3D Process Modeling - A Novel and Efficient Tool for MEMS Foundry Design Support

Transcription

1 3D Process Modeling - A Novel and Efficient Tool for MEMS Foundry Design Support Gisbert Hölzer, Roy Knechtel X-FAB Semiconductor Foundries, AG Stephen Breit, Gerold Schropfer Coventor, Inc.

2 Overview A tool for 3D process modeling How it works Virtual fab run Application to X-FAB surface micromachining process Case Study 1 virtual fab run using a customer design Case Study 2-3D design checking Case Study 3 - process development Conclusions

3 How it works SEMulator3D, a unique software tool for MEMS and semiconductor fabs GDSII Layout Visualization 3D Modeling Engine builds voxel models by applying a sequence of primitive operations Process Description Simulation Mesh Voxels are 3D pixels Customizable to any process technology

4 MEMS design <-> MEMS foundry MEMS designer needs detailed information how 2D masks are translated into 3D structures to create a correct design goes up a learning curve -> design / fab / test loops MEMS foundry must provide additional customer support to promote its foundry technologies, to become more attractive to customers with little MEMS experience supports design process by accelerating the learning process catches design errors even before tape-out saves time and expense -> avoid unproductive real fab runs Use the concept of virtual fab run

5 Virtual Fab Run Import 2D layout as GDS file (-> designer) Add process script (-> foundry) using process editor or Python script + library of standard process steps (parametrized) 3D Modeling Engine Specialized 3D visualization cross sections, capture 3D images, animations Virtual Fab Run Pads and comb drive structures

6 Schematic flow X-FAB surface micromachining technology 1. Etch isolation trenches 2. Fill isolation trenches, deposit intermediate isolator 3. Deposit and pattern metal layer 4. DRIE mechanical structure 5. Passivate sidewalls, then open bottom of trenches 6. Isotropic etch to release mechanical structure (structure width determines which parts are freed) 7. Strip etch mask, sidewall passivation and buried oxide leaving single-crystal mechanical structure 8. Cap sensor wafer by glass frit wafer bonding

7 Case 1: Virtual fab run using a custom design 1. Etch isolation trenches 2. Fill isolation trenches, planarize 3. Deposit and pattern intermediate isolator 4. Deposit and pattern metal 5. DRIE mechanical structure 6. Passivate sidewalls, then open bottom of trenches 7. Isotropic release etch 8. Strip etch mask, sidewall passivation + buried oxide SEM picture of gyroscope chip with open cap wafer 9. Cap wafer by glass frit wafer bonding

8 Application SEM image images created with SEMulator3D X-FAB uses virtual fab runs for Customer support, marketing of MEMS foundry technologies Checking new designs prior to actual fabrication Process development Failure analysis

9 Case 2: 3D design check Example: A design error that was caught before mask tape-out Oxide Metal Top view of SEMulator3D model Visual inspection of SEMulator3D model showed isolation trench structure would have been improperly exposed to subsequent DRIE Design Error DRIE Oxide Mask

10 Case 3: Process development During development of X-FAB s technology, undesired pockets formed in mechanical layer during release etch Cut line for cross section Detailed 3-D process model of the protective oxide layer confirmed the hypothesis about the process failure: The release etch for the movable parts was etching through thin spots in the protective oxide layer 3-D Model

11 Conclusions 3-D process modeling is a novel tool for MEMS foundries and their customers, enabling virtual fab runs that capture Full MEMS devices Complete technology sequences X-FAB routinely uses and benefits from 3-D process modeling Provides important additional foundry customer support Saves masks and test wafers Saves design/fab/test cycles Reduce time to volume Process Development Process Integration Documentation & Training Ramp-up DfM for Designers Design Review Failure Analysis Volume Production Yield Enhancement 3-D process modeling is useful throughout the product development cycle

12 For more information and additional details, see: Gisbert Hölzer, et al, 3-D Process Modeling - A Novel and Efficient Tool for MEMS Foundry Design Support, 2009 Advanced Semiconductor Manufacturing Conference, 1. Stephen Breit, et al, 3-D Process Modeling - A Novel and Efficient Tool for MEMS Foundry Design Support, SEMICON West, July The authors acknowledge the help of the European Commission Framework 7 project CORONA for partial support of this work.