Electrical Atomic Force Microscopy for Nanoelectronics

The invention of scanning tunneling microscopy (STM), rapidly followed by atomic force microscopy (AFM), occurred at the time when extensive research on sub-µm metal oxide field-effect transistors (MOSFET) was beginning. Apparently uncorrelated, these events have positively influenced one another. In fact, ultra-scaled semiconductor devices required nanometer control of the surface quality, and the newborn microscopy techniques provided unprecedented sensing capability at the atomic scale. This alliance opened new horizons for materials characterization and continues to this day, with AFM representing one of the most popular analysis techniques in nanoelectronics. This book discusses how the introduction of new devices benefited from AFM, while driving the analysis and sensing capabilities in novel directions. Here, the goal is to introduce the major electrical AFM methods, going through the journey that has seen our life changed by the advent of ubiquitous nanoelectronics devices, and has extended our capability to sense matter on a scale previously inaccessible.

Conductive atomic force microscopy has become a valuable tool for investigation of electronic transport properties with utmost lateral resolution. In this chapter, we prevent an overview about C-AFM applications to high-k semiconductors, which are key materials for future energy-efficient information technology.

Probing the distribution of charge carriers in semiconductor device structures is of crucial importance to better understand semiconductor fabrication processes and how they affect the incorporation, diffusion and activation of dopants and hence the final device performance. Scanning spreading resistance microscopy (SSRM) has emerged as the most valuable technique for 2D and 3D carrier mapping in semiconductor device structures due to its excellent spatial resolution, sensitivity and ease of quantification. The present chapter first introduces the principles of the technique, thereby discussing the underlying physical mechanisms such as the nanometer-size probe-semiconductor contact. Faced with the stringent requirements imposed by advanced 3D device architectures, novel approaches and concepts such as 3D carrier profiling and fast Fourier transform-SSRM (FFT-SSRM) have been developed in the recent years. These methods aid in extending conventional SSRM toward quantitative carrier profiling in aggressively scaled 3D device structures which is illustrated on the example of selected relevant applications such as FinFETs and nanowire-based transistors.

As the semiconductor technology matures from research to development and eventually entering manufacturing, there is a consistent focus on reducing defects and yield detractors. This results in engineers utilizing the Failure Mode and Effects Analysis (FMEA) duplicate of integrated circuits. In failure analysis (FA) of integrated circuits, Scanning Capacitance Microscopy (SCM) has been used to identify failure mechanisms, such as regions of incorrect doping and electrical shorts, thereby indicating the appropriate corrective actions required to remedy the device. Because sample preparation and data interpretation are relatively straightforward, FA applications of SCM can be performed with quick turnaround and with few ambiguities that can arise in quantitative applications. In this chapter, we will focus on SCM applications, highlighting work performed at the state-of-the-art chip manufacturing facility of GLOBALFOUNDRIES.

The strength of scanning probe lithography (SPL) lies in the operation at ambient conditions, sub-10 nm resolution capabilities, the in situ non-destructive inspection of the fabricated structures, the nanometric accuracy in positioning, the versatility in modifying any kind of materials, and the freedom in the patterning geometries. On the other hand, the tip size and lifetime-related issues hinder the achievable throughput, and a precise niche of application has yet to be determined for its implementation in technological applications. The complementarity of the high-resolution and precise positioning patterning by SPL and the high throughput and low-resolution patterning by other well-established lithographies (optical, electron beam, nanoimprint) can be achieved by the development of mix-and-match lithography strategies.

Atomic Force Microscopy (AFM) arises as an all-in-one characterization technique, capable of measuring several physical quantities by slight equipment’s modifications. In particular, for piezo and ferroelectricity properties, the AFM overcame the limitations of macroscopic techniques. This chapter covers all the aspects of piezo and ferroelectricity measurements performed with an AFM. The chapter is divided in three main parts, one for each available technique: Piezoresponse Force Microscopy (PFM), Nano-PUND method and Direct Piezoelectric Force Microscopy (DPFM). While PFM method is based in the converse piezoelectric effect, nanoPUND measures polarization charges and DPFM measures the direct piezoelectric effect. The working principle and characteristics for each AFM mode is fully exploited and explained from entry level to more advanced users. The chapter also focuses in useful guidelines and practical hands-on explanation for maximizing the image quality and data acquisition. Finally, a set of different application based in the use of piezo and ferroelectric materials is depicted, in which the AFM characterization took an important role as the primary characterization technique.

Resistive switching (RS), the property of reversible changes in electrical resistance of a metal/insulator/metal cell upon electrical stimulation, has been widely studied in the last few decades for non-volatile memories and, more recently, for logic, alternative computation and sensor purposes. Atomic force microscopy (AFM) has been widely used to characterize switching behaviors and understand their underpinning mechanisms due to its unique capability and versatility for highly localized in situ and ex situ studies. The present chapter provides a brief introduction to the physics of RS and AFM schemes used to study RS, followed by an overview of recent research on RS performed by means of AFM. A particular emphasis is given to innovative AFM techniques and AFM-based studies of significant scientific contribution to the field of RS in the last few decades.

By coating a tip of a non-contacting scanning probe with a magnetic material, scanning probe microscopy can become sensitive to a stray field from the surface of magnetic materials and devices, magnetic force microscopy. The behaviour of such magnetic samples is well-known to be controlled by the formation and reversal of magnetic domains, each of which has a uniform magnetic moment separated by a region with moment rotation, a magnetic domain wall, to minimise total energy. The formation of the magnetic domains and walls is dependent upon size changes even at an atomic scale, which defines a critical length scale in much more strict manner than a semiconductor and metallic sample. It is therefore important to image magnetic domain structures of the magnetic samples precisely to reveal the corresponding performance. Magnetic force microscopy is one of the most convenient techniques for magnetic imaging with nanometric resolution as detailed in this chapter.

Fine description of the electrical properties of solids at their surfaces is a very old problem, difficult to tackle because the surface of a solid itself represents a break in the periodic structure of crystallized materials, hence a defect, and most importantly because of the potential impact of surface oxidation, contamination, humidity, atmosphere, etc., on the material response (Galembeck et al. in Polymer 42:4845, 2001 [1]). For dielectrics, electrical charging of the surface leads to the build-up of a surface potential. The occurring mechanisms depend on the kind of charges being deposited, e.g. by triboelectrification, and are particularly difficult to anticipate (Lacks and Sankaran in J Phys D Appl Phys 44:453001, 2001 [2], Shinbrot et al. in Phys Rev E 96:032912, 2017 [3]). Aside these difficulties in defining the surface properties, nanosciences and nanomaterials have brought us new paradigms with the tremendous increase of the amount of interfaces between particles and host matrix, and with the variety in the material nature and interface linked to the different elaboration processes. In a way it may constitute a chance to better describe what interfaces on an electronic properties standpoint are, because materials are better controlled. Besides the nanostructuration of materials, the miniaturization of devices is a further challenge to face. When dealing with thin layers (thicknesses of less than 100 nm) the rules for bulk properties behavior are broken. Obviously, in both cases the experimental approach is more demanding, since the tools that are implemented for the study must have a spatial resolution compatible with the scale at which phenomena should be probed. In this Chapter we illustrate on a few examples the need for ever lower scale characterization of the electrical properties of dielectric materials.

Two-dimensional materials (2DM), such as the semimetal graphene, semiconducting MoS2 and insulating h-BN, are currently the object of wide interests for next generation electronic applications. Despite recent progresses in large area synthesis of 2DMs, their electronic properties are still affected by nano- or micro-scale defects/inhomogeneities related to the specific growth process. Electrical scanning probe methods, such as conductive atomic force microscopy (C-AFM), are essential tools to investigate charge transport phenomena in 2DMs with nanoscale resolution. This chapter illustrates some case studies of C-AFM applications to graphene, MoS2 and h-BN. Furthermore, the results of the nanoscale electrical characterization have been correlated to the behavior of macroscopic devices fabricated on these materials.

The superior properties of diamond being the hardest, best thermally conductive, high chemical inert and low friction material makes it very attractive for use as a tip material in scanning probe microscopy (SPM). The commercial availability of micromachined Si probes at the beginning of the 1990s triggered soon the interest and need for different tip coatings such as diamond which was first wanted for increasing the tip lifetime. Although first reports on diamond growth from the wafer phase were first reported in the 1980s, it took until the early 1990s before first applications using diamond grown by chemical vapor deposition (CVD) appeared on the market. Therefore, the development of fabrication processes for diamond tips, especially for electrically conductive ones, required also substantial efforts on the development of the diamond coating knowhow itself. As commercial probe companies considered diamond probes as specialty probes with a small market size in the early days, it explains well why most diamond tip innovations were established by universities and research centers.

Scanning Microwave Impedance Microscopy (sMIM) is a sensitive electrical measurement technique which can characterize local static and temporal variations of electrical permittivity, and conductivity of materials and devices as well as for failure analysis. It is being used to characterize dielectrics, semiconductors and their doping response, and metals. Measurements can be made at room temperature down to cryogenic temperatures where quantum effects become important. Leveraging near-field electrical interactions between a probe and the sample, sMIM can measure and image electrical properties and operation at the nanoscale to micron scale by incorporation into an atomic force microscope. sMIM is being applied to a wide range of industrial and scientific applications to improve fundamental and functional understanding and operational performance of advanced, exploratory and quantum electronic devices and materials and their fabrication.