Peter C. Van Buskirk

Metalorganic Chemical Vapor Deposition of Complex Metal Oxide Thin Films by Liquid Source Chemical Vapor Deposition

The implementation of ferroelectric thin films in advanced semiconductor devices is near ; facile integration at ULSI geometries requires chemical vapor deposition (CVD) process technology. The low volatility and thermal stability of many of the existing source reagents has driven the development of liquid source CVD, in which composition is set by volumetric metering of liquids followed by flash vaporization. The methodology as well as early results for Ba 1-x Sr x TiO 3 , Pb 1-x (La x Zr 1-y Ti y ) 1-z/4 O 3 and SrBi 2 Ta 2 O 9 thin films, which are among the best reported for any deposition method, will be reviewed. These results establish liquid source CVD as a leading candidate to become the predominant deposition technology enabling the integration of ferroelectric thin films in ULSI devices.

MOCVD of BaSrTiO3 for ulsi drams

Abstract The CVD of high permittivity materials such as BaSrTiO3 presents new challenges to the semiconductor equipment and materials industries. The electrical properties of the material are a strong function of composition, microstructure and dopant concentration (electronic and ionic). However, the source reagents are typically low vapor pressure liquids, solids or solids dissolved in liquids which are challenging to manufacture with ultra-high purity and difficult to deliver with high accuracy and precision. Reactor walls must be heated to avoid condensation of the source materials and deposition temperatures are high where radiative heat transfer becomes significant. Reaction products are difficult to remove by standard dry chemical etching techniques because the halides of many of the metals are involatile inorganic salts. Design strategies to overcome these challenges and the resulting properties of BaSrTiO3 films will be discussed.

Plasma‐enhanced metalorganic chemical vapor deposition of BaTiO3 films

BaTiO3 films have been grown by plasma‐enhanced metalorganic chemical vapor deposition (PE‐MOCVD) for the first time. The BaTiO3 films were grown on Pt‐coated Si substrates in an inverted vertical reactor with a remote O2 plasma at 450 mTorr. Plasma powers exceeding 10 W reduced or eliminated the presence of CO3 in the as‐grown films at 525 and 600 °C, respectively. Films deposited at 600 °C by PE‐MOCVD were polycrystalline BaTiO3 with perovskite structure and partial texture in the [100] direction; films grown at 525 °C were amorphous. The polycrystalline BaTiO3 films had dielectric constants as large as 300, loss tangents of 0.02, and resistivities exceeding 109 Ω cm at room temperature.

Common and unique aspects of perovskite thin film CVD processes

Abstract In the past 5 years there has been a large amount of work to develop CVD technology for the deposition of the predominant perovskite oxide thin films, (Ba, Sr)TiO3, SrBi2Ta2O9 and Pb(Zr, Ti)O3. For each of these families of materials, CVD processes have matured such that state-of-the-art film properties may be achieved with this technique. Much of the progress is attributed to the use of the liquid delivery technique to transfer relatively involatile metalorganic precursors to the reactor. This paper will discuss common attributes of these thermal CVD processes, particularly the precursors, delivery methodology and reactor hardware. The paper will also highlight unique aspects that differentiate the processes, including the CVD decomposition regime, strategies for film composition control and approaches for forming the crystalline perovskite phase. Representative film properties are presented, demonstrating that these processes are becoming increasingly mature.

Single molecular precursor metal-organic chemical vapor deposition of MgAl2O4 thin films

MgAl 2 O 4 films have been grown epitaxially on both Si(100) and MgO(100) by a novel single source metal-organic chemical vapor deposition (MOCVD) process. A single molecular source reagent [magnesium dialuminum isopropoxide, MgAl 2 (OC 3 H 7 ) 8 ] having the desired Mg: Al ratio was dissolved in a liquid solution and flash-vaporized into the reactor. Both thermal and plasma-enhanced MOCVD were used to grow epitaxial MgAl 2 O 4 thin films. The Mg: Al ratio in the deposited films was the same as that of the starting compound (Mg: Al = 1:2) over a wide range of deposition conditions. The deposition temperature required for the formation of crystalline spinel was found to be significantly reduced and crystallinity was much improved on Si by using a remote plasma-enhanced MOCVD process. The epitaxial nature of the MgAl 2 O 4 films was established by x-ray pole figure analysis.

Voltage scaling of ferroelectric thin films deposited by CVD

Abstract For many applications of ferroelectric ICs it is desirable to operate ferroelectric memory at the lowest possible power and voltage. One way to reduce the operating voltage is to reduce film thickness. We report on the electrical properties of MOCVD deposited PZT 40/60 and 20/80 films as a function of film thickness. As the thickness is reduced, switched polarization at saturation (P∗-P⁁) is reduced, but the coercive E-field is not substantially changed. Films also have imprint and fatigue behavior that is independent of film thickness when operated at constant electric field. For films below 60nm the leakage current rises rapidly; this is likely due to the effects of film roughness. For 65nm films of the PZT 20/80 material, we observed well formed hysteresis loops and PSW > 55μC/cm2 at 1.2V; polarization was greater than 90% saturated at that voltage.

Chemical vapor deposition of Pb1−xLaxTiO3

Abstract We report chemical vapor deposition (CVD) of PbLaTiO3 films for integrated pyroelectric devices. Pb(thd)2, La(thd)3 and Ti(O-Pr)2(thd)2 were introduced to the reactor via a single liquid precursor solution that is vaporized. Substrate temperatures were approximately 535°C and post deposition annealing was not used. Films were deposited on fused silica and Pt metallized Si substrates. The liquid delivery technique permitted excellent composition control and films on fused silica were predominantly [100] oriented with trace amounts of [110] and [111] present. Pyroelectricity for 0.7μm thick films deposited on Pt metallized Si was measured using a modified Byer-Roundi technique and pyroelectric coefficients as high as 90 nC/cm2·K were observed. The high crystalline quality and pyroelectric properties are attributed to the excellent composition control afforded by the liquid delivery CVD technique.

Metalorganic Chemical Vapor Deposition of Thin Film ZrO2 and Pb(Zr,Ti)O3: Precursor Chemistry and Process Characteristics.

Metalorganic chemical vapor deposition (MOCVD) process characteristics of several zirconium source reagents were investigated. These source reagents included metal β-diketonates [e.g., Zr(thd)4 where thd=(2,2,6,6-tetramethyl-3,5-heptanedionate)] and metal alkoxide/β-diketonates [e.g., Zr(OiPr)2(thd)2 and Zr(OtBu)2(thd)2]. Thermal properties and transport behaviors of these precursors were examined by thermogravimetric analysis. Zirconium oxide films were deposited on silicon substrates at reduced pressure. Under the process conditions examined, the deposition behavior was mass-transport controlled, and Zr(OiPr)2(thd)2 and Zr(OtBu)2(thd)2 behaved similarly. The films exhibited low carbon content. Pb(Zr, Ti)O3 (PZT) films were deposited on iridium-coated silicon substrates under reduced pressure. Zirconium incorporation efficiency was significantly improved for Zr(OiPr)2(thd)2 when compared to Zr(thd)4. Use of M(OtBu)2(thd)2 (where M=Zr or Ti) as source reagents for MOCVD of PZT was examined and compared to M(OiPr)2(thd)2 analogues. In this case, higher process pressures were needed to improve the incorporation efficiencies of M(OtBu)2(thd)2 precursors.

Atomic layer deposition of CeO2 using a heteroleptic cyclopentadienyl-amidinate precursor

Cerium oxide thin films were deposited on fused silica using atomic layer deposition (ALD). The novel Ce precursor, Ce(iPrCp)2(N-iPr-amd) [bis-isopropylcyclopentadienyl-di-isopropylacetamidinate-cerium] is a room-temperature liquid with good thermal stability and evaporates cleanly. Water vapor was used as the oxygen source. The growth characteristics and film properties of ALD CeO2 were investigated. A relatively broad ALD window of 165–285 °C resulted in a constant growth rate of 1.9 A/cycle and good thickness uniformity. The films deposited at 240 °C were found to be polycrystalline with cubic structure without a preferential direction in as-deposited condition. However, films grown at 335 °C slightly favored a (200) preferred orientation. XPS analysis showed that films are free from contamination, and the Ce:O stoichiometry analysis revealed the existence of oxygen vacancies in the films with composition CeO1.74.Cerium oxide thin films were deposited on fused silica using atomic layer deposition (ALD). The novel Ce precursor, Ce(iPrCp)2(N-iPr-amd) [bis-isopropylcyclopentadienyl-di-isopropylacetamidinate-cerium] is a room-temperature liquid with good thermal stability and evaporates cleanly. Water vapor was used as the oxygen source. The growth characteristics and film properties of ALD CeO2 were investigated. A relatively broad ALD window of 165–285 °C resulted in a constant growth rate of 1.9 A/cycle and good thickness uniformity. The films deposited at 240 °C were found to be polycrystalline with cubic structure without a preferential direction in as-deposited condition. However, films grown at 335 °C slightly favored a (200) preferred orientation. XPS analysis showed that films are free from contamination, and the Ce:O stoichiometry analysis revealed the existence of oxygen vacancies in the films with composition CeO1.74.

Process monitoring during metalorganic chemical vapor deposition using FTIR spectroscopy

The ability of Fourier transform infrared spectroscopy to perform in-situ measurements of ferroelectric thin film properties during metalorganic chemical vapor deposition is demonstrated. Infrared measurements of film reflectance and radiance allowed determination of film composition, thickness and temperature in real-time. These spectra could also be used to follow process changes, determine deposition rate, and extract the wavelength dependent dielectric function. These data, along with computer software and optical hardware developments, are presented.