Combinatorial Chemical Vapor Deposition of Metal Silicate Films Using Tri( t -butoxy) silanol and Anhydrous Metal Nitrat
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Combinatorial Chemical Vapor Deposition of Metal Silicate Films Using Tri(t-butoxy) silanol and Anhydrous Metal Nitrates Lijuan Zhonga, Fang Chenb, Stephen A. Campbellb and Wayne L. Gladfeltera a Deptartment of Chemistry, bDepartment of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455, U.S.A. ABSTRACT A modified low-pressure chemical vapor deposition reactor was used to create compositional spreads of MO2/SiO2 films (M = Hf, Zr and Sn) using tri(t-butoxy) silanol and anhydrous metal nitrates of hafnium, zirconium and tin at temperatures below 250 °C. The compositional spreads formed by this process were characterized by ellipsometry and Rutherford backscattering spectrometry. A survey of possible reactions involved in the deposition is included. INTRODUCTION The search for a dielectric material to replace SiO2 in field effect transistors has focused on combinations of a high dielectric constant (κ) metal oxide with a glass forming material, such as SiO2 [1]. Both the microstructure and the film properties are related to the composition. Even for a two-component mixture, however, exploring all compositions is a time-consuming task. In our group’s previous study, we created compositional spreads of HfO2 (or ZrO2), SnO2 and TiO2 by balancing the fluid dynamics and precursor chemistry in a modified cold-wall, low-pressure CVD reactor [2, 3]. Considering that their identical ligands would lead to similar deposition kinetics, the anhydrous metal nitrates of all four metals were used as precursors. In this report, we used tri(t-butoxy) silanol and anhydrous metal nitrates to codeposit MO2/SiO2 films (M = Sn, Zr and Hf) and create compositional spreads at temperatures below 250 oC. The maximum growth rate reached a significant value of 3000 Å/min, which is unusual in any chemical vapor deposition processes at such low temperatures. Possible reactions involved in this process are discussed. EXPERIMENTAL DETAILS Tri(t-butoxy) silanol [(tBuO)3SiOH, 99.9%] was purchased from Aldrich Company and used as received as the source for silicon. Anhydrous metal nitrates of Hf, Zr and Sn [Hf(NO3)4, Zr(NO3)4 and Sn(NO3)4] were synthesized via the reaction of the metal chloride and N2O5 using a modification of literature procedures [4, 5]. The modified cold-wall, low-pressure CVD reactor with the precursor outlets extended directly over the substrate surface at a height of 1 cm has been described in detail elsewhere [2]. Si (100) wafers were approximately 1¨ x 1¨ in size. The (tBuO)3SiOH precursor vessel was cooled to 0 °C in an ice/water bath or kept at room temperature. The metal nitrate vessels were heated using Variac-controlled heating tape to the desired temperatures. The high-purity N2 flow rate was regulated by mass flow controllers and set to 3-10 sccm. Overall reactor pressure of 0.3 Torr was maintained during the process. The
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molybdenum susceptor was heated to the desired deposition temperature (130 – 500 °C) using a Variac-controlled 1000-W halogen lamp. Rutherford backsca
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