Inductively coupled plasma chlorine corrosion testing (ICP-Cl) is an accelerated reliability evaluation in which semiconductor wafers, devices, and material samples are exposed to reactive chlorine radicals generated by a radio-frequency inductively coupled plasma. The method is widely used by accredited third-party laboratories and in-house reliability teams to assess the corrosion resistance of aluminum and copper metallization, bond pads, passivation layers, and packaging materials. This article explains the test principle, typical sample types, evaluated parameters, operating procedures, industrial applications, and frequently asked questions.
Technical Overview
Inductively coupled plasma chlorine corrosion testing is a specialized accelerated corrosion technique developed for the semiconductor and microelectronics industries. In this test, a process gas such as chlorine or a boron trichloride/chlorine mixture is dissociated inside a vacuum chamber by a radio-frequency inductively coupled plasma (ICP) source, typically operating at 13.56 MHz. The plasma produces a high density of reactive chlorine radicals, ions, and energetic species that chemically attack exposed metal surfaces, forming volatile or hygroscopic metal chlorides such as aluminum chloride. When these chlorides absorb traces of moisture, they hydrolyze into acidic byproducts that drive rapid electrochemical corrosion of thin-film interconnects.
The test exists because chlorine-bearing plasmas are routinely used in wafer fabrication for etching aluminum, copper, and dielectric layers. Residual chlorine left on the die surface after etching or cleaning is one of the most aggressive contaminants in microelectronics and is a well-documented cause of pad corrosion, interconnect leakage, and field failures. By deliberately exposing samples to a controlled chlorine plasma environment, the ICP-Cl test amplifies latent corrosion mechanisms in a short time, allowing manufacturers to qualify processes, screen weak lots, and compare materials with high sensitivity and good repeatability.
- Test principle: controlled exposure to reactive chlorine species generated by an inductively coupled RF plasma source
- Main failure mechanism simulated: chlorine residue driven chemical and electrochemical corrosion of thin-film metallization
- Typical equipment: ICP etching chamber with RF generator, mass flow controllers for Cl2/BCl3/Ar/N2, vacuum pumping system, and heated or biased sample stage
- Standard framework: specific exposure recipes are usually defined by customer or foundry specifications, while the general philosophy of accelerated corrosion assessment aligns with environmental testing families such as IEC 60749 and its national equivalent GB/T 4937 for semiconductor devices
- Execution: performed in accredited third-party laboratories or in-house reliability centers equipped with toxic gas handling infrastructure
Testing Samples
Wafer-Level Test Structures
Dedicated test vehicles such as serpentine and comb interdigitated patterns, metal meander lines, via chains, and bond pad arrays are the most common samples. These structures translate localized corrosion directly into measurable leakage current or resistance shift, providing quantitative sensitivity to minute attack. Full wafers up to 300 mm, wafer pieces, and reticle-level coupons can all be accommodated.
Packaged Semiconductor Devices
Molded integrated circuits, sensors, discrete power devices, and cavity packages may be subjected to plasma exposure followed by humidity dwell to evaluate whether encapsulation and passivation effectively block the migration of corrosive species toward the die surface. Delidded or decapsulated units are often used when the objective is to inspect die-level metallization directly.
Bare Die and Chip Samples
Sawn die, known-good die intended for multi-chip modules, and flip-chip bumps can be tested to verify surface cleanliness after dicing and to confirm the corrosion immunity of pad metallization and under-bump metallurgy prior to assembly.
Material Coupons and Thin Films
Deposited metal thin films, barrier and liner stacks such as tantalum-based layers for copper, seed layers, capping films, passivation coatings, and molding compound coupons are exposed to rank materials, compare suppliers, or validate new process modules against corrosion attack.
Testing Items
The evaluation scope of an ICP-Cl campaign typically combines electrical, morphological, and compositional measurements, selected according to the applicable specification:
- Visual and optical microscopic inspection for corrosion spots, pitting, discoloration, and pad darkening
- Scanning electron microscopy observation of corrosion morphology and attack localization at grain boundaries, pad edges, or passivation openings
- Energy dispersive spectroscopy identification of chlorine-containing corrosion products on attacked regions
- Electrical leakage current measurement on comb and serpentine structures before and after exposure
- Line resistance and via chain resistance shift quantification for interconnect reliability assessment
- Continuity and contact resistance verification of bond pads and probe points
- Passivation and barrier layer integrity verification against chlorine permeation and undercut attack
- Film thickness and surface roughness change measurement on material coupons
- Corrosion classification and rating against defined acceptance criteria supplied by the customer
Testing Methods
Test Procedure
A typical test flow begins with incoming inspection and baseline characterization of the samples, including optical imaging and electrical parametric measurement. Samples are then loaded onto the chamber stage, the chamber is evacuated, and process gases are introduced at controlled flow rates. The ICP source is ignited to generate the reactive chlorine environment, and the samples are exposed for a defined duration under specified pressure, power, and substrate temperature conditions. Optional electrical bias can be applied to test structures during exposure to replicate powered operating conditions. After exposure, samples are transferred under protective dry conditions, optionally subjected to a controlled humidity dwell to activate hydrolysis of adsorbed chlorides, and finally inspected and electrically re-measured within the time window defined by the specification.
Typical Exposure Conditions
Exact recipes vary by specification, but representative operating windows include the following ranges, which are adjusted to balance acceleration with realistic failure mechanisms:
- RF source power: several hundred watts, selected to set chlorine radical density
- Process gases: chlorine, boron trichloride mixtures, often diluted with argon or nitrogen
- Chamber pressure: low millitorr range typical of ICP chambers
- Substrate temperature: ambient to moderately elevated setpoints
- Exposure time: from a few minutes up to tens of minutes depending on acceleration target
- Optional bias: fixed voltage applied across test structures during exposure
- Post-exposure dwell: controlled temperature and humidity conditioning to promote chloride hydrolysis
Post-Exposure Evaluation and Judgement
Corroded samples are first examined non-destructively by optical microscopy to map corrosion distribution, followed by electron microscopy and elemental analysis to confirm chlorine involvement. Electrical structures are re-measured under the same conditions as baseline, and the percentage resistance shift or leakage increase is compared with pass or fail limits. Material coupons are assessed by quantified attack depth and morphology. Results are reported with full exposure parameters, inspection images, electrical data, and a conclusion referencing the acceptance criteria of the governing customer specification.
Safety and Environmental Controls
Chlorine and boron trichloride are highly toxic and corrosive gases. Laboratories performing this test must operate gas cabinets with automatic shutoff, continuous gas detection, dedicated exhaust with alkaline scrubbing, and rigorous operating procedures. These requirements are a key reason the test is frequently outsourced to accredited third-party laboratories that maintain the necessary chemical infrastructure.
Applications
Inductively coupled plasma chlorine corrosion testing supports quality and reliability activities across the semiconductor value chain:
- Wafer-level reliability qualification of aluminum and copper interconnect processes, including evaluation of etch residue cleanliness and post-etch passivation effectiveness
- Process development and release for dry etch modules, comparing chlorine scavenging steps, rinse chemistries, and anti-corrosion capping layers
- Package qualification and molding compound evaluation, screening encapsulation materials for their ability to suppress chlorine-driven corrosion in humid environments
- Failure analysis support, where the test is used to reproduce field or reliability failures and confirm chlorine-related root cause hypotheses
- Incoming material and supplier comparison for metallization stacks, barrier liners, and surface finish coatings
- Reliability programs for automotive, industrial, and communication electronics, where corrosion robustness of fine-pitch metallization is a critical qualification requirement
- Research on advanced nodes, including corrosion immunity of new conductor materials, bonding metallurgies, and heterogeneous integration structures
FAQ
How does ICP chlorine corrosion testing differ from salt spray or HAST testing?
Salt spray and highly accelerated stress testing expose samples to chloride ions in humid atmospheric conditions, which is suitable for macroscopic hardware and enclosures. The ICP-Cl test instead generates neutral reactive chlorine radicals in a dry vacuum plasma, targeting micro-scale thin-film metallization with far higher chemical aggressiveness and much shorter exposure times, making it the preferred method for wafer-level and die-level corrosion assessment.
Is electrical bias required during exposure?
Bias is optional and specification dependent. Applying bias during plasma exposure accelerates electrochemical attack at anodic sites and better simulates powered device operation, which is valuable when evaluating galvanic and bias-assisted corrosion mechanisms in interconnect test structures.
What sample formats can be accepted?
Full wafers, wafer pieces, bare die, decapsulated packaged devices, molded units, and deposited thin-film coupons can all be tested. Sample holders and stage configurations are adapted to each format, and electrical probing before and after exposure is available for structures with accessible pads.
How long does a typical test take?
Plasma exposure itself usually lasts from several minutes to tens of minutes. Including baseline characterization, optional humidity dwell, and post-test microscopy and electrical measurement, a complete campaign is typically completed within a few working days.
What are the common acceptance criteria?
Acceptance criteria are defined by the customer or foundry specification. Typical requirements include no visible corrosion under optical inspection at defined magnification, leakage current and resistance shift within specified percentage limits, and no chlorine-bearing corrosion product confirmed by elemental analysis at critical locations.
Which standards govern the test?
There is no single international standard that fully defines ICP chlorine plasma exposure parameters, so recipes are normally established by customer specifications or internal reliability qualification documents. The general framework of accelerated environmental and corrosion assessment for semiconductor devices is consistent with the philosophy of IEC 60749 and its national counterpart GB/T 4937, and testing is commonly executed by accredited third-party laboratories under controlled and documented procedures.
Why is chlorine contamination such a serious concern in semiconductor manufacturing?
Chlorine residues from etch processes combine with trace moisture to form corrosive acidic species and metal chlorides that attack aluminum and copper metallization at grain boundaries and pad peripheries. Because device geometries are extremely small, even nanometer-scale corrosion can produce leakage, opens, or latent field failures, which is why a sensitive, accelerated screening method such as the ICP-Cl test is essential.