produced the first commercial used form of SPM,many other instrument in 1965.A number of SPM techniques have been improvements have occurred since developed which provide informa- this time,resulting in an increase tion on differences in friction, in resolution from 50nm in 1942 adhesion,elasticity,hardness, to-0.7nm today.Besides the electric fields,magnetic fields, development of morphological carrier concentration,temperature imaging,the SEM has been distribution,spreading resistance, developed to detect signals which and conductivity. are used to determine composi- tional information,such as X-rays, backscattered electrons, Imaging Mechanisms cathodoluminesce,Auger elec- trons,and specimen current. Scanning Electron Microscopy ×300 25KV 100UE The operation of the SEM The development of the AFM was consists of applying a voltage preceded by the development of between a conductive sample and Figure 3.SEM image of an integrated single crystal the Scanning Tunneling Micro- filament,resulting in electron silicon cantilever and tip which has an end radius of 2 scope(STM)in 1981 at IBM emission from the filament to the to 10nm.Tips for AFM are typically made of silicon or Zurich Research Laboratory by silicon nitride.Bar=100um. sample.This occurs in a vacuum Binnig and Rohrer(4).Its ability environment ranging from 10to to view the atomic lattice of a 10-10 Torr.The electrons are sample surface earned the inven- guided to the sample by a series of tors the Nobel Prize in Physics in electromagnetic lenses in the 1986.Although the STM pro- electron column.A schematic of a vides subangstrom resolution in all typical SEM is shown in Figure 2. three dimensions,it is limited to The resolution and depth of field conductive and semiconductive of the image are determined by samples.To image insulators as the beam current and the final well as conductors,the Atomic spot size,which are adjusted with Force Microscope(AFM)was one or more condenser lenses and developed in 1986(5),and the the final,probe-forming objective first commercial AFMs were lenses.The lenses are also used to produced in 1989 by Digital shape the beam to minimize the Instruments effects of spherical aberration, chromatic aberration,diffraction, AFM provides three-dimensional and astigmatism. surface topography at nanometer lateral and subangstrom vertical The electrons interact with the Figure 4:TappingMode AFM image of 1.4A resolution on insulators and sample within a few nanometers monoatomic steps on epitaxial silicon deposited on (100)Si.1um scan. conductors.From this beginning, to several microns of the surface, the field of Scanning Probe depending on beam parameters Microscopy(SPM)was born and sample type.Electrons are which consists of a family of emitted from the sample primarily techniques that involves scanning a as either backscattered electrons or sharp tip across the sample surface secondary electrons.Secondary while monitoring the tip-sample electrons are the most common interaction to form a high resolu- signal used for investigations of tion image.Although the AFM surface morphology.They are has become the most commonly produced as a result of interac- 22 produced the first commercial instrument in 1965. A number of improvements have occurred since this time, resulting in an increase in resolution from 50nm in 1942 to ~0.7nm today. Besides the development of morphological imaging, the SEM has been developed to detect signals which are used to determine composi￾tional information, such as X-rays, backscattered electrons, cathodoluminesce, Auger elec￾trons, and specimen current. The development of the AFM was preceded by the development of the Scanning Tunneling Micro￾scope (STM) in 1981 at IBM Zurich Research Laboratory by Binnig and Rohrer (4). Its ability to view the atomic lattice of a sample surface earned the inven￾tors the Nobel Prize in Physics in 1986. Although the STM pro￾vides subangstrom resolution in all three dimensions, it is limited to conductive and semiconductive samples. To image insulators as well as conductors, the Atomic Force Microscope (AFM) was developed in 1986 (5), and the first commercial AFMs were produced in 1989 by Digital Instruments. AFM provides three-dimensional surface topography at nanometer lateral and subangstrom vertical resolution on insulators and conductors. From this beginning, the field of Scanning Probe Microscopy (SPM) was born which consists of a family of techniques that involves scanning a sharp tip across the sample surface while monitoring the tip-sample interaction to form a high resolu￾tion image. Although the AFM has become the most commonly used form of SPM, many other SPM techniques have been developed which provide informa￾tion on differences in friction, adhesion, elasticity, hardness, electric fields, magnetic fields, carrier concentration, temperature distribution, spreading resistance, and conductivity. Imaging Mechanisms Scanning Electron Microscopy The operation of the SEM consists of applying a voltage between a conductive sample and filament, resulting in electron emission from the filament to the sample. This occurs in a vacuum environment ranging from 10-4 to 10-10 Torr. The electrons are guided to the sample by a series of electromagnetic lenses in the electron column. A schematic of a typical SEM is shown in Figure 2. The resolution and depth of field of the image are determined by the beam current and the final spot size, which are adjusted with one or more condenser lenses and the final, probe-forming objective lenses. The lenses are also used to shape the beam to minimize the effects of spherical aberration, chromatic aberration, diffraction, and astigmatism. The electrons interact with the sample within a few nanometers to several microns of the surface, depending on beam parameters and sample type. Electrons are emitted from the sample primarily as either backscattered electrons or secondary electrons. Secondary electrons are the most common signal used for investigations of surface morphology. They are produced as a result of interac￾Figure 3. SEM image of an integrated single crystal silicon cantilever and tip which has an end radius of 2 to 10nm. Tips for AFM are typically made of silicon or silicon nitride. Bar=100µm. Figure 4: TappingMode AFM image of 1.4Å monoatomic steps on epitaxial silicon deposited on (100) Si. 1µm scan