Influence of Atomic Layer Deposition Temperatures on TiO₂/n-Si MOS Capacitor

Abstract

This paper reports on the influence of deposition temperature on the structure, composition, and electrical properties of TiO 2 thin films deposited on n-type silicon (100) by plasma-assisted atomic layer deposition (PA-ALD). TiO 2 layers ∼20 nm thick, deposited at temperatures ranging from 100 to 300 • C, were investigated. Samples deposited at 200 • C and 250 • C had the most uniform coverage as determined by atomic force microscopy. The average carbon concentration throughout the oxide layer and at the TiO 2 /Si interface was lowest at 200 • C. Metal oxide semiconductor capacitors (MOSCAPs) were fabricated, and profiled by capacitance-voltage techniques. The sample prepared at 200 • C had negligible hysteresis (from a capacitance-voltage plot) and the lowest interface trap density (as extracted using the conductance method). Current-voltage measurements were carried out with top-to-bottom structures. At −2 V gate bias voltage, the smallest leakage current was 1.22 × 10 −5 A/cm 2 for the 100 9 and smaller leakage current density are highly desirable. The insulator deposition temperatures should be below 500• C, because capacitors are expected to be deposited after transistors formation.10 However, further research on the high dielectric materials is needed to fulfill those requirements.In the present study, plasma-assisted atomic layer deposition (PA-ALD) was employed to deposit thin insulating TiO 2 films, because it offers excellent atomic level control of layer thickness with good uniformity and conformality.11 With an O 2 plasma, the deposition can be conducted at a lower temperature and with a shorter purge time in cold-wall reactors than a conventional thermal ALD system. 12These characteristics are particularly suitable for growing capacitor dielectrics for use in DRAM, as it uses a three dimensional structure with a high aspect ratio to increase the effective surface area. 13The present work reports on the impact of the deposition temperature on the properties of TiO 2 films prepared by PA-ALD and on the performance of said films in silicon MOSCAPs. By correlating the oxide structure, surface morphology and impurity concentration with electrical properties (hysteresis, interface trap density and leakage current), an optimal deposition temperature is identified. ExperimentalTiO 2 ALD Film growth and metal contact deposition.-Before deposition, the n-type Si (100) substrates were cleaned with acetone and isopropyl alcohol (IPA) for 5 minutes at 40• C. TiO 2 was deposited by PA-ALD in an Oxford Instruments FlexAL ALD reactor with tetrakisdimethylamino titanium (TDMAT) kept at 39• C as the titanium precursor, and oxygen plasma as the oxidizing agent. The ALD growth temperatures were 100• C, 150• C and 300• C. All ALD depositions consisted of 400 cycles and each ALD cycle included a 0.4 second dose of TDMAT followed by a 4 second * Electrochemical Society Active Member.z E-mail: edgarjh@ksu.edu purge with Ar gas, and a 3 second exposure to the oxygen plasma followed by a 3 second purge. The plasma power and...

MOS Capacitance Measurements for PEALD TiO2 Dielectric Films Grown under Different Conditions and the Impact of Al2O3 Partial-Monolayer Insertion

“…Figure 7d shows the dark J-V curve in semi-logarithmic scale under positive and negative biases at room temperature. As can be seen, the leakage current density at −2 V is in the order of 10 −5~1 0 −4 A/cm 2 , which is in the same order of magnitude reported by Wei et al [5] and Baek et al [1] that used PEALD and tetrakis dimethylamino titanium (TDMAT) as precursor to growth TiO 2 (20 nm) on Si.…”

“…The increase of oxygen content in PEALD TiO 2 films may be related to the higher reactivity of O 2 plasma compared to the water precursor used in thermal ALD. In a recent study, Wei et al [5] showed the influence of temperatures on the PEALD process applied to the growth of TiO 2 films in Si for the manufacture of MOS capacitors, where they used O 2 plasma at 400 W of RF power. They varied the temperature from 100 to 300 • C, with steps of 50 • C. Using the X-ray photoelectron spectroscopy (XPS) technique, they verified that the TiO 2 films had O/Ti stoichiometry ranging from 2.08 to 2.32.…”

“…Titanium dioxide (TiO 2 ) thin films and nanolaminates have a significant number of promising applications in different areas, such as microelectronics [1][2][3][4][5][6], photovoltaics [7,8], photocatalysis [9][10][11] fuel cells [12], sensors [13][14][15][16], anti-reflective coating applications [17], biomedical coatings [18,19] and food packaging applications [20]. The properties and applicability of TiO 2 thin films are intrinsically related to their crystal structure.…”

High performance sol–gel spin-coated titanium dioxide dielectric based MOS structures

“…The Table 1 shows a comparison of the physical and electrical properties of the anatase TiO 2 films obtained by various methods like DC sputtering, PECVD, ALD and LTAVD with the present work [33][34][35][36]. The results demonstrate that the TiO 2 films obtained by the present protocol showed comparable dielectric constant and very low leakage currents with excellent surface morphology.…”

Titanium dioxide thin films by atomic layer deposition: a review

“…x [561,683,[735][736][737][738][739][740][741][742][743]; [384,646,744]; [384,646,651,741,[745][746][747][748][749][750][751][752][753][754][755][756][757][758][759][760][761];…”