Diagnostics of sputtering plasma variations affecting Y–Ba–Cu–O thin film growth and properties

Abstract

Optical emission spectroscopy and Langmuir probe measurements have been performed under varying conditions, close to those previously optimized for high-pressure on-axis DC sputter deposition of YBa 2 Cu 3 O 7−x (Y123) films. The electron temperature and density of the plasma were mapped between the target and substrate. The aim of the investigation was to discern the effect of small variations of plasma environment on film growth and thus to enable precise tuning of the deposition conditions for Y123 and YBa 2 Cu 4 O 8 (Y124) films for different applications. The input parameters varied were: Ar-to-O 2 ratio in the sputtering gas and small additions of He, H 2 or H 2 O; total pressure; target composition (Y123 or Y124); and deposition temperature T s . The films were characterized by four-point and inductive T c measurements, x-ray diffractometry, Raman spectroscopy, Auger electron spectroscopy, Rutherford back scattering, x-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and x-ray energy dispersive spectrometry. A model has been developed to account for the structural peculiarities observed in the x-ray diffractograms of hydrogen-loaded Y123 films deposited in O 2 /Ar + H 2 O presented.

Second derivative Langmuir probe diagnostics of Ar/O2gas discharge for DC YBCO-124 sputtering

“…This work is a continuation of our previous investigations [1][2][3][4], where the plasma composition was discussed in detail.…”

“…The film composition was measured by energy dispersive x-ray analysis. Figure 5 (samples A-E) shows the relative deviation of the measured content of the respective elements from the desired atomic content ( 17 for Y, 2 7 for Ba and 4 7 for Cu). The films deposited in the O 2 -rich atmosphere had larger divergence (A and C), which is in qualitative agreement with the data presented in table 1, namely the presence of higherenergy population of the EEDF tail.…”

“…The second term describes the effect of plasma depletion caused by the drain of charged particles to the probe surface. The geometric factor γ = γ (r p /λ e ) assumes values in the range 4 3 γ 0.71 (γ = 4 3 at r p /λ e 1, and γ = 0.71 at r p /λ e 1). When r p /λ e 1 the approximation for a cylindrical probe γ = 0.71 + 0.25λ e /r p can be used [10].…”

The control of thin film deposition and recent developments in oxide film growth

“…These enable optimisation of deposition parameters for the highest quality layer-by-layer growth of the required crystalline phases and for the development of novel materials and structures. Other techniques, such as emission and absorption spectroscopy are now quite widely used for in situ monitoring of film deposition parameters 46,88 and for feedback control. In addition, there is a wide range of in situ optical monitoring techniques (e.g.…”

“…An alternative method is high pressure sputtering, in which the target and substrates are parallel, but gas pressures of, for example, .100 Pa lead to energy reducing collisions for the energetic ions. 46 Although solving the problem of high energy film bombardment and stoichiometry control, these methods result in a rather inefficient process, very slow film growth and are often difficult to monitor and control. Alternatively, or in addition, stoichiometry may be achieved through the use of compensated target compositions, although the precise composition is a function of so many deposition variables that this is not only very difficult to predict, but locks the process into a single set of deposition parameters.…”