Tom Morrow, Vice President, Global Expositions & Marketing, SEMI
The MEMS industry is changing from a one-process-per-product technology to a one-process-many-product one. Critical to this transformation are industry standards that reduce costs and spur meaningful innovation. The SEMI MEMS Technical Committee has been meeting this challenge since 2003, developing several important standards that have yielded significant benefits to developers, manufacturers and suppliers.
The charter of the MEMS Technical Committee is to develop standards for MEMS devices that cannot be handled by existing semiconductor technical committees. Current topics include Wafer Bonding Alignment Targets; Step-Height Measurements of Thin, Reflecting Films using an Optical Interferometer; and Ultra High Purity Microscale Fluidic Systems for Use in Scalable Process Environments. Recently SEMI announced the latest in the series of MEMS standards, MS8 Guide to Evaluating Hermeticity of MEMS Packages, available to users on-line immediately. The hermeticity guide is the first to address MEMS packaging and further efforts to standardize the methods used to evaluate MEMS packaging are being evaluated.
One of the goals of the new MS8 guide was to gather and summarize all the hermeticity aspects of MEMS. As more data and MEMS-specific details are gathered, sections of MS8 will be removed, revised, or expanded upon leading to publication of a specification or test method standard.
One topic that the committee is now looking at more closely involves the permeability of sealing materials. For example, assuming one has inspected the seal for integrity, the bond quality is good at both interfaces and there are no direct leak paths between the external and internal environments, the next concern would be the actual permeation of gases through the seal. Permeation is dependent on both the seal geometries and material properties. The minimum allowable seal width for a given lifetime expectancy of the enclosed device depends on both the seal thickness and the permeability of the material itself. The Committee has prioritized this area because there is little published data on permeability of seal materials used for MEMS.
Another issue of concern is the validity of the current test methods utilized for leak testing and residual gas analysis. Current standardized test methods were developed for packages with larger cavity volumes and have proven to be not reliable or not applicable for smaller volume packages, typically <0.02 cc. The published guide discusses the relevant standard test methods as well as more recently introduced methods, providing an objective opinion on the advantages and disadvantages for each.
Ideally, as the production volume of commercially available hermetic-packaged MEMS increases, a method that supports high-throughput non-destructive hermetic QC of the MEMS devices will emerge. Perhaps one of the methods discussed in the MS8 guide will become a self-contained standard, but further investigation and input from the MEMS industry is required to develop consensus.
SEMI has published seven other standards related to MEMS and is looking forward to publishing more as needed by the industry. Participating in the standards development process provides industry benefits, provides company benefits, and helps advance the knowledge and enjoyment of the individual participants. Please join us in helping advance the industry in proven and productive ways.