Ferroelectric random access memory (FeRAM) is an attractive candidate technology for embedded nonvolatile memory, especially in applications where low power and high program speed are important. Market introduction of high-density FeRAM is, however, lagging behind standard complementary metal-oxide semiconductor (CMOS) because of the difficult integration technology. This paper discusses the major integration issues for high-density FeRAM, based on SrBi2Ta2O9 (strontium bismuth tantalate or SBT), in relation to the fabrication of our stacked cell structure. We have worked in the previous years on the development of SBT-FeRAM integration technology, based on a so-called pseudo-three-dimensional (3D) cell, with a capacitor that can be scaled from quasi two-dimensional towards a true three-dimensional capacitor where the sidewalls will importantly contribute to the signal. In the first phase of our integration development, we integrated our FeRAM cell in a 0.35μm CMOS technology. In a second phase, then, possibility of scaling of our cell is demonstrated in 0.18μm technology. The excellent electrical and reliability properties of the small integrated ferroelectric capacitors prove the feasibility of the technology, while the verification of the potential 3D effect confirms the basic scaling potential of our concept beyond that of the single-mask capacitor. The paper outlines the different material and technological challenges, and working solutions are demonstrated. While some issues are specific to our own cell, many are applicable to different stacked FeRAM cell concepts, or will become more general concerns when more developments are moving into 3D structures.

International audienceCross-sectional nanoindentation (CSN) is a recent method for adhesion measurement of nanoscale thin films in ultra-large scale integrated circuits. In the case of ductile thin films, plastic deformation during the test and complex geometry of delaminated areas require 3D finite element modeling (FEM) for adhesion energy calculation. In this paper the adhesion of various copper (Cu) films on blanket and patterned structures is studied by CSN test. The experimental procedure and qualitative analysis of the test are presented in detail. Crack propagation is studied on blanket and patterned substrates. The dimensions of delaminated blisters are measured by scanning electron microscope (SEM) for each sample. Results show that a geometrical ratio can be used to give a quick and qualitative measurement of adhesion. A new 3D FEM model is then proposed to assess quantitative analysis of CSN test. The deformation energy of Cu blister is calculated for each sample. The mechanical properties of the Cu films required for numerical calculations are measured by instrumented indentation. The influence on these measurements of the evolution of the Cu deformation with penetration depth is discussed in detail with the aid of 2D numerical simulation. The results of numerical modeling correlate well with qualitative evaluation of adhesion

The thermal and mechanical stability of Ir and Ir\Pt metals spacers deposited on top of Ti(Al)N\Ir\IrO 2 patterned structures has been investigated in pseudo 3D stacked SrBi 2 Ta 2 O 9 (SBT) capacitors. Their stability was compared to standard TEOS spacers. The high compressive stress at the edge of patterned electrodes, as a consequence of the high thermal expansion mismatch between the metals used in the electrode and TEOS, make the system mechanically unstable at the SBT crystallization conditions (700 • C for 1 hour). The mechanical problems could be overcome if the same noble metals used in the electrode are incorporated as spacers. However, thermal stability during the SBT crystallization conditions is still an issue. For the case of Ir, surface oxidation decreases the SBT polarization values. In the case of Ir\Pt, Ir diffuses through Pt and oxidizes, leading to unstable patterned structures and to the oxidation of the Ti(Al)N layer.

This paper introduces a novel electrochemical technology called electrografting (eG™). After describing electrografting the main characteristics, it will be shown that this technology can be successfully applied to the formation of thin, conformal, and uniform seed layers for IC copper interconnects. Seed layer thicknesses down to 10nm thick are deposited on various copper diffusion barrier materials and characterized in terms of sheet resistance, morphology, conformality, adhesion, and gapfilling capability. Initial results pointed out that the technology can be extended to seedless direct filling of interconnect structures. Electrografting FundamentalsElectrografting can be defined as a surface initiated electrochemical process for organic and organometallic film deposition, i.e. a process in which a single, usually Faradaïc, electrochemical reaction is coupled to a range of non-Faradaïc chemical reactions giving rise to the formation of a film. This technology works on any conducting and semi conducting surface. Figure 1 illustrates the main characteristics of electrografting in the example of an organic precursor:• As an electro-initiated reaction, electrografting requires very low amount of electrical current, as shown in the voltammogram of Figure 1a. This constitutes an essential feature of electrografting which induces very little ohmic drop and makes it operative and equally uniform on large substrates with a very wide range of substrate resistivities: PVD TaN, PVD TaN/Ta, ALD TaN,…etc ( Figure 1c); • Most electrografting reactions are based on electrically neutral molecular precursors: they are thus mainly fed by diffusion, and very little by migration, as the precursors are insensitive to local electric fields during the process. A straightforward consequence of this is that electrografting delivers coatings which are intrinsically conformal, even on very demanding surfaces with high aspect ratios ( Figure 1d); • Electrografted reactions are usually linked with intimate surface/molecule charge transfer leading to the formation of strong chemical bonds, which can often survive the overall coupled chemistry and sometimes be detected post-mortem in the electrografted film ( Figure 1b) (1). At a more macroscopic scale, electrografted films usually show very strong adhesion to the substrate on which they have been grafted, in line with the interface management which is forced during the initial charge transfer process.

PACS 81.15.Cd, 81.15.Gh, 85.50.Gk In this work recent achievements for integrating SrBi 2 Ta 2 O 9 -based non-volatile ferroelectric memories in the 0.35 µm CMOS technology are discussed. The main challenges in the development of a suitable bottom electrode compatible with the SrBi 2 Ta 2 O 9 crystallization step and the subsequent integration processing such as etching development and hydrogen sealing will be reviewed.