Semiconductor process tools – including PVD, ALD, CVD, ion implantation, and advanced etch systems – use UHV or near-UHV conditions to minimize surface contamination and improve film purity. Hermetic feedthroughs carry electrical power, RF signals, thermocouples, and motion actuators through chamber walls without introducing leak paths. Selecting feedthroughs with the correct current rating, dielectric strength, thermal stability, and leak-rate qualification is critical to process repeatability and tool uptime.
Why Semiconductor Tools Operate at UHV
At the dimensions of modern semiconductor nodes, even sub-monolayer contamination at a wafer surface can affect device performance. A single monolayer of water vapor or hydrocarbon deposited on a wafer between process steps can alter interface chemistry, introduce defects, or change film stoichiometry. Operating at UHV or near-UHV (typically 10⁻⁷ to 10⁻⁹ torr) suppresses the contaminant arrival rate at the wafer surface to a level that no longer limits process quality.
Beyond cleanliness, UHV extends the mean free path of process species – sputtered atoms, ions, or reactive radicals – so they travel from source to wafer without collisions, improving deposition uniformity and directional control in PVD and ion-based processes.
Types of Feedthroughs Used in Semiconductor Tools
Electrical Power Feedthroughs
Heater elements, electrostatic chucks (ESCs), and bias electrodes require power feedthroughs that carry currents ranging from a few amps to hundreds of amps at voltages from tens to thousands of volts. Ceramic-to-metal brazed feedthroughs are standard for these applications because of their high dielectric strength, low outgassing, and compatibility with bakeout. Multi-pin configurations carry multiple circuits through a single CF-flanged assembly, minimizing the number of vacuum penetrations.
RF Feedthroughs
Plasma-enhanced CVD, ALD, and etch tools use RF power delivered at 13.56 MHz, 27 MHz, or higher frequencies to generate and sustain plasma. RF feedthroughs must maintain impedance matching from the generator through the vacuum boundary to the electrode. Ceramic-to-metal coaxial feedthroughs with well-controlled dielectric geometry provide consistent impedance (typically 50 ohms) and low insertion loss at UHV, while maintaining hermetic integrity under repeated RF power cycling.
Thermocouple Feedthroughs
Wafer temperature control is critical in every thermal process. Thermocouple feedthroughs use matched thermocouple wire pairs (Type K, Type N, Type J, or others) brazed into a hermetic feedthrough body and connected to external instrumentation. The feedthrough must maintain the thermoelectric junction integrity and avoid introducing EMF errors from material transitions at the vacuum boundary.
Motion Feedthroughs
Wafer handling robots, chuck lift pins, shutter mechanisms, and tilt stages inside process chambers require motion feedthroughs that translate rotary or linear motion from atmospheric-side actuators into the UHV environment. Ferrofluidic rotary feedthroughs and bellows-based linear feedthroughs are common designs. Hermetic integrity must be maintained through the full range of motion and over millions of actuations.
Signal and Instrumentation Feedthroughs
Pressure gauges, optical emission spectroscopy (OES) probes, Langmuir probes, and other diagnostics require signal feedthroughs that pass low-level electrical signals or fiber optic lines through the chamber wall. Shielded and twisted-pair configurations reduce EMI pickup in the high-noise environment of a plasma chamber.
Leak Rate Requirements in Semiconductor Tools
Semiconductor tool vendors typically specify chamber leak rates in units of torr·L/s or atm·cc/sec. A common target for UHV process chambers is a total system leak rate below 1×10-9 atm·cc/sec, with individual feedthrough leak rates specified at 1×10-9 to 1×10⁻¹¹ atm·cc/sec. These specifications are verified by helium mass spectrometer leak detection in accordance with ASTM E498 and E499.
Bakeout Compatibility
New process chambers and rebuilt chambers undergo bakeout at 150–250°C while pumping to outgas water and hydrocarbons from internal surfaces. All feedthroughs must survive repeated bakeout cycles without degradation of the hermetic joint or change in electrical performance. Ceramic-to-metal brazed assemblies on CF flanges are the standard configuration because they are compatible with bakeout temperatures up to 250°C, depending on the braze alloy and flange material selected.
Material Compatibility with Process Chemistries
Semiconductor processes use corrosive gases including halogen compounds (Cl₂, HCl, HF, NF₃, SF₆), strong oxidizers (O₂, O₃), and other reactive species. Feedthrough materials exposed to these gases must be evaluated for chemical compatibility. Alumina ceramic and stainless steel are compatible with most halogen-based chemistries. Copper braze and Kovar may require protection or substitution with more resistant materials in particularly aggressive environments.
Selecting Feedthroughs for Semiconductor Applications
- Match the current and voltage rating to the actual load with appropriate derating.
- Specify CF flanges on all feedthroughs that penetrate the UHV chamber boundary.
- Verify helium leak-rate test data at or below your system’s specification.
- Confirm bakeout compatibility to at least 200°C for new tool builds.
- Evaluate material compatibility with your specific process chemistry.
- Consider multi-pin configurations to minimize the number of chamber penetrations.
Working with MPF Products
MPF Products designs and manufactures ceramic-to-metal hermetic feedthroughs, RF coaxial feedthroughs, thermocouple feedthroughs, and motion feedthroughs on CF and other vacuum-rated flange configurations for semiconductor process tool applications. Engineering support is available to match feedthrough specifications to tool design requirements.