Pulsed CVD of Tungsten Thin Film as a Nucleation Layer for Tungsten Plug-Fill

Abstract

Tungsten ͑W͒ thin film as a nucleation layer for a W plug-fill process was deposited using a modified chemical vapor deposition ͑CVD͒ called pulsed CVD, and properties of the films were investigated. Basically, the deposition stage was composed of four separate steps for one deposition cycle: (i) reaction of WF 6 with SiH 4 ; (ii) inert gas purge; (iii) SiH 4 exposure without WF 6 ; and (iv) inert gas purge. A higher deposition rate, ϳ1.5 nm/cycle, was obtained as compared to that of atomic layer deposition ͑ALD͒ (ϳ0.25 nm/cycle). The film deposited by pulsed CVD showed a much lower root mean square ͑rms͒ roughness ͑0.87 nm͒ and better conformality at the contact holes with an aspect ratio of 14 ͑contact height: 3.51 m and top diameter: 240 nm͒ as compared to the layer deposited by conventional CVD using WF 6 and SiH 4 .Chemical vapor deposited ͑CVD͒ tungsten ͑W͒ has been used as a plug material in etched oxide contacts and vias at high aspect ratio in multilevel metallization of dynamic random access memory ͑DRAM͒. 1-5 The conventional W plug-fill process is composed of three steps: 1 (i) silane (SiH 4 ) pretreatment, (ii) W nucleation, and (iii) W plug-fill. Prior to W deposition, Ti/TiN is typically deposited as a glue/barrier layer because of poor adhesion of W on SiO 2 . The first step, a SiH 4 pretreatment induces a homogeneous nucleation of W film on TiN, resulting in a continuous and uniform W film less than 20 nm thick. 5 In the nucleation step, WF 6 is reduced with SiH 4 for fast deposition on TiN with little incubation time while H 2 reduction is used in the plug-fill step with an excellent conformality ͑Fig. 1͒.Generally, the SiH 4 reduction in the W nucleation step produces poor step coverage of W films in deep contacts compared to H 2 reduction. Thus, a thin nucleation layer is favored to minimize the effect on the W plug-fill. However, a thin nucleation layer is subject to be attacked by WF 6 during the plug-fill step, leading to volcano formation. 6 Moreover, as the contact and via sizes continuously shrink with increased aspect ratio, the poor step coverage of the W nucleation layer becomes more problematic. In this respect, a deposition process with better conformality is required. Atomic layer deposition ͑ALD͒ of W is considered as a most promising solution with a superior conformality at the aggressive topographic structures. 7-9 Using Si 2 H 6 , 7 SiH 4 , 8-9 and B 2 H 6 9 as reducing agents of WF 6 , ALD-W films were deposited with very smooth surface and excellent step coverage as compared to those of CVD-W. However, an ideally very low deposition rate of 1 monolayer of W ͑0.25-0.3 nm͒ per cycle as compared to conventional CVD-W process 7,9 may limit its applications in the semiconductor processing.In this article, we report the modified CVD-W nucleation process, called pulsed CVD. We introduced an additional SiH 4 exposure without WF 6 after a short CVD reaction of WF 6 with SiH 4 . And, between the two steps, a purge step using inert gas was carried out to prevent a possible gas-phase rea...

Gas‐Pulsed CVD for Film Growth in the CuNiN System

“…For Ni 3 N it is observed that the growth is low at short (Ni(thd) 2 substrates. [24] The curve in Figure 4A is expected for a deposition process with nucleation problems.…”

“…In a previous work, both Cu 3 N and Ni 3 N have been deposited by CVD and atomic layer deposition (ALD) from Cu(hfac) 2 and Ni(thd) 2 , respectively, with NH 3 as the nitrogen source. [22][23][24] The CVD processes have overlapping temperature and total pressure regions to reach surface kinetics control.…”

“…In practice this means a combination of two sequential CVD processes, where the host material is deposited to a thickness of about one monolayer in the first CVD process, and the deposition and diffusion of the other atoms into the host material occurs in a second, subsequent CVD process (i.e., pulses of CVD processes are used). Such a process scheme also has other advantages e.g., increasing the time for surface diffusion, improving step coverage, [1,2] but also eliminating the risk of chemical reactions between deposition precursors in multi-component systems with consequences of blocking surface sites and inhibiting the deposition process. Different pulsed-CVD process concepts have been demonstrated before.…”

“…Short CVD pulses have been employed previously to increase step coverage in copper and tungsten deposition. [1,2] Alternating supply of metal precursors has been demonstrated to increase the purity of metal-organic (MO)CVD films of PZN (Pb(Zn 1/3 Nb 2/3 )O 3 ). The perovskite structure was fabricated by a sequential supply of Pb for the A-sites and of Zn and Nb for the B-sites.…”

Synthesis and optimization of tungsten and tungsten oxide films produced by laser ablation

“…In recent years significant effort has been devoted towards developing surface acoustic wave (SAW) sensors based on WO 3 sensing films, to be used for detection of gases like NO, H 2 S, NO 2 , SO 2 , CO, CO 2 . The WO 3 films have been deposited by various techniques as magnetron sputtering [1,2,3], electrochemical deposition [4,5], chemical vapor deposition [6,7], as well as laser ablation technique [8,9,10].…”