Semiconductor plasma chlorine corrosion testing evaluates the susceptibility of wafers, metal interconnects, and packaged devices to corrosion caused by residual chlorine species originating from chlorine-based plasma etch processes such as Cl2, BCl3, and HCl plasmas. This testing is essential for qualifying etch recipes, validating post-etch cleaning steps, and preventing latent field failures driven by chloride-induced attack on aluminum and other metallization layers. Accredited third-party laboratories perform these evaluations using surface analysis, ionic contamination measurement, and accelerated environmental stress methods aligned with IEC, ASTM, JEDEC, and IPC standards.
Technical Overview
Chlorine-based plasma etching is a cornerstone of semiconductor fabrication, widely used for patterning polysilicon, aluminum metallization, and stacked metal layers, as well as for descum and cleaning operations in front-end and back-end processes. During etching, reactive chlorinated species combine with exposed metals and silicon to form volatile or semi-volatile chloride compounds. When the plasma step is completed, a fraction of chlorine and metal chloride residue frequently remains adsorbed on wafer surfaces, inside high-aspect-ratio vias and trenches, and beneath photoresist layers.
The corrosion risk becomes acute once the wafer or device is exposed to ambient moisture. Residual chlorides hydrolyze to form localized hydrochloric acid, which aggressively attacks aluminum interconnects, bond pads, and adjacent barrier layers such as TiN and Ti. The resulting damage includes pitting corrosion, galvanic corrosion between dissimilar metals, intergranular attack, and stress-driven corrosion at line edges. Corrosion can initiate within hours to days after etching, producing open circuits, increased line resistance, junction leakage, and degraded bondability well before the product reaches the field.
Semiconductor plasma chlorine corrosion testing is therefore designed to answer three core questions: how much residual chlorine remains on the material or device after processing, how susceptible the metallization and structures are to chlorine-driven corrosion under moisture and temperature stress, and how effective post-etch treatments such as water rinses, in-situ fluorination passivation, or anneals are at eliminating the corrosion mechanism. Testing combines quantitative surface chemistry, morphological inspection, electrical characterization, and accelerated environmental exposure to provide a complete reliability picture.
Testing Samples
Post-Etch Wafers and Patterned Test Structures
Whole wafers, wafer coupons, and dedicated test vehicles are submitted after chlorine plasma etch steps. Common test structures include comb and serpentine interconnect patterns, Kelvin resistance structures, via chains, and blanket films of aluminum, aluminum-copper alloys, Ti/TiN stacks, and polysilicon. These samples allow direct measurement of residual chlorine levels and corrosion sensitivity as a function of etch recipe, chamber condition, and clean sequence.
Packaged Semiconductor Devices and Components
Finished integrated circuits in molded, flip-chip, wafer-level, and ceramic packages can be evaluated where chlorine exposure is suspected during assembly or where chloride contamination affects long-term reliability. Sample types include molded units, leadframes, bond wires, bond pads, solder bumps, and BGA substrates. Testing verifies package robustness against chlorine-containing environments and confirms that assembly chemistries have not introduced harmful chloride residues.
Materials, Films, and Process Consumables
Bare and processed materials such as metallization films, barrier layers, dielectric coatings, photoresists, encapsulants, and molding compounds may be characterized for intrinsic chloride content and corrosion behavior. This supports material selection, supplier qualification, and incoming inspection programs where ionic cleanliness directly influences corrosion risk.
Field Returns and Failure Analysis Units
Devices returned from the field or units that failed burn-in, environmental stress screening, or final test are analyzed for evidence of chlorine-related corrosion. These samples are handled with strict contamination-control protocols to preserve chloride evidence before destructive analysis begins.
Testing Items
Typical test items for semiconductor plasma chlorine corrosion evaluation include:
- Residual chlorine and chloride concentration on surfaces, reported as atomic percentage, areal density, or extracted ion concentration per unit area
- Chloride ionic contamination levels determined by extraction and ion chromatography
- Corrosion morphology classification, including pitting, galvanic corrosion, intergranular attack, filiform corrosion, and line-edge corrosion
- Identification of corrosion products such as aluminum hydroxide, hydrated aluminum chloride, and oxychloride species
- Electrical degradation metrics, including interconnect resistance drift, leakage current, continuity of via and comb-serpentine structures, and bond pad contact resistance
- Time-to-corrosion and corrosion incubation behavior under controlled temperature and humidity conditions
- Effectiveness of post-etch passivation, rinse, and cleaning processes in suppressing chlorine residue
- Distribution and depth profiling of chlorine within vias, trenches, and beneath dielectric layers
Testing Methods
Surface Chemical Analysis
X-ray photoelectron spectroscopy (XPS) is the primary method for quantifying residual chlorine on wafer surfaces and identifying its chemical state, which distinguishes chemisorbed atomic chlorine from metal chloride corrosion precursors. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) provides high-sensitivity chlorine imaging and lateral distribution mapping at sub-micron resolution, making it suitable for localized contamination inside vias and trenches. Auger electron spectroscopy (AES) supplements these techniques for small-area analysis at bond pads and defects.
Ion Chromatography and Ionic Contamination Measurement
Extractable chloride is measured by boiling-water, steam, or solvent extraction followed by ion chromatography, following the general principles of IPC-TM-650 test methods for ionic cleanliness. Results quantify total chloride burden in micrograms per square centimeter or equivalent units, enabling lot-to-lot comparison and clean-process verification.
Morphological and Structural Inspection
Scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDX) is used to inspect bond pads, line edges, and via structures for pitting and corrosion deposits, while EDX element mapping confirms the co-localization of chlorine with corrosion damage. Optical microscopy and automated optical inspection support rapid screening of visible corrosion. Focused ion beam (FIB) cross-sectioning and transmission electron microscopy (TEM) reveal subsurface and interfacial corrosion not visible from the surface.
Accelerated Corrosion and Environmental Stress Testing
Mixed flowing gas (MFG) testing exposes samples to controlled atmospheres containing low parts-per-billion levels of chlorine gas together with humidity and other corrosive gases, following IEC 60068-2-60 (Test Ke) and the practices described in ASTM B827 and ASTM B845. These tests accelerate chloride-driven corrosion mechanisms relevant to semiconductor metallization and contacts. Complementary humidity-bias stress testing is performed per JEDEC JESD22-A101 for steady-state temperature-humidity bias and JESD22-A110 for highly accelerated stress testing (HAST), which amplify moisture-driven chloride attack on interconnects and die surfaces. Electrical measurements before and after stress quantify parametric drift and functional degradation attributable to corrosion.
Electrical and Comparative Susceptibility Testing
Continuity, leakage, and resistance measurements on comb-serpentine and Kelvin structures provide direct correlation between chlorine residue and electrical failure. Comparative drop-tests and controlled-humidity storage comparisons are also used to rank the corrosion susceptibility of different etch recipes, cleans, or material stacks during process development.
Applications
Semiconductor plasma chlorine corrosion testing supports a wide range of engineering and quality activities across the electronics supply chain:
- Etch process window definition, recipe transfer, and plasma tool qualification for chlorine-based processes
- Verification of post-etch residue removal and validation of rinse, passivation, and anneal sequences
- Reliability qualification of new products, where corrosion testing complements standard JEDEC-based qualification flows
- Root cause analysis of electrical failures suspected to involve chloride contamination or moisture-driven corrosion
- Supplier qualification and incoming inspection for wafers, packages, substrates, and molding materials with ionic cleanliness requirements
- Robustness demonstration for automotive, industrial, and aerospace devices operating in chlorine-containing or humid environments
- Advanced packaging and advanced node development, including copper/low-k integration, wafer-level packaging, and high-aspect-ratio etch applications where chloride entrapment is difficult to eliminate
FAQ
Why is chlorine corrosion a particular concern after plasma etching?
Chlorinated plasma species react with exposed aluminum and other metals to form metal chlorides that remain on the surface after the plasma is extinguished. When ambient moisture contacts these residues, hydrolysis produces localized hydrochloric acid that pits and dissolves the metallization. Because the attack is localized and time-dependent, affected wafers or devices may pass immediate electrical test yet fail days or weeks later.
Which standards apply to this testing?
Surface analysis and ionic cleanliness evaluations follow general practices consistent with IPC-TM-650 methodology. Mixed flowing gas corrosion testing is governed by IEC 60068-2-60 (Test Ke), ASTM B827, and ASTM B845. Humidity-bias and accelerated stress tests follow JEDEC JESD22-A101 and JESD22-A110. Accredited third-party laboratories select the appropriate combination based on the failure mechanism under investigation and the applicable product qualification requirements.
What sample sizes and quantities are required?
For surface residue analysis, wafer coupons or sample pieces of a few square centimeters are usually sufficient, while TOF-SIMS and XPS can work with millimeter-scale areas. For environmental stress testing, statistically meaningful groups of packaged units or test structures, typically five to twenty-five per condition, are recommended so that pass-fail decisions can be made with confidence.
How much residual chlorine is considered acceptable?
Acceptance limits depend on the metallization scheme, device technology, and product reliability targets, and are normally defined in internal process specifications. In practice, XPS chlorine levels below approximately 0.5 to 1.0 atomic percent, or chloride extraction results at or near the detection limit, are commonly targeted for corrosion-sensitive aluminum metallization. Testing laboratories report measured values against the client's specified limits.
How long does testing take?
Surface analysis and ion chromatography results are typically available within a few business days to two weeks. Mixed flowing gas exposure and humidity-bias stress tests run from several days to four weeks or longer, depending on the stress level and sample readout plan. Failure analysis projects are scoped individually based on the complexity of the investigation.
Can testing be performed on field-failed units?
Yes. Non-destructive inspection, X-ray, and external surface analysis are performed first to preserve evidence, followed by decapsulation and cross-sectional analysis where required. Chlorine mapping combined with corrosion morphology allows analysts to distinguish plasma-etch-related chloride attack from other failure mechanisms such as flux residue contamination or electrochemical migration.