MEMS Devices Driving Special Requirements for CMP and Substrate Thinning

As the market for MEMS devices continues to grow along with the development of the “Internet of Things”, Axus Technology’s process group is spending an increasing amount of time developing processes and providing manufacturing support for the growing number of MEMS producers.  As a provider of process development services and equipment, Axus provides process integration planning which can also guide users in selecting the optimal tool set for their production requirements.MEMS features

MEMS manufacturers often find that they can build their products in established semiconductor fabs.  These facilities rely on having very competitive operating costs, taking advantage of lower or depreciated capital equipment, with tool sets capable of supporting IC device manufacturing with critical dimensions ranging from 0.5 microns down to around 130nm.  Many times, the manufacture of MEMS devices requires additional film layers to support the desired functionality of the MEMS sensor or actuator.  Fabrication of these additional layers requires creative process solutions and often creates an opportunity for clever equipment improvements to support the special CMP and thinning processes needed when adding these layers. 

An example of this type of development is the formation of stacks of multiple substrates that contain special cavities.  In this case the process flow required includes:

  1. Deposit SiO2 on both faces of a wafer pair that is to be bonded
  2. Process both oxide faces using a CMP process that provides the best planarity and lowest roughness
  3. Permanently bond the wafer pair, enclosing the cavity
  4. Thin the top substrate, bringing the desired feature or sensor to the surface or close to it
  5. Perform an edge-trim process to the top substrate, eliminating the fragile and less-uniform edge
  6. Polish the top surface to restore a near-prime and low-defect surface

The sequence can then be repeated as additional substrates may be bonded to the processed wafer pair.

MEMS Stacking

MEMS devices with novel interconnect schemes create another opportunity to provide advanced CMP solutions.  The function of the MEMS device can add large features among an array of finely structured interconnect wires, creating a wide range of feature sizes to be planarized.  For interconnect wiring that utilizes metal etching, the Inter Layer Dielectric (ILD) step requires an advanced high-efficiency planarization step in order to maintain die uniformity specifications.  Similarly, large features arranged with the interconnect wiring requires a novel approach to processing that is further enabled by related hardware improvements.  Along with developing creative multi-step processes for these challenging planarization needs, Axus Technology has developed carrier upgrades that can be applied to older CMP platforms -- delivering state-of-the-art capability to earlier-generation tooling.  The Axus Technology process lab and foundry has applied this advanced membrane carrier technology to several CMP tools in our own development facility and we deliver membrane carrier upgrades to CMP users seeking the same advanced process capabilities.

The growth in the market for MEMS devices, along with their novel architecture has driven quite of bit of creativity in process and equipment development. There is a growing range of novel CMP processes that are coupled with and enabled by additional process tool refinements.  The mechanical nature of MEMS devices capitalizes on the use of well-known fabrication technologies to construct three-dimensional structures that integrate into a semiconductor device structure.  Managing process integration challenges and the often-complex process sequence, along with developing effective CMP and thinning processes, requires a deep understanding of process and production technologies.  Fortunately, Axus Technology has the process engineering team and the process equipment expertise needed by today’s MEMS manufacturers.  Let us know if there are any MEMS (or other) CMP applications that we can help you with.