MEMS being driven by innovation

The MEMS (microelectromechanical systems) business continues to be driven by innovation. Following the demand for MEMS devices for mobile phones, users want to have smaller, higher performance and less costly dies.

For the toolmakers, it means a continuous development effort for new processes for quicker deep etch rate, cleaner sacrificial etching, new metallic bonding, 3D packaging approaches and wafer level testing to name a few.

The new Yole report ‘World MEMS Equipment & Materials Market 2009’ (WMEM 09) describes the trends and opportunities for equipment and materials for MEMS production.

The report gives market forecasts for these devices and the associated MEMS equipment and materials. Although the sector will remain flat overall for the next year or so, there are growth sectors and room for innovation for inertial MEMS (for mobile phones), RF switches, energy harvesting and µmirrors.

The MEMS production tool market will be flat for 2009/2010, but equipment R&D is still active as players prepare for a ramp-up in 2011. By 2012, the equipment market will reach $615m.

The WMEM 09 report provides in-depth analysis for the different types of tools for MEMS production: deep etching, sacrificial etching, deposition and cleaning, bonding and lithography.

For each type of equipment, the report provides information about the market and technology trends.

For example, there are currently many competing sacrificial release technologies, but we see a growing interest for XeF2 sacrificial etching.

This is a very particular technology as it cannot be used for SiO2 but for Si, SiGe, polySi, W, Ti and Mo. Although it was restricted to some niche applications with only one large volume production (iMoD from QMT), it seems there is an increased interest in this technology.

Another specific process, bonding, is moving away from glass and anodic to more metal based, for better hermeticity and thinner line widths, but the bulk is still the traditional processes and the push there is to reduce the quantity of silicon real estate taken up by the glass frit to get more devices on a wafer without giving up performance.

Although, technically speaking, there are no MEMS that require only stepper lithography for all layers in the stack, the motivations currently causing a shift from aligners to stepper lithography for MEMS are manufacturability issues and infrastructure evolution issues.

Something new is the possible coming for standard processes for MEMS.

For a long time, the production rule has been ‘one product, one process, one package!’ But European foundries and R&D institutes argue standard process modules are possible for MEMS production.

Silex is leading the way, inspired by its through-wafer via and WLP platform: the more a fabs customer can use identical process blocks, modules or platforms, the better the process control and yield and the lower the costs. Other players are CEA-Léti for standard processes on 8-in wafers for R&D fabs. Examples of modules include TSV , WL packaging, hermetic bonding or Si membrane.

Integrating different modules together creates a function (sensor, actuator etc). This approach is competing with use of the CMOS process for MEMS structures.

Packaging is key for new MEMS design. "For example, 3D integration with TSV is now an industrial reality with continuous growth expected,” explained Dr Eric Mounier, project manager at Yole Développement.

“3D integration with TSV for MEMS is likely to be the next relay of growth for the DRIE market and 3D TSV is pushing the need for quicker etch rate, towards 100 µ/min!” said Mounier.

DRIE is currently used mostly for inertial MEMS manufacturing and is also increasingly used in replacement of wet for microphones and pressure sensors (because of better control of feature profile, depth and uniformity across the wafer).

Current challenges for DRIE are the removal of polymer after the Bosch process, sidewall roughness, end-point detection, reproducibility and reliability, and increased etch rate.

Materials for MEMS will be a $577m market in 2012. In terms of wafer size, there is a transition from 6 to 8 in for the companies involved in high-volume MEMS applications.

There are 10 MEMS companies already processing 8-in wafers with five new announcements in 2009. SOI wafers are used and represent about 23% of total processed wafer in dollar value.

Thick SOI (0.2 to 60 µ) is used for sacrificial release.

Yole’s research draws on the ongoing work of its analysts tracking 150 MEMS applications, aggregated into 12 major categories of devices: ink jet heads, pressure sensors, microphones, accelerometers, gyroscopes, MOEMS, micro bolometers, micro displays, micro fluidics, RF MEMS, micro tips and emerging MEMS devices.