Micro-Contamination Control and Risk Management

Technology transitions are a challenge. As the semiconductor industry now requires nanoscale control, achieving and maintaining yield targets are increasingly complex. In part, this is due to higher device performance variability at advance nodes. Everything from fab air quality, chamber part cleanliness, wafer quality, chemical and water purity to the cleanroom consumables can contribute to process excursions. Ensuring that a robust micro-contamination analytical testing and monitoring process is developed and implemented is a key requirement to minimize the fab variability.

ChemTrace has over 25 years of experience in micro-contamination control and risk management to improve fab results. Our highly qualified chemists, engineers and technologists engage closely with our customers’ process and equipment engineers, micro-contamination experts, internal laboratory staff, facility and quality engineers, field operations, R&D staff, chemists and physicists. Broad-based engagements enable us to customize analytical solutions that support robust contamination monitoring programs. The ability to monitor the full value chain is essential, and our ChemTrace experts understand the unique requirements of the construction, supply chain, chemical delivery, and chip manufacturing processes.

ChemTrace provides analytical services through a network of accredited commercial testing laboratories located around the globe. These Advance Accredited ChemTrace Labs (AACL) maintain cleanrooms and utilize class 100 or better mini-environments to provide contamination-free preparation and testing of high purity samples. This ensures accurate and precise identification and quantification of the samples sent to our laboratories for analysis.

Fundamental to fab performance and device yield is managing the airborne molecular contamination (AMC) of the cleanroom environment. Ensuring AMC levels are below targets requires identification of the impact all the materials are used in the construction, operation and maintenance of the fab have on the overall contamination load.

A fab’s in-line air quality monitoring provides real-time identification of deviation from the baseline. However, this monitoring methodology lacks the sensitivity and analytical breadth to monitor sub-detection contamination level increases and trigger maintenance events.

Our Advance Accredited ChemTrace Labs (AACL) provide comprehensive cleanroom AMC monitoring programs for metallic, ionic and organic contamination to enable the fab to remain consistently and reliably below AMC target levels. Benefits of AMC monitoring includes identification of required preventative maintenance activities which lead to reduction of cleanroom cost-of-ownership and identification of AMC-related wafer contamination and scrap sources.

In addition to overall cleanroom monitoring, UCT offers processes and methodologies to monitor process tool environment AMC. Our micro-contamination experts provide guidance for monitoring and control of AMC to mitigate excursions, whether monitoring inspection and lithography tools to ensure the local environment contamination levels are low enough to support reliable measurements or troubleshooting contamination issues in a deposition or removal chamber.

Airborne Molecular Contamination Sources
  • Paints, walls, floor tiles, HEPA/ULPA filters, curtains, gel, sealants, potting compounds, air handling systems, cleanroom wipes, cleanroom gloves, wet benches, etc.
Potential AMC Contamination/Issues
  • Organic contamination of wafer surface
    • Wafer hazing and surface layers formation
    • Poor film adhesion
    • Modification to surface wetting behavior
  • Particle on the wafer surfaces
    • Electrical shorts
    • Current leakage
    • Lithography defects
  • Trace metals, ion and cation contamination
    • Degraded gate oxide integrity
    • Counter doping
  • Equipment impacts:
    • Hazing of optics and masks
    • Corrosion of instruments, including wiring, hard drive disks and substrates

High purity chemicals are critical to delivering high device yield. In addition to understanding the concentration of the chemical, fully characterizing and controlling the impurity profile is essential to reducing semiconductor variability. This requires identifying not only impurities present after production, but contaminants from the entire chemical packaging, transportation and fab bulk chemical distribution systems (BCDS).

The rapid adoption of new elements into the semiconductor manufacturing process increases the need to understand impurity profile across the entire production flow. The risk of bulk diffusion or electro-migration of impurities to these newly introduced films and carefully constructed compositional profiles increases the value of routine monitoring of impurity concentration levels. Historically, small variations may not have impacted overall device functionality but today could contribute to performance variability.

In addition, the long-term stability of chemical delivery systems for these new, often expensive and highly complex modules or solutions may not be fully characterized. Establishing a monitoring process will assist in identifying possible reactivity of adsorbed chemicals on delivery lines or storage containers as well as decomposition byproducts and agglomeration behavior and maintain high purity chemical delivery across the production lifetime of the tool.

Our Advance Accredited ChemTrace Labs deliver traceability across the full value chain, from initial production to on-wafer film purity. Our suite of analytical testing techniques enables us to provide sensitivities meeting today’s requirements.

Process chemicals:
  • CVD: precursors, dopants (TEB), reactant
  • ALD: precursor, reactant
  • Etch: etchant
  • Litho: photoresist
  • Clean: etchant, surfactants, solvents
  • CMP: slurry, surfactants
  • Plating: electro-chemical or electro-less solution
  • Implant: dopants
  • Raw wafer manufacturing: surfactants
Contamination sources
  • Chemical production
    • Raw materials
    • Equipment
    • Baselining & lot-to-lot variability
  • Chemical containment
    • Containers (drums, totes, canisters)
    • Seals
    • Valves & valve manifold boxes (VMB)
    • Shelf-life studies
    • Transportation efficacy
  • Within-fab distribution
    • Bulk chemical delivery system: pipes, valves & VMB
    • Process tool
    • Chemical storage: bulk, point-of-use and day tanks
Potential contamination/Issues
  • Gaseous chemicals
    • Concentration
    • Particle count, size distribution and composition
    • Trace metals & ionics
    • Particles
    • Organic impurities
  • Wet Chemicals & Slurries
    • Trace metals & ionics
    • Particle count, size distribution, and composition
    • Solvent impurity & moisture content
    • Concentration variation (incl. dilution/blending).
    • Organic impurities

Cleanroom materials are one of the most challenging elements of micro-contamination management. There are semiconductor-grade materials available, but producers typically manufacture for a variety of industries and are challenged to operate with required high process-control levels. Re-qualification and re-certification of these materials for advanced nodes typically does not fall within the scope of work of a production team and, at best, is a late-stage assessment.

Although these materials seldom come in direct contact with the process wafer, they introduce volatile organic compounds, ionics and trace metals into the cleanroom environment that can transfer to the wafers. Our series of Advance Accredited ChemTrace Labs have decades of experience in testing the broad variety of cleanroom materials including:

  • Construction: paint, caulking, sealants, tiles, filters
  • Packaging: part transfer boxes, vacuum packaging plastics
  • Cleaning: cleanroom wipes, gloves, gowns

UCT’s established processes ensure fast and accurate assessments of common semiconductor specs like trace metal, ionic, outgassed organics and particles that may be lacking in supplier specifications. This knowledge base provides a databank of critical properties and the capability to rank suppliers by target specs. Monitoring programs validate cleanliness requirements of products from established suppliers.

Every wafer produced has a different path through the fab (or lab) when tracked to the process chamber-level. When considering contributors to device performance variability, the processing chamber is a key control point that needs to be assessed. As ceramic, metal and polymeric components wear and are replaced across the lifetime of the tool, we must understand and control the chamber environment, characterizing and systematically monitoring at the chamber- and tool-level. As critical dimensions shrink, this moved beyond something that supports consistently high yields to something that is critical for managing device variability.

Particles, organics, trace metals, anions and cations are possible forms of micro-contamination that occur within chamber environments. Advance Accredited ChemTrace Labs participate in the analysis of components in all stages of the production process – from cleanliness validation of a cleaned machined part to the in-chamber qualification of a part and/or process, to the certification of analysis (COA) of a cleaned, recycled part that will return into the fab (or lab) environment. Beyond the analysis of a single part, UCT engineers and technologists are experts in Parts Quality Monitoring Programs (PQMP™) which use statistical evaluation methodologies to set up cleanliness specifications with control limits to reduce variability.

Key analysis support
  • Part manufacturing & spare parts: ensures all production residues removed
  • Part baselining: “out-of-the-bag” cleanliness verification
  • Part recycling: validation that part meets target cleanliness standards
  • Chamber troubleshooting: identification and root cause analysis
  • Control limit set up: identification of key contamination contributors and acceptable limits
  • Supply Chain qualification: establish benchmark cleanliness capability

Ultra-pure water (UPW) has direct contact with the wafer surface during multiple production steps due to its use in wet chemical dilution, wafer cleaning and immersion lithography operation. In part, tighter trace metal specifications are emerging to control performance and minimize variability of new oxide films in the front-end-of-line transistor formation. More stringent particle specs are required as thinner films and tighter feature spacing are introduced with node transitions. The purity requirements and contamination risks to yield vary by process, making high sensitivity, UPW analysis critical for overall process control.

To ensure point-of-use purity specifications are consistently met, our Advance Accredited ChemTrace Labs offer test methods for monitoring and identifying multi-point sampling requirements. Our tests supplement inline monitoring devices by verifying correlation between inline and offline techniques.

The sensitivity of ChemTrace analysis offerings is aligned to SEMI’s F63-0918 guidelines; however, can be customized to meet customer-specific specifications which can be more stringent than published standards.

Implementing a systematic ultra-pure water monitoring processes ensures yield limiters as well as incoming quality and distribution issues are identified and addressed.

Foundational to high yield is wafer cleanliness. At advanced nodes, reducing variability is often a critical factor for establishing and implementing micro-contamination specifications. The variability control can be related to the virgin wafer quality; more typically, however, it is closely tied to process recipe development and process chamber performance. New or optimized processes have multiple contributors to wafer micro-contamination variability:

  • Cleanroom environment: airborne molecular contamination, handling/inspection contamination
  • Chamber parts: cleanliness, coating quality, byproduct adhesion
  • Process recipe: gas purity, film quality, bevel deposition

Bevel deposition and cleanliness are increasingly critical primarily to avoid performance impacts in subsequent production steps. These impacts include film delamination and peeling as well as particle generation. In addition to typical shorting and bridging issues of surface particles, the particles created by metal films contribute to arcing events resulting in structural damage to the wafer. Increasingly, bevel etch steps are being introduced and characterization of the efficacy of these process steps is a growing area of analysis.

Our Advance Accredited ChemTrace Labs (AACL) provide wafer surface analysis techniques with high sensitivity for trace metals, organics and particles ─ contaminants that can directly impact device performance. Whether the area of concern is the full wafer surface, a target surface region or a profile into the film, our suite of techniques delivers results.

We are experts in the combination of witness wafers and process wafers required to address the broad spectrum of fab requirements. Whether you are seeking a comprehensive micro-contamination profile, enabling high-impact monitoring protocols to be implemented, baselining a chamber or troubleshooting a production issue, ChemTrace has the analytical support our customers require.

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