Study on the Step Coverage of Metallorganic Chemical Vapor Deposited TiO[sub 2] and SrTiO[sub 3] Thin Films

Abstract

The growth behavior and step coverage of TiO 2 thin films deposited by liquid-delivery metallorganic chemical vapor deposition ͑MOCVD͒ at temperatures ranging from 410 to 490°C were investigated. The film growth rates were controlled by the gas phase thermal decomposition reaction of the precursors, and the reaction shows an apparent activation energy of ϳ90 kJ/mol. The gas phase thermal decomposition produced several intermediate precursor molecules with different sticking coefficients. The intermediate precursors played a crucial role in the film growth and step coverage change. As the growth rate decreases, the step coverage degrades, which can be explained by Langmuir's isothermal adsorption model of the precursors with the assumption of the various intermediate molecular structures of the precursors. The bulkier intermediate molecular structure of the precursor increases the steric hindrance between the previously adsorbed molecules and the impinging molecules so that the step coverage improves. The unusual step coverage of an MOCVD SrTiO 3 film previously observed for a low precursor injection rate was successfully explained using the results derived from the TiO 2 MOCVD and nonsticking property of the Ti-precursor molecules on the SrO surface.The ceramic thin films ͑Ba,Sr͒TiO 3 ͑BST͒, 1-4 SrTiO 3 ͑STO͒, 5 and Pb͑Zr,Ti͒O 3 6-8 deposited by metallorganic chemical vapor deposition ͑MOCVD͒ have been investigated by many researchers as capacitor materials of dynamic random access memories or ferroelectric random access memories. Considering the shrinking cell area of memory devices, these materials should be deposited on three-dimensional ͑3D͒ structures as contact holes. 9,10 The MOCVD method can produce these films with satisfactory growth rate, electrical properties, and conformal deposition over the severe 3D structures applicable to mass production. However, a nonuniform cation composition of the deposited film over a 3D contact hole has been reported even with the MOCVD technique when the contact hole diameter is below 150 nm. 11 In some cases, the films grew predominantly at the bottom corner of the contact hole, which is unusual. 11 To improve the thickness and composition uniformity of the multication oxide films, an understanding of the deposition behavior of the films on contact holes is necessary. However, it is not easy to understand the details of MOCVD of multicomponent oxide thin films because the deposition is affected by many complex factors. The above-mentioned materials commonly have a Ti component. Therefore, the MOCVD behavior and step coverage of the TiO 2 films are investigated first in this study. From these experimental results, the experimental results on the compositionally nonconformal STO thin film deposition that were previously reported by the authors are analyzed again in this paper. Figure 1 shows the schematic diagram of the system for the deposition of TiO 2 thin films. It is composed of an inverted vertical MOCVD reactor, where the sample surface faces downward, and a liquid...

Supercritical Fluid Deposition of Conformal SrTiO[sub 3] Films with Composition Uniformity in Nanocontact Holes

“…12 Thus, to obtain chemically uniform STO films, the conformality of each component ͑TiO 2 and SrO͒ should be achieved. In fact, by using ALD, much improved chemical uniformity along the 3D contact hole was obtained.…”

“…The low growth rate below 130°C originated from the reduction of reaction rate of Sr and Ti precursors with H 2 O 2 oxidant for the formation of SrTiO 3 phase. 12,16 The growth rate was not changed significantly between 75 and 200 atm, while it decreased abruptly above 200 atm ͑Fig. 3b͒.…”

“…One widely studied deposition technique for STO thin films is metallorganic chemical vapor deposition ͑MOCVD͒. [10][11][12][13] Although relatively good composition controllability can be achievable by MOCVD, it is difficult to obtain highly conformal deposition on nanoscale 3D structures. In addition, compositional variation in deep trenches or nanoholes is also a significant problem.…”

“…10 The nonuniform Sr/Ti ratio of the MOCVD STO films inside nanoholes was attributed to the different deposition characteristics of Ti and Sr precursors, depending on arriving rates and sticking coefficients of the precursors during MOCVD. [10][11][12] Atomic layer deposition ͑ALD͒ was suggested as an alternative technique for MOCVD STO. [14][15][16][17] Generally, ALD enables a deposition with atomic thickness uniformity, high conformality in nanoscale holes and trenches, and large-area uniformity.…”

Potential Step Coverage for Supercritical Fluid Deposition of TiO2 by Numerical Simulation and Microcavity Analysis

“…Compared with CVD, SCFD provided superior conformal deposition capability because of the higher ks D values of TiO 2 −CVD, which were calculated to be about 3 × 10 5 m −1 from sticking probability (η = 0.04). 15 ALD, which is currently used for DRAM fabrication, has unrivaled capability for conformal film deposition. Blanquart et al 16 demonstrated conformal TiO 2 deposition on deep trenches having an aspect ratio of about 60 (125-nm width, 6.75-μm depth) from Ti(C 2 H 7 N) 2 (O−i−C 3 H 7 ) 2 at 275 • C. The growth rate of TiO 2 −ALD is, however, typically less than 0.5 nm/min.…”