Detailed Analysis Techniques

  • Main Analytical Techniques

    Optical microscopy

    • Part identification, package and die markings, die photograph
    • Layer-by-layer layout analysis,
    • Diffusion layout with copper staining,
    • Stereo microscopy applied in package analysis,
    • Cross-sectional stained diffusion analysis with application in well structure.

    X-ray

    • X-ray imaging: Encapsulated die analysis
    • X-ray diffractometry (XRD): Analysis of thin film grain structure and orientation, crystallography, heterostructures, etc.

    Energy Dispersive X-Ray Spectroscopy (EDS) for material identification, especially metals and silicides. This technique is used in conjunction with electron microscopy (SEM or TEM). The spatial resolution is approximately 1 μm2 for SEM prepared samples and down to 10 nm2 for TEM prepared samples. It identifies elements with a relative concentration of 0.1% or higher. Sensitivity is greater for heavier elements. Wavelength Dispersive X-ray Spectroscopy (WDS) is similar to EDS (analysis by wavelength rather than energy) but allows approximately ten times greater sensitivity.

    Electron microscopy

    • SEM (FESEM) cross-sectional analysis. The most used technique in the structural analysis of the semiconductor devices (both FEOL and BEOL) and critical design measurements. Staining allows the identification of the diffused region (diffusion staining) and different dielectric layers (Glass staining). Magnification is limited to approximately 100,000 X.
    • SEM topographical analysis. A complementary technique to the optical investigation. Critical levels in processes below 180nm need SEM investigation since the features are too small for optical microscopy. Layer-by layer de-layering or bevel polishing may be used for sample preparation.
    • TEM cross-sectional microscopy. Better resolution and magnification than SEM (up to 106X). This technique must be used for thin film measurements of a few atomic layers (gate oxide, capacitor dielectrics) and grain analysis (poly structure for instance). Plan view samples can be prepared, giving useful views of DRAM capacitors and Flash floating gates. Diffraction images, tilted lattice images and other TEM equipment (EELS, EDS/WDS, etc.) may offer additional tools for the structural analysis. Our advances in sample prep automation have made TEM more affordable as a mainstream analysis technique for sub 50nm process nodes.

    Spreading Resistance Profiling (SRP) Spreading Resistance Profiling is a technique commonly used to examine semiconductor doping levels. Mathematical modeling of the spreading resistance data extracts the carrier concentration in the semiconductor. The SRP probes scan in only one direction so the result is essentially one dimensional - concentration versus depth. May be imprecise close to the surface (source/drain diffusion influence). 

    UBM TechInsights has traditionally used SRP analysis to determine the carrier concentration and depth of wells in devices. SRP is limited to structures greater than 20 μm wide by 100 μm long. This limitation becomes critical in advanced logic parts.

    Secondary Ion Mass Spectroscopy (SIMS) counts the atoms sputtered from the surface of a device. SIMS is useful for characterizing the presence or concentration (using standards) of elements as light as helium. Depending on the element to be characterized, the preparation of the sample, and the quality of the available standard, SIMS can accurately detect the concentration of particular elements down to the ppm range. SIMS typically requires areas on the order of 100 μm by 100 μm with specific topography in order to acquire good data. This is a major drawback for semiconductor doping characterization (for instance for poly doping or channel doping we need a wide (minimum of 50 x50 μm2) MOS capacitor that is typically not available on sub-micron parts.

    • TOF SIMS is a new technique, in development that permits SIMS analysis on analytical areas as small as 2 μm2 in some samples. Major drawback is the lack of standards for quantitative measurements so that mainly qualitative measurements (element identification) are presently available.
    • The use of a Ga primary beam also allows greatly reduced sputtering area requirements. This technique is also in development with areas as small as 15 x 15 μm2 analyzed.
    • A third technique is under development to allow SIMS analysis of beveled sections in order to ease the requirements of traditional SIMS with regards to topography of the sample.

    Typically, UBM TechInsights uses SIMS either to analyze the intermetal dielectrics of devices or to investigate the concentration of dopant atoms in the semiconductor substrate. The analysis of electrically active substrate dopants in areas too small for SIMS can often be accomplished by Scanning Capacitance Microscopy.

    Electrical probing. DC I-V characteristics of transistors including transfer and output characteristics and measurement of electrical parameters (threshold voltage, transconductance, breakdown voltage, etc.). It is also possible to measure the sheet resistance of thin metal or polysilicon film resistors.

    Special purpose techniques:

    Electron Energy Loss Spectroscopy (EELS) is a type of filter applied to the TEM beam to identify materials based on their absorption of electrons. It can be used to create two-dimensional color maps of the various elements present in a device structure. It is especially useful for identifying TiN which cannot be performed by TEM/EDS due to the overlapping x-ray energies of the two elements. It is also used as a complementary technique to EDS to effectively identify lighter elements.

    Fourier Transform Infrared Spectroscopy (FTIR), micro-FTIR and Raman spectroscopy are employed for detailed compositional analysis and are especially useful for identifying polymers and atomic bonding information.

    Scanned Probe Microscopy (SPM). Several techniques fall under this category. All of these start with the basic technique known as Atomic Force Microscopy (AFM). AFM detects topographical changes in a sample down to the sub-nanometer with nanometer-scale lateral resolution. The use of a conductive probe allows the capability of the technique to be extended to two-dimensional carrier profiling in semiconductors with similar spatial resolution to AFM. This may be done with either Scanning Spreading Resistance Microscopy (SSRM) or Scanning Capacitance Microscopy (SCM) although the latter is preferred for the reverse engineering of microelectronic devices.

    SCM allows accurate determination of source/drain junction depth as well as the shape and extent of very small doped regions such as source/drain extensions. The data may be calibrated using a standard with known doping to allow accurate (well within one order of magnitude) carrier profiling.

    Auger Electron Spectroscopy (AES). Good for light elements, complementary to the EDS technique. Sensitive to approximately 0.1 % concentration. This is a very surface sensitive materials analysis technique providing data less influenced by material surrounding the region of interest.

    X-ray Diffraction (XRD) is used to identify the orientation of crystal planes. It may be used to determine the preferred orientation of planes in polycrystalline structures (e.g. polysilicon and aluminum grains).

    Process/Device Simulation is used to present a complete graphical representation of the process steps used in manufacture. It requires data from other sources such as SIMS or SCM which is then used in standard semiconductor physics equations to simulate each process in two dimensions. Used in conjunction with the standard analytical techniques coupled with dc transistor characteristics obtained from electrical probing, the simulation can create a very accurate picture of the device structure and process steps used to create it. It can be very useful to show the location of the regions of the device (e.g. source, drain and channel) for various bias conditions, which would be difficult or impossible to analyze physically.