Effects of substrate temperature on electrical and structural properties of copper thin films

This paper addresses the effects of substrate temperature on electrical and structural properties of dc magnetron sputter-deposited copper (Cu) thin films on p-type silicon. Copper films of 80 and 500 nm were deposited from Cu target in argon ambient gas pressure of 3.6 mTorr at different substrate temperatures ranging from room temperature to 250 °C. The electrical and structural properties of the Cu films were investigated by four-point probe and atomic force microscopy. Results from our experiment show that the increase in substrate temperature generally promotes the grain growth of the Cu films of both thicknesses. The RMS roughness as well as the lateral feature size increase with the substrate temperature, which is associated with the increase in the grain size. On the other hand, the resistivity for 80 nm Cu film decreases to less than 5 μΩ-cm at the substrate temperature of 100 °C, and further increase in the substrate temperature has not significantly decreased the film resistivity. For the 500 nm Cu films, the increase in the grain size with the substrate temperature does not conform to the film resistivity for these Cu films, which show no significant change over the substrate temperature range. Possible mechanisms of substrate-temperature-dependent microstructure formation of these Cu films are discussed in this paper, which explain the interrelationship of grain growth and film resistivity with elevated substrate temperature.     

Improved properties of Al-doped ZnO film by electron beam evaporation technique

High-quality Al-doped ZnO (AZO) thin films have been fabricated by electron beam evaporation technique. The effect of the growth temperature on the optical and electrical properties of the electron-beam (e-beam) evaporated AZO film is investigated. X-ray diffraction measurements have shown that e-beam evaporated films are highly c-axis oriented at appropriate growth temperature. Transmittance measurement showed that the best optical and structural quality of the e-beam evaporated AZO film occurred at 200 °C. The scanning electron microscope images have shown that the surfaces of the e-beam evaporated AZO became smoother for the growth temperature at and above 200 °C. Finally, the maximum electrical resistivity of 2.5×10⁻⁴ Ω cm and optical transmittance of more than 85% has been found at 200 °C growth temperature, which explains its relation with the crystal quality of the film.     

Morphology evolution in TiN/Al-0.5Cu/Ti interconnection during chamber long stay and post-deposition annealing correlated to defect formation in metallization processing

TiN/Al-0.5Cu/Ti film stacks deposited on SiO₂ substrate were studied by X-ray diffraction and electron microscopy to clarify the effects of the chamber long stay and post-deposition annealing on the morphology evolution. Experimental results indicated that the chamber idleness at 270 °C resulted in significant Al₂Cu precipitation and hillock growth for the Al-Cu films, which enhanced the occurrence rate of the microcorrosion-induced bridging defects and caused yield degradation on production line while post-deposition annealing at 400 °C for 30 min was proven to effectively regain good yield for the chamber-idled wafers. The yield recovery could be attributed to the fast Al₂Cu dissolution and hillock mitigation at the annealing temperature. The electrical sheet resistance of the Al-Cu films would somewhat increase due to the formation of the Al₃Ti phase during annealing, but the Al₂Cu precipitates and surface hillocks formed during chamber idleness would scarcely change the electrical property of the films. This study suggests that the evolutions of second phase and surface hillocks can be controlled by the processing duration and post-deposition treatment rather than the deposition temperature or Cu addition amount of Al-Cu alloy.     

Enhancing the reliability of n-p junction diodes using plasma treated tantalum barrier film

The properties of Ta barrier films treated with various plasma nitridations have been investigated by Cu/barrier/Si. An amorphous layer is formed on Ta barrier film after plasma treatments. The thickness of the amorphous layer is about 3 nm. Plasma treated Ta films possess better barrier performance than sputtered Ta and TaN films. It is attributed to the formation of a new amorphous layer on Ta surface after the plasma treatment. Cu/Ta(N,H)/Ta (10 nm)/Si remained stable after annealing at 750 °C. Ta(N,H)/Ta possesses the best thermal stability and excellent electrical properties. Cu/Ta/n⁺-p and Cu/Ta(N,O)/Ta/n⁺-p diodes resulted in large reverse-bias junction leakage current after annealing at 500 °C and 600 °C, respectively. On the other hand, Ta(N,H)/Ta and Ta(N)/Ta diffusion barriers improve the thermal stability of junction diodes to 650 °C. Ta(N,H)/Ta barrier film possesses lowest resistivity among Ta, Ta(N,O)/Ta, and Ta(N)/Ta films. Hydrogen plays an important role in enhancement of barrier properties. It is believed that hydrogen not only induces amorphization on Ta, but also eliminates the oxygen in the film. It is believed that the enhancement of ability against the copper diffusion is due to the combined effects of the hydrogen reaction and nitridation.     

Thickness dependence of the structural and electrical properties of copper films deposited by dc magnetron sputtering technique

This paper addresses the influences of film thickness on structural and electrical properties of dc magnetron sputter-deposited copper (Cu) films on p-type silicon. Cu films with thicknesses of 130-1050 nm were deposited from Cu target at sputtering power of 125 W in argon ambient gas pressure of 3.6 mTorr at room temperature. The electrical and structural properties of the Cu films were investigated by four-point probe, atomic force microscopy (AFM) as well as X-ray diffraction (XRD). Results from our experiment show that the grain grows with increasing film thickness, along with enhanced film crystallinity. The root mean square (RMS) roughness as well as the lateral feature size increase with the Cu film thickness, which is associated with the increase in the grain size. On the other hand, the Cu film resistivity decreases to less than 5 μΩ-cm for 500 nm thick film, and further increase in the film thickness has no significant effects on the film resistivity. Possible mechanisms of film thickness dependent microstructure formation of these Cu films are discussed in the paper, which explain the interrelationship of grain growth and film resistivity with increasing Cu film thickness.     

Void control during plating process and thermal annealing of through-mask electroplated copper interconnects

The quality of the sputtered copper film, which serves as the seed layer for sequent electroplating, becomes critical when the size of crack on the surface of the sputtered film is close to the feature size of the electroplated copper interconnect. The crack results in void formation in electroplated copper before thermal annealing and this phenomenon limits attainable highest anneal temperature. To solve this problem, the sputtered seed layer was slightly etched before electroplating process and a TaN passivation layer was deposited on the electroplated Cu interconnect before thermal annealing. Those processes not only suppressed void formation during the electroplating and annealing process at 300 °C, but also resulted in lower electrical resistance in the copper interconnects.     

Comparison of the agglomeration behavior of Ag(Al) films and Ag(Au) films

It is essential to suppress agglomeration of Ag films caused by thermal treatment for their successful application as new metallization materials. Co-sputtered Ag(Al) and Ag(Au) films were investigated, with regard to their change in morphology and electrical resistivity after vacuum annealing. As a result, agglomeration of the Ag(Al) film (Al: 4.3 at.%) was not recognized even after annealing at 600 °C. However, void formation followed by de-wetting was observed for the Ag(Au) film after annealing, similar to that for a pure Ag film. The morphological change was accompanied by an increase in the resistivity of the Ag(Au) films with annealing temperature. On the other hand, the resistivity of the Ag(Al) films did not increase by annealing at temperatures from 400 to 600 °C. However, the film with the highest Al content, which was most resistive to agglomeration, had too high resistivity for use as a metallization material. By analysis of the Auger depth profile, the presence of very thin oxide layers at the surface of the film and at the interface with the substrate was confirmed for Ag(Al) films after annealing. This was considered to be the reason for the large difference in agglomeration behavior between the Ag(Au) and Ag(Al) films.     

RTD characteristics for micro-thermal sensors

The physical and electrical characteristics of MgO (medium layer) and Pt (sensor material) thin films deposited by a reactive RF sputtering method and a magnetron sputtering method, respectively, were analyzed as a function of the annealing temperature and time by using a four-point probe, SEM, and XRD. After being annealed at 1000 °C for 2 h, the MgO layer showed good adhesive properties on both layers (Pt and SiO₂ layers) without any chemical reactions, and the surface resistivity and the resistivity of the Pt thin film were 0.1288 Ω/□ and 12.88 μΩ cm, respectively. Pt resistance patterns were made on MgO/SiO₂/Si substrates by the lift-off method, and Pt resistance thermometer devices (RTDs) for micro-thermal sensor applications were fabricated by using Pt-wire, Pt-paste, and spin-on-glass (SOG). From the Pt RTD samples having a Pt thin film thickness of 1.0 μm, we obtained a temperature coefficient of resistor (TCR) value of 3927 ppm/°C, which is close to the Pt bulk value, and the ratio variation of the resistance value was highly linear in the temperature range of 25-400 °C.     

Influence of rapid thermal annealing temperature on structure and electrical properties of high permittivity HfTiO thin film used in MOSFET

HfTiO thin films were prepared by r.f. magnetron co-sputtering on Si substrate. To improve the electrical properties, HfTiO thin films were post heated by rapid thermal annealing (RTA) at 400 °C, 500 °C, 600 °C and 700 °C in nitrogen. It was found that the film is amorphous below 700 °C and at 700 °C monoclinic phase HfO₂ has occurred. With the increase of the annealing temperature, the film becomes denser and the refractive index increases. By electrical measurements, we found at 500 °C annealed condition, the film has the best electrical property with the largest dielectric constant of 44.0 and the lowest leakage current of 1.81 × 10⁻⁷ A/cm², which mainly corresponds to the improved microstructure of HfTiO thin film. Using the film annealed at 500 °C as the replacement of SiO₂ dielectric layer in MOSFET, combining with TiAlN metal electrode, a 10 μm gate-length MOSFET fabricated by three-step photolithography processes. From the transfer (I_DS–V_G) and output (I_DS–V_DS) characteristics, it shows a good transistor performance with a threshold voltage (V_th) of 1.6 V, a maximum drain current (I_ds) of 9 × 10⁻⁴ A, and a maximum transconductance (G_m) of 2.2 × 10⁻⁵ S.     

Diffusional creep induced stress relaxation in thin Cu films on silicon

The results of stress measurements during annealing of thin copper films deposited on 100 μm Si substrates are presented. The stress in thin films was determined by using an optical system for curvature measurements. The annealing experiments were done during thermal cycles of heating and cooling procedures from room temperature up to 400 °C with a rate 10 °C/min. The total thickness of thin films was between 20 and 100 nm. The obtained results showed that the difference between the end and the initial values of the ratio of force to width increases with the thickness of the samples. The initial linear shape of the temperature-stress plots reaches higher temperature values with an increase in film thickness. In order to explain the observations, the dependence of stress on temperature was calculated using the rate of Coble creep. It was found that the theoretical curves reveal the same features as the experimental data. It was concluded that diffusional creep mechanism dominates for thin film of thickness below 100 nm.     

Thermal stability of Cu(W) and Cu(Mo) films for advanced barrierless Cu metallization: Effects of annealing time

The current study investigates the effects of insoluble substances (W and Mo) in pure Cu films on the thermal stability, microstructure, and electrical properties of the films. The results can be used to assess the feasibility of the barrierless Cu film in the metallization process. The films investigated were deposited using magnetron sputtering onto the barrierless Si (100) substrate and then annealed between 400°C and 450°C in vacuum for long periods of time. After annealing, the film properties were examined by x-ray diffraction (XRD), the four-point probe method, leakage current measurements, and focused ion beam (FIB) analysis. The results indicate that no detectable copper silicide is formed after 48-h annealing of Cu(W) films at 400°C. In contrast, for the Cu(Mo) film, copper silicide is formed after 18-h annealing at the same temperature and hence electrical properties are poor. This evidence suggests that the Cu(W) film has better thermal stability during long periods of annealing and is suitable for an advanced barrierless metallization process.     

Optimization of Pb(Zr0.53,Ti0.47)O3 films for micropower generation using integrated cantilevers

Lead zirconate titanate, Pb(Zr_0.53,Ti_0.47)O₃ or PZT, thin films and integrated cantilevers have been fabricated for energy harvesting applications. The PZT films were deposited on PECVD SiO₂/Si substrates with a sol-gel derived ZrO₂ buffer layer. It is found that lead content in the starting solution and ramp rate during film crystallization are critical to achieving large-grained films on the ZrO₂ surface. The electrical properties of the PZT films were measured using metal-ferroelectric-metal and inter-digital electrode structures, and revealed substantial improvement in film properties by controlling the process conditions. Functional cantilevers are demonstrated using the optimized films with output of 1.4 V peak-to-peak at 1 kHz and 2.5 g.     

Effect of Si/Ta and nitrogen ratios on the thermal stability of Ta-Si-N thin films

Ta-Si-N thin films were fabricated by using reactive magnetron cosputtering at different Si/Ta power ratios and nitrogen (N₂) to total gas (Ar + N₂) flow ratios (FN₂% = FN₂/(FAr + FN₂) × 100%). Both levels of high-vacuum furnace annealing (FA) and low vacuum rapid thermal annealing (RTA) were performed to investigate the thermal stability of films. The microstructure, morphology and electrical property of the Ta-Si-N thin films were characterized by grazing incidence X-ray diffraction, scanning electron microscope and four-point probe method, respectively. Ta-Si-N thin films at low FN₂% could endure temperature up to 900 °C for 1 h under high-vacuum FA at 6.5 × 10⁻³ Pa while their phase and morphology had changed under RTA at 750-900 °C for 1 min at 2.6 Pa. The resistivity increased with increasing both FN₂% and Si/Ta power ratios. However, the variation percentage of resistivity of Ta-Si-N films at high-temperature annealing decreased with increasing Si/Ta power ratio and inversely increased with increasing FN₂%. In brief, the thermal stability of Ta-Si-N films increased with increasing level of vacuum and Si/Ta power ratio. Increasing FN₂% and Si/Ta power ratio could enhance the thermal stability of films at RTA but also increased the resisitivity of films. Therefore, Ta-Si-N films prepared at 2 FN₂% and Si/Ta power ratio of 2/1 can be a good candidate for the application of diffusion barrier with low resistivity, low variation percentage and high stability of microstructure.     

Sol-gel-derived ZnO/Cu/ZnO multilayer thin films and their optical and electrical properties

Sol-gel preparation of transparent conducting ZnO/Cu/ZnO multilayer thin films has been investigated. CuO thin films were deposited on glass substrates via a dip-coating method. The CuO thin films were further subjected to reductive annealing in hydrogen to form highly conductive Cu thin films with sheet resistances as low as 10 Ω/□. ZnO/Cu/ZnO multilayers were successfully prepared in a similar way by reducing ZnO/CuO/ZnO. The sheet resistance of the ZnO/Cu/ZnO multilayer thin films is about 10 kΩ/□, which is much higher than that of the pure Cu thin films. The formation of large discrete Cu crystallites in the multilayers explains the poor electrical conductivity of the sol-gel-derived ZnO/Cu/ZnO multilayers.     

Solid phase epitaxial growth of Dy-germanide films on Ge(0 0 1) substrates

Dy thin films are grown on Ge(0 0 1) substrates by molecular beam deposition at room temperature. Subsequently, the Dy film is annealed at different temperatures for the growth of a Dy-germanide film. Structural, morphological and electrical properties of the Dy-germanide film are investigated by in situ reflection high-energy electron diffraction, and ex situ X-ray diffraction, atomic force microscopy and resistivity measurements. Reflection high-energy electron diffraction patterns and X-ray diffraction spectra show that the room temperature growth of the Dy film is disordered and there is a transition at a temperature of 300-330 °C from a disordered to an epitaxial growth of a Dy-germanide film by solid phase epitaxy. The high quality Dy₃Ge₅ film crystalline structure is formed and identified as an orthorhombic phase with smooth surface in the annealing temperature range of 330-550 °C. But at a temperature of 600 °C, the smooth surface of the Dy₃Ge₅ film changes to a rough surface with a lot of pits due to the reactions further.     

The structural,optical, and electrical properties of vacuum evaporated Cu-doped ZnTe polycrystalline thin films

We have studied the structural, optical, and electrical properties of thermally evaporated, Cu-doped, ZnTe thin films as a function of Cu concentration and post-deposition annealing temperature. X-ray diffraction measurements showed that the ZnTe films evaporated on room temperature substrates were characterized by an average grain size of 300Å with a (111) preferred orientation. Optical absorption measurements yielded a bandgap of 2.21 eV for undoped ZnTe. A bandgap shrinkage was observed for the Cu-doped films. The dark resistivity of the as-deposited ZnTe decreased by more than three orders of magnitude as the Cu concentration was increased from 4 to 8 at.% and decreased to less than 1 ohm-cm after annealing at 260°C. For films doped with 6–7 at.% Cu, an increase of resistivity was also observed during annealing at 150–200°C. The activation energy of the dark conductivity was measured as a function of Cu concentration and annealing temperature. Hall measurements yielded hole mobility values in the range between 0.1 and 1 cm²/V·s for both as-deposited and annealed films. Solar cells with a CdS/CdTe/ZnTe/metal structure were fabricated using Cudoped ZnTe as a back contact layer on electrodeposited CdTe. Fill factors approaching 0.75 and energy conversion efficiencies as high as 12.1% were obtained.     

Variation of the structural,optical and electrical properties of CBD CdO with processing temperature

Nanostructures of CdO thin films are prepared by chemical bath deposition (CBD) technique. The synthesized film is annealed in static air by using the hotplate at 373, 473, 573 and 673 K for 10 min. The effect of annealing temperature on structural, morphological, optical and electrical properties of CdO thin films has been investigated. The prepared thin films are characterised by X-ray diffraction (XRD), atomic force microscope (AFM), optical reflection microscope (ORM), UV–Visible Spectrophotometer and electrical resistivity. XRD shows the emergence of the cubic phase of CdO film in a preferred orientation (111) plane at 573 K. The AFM and ORM show that CdO films have smooth homogeneous surface in the formula with the emergence of nanoclusters gathering as nanoparticles with the average of grain size about 100 nm at 573 K. The optical properties prove that deposited films have high transparency within the visible range of the spectrum that reaches to more than 85% with a wide band gap that extends from 2.42 eV to 2.7 eV. The electrical properties of the CdO films show that resistivity decreases with increased annealing temperatures. In addition, it is proved that more than one activation energy appears and they change according to the temperature of annealing and this comes as a result of the polycrystalline structure. This study indicates that the properties of CdO thin films could be improved with annealing temperature and these films can be used in many technological applications.     

On the electrical resistivity and chemical etching of TiSi2 thin films sputtered from a composite target

The electrical resistivity of TiSi₂ thin films sputtered onto an oxidised Si substrate using a composite alloy target is studied. It is found that the as-deposited films show high resistivity. Annealing the films at an elevated temperature leads to a significant fall in the resistivity. An optimum sheet resistance of 2om tq⁻¹ is obtained after annealing at 800°C for 30 min in argon ambient. The effect of annealing temperature on resistivity is studied. The sheet resistance is also found to be affected by the magnitude of the substrate bias during film deposition. The data are given. The patterning of TiSi₂ thin films by wet chemical etching for device applications is described.     

退火温度对Cr-Si压阻薄膜电性能的影响

采用射频磁控溅射法在氧化铝陶瓷基底上制备了Cr-Si-Ni-Ti压阻薄膜,研究了不同退火温度对薄膜电性能的影响.结果表明:在溅射态及退火温度低于600℃时,薄膜为非晶态.随着退火温度的升高,薄膜的电阻温度系数(TCR)逐渐增大,应变因子(GF)先增大后减小,室温电阻率(ρ)则逐渐降低.在退火温度为300℃时,Cr-Si...     

Fabrication and characterisation of high quality ZnO thin films by reactive electron beam evaporation technique

High quality zinc oxide thin films have been deposited on silicon substrates by reactive e-beam evaporation in an oxygen environment. The effect of the growth temperature and air annealing on the structural, optical and electrical properties has been investigated. X-ray diffraction measurements have shown that ZnO films are highly c-axis-oriented and that the linewidth of the (002) peak is sensitive to the variation of substrate temperature. The optimum growth temperature has been observed at 300 °C. Raman spectroscopy has been found to be an efficient tool to evaluate the residual stress in the as-grown ZnO films from the position of the E₂ (high) mode. On the other hand, the vanishing of the 574 cm⁻¹. Raman feature after annealing has been explained as due to an increase of grain size and the reduction of O-vacancy and Zn interstitial. The SEM images have shown that the surfaces of the electron beam evaporated ZnO became smoother for the growth temperatures higher than 300 °C. The optical transmittance is the highest at 300 °C and has been increased after annealing in air showing an improvement of the optical quality. Finally, the maximum electrical resistivity has been found at 300 °C, which explains its relation with the crystal quality and increased from 5.8×10⁻² Ω cm to reach an approximate value of 10⁹ Ω cm after annealing at 750 °C.