Ni-Based Ohmic Contacts ton-Type 4H-SiC: The Formation Mechanism and Thermal Stability

Abstract

The fabrication of low-resistance and thermal stable ohmic contacts is important for realization of reliable SiC devices. For then-type SiC, Ni-based metallization is most commonly used for Schottky and ohmic contacts. Many experimental studies have been performed in order to understand the mechanism of ohmic contact formation and different models were proposed to explain the Schottky to ohmic transition for Ni/SiC contacts. In the present review, we summarize the last key results on the matter and post open questions concerning the unclear issues of ohmic contacts ton-type SiC. Analysis of the literature data and our own experimental observations have led to the conclusion that the annealing at high temperature leads to the preferential orientation of silicide at the heterointerface (0001)SiC//(013)δ-Ni2Si. Moreover, we may conclude that onlyδ-Ni2Si grains play a key role in determining electrical transport properties at the contact/SiC interface. Finally, we show that the diffusion barriers with free diffusion path microstructure can improve thermal stability of metal-SiC ohmic contacts for high-temperature electronics.

Ohmic contacts to n-type 3C-SiC using Cr/Ni/Au and Ni/Cr/Au metallizations

“…have been reported by Spera [19] with a value of ρc of 3.7 x 10 -3 Ω.cm 2 . The measurements of 9 ρc in the present study were also in agreement with calculations of the contact resistance of 10 ohmic contacts to n-type 4H-SiC annealed at 950-1050 °C using thermionic emission and 11 thermionic field emission models and with experimental data [5]. Contact resistances of 2 x 12 10 -3 Ω.cm 2 at ND = 1 x 10 17 cm -3 and 1 x 10 -5 Ω.cm 2 at ND = 1 x 10 19 cm -3 were calculated in the model assuming a barrier height of 0.35 eV [5].…”

“…Low values of ρc have been reported in ohmic contacts of Ni/n-type SiC after annealing at 900-1000 ºC [2][3][4]. These properties have been variously attributed to the formation of Ni2Si phase and accumulation of graphitic carbon at the interface [2][3][4], the generation of carbon vacancies near to the interface [2,3] and to the recrystallization of Ni2Si after annealing at >900 ºC with lowering of the barrier height [5]. But annealing at 900-1000 °C has also been accompanied by a roughening of the surface morphology and the formation of interfacial voids.…”

Nickel Film Deposition with Varying RF Power for the Reduction of Contact Resistance in NiSi

“…Figure 7 shows the plot of total resistance measured as a function of the gap space between the inner and outer rings of the NiSi layers for RF-1, RF-2, and RF-3. The lower total contact resistivities of 5.84 × 10 −5 Ω-cm 2 for n-Si and 6.58 × 10 −5 Ω-cm 2 for p-Si are obtained for the RF-2 film, respectively, and the reduction in contact resistance is lower than the Ni Ohmic contacts previously reported [28]. Thus, by controlling the film deposition using RF power, the quality of the NiSi formation can be controlled.…”

Inter-diffusion, melting and reaction interplay in Ni/4H-SiC under excimer laser annealing

“…Despite this approach has been already applied as reported in literature [3,6], a clear understanding of the mechanisms governing the silicide formation on 4H-SiC under laser irradiation is still lacking since the interaction between Ni, Si and C is very complex. Indeed, several interrelated phenomana come into play such as inter-diffusion of species [15,16,17,18,19,20,21], silicide reactions [22,23,24,25,26,27,28] and eventually melting processes [29].…”

“…While diffusing, Ni and Si could react with the formation of different silicide phases whose stoichiometry depends on the relative amount of the species and on the local temperature. They arise from the thermodynamic equilibrium and the kinetic conditions during the annealing process and during the cooling ramp down [22,25,26,27,28]. Rum-up and down are likewise important in time-dependent temperature fields that are also locally changeable.…”