Methods to Measure Mechanical Properties of NEMS and MEMS: Challenges and Pitfalls

Wolf, Ingrid De; Kalicinski, Stanislaw; Coster, J. De; Oprins, Herman

doi:10.1557/proc-1185-ii04-06

Cited by 2 publications

(3 citation statements)

References 18 publications

(20 reference statements)

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“…Several groups have shown micro-Raman spectroscopy is an effective technique for the measurement of mechanical stress in silicon 30,31,32,33,34,35,36,37,38 and silicon MEMS devices. 39,40,41,42,43,44,45,46 In micro-Raman spectroscopy, laser light is focused on the sample through a microscope to a spot size of ~1 μm in diameter. A laser beam ( = 532 nm) is used to irradiate the sample and the scattered light, which carries the Raman signals, is collected and directed into a spectrometer.…”

Section: Micro-raman Spectroscopymentioning

confidence: 99%

Using Micro-Raman Spectroscopy to Assess MEMS Si/SiO2 Membranes Exhibiting Negative Spring Constant Behavior

Starman

Coutu

2012

Exp Mech

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We introduce a novel micro-mechanical structure that exhibits two regions of stable linear positive and negative stiffness. Springs, cantilevers, beams and any other geometry that display an increasing return force that is proportional to the displacement can be considered to have a "Hookean" positive spring constant, or stiffness. Less well known is the opposite characteristic of a reducing return force for a given deflection, or negative stiffness. Unfortunately many simple negative stiffness structures exhibit unstable buckling and require additional moving components during deflection to avoid deforming out of its useful shape. In Micro-Electro-Mechanical Systems (MEMS) devices, buckling caused by stress at the interface of silicon and thermally grown SiO2 causes tensile and compressive forces that will warp structures if the silicon layer is thin enough. The 1 mm 2 membrane structures presented here utilizes this effect but overcome this limitation and empirically demonstrates linearity in both regions. The Si/SiO2 membranes presented deflect ~17 μm from their pre-released position. The load deflection curves produced exhibit positive linear stiffness with an inflection point holding nearly constant with a slight negative stiffness. Depositing a 0.05 μm titanium and 0.3 μm layer of gold on top of the Si/SiO2 membrane reduces the initial deflection to ~13.5 μm. However, the load deflection curve produced illustrates both a linear positive and negative spring constant with a fairly sharp inflection point. These results are potentially useful to selectively tune the spring constant of mechanical structures used in MEMS. The structures presented are manufactured using typical micromachining techniques and can be fabricated in-situ with other MEMS devices.

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Section: Micro-raman Spectroscopymentioning

confidence: 99%

Using Micro-Raman Spectroscopy to Assess MEMS Si/SiO2 Membranes Exhibiting Negative Spring Constant Behavior

Starman

Coutu

2012

Exp Mech

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“…Several groups have shown micro-Raman spectroscopy is an effective technique for the measurement of mechanical stress in silicon 4,5,6,7,8,9,10,11,12,13 and silicon MEMS devices. 14,15,16,17,18,19,20,21 Raman stress profiles obtained during post-fabrication processes indicate significant stress reduction is possible in the polysilicon layers of the Multi-User MEMS Processes (MUMPs) foundry process. 1 Stress reduction is assessed and verified through on-chip test structures (cantilevers, comb resonators, and buckling beam arrays).…”

Section: Introductionmentioning

confidence: 99%

“…(a) Heat loss mechanisms for a polysilicon microbridge20,23 and (b) an equivalent thermal circuit model When using Raman spectroscopy, heat generation due to laser heating must be eliminated or significantly reduced to minimize thermal effects on the Raman stress profiles. Thus, the thermal radiation conductance component is omitted in the thermal circuit model ofFig.…”

mentioning

confidence: 99%

Stress Monitoring of Post-processed MEMS Silicon Microbridge Structures Using Raman Spectroscopy

Starman

Coutu

2012

Exp Mech

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Inherent residual stresses during material deposition can have profound effects on the functionality and reliability of fabricated Micro-Electro-Mechanical Systems (MEMS) devices. Residual stress often causes device failure due to curling, buckling, or fracture. Typically, the material properties of thin films used in surface micromachining are not well controlled during deposition. The residual stress; for example, tends to vary significantly for different deposition methods. Currently, few nondestructive techniques are available to measure residual stress in MEMS devices prior to the final release etch. In this research, micro-Raman spectroscopy is used to measure the residual stresses in polysilicon MEMS microbridge devices. This measurement technique was selected since it is nondestructive, fast, and provides the potential for in-situ stress monitoring. Raman spectroscopy residual stress profiles on unreleased and released MEMS microbridge beams are compared to analytical and FEM models to assess the viability of micro-Raman spectroscopy as an in-situ stress measurement technique. Raman spectroscopy was used during post-processing phosphorus ion implants on unreleased MEMS devices to investigate and monitor residual stress levels at key points during the post-processing sequences. As observed through Raman stress profiles and verified using on-chip test structures, the post-processing implants and accompanying anneals resulted in residual stress relaxation of over 90%.

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Methods to Measure Mechanical Properties of NEMS and MEMS: Challenges and Pitfalls

Cited by 2 publications

References 18 publications

Using Micro-Raman Spectroscopy to Assess MEMS Si/SiO2 Membranes Exhibiting Negative Spring Constant Behavior

Using Micro-Raman Spectroscopy to Assess MEMS Si/SiO2 Membranes Exhibiting Negative Spring Constant Behavior

Stress Monitoring of Post-processed MEMS Silicon Microbridge Structures Using Raman Spectroscopy

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