Parameter-dependent oxidation of physically sputtered Cu and the related fabrication of Cu-based semiconductor films with metallic resistivity

Abstract

tered Cu atoms. It thus can be imaged that the sufficient oxygen source would lead to a partial or even full oxidation of the growing Cu film. Obviously, such undesirable oxidation would influence the performance, stability and lifetime of Cu film used as interconnection in ULSIC. Moreover, the parameter-dependent oxidation of Cu during physical sputtering deposition has not been investigated systemically yet. Thus, study on the parameter-dependent oxidation of physically sputtered Cu is crucial not only to mechanism understanding but also to practical avoidance of the undesirable oxidation.On the other hand, one recent interest in material research is the fabrication of high mobility semiconductors such as graphene-like MoS 2 [5] for the application in optoelectronic devices. Among Cu-based family, Cu is a typical metal material with a low resistivity of 1.67×10 −6 Ω cm, while its oxide Cu 2 O is a representative p-type semiconductor material with a band gap of 2.17 eV and a high resistivity of 3×10 6 Ω cm. Switzer et al. [6] found that the resistivity of layered Cu/Cu 2 O film could be tuned from 3.0×10 6 to 8.1×10−5 Ω cm. In spite of this, the optical property of the layered Cu/Cu 2 O film with a metallic resistivity was not studied in Ref. [6]. Thus, it is imperative to fabricate a certain structure of Cu-based films which can exhibit both metal and semiconductor characteristics.With the above considerations, we particularly studied the parameter-dependent oxidation of physically sputtered Cu and fabricated Cu-based semiconductor films with metallic resistivity. It was found that various Cu-based (oxide) films such as pure Cu, Cu 2 O, CuO films and Cu/ Cu 2 O, Cu 2 O/CuO composite films could be obtained by simply adjusting the deposition parameters during physical sputtering deposition. The main oxygen source for the oxidation of Cu and the parameter-dependent oxidation mechanisms were explored. Further, the electrical and op-ABSTRACT In this paper, we report the parameter-dependent oxidation of physically sputtered Cu and the related fabrication of Cu-based semiconductor films with metallic resistivity. It was found that various Cu-based (oxide) films such as pure Cu, Cu2O, CuO films and Cu/Cu2O, Cu2O/CuO composite films could be obtained by simply adjusting the deposition parameters during physical sputtering deposition. The main oxygen source for the oxidation of Cu and the parameter-dependent oxidation mechanisms were explored. Further, the electrical and optical testing results show that the obtained pure Cu film and Cu/Cu2O composite film both present an intriguing combination of metal and semiconductor characteristics.

Selective bias deposition of CuO thin film on unpolished Si wafer

“…It can be found that the band gap of CuO thin films deposited on polished and unpolished Si wafers is estimated to be 2.03 and 1.94 eV respectively, which are both much larger than that of bulk CuO (1.2 eV). Since the band gap of a semiconductor film is affected by some factors such as quantum size or nanosize effect, doping and defect [15]. In the present case, the nanosize effect including effects of film thickness and building particle and sheet sizes, and the crystal defect in the film may both influence the band gap.…”

“…The other details and parameters can be found in [13]. It has been demonstrated that the residual O 2 in the pre-pumped vacuum chamber is the main oxygen source for the oxidation of sputtering Cu atoms [15]. Relative to the case in [13][14][15], the higher base pressure (2.0×10 −3 versus 5.0×10 −4 Pa) in this work can provide more sufficient O 2 (2.08×10 11 versus 5.2×10 10 atoms/cm 3 , four times) for the oxidation of Cu atoms, which may result in the formation of CuO rather than Cu and Cu 2 O.…”

“…It has been demonstrated that the residual O 2 in the pre-pumped vacuum chamber is the main oxygen source for the oxidation of sputtering Cu atoms [15]. Relative to the case in [13][14][15], the higher base pressure (2.0×10 −3 versus 5.0×10 −4 Pa) in this work can provide more sufficient O 2 (2.08×10 11 versus 5.2×10 10 atoms/cm 3 , four times) for the oxidation of Cu atoms, which may result in the formation of CuO rather than Cu and Cu 2 O. The as-achieved CuO thin films were then characterized by a field-emission scanning electron microscope (SEM, ZEISS SUPRA 55), a powder x-ray diffractometer (XRD, RIGAKU D/Max 2500 PC) and an ultraviolet-visible (UV-vis) spectrophotometer (METASH UV-9000S) to study their surface morphology, crystal structure and optical properties.…”

Nanoinstabilities of Cu2O porous nanostructured films as driven by nanocurvature effect and thermal activation effect

“…As a consequence, the PNFs tend to change the morphology and crystal structure of their building nanostructures thermodynamically. In addition, the valence state of Cu element in Cu2O is +1 (Cu 1+ ), which is also unstable as driven by the tendency of decreasing the free energy [14].…”

Diffusion-controlled synthesis of Cu-based for the Rochow reaction

“…In the last several years, the controllable synthesis of Cu 2 O microand nano-sized crystals with a vast array of architectures, including core-shell Cu 2 O spheres [13], hollow Cu 2 O spheres [14], and porous Cu 2 O spheres [15] has been achieved using electrodeposition method, thermal relaxation method, sonochemical method, vacuum evaporation method, γ-irradiation method, and liquid-phase reduction method [16][17][18]. Additionally, metallic copper (Cu) and copper oxide (CuO) with various structures have also received intense attention, as they can be used in catalysis, sensors, and electronics [19][20][21][22][23][24][25][26]. However, the aforementioned synthesis approaches often involve the use of surfactants, template, and high temperature and pressure to obtain morphology-controllable Cu 2 O structures, which undoubtedly increases the synthesis cost and thus limits their large-scale production.…”