# Presentation: 009456

## Reliability and Quality Assurance Issues & Methods for Commercial MEMS

- Gisela Lin, Stephen A. Raccio, Walter Li
- Nevenka C. Liakopoulos, Raji Mali
- Standard MEMS, Incorporated

- JPL MRQW, Pasadena, California, December 12, 2001

## Outline

- Introduction
- SMI Commercial Device Examples
- MEMS with integrated CMOS
- Bulk Micromachining
- Surface Micromachining
- Reliability and QA issues & testing
- Process level
- Device level
- Further reliability and QA challenges
- Conclusions

## Introduction to SMI

- Standard MEMS, Incorporated
- Founded in 1995
- Independent, contract manufacturer of MEMS and CMOS ICs.
- Shipped 50 Millionth MEMS device in October 2001
- Cover many application areas
- Two MEMS/IC fabrication facilities
- 4” and 6” wafer production

## Tri-color Ink-Jet Printhead

- Bulk micromachined nozzle with integrated CMOS

- Fabricated at Standard MEMS Inc.

- Ink is resistively flash heated and propelled out nozzle.

## DNA Analysis Chip

- Fabricated at Standard MEMS Inc. for Nanogen

## Bulk Micromachining - Blades

-  Silicon microblades formed via chemical etching
-  Used for delicate microsurgery
-  Microneedles fabricated in a similar fashion

- Fabricated at Standard MEMS, Inc.

## Standard MEMS, Inc. Triple-Poly Process

- Silicon Substrate

- Nitride (0.6m)

- Polysilicon #0 (0.5m)

- Oxide #1 (2m)

- Polysilicon #1 (2m)

- Oxide #2 (0.75m)

- Polysilicon #2 (1.5m)

- Metal (0.5m)

## MEMS Gyroscope

- Fabricated at Standard MEMS Inc.

## Reliability & QA Issues at SMI

- Fabrication process validation
- Film quality (thickness, stress, grain size, etc.)
- Feature uniformity (run to run, wafer to wafer)
- In-situ diagnostics and sets of test structures
- Product performance
- Performance validation (both MEMS and ICs)
- Environmental test (elevated temperature, pressure, humidity, under bias, etc.)
- Accelerated lifetime test
- Next: examples of each...

## Process Validation Example

- Square plates fabricated in Poly1, Poly2, and Poly1 + Poly2
- Curvature measured using non-contact, surface mapping interferometric microscope (Wyko), in both x and y direction.
- Plate size varies from 100μm square to 700μm square.
- Plates annealed at 1000°C for 1 hour.

***Residual stress characterization in polysilicon thin films via plate curvature test structures:***

## Example Data for Polysilicon

- Poly1
- 3 die from random locations on a single wafer

- Poly2
- 3 die from random locations on a single wafer

## Thin Film Residual Stress 

- By controlling annealing conditions, we can control stress in polysilicon films
- 0 – 50MPa (typical)
- Low compressive to low tensile
- Similar stress control methods in silicon nitride, silicon carbide films

## Pull-in Voltage Test Structure

- Poly1, poly2, or poly1 + poly2 stack

- Poly0

- Silicon substrate

- Silicon nitride

- Length of beam varies from 100μm – 1mm
- Beams test structures of 2 types:
- (1) fixed-free and (2) fixed on both sides
- Test structures have 2 kinds of pull down electrode:
-  (1) Poly0 ground plane (2) bare silicon substrate

## Data for Beam Arrays

- Cantilever beams

- Double clamped beams

## Additional Process Validation Tests

- Buckled beam strain measurements
- Film thickness, critical dimension measurement and validation
- Sheet resistance, contact resistance
- Tensile testing of thin films
- Bi-axial stress characterization
- Guckel rings
- Clamped-free and doubly clamped beams

## Device Performance Example

***Bulk micromachined, piezoresistive pressure transducer, rated to 100psi:***

- Silicon

- Input bias

- Ground

- Pressure sensor output #1

- Membrane

- 1

- 2

- 3

- 4

- Pressure sensor output #2

## Nominal Resistance Data

- Bridge resistance specification is 4700Ω  800Ω
- 180 out of 19,544 die tested were out of spec
- Yield = 99%

## Wheatstone Bridge Offset Data

- Offset specification is –4mV  4mV
- 337 out of 19,427 die tested were out of spec
- Yield = 98%

## Device Linearity Testing

- Span = Full-scale output range (in mV)
- Data replotted as % of span (i.e. deviation from non-linearity if endpoints used as fitting points)

## Device Linearity Data

- 10 devices tested per wafer in a 25 wafer lot

## Additional Performance Tests

- For pressure sensors:
- Initial zero, full scale error, span error, sensitivity...
- Packaged, unpackaged
- In general for MEMS and CMOS ICs:
- Environmental test (elevated temperature, pressure, humidity, under bias, etc.)
- Electrical testing (impedance, breakdown voltage, resistance, etc.)
- Accelerated lifetime test

## Further Issues & Challenges

- Application specific reliability and QA
- Performance and process “windows” of acceptance
- Standard tests (first order influences)
- Specific tests (second order influences)
- Multi-level reliability and QA
- Process (microscopic)
- Device, package, system (macroscopic) ...
- Design of appropriate test structures and diagnostic tools
- Complex, integrated systems

## Conclusions

- SMI has several standard processes:
- MEMS with integrated CMOS
- Bulk Micromachining
- Surface Micromachining
- Each requires reliability and QA testing
- Process level (test structures, microscopy, etc.)
- Device level (environmental, electrical, etc.)
- Further reliability and QA challenges:
- Specific testing for certain applications
- Levels: process, device, package, system

**www.stdmems.com**