Holm Geisler

Depth dependence of ultraviolet curing of organosilicate low-k thin films

UV radiation curing has emerged as a promising postdeposition curing treatment to strengthen organosilicate interlayer dielectric thin films. We provide the evidence of film depth dependent UV curing which has important effects on through thickness mechanical and fracture properties. Force modulation atomic force microscopy measurements of the elastic modulus through the thickness of the films revealed evidence of periodic modulations of the glass stiffness which increased in magnitude with UV curing time. Furthermore, while significant increases in fracture energy were observed with UV curing time at the top of the organosilicate film, much lower increases were observed at the bottom. The increase in fracture energy with UV curing was film thickness dependent. The cohesive fracture resistance was less sensitive to UV curing. Possible explanations for the stiffness modulations through the film thickness involving UV light interference or phase separation by spinodal decomposition during the cure process a...

Tuning depth profiles of organosilicate films with ultraviolet curing

This study demonstrates that ultraviolet (UV) radiation curing can control depth profiles of organosilicate films. Striking differences between the effects of monochromatic and broadband UV irradiation were observed. For the same as-deposited organosilicate film and cure duration, monochromatic radiation has a greater impact on film structure, elastic modulus, and fracture resistance, but also results in a greater degree of depth dependent properties. Oscillating elastic modulus through the film thickness was observed with force modulation atomic force microscopy. We present a new standing wave model that accurately predicts the resulting depth dependent stiffness variations considering changes in film shrinkage and refractive index in terms of curing time, and can further be used to account for initial film thickness dependence of UV curing and film absorption. Promising applications of the depth dependent UV curing to produce multifunctional ultralow-k layers with a single postdeposition curing process ...

Analytics and Metrology of Strained Silicon Structures by Raman and Nano‐Raman Spectroscopy

Straining the active regions in MOSFET devices is one of the key contributors to increase device performance in present and future technology nodes. Since dedicated strain on the transistor level is required with opposite sign for NMOS and PMOS transistors, the need to measure strain locally has become a challenge for analytics and metrology. Raman spectroscopy is capable of obtaining strain information non‐destructively on the sub‐μm scale, and therefore, this technique has been considered for process monitoring. In this paper it will be shown for silicon‐germanium thin films, how both strain and composition can be determined independently by measuring two phonon modes of the film. This technique enables fast measurement of mechanical strain and chemical composition with high accuracy on the μm‐scale. Thus, the micro‐Raman technique is well suited for metrology of strained silicon test structures. Furthermore, it is shown that mechanical strain close to silicon‐germanium structures can be measured with n...

CPI challenges to BEOL at 28nm node and beyond

We address package-induced degradation of BEOL interconnects and approaches for recovery. For dielectrics, we cover process options and position in stack for ULK films and how these lead to differences in strength. Experiments were designed to cross-compare multiple methods to test susceptibility of BEOL interconnect to CPI damage. We also address how Chip Package Interaction changes as BEOL features and layout evolve.

Chip-package interaction: Challenges and solutions to mechanical stability of Back end of Line at 28nm node and beyond for advanced flip chip application

Fhis paper discusses the extensive development work carried out by GLOBALFOUNDRIES to mitigate chip-package interaction (CPI) risks for the silicon Backend of Line (BEOL) during IC package assembly. Particularly, material property data for different ultra low k (ULK) materials, CPI qualification results and key findings made during the technology development are discussed. Newly developed test and modeling methods to expedite technology learning are also described in detail.

Novel Carbon-Cage-Based Ultralow-

A new class of materials is presented that is supposed to be a potential candidate for isolating ultra low-k thin films between metal on-chip interconnects in future CMOS technology nodes. The ideal structure of the novel carbon-cage-based materials is described by a model that assumes an ordered network (mosaic structure) with fullerenes (C60) as the nodes and linker molecules along the edges of the mosaic cells. The interior of the network represents a nanopore of a 1-nm scale. According to the molecular design-based model, structures with simple cubic and diamond-like topology of the network are considered promising candidates. A dielectric constant (k value) of 1.7 and an elastic bulk modulus of about 20 GPa are predicted of ideal combinations of network topology and linker molecules. First experimental results, based on electron energy loss spectroscopy, X-ray absorption spectroscopy, nanoindentation, and atomic force microscopy are presented. A more controlled film fabrication process is needed to get more homogeneous thin films with characteristic material parameters as predicted by the model.

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This article deals with uncertainty in the analysis of strain in silicon nanoscale structures and devices using nanobeam electron diffraction (NBED). Specimen and instrument related errors and instabilities and their effects on NBED analysis are addressed using a nanopatterned ultrathin strained silicon layer directly on oxide as a model system. We demonstrate that zero-loss filtering significantly improves the NBED precision by decreasing the diffuse background in the diffraction patterns. To minimize the systematic deviations the acquired data were verified through a reliability test and then calibrated. Furthermore, the effect of strain relaxation by specimen preparation using a FIB is estimated by comparing profiles, which were acquired by analyzing slices of strained structures in a 220-nm-thick region of the sample (invasive preparation) and the entire strained nanostructures, which are embedded in a thicker region of the same sample (noninvasive preparation). Together with the random deviation, the corresponding systematic shift results in a total deviation of ∼1 × 10(-3) for NBED analyses, which is employed to estimate the measurement uncertainty in the thinner sample region. In contrast, the strain in the thick sample region is not affected by the preparation; the systematic shift reduces to a minimum, which improves the total deviation by ∼50%.

Materials: Modeling and First Experiments

The introduction of fragile ultralow-k materials as interlayer dielectrics in backend-of-line interconnect stacks asks for a thorough analysis of potential risks due to chip-package interaction. This paper shows how the application of several ex-situ and in-situ experimental approaches can be effectively used to assess such risks on the wafer level already at early stages of the development phase. The respective analytical techniques try to mimic chip-package interaction loading conditions. Most of the tests transfer loads to interconnect stacks via individual copper pillars. The investigations take place on the scale of about 100μm down to 1μm.

Improving accuracy and precision of strain analysis by energy-filtered nanobeam electron diffraction.

The stress levels induced by chip‐package interaction (CPI) impose an increased risk of mechanical failure on advanced backend‐of‐line (BEOL) layer stacks in microelectronic circuits if they contain fragile ultralow‐k (ULK) interlayer dielectric (ILD) films. On the one hand, multilevel finite element modeling is used to assess the potential risk at an early stage of the development of new microelectronic products. On the other hand, the theoretical models need as accurate as possible materials parameters as an input to provide realistic results. Moreover, it is highly desirable to have multi‐scale experimental probes available which can provide complementary data to support the modeling calculations. The present paper provides an overview about various mechanical probing techniques which operate on the scale of less than 100 nm up to more than 100 μm. In this way, typical feature sizes are covered which occur from the package level via solder bumps or copper pillars down to small Cu/ULK interconnect struc...

Experimental analyses of the mechanical reliability of advanced BEOL/fBEOL stacks regarding CPI loading

Integration of compliant and brittle ultralow-k (ULK) interlayer dielectric (ILD) materials in advanced backend-of-line (BEOL) layer stacks requires a careful characterization of the mechanical stability of the BEOL stack to assure reliability during chip packaging and under field condition. We present a novel experimental technique which applies normal and shear forces on Cu pillars to test the stability of BEOL layer stacks beneath individual pillars. Critical forces and displacements are recorded with high sensitivity. The test directly verifies if the BEOL withstands the applied stress levels or if mechanical failure occurs.