Chlorine Plasma Corrosion Testing of Semiconductor Devices

Chlorine plasma corrosion testing is a specialized reliability evaluation that detects and quantifies residual chlorine contamination on semiconductor devices after chlorine-based dry etching and assesses the resulting risk of metallization corrosion. By combining advanced surface analysis techniques with accelerated humidity stress testing, accredited third-party laboratories help manufacturers prevent latent corrosion failures, qualify fabrication processes, and comply with international standards such as IEC 60749 and the JEDEC JESD22 series. This article explains the corrosion mechanism, applicable sample types, test items, analytical methods, and practical applications of chlorine plasma corrosion testing for electronic devices.

Technical Overview

Chlorine-containing plasmas generated from gases such as Cl2, BCl3, HCl, and SiCl4 are widely used in semiconductor manufacturing to etch aluminum and aluminum-alloy interconnects, polysilicon gates, and other device layers with high selectivity and anisotropy. After etching and photoresist stripping steps, however, reactive chlorine species frequently remain adsorbed on die surfaces, bond pads, and sidewall residues. When these residues are exposed to atmospheric moisture, they hydrolyze to form hydrochloric acid and chloride ions that aggressively attack aluminum metallization.

The corrosion reaction produces aluminum chloride, a hygroscopic salt that continuously absorbs water and sustains further attack in an autocatalytic manner. Typical manifestations include darkened or blackened bond pads, pitting of metal lines, corrosion blooms extending across the die surface, formation of conductive dendrites, and eventual electrical opens, shorts, or leakage current degradation. Because these failures often appear only after days, weeks, or months of humid service, chlorine plasma corrosion is classified as a latent defect mechanism that must be controlled through dedicated testing.

Chlorine plasma corrosion testing therefore serves two complementary purposes: quantifying the amount of residual chlorine left on the device, and accelerating the corrosion process under controlled temperature-humidity conditions to evaluate whether the contamination level poses an acceptable reliability risk. The supporting methodologies are aligned with the IEC 60749 series for semiconductor device testing, the IEC 60068-2 environmental testing series, the JEDEC JESD22 test method suite, and the corresponding GB/T 4937 and GB/T 2423 standards.

Testing Samples

Wafers and Bare Dies

Monitor wafers, product wafers, and diced dies collected directly after chlorine-based etch, clean, or passivation steps represent the most common samples. Testing at the wafer level allows fabrication lines to verify the effectiveness of post-etch residue removal and to establish statistical process control limits for residual chlorine.

Packaged Integrated Circuits

Molded and hermetic packages, including QFP, BGA, SOP, and DIP formats, can be evaluated either for chloride originating from mold compounds or, after chemical decapsulation, for residues on the exposed die surface. Packaged units suspected of chlorine-related field failures are typically submitted for combined contamination and corrosion analysis.

Discrete and Optoelectronic Devices

Diodes, transistors, power devices, LED chips, and MEMS structures processed with chlorinated plasma chemistries are tested to confirm that exposed aluminum pads, reflectors, or moving structures are free of corrosive residues before assembly.

Metallization Test Structures and Coupons

Purpose-built comb, serpentine, and bond pad test structures provide sensitive electrical indicators of corrosion initiation and are frequently evaluated alongside production material during process qualification.

Testing Items

Depending on the sample form and the objective of the evaluation, a chlorine plasma corrosion assessment may include the following items:

• Residual surface chlorine concentration, typically reported in ng/cm² of die or pad area
• Extractable chloride ion content determined from aqueous or solvent extraction
• Total chlorine content by combustion ion chromatography for complete sample matrices
• Chemical state analysis of chlorine species, distinguishing inorganic chloride from organochlorine residues
• Corrosion morphology characterization, including pitting, discoloration, dendrite growth, and residue distribution
• Identification of corrosion products such as aluminum chloride, aluminum hydroxide, and aluminum oxide
• Electrical integrity of metallization, covering continuity, leakage current, sheet resistance, and interconnect resistance shifts
• Bond pad and wire bond integrity after accelerated humidity exposure
• Corrosion susceptibility classification under steady-state and cyclic humidity stress

Testing Methods

Surface Chemical Analysis

X-ray photoelectron spectroscopy (XPS) performed in accordance with ISO 15470 is the primary technique for measuring surface chlorine. XPS quantifies chlorine within the outermost few nanometers of the die surface, provides binding-energy information that reveals the chemical state of the chlorine, and supports argon sputter depth profiling to distinguish surface contamination from chlorine embedded in metal or passivation layers. Auger electron spectroscopy (AES), following ISO 15471, offers complementary high-spatial-resolution analysis of localized corrosion sites.

Ion Chromatography Methods

Ion chromatography (IC) quantifies chloride ions extracted from the device surface using ultrapure water or isopropanol-water mixtures, delivering accurate results down to the low ng/cm² range. Combustion ion chromatography (CIC) extends this capability to total chlorine determination by pyrolyzing the whole sample and trapping the evolved halides, which is useful when chlorine may be trapped inside residues or organic matrices.

Electron Microscopy and Microanalysis

Scanning electron microscopy (SEM) documents corrosion morphology, while energy-dispersive X-ray spectroscopy (EDS) maps chlorine and corrosion products at suspect locations. Cross-sectional transmission electron microscopy with EDS may be applied for advanced investigations of intergranular attack within aluminum lines.

Accelerated Humidity Stress Testing

To evaluate corrosion susceptibility directly, samples are subjected to steady-state temperature-humidity bias testing at 85 °C and 85 % RH per IEC 60749 and JEDEC JESD22-A101, highly accelerated stress testing (HAST) at 110–130 °C and 85 % RH per JEDEC JESD22-A110, or damp-heat cycling per IEC 60068-2-30 and the equivalent GB/T 2423 procedures. Post-stress inspection and electrical measurements reveal whether the residual chlorine level is sufficient to initiate corrosion under realistic service conditions.

Electrical Characterization

Continuity, leakage, insulation resistance, and parametric measurements taken before and after environmental stress provide quantitative pass/fail evidence of corrosion-induced degradation and support correlation with measured contamination levels.

Applications

Chlorine plasma corrosion testing supports quality and reliability activities across the entire electronics supply chain:

• Qualification of new etch processes, post-etch cleans, and passivation recipes in wafer fabrication
• Statistical process control of residual chlorine levels during mass production
• Reliability qualification of new devices prior to product release
• Root cause analysis of corrosion-related field returns and production yield losses
• Incoming and outgoing inspection of dies and packaged components by assembly houses and OEMs
• Evaluation of mold compounds, underfills, and cleaning agents that may introduce chloride
• Compliance demonstrations for automotive, industrial, telecommunications, and consumer electronics reliability requirements
• Shelf-life and long-term storage studies for moisture-sensitive devices handled in accordance with JEDEC J-STD-020 and J-STD-033 guidelines

FAQ

Why does chlorine plasma corrosion appear long after manufacturing?

Residual chlorine often remains chemically dormant until the device encounters sufficient moisture. Hydrolysis of the chlorine species generates chloride ions and acid that then attack aluminum, and the hygroscopic aluminum chloride product sustains the reaction autocatalytically, so failures frequently emerge only after extended field exposure.

What level of residual chlorine is acceptable?

Acceptance limits are defined by each manufacturer's internal specifications and are commonly set in the range of a few to a few tens of ng/cm² of die surface, depending on device sensitivity and application requirements. Test reports should therefore compare measured values against the applicable customer or industry limit rather than a universal threshold.

Can packaged devices be tested without decapsulation?

Surface-oriented techniques such as XPS require direct access to the die, so chemical decapsulation is generally performed first. However, extractable chloride testing on the package exterior, humidity stress testing with electrical monitoring, and scanning acoustic microscopy can provide meaningful screening data on intact units.

How is corrosion susceptibility accelerated in the laboratory?

Laboratory acceleration uses elevated temperature and humidity, typically 85 °C/85 % RH for steady-state testing or 110–130 °C/85 % RH for HAST, optionally with applied bias. These conditions reproduce years of humid service exposure within tens to hundreds of hours while allowing corrosion behavior to be measured quantitatively.

Which standards govern chlorine plasma corrosion testing?

There is no single dedicated international standard for this failure mechanism. Testing is instead assembled from recognized building blocks: ISO 15470 and ISO 15471 for surface chemical analysis, IEC 60749 and IEC 60068-2 together with JEDEC JESD22 for environmental and humidity stress, and GB/T 4937 and GB/T 2423 as widely used regional equivalents.

How should samples be submitted for testing?

Samples should be stored in clean, inert containers such as fluoropolymer bags or nitrogen-purged jars immediately after processing, since exposure to ordinary ambient air can alter surface residues and bias results. Information on the etch chemistry, cleaning sequence, and any observed visual anomalies helps the laboratory select the most appropriate analytical strategy.