J. S. Chen

Tantalum‐based diffusion barriers in Si/Cu VLSI metallizations

We have studied sputter-deposited Ta, Ta36Si14, and Ta36Si14N50 thin films as diffusion barriers between Cu overlayers and Si substrates. Electrical measurements on Si n + p shallow junction diodes demonstrate that a 180-nm-thick Ta film is not an effective diffusion barrier. For the standard test of 30-min annealing in vacuum applied in the present study, the Ta barrier fails after annealing at 500 °C. An amorphous Ta74Si26 thin film improves the performance by raising the failure temperature of a /Ta74Si26(100 nm)/Cu(500 nm) metallization to 650 °C. Unparalled results are obtained with an amorphous ternary Ta36Si14N50 thin film in the Si/Ta36Si14N50 (120 nm)/Cu(500 nm) and in the Si/TiSi2(30 nm)/Ta36SiN50 (80 nm)/Cu(500 nm) metallization that break down only after annealing at 900 °C. The failure is induced by a premature crystallization of the Ta36Si14N50 alloy (whose crystallization temperature exceeds 1000 °C) when in contact with copper.

Properties of reactively sputter-deposited TaN thin films

Abstract We deposited TaN films by reactive r.f. sputtering from a Ta target with an N 2 Ar gas mixture. Alloys over a composition range 0–60 at.% N have been synthesized. We report on their composition, structure and electrical resistivity before and after vacuum annealing in the temperature range 500–800 °C. We found that the film growth rate decreases with increasing ratio of the nitrogen flow rate to the total flow rate, while the nitrogen content in the films first increases with the N 2 partial flow rate and then saturates at about 60 at.%. B.c.c.-Ta, Ta 2 N, TaN and Ta 5 N 6 appear in succession as the nitrogen content rises, with Ta 2 N being the only single-phase film obtained. The atomic density of the films generally increases with the nitrogen content in the film. Transmission electron micrographs show that the grain size decreases from about 25 to 4 nm as the nitrogen concentration increases from 20 to 50 at.%. The Ta 2 N phase can exist over a wide range of nitrogen concentration from about 25 to 45 at.%. For as-deposited films an amorphous phase exists along with polycrystalline Ta 2 N in the center portion of that range. This phase crystallizes after vacuum annealing at 600 °C for 65 min. A diagram of stable and metastable phases for TaN films based on X-ray diffraction and transmission electron microscopy results is constructed. The resistivity is below 0.3 m ohms cm for films with 0–50 at.% N and changes little upon vacuum annealing at 800 °C.

Sputtered Ta-Si-N diffusion barriers in Cu metallizations for Si

Electrical measurements on shallow Si n/sup +/-p junction diodes with a 30-nm TiSi/sub 2/ contacting layer demonstrate that an 80-nm-thick amorphous Ta/sub 36/Si/sub 14/N/sub 50/ film prepared by reactive RF sputtering of a Ta/sub 5/Si/sub 3/ target in an Ar N/sub 2/ plasma very effectively prevents the interaction between the Si substrate with the TiSi/sub 2/ contacting layer and a 500-nm Cu overlayer. The Ta/sub 36/Si/sub 14/N/sub 50/ diffusion barrier maintains the integrity of the I-V characteristics up to 900 C for 30-min annealing in vacuum. It is concluded that the amorphous Ta/sub 36/Si/sub 14/N/sub 50/ alloy is not only a material with a very low reactivity for copper, titanium, and silicon, but must have a small diffusivity for copper as well.<<ETX>>

Amorphous Ta-Si-N diffusion barriers in Si/Al and Si/Cu metallizations

Abstract Thin films of amorphous Ta-Si-N alloys were deposited by reactive RF sputtering of a Ta5Si3 target in an Ar/N2 ambient. These alloy films were tested as diffusion barriers between Al and Si, as well as between Cu and Si. Electrical measurements on Schottky diodes and on shallow n+p junction diodes were used to evaluate the thermal stability of the 〈Si〉 /W48Si20N32(20 nm)/Ta36Si14N50(80 nm)/Al(1000 nm) metallization. The amorphous W48Si20N32 contacting layer was added to raise the Schottky barrier height of the metallization on n-type Si. Both the shallow junctions and the Schottky diodes are stable up to 700°C for 20 min (above the Al melting point of 660°C) which makes this material the best thin-film diffusion barrier on record. Furthermore, the same Ta36Si14N50 amorphous film maintains the integrity of the I–V characteristics of the shallow n+p junctions with the 〈Si〉 /TiSi2(30 nm)/Ta36Si34N50(80 nm)/Cu(500 nm) metallization up to 900°C for 30 min annealing in vacuum. The TiSi2 contacting layer was added to assure an ohmic characteristic of the contact. For comparison, the same shallow junctions with 〈Si〉 /Cu metallizations were shorted after annealing at 300°C.

Interfacial reactions of W thin film on single-crystal (001) β-SiC

Abstract Interfacial reactions between a W thin film and a single-crystal (001) β-SiC substrate on rapid thermal annealing from 600 °C to 1100 °C for 60 s were investigated by backscattering spectrometry, X-ray diffraction, secondary ion mass spectrometry and cross-sectional transmission electron microscopy. Backscattering spectrometry shows that W reacts with SiC at 950 °C. The product phases identified by X-ray diffraction are W5Si3 and W2C. At 1100 °C no more unreacted W is detected. Current-voltage measurements show that ohmic contacts are already obtained on as-deposited W. Contact resistivity measured using the circular transmission line model is about 10−3 Ω cm2. Thermodynamic studies of the solid phase stability in the ternary WSiC system help us to understand the chemical stability of W thin film.

Contact resistivity of Re, Pt and Ta films on n-type β-SiC: Preliminary results

Abstract Contact resistivities of as-deposited and annealed Pt, Re and Ta films on n-type single-crystalline β-SiC(001) are characterized using a circular contact pattern and the circular transmission-line model method. The β-SiC substrates used in the experiment are n-type doped either non-intentionally to a carrier concentration of about 10 17 cm −3 , or by nitrogen implantation and annealing to a concentration of 5 × 10 19 cm −3 . The effect of a finite resistance along the circular contact rings on the measured potentials is corrected with a resistance network model. On the non-intentionally doped β-SiC substrates, Pt contacts are non-ohmic regardless of the heat treatment. The as-deposited Ta and Re contacts are ohmic with contact resistivities of 5 × 10 −5 Ω cm 2 and 4 × 10 −4 Ω cm 2 respectively. Upon annealing at 500 °C for 30 min, the resistivity of Ta increases slightly while that of Re decreases slightly. Both Ta and Re contacts become non-ohmic by annealing at 900 °C for 30 min. The as-deposited Ta, Pt and Re contacts are all ohmic on the nitrogen-implanted β-SiC substrate. The contact resistivity of the as-deposited Ta contact is the lowest and in the order of high 10 −7 Ω cm 2 , stays about the same at 500 °C and degrades to 4.3 × 10 −6 Ω cm 2 at 1000 °C. The as-deposited Re contact has the highest contact resistivity of 1 × 10 −4 Ω cm 2 but it improves to 1 × 10 −5 Ω cm 2 upon annealing at 900 °C. The contact resistivity of the as-deposited Pt contacts is 6 × 10 −6 Ω cm 2 and increases to 1 × 10 −5 Ω cm 2 at 500 °C. After annealing at 900 °C for 30 min, the Pt contact on the nitrogen-implanted β-SiC is no longer ohmic. The results are compared with the reactions that take place in those systems.

Stability of rhenium thin films on single crystal (001) β‐SiC

Thermal reactions of Re thin films in contact with single crystalline (001) β‐SiC at temperatures between 700 and 1100 °C for 30 min are investigated by MeV He++ backscattering spectrometry, x‐ray diffraction, secondary ion mass spectrometry, and transmission electron microscopy (plan‐view and cross‐sectional). No reaction between Re and SiC is observed for any annealing conditions. The average grain size of the as‐deposited Re film is 220 nm and increases to 280 nm after annealing at 1100 °C for 30 min. A strong {0001}Re fiber texture is also observed after annealing. The chemical stability of Re thin films on SiC is consistent with the earlier study of solid‐phase stability in the ternary Re‐Si‐C system which shows that Re and its silicides have tie lines with SiC at 1600 °C. It also coincides with calculations of the free energy of reaction from assessed thermodynamic data for rhenium silicides and SiC. The implications of this Re stability with SiC for applications of Re as a metal for electrical cont...

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 ...

Instability of a GexSi1−xO2 film on a GexSi1−x layer

The stability of an amorphous GexSi1−xO2 in contact with an epitaxial (100)GexSi1−x layer obtained by partially oxidizing an epitaxial GexSi1−x layer on a (100)Si substrate in a wet ambient at 700 °C is investigated for x=0.28 and 0.36 upon annealing in vacuum at 900 °C for 3 h, aging in air at room temperature for 5 months, and immersion in water. After annealing at 900 °C, the oxide remains amorphous and the amount of GeO2 in the oxide stays constant, but some small crystalline precipitates with a lattice constant similar to that of the underlying GeSi layer emerge in the oxide very near the interface for both x. Similar precipitates are also observed after aging for both x. The appearance of these precipitates can be explained by the thermodynamic instability of GexSi1−xO2 in contact with GexSi1−x. In water at RT, 90% of GeO2 in the oxide is dissolved for x=0.36, while the oxide remains conserved for x=0.28.