disturbance and its effect as a feature response. We study the impact of modeling spatial distribution of a feature response as calculated by diffractive optical CD metrology (scatterometry) and relate it to a programmed process disturbance. Process disturbances are classified in terms of time characteristics that define their spatial distribution. We demonstrated feature response to a disturbance behavior as statistical values as well as spatial profile. We identified that CD response is not sufficient to determine the sources of process disturbance and accordingly added responses from other features, which add to detection of CDU sources of error. The added respsonses came from scatterometry principle based on model difinition of a litho patter described by its shape with characteristic features: bottom CD, resist thickness, sidewall angle and bottom antireflective layer thickness. Our results show that process errors with continuous intra-wafer variation, such as PEB and BARC thickness have larger effects on CDU compared to process errors with discrete intra-wafer behavior, such as dose and defocus. Correlation between multiple feature responses to process disturbance was characterized as spatial covariance between CD to resist thickness and CD to SWA. Spatial feature covariance enhances capability to infer sources of process disturbance from metrology data.

Proceedings Article | 17 December 2003 Paper

Optical critical dimension (OCD) measurments for profile monitoring and control: applications for mask inspection and fabrication

Ray Hoobler, Ebru Apak

Proceedings Volume 5256, (2003) https://doi.org/10.1117/12.517931

KEYWORDS: Etching, Reflectivity, Photomasks, Photoresist materials, Inspection, Process control, Quartz, Critical dimension metrology, Control systems, Spectroscopic ellipsometry

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Optical Critical Dimension (OCD) measurements using Normal-Incidence Spectroscopic Ellipsometry (polarized reflectance) allow for the separation of transverse electric and transverse magnetic modes of light reflected from an anisotropic sample as found in a periodic grating structure. This can provide the means for determining linewidths and analyzing complex profiles for a variety of structures found in mask fabrication. The normal-incidence spectroscopic ellipsometer maintains much of the simplicity in mechanical design found in a standard reflectometer and the additional polarizing element has no effect on the footprint making the system amenable for integration, inline monitoring and advanced process control. The rigourous coupled wave analysis (RCWA) method provides an exact method for calculating the diffraction of electromagnetic waves by periodic grating structures. We have extended OCD technology to critical measurement points in the mask fabrication process: After development inspection (ADI), where OCD evaluates mask writer performance and after etch inspection (AEI) for monitoring and control of etched quartz structures for phase shift applications. The determination of important, critical dimensions via optical techniques is appealing for several reasons: the method is non-destructive to photoresist and the sample is not subject to charging effects; the technique is capable of measuring the critical dimensions of grating structures down to approximately 40 nm; minimal facilities are required for installation (no high vacuum, cooling or shielding of electromagnetic fields); like optical thin film metrology, OCD technology can be integrated into process tools enabling Advanced Process Control (APC) of the etch process. Results will be presented showing the capabilities of OCD metrology for ADI and AEI applications. Comparisons will be made with both CD-SEM and X-SEM and the application to monitoring/controlling the quartz etch process will be discussed.

Proceedings Article | 15 July 2003 Paper

Depth profile characterization of hydrogen implanted silicon using spectroscopic ellipsometry

Thomas Gubiotti, David Jacy, Ray Hoobler

Proceedings Volume 5041, (2003) https://doi.org/10.1117/12.499100

KEYWORDS: Silicon, Hydrogen, Semiconducting wafers, Data modeling, Ions, Metrology, Ion beams, Silica, Nondestructive evaluation, Ellipsometry

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Proceedings Article | 16 July 2002 Paper

Characterization of interfacial layers and surface roughness using spectroscopic reflectance, spectroscopic ellipsometry, and atomic force microscopy

Ray Hoobler, Rahul Korlahalli, Ed Boltich, Joe Serafin

Proceedings Volume 4689, (2002) https://doi.org/10.1117/12.473520

KEYWORDS: Reflectance spectroscopy, Silica, Surface roughness, Spectroscopy, Reflectivity, Data modeling, Atomic force microscopy, Aluminum, Oxides, Spectroscopic ellipsometry

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In modeling the optical properties of thin films, incorporation of roughness or interfacial layers is often required in the analysis of spectroscopic ellipsometric and spectroscopic reflectance data in order to achieve good agreement between the model and experimental data. The location of the roughness or interfacial layer is usually discernable from the spectroscopic ellipsometric data; however, their location is not always unambiguous from spectroscopic reflectance data. In the current work, we have explored how the spectroscopic determination of the interfacial and surface roughness layers correlates with direct measurements of the surface using atomic force microscopy (AFM). Spectroscopic reflectance and subsequent analysis of several thick films demonstrate the difficulty in placement of a roughness or interfacial layer in the optical model. The samples involved in this study have films deposited on metal substrates and include stainless steel and aluminum. We have used AFM to directly measure the surface roughness in order to improve the optical characterization and model development. As an example, we have examined an 8,000 nm silicon dioxide film on stainless steel. Models with the placement of an interfacial layer between the substrate and film, or placement of a roughness layer at the surface produce fits with nearly equivalent mean squared error values; however, the surface roughness layer is nearly an order of magnitude larger than that of the interfacial layer. Analysis using AFM shows a surface topography consistent with the magnitude of the interfacial roughness layer. In this example, the silicon dioxide layer was too thick for standard spectroscopic ellipsometry and spectroscopic reflectance was used exclusively in the analysis. For several samples with silicon dioxide on an aluminum substrate, an interfacial layer was necessary to produce a good model fit with the experimental data. These films of 500-1,000 nm thickness were analyzed using both spectroscopic ellipsometry and spectroscopic reflectance. The analysis for all films shows good agreement between the interfacial roughnesses calculated using an effective medium approximation (EMA) with AFM measurements, indicating the transfer or correlation of the substrate roughness to the surface.

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