Low Temperature Deposition of WN_xC_yDiffusion Barriers Using WN(NEt₂)₃as a Single-Source Precursor

Abstract

Deposition of high quality WN x C y barrier films at very low temperature using aerosol-assisted chemical vapor deposition (AACVD) is reported. The single-source tungsten nitrido complex, WN(NEt 2 ) 3 , was designed to reduce the temperature required for WN x C y film deposition in an effort to minimize thermal stresses on neighboring layers in device structures. Using either pyridine or heptane as a solvent, WN x C y films were successfully deposited at temperatures from 100 to 650 • C. Film growth in pyridine and heptane at low temperature (100-350 • C and 125-550 • C, respectively) showed weak temperature dependence consistent with mass-transfer limited growth. At higher temperature the growth rate decreased rapidly with apparent activation energy of 0.375 ± 0.057 eV. The effects of solvent choice on film properties including composition, crystallinity, density, and surface roughness are discussed. Films deposited at low temperature (<350 • C) were highly smooth, amorphous and with a stoichiometry approaching W 2 NC; characteristics desirable for diffusion barrier applications. In Cu diffusion barrier tests, Cu (∼ 100 nm)/WN x C y (∼ 5.5 nm)/Si stacks subjected to a 500 Thin interlayer materials are increasingly being used in electronic devices to modify interfacial characteristics, including the film work function, chemical, thermal and charge transport rates, surface tension, and adhesion. Due to their low resistivity, appropriate work function, and thermal stability, refractory metal nitrides have been proposed for a number of applications, ranging from wafer level hermetic sealing 1 to field effect transistor (FET) gate electrodes. 2 In particular, the tungsten-based materials WN x and WN x C y have been considered as an alternative for both diffusion barriers 3,4 and gate electrodes 5 due to their low resistivity, appropriate and tunable work function (4.39-5.01 eV 6 ), thermal and mechanical stability, good barrier performance, and processing simplicity. 7,8 Depositions of WN x and WN x C y typically use ammonia and WCl 6 , WF 6 or W(CO) 6 as co-reactants. 4,[9][10][11][12] Despite being volatile, simple, and cost-effective, these chemistries generally require high deposition temperature, can introduce impurities, and can yield corrosive byproducts. To overcome these drawbacks, organometallic precursors have drawn considerable interest for metal-organic CVD (MOCVD). Typically, these complexes include nitrogen-bound moieties such as amido, imido, hydrazido, amidinate or guanidinate ligands, 13,14 and have been used in single-source or NH 3 /H 2 co-reacting conditions to deposit WN x . Unfortunately, many of these precursors still require relatively high deposition temperature (>350• C) 15-22 that can compromise contact level structures 2,23 and neighboring dielectrics. 24In addition, the development of ultra-low temperature CVD WN x C y has potential application to flexible and organic devices. Therefore, there is interest in developing organometallic precursors for ultra-low deposition temperature. We h...

Synthesis and Characterization of Tungsten Nitrido Amido Guanidinato Complexes as Precursors for Chemical Vapor Deposition of WNxCy Thin Films

“…Considerations employed in the design of WN(NMe 2 ) 3 ( 2 ), included a multiply bonded W≡N moiety, only N-bound ligands, and facile access to a small library of derivatives. [5f, 5g] The incorporation of a terminal nitrido moiety was associated with a low film deposition temperature (125 °C) from this precursor. The relationship between the volatility of WN(NR 2 ) 3 complexes and amido ligand structure was also explored in order to improve the vapor-phase transport of the precursors, which is a critical property in deposition methods that use bubblers for volatilization, such as CVD and ALD.…”

“…The attempted synthesis of N- tert -butyl guanidinato derivatives of 1 by addition of N,N′-di- tert- butylcarbodiimide to solutions of 2 resulted in recovery of starting material, even after extended reflux at temperatures up to 115 °C, suggesting steric limitations to the insertion reaction. Because 2 readily undergoes transamination with secondary amines to access different amido ligands, [5g] a similar procedure was attempted to generate additional dialkylamido derivatives of 1 . However, this strategy was ultimately unsuccessful.…”

“…[4] Previously reported single source precursors for deposition of WN x C y have utilized N-bound ligands such as nitrido, imido, hydrazido, amido, guanidinato, and amidinato moieties to provide the nitrogen in the resulting material. [5] Optimization of the precursors has primarily targeted low temperature deposition (<350 °C) to minimize and thermal damage to the substrate. Our studies of tungsten nitrido complexes of the type WN(NR 2 ) 3 demonstrated that the W≡N and W–NR 2 moieties are acceptable sources of N in depositions carried out at temperatures as low as 125 °C.…”

“…In addition, variation of the substituents in the amido moieties of WN(NR 2 ) 3 provided a means to tune the precursor volatility. [5g],[6]…”

“…Our previous study of the tungsten imido guanidinato precursor W(N i Pr)Cl 3 [( i PrN) 2 CNMe 2 ] demonstrated that guanidinato ligands are suitable for use in precursors for the AACVD of WN x C y . [5d] We now report the synthesis of tungsten nitrido amido guanidinato precursors along with a demonstration of the use of WN(NMe 2 )[(N i Pr) 2 C(NMe 2 )] 2 ( 1 ) as a single source precursor for the AACVD of WN x C y thin films.…”