E. Ghegin

Towards contact integration for III–V/Silicon heterogeneous photonics devices

Silicon photonics is of great interest as it opens the way to large bandwidth and high data rates. A pioneer Silicon photonics scheme consists in integrating III-V lasers on the SOI substrates containing the passive components. However, key developments are necessary to co-integrate III-V devices with CMOS very large scale integration (VLSI). In this paper we propose a CMOS-compatible integration scheme of contacts (i.e. semiconductor metallization and plug) on III-V surfaces taking into account the limitations fixed by the operating laser device. Based on metallurgical, morphological, optical and electrical studies, processes are submitted and reviewed for the purpose of forming stable and reproducible contacts with low resistivity in a 200 millimeters fab line.

Formation of Ni3InGaAs phase in Ni/InGaAs contact at low temperature

The composition and morphology of the product phase after the reaction of Ni thin film with In0.53Ga0.47As substrate at 350 °C were investigated by atom probe tomography, X-ray diffraction, and scanning electron microscopy. Results show the formation of a unique Ni3(In0.53Ga0.47)As phase with a low concentration in-depth gradient of Ni and the decoration of the grain boundaries by In atoms. These analyses indicate that Ni is the main diffusing specie during the growth of Ni3(In0.53Ga0.47)As phase. The volume of the product phase is higher than the volume of the consumed Ni film as expected for the formation of Ni3(In0.53Ga0.47)As phase.

Phase formation sequence in the Ti/InP system during thin film solid-state reactions

The metallurgical properties of the Ti/InP system meet a great interest for its use as a contact in the scope of various applications such as the Si Photonics. The investigations conducted on this system highlight the initiation of a reaction between the Ti and the InP substrate during the deposition process conducted at 100 °C. The simultaneous formation of two binary phases, namely, Ti2In5 and TiP, is attributed to the compositional gradient induced in the InP by the wet surface preparation and enhanced by the subsequent in situ Ar+ preclean. Once formed, the TiP layer acts as a diffusion barrier inhibiting further reaction up to 450 °C in spite of the presence of an important Ti reservoir. At higher temperature, however, i.e., from 550 °C, the reaction is enabled either by the enhancement of the species diffusion through the TiP layer or by its agglomeration. This reaction gives rise to the total consumption of the Ti2In5 and Ti while the TiP and In phases are promoted.

200mm full CMOS-compatible hybrid III-V/Si laser process integration on a mature silicon-photonic platform (Conference Presentation)

Silicon photonic platforms are becoming more and more mature with competitive devices suitable for increasing needs of HPC (High Performance Computing) systems and datacenters. Compared to bulk III-V technologies, Si photonic technologies are suffering from the lack of integrated light source. Several works have been done in the past years to integrate laser on silicon using III-V direct bonding on top of patterned silicon. These demonstrations were using a CMOS compatible process for the silicon part but all the process steps following the introduction of the III-V material were done with small wafer diameter III-V fabrication lines. With such integrations, the cost advantage of silicon photonics based on the use of CMOS platforms and large wafer format is no more valid. In this paper we present the integration of a hybrid III-V/Si laser using a fully CMOS compatible 200mm technology. The laser is integrated in a mature photonic platform. The additional process modules required for this integration will be deeply described. These modules are localized silicon thickening using damascene process, Bragg reflector patterning with DUV lithography, III-V patterning and ohmic contact formation with no lift-off and without noble metal. This integration is compatible with a multi metal levels planar BEOL, mandatory for photonic circuit design. The first DFB lasers fabricated with this new platform are operating at 1310nm with a threshold current around 60mA, a SMSR larger than 45dB and more than 1.5mW optical power in the output waveguide. New laser designs, specifically adapted for this new process, will be introduced and fabricated.

InGaAs surface pretreatment prior to metal solid-state reactions for low resistance contacts

We have investigated the impact of various plasma treatments on InGaAs layers. Argon- and helium-based direct plasmas are more efficient than remote plasmas for the removal of InGaAs native oxides. We have demonstrated that the nature of direct plasma influences the InGaAs oxides removal efficiency. Indeed, both types of plasma seem to be efficient for removing arsenic oxides whereas the elimination of In oxides is more effective with Ar plasma. Hydrogen addition in He plasma impacts the removal of InGaAs oxides and appears to have a reducing effect on indium atoms. Whatever the nature of the pretreatment, the surface morphology and roughness of InGaAs layers were not significantly impacted.

Elaboration of Ni/InP contacts: Solid state reactions and associated mechanisms

The metallurgical properties of the Ni/n-InP system have been investigated. We report the formation of a compositionally nonuniform Ni-In-P amorphous layer during the DC sputtering metal deposition process which includes an Ar+ cleaning. During various heat treatments the simultaneous appearance of the Ni2P and Ni3P binary phases and the Ni2InP ternary phase were observed. For temperature equal to or greater than 350°C we highlighted the partition and precipitation of In. Thanks to RTP and longtime annealings we pointed out the predominance of diffusion on the formation of the Ni2P, Ni3P and Ni2InP phases and that of nucleation on the partition and precipitation of In.

Solid state reaction of Ni thin film on n-InP susbtrate for III-V laser contact technology

The metallurgical properties of the Ni/n-InP system have been investigated. We report the formation of a compositionally nonuniform Ni-In-P amorphous layer during the DC sputtering metal deposition process which includes an Ar+ cleaning. After RTP and long in situ annealing treatments the simultaneous appearance of the Ni2P and Ni3P binary phases and the Ni2InP ternary phase were observed. Kinetics and nucleation phenomena were highlighted by the precipitation of In during the RTP.

In situ cleaning/passivation of surfaces for contact technology on III-V materials

In this work we introduce the use of physical plasmas (e.g. Ar- and He-based plasmas) in order to study the in situ cleaning (prior to metal deposition) of InGaAs layers dedicated to the realisation of self-aligned contacts. For the characterisation of cleaning efficiency, we performed surface analyses like X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy in attenuated total reflection mode. The first results described in this work are encouraging. We have found efficient processes for removing totally or partially III-V native oxides.