Growth of CaF2 buffer on Si using low energy cluster beam deposition technique and study of its properties

Abstract

Calcium Fluoride bu er lavers were grown on Si 100 substrates using the low energy cluster beam deposition technique. The lms were annealed at various temperatures ranging between 500 o C and 700 o C. The SEM studies showed that as-deposited lms were well oriented along the c-axis and had very smooth surface morphology. The annealed lms on the contarary, showed lowering of peak intensities and roughening of the surface. The dielectric constant derived from the C-V measurements at 1 MHz were 2.01 and 18 for as-deposited and annealed lms respectively. I IntroductionIt seems highly probable that High Tc superconducting thin lms will have an impact on microelectronics by making it possible to grow l o w dispersion, high speed dense superconducting interconnects 1 . Another major area where the low-loss properties of the superconductors will potentially have an impact is the devices operating at microwave frequencies 2 . One major obstacle to the above applications is the di culty to grow high Tc superconducting lms on silicon. This arises due to the fact that silicon di uses into the superconducting lm during annealing at elevated temperatures resulting in broad transitions and low critical current densities 3,4 . Hence a class of materials called alkaline earth uorides, or lIa-uorides as they are commonly known, have been investigated for its usefulness to overcome this di culty. These compounds have a low dielectric constant which decreases with decreasing temperature 5 . Moreover, they are chemically stable and structurally compatible with a number of semiconductors viz., Si, GaAs etc 6 . They also have good thermal match o wing to their ionic nature 7 . The surface elds in an ionic compound decreases exponentially leading to an interface wherein the bonds across the interface tend to be weak. This allows to overcome the lattice mismatch strain by rearrangement of dislocations.Various techniques such as sputtering 8 , pulsed laser deposition 9 etc., have been employed to obtain good quality bu er layers on silicon. The low energy cluster beam deposition technique, a variant of ionized cluster beam deposition technique, involves formation of clusters of the materials to be deposited which i s charged in a specially designed crucible. The material vapours escaping the nozzle of the crucible undergo sudden adiabatic expansion and some of it form clusters. These clusters subsequently move t o wards the substrate at an ejection velocity and deposit on it. One of the greatest advantages of the low energy cluster beam deposition technique is the absence of electrical charge e ect which can in uence the nucleation and growth process.

Calcium fluoride as high-k dielectric for 2D electronics

“…The polycrystallization of the CaF 2 film, which is an unwanted phenomenon if used as gate dielectric in FETs, may be related to the relatively low pressure used during the evaporation process, which introduces oxygen impurities non-uniformly distributed at the CaF 2 /Si interface, as confirmed by the Auger electron spectroscopy depth profiles. One possible solution for this issue may be the use of additional power sources to assist the deposition process, such as laser, 49 plasma, 50 magnetron field, 51 cluster beam, 52 and electron beam evaporation. 53 Electron beam evaporation was used to deposit 200 nm CaF 2 as a buffer layer to grow diamond on the Ir/CaF 2 /Si surface at 500 C. 53 Cook et al 51 utilized radio frequency (RF) magnetron sputtering to decrease the substrate temperature down to 450 C, and this value was further decreased to 200 C in Ref.…”

Microwave characterisation of CaF2 at cryogenic temperatures using a dielectric resonator technique

“…To obtain precise values of R SM we have measured S-parameters (S 21 , S 11 , and S 22 ) around the resonance of the Hakki-Coleman resonator with the sapphire rod and copper cavity. The measured data sets were processed with the Transmission Mode Q-Factor Technique 3,4 to obtain the loaded Q L -factor and coupling coefficients as mentioned in Section 1. The TMQF method accounts for noise, delay due to uncalibrated transmission lines and its frequency dependence, and crosstalk in measurement data and hence provides accurate values of Q L and the coupling coefficients 1 and 2 .…”