R. Ruiz

Evaluation of amorphous (Mo, Ta, W)SiN diffusion barriers for 〈Si〉|Cu metallizations

Abstract Amorphous binary M(= Mo, Ta or W)-Si and ternary MSiN, r.f.-sputtered from M 5 Si 3 and WSi 2 targets, are assessed as diffusion barriers between silicon substrates and copper overlayers. By I ( V ) tests of the metallizations on n + p shallow junction diodes, the ternary MSiN barriers prevent copper from reaching the silicon at 800 °C or higher during a 30 min heat treatment in vacuum. Failure of the metallizations correlates with the crystallization temperature of the barrier, which is presumably a prelude to fast grain-boundary diffusion. Metal-rich MoSiN and WSiN barriers liberate nitrogen during annealing, which poses a limitation to their crystallization temperatures. No reaction products of copper with metal-rich MSi or MSiN barriers are observed, which is in agreement with our recent thermodynamic modelling of the MSiCu ternary systems.

Amorphous (Mo, Ta, or W)-Si-N diffusion barriers for Al metallizations

M–Si–N and M–Si (M=Mo, Ta, or W) thin films, reactively sputtered from M5Si3 and WSi2 targets, are examined as diffusion barriers for aluminum metallizations of silicon. Methods of analysis include electrical tests of shallow-junction diodes, 4He + + backscattering spectrometry, x-ray diffraction, transmission electron microscopy, scanning electron microscopy, and secondary-ion-mass spectrometry. At the proper compositions, the M–Si–N films prevent Al overlayers from electrically degrading shallow-junction diodes after 10 min anneals above the melting point of aluminum. Secondary-ion-mass spectrometry indicates virtually no diffusivity of Al into the M–Si–N films during a 700 °C/10 h treatment. The stability can be partially attributed to a self-sealing 3-nm-thick AlN layer that grows at the M–Si–N/Al interface, as seen by transmission electron microscopy.

Reactively sputtered Ti-Si-N films. II. Diffusion barriers for Al and Cu metallizations on Si

Ti-Si-N films synthesized by reactively sputtering a TiSi2, a Ti5Si3, or a Ti3Si target in Ar/N2 gas mixture were tested as diffusion barriers between planar (100) Si substrates and shallow n+p Si diodes, and Al or Cu overlayers. The stability of the Ti-Si-N barriers generally improves with increasing nitrogen concentration in the films, with the drawback of an increase in the film’s resistivity. Ti34Si23N43 sputtered from the Ti5Si3 target is the most effective diffusion barrier among all the Ti-Si-N films studied. It works as an excellent barrier between Si and Cu. A film about 100 nm thick, with a resistivity of around 700 μΩ cm, maintains the stability of Si n+p shallow junction diodes with a 400 nm Cu overlayer up to 850 °C for 30 min vacuum annealing. When it is used between Al and Si, the highest temperature of stability achievable with a 100-nm-thick film is 550 °C. A thermal treatment at 600 °C causes a severe intermixing of the layers. The microstructure, atomic density, and electrical resistivi...

W-B-N diffusion barriers for Si/Cu metallizations

Reactively sputtered from a W2B target, amorphous W-B-N thin films are investigated. The physical properties of the films, namely density, resistivity, crystallization behavior and reaction temperature with silicon, are given as functions of composition. Additionally, the films are assessed as diffusion barriers between silicon substrates and copper overlays. By I(V) measurements of shallow-junction diodes, a 100 nm W64B20N16 barrier prevents copper from reaching the silicon during an 800 °C, 30 min heat treatment in vacuum. W79B21 films are able to prevent diffusion into the diodes only up to 500 °C. High resolution transmission electron microscopy shows that W64B20N16 and W79B21 films are both marginally amorphous with local ordering of less than 1.5 nm.

Microstructure of polycrystalline CuInSe2/Cd(Zn)S heterojunction solar cells

Abstract Polycrystalline CuInSe 2 /Cd(Zn)S heterojunction solar cells deposited on Corning 7059 or soda-lime glass are characterized structurally and chemically by scanning electron microscopy and transmission electron microscopy in conjunction with energy-dispersive analysis of X-rays. Scanning electron micrographs reveal rough and uneven surfaces and cross-sectional morphologies of the Cd(Zn)S and CuInSe 2 layers. The crystallography and defect structure of the individual Cd(Zn)S, CuInSe 2 and molybdenum layers are examined by conventional and high resolution transmission electron microscopy. The crystal structures for Cd(Zn)S, CuInSe 2 and molybdenum are wurtzite, chalcopyrite and b.c.c. respectively. The Cd(Zn)S layer exhibits stacking faults on hexagonal basal planes. Planar defects such as twins and stacking faults on {112} chalcopyrite planes are identified in the CuInSe 2 layer. The most significant features obtained from these cross-sections are (i) the lateral non-uniformity of the Cd(Zn)S and CuInSe 2 layers, (ii) the intimate bonding between these two layers, and an epitaxial relationship between grains of Cd(Zn)S and CuInSe 2 at the interface ({0001} Cd(Zn)S ∥ {112} CuInSe 2 ), and (iii) the presence of voids and fractures in the CuInSe 2 layer. A correlation between the formation of fractures and voids and the defect structure in CuInSe 2 layer, and the mechanical stresses induced by differential thermal contraction of the substrate/film assembly is discussed.

REACTION OF TA THIN FILM WITH SINGLE CRYSTALLINE (001) BETA -SIC

The reaction between a sputter‐deposited Ta film (320 nm thick) and a single crystalline (001) β‐SiC substrate induced by vacuum annealing at temperatures of 600–1200 °C for 1 h (30 min at 1100 °C) is investigated by 3 MeV He++ backscattering spectrometry, x‐ray diffraction, secondary ion mass spectrometry, and transmission and scanning electron microscopies. No significant reaction is observed at 800 °C or at lower temperatures. At 900 °C, the main product phases are Ta2C and carbon‐stabilized Ta5Si3. A minor amount of unreacted Ta is also present. After annealing at 1000 °C, all the tantalum has reacted; the reaction zone possesses a multilayered structure of β‐SiC/TaC/carbon‐stabilized Ta5Si3/α‐Ta5Si3/Ta2C. The diffusion path at 1000 °C is plotted on the isothermal section of the Ta‐Si‐C phase diagram. At 1100 °C, the reacted layer has an interface with the SiC substrate that is still quite flat but has a rough surface due to the formation of macroscopic voids within the reacted layer. The equilibrium ...

Gold metallization for aluminum nitride

A metallization scheme for gold on AlN is investigated that incorporates three layers sputter-deposited in succession on the AlN substrate, without breaking vacuum: 20 nm of Ti to promote adhesion, a 100 nm thick TiSiN barrier layer, and 230 nm Au. The stability of the scheme was studied after annealing in vacuum up to 800 °C for 30 min and at 400 °C in Ar ambient for 300 h, using 2 MeV 4He++ backscattering spectrometry, sheet resistance measurements, and adhesion tests. It is shown that the incorporation of the diffusion barrier prevents the interaction of the Ti from the adhesion layer with the gold layer and thereby preserves the integrity of the metallization scheme. This metallization scheme may be applicable to other substrate materials.

Characterization of the Al/Ta-Si-N/Au metallization

Abstract The thermal stability of amorphous, r.f.-sputtered Ta 36 Si 14 N 50 films is studied for application as a diffusion barrier between aluminum and gold layers. Analyses by backscattering spectrometry, scanning electron microscopy together with energy-dispersive analysis of X-rays, and optical microscopy are performed to evaluate the effectiveness of the diffusion barriers. A 300 nm thick Ta 36 Si 14 N 50 film prevents the intermixing between aluminum and gold contacts up to 30 min annealing at 550°C in vacuum. Films about 150 nm and 80 nm in thickness fail already during 30 min annealings at 550°C and 500°C respectively. The failure of the metallization is caused by the Al-Au interdiffusion which takes place in a highly localized manner through the ternary thin films.

OHMIC CONTACTS TO N-GAAS WITH A PT/GE/AU CONTACTING LAYER AND A TA-SI-N BARRIER : ELECTRICAL AND METALLURGICAL CHARACTERISTICS

Pt/Ge/Au trilayers of various Pt:Ge compositions, overlaid with a Ta‐Si‐N barrier layer and an Au metallization layer, are investigated as ohmic contacts to n‐type GaAs. After annealing in flowing argon at 450 °C for 15 min, a contact resistivity of 3.7×10−6 Ω cm2 is obtained for the sample of atomic ratio Pt/Ge=1. The contact resistivity of this sample degrades only slightly to 5.0×10−6 Ω cm2 upon aging at 450 °C for 60 h, while the surface stays smooth. Contact resistivities of samples with other Pt/Ge atomic ratios are in the range of 10−5–10−4 Ω cm2. To understand this electrical behavior, the contacts are characterized by backscattering spectrometry, x‐ray diffraction, and transmission electron microscopy in conjunction with energy‐dispersive analysis of x rays. The reaction products vary with the Pt:Ge compositions due to the difference of the chemical reactivity between Pt, Ge, and GaAs. The formation and distribution of a ternary PtGe:As phase are the determining factors for the contact resistivit...

Amorphous W40Re40B20 diffusion barriers for /Al and /Cu metallizations

The performance of W40Re40B20 metallic amorphous thin film alloys as diffusion barriers between monocrystalline silicon substrates ( ) and aluminum or copper overlayers is reported. The films are deposited using d.c. and r.f. magnetron co-sputtering. Their crystallization temperature and resistivity are about 900°C and 200 μohmscm, respectively. The /W40Re40B20/Al and /W40Re40B20/Cu metallizations were vacuum-annealed at different temperatures for 30 min and characterized by 4He backscattering spectrometry, X-ray diffraction, scanning electron microscopy in combination with energy-dispersive analysis of X-rays, and electrical measurements on shallow junction diodes. The /W40Re40B20/Al structure was stable up to 500 °C and failed at 550 °C due to chemical reactions between the barrier and aluminum. A formation of cracks in the bilayer /W40Re40B20/Cu structure is responsible for its failure at 600 °C. The results demonstrate that it is fruitless to raise the crystallization temperature of an amorphous metallic film if its ability to react with the adjacent materials is not suppressed as well.