MEMS Design and Fabrication

You cannot build a high-quality sensor if you do not really know how it is going to perform, and you cannot push that performance to the cutting-edge if you don’t deeply understand the physics of what’s going on inside. That is why IC2 starts every development effort with physics-based, reduced-order modeling of the system. This lumped-element model captures the key physics in a clear manner to gain an intuitive understanding of the factors that affect performance. It is that deep understanding that enables rapid convergence to a sensor design that meets targeted specifications.

We then take it a step further through formal optimization. Once the lumped element model clearly reflects the underlying physics, we plug that model into a formal optimization routine to push the performance as far as possible while still meeting fabrication constraints. The result is a high-performance, fully-buildable sensor design.

Finally, we use finite element modeling / analysis (FEM / FEA) to verify our sensor designs at any stage along the way. With proper usage, FEM can provide very detailed, highly accurate simulation results, thereby adding confidence in the sensor design. By using lumped-element modeling early in the process and saving FEM for verification we can rapidly converge on an optimal solution to meet targeted specifications.

IC2’s modeling and simulation services and capabilities include:

• Lumped-element (reduced-order) modeling
• Finite element modeling and analysis (FEM / FEA)
  Modeling of transduction
• Capacitive, piezoelectric, piezoeresistive, and optical transduction
• Acoustic, mechanical, electrical, and optical sensing
• Formal optimization through Pareto optimization methods
• Predictions of sensor performance for a range of designs
• Bandwidth, sensitivity, noise floor, dynamic range, linearity, and resolution
• Guidance on how to improve performance through geometric or material changes

Before any MEMS fabrication work can proceed, a detailed process flow is required. The process flow ensures that all steps are compatible and aligned with the desired end product. We begin all process flow development with a high-level overview, selecting a general approach and outlining the major steps and processes. Then we dive deeply into each process step, defining all steps and sub-steps in great detail. At this stage, we also nail down specific recipes and process parameters for particular fabrication equipment. Finally, we produce a formal process traveler that will accompany the wafers through the fabrication process, providing sufficient detail to direct a MEMS Process Engineer or Fabrication Technician through the full processing of your MEMS devices.

We have existing process flows that we can adapt for your needs, or we can start from scratch and develop a fully custom process flow if that is what you need.

• Our existing process flows are capable of producing piezoelectric, capacitive, and optical MEMS devices, using silicon, quartz, Pyrex, and silicon-on-insulator (SOI) wafers as substrates.
• Material options for layers include aluminum, gold, titanium, platinum, molybdenum, silicon dioxide, silicon nitride, aluminum nitride, and many others.
• Process step options include etching (dry/plasma and wet/chemical), deposition (sputtering and evaporation), oxidation, patterning, wafer bonding, thin back, chemical-mechanical polishing (CMP), cleaning, dicing, and metrology .

Our MEMS process flow design service is designed to be comprehensive and generally includes the following stages:

• High-level approach
• Detailed process flow design
• Recipe development and definition
• MEMS Process traveler
• Final design review

Once you have a sensor’s design geometry nailed down (whether it’s your design or ours), we can translate that geometry into a set of photolithographic masks via our mask layout service. In order to fabricate MEMS devices, you will first need that set of photomasks, one for each layer to be patterned. Our comprehensive layout service will provide you with finalized layout files and physical masks in either soda-lime or quartz. We regularly work with major photomask manufacturers and are intimately familiar with all the intricacies of the design and ordering process, ensuring that you get the desired end product. Our photomask design and layout service includes any or all of the following options, depending on your needs:

• Design Review
• We ensure your MEMS designs are finalized, ready for layout, and fully compatible with your MEMS process flow
• Test Structure Design
• We can help you develop useful test structures to include on your masks to verify material properties (e.g. mechanical properties like residual stress, Young’s modulus, density, etc., or electrical properties like contact resistance, sheet resistance, and layer-to-layer capacitance), as well as to obtain other valuable information like layer thickness, or etch profiles.
• Software Layout
• We translate your designs into geometric patterns including layouts for individual devices, test structures, and the overall wafer layout, using the latest CAD software
• Mask Review
• We verify the mask layout against finalized designs and process flow to ensure the photolithography will achieve the desired results.
• Mask Ordering
• We work directly with the photomask manufacturer to place the order and inspect the received photomasks for quality and conformance.

IC2 has access to, and experience with, a wide range of microfabrication tools and services for 4″ (100mm) and 6″ (150mm) diameter wafers through its network of academic clean room facilities and commercial fabrication service providers. Our in-house MEMS process engineers are available to perform single processes up to full MEMS device fabrication with either IC2-designed or customer-provided photolithography masks.

Below is a list of our typical materials:

• Silicon
• Silicon Oxide
• Silicon Nitride
• Aluminum Nitride
• Aluminum Oxide
• Aluminum
• Chromium
• Gold
• Molybdenum
• Nickel
• Platinum
• Titanium

IC2 can also work with other oxides and metals, depending on how exotic they are, but typically would need to do process development for deposition and patterning.

IC2 is capable of providing R&D prototype and limited-run production services from single-wafer runs to larger multi-wafer lots. For high-volume production, we can help guide you in evaluating and selecting a commercial MEMS foundry that will meet your needs.