Plasma-Enhanced Atomic Layer Deposition of TaCx Films Using Tris(neopentyl) Tantalum Dichloride and H2 Plasma

Abstract

TaC x films were deposited by plasma-enhanced atomic layer deposition (PEALD) at a wafer temperature of 300 C using a novel nitrogen-free Ta precursor, tris(neopentyl) tantalum dichloride, Ta[CH 2 C(CH 3 ) 3 ] 3 Cl 2 and H 2 plasma as the reactant. Self-limiting film growth was observed with both the precursor and reactant pulsing time. Both X-ray diffraction and electron diffraction analysis consistently showed that a cubic TaC phase formed, even though the film was Ta-rich TaC x (C/Ta ¼ $0.36). The film resistivity decreased with increasing H 2 plasma pulsing time from 900 to 375 X cm. In this study, a performance of TaC x as a diffusion barrier for Cu interconnects was evaluated. The results showed that the structure of Cu (100 nm)/ALD-TaC x (15 nm)/Si was stable after annealing at 650 C for 30 min.Tantalum (Ta)-based thin films, such as Ta, TaN x , TaC x and TaC x N y , have been investigated for decades for semiconductor microelectronic devices applications owing to their excellent properties, such as high electrical conductivity, chemical, mechanical and thermal stability. 1-6 Although the main applications of these materials are as a diffusion barrier for copper metallization, 1-5 they are also considered to be a metal gate with high-permittivity gate dielectrics. 6 For these applications, they need to be deposited uniformly at high aspect ratio (AR) structures with a conformal thickness as the demand for shrinking dimensions is increased. In addition, a deposition technique with high process controllability and large-area uniformity is needed. Atomic layer deposition (ALD) is a viable solution because ALD uses a self-limiting film growth mode through surface-saturated reactions, which enables atomicscale control of the film thickness and composition with excellent step coverage. 7 Currently, ALD of Ta-based films has attracted increasing attention for the preparation of Ta nitrides. The most critical issue in the TaN x -ALD process is to obtain highly conductive TaN films. Ta 3 N 5 , which is nitrogen-rich phase in the Ta-N binary system and a dielectric material, was deposited using TaCl 5 and NH 3 and its resistivity was as high as $200 X cm. 8 highly conductive TaN film can be deposited using an additional reducing agent, such as Zn (Ref. 8) or trimethyl aluminum (TMA), 9 but its resistivity was still high, from $900 to $1300 X cm. Moreover, small amounts of Zn impurities ($4 atom %) can cause severe problems if they diffused into the Si substrate. In addition, the use of inorganic precursors, such as TaCl 5 and TaBr 5 , has the potential problem of the incorporation of corrosive halogen elements in the film, particularly when the deposition temperature is as low as 400 C. 8,9 The successful deposition of low-resistivity TaN (q: 350-610 mX cm) with inorganic precursors of TaCl 5 (Ref. 10) and TaF 5 (Ref. 11) is possible using N 2 / H 2 plasma as a reducing agent of the precursors, in contrast to the highly-resistive Ta 3 N 5 growth by the reaction of TaCl 5 with molecular NH 3 .Ta nitride ALD was also ...

TaCx Thin Films Prepared by Atomic Layer Deposition as Diffusion Barriers for Cu Metallization

“…Previously, the C‐to‐Ta ratio (C/Ta) of the film deposited at 300°C was reported to be 0.36 with ~11.7 at.% Cl incorporated into the film . This study reports the composition of the film deposited at a higher deposition temperature, 400°C.…”

“…(a)] revealed a nanocrystalline or amorphous structure. It was hard to detect the crystalline grains in the plan‐view BF TEM image, and grains, ~3 nm in size, were confirmed by plan‐view dark‐field (DF) TEM . The microstructure of the ALD‐TaC x film deposited at 400°C [Fig.…”

“…The corresponding selected‐area diffraction pattern (SADP) [inset of Fig. (d)] was clearer and more spotty than that of the ALD‐TaC x film deposited at 300°C, indicating an increase in crystallinity and grain size. The SADPs of both films were similar to those of the rock‐salt TaC crystal structure and GIAXRD patterns (Fig.…”

“…The composition of the ALD‐TaC x films deposited at 300°C was analyzed according to the reactant pulse time by SIMS depth profiling. The SIMS results were calibrated with the data from RBS of the film deposited at 300°C with the pulse condition of 12s‐10s‐8s‐10s . Figure (a) shows the SIMS depth profile of a film deposited on a SiO 2 substrate at a reactant pulse time of 15 s. The amount of Ta and C was uniform throughout the film and the C‐to Ta‐ratio was approximately ~0.21.…”

“…ALD is a viable option because it involves a self‐limited film growth mode through surface‐saturated reactions, which enables atomic‐scale control of the film thickness and composition with excellent step coverage . In contrast to the extensive studies of Ta‐based nitrides ALD, there are few reports on TaC x ALD process . Plasma‐enhanced ALD (PEALD) Ta‐rich TaC x films with a growth rate of ~1 Å per cycle were deposited using an inorganic precursor and a carbon‐containing gas, but the process details were not reported .…”