Semiconductor oxygen plasma corrosion testing evaluates the resistance of wafers, packaged devices, and semiconductor materials to degradation caused by exposure to reactive oxygen plasma. As oxygen plasma is widely used in fabrication and packaging steps such as photoresist stripping, descum, and surface activation, this test is essential for verifying material compatibility, package reliability, and process robustness. This article explains the technical principles, applicable sample types, test items, methods, and typical applications of semiconductor oxygen plasma corrosion testing performed by accredited third-party laboratories.
Semiconductor oxygen plasma corrosion testing is a specialized reliability and compatibility evaluation in which samples are exposed to a radio-frequency excited oxygen plasma under controlled conditions, and any resulting oxidation, erosion, or degradation is systematically characterized. It plays a critical role in qualifying materials and processes across wafer fabrication, advanced packaging, and microelectronics assembly.
Technical Overview
Oxygen plasma is generated by introducing oxygen gas into a low-pressure vacuum chamber and coupling radio-frequency energy, commonly at 13.56 MHz, into the gas. The resulting plasma contains highly reactive species, including atomic oxygen radicals, oxygen ions, ozone, excited molecules, and vacuum ultraviolet photons. Among these, atomic oxygen is the dominant chemically active species and is extremely aggressive toward organic and oxidizable materials.
In semiconductor manufacturing, oxygen plasma is routinely used for photoresist stripping and ashing, descum before die bonding, wire bonding, and encapsulation, surface activation and cleaning, and as an additive gas in dry etch chemistries. While these processes are indispensable, unintended or excessive plasma exposure can cause measurable damage: oxidation of exposed metallization such as copper or silver, erosion and roughening of polymer die attach adhesives, degradation of molding compounds, attack on passivation and low-k dielectric layers, interfacial delamination, and electrical parameter drift due to charging or oxidation effects.
Oxygen plasma corrosion testing therefore simulates realistic plasma exposure in a controlled laboratory environment and quantifies the material or device response. By comparing pre-test and post-test geometry, chemistry, morphology, and electrical performance, engineers can determine whether a material, structure, or package is sufficiently robust for its intended process flow, and can establish safe process windows for power, pressure, and exposure time.
Testing Samples
Wafers and Die-Level Structures
Bare silicon wafers, patterned wafers, diced die, and test structures are tested to evaluate the plasma resistance of surface films such as passivation layers, polyimide, low-k dielectrics, barrier layers, and metal interconnects. These tests are frequently performed during process development and qualification.
Packaged Semiconductor Devices
Finished packages such as QFN, BGA, CSP, flip-chip, and molded modules can be exposed to oxygen plasma to assess whether upstream or downstream plasma steps cause package-level degradation, including surface erosion, discoloration, delamination, or electrical failure.
Packaging and Assembly Materials
Epoxy molding compounds, die attach adhesives, underfill materials, substrate laminates, bonding tapes, and other polymeric materials are tested as raw materials or as representative coupons to characterize mass loss, surface roughening, and oxidation behavior under plasma exposure.
Functional Layers and Thin Films
Silicon nitride, silicon oxide, organic coatings, anti-reflective coatings, photoresists, and metal thin films can be individually evaluated for etch rate, oxidation sensitivity, and surface chemistry changes caused by oxygen radicals and ions.
Display and Microelectronics Assemblies
OLED and flat panel display components, flexible circuits, MEMS devices, and PCB or substrate assemblies may also be submitted for oxygen plasma exposure testing when plasma cleaning or activation steps are part of the production sequence.
Testing Items
Depending on the sample type and customer specification, typical evaluation items include:
- Mass loss or mass change determined by high-precision gravimetric measurement before and after plasma exposure
- Etch rate, erosion depth, and thickness reduction of films and coatings
- Surface morphology changes, roughness variation, pitting, cracking, and blistering assessed by optical microscopy, SEM, profilometry, or AFM
- Oxidation and surface chemistry analysis using EDS, XPS, or FTIR to identify oxide formation and chemical state changes
- Visual defects such as discoloration, haze, delamination, or exposed underlying layers
- Interfacial adhesion degradation evaluated through die shear, wire pull, or peel testing after exposure
- Electrical performance drift, including leakage current, contact resistance, threshold voltage shifts, and functional parametric comparison
- Surface energy and wettability changes measured by contact angle analysis
- Comparative lifetime or repeated-cycle exposure behavior to simulate multiple plasma process steps
Testing Methods
Testing is typically performed in a benchtop or production-type RF plasma asher or reactive ion etch system equipped with oxygen gas delivery, vacuum control, and programmable process recipes. A standard test sequence consists of the following stages:
- Sample preparation: cleaning, drying, conditioning, and documentation of initial state, including baseline photography, dimensional metrology, mass measurement, and electrical characterization where applicable
- Plasma exposure: samples are placed in the chamber and exposed to oxygen plasma under defined parameters, typically including RF power in the range of tens to several hundred watts, oxygen flow rate of tens to hundreds of standard cubic centimeters per minute, chamber pressure in the millitorr range, and exposure durations from a few minutes to several hours depending on the specification
- Multiple-cycle testing: where a device will encounter plasma several times in the real process flow, repeated exposure cycles may be applied with intermediate inspections
- Post-test characterization: gravimetric and dimensional re-measurement, microscopic inspection, surface chemical analysis, adhesion testing, and electrical retest are conducted using the same methods as the baseline to enable direct comparison
- Evaluation and reporting: results are compared against acceptance criteria defined by the customer, internal engineering specifications, or recognized microelectronics reliability frameworks, and a full test report with conditions, data, and photographic evidence is issued
Where applicable, test design and evaluation reference established microelectronics and environmental testing frameworks such as MIL-STD-883 test methods, the IEC 60068-2 series for environmental testing, and relevant JEDEC guidelines, while laboratory operations are generally conducted in accordance with ISO/IEC 17025 quality management requirements.
Applications
Semiconductor oxygen plasma corrosion testing supports a wide range of engineering and quality activities:
- Qualification of plasma descum, ashing, and cleaning steps in wafer-level and packaging process flows
- Material selection and comparative evaluation of molding compounds, adhesives, underfills, and dielectric polymers
- Process window definition for RF power, pressure, and exposure time to prevent plasma-induced damage
- Package reliability assessment for devices that experience plasma exposure before or after molding
- Failure analysis and root cause investigation of oxidation, delamination, or parametric drift attributed to plasma steps
- Incoming material inspection and supplier or lot acceptance verification for plasma-sensitive components
- Research and development of plasma-resistant coatings, low-k dielectrics, and advanced packaging materials
FAQ
What is semiconductor oxygen plasma corrosion testing?
It is a laboratory test in which semiconductor materials, wafers, or packaged devices are exposed to controlled oxygen plasma, and any resulting oxidation, erosion, roughening, delamination, or electrical degradation is measured and compared against acceptance criteria.
Why is oxygen plasma so aggressive to materials?
RF-excited oxygen plasma produces atomic oxygen radicals that react strongly with organic compounds and oxidizable metals. Organic materials are converted into volatile products and gradually eroded, while exposed metal surfaces can oxidize, leading to corrosion-like damage.
What test conditions are typically used?
Typical recipes use RF excitation at 13.56 MHz with power from roughly 100 to 600 W, oxygen flow rates of 50 to 300 sccm, chamber pressure in the tens to hundreds of millitorr range, and exposure times from several minutes to several hours, adjusted to the customer specification or intended production process.
Which standards are referenced?
Depending on the product and specification, testing may reference frameworks such as MIL-STD-883, the IEC 60068-2 environmental testing series, and JEDEC guidelines, and is performed under ISO/IEC 17025 laboratory quality systems in accredited third-party laboratories.
How are test results judged?
Acceptance is usually based on quantitative limits, such as maximum mass loss, thickness change, roughness increase, or electrical parameter drift, together with qualitative criteria such as the absence of visible corrosion, cracking, or delamination after defined exposure conditions.
What sample forms can be submitted?
Accepted samples range from material coupons, films, and coated substrates to diced die, packaged components, and full assemblies, provided the sample geometry and baseline state can be documented for before-and-after comparison.