Wafer Carrier

• Overmolding Ensures Dimensional Stability and Low Particulate Levels

Modern automated wafer handling processes have increased the need for tighter tolerances on wafer carriers. Entegris, Inc., is the first company to make significant changes to the original linear wafer carriers developed in the early 1970’s. Its new KA250 Advanced Wafer Transport Carrier features polycarbonate overmolded with a conductive RTP 2200 Series specialty compound based on Victrex PEEK™ resin.

“Heightened wafer-carrier requirements are largely a result of technological advancements in semiconductor processes,” said Sanjiv M. Bhatt, Ph.D., Project Engineer at Entegris. “The dramatic increase in the level and complexity of automation requires a wafer carrier that offers improved mechanical interface capabilities with automated material-handling systems and process tools. In addition, wafer location in the carrier must be consistent and reliable to support fast, safe wafer access by robotic end effectors.”

The driving force in material selection and design of the Entegris KA250 was improved price-to-performance ratios. “No single wafer-carrier material provides high performance and low cost,”continued Bhatt. “Through the manufacturing technology of overmolding, however, a wafer carrier can be created from two distinct materials.” Entegris’ innovative, patent pending technology uses two fab-proven materials to create a single carrier, thereby reducing costs and optimizing carrier performance.

The Entegris design maintains important properties while reducing material costs. RTP Company’s carbon fiber-filled PEEK™ compound provides a grounding path and lines the carrier in areas where it may contact a wafer or equipment.

The PEEK™ compound offers dimensional stability with tensile strength of 17,500 psi (121 MPa) and tensile modulus of 1.65 x 10⁶ psi (11369 MPa); abrasion resistance; high continuous use temperature; and surface resistivity of 10⁵ to 10⁹ ohms/sq.

The remainder of the carrier is molded from polycarbonate, which offers low-cost dimensional strength, transparency, and toughness. Using polycarbonate results in a more precise carrier and eliminates many of the difficulties of molding carbon fiber-filled materials.

According to Entegris tests, the bond between the PEEK™ compound and the polycarbonate material is strong. The average fracture energy of the bond is 1.6 kJ/m², and the tensile modulus of the composite is 2.2 GPa, almost twice that of polypropylene. The design has also increased the impact strength of the carrier. Drop tests indicate a critical drop height of 59.25 inches (1.51 m), approximately 3.4 times greater than carriers containing only PEEK™ material.

One-third to one-half of all semiconductor manufacturers rely on colored carriers for product and process distinction. Tinting the transparent polycarbonate base in clear, red, blue, or green allows for easy identification from all angles. This added feature eliminates the need to utilize high levels of colorants required for carbon fiber-based materials.

Wafer processing causes great opportunities for particle generation. The wafers abrade carrier surfaces during robotic transfers and other processing steps. The PEEK™ compound was developed to meet the semiconductor industry’s standards for particle generation while maintaining a low level of ionic contaminants and out-gassed substances. Entegris tests show comparable purity standards between the new carriers and traditional all-PEEK™ carriers with no increase in particle counts.

The overmolded design offers several benefits for semiconductor manufacturers, including lower initial purchase price of the carrier, reduced setup and calibration time due to improved dimensional precision and integrity, and significant reduction in equipment downtime.

Corporate headquarters for Entegris, Inc., is in Chaska, Minnesota. Contact them at (612) 448-8181 or visit their website at www.entegris.com.

PEEK™ is a trademark of Victrex plc.