Using tabulated thermodynamic data, a comprehensive investigation of the thermo-dynamic stability of binary oxides in contact with silicon at 1000 K was conducted. Reactions between silicon and each binary oxide at 1000 K, including those involving ternary phases, were considered. Sufficient data exist to conclude that all binary oxides except the following are thermodynamically unstable in contact with silicon at 1000 K: Li2O, most of the alkaline earth oxides (BeO, MgO, CaO, and SrO), the column IIIB oxides (Sc2O3, Y2O3, and Re2O3, where Re is a rare earth), ThO2, UO2, ZrO2, HfO2, and Al2O3. Of these remaining oxides, sufficient data exist to conclude that BeO, MgO, and ZrO2 are thermodynamically stable in contact with silicon at 1000 K. Our results are consistent with reported investigations of silicon/binary oxide interfaces and identify candidate materials for future investigations.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400010384

Thermodynamic stability of binary oxides in contact With silicon

Using tabulated thermodynamic data, a comprehensive investigation of the thermodynamic stability of binary oxides in contact with silicon at 1000 K was conducted. Reactions between silicon and each binary oxide at 1000 K, including those involving ternary phases, were considered. Sufficient thermodynamic data exists to conclude that all binary oxides except the following are unstable in contact with silicon at 1000 K: LiO2, the alkaline earth oxides (BeO, MgO, CaO, SrO, and BaO), the column IIIB oxides (Sc2O3, Y2O3, and Re2O3 where Re is a rare earth), ThO2, ZrO2, HfO2, and Al2O3. Of these remaining oxides, sufficient thermodynamic data exists to conclude that MgO, CaO, and ZrO2 are thermodynamically stable in contact with silicon at 1000 K.

Thermodynamic Stability of Binary Oxides in Contact with Silicon

Copper deposition and thermal stability issues in copper-based metallization for ULSI technology

Ternary amorphous metallic thin films as diffusion barriers for Cu metallization

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. >

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

A comparative study between the high‐temperature diffusion barriers against either Al or Cu has been made. Several conducting oxides (RuO2, Mo–O) and nitrides (W–N) were examined using cross‐sectional transmission electron microscopy, Auger electron spectroscopy and x‐ray diffraction. Copper was chosen as a less reactive metal than aluminum, and it is widely used in Al–Cu interconnections. Al was found to reduce both oxides to form a thin self‐limiting layer of Al2O3, which hinders interdiffusion between Al and Si. In addition, a localized and nonuniform reaction occurs at the RuO2/SiO2 interface giving rise to the metal‐rich silicide Ru2Si. Cu was fully oxidized by reduction of RuO2 to form Cu2O but did not reduce Mo–O. For Cu on W–N, no reactions occur. However, we observe a significant modification of the Al/W–N interface. A nonuniform reaction giving WAl12 and a continuous thin amorphous layer which appears to be N‐rich aluminum are present. When the W–N is exposed to air before Al deposition, an alum...

A comparison between aluminum and copper interactions with high‐temperature oxide and nitride diffusion barriers

Tungsten–rhenium alloys have been investigated as possible diffusion barriers between aluminum and silicon for high‐temperature metallization of microelectronic devices. Al/W–Re/Si structures with the alloy compositions W–30 wt. % Re, W–61 wt. % Re, and W–72 wt. % Re were prepared by electron beam evaporation of W–Re and Al on Si wafers. Thin W–Re films, without Al, were also deposited on Si3N4 windows. The samples were annealed at different temperatures and characterized using Rutherford backscattering spectroscopy, x‐ray diffraction, and transmission, and scanning electron microscopy (TEM and SEM). The W–30% Re sample was crystalline with a β‐W structure after deposition, while the W–61% Re and the W–72% Re samples were amorphous and crystallized into the α‐Mn structure (χ phase) at a temperature of 700 and 600 °C, respectively. All Al/W–Re/Si structures were stable against Al penetration up to 500 °C. At an annealing temperature of 550 °C signs of a reaction leading to the formation of (W,Re)–Al12 coul...

Tungsten–rhenium alloys as diffusion barriers between aluminum and silicon

The Interfacial reactions between Al and RuO2, MoOx and WNx diffusion barriers on Si (100) wafers have been studied. The diffusion barrier structures were analyzed before and after various heat treatments using Auger electron spectroscopy (AES) and cross-sectional transmission electron microscopy (XTEM). Al was found to reduce the oxides of both Ru and Mo. A 100 A thick Al2O3 layer developed between the Al and the RuO2 films during annealing at 500°C for 30 minutes. The formation of interfacial Al2O3 efficiently prevents Al penetration but may cause a too high contact resistance for applications in contact structures of microelectronic devices. The WNx barrier was stable after annealing at 600°C for 30 minutes, if the film was exposed to air prior to Al deposition. If, instead, the Al was deposited in situ, the structure failed after annealing at 500°C due to a reaction between Al and W giving WAl12. A thin Al2O3 layer was detected between the Al and the WNx films of the air exposed sample. This layer had the effect of retarding the Al–W reaction and thereby raised the failure temperature of the barrier by at least 100°C.

Interfacial reactions between Al and RuO2, MoOx and WNx diffusion barriers on Si

A low‐energy nitrogen ion beam has been used to transform part of a TiSi2 layer on Si to TiN. This process, in conjunction with a self‐aligned TiSi2 process, forms a self‐aligned TiN barrier layer. The nitriding was performed using a broad beam Kaufman ion source operated in N2 at 300‐eV beam energy. Various substrate temperatures and N2 ion doses were evaluated. Auger electron spectroscopy, cross‐sectional transmission electron microscopy, and etching in HF were used to characterize the samples. The results show that the nitrided surface layer grows in thickness with substrate temperature and exposure time to the ion beam, and that an equilibrium thickness can be reached. A comparison with films produced by conventional annealing in NH3 shows that superior film properties can be achieved by ion beam nitriding at temperatures below 500 °C.

TiN formed by ion beam nitriding of TiSi2

Diffusion barrier layers with improved stability are needed in very large scale integrated (VLSI) devices to prevent aluminum from interacting with silicon, under the demanding constraints of shallow junctions and processing heat cycles. We present a comparison of the mechanisms controlling the integrity or failure of diffusion barriers at temperatures above 500 °C. Three classes of high‐temperature barrier materials are discussed: amorphous metal alloys, conducting nitrides, and conducting oxides. The advantage of an amorphous barrier is shown to be minimal. Amorphous refractory metal alloys (W–Re) fail by intermetallic reaction with Al at ∼525 °C, well below their crystallization temperature, to form Al12(W,Re). This performance is only slightly better than a polycrystalline film of the same composition, and offers little improvement over pure W. Conducting nitrides (TiN, W–N) have been shown to be effective barriers up to 600 °C or higher, but only if exposed to air prior to Al metallization. In this c...

Mechanisms for success or failure of diffusion barriers between aluminum and silicon

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