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Stress in boron nitride nanofilms prepared by rapid thermal annealing ♣

K. CHRISTOVA1,* , I. BORADJIEV1, D. SPASSOV1, G. BESHKOV1

Affiliation

  1. Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria

Abstract

Boron Nitride (BN) nanofilms (5-7 nm) were prepared by Rapid Thermal Annealing (RTA) of boron layers deposited on sapphire (Al 2O 3) substrates in NH 3 ambient in vacuum (5x10-2 Torr). The RTA process temperatures used were: 800, 1000, 1200 and 1400 ºC, each applied for times of 15, 30, 60 and 180 s. The mechanical stress in the BN films, as a function of these processing parameters of the RTA process and its correlation to other film characteristics, were studied. Stress measurements showed that a transition from compressive to tensile stress occurs. The stress changed over a wide range of values, depending on the RTA process parameters. For example, the stress in the film before annealing is compressive, viz– 1.75x10 10 N.m-2, and after RTA for 15 s, it is tensile with values of 0.75, 1.41, 2.65 and 2.28 x10 10 N.m-2 for annealing temperatures of 800, 1000, 1200 and 1400 ºC respectively. The stress increase is due to increased nitrogen sorption on the substrate and the formation of BN films at higher (1200-1400 ºC) temperatures. Boron nitride film morphology shows that films annealed at 800-1000 ºC exhibit a homogeneоus morphology, while for those annealed at 1200 ºC, a needle-like morphology starts to be formed. Our results show that stress is in good correlation with XPS and the ohmic resistance measured for these films. Mechanical stress results are discussed on the basis of the N/B ratio and phase transformations in the boron nitride films..

Keywords

Nanofilms, Mechanical stress, Boron nitride, Rapid thermal annealing.

Submitted at: Nov. 5, 2008
Accepted at: Oct. 3, 2009

Citation

K. CHRISTOVA, I. BORADJIEV, D. SPASSOV, G. BESHKOV, Stress in boron nitride nanofilms prepared by rapid thermal annealing ♣, Journal of Optoelectronics and Advanced Materials Vol. 11, Iss. 10, pp. 1557-1560 (2009)