J. D. Wiley

Au diffusion in amorphous and polycrystalline Ni0.55 Nb0.45

Diffusion of Au in amorphous and polycrystalline Ni0.55 Nb0.45 has been studied by Rutherford backscattering spectroscopy of heat‐treated Au/NiNb couples. The diffusion process is characterized by interdiffusion of Nb and Au with NiNb showing a Au miscibility of ∼20 at. %. The Au diffusion coefficient in polycrystalline NiNb at 400 °C was found to be 1.6×10−15 cm2/s. The diffusion coefficient for Au in amorphous NiNb was found to be substantially less, ∼10−21 cm2/s at 400 °C. These results support the concept of using amorphous films as metallizations or diffusion barriers in high‐temperature solid‐state device applications.

Au diffusion in amorphous and polycrystalline Ni/sub 0. 55/ Nb/sub 0. 45/

Diffusion of Au in amorphous and polycrystalline Ni0.55 Nb0.45 has been studied by Rutherford backscattering spectroscopy of heat‐treated Au/NiNb couples. The diffusion process is characterized by interdiffusion of Nb and Au with NiNb showing a Au miscibility of ∼20 at. %. The Au diffusion coefficient in polycrystalline NiNb at 400 °C was found to be 1.6×10−15 cm2/s. The diffusion coefficient for Au in amorphous NiNb was found to be substantially less, ∼10−21 cm2/s at 400 °C. These results support the concept of using amorphous films as metallizations or diffusion barriers in high‐temperature solid‐state device applications.

Investigation of amorphous Ni0.60Nb0.40 diffusion barriers

Interactions of Ni0.60Nb0.40 amorphous alloys with polycrystalline overlayers of gold and copper and single-crystal substrates of silicon. GaAs and GaP were observed with Auger depth profiling. The Ni-Nb layer was deposited by r.f. sputtering and was approximately 5000 A thick. The overlayers were evaporated to a thickness of 1000 A. The amorphous metal reacted with the gold overlayers and the GaAs and GaP substrates at temperatures well below the nominal crystallization temperature of 650 °C. The Cu/Ni-Nb/Si system, in contrast, was stable at 600 °C for at least 1 h. Samples were also measured that had been contaminated with approximately 5–10 at.% O. Complete separation of the niobium and nickel into distinct layers was seen. For the samples on silicon substrates this separation was accompanied by the formation of a nickel silicide layer.

Crystallization of sputter deposited amorphous metal thin films

Abstract We have studied the crystallization of DC sputter deposited amorphous W-Si alloys under three separate conditions: free standing films, amorphous films deposited on Si substrates, and films with one of four different overlayers. In the case of the free standing films the crystallization temperature versus composition was measured by differential thermal analysis (DTA) for films with Si contents from 5 at% to 38 at%. Films with Si concentrations of 38% to 22% were amorphous as deposited, while those with less Si were crystalline. The crystallization temperature was a strong function of composition with a maximum T c of 915°C (at a heating rate of 20 K/min) in alloys with 28% Si. Overlayers of W, Cu, Au and Al were investigated. Both the W and Cu overlayers had little effect on the stability of the underlying W-Si, while both the Au and Al reduced the crystallization temperature by at least 100°C. The results reported here reinforce the observation that the choice of overlayer plays a critical role in determining the overall stability of metallization systems that include amorphous layers as diffusion barriers.

Atomic interdiffusion in Au/amorphous NiNb/ semiconductor systems

Abstract Backscattering measurements were performed to assess the stability of amorphous NiNb for contacts of high temperature electronics. The interdiffusion of amorphous NiNb and three semiconductors—silicon, GaAs and GaP—was measured to study the stability for primary metallization applications. Diffusion of gold with amorphous NiNb and the same three semiconductors was also investigated in order to address diffusion barrier applications of amorphous metals. The results indicate that the use of amorphous NiNb as a contact or a diffusion barrier could extend the useful operation temperature range for GaP devices to above 550°C.

Thermal stability of amorphous NiNb on semiconductor substrates

Abstract The thermal stability of amorphous metal films is of prime importance in high temperature semiconductor device applications. Suitable thin film deposits of amorphous Ni-Nb, 58 at % Ni have been prepared by sputter deposition onto Si, GaAs, and GaP substrates. The amorphous character and crystallization behavior of the films have been monitored by x-ray diffraction (XRD). Polycrystalline Au and Ni overlayers were found to lower the NiNb crystallization temperature by about 100 and 150°C, respectively. In addition, Auger depth profiles were used to monitor the various interdiffusion reactions between the amorphous metal, polycrystalline metal overlayers and semiconductor substrates. For example, the feasibility of NiNb as a diffusion barrier between Au and a semiconductor substrate was found to depend on the substrate. Following a one hour 500°C anneal, very little interdiffusion was observed in the Au/NiNb/Si system. However on a GaAs or GaP substrate the Au and NiNb interdiffused extensively. These studies have demonstrated the viability of amorphous metal films as effective diffusion barriers in semiconductor contact applications, but emphasize the need for careful selection of compatible material combinations.

Interfacial Reactions Between Amorphous W-Si Thin Films And Polycrystalline Overlayers

Interactions between amorphous metal thin films and either a substrate or an overlayer can limit their effectiveness as diffusion barriers. We have found in previous studies that Au and Al polycrystalline thin films in contact with amorphous W-Si lowers the crystallization temperature of the a-(W-Si) by at least 100C. In contrast Cu and Mo have no apparent effect on the stability of the amorphous layer. The mechanisms leading to premature crystallization are not well understood. Amorphous W .72 Si .28 was deposited by D.C. sputtering onto single crystal Si substrates. Overlayers of Al were then evaporated onto the W-Si. Using Auger electron spectroscopy depth profiling coupled with cross-section TEM, we have studied interfacial reactions between the amorphous layer and polycrystalline Al. Auger profiling results show that in the case of Al overlayers, W and Si diffuse out of the a-(W-Si) into the Al where WAl 12 forms. These results can be explained in the context of three binary diffusion couples, W-Si, W-Al, Al-Si, and the individual interactions associated with these couples.

Reaction of Amorphous Minb Films with Crystalline Metal Overlayers

In many cases the stability of amorphous films is influenced by interaction with metallic crystalline overlayers. Such interactions between Au, Ni, Nb and Ta overlayers and a-(Ni-Nb) films are reported. During interdiffusion Au overlayers reacted with a-(Ni-Nb) to form two different adjacent crystalline layers. In order to study the influence of relaxation of the amorphous film on overlayer reaction several a-(Ni-Nb) samples were pre-annealed prior to Au deposition. High depth resolution Rutherford Backscattering Spectrometry (RBS) demonstrates that preannealing lowers the diffusion poefficient of Au in a-(Ni-Nb) at 4500C from 7.5×10 −22 m 2 /s to 8.7×10 −23 m 22 /s. During interdiffusion Ta was discovered to be substantially more inert than Au. For example, negligible interdiffusion between Ta and a-(Ni-Nb) at 505°C after 25 hours implies a diffusivity of less than 5×10 −24 m 2 /s. These observations allow assessment of some of the requirements for increasing the stability of crystalline-amorphous metal film layered structures.

Calculation of temperature profiles in radiantly heated and cooled silicon wafers

Temperature gradient zone melting can be utilized to force metallic migration through a semiconducting wafer. The rate of metallic migration is dependent on the temperature profile within the wafer. Kellett’s model is applied to determine the temperature gradient within a radiantly heated wafer. This model includes the absorption and reradiation of energy along with strictly conductive heat transfer. Computer calculations based on the model show that the temperature gradient is constant inside the wafer and that it tends to zero near the wafer surfaces. This indicates that heat transfer is primarily by conduction inside the wafer and by radiation near the surface.

Columnar microstructure and stress measurements in amorphous W0.75Si0.25 thin films

Columnar microstructure has been observed in direct‐current sputter deposited amorphous metal thin films of W0.75Si0.25. Transmission electron microscopy was used to examine the films, both in cross section and plan view. Individual columns are 50–150 A in diameter and the morphology is typical of a zone 1 structure. In contrast, films of the same composition deposited by magnetron sputtering did not exhibit a columnar microstructure. The dc sputtered films were also found to be in tensile stress when deposited on silicon substrates. Measured stresses ranged from 6.5×108 Pa for 4000 A films with a linear increase to 8×108 Pa for 33 000 A films. For films thinner than 4000 A the stress in the films dropped off rapidly. The linear increase in stress seen was attributed to mutual attractive forces between adjacent columns.