Au - Be/Ru/Au multilayer metallization as a stable ohmic contact scheme to p-type InP

Abstract

An attempt has been made to improve the electrical and metallurgical stability of Au-Be alloyed contacts to moderately doped p-type InP by minimizing the thickness of the Au-Be contact layer and using an Ru layer as a new, more effective diffusion barrier between the Au-Be and a thick Au top layer. It was found that the Au-Be contact layer only 40-50 nm thick is sufficient to give excellent ohmic contacts with specific contact resistance values as low as 2 × 10 −8 and 7 × 10 −8 m 2 (for N A -N D = (3-4) × 10 24 and (0.8-1) × 10 24 m −3 respectively). When subjected to an aging test at 280 • C for 50 h in N 2 gas, the 50 nm Au-Be/50 nm Ru/300 nm Au contacts alloyed at an optimum temperature of about 425 • C exhibit good thermal stability and no substantial increase in the specific contact resistance. The remarkable metallurgical stability of such contacts was confirmed by secondary neutral mass spectroscopy (SNMS) in-depth profile measurements. A comparison with the previously investigated diffusion barrier metals (such as Cr, Ti, Pt, etc) shows that the Ru layer is a much better barrier against the migration of Au into the InP substrate and, at the same time, it suppresses the out-diffusion of In and P from the semiconductor.

Related Electrical and Metallurgical Properties of Pd/Zn/Pd/Ge and Pd/Zn/Pd/Au Contact Systems to p-InGaP

“…The obtained minimum resistivity values conform to the moderate doping level of the InGaP epitaxial layers ( p % 2 Â 10 18 cm --3 ) and in spite of the larger bandgap ($1.9 eV) of InGaP, they are fully comparable to those for alloyed Au(Be, Zn) [5,18] and non-alloyed Ge/Pd(Zn) [14,15] Ohmic contacts to p-type InP with similar doping concentration.…”

“…Although Au-based contacts to InP and related compounds yield satisfactory contact resistivities, some problems (such as nonuniform surface and spiking interface and deep migration of Au into semiconductor) can arise at higher temperatures, which can cause device degradation and/or early failure [3]. To minimize the undesirable interfacial reactions and the migration of Au, various technological measures have been proposed [4][5][6]. Most of the effort, however, has been devoted to the development of low-resistance, shallow, non-Au-based Ohmic contacts, particularly those where the Au contact layer is replaced by Pd.…”

Shallow and Thermally Stable Ohmic Contacts to p-InAsP

“…Because V and Ti might readily react with Au, we inserted a Pt or Ru layer beneath the Au capping layer. Platinum is often used to suppress Au indiffusion in other contacts, and Ru is a good diffusion barrier for Au, as shown by Malina et al 8 However, as shown in Table I, high specific contact resistances from mid-10 −6 to mid-10 −5 ⍀ cm 2 were observed for the as-deposited V/Pt/Au ͑40:40:80 nm͒, Ti/Pt/Au ͑40:50:80 nm͒, and Ru/V/Ru/Au ͑2:40:20:80 nm͒ contacts. Therefore, contacts with Ni, Pt, and Pd layers deposited directly on the semiconductor were next tested.…”

Lower limits to metal-semiconductor contact resistance: Theoretical models and experimental data

“…8(j), Malina et al 57 obtained extremely low contact resistivities for p-InP. Here, 57 Au-Be was used for contacting the semiconductor and q c ¼ 2 Â 10 À8 X cm 2 was obtained after annealing, for a carrier concentration of (3-4) Â 10 18 cm À3 . The low q c could be a result of increased carrier concentration at the interface due to Be dopant diffusion in InP.…”