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Scanning Probe Microscopy (SPM) scans a sample using a probe placed close to the sample’s surface. It can be conducted in the atmosphere and is able to show a sample’s surface topography with an atomic-level resolution. |
Scanning Tunneling Microscopy (STM) was developed as early as 1981. It was suitable for use on conductive materials. It wasn’t until 1986 that Atomic Force Microscopy (AFM), which could be used to measure both conductive and non-conductive materials, was developed. Subsequently, AFM became the basis for the development of a whole series of new technologies, including Scanning Capacitance Microscopy (SCM), Magnetic Force Microscopy (MFM), Kelvin Probe Force Microscopy (KPFM), Quantitative Nanomechanical Microscopy (QNM) and more. Essentially, the idea is to use a combination of special probes and different sensors to measure a range of functions, such as mechanical properties, magnetic properties, electrical properties, and thermal properties.
SPM can be used in the IC industry (for the analysis of silicon, silicon carbide substrates, non-metal/metal thin films, HEMT structures, and III-V semiconductors, etc.), the photoelectric industry (for the analysis of sapphire substrates, LED/LD chips, ITO films, optical communication components, and CMOS image sensors), the packaging industry (for the analysis of PI, solder balls, Gate Pad craters, and copper foil, etc.) and beyond.
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Surface Roughness and Topography｜Atomic Force Microscopy, AFM |
AFM can be used to measure the surface roughness and shape of a sample. It uses probes of only nanometers in size to scan the surfaces of samples based on the attraction and repulsion caused by the Van der Waals forces between atoms. This is coupled with use of the cantilever as the reflection interface for the laser light. By recording the offset values of the laser when the probe is attracted or repelled by the surface reveals the surface topography of the sample.
Figure 1 (left) shows the surface roughness of the GaN film layer of an HEMT component, where the result was Z Range: 28.1 nm; Ra: 1.23 nm. Figure 1 (right) is a micro lens cross section analysis of a CMOS image sensor (CIS). The light collection of the CIS is usually affected by the uniformity, quality and thickness of the micro lens.
 Figure 1. GaN Film Surface Roughness (Left); Micro Lens Cross Section Analysis (Right) |
▻ (Click here for a more detailed explanation of AFM)
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Doping Distribution｜Scanning Capacitance Microscopy (SCM) |
If you want to know the N/P doping distribution of a component and measure the dimensions of these areas (such as doping thickness, channel length, trench doping depth, Source/Drain size, N/P well interface and other information), you can do so by using SCM to obtain two-dimensional doping images. This can enable you to distinguish between N-type and P-type regions, identify faults caused by abnormal doping distributions and even perform reverse engineering analysis.
SCM analysis technology can make up for the deficiencies of other analysis technologies. For example, the Spreading Resistance Probe (SRP) can only present one-dimensional distributions. There is also the difficulty with precise etching rate control that occurs when using the Scanning Electron Microscope (SEM) in combination with chemical etching and stain analysis.
SCM places a metal probe against the sample’s surface to form a tiny MOS structure. During analysis, an AC voltage (equal to the gate voltage of the MOS) is applied to the metal-coated probe, causing the accumulation or depletion of carriers and producing capacitance changes. The dC/dV signal measured is converted into a two-dimensional doping profile. This allows N-type and P-type regions and their interfaces to be distinguished. As such, this is used mainly to measure the doping distribution of samples.
SCM‘s doping concentration detection range is E14~E20 atom/cm3, and its planar resolution can reach 50nm. It can be applied to IC components (power electronic components, GBT/FRD components, triodes, laser diodes, DRAM components, and MOSFETs) and optoelectronic industry applications (CMOS Image Sensors, VCSELs, optical communication components, LEDs). Figure 2 shows the location of the electrical bright spot in a defective SiC triode device. Comparing the bright spots in the SEM images of good and defective products showed that the doping distribution in defective products differed significantly from that of good products.
 Figure 2. Failure Analysis of Defective SiC Triode Device |
▻(Click here for a more detailed explanation of SCM)
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Magnetic Distribution｜Magnetic Force Microscopy (MFM) |
The distribution of magnetic domains on the surface of magnetic materials containing iron, cobalt, and nickel, etc. can be determined via MFM scanning. The principle behind MFM is similar to that of AFM. The difference lies mainly in the use of magnetic probes. Magnetic material analysis is conducted using the Life Mode. MFM can simultaneously collect information on surface topography and magnetic signals through the detection of magnetic force changes on the surface of the sample. This enables it to show the distribution of magnetic domains. Both frequency and phase changes can be imaged using the amplitude of the magnetic interaction between the probe and the sample. This is tool is suitable for use on magnetic thin films, magnetic storage devices and magnetic recording assemblies.
Figure 3 shows the magnetic domain and intensity images of a magnetic tape (left) and hard disk (right). Different magnetic recording methods and densities can be understood through the MFM results. In contrast to other magnetic imaging techniques, MFM does not require special sample preparation, does not destroy the sample, and can have a high resolution even when performed in the atmosphere.
 Figure 3. Magnetic Distribution of Magnetic Tape (Left) and a Hard Disk (Right) [1] |
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Potential Energy Distribution｜Scanning Kelvin Probe Microscopy (SKPM) |
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The surface potential, work function, film uniformity, and coverage of conductors/semiconductors can all be measured via KPFM, also known as SKPM. KPFM is a type of Electrostatic Force Microscopy (EFM) technique. The principle involves vibrating the probe cantilever using an AC voltage while simultaneously applying a DC bias to compensate for the difference in potential between the sample and the cantilever, making the cantilever amplitude equal to zero. By detecting the voltage to be compensated, the distribution of surface potential can be obtained.
Using the Kelvin method to measure the difference in potential (potential energy) between the probe and the sample surface with a high surface resolution (nanoscale) is a type of quantitative measurement. It can be applied to dielectric layer analysis, metal contamination analysis, tin-lead soldering, corrosion observation, graphene analysis and more. Figure 4 shows the surface morphology and potential energy distribution of three different materials (Al, Si, and Au). |
 Figure 4. Surface Morphology and Potential Energy Distribution of Al/Si/Au |
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Mechanical Analysis｜Quantitative Nanomechanical Microscopy (QNM) |
QNM can be used to measure quantified nanomechanical properties while simultaneously obtaining the distribution of surface topography, mechanical properties and mechanical measurements. Quantified mechanical properties (elastic modules, adhesion between probes and samples, energy dissipation and maximum strain) are derived from the force-distance curves for maximum attractive force, repulsive slope, and the integral area of the curve described by the round-trip scanning of the probe. This data can be obtained through numerical analysis conducted using the Derjaguin-Muller-Toporov (DMT) model.
QNM allows for precise control of the imaging force so that non-destructive, high-resolution images can be obtained. It can handle from 1 kPa to 100 GPa moduli and 10 pN to 10μN adhesion for various samples. It can be applied to polymer materials, tungsten carbide steel, stainless steel and metal materials, etc. Figure 5 is a QNM analysis result of polymer materials, displaying adhesion, dissipation, Young’s Modulus, and deformation.
 Figure 5. Mechanical Analysis of Polymer Materials |
MA-tek provides SPM sample surface topography and roughness measurement and SCM failure analysis for the IC, optoelectronic and other industries, as well as reverse engineering. New technologies have also brought us MFM, KPFM and QNM, which can obtain localized, high spatial resolution (nanometer scale) information on samples. All this and more make us the industry’s top choice inＲ&D partners!
