Backside Secondary Ion Mass Research Articles

Ohmic contacts on p-In0.53Ga0.47As prepared by Zn implantation into Pd-based metallizations

A new technique is presented for the fabrication of low-resistivity Ohmic contacts on p-In0.53Ga0.47As doped below 1×1019 cm−3 consisting of dopant implantation into the contact metal and subsequent rapid thermal annealing. Zn-implanted and annealed Pd/Au/Pt/Au, Pd/LaB6/Au, and Pd/Ge contacts exhibit drastically lowerer contact resistivity in comparison to corresponding systems prepared without implantation. A resistivity decrease by approximately one and a half orders of magnitude is observed in cases of Pd/Au/Pt/Au and Pd/LaB6/Au contacts. The lowest value is found for Pd/Au/Pt/Au on p-In0.53Ga0.47As doped to 4×1018 cm−3 with 1×10−6 Ω cm2, whereas 1–2×10−5 Ω cm2 is obtained for Pd/Ge contacts on p-In0.53Ga0.47As doped to 7×1018 cm−3. The elemental redistribution and the interface morphology of annealed contacts have been studied with backside secondary ion mass spectroscopy and cross-sectional transmission electron microscopy. No contact penetration and a planar interface are found in the case of Pd/Ge, whereas significant penetration of contact components into the semiconductor and nonplanarity of the interface are observed in Pd/Au/Pt/Au and Pd/LaB6/Au contacts. In contacts annealed at conditions for minimal resistivity the penetration depth is 200 and 105 nm, respectively. Implanted Zn is redistributed toward the contact interface during thermal processing. Thus the resistivity lowering is attributed to enhanced p-doping by Zn, which diffused from the contact into the underlying semiconductor. Residual implantation damage is discussed as the essential cause of the comparably high resistivity of implanted and annealed Pd/Ge contacts.

Secondary ion mass spectroscopy study of Zn or Cd implanted and rapid thermally annealed Pd/Ge contacts to p-In0.53Ga0.47As

Backside secondary ion mass spectroscopy is used to examine elemental redistribution in Zn or Cd implanted Pd/Ge contacts to p-InGaAs. A quaternary Pd-In-Ga-As layer is observed at annealing temperatures of 200–250 °C. At temperatures ≳250 °C, this layer disappears due to PdGe formation and InGaAs regrowth. Excess Ge diffuses to the contact interface. Cd and Zn accumulate inside the regrown InGaAs creating a thin, highly doped layer. Due to its abrupt interface and the formation of a highly doped layer beneath the contact, this implanted Pd/Ge contact scheme is a promising candidate for shallow ohmic contacts to p-InGaAs.

Backside secondary ion mass spectrometry study of a Ge/Pd ohmic contact to InP

High-resolution SIMS (secondary ion mass spectrometry) depth profiles of Ge/Pd ohmic contacts on InP are obtained by sputter-etching from the back (semiconductor) side. The samples contain an InGaAs-etch stop layer, to allow chemical thinning, and InGaAsP marker layers, which allow alignment and calibration of the depth profiles on the nm scale. At 200 °C, a Pd-In-P alloy layer is observed to form at the contact interface. The thickness of this layer is dependent on the amount of metallic Pd available for reaction. Subsequent processing at 325 °C results in the partial dissolution of this alloy layer, as PdGe forms at the contact interface, and regrowth of the liberated InP. Ge is detected in the regrown region but is not observed to diffuse into the substrate. Ge epitaxy is not observed at the contact interface at 325 °C, in contrast to the behavior of the Ge/Pd-GaAs contact. The experimental evidence suggests that regrowth is a key step in the formation of the ohmic contact.

Ge/Pd and Si/Pd/Ge/Pd Non-Alloyed Ohmic Contacts to InP Examined by Backside Secondary Ion Mass Spectrometry

ABSTRACTHigh resolution SIMS (secondary ion mass spectrometry) depth profiles of Ge/Pd and Si/Pd/Ge/Pd non-alloyed ohmic contacts on InP are obtained by sputter-etching from the back (semiconductor) side. The samples contain an InGaAs etch stop layer, to allow chemical thinning, and InGaAsP marker layers, which allow alignment and calibration of the depth profiles. Detailed comparisons are made to corresponding contacts on GaAs, processed and analyzed under similar conditions. The importance of interfacial alloy formation, semiconductor regrowth, and dopant incorporation are highlighted.

Backside secondary ion mass spectrometry investigation of ohmic and Schottky contacts on GaAs

A backside secondary ion mass spectrometry (SIMS) technique is employed to examine seven distinctive metallic contacts on GaAs at various stages of formation. The contacts are formed on multilayered GaAs/AlGaAs structures grown by molecular beam epitaxy (MBE), each containing an AlGaAs etch-stop layer and AlGaAs marker layers for precise alignment of the SIMS depth profiles. After removal of the substrate, the contact structures are profiled from the backside to avoid depth resolution degradation, which results when sputtering through a nonuniform multilayered metallic contact. The seven contacts examined are TaSix, Au/Ge/Ni, Au/Ge/Pd, Ge/Pd, Si/Pd, In/Pd, and Si/Ni/Mg. The TaSix Schottky contact exhibits extensive interdiffusion. The Au/Ge/Ni contact reveals extensive GaAs consumption. Much less consumption occurs in the Au/Ge/Pd contact. The absence of Au in the Ge/Pd contact leads to an extremely abrupt contact interface, with the Ge concentration dropping by four orders of magnitude within ∼100 Å of the interface. The Si/Pd contact is similar, with evidence of a complex compound formation within 200 Å of the interface. An ∼200 Å InGaAs region is in evidence at the In/Pd contact interface. The Si/Ni/Mg p-type ohmic contact profiles illustrate the progressive development of NiSi with the Mg layer serving as a diffusion barrier. The results are supplemented by transmission electron microscopy (TEM), and compared to various models of ohmic contact formation.

Ge redistribution in solid-phase Ge/Pd/GaAs ohmic contact formation

A backside secondary ion mass spectrometry technique is employed to examine elemental redistribution in the Ge/Pd/GaAs ohmic contact as a function of annealing conditions. Dilute Al containing marker layers (Ga1−x Alx As) in the GaAs permit precise calibration and alignment of the elemental depth profiles. Double etch-stop thinning yields high depth resolution. The onset of ohmic behavior is found to occur when Ge is detected at the GaAs surface. Good ohmic behavior is observed when an interfacial layer of reacted Pd4GaAs is dispersed and complete coverage of Ge occurs. The Ge/GaAs interface is abrupt with the Ge concentration dropping by over three orders of magnitude within 100 Å. About 40 Å of GaAs is found to be consumed during the ohmic contact formation. Degradation of the ohmic contacts, as a result of further heat treatment, was found to correlate with Ge in-diffusion into the GaAs. The results place strict limitations on doping and heterointerface models of ohmic behavior for this contact.

Ohmic Contact Formation Mechanism in the Ge/Pd/N-GaAs System

ABSTRACTAnnealed Ge/Pd/n-GaAs samples utilizing substrates with superlattice marker layers have been analyzed using high resolution backside secondary ion mass spectrometry and cross-sectional transmission electron microscopy. Interfacial compositional and microstructural changes have been correlated with changes in contact resistivity. The onset of good ohmic behavior is correlated with the decomposition of an intermediate epitaxial Pd4(GaAs,Ge2) phase and solid-phase regrowth of Ge-incorporated GaAs followed by growth of a thin Ge epitaxial layer.

A High Depth Resolution Backside Secondary Ion Mass Spectrometry Technique Used for Studying Metal/Gaas Contacts

ABSTRACTUnderstanding metal/semiconductor contacts is important for the fabrication of device structures. To date most studies have been aimed at understanding the metallurgical or the electrical properties. Directly measuring the impurity concentrations immediately beneath a contact rather than inferring it from electrical measurements has up until now been difficult. This paper describes a backside SIMS technique which not only demonstrates the ability of measuring doping concentrations close to a metal/semiconductor contact but also is capable of measuring the consumption of semiconductor material during a metal/semiconductor reaction. The sample preparation technique can be used to enable backside profiling using other profiling techniques such as Auger and x-ray photoelectron spectroscopy depth profiling, Rutherford backscattering, and backside electrical evaluation. The Ge/Pd/GaAs solid phase ohmic contact is used to demonstrate the technique.