Diboride diffusion barriers in silicon and GaAs technology

Abstract

TiB2 and ZrB2 are members of the larger group of interstitial compounds which the transition metals form with boron, carbon, and nitrogen. Such materials are of significant interest for microelectronic application owing to a combination of low resistivity and outstanding diffusion barrier properties. We report here studies on the application of these diborides as diffusion barriers for both Si and GaAs based device technology. rf diode sputtered thin film ZrB2 has an annealed resistivity of 25 μΩ cm, rivaling that of its most widely employed silicide competitor, TiSi2 (18 μΩ cm). In addition, in experiments with bilevel structures consisting of first-level ZrB2 and second-level Al, no evidence of reaction has been observed in RBS spectra for samples heat treated in N2 at 625 °C for 2 h. These compounds thus appear to offer the prospect of serving the dual role of low resistivity contact metal as well as a self-diffusion barrier in multilevel contact structures. Recent work on the application of these materials for GaAs contact technology is even more significant. Alloyed Ohmic contacts to n-GaAs, a traditionally difficult technological problem, have been fabricated in which the Ohmic metallization (Ni/Ge/Au) in contact with the GaAs substrate is separated from the overlying thick Au upper contact by an intervening e-beam deposited TiB2 layer. The resultant structure shows improved electrical stability on aging at 350 °C to those of a more conventional nature prepared similarly, but employing a Ni film in place of the TiB2. This improved stability is attributed to the effectiveness of the diboride as a diffusion barrier to the in-migration of Au, thus preventing further modification of the Ohmic contact metallurgy obtained on alloying.

Improved Schottky Contacts on n-Type 4H-SiC Using ZrB2 Deposited at High Temperatures

“…In addition, Zr is known to be quite reactive with oxygen, and in this case, it may also be gettering oxygen from the heated SiC surface. 44,45 The RBS spectra further reveal an absence of any substantial reaction between the ZrB 2 film and the SiC, indicating the thermal stability of this contact. However, a minimal interaction with possible silicide or carbide formation cannot be completely ruled out from these spectra, and additional analysis is underway to further study the interface chemistry of the ZrB 2 /SiC contact deposited at elevated temperatures.…”

ZrB2 thin films grown by high power impulse magnetron sputtering from a compound target

“…While the bulk resistivity of ZrB 2 is about 10 µΩcm [13], thin film ZrB 2 grown by magnetron sputtering techniques thus often shows significantly higher resistivity values than for bulk, ranging from 160 to 440 µΩcm [1,8,11,12]. Annealing experiments causing recrystallisation has, however, been shown to decrease the film resistivity to ~25 µΩcm [1,14]. It has been shown that elevated deposition temperatures or intense ion irradiation of the film during growth enhances the crystalline quality and alters the preferred orientation [15,16].…”

“…Moreover, the material system efficiently absorbs, and is strongly influenced by contaminations [1,2,4,7,10,11], which may affect the electrical properties [12]. While the bulk resistivity of ZrB 2 is about 10 µΩcm [13], thin film ZrB 2 grown by magnetron sputtering techniques thus often shows significantly higher resistivity values than for bulk, ranging from 160 to 440 µΩcm [1,8,11,12]. Annealing experiments causing recrystallisation has, however, been shown to decrease the film resistivity to ~25 µΩcm [1,14].…”

“…For example, composition in the films deviating -at times very much -from that of the source has been reported [4][5][6][7][8][9]. Moreover, the material system efficiently absorbs, and is strongly influenced by contaminations [1,2,4,7,10,11], which may affect the electrical properties [12]. While the bulk resistivity of ZrB 2 is about 10 µΩcm [13], thin film ZrB 2 grown by magnetron sputtering techniques thus often shows significantly higher resistivity values than for bulk, ranging from 160 to 440 µΩcm [1,8,11,12].…”

“…Owing to its properties, the material has potential for serving as diffusion barrier in microelectronics [1,2]. Ceramic films, e.g., oxides, nitrides, carbides, and borides can be grown by magnetron sputtering techniques from a compound target of the desired composition.…”