TEA Systems Weir PW Solutions http://www.TEAsystems.com
TEA Systems process Solution - Rapid and cost effective monitor of Reticle Haze
Controlling Process Reticle-Haze & Lens Film buildup
during the production cycle
See Also: Weir PW Brochure,
Related Tutorials: Focus and Depth-of-Focus Uniformity
Publication: Monitoring Feature Profiles for Lens Film Deposits
Applications: Reticle front & backside haze, pellicle degradation, lens contamination, lens film deposition, illuminator problems.
Other tutorials in the user's section:
Accurate and cost effective method of reticle-haze and dose uniformity measurement using Weir PW for analysis and Weir DMA for automated data monitor.
Keywords: Dose Map, Dose, Exposure-Dose, Exposure, Contour, Process window, Reticle Haze, Yield Enhancement, lens contamination
Table of Contents
Weir PW Reticle Haze monitor software provides the earliest detection and mapping of the onset of image degradation due to both front and backside reticle haze. Lens film contamination can also be monitored.
The Reticle Haze monitor detects image degradation in the earliest phases of contamination. A Weir PW Reticle Haze inspection is performed on a test wafer that has been measured by offline or in-situ OCD or CD-SEM metrology. Inspection and analysis are performed in one-tenth of the time required for direct inspection of the reticle using automated inspection hardware costing over $1 million dollars. The technique requires the use of a focus-dose exposure matrix of the product reticle, a metrology tool and Weir PW software. The same data can be used to calculate and monitor process window settings thereby saving additional time and money.
Reticle haze is a problem that occurs in DUV and lower wavelength environments. Reticle haze was initially observed as a reticle back-side phenomenon but has recently been recognized as a contaminant that can appear on the chrome or 'object' side of the reticle. Haze is a contaminant that is caused by mask-making chemicals, process residue, reticle-container outgassing or through localized high-energy interactions with environmental gases in the exposure tool environment.
Reticle haze on DUV process tools is rising in significance as a serious source of yield and capacity loss in device manufacturing. Reticle front or back-side haze causes non-uniform transmission loss across the reticle. Observed as a gradual shift in exposure-dose, the effects increasingly degrade imaging with time and usage.
A similar response for degradation of exposure-dose can be encountered with the onset of film depositions on the final lens of the exposure tool. Film deposition is created by photoresist or other chemical radical dissolution during latent image formation that results in a subsequent deposition of vapor-phase polymers on the lens-surface. Lens films are less localized in their appearance than the haze phenomenon.
Hardware-based reticle inspection tools, such as KLA-Tencor's TeraStar , currently offer a direct method of reticle inspection that takes over 3 hours using a 90 nanometer (nm) pixel size. The scan process relies on the tool's ability to visually detect the presence of very thin films (the haze) at a different wavelength than production-device exposure.
A much more cost effective and precise method is to use Weir PW software with already existing Critical Dimension (CD) metrology tools.
Weir PW area sampled searches for the onset of haze are very much faster than inspection of the whole reticle and can be performed in less than 20 minutes exposure and metrology time. The technique is more exact than die-to-database comparisons or film scanning because the analysis directly measures the dose and feature profile changes caused by the haze. Dose variation and feature size are the critical yield factors for device yield and wafer-fab capacity. Here we highlight "capacity" because larger doses caused by haze not only reduces yield by also reduce the wafer throughput of the exposure tool.
Device Yield is lowered because haze growth is gradual, continuous with use and influences CD distributions in a non-uniform manner. As a results features are produced at the wrong size as the size of the process window slowly degrades. Lens aberrations also interacts differently with the haze resulting in additional degradation of the CD uniformity and profiles.
Weir PW Haze Detection does not require special test recipes or techniques. The product reticle is exposed onto a normal focus-dose matrix wafer that can also be used to setup and validate the current Process Window setting. Data is then measured and analyzed by Weir PW or Weir DMA, as an automated dose-uniformity analysis, to determine the presence and level of Reticle Haze or lens surface contamination.
Depending upon the cause of reticle haze formation, haze can form on arbitrary sections of the reticle however that does not mean that an analysis needs to measure all sites on the reticle. Haze is not confined to only a single line or reticle site. Haze is a process phenomenon that will build up over areas of the reticle initially covering several centimeters. The difficulty in detection is that haze build-up is gradual so unless it is rigorously monitored OR compared against a standard it cannot be seen until the effects of the dose-reduction are great enough to significantly influence yields.
A typical analysis uses OCD or CD-SEM Metrology to measure a total of nine ( 9 ) sites on the reticle and fifteen ( 15 ) exposure on the focus-dose matrix wafer for a total of 135 measurement. Greater areas on the reticle can be measured with little loss in time. The figure shown below illustrate a typical dose-uniformity contour of a reticle with and without contaminant hazing. This same data sample also is used to confirm the current placement and characteristics of the process window.
A CD SEM is the slowest and least appropriate tool since it measures a small area on a single feature profile. A scatterometer or ellipsometer (i.e. OCD tool) is preferred since it measures a target that consists of a 50x50 micron square area of lines and spaces for each measurement. The probability of finding the early onset of haze is thus greater. The OCD tool is faster than a CD-SEM since it runs at about 3 seconds per measurement with no vacuum pumpdown. So metrology on an OCD tool would be 135 * 3 = 405 seconds = 6 to 10 minutes. Weir PW or Weir DMA analysis requires less than 3 additional minutes. This analysis compares with 3 to 5 hours on a dedicated inspection tool.
Weir PW and Weir DMA are available for use on Windows 2000 and Windows XP. System should be a Pentium IV or later with 1GHz clock speed. 1.5 Gigabytes internal free drive space is needed for data and software. Fixed-node or floating node (multi-user) licenses are available.
Report Publishing to the WebDoseUniformity_atBF
Weir Reports are stored on Microsoft Excel spreadsheet format. This means you can publish modify, annotate and publish them to any web site by the the "File/SaveAs" menu command and selecting the "html" format. Weir PW can easily plot similar plots for the Focus, EL% and DoF variables.
Moving to Other Weir Interfaces
Weir program interfaces work interactively. The user can move from Weir Main to any of the other five interfaces using the button-bar keys or the menu. Data is automatically transferred between interfaces. Any interface can load and, using the Weir Layout Library, configure exposure layouts for the arrays. Only the Weir Main interface can create Layout and Reticle Library Entries and Macros for the Weir Daily Monitor and DMA programs.
TEA Systems offers products to model films, photomasks, wafers, feature profiles, process and lens data for characterization and setup of semiconductor design, simulators, tools and the process.
TEA Systems, a privately held corporation since 1988, specializes in advanced, intelligent modeling of the semiconductor process and toolset. Products from TEA allow the user to decouple process, tool and random perturbations for enhanced process setup & control.
TEA Systems products include:
Weir PSFM: Full-wafer/field/scan analysis tool for FOCUS derived from proprietary defocus sensitive features.
Weir PW: Reticle/Full-wafer/field/scan analysis for any metrology with advanced process window capabilities for both wafer and photomask control.
Weir DMA: Macro Automation interface for Weir PSFM and Weir PW for external program calling, automated data gathering or one-button analysis of commonly used sequences. Includes data trending and web interface.
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