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Volumn 298, Issue 5596, 2002, Pages 1215-1218

Fatigue failure in polysilicon not due to simple stress corrosion cracking

Author keywords

[No Author keywords available]

Indexed keywords

BRITTLENESS; CYCLIC LOADS; FATIGUE OF MATERIALS; FRACTURE MECHANICS; STRESS CORROSION CRACKING; TENSILE STRESS;

EID: 0037044914     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: None     Document Type: Article
Times cited : (161)

References (31)
  • 2
    • 2142640460 scopus 로고    scopus 로고
    • note
    • 2O molecules react with crack-bridging Si-O-Si bonds and create two Si-O-H surface groups, with localized crack extension (27).
  • 12
    • 2142699661 scopus 로고    scopus 로고
    • note
    • The growth of a thin oxide layer on silicon at room temperature, sometimes called a "native oxide," is well established (28). It typically becomes ∼2 nm thick after exposure to air and gradually thickens to a maximum of ∼4 nm.
  • 15
    • 2142708239 scopus 로고    scopus 로고
    • note
    • 2 layer beneath the fabricated structures, which allows portions of a device to be free from the substrate while remaining anchored at discrete points. The details of our MEMS fabrication can be found in (8).
  • 17
    • 2142658952 scopus 로고    scopus 로고
    • note
    • Three polysilicon films were used in this investigation. Two were 3.0 μm thick and deposited with LPCVD at 580°C. This deposition temperature results in an as-deposited residual tensile stress of ∼300 MPa. The first film was annealed at 910°C in argon, and the residual stress was reduced to 69 MPa. The second film was annealed for a longer time at 910°C in argon, and the residual stress was reduced to 56 MPa. The third polysilicon film was a 3.7-μm-thick multilayer and consisted of nine layers, each between 0.2 and 0.8 μm thick. This film was deposited at alternating temperatures of 570°C and 615°C, as described in (16). The layers deposited at 570°C contained tensile residual stresses on the order of 300 MPa, and the layers deposited at 615°C contained compressive residual stresses, also on the order of 300 MPa. The overall residual stress of the as-deposited multilayer was 69 MPa, but after annealing at 1000°C in nitrogen, the overall residual stress decreased to 44 MPa. The stresses of the individual layers probably differ from the overall value. However, these local stresses do not affect the behavior of the crack tips in these multilayer polysilicon films, as was confirmed by fracture toughness investigations of polysilicon films of varying microstructures, as described in (25).
  • 18
    • 2142812512 scopus 로고    scopus 로고
    • note
    • IC with modest crack extension.
  • 20
    • 2142706770 scopus 로고    scopus 로고
    • note
    • IC.
  • 21
    • 2142811124 scopus 로고    scopus 로고
    • note
    • The procedure for this experiment is described as follows. The actuators were mechanically displaced to produce a tensile stress at the notch tip of 3.6 GPa. Next, a dc voltage was applied between the actuator and the substrate, clamping the actuator to the substrate, and a drop of water was placed on the actuator. When the water evaporated, the capillary forces brought the actuator and substrate into intimate contact, generating van der Waals forces. These forces, sometimes referred to as "stiction" in the micromachining literature, are quite strong when compared to the size of the devices, and they secured the actuator permanently in place, even when the voltage was removed.
  • 22
    • 2142813924 scopus 로고    scopus 로고
    • note
    • As the applied dc bias voltage causes the actuator to deflect, this increases the stiffness of the actuator support beams, causing small changes in the resonant frequency of the microdevice.
  • 23
    • 2142716926 scopus 로고    scopus 로고
    • note
    • 4 cycles.
  • 24
    • 2142754063 scopus 로고    scopus 로고
    • note
    • For a semicircular flaw, k = 0.71 (30).
  • 26
    • 2142714100 scopus 로고    scopus 로고
    • note
    • Although the five specimens tested with R > 0 (tensile stresses only) appeared to exhibit strengths greater than the measured monotonic bend strength, these five data varied between 4.3 and 5.3 GPa. In comparison, the nine samples tested under monotonic loading had strengths between 3.0 and 4.8 GPa. We think that these differences are merely statistical and reflect the vagaries of processing brittle materials such as silicon; Eq. 1 indicates that the flaw size corresponding to a strength of 3.0 GPa is 35 nm, whereas the flaw size that corresponds to a strength of 5.3 GPa is 11 nm. When taken as a single population, the 14 measurements obey Weibull statistics, with a mean strength of 4.3 GPa and a Weibull modulus of 6.3.
  • 31
    • 2142655970 scopus 로고    scopus 로고
    • note
    • We thank Y. Wang for the finite element analysis of the doubly clamped beams. This work was supported by the Defense Advanced Research Projects Agency under contract N00014-00-1-0881.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.