Mao-Chieh Chen

Sputter-deposited Mo and reactively sputter-deposited Mo-N films as barrier layers against Cu diffusion

This work studied the barrier capability of sputter-deposited Mo and reactively sputter-deposited Mo-N layers against Cu diffusion in a device structure of Cu/barrier/p+n junction diodes. With a 500 A thick Mo film as barrier layer, the Cu/Mo/p+n junction diodes were capable of withstanding 30 min of thermal annealing at temperatures up to 500°C without causing degradation to the devices electrical characteristics. The incorporation of nitrogen in the Mo layer improved the barrier capability of the metal layer. In particular, the Mo-N films sputterdeposited in a gas mixture of Ar and N2 with Ar/N2 flow rates of 24/8 to 24/12 sccm were found to possess the best barrier capability. With a 500 A thick Mo-N barrier layer, the thermal stability of Cu/Mo-N/p+n junction diodes were found to reach 600°C. At temperatures exceeding the thermal stability limit, we presumed that the failure of Cu/barrier/p+n junction diodes arose from two mechanisms: the grain boundary diffusion for the Mo film and the Mo-N films deposited with small N2 flow rates, and the defects diffusion for the Mo-N barriers deposited with large N2 flow rates. For the Mo-N films deposited in a gas mixture of medium nitrogen content (e.g. N2 flow rate of 8 to 12 sccm), both of the failure mechanisms might exist simultaneously.

Properties of thin Ta–N films reactively sputtered on Cu/SiO2/Si substrates

Abstract This work studied the thin film properties of 200 A Ta and Ta–N films reactively sputtered on the Cu/SiO 2 /Si substrates. The nitrogen atomic concentration in the Ta–N film was found to saturate at about 30%. Excessive sputtering gas flow, especially the N 2 gas, caused surface damage to the sputter deposited films. Thermal annealing in N 2 ambient at temperatures up to 700°C did not change the atomic concentrations and the chemical states of Ta and N in the Ta and Ta–N films. The thermal annealing resulted in the grain growth and the healing of sputter damage, but it also induced new defects in the Ta–N films due to thermal stress. This presents a reliability problem in process application involving high temperature thermal cycle.

Sputtered Cr and reactively sputtered CrNx serving as barrier layers against copper diffusion

The barrier capability of sputter deposited Cr and reactively sputter deposited CrN x films against Cu diffusion in a structure of Cu/barrier/p n junction diodes was investigated by means of thermal annealing at elevated temperatures in conjunction with electrical measurements and material analysis. For a 500 A thick barrier layer, the barrier capability of a pure Cr layer was limited to temperatures up to 500°C, while CrN x films sputter deposite in a gas mixture of Ar and N 2 showed improved barrier capabilities. With Ar/N 2 flow rates of 24/6 to 24/12 standard cubic centimeters per minute, the deposited CrN x films possessed a much improved barrier capability. In particular, the Cu/CrN x (24/9)/p - n junction diodes were capable of sustaining 30 min of t ermal anneal at temperatures up to 700°C without degradation of the diodes electrical characteristics. The failure of Cu/Cr/p + n and Cu/CrN x /p + n junction diodes under extreme thermal treatment was presumed to arise from two mechanisms: grain boundary diffusion for lightly nitrogen doped CrN x and pure Cr barriers, and localized defect (microcrack) diffusion for excessively nitrogen doped CrN x barriers.

Preparation and characterization of some tin oxide films

Tin oxide films were successfully prepared by the reactive evaporation method with a d.c. glow discharge of oxygen. The structure and composition of the films were characterized by Mossbauer spectroscopy, X-ray diffraction and scanning electron microscopy. The valency of tin atoms in the films determined by Mossbauer spectroscopy is mostly divalent in the samples prepared without discharge, but mostly tetravalent in the samples prepared with discharge. Measurements of electrical conductivity and Hall mobility were also carried out and the data were found to correlate with the concentration ratio [Sn4+]/[Sn2+] determined from Mossbauer spectroscopy.

Rapid Thermal Annealed Cr Barrier Against Cu Diffusion

Rapid thermal annealing (RTA) of Cr films in an NH 3 ambient was found to be effective in improving the barrier capability of Cr films in a Cu metallization system. The Cu/Cr/p + n junction diodes whose Cr harrier was RTA treated at a temperature of 400°C were able to sustain a 30 min thermal annealing at temperatures up to 700°C without causing degradation to the electrical characteristics of the diodes. This is a 200°C improvement over the junction diodes using a Cr harrier without RTA treatment. Nitrogen degradation in the grain boundaries of the Cr layer was presumably responsible for the improvement in the barrier capability. However, the efficiency of improvement in the barrier capability was reduced for RTA treatment at temperatures above 600°C. With RTA treatment at 800°C, the material analysis indicated that SiO 2 was formed in addition to oxygen segregation at the Cr/Si interface. The SiO 2 thus formed resulted in a poor Cr/Si interface that caused larger leakage currents for the Cu/Cr/p n junction diodes under reverse bias. Moreover, outward diffusion of Si was found in the 800°C RTA-treated Cr layer, which facilitated formation of Cu 3 Si within the Cr layer for the 800°C annealed Cu/Cr/Si samples. In summary, the improvement in the harrier capability of the Cr layers is closely related to the RTA temperature, and the optimum temperatures were determined to be between 400 and 600°C.

Formation of CrO and CrNO films serving as Cu oxidation resistant layers and their N2 pre-sintering effect

This study investigates the Cu oxidation resistant layers of sputter deposited Crue5f8O and reactively sputter deposited Crue5f8Nue5f8O of 200 A thickness, with and without, thermal N2 pre-sintering treatment. The resistance against Cu oxidation (or the highest annealing temperatures without causing Cu oxidation) of the Crue5f8O and Crue5f8Nue5f8O covered Cu films were found to be 350 and 500°C, respectively, in an O2 ambient. The inherent defects in the Crue5f8O layers and the nitrogen doping in the Crue5f8Nue5f8O layers were believed to be the principal causes for the distinction of the resistance against Cu oxidation. With N2 pre-sintering treatments on the Crue5f8O or Crue5f8Nue5f8O covered Cu films, the ability of resistance against Cu oxidation was degraded. The higher the N2 pre-sintering temperature was, the lower the oxidation temperature of Cu became. The N2 pre-sintering thermal process led to formation of defects on the Crue5f8O and Crue5f8Nue5f8O layers, resulting in the degradation of the ability of resistance against Cu oxidation. Thus, the application of Crue5f8O or Crue5f8Nue5f8O as a resistant layer against Cu oxidation should avoid such an excess thermal treatment.

Formation of self-aligned cobalt silicide in normal flow nitrogen furnace

Abstract Cobalt can be completely transformed into cobalt silicide during annealing in a normal flow nitrogen furnace above a certain temperature which depends on the thickness of the cobalt film deposited on the silicon substrate. For a 400 A cobalt film this temperature is 500 °C and for a 1500 A cobalt film it is 650 °C. Loading the wafer into the furnace tube is a critical step to prevent the cobalt from oxidation before silicidation in the annealing process. Lateral growth of silicide is not observed using this silicidation scheme. The cobalt oxide together with the underlying cobalt over the silicon oxide can be removed by hot 3HCl + H 2 O 2 + 3H 2 O solution if the annealing is performed at a temperature below 650 and 900 °C for a cobalt film thickness of 400 and 1500 A respectively. The optimum condition for practical silicide formation is defined. The products and microstructure over the silicon and silicon oxide are characterized by X-ray diffraction spectra, Auger electron spectroscopy depth profiles, sheet resistance measurements and scanning electron microscopy inspection.

Passivation of copper films with magnesium doping using recoil ion implantation

Abstract This work investigates the effects of Ar + ion implantation through a multilayer structure of SiO 2 (100 nm)/Mg(20 nm)/Cu/SiO 2 /Si on the oxidation resistance of Cu films. Experimental results indicate that implantation at 130 keV to a dose of 5×10 15 cm −2 significantly enhances the oxidation resistance at temperatures up to 375°C. At this energy, a small number of Mg atoms are knocked out, leading to formation of an impervious MgO barrier layer on the Cu surface, which effectively suppresses the oxidizing diffusion paths.

Selective tungsten CVD on submicron contact hole

Abstract This work investigates the deposition properties of selective chemically vapor-deposited tungsten for filling the deep sub-half micron contact holes using the process of silane reduction of tungsten hexafluoride. Low-resistivity tungsten with excellent selectivity and conformal coverage can be obtained with a SiH 4 WF 6 flow rate ratios less than 0.6 at deposition temperatures between 280 to 350 °C. Junction leakage and contact resistance of the AlSiCu/W n + P and AlSiCu/W/p + n diodes as well as the electromigration properties of the AlSiCu/W n + p structure were investigated.

Deposition properties of selective tungsten chemical vapor deposition

Abstract This work investigates the basic deposition properties of selective tungsten chemical vapor deposition (W-CVD) using the process of silane reduction of WF6 with the SiH4/WF6 flow rate ratio less than 0.6 over the temperature range 280–350 °C. Selective W-CVD was performed on a contact hole patterned silicon substrate with in situ NF3 plasma etching of the silicon substrate prior to the selective tungsten deposition. The W deposition rate, deposition selectivity and W film resistivity were investigated with respect to the SiH4 partial pressure, WF6 partial pressure, total (SiH4 + WF6) deposition pressure, as well as the flow rate of the hydrogen carrier gas. It was found that the deposition rate is proportional to the SiH4 partial pressure. With a constant SiH4/WF6 flow rate ratio, the deposition rate increases with total pressure. At given flow rates of SiH4 and WF6, the deposition rate and film resistivity are dependent on the flow rate of the carrier gas. The experimental results show that the reverse bias junction leakage for the wet etching pretreated W/p+-n junction diode is smaller than that of the plasma pretreated diode. On the other hand, the contact resistance of the Al/W/n+p diode is smaller than that of the Al/W/p+n diode.