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Title: Role of microstructure and doping on the mechanical strength and toughness of polysilicon thin films

We investigated the role of microstructure and doping on the mechanical strength of microscale tension specimens of columnar grain and laminated polysilicon doped with different concentrations of phosphorus. The average tensile strengths of undoped columnar and laminated polysilicon specimens were 1.3 ± 0.1 and 2.45 ± 0.3 GPa, respectively. Heavy doping reduced the strength of columnar polysilicon specimens to 0.9 ± 0.1 GPa. On grounds of Weibull statistics, the experimental results from specimens with gauge sections of 1000 μm × 100 μm × 1 μm predicted quite well the tensile strength of specimens with gauge sections of 150 μm × 3.75 μm × 1 μm, and vice versa. The large difference in the mechanical strength between columnar and laminated polysilicon specimens was due to sidewall flaws in columnar polysilicon, which were introduced during reactive ion etching (RIE) and were further exacerbated by phosphorus doping. Moreover, the removal of the large defect regions at the sidewalls of columnar polysilicon specimens via ion milling increased their tensile strength by 70%-100%, approaching the strength of laminated polysilicon, which implies that the two types of polysilicon films have comparable tensile strength. Measurements of the effective mode I critical stress intensity factor, KIC,eff, also showedmore » that all types of polysilicon films had comparable resistance to fracture. Therefore, additional processing steps to eliminate the edge flaws in RIE patterned devices could result in significantly stronger microelectromechanical system components fabricated by conventional columnar polysilicon films.« less
Authors:
 [1] ;  [2] ;  [1]
  1. Univ. of Illinois at Urbana-Champaign, Champaign, IL (United States)
  2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
OSTI Identifier:
1109313
Report Number(s):
SAND-2013-6879J
Journal ID: ISSN 1057-7157; 472177
Grant/Contract Number:
AC04-94AL85000
Type:
Accepted Manuscript
Journal Name:
Journal of Microelectromechanical Systems
Additional Journal Information:
Journal Volume: 24; Journal Issue: 5; Journal ID: ISSN 1057-7157
Publisher:
IEEE
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; critical stress intensity factor; Weibull; grain size; MEMS; size effects; doping; microstructure