Using SEMI F57 compliance to improve semiconductor fluid-handling systems
Gaining SEMI F57 compliance can help reduce commissioning time of fluid-handling systems, improve wafer yields, increase semiconductor equipment life and round off your contamination-control program
BY WILEY WILKINSON
As fluid-handling systems face rapid technology advancements and increased system uptime requirements, improved system performance is critical. New technology nodes require increased fluid-purity levels to maintain acceptable wafer yields, putting greater demands on fluid-handling systems. Additionally, these systems must be commissioned quickly since extended leaching periods can delay equipment and/or fab start-up.
Today, production fabs often benchmark with research; and development fabs on the leading edge of line width technology use fully passivated fluid-handling systems. Reducing or eliminating a fluid system-leaching period is rapidly gaining prominence as a key strategic benefit.
Fab operators have learned that starting with a high-purity fluid-handling system can lead to a faster return on investment. With faster commissioned systems, higher wafer yields and decreased maintenance levels can be achieved.
Operators now also understand the value delivered by a complete high-purity fluid-handling system versus single components. This is especially true in the case of PFA tubing, which provides the greatest exposed surface area to ultra-high purity (UHP) chemicals. Well-documented cases show that as the number of compliant components increases in a system, the total extractable level of the system decreases-a factor that has often presented significant challenges until now.
SEMI's new F57
The new SEMI specification, SEMI F57-0301, may provide relief for users of fluid-handling components who want to comply with new standards for excellence.
Applied to polymer components used in ultrapure water and liquid chemical distribution systems, SEMI F57-0301 specifies the minimum performance requirements for UHP polymer components used throughout semiconductor ultrapure water and liquid chemical distribution systems, including bulk supply, facility distribution and process equipment applications.
The SEMI F57 standard requires fluid-component manufacturers to follow best practices in material science and not contaminate UHP processes with extractable ions, metallics or total organic carbon (TOC)—areas that can negatively impact yield and reduce the life of semiconductor equipment.
The standard also provides guidelines for wetted surface area roughness, product reliability, certification, traceability, packaging and testing. While the specification is currently considered provisional—because it lacks a complete set of requirements and test methods for particles—the standard will be updated as tests and requirements are finalized.
To recognize the true benefit of F57, semiconductor manufacturers can benefit most from using a complete solution package of compliant-components in their manufacturing systems. IDM, OEM and facility contractors can also refer to the new standard when procuring fluid-handling components and specify required component performance for UHP bulk chemical supply, facility distribution and process equipment applications.
Which fluid-handling components are affected?
The new SEMI F57-0301 specification provides complete test requirements for several fluid-handling components, including: pipe, tubing, fittings, valves, filter housings, pressure transducers, flowmeters, gauge protectors and regulators made from perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF).
Fluid-handling component compliance testing
• Surface Extractable Ionic Contamination Testing. Ionic contamination can sometimes etch or corrode a wafer during production, negatively affecting yields. The SEMI F57 specification identifies allowable limits for seven different aqueous leachable anions: bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate.
Specification limits and individual values for each anion and component tested per SEMI F57.
The F57 document also calls out test sample preparation, per SEMI F40, including a room-temperature deionized water soak for two minutes, followed by draining—a process that is repeated 10 times. The final deionized water-fill sample soaks for seven days at 85° C before being analyzed for leachable anion levels, per SEMI F57.
Figure 1 shows specification limits and individual values for each anion and component. Each component shows values well below the acceptable limits, indicating minimized wafer contamination concerns from the effects of the noted leachable anions.
Values for tubing, fittings and valves are well below acceptable limits, minimizing wafer contamination.
• Surface Extractable Metallic Contamination Testing. Metallic contamination during wafer production can negatively affect yields by changing the electrical properties of a device. The SEMI F57 specification identifies allowable limits for 16 different metals: aluminum, barium, boron, calcium, chromium, copper, iron, lead, lithium, magnesium, manganese, nickel, potassium, sodium, strontium and zinc.
A SEMI F40 component test sample preparation process is used to prepare samples, which are then analyzed for metallic levels. The test sample solution is acidified using ultrapure nitric acid at a 5-percent concentration, which serves to stabilize the solution, preventing some metals from precipitating out. All measurements are made using Inductively Coupled Plasma Mass Spectrometry (ICP-MS).
Figure 2 reflects the specification limit and individual value for each metal and component. The data for tubing, fittings and valves shows values well below acceptable limits, minimizing wafer contamination concerns from the effects of the noted metals.
• Surface Extractable Total Organic Carbon (TOC) Contamination Testing. Elevated levels of total organic carbon (TOC) can introduce variation during the etching process and can have a negative effect on silicon oxidation. To prevent wafer contamination, TOC levels need to be minimized within a fluid-handling system.
To test for TOC contamination, tubing, fittings and valve samples are prepared per SEMI F40. Table 1 reflects the specification limit and individual values well below the acceptable limit of 60,000 Σ µg/m2 for each component, minimizing wafer etching and oxidation concerns from the effects of TOC when using polymer material components.
F57 specifications for surface roughness apply to wetted surface areas within a fluid-handling system. A rough, wetted surface area can contribute to micro-contaminate entrapment and/or provide unwanted polymer shedding.
Before testing, an analysis compares two measurement methods: surface profilometry and atomic force microscopy (AFM). The preliminary study compares the non-contact (AFM) method to the contact (profilometry) method, using both extruded tubing and injection-molded components to address measurement variation that might be introduced with the contact method (due to the flexible nature of the polymer materials).
Both surface profilometry and atomic force microscopy (AFM) measurement techniques provide accurate results.
Figure 3 compares the two measurement techniques and indicates that both are capable of providing accurate results. Note that the y-scale indicates nanometers, providing enough resolution to make an educated comparison. Once enough empirical data was gathered to rule out any unwanted measurement variation, compliance testing resumed.
Values for polymer materials are well below the limit, minimizing micro-contaminate entrapment.
Figure 4 and Table 2 reflect the specification limit and individual value for each component. Data for tubing, fittings and valves made of polymer materials shows values well below the acceptable limit of 0.25 and 0.38 µm, minimizing micro-contaminate entrapment and/or unwanted polymer shedding.
Along with stringent purity requirements, the SEMI F57 specification calls out guidelines for mechanical requirements of fluid-handling components. These include pressure and temperature ratings, chemical resistance ratings and reliability checks.
To ensure high-quality, safe products, qualification tests may be performed to qualify and validate performance specifications, determine extended life via accelerated means and identify design deficiencies.
Planning for the future
Fluid-handling component selection in the semiconductor industry is a critical step that enables semiconductor companies to reduce the commissioning time of fluid-handling systems, plan for future technology advancements, improve wafer yields, decrease preventative maintenance intervals and increase the life of semiconductor equipment.
Specifying SEMI F57-0301-compliant products in fluid-handling systems in advance can provide substantial value immediately and well into the future; however, it takes more than a few components. The total system, consisting mainly of tubing, fittings and valves, comprise most of the wetted surface area.
It's also important to recognize that polymer molding, machining and assembly methods vary significantly and have a large impact on the final component bulk and surface contaminant levels.
WILEY WILKINSON is marketing director for Entegris' fluid-handling systems. He has been with the company for eight years. Additional contributors include: Rich Hoffman, lab scientist; Dr. Chuck Extrand, principal engineer; Ken Perkins, project engineer.
SEMI F57 0301—"Provisional Specification for Polymer Components Used in Ultrapure Water and Liquid Chemical Distribution Systems"
SEMI F40 0669—"Practice for Preparing Liquid Chemical Distribution Components for Chemical Testing"