Jyh-Shin Chen

Low Temperature Radio-Frequency-Sputtered ( Ba , Sr ) TiO3 Films on Pt/TiN/Ti/Si Substrates with Various Oxygen/Argon Mixing Ratios

(Ba,Sr)TiO 3 (BST) films were fabricated on Pt/TiN/Ti/Si substrates by low temperature radio frequency magnetron cosputtering at 300°C. Material and electrical properties of BST films sputtered at low temperatures are significantly affected by the O 2 /(Ar + O 2 ) mixing ratio (OMR). Plasma emission spectra indicate that the deposition rate declines at a higher OMR due to oxide formation on the target surface. The dielectric constant of the BST films can reach a maximum of 364 at 5% OMR. The ten-year lifetime of the time-dependent dielectric breakdown implies that the reliability of the capacitor can be enhanced at a higher OMR due to compensation of oxygen vacancies and smaller grain sizes. Current-voltage analysis indicates that the leakage current of the Pt/BST/Pt capacitor is limited by Schottky emission (SE)/Poole-Frenkel emission (PF) at a lower/higher applied field. The applied field boundary between SE and PF shifts toward higher field as OMR increases. Moreover, an energy band model was proposed and this leakage mechanism was discussed.

Effect of rapid-thermal-annealed TiN barrier layer on the Pt/BST/Pt capacitors prepared by RF magnetron co-sputter technique at low substrate temperature

Abstract This investigation reports the effect of rapid-thermal-annealing (RTA) on metallic barrier TiN against the interdiffusions of Ti and Si into barium strontium titanate (BST) in Pt/BST/Pt/TiN/Ti/Si capacitors. In the integration of BST capacitors, the thermal budget of the BST deposition would cause the inter-diffusions of Ti and Si from Ti adhesion layer and Si plug respectively. This event would degrade the BST capacitors. To address this issue, rapid-thermal-annealed TiN barriers were deposited between the bottom electrode Pt and adhesion layer Ti. Optimal RTA condition for TiN were found in this experiment. Excellent electrical characteristics of Pt/BST/Pt/TiN/Ti/Si capacitors, including high dielectric constant (er=320), low leakage current (1.5×10−8 A/cm2) under 0.1 MV/cm, and greater than 10 year lifetime under 1.6 MV/cm were obtained with Ar+O2 mixed ambient at a low substrate temperature (300°C).

Effects of post-oxygen plasma treatment on Pt/(Ba,Sr)TiO3/Pt capacitors at low substrate temperatures

We investigated how oxygen plasma post-treatment improves leakage characteristics of Pt/(Ba,Sr)TiO3 (BST)/Pt capacitors prepared by the radio-frequency (RF) cosputtering technique. Experimental results indicate that oxygen plasma treatment can effectively passivate the oxygen vacancies of (Ba,Sr)TiO3 (BST) films, thus decreasing the electric conduction paths of leakage currents. By this low-temperature (250°C), and short-duration (~5 min) process, the leakage current is reduced by as many as two orders of magnitude. The reliability characteristics of time-dependent dielectric breakdown (TDDB) are improved as well. However, the usage of oxygen plasma treatment is not unrestricted. Plasma treatment for an extended period (more than 10 min) degrades both the leakage and reliability characteristics, due to plasma damage. Excellent electrical characteristics, including low leakage current (1.5 ×10-8 A/cm2) under 0.1 MV/cm, high dielectric constant (288), and a lifetime longer than 10 years under 2 MV/cm can be achieved. Therefore, the proposed technique for as-deposited BST films is a highly promising means of improving the electrical characteristics of BST thin films.

Dependence of polarization on temperature coefficient resistance of (Ba, Sr)TiO3 thin films post-treated by RTA

The temperature coefficient of resistance (TCR) characteristics of Pt/(Ba 0 . 8 Sr 0 . 2 )TiO 3 (BST)/Pt thin-film resistors are studied for the BST films with rapid thermal annealing (RTA) treatments. The polarizations induced by bias voltages greatly influence the TCR characteristics. The RTA-treated BST thin film exhibits negative TCR (NTCR) behavior at a negative voltage, but, intriguingly, positive TCR (PTCR) behavior at a positive voltage. According to the leakage current analysis, Schottky emission dominates the negatively biased current at the upper interface, but Heywang barrier scattering confines the positive biased current.

Effects of Thermal Stabilities for the Ultra Thin Chromium Layers Applied on (Ba, Sr)TiO3 Thin Films

This work reports the temperature-electric properties for the (Ba, Sr)TiO3(BST) thin film capacitor using the multi-film structure of BST/ultra-thin-chromium(Cr) layer/BST. The BST(200 nm)/Cr(1–3 nm)/BST(200 nm) multi-films reveal excellent properties in the thermal stabilities of dielectric property, low leakage current and less power dissipation.

Studying layer uniformity of sputter coatings by intensity distribution of plasma spectrum

Abstract This study conducted a simulation work on the layer uniformity of sputter coatings in a vacuum chamber based on deconvolution of measuring plasma emission spectra, and compared to the corresponding measurements of film thickness distribution. The simulative method started from an Ar-normalized Sr intensity distribution derived from deconvoluting the plasma spectra by using Abel inversion method, which was considered as the spatial distribution of the sputtering rate of the source target. The thickness profile on the substrate was then calculated based on the source with n th power of cosine law assumption. It was observed that the exponent of cosine law approached zero due to collisions of species. Good agreement between simulation and experimental observation revealed that the simulation method based on spectroscopic measurement could be used as an in situ estimation of the deposition uniformity of similar systems.

Low-temperature process to improve the leakage current of (Ba, Sr)TiO3 films on Pt/TiN/Ti/Si substrates

In this study, we employed an oxygen plasma post-treatment to improve the leakage characteristics of Pt/(Ba, Sr)TiO3(BST)/Pt capacitors prepared by the RF cosputtering technique. Applying oxygen plasma treatment to BST thin films can effectively passivate the oxygen vacancies of the BST films, thus decreasing the electric conduction paths of leakage current. The leakage current is reduced by as many as two orders of magnitude by this low-temperature (250°C) and short duration (~5 min) process. However, the usage of oxygen plasma treatment is not unrestricted. Plasma treatment over a long time (more than 10 min) degrades the leakage characteristics, due to plasma damage. Therefore, a proper oxygen plasma treatment for as-deposited BST films is desired to improve leakage characteristics of BST thin films.

Effect of TiN Treated by Rapid Thermal Annealing on Properties of BST Capacitors Prepared by RF Magnetron Co-sputter System at Low Substrate Temperature

In this work, (Ba 0.7 Sr 0.3 )TiO 3 thin films on Pt/TiN/Ti/Si substrate were deposited by an RF magnetron co-sputter system at 300°C in an Ar+O 2 mixed ambient. In the integration of BST capacitors, the diffusion barrier (TiN) under bottom electrodes is one of the key issues. To obtain a stable and excellent diffusion barrier against inter-diffusion between Pt and Si, as well as against being oxidized during BST deposition, TiN was treated by a rapid thermal annealing (RTA) process. Experimental results indicated that proper RTA treatments resulted in a superior TiN barrier layer. In addition, low substrate temperature during BST deposition suppressed the phenomena of inter-diffusion and barrier oxidation. Furthermore, Pt hillocking, another problem during BST deposition because of high thermal budget, was also solved by reducing substrate temperature during BST deposition. The MIM (Pt/BST/Pt) structure was used in the experiments for electrical properties measurement. High dielectric constant (e r =300), low leakage current (l.5×10 −8 A/cm 2 ) under 0.1MV/cm, and 10 year lifetime under 1.6MV/cm were achieved with an Ar+O 2 mixed ambient at a low substrate temperature (300°C).

Characteristics of low-temperature-prepared (Ba,Sr)TiO/sub 3/ films post treated by novel excimer laser annealing

Thin (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ (BST) films were sputtered on Pt/TiN/Ti/Si multilayer substrates at very low temperature (150/spl deg/C). A novel process, using wavelength 248-nm KrF excimer laser annealing (ELA), has been undertaken to implement barium strontium titanate (BST) films at a low process temperature of 300/spl deg/C. The crystallinity and dielectric constant are greatly improved after ELA treatment. In this work, the variation of texture was investigated. Besides, the escaped oxygen atoms from BST films were detected in-situ using a residual gas analyzer (RGA) during ELA process. Thus, the degradation of upper surface is strongly influenced by the laser energy fluence for an ELA-BST film.

Deposition of high dielectric (Ba, Sr)TiO3 thin films by rf magnetron co-sputtering

Abstract This study investigates the characteristics of BST films deposited by rf magnetron co-sputtering of BaTiO3 and SrTiO3 targets. BST films were prepared on four types of substrates at deposition temperatures ranging from 250°C to 450°C. The four substrates included Pt/Ti/SiO2/Si, Pt/Ta/SiO2/Si, Mo/SiO2/Si, and W/SiO2/Si. The dielectric constant and the leakage current density of BST films deposited on Pt/Ti/SiO2/Si substrates were higher than other substrates in the absence of oxygen. Introducing oxygen reduced the leakage current density as a consequence of the few oxygen vacancy and small surface roughness. The dielectric constant of 348 and leakage current density of 1.2x10−7 A/cm2 at IV were obtained in the 160nm-thick BST film deposited on Pt/Ti/SiO2/Si substrates at a deposition temperature of 450°C with a O2:Ar=2:40 gas ratio. The co-sputtering method can obtain high quality BST films at a deposition temperature of 450°C.