Stress Formation in Boron Nitride Films Prepared by Ion Beam Assisted Deposition
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ABSTRACT The stress formation during N/Ar ion assisted deposition of boron nitride films on Si(001) substrates was measured in-situ by a very sensitive capacity technique in dependence on the ion energy, temperature during deposition and the ion to atom arrival rate. The stress evolution in dependence on the layer thickness is characterized by a high tensile stress in the initial stage of the film growth, followed by a transition from the tensile to the compressive stress state, a strong increase of the compressive stress with the film thickness. A simultaneous UV-light irradiation during the deposition process leads to a reduction of the compressive stress. INTRODUCTION An additional low-energy ion bombardment during boron deposition is necessary to prepare the cubic phase of boron nitride. These synthesized c-BN films are characterized by a small mean diameter of the crystallites, an interlayer of sp 2-hybridized boron nitride (amorphous and/or hexagonal BN) at the substrate-film interface and large compressive stress (see e. g. ref. [1]). There are several models [2-5] which try to explain the formation of c-BN by aid of ion bombardment induced stress. The formation of c-BN can be explained by the generation of high compressive stress by ion bombardment of the growing film [2-5]. Consequently, accurate measurements of stress and
stress evolution dependent on deposition and ion irradiation conditions are important. But, only a few measurements of stress in BN films are known. McKenzie et al. [2] have found that a defined threshold stress value of about 4 GPa is necessary to form the c-BN phase. A correlation between the relative c-BN content and the compressive stress was found by Cardinale et al. [6]. Recently, the high-sensitive in-situ stress evolution during ion assisted deposition of boron nitride films has been demonstrated [7,8]. In this paper, the results of in-situ stress measurements during deposition of boron nitride films on silicon substrates by nitrogen/argon ion assisted boron deposition are given. The stress evolution and the final stress is studied in dependence on ion energy and substrate temperature. EXPERIMENT Boron nitride films on Si(100) substrates were prepared by electron beam evaporation of
boron and simultaneous bombardment with nitrogen and argon ions in high vacuum, where the nitrogen to argon ratio was always constant at 3. The ion energy El was varied between 150 and 650 eV and the substrate temperature T, between room temperature (RT) and 500 'C. The ion
current density and the boron atom deposition rate were chosen so that the ion to atom arrival ratio, I/A, varies between 0 and 2. The stress evolution in the growing boron nitride films was measured in situ and continuously during the film deposition with a cantilever beam device (for 153 Mat. Res. Soc. Symp. Proc. Vol. 585 © 2000 Materials Research Society
details see refs. [8,9]). The substrate deflection was determined with highly sensitive capacitance bridge and three capacitor plates. The reason for three capacitors is t
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