450mm standards update

USA: Since the submission of the first 450mm proposal in 2007, the SEMI Standards Program has developed over fifteen 450mm wafer-related standards, and work continues to ensure that critical framework is in place to support future high-volume manufacturing.

This vital work continued at a packed SEMICON West 2013 session entitled "Silicon Wafers - Future Standardization to Enable the Transition", with new proposals along with new approvals. The transition to 450mm manufacturing is accompanied by the development of various standards aimed at achieving cost, efficiency and technology improvements.

The most notable new proposal concerns development of a specification for a notchless 450mm wafer. Document 5604, Revision to SEMI M1-0413, Specification for Polished Single Crystal Silicon Wafer (Re: Addition of Notchless 450 mm Wafers). While a wafer notch is useful for alignment and orientation, there are impacts on yield and cost, with some estimating a loss of one to four dies per wafer.

The existing SEMI M76-0710, Specification for Developmental 450 mm Diameter Polished Single Crystal Silicon Wafers, notes that a wafer notch impacts wafer symmetry, creating a stress area, and that while eliminating the notch would improve symmetry and stress issues, and new alignment method would be required.

Work will take place in the Silicon Wafer Committee's International 450 mm Wafer Task Force, with the group focusing on replacing the notch with a fiducial mark scribed on the wafer. (Laser-inscribed fiducial marks have been discussed in previous wafer size transitions.) Items for consideration will include mark design, position, readability, speed, and impact on wafer integrity through the entire IC manufacturing process.

A related proposal calls for reducing wafer edge exclusion, the peripheral portion of a wafer where no viable device structure is possible. The current 450mm wafer specification (SEMI M76-0710), originally published in 2010, calls for a 2mm edge exclusion zone, but some device makers believe that this area can be further reduced, increasing yield. The preliminary proposal was discussed by the Silicon Wafer Committee during SEMICON West and will be refined and presented again during the North American Fall Standards Meetings at SEMI HQ in San Jose, California.

Another new proposal started at SEMICON West is an effort to revise SEMI M1-0413, Specification for Polished Single Crystal Silicon Wafers (Doc. 5605), adding site flatness quality requirements (SFQR) for the 16 nm technology generation, including 450mm wafers.

In addition to these two new proposals, the Silicon Wafer Committee approved an update to SEMI M73-0309, Test Methods for Extracting Relevant Characteristics from Measured Wafer Edge Profiles to include 450 mm wafers, and will be published in the coming months pending successful procedural review, joining two other recently published new 450mm standards:

* SEMI E166-0513 - Specification for 450 mm Cluster Module Interface: Mechanical Interface and Transport Standard.
* SEMI G95-0613 - Mechanical Interface Specification for 450 mm Load Port for Tape Frame Cassettes in the Backend Process.