Thin, Continuous, and Conformal Copper Films by Reduction of Atomic Layer Deposited Copper Nitride

Abstract

Thin and continuous copper films serve as seed layers for electrodeposition of interconnects in microelectronic devices. Gaps in the continuity of these Cu films must be avoided, because they can generate voids that later lead to failure of the devices. It is difficult to sputter completely continuous copper-seed layers into the increasingly narrow trenches and holes in modern interconnects. Here we report a method for producing thin, completely continuous, and highly conductive copper films conformally inside very narrow holes with aspect ratios of over 40:1. The first step in our process is atomic layer deposition (ALD) of copper(I) nitride, Cu 3 N, by the alternating reactions of copper(I) N,N′-di-sec-butylacetamidinate vapor and ammonia on surfaces heated to approximately 160°C. At this temperature, Cu 3 N is thermally stable, but is readily reduced to copper metal by exposure to molecular hydrogen gas (H 2 ). Copper layers as thin as 0.8 nm (about 3 monolayers) are electrically continuous and show the electrical resistivity predicted by a grain-boundary-scattering model for continuous films of that thickness. 3 nm thick copper films on 2 nm of ruthenium have a sheet resistance of less than 50 X/ᮀ, a value low enough to serve as seed layers for advanced electroplating techniques.

CVD of Copper(I) Nitride

“…[17] When the metastable Cu 3 N is heated, it decomposes into metallic copper and nitrogen gas, a behavior that could be exploited in copper metallization. [18,19] Cu 3 N is also expected to be a good host material for Li or Cu atoms, [20] since it exhibits the anti-ReO 3 structure, which is rather open with the Cu atoms occupying the midpoints of the edges and the N atoms occupying the cell corners. The experimentally measured band gap (indirect) for Cu 3 N films seems to be dependent upon the nitrogen content, and has been reported to be in the range 1.3-2.1 eV.…”

Copper(I) carbene hydride complexes acting both as reducing agent and precursor for Cu ALD: a study through density functional theory

“…There have been similar attempts to convert other copper binary compounds like Cu 3 N [12] into copper metal by using molecular hydrogen. However in order to crack the H-H bond, energy in excess of 400 kJ/mol is required [13].…”

Ultrathin CVD Cu Seed Layer Formation Using Copper Oxynitride Deposition and Room Temperature Remote Hydrogen Plasma Reduction

“…These values are similar to the resistivity of sputtered Cu at the corresponding thicknesses. 15 Thus, the reduced Cu film has a high density and high purity.…”

“…This precursor's reactivity at a low substrate temperature has been reported under ALD conditions. 9,15 Cu oxide, Cu nitride, and CuON are formed by using Cu amidinate with H 2 O and NH 3 as reactant gases. The Cu compound films were then reduced by H 2 remote-plasma treatment because atomic hydrogen is one of the strongest reducing agents, which can enable room temperature reduction and minimize agglomeration of the copper.…”