Effect of H[sub 2] Pulse on Pulsed MOCVD of Cu Seed Layers

Abstract

Pulsed metallorganic chemical vapor deposition ͑MOCVD͒ of conformal copper seed layers, for the electrodeposition Cu films, has been conducted by an alternating supply of a ͑hexafluoroacetylacetonate͒Cu ͑I) ͑3,3-dimetyl-1-butene͓͒͑hfac͒Cu͑DMB͔͒ source and H 2 reactant at low deposition temperatures between 50 and 100°C. The growth rate increased proportionally to the number of cycle, ranging from 3.5 to 5.4 Å/cycle, indicating the ability to control the nano-scale thickness. As-deposited films show very smooth surfaces and the low resistivities of 3.3 ⍀ cm for 30 nm thick films. About a 90% step coverage was obtained inside trenches, with an aspect ratio greater than 30:1. H 2 , introduced as a reactant gas, can play an active role in achieving highly conformal coatings, with negligible impurities and excellent adhesion of Cu films to the TiN substrate.The downscaling of the dimensions of microelectronic devices, to below 100 nm has led to the replacement of aluminum-based metallization with copper, as Cu exhibits lower resistivity, superior electromigration resistance, and higher resistance to stress-induced voids. 1-7 This also necessitates the consideration of devices fabricated by conformal filling of Cu, over high aspect ratio contacts and vias in the damascene structure. Cu electroplating is the most common technology employed for void-free filling of via and hole structures at a near bulk resistivity, with high growth rates in scaled deep submicrometer metallization schemes. 8,9 However, this method requires the conformal deposition of a thin Cu seed layer prior to the electroplating of a thicker Cu layer. In considering methods for the deposition of a Cu seed layer, conventional physical vapor deposition encounters several problems, such as poor conformal coverage, especially on the sidewalls, and the overhang at the opening of vias. 2,3,10 Therefore, most current research focuses on developing an alternate deposition technique for the seed layer, which must be continuous, smooth, conformal, and thin enough for a critical dimension of 100 nm and below. 11 In addition, nano-scale thickness control is required for the design of the interface properties between the Cu seed layer and the barrier, which significantly affects the reliability. 12 A copper atomic layer deposition ͑ALD͒ process using an organometallic Cu͑II͒ source and H 2 reducing agents shows various degrees of success in producing highly conformal layers of Cu thin films, with atomic layer thickness control, due to its selflimiting character. 13-18 Compared with ALD Cu using Cu͑II͒, pulsed metallorganic chemical vapor deposition ͑MOCVD͒ by a Cu͑I͒ source provides a wide range of growth rate, depending on the deposition temperature, and the amount of Cu precursor introduced into the chamber. 19 In addition, the use of additional reactants pulsing can affect the nano-scale deposition characteristics, and thus provides an ability to control the microstructure, film quality and conformal coating.In this study, the pulsed MOCVD of a Cu seed layer, u...