Reduction of Latent Defects in Semiconductor Films

Nanoindenters are precise, adaptable, and user-friendly tools for performing nanoscale mechanical testing on various films and surfaces.

Nanoindentation systems with electromagnetic actuation achieve a wide dynamic range of force and displacement. They allow users to measure Young’s modulus and hardness following ISO 14577 standards and deformation across six orders of magnitude, from nanometers to millimeters.

Here, KLA Instruments introduces the Nano Indenter® G200X Semi Pack, a versatile tool for materials characterization for semiconductor and compound semiconductor device fabrication.

Film adhesion failure and brittleness are influenced by numerous external forces. The G200X Semi Pack characterizes adhesion failure (top) and brittleness failure (bottom) through measurements of various nanomechanical properties. Results can be used to optimize semiconductor and compound semiconductor film processes

Figure 1. Film adhesion failure and brittleness are influenced by numerous external forces. The G200X Semi Pack characterizes adhesion failure (top) and brittleness failure (bottom) through measurements of various nanomechanical properties. Results can be used to optimize semiconductor and compound semiconductor film processes. Image Credit: KLA Instruments

Semiconductor and compound semiconductor processing can cause subcritical faults that manifest themselves long after production, generally as field reliability difficulties.

These costly latent defects could be caused by microcrack propagation, mismatched crystallography, or different thermal expansion coefficients between adjacent materials.

Although inspection equipment identifies existing problems at the time of inspection, it cannot predict whether future defects will emerge during manufacturing or while the devices are in use.

The G200X Semi Pack is a high-performance hardware and software bundle optimized for semiconductor and compound semiconductor applications.

The Semi Pack includes the most well-known methods for nanomechanically evaluating films, surfaces, and interfaces to eliminate latent defects such as adhesion and brittleness.

This additional knowledge can be leveraged to construct an engineering feedback loop, resulting in stronger material systems and higher device yield and reliability.

Adhesion Failure

Adhesion failure, as seen in Figure 1 (top), happens when external forces produce stress concentration at the interface, resulting in a debonding event. External forces such as point loads, heat activity, and process handling are the principal causes of stress concentration at interfaces where different materials meet.

The mismatch in crystallography prevents the material from moving in synchrony, resulting in separation—a debonding adhesion failure.

Material systems that do not fail due to debonded blistering require additional test procedures for indirect adhesion measurement, such as Thin Film Scratch measurement. The G200X Semi Pack detects material and system parameters that cause adhesion failures, resulting in greater yields and dependability.

Brittleness

The brittleness of a material refers to the start and propagation of cracks within the material system. Brittle failures can occur due to the dispersion of existing defects in the material or the nucleation of new flaws.

Mismatched thermal expansion coefficients, electrical piezo forces, mechanical loads, and/or film tensions are common stressors that cause brittle failures in semiconductor material systems.

To avoid brittle failures, it is recommended that users define a stress safety margin that minimizes defect dispersion while optimizing material strength. The G200X Semi Pack monitors material and system parameters that contribute to brittle failures, driving greater yields and dependability.

The G200X Semi-Pack

The G200X Semi Pack consists of the following hardware and software components:

  • Four-point wafer tilt chuck (either 100 mm + 150 mm or 150 mm + 200 mm size)
  • Enhanced measurement algorithms:
    • AccuFilm Ultra Method Pack for fast precision measurement of elastic modulus and hardness
    • Adhesion Method Pack
    • Fracture Toughness Method Pack
    • Thin Film Scratch Method Pack
  • Analytical Scanning Probe Microscopy (SPM)
  • Automated measurement routines:
    • Test
    • Image capture
    • Survey scan

Wafer Tilt Chuck

How to Reduce Latent Defects in Semiconductor Films

Image Credit: KLA Instruments

Alignments are crucial for performing wedge tip adhesion analysis or wedge tip scratch testing, and the four-point wafer tilt chuck makes these alignments possible. Wedge tip geometries are suitable for creating flat strain conditions during indentation, simplifying failure analysis.

In these tests, the line edge of the wedge tip must be parallel to the wafer surface so that stress concentration at the wedge’s corners does not cause failure events that contradict 2D adhesion model predictions.

After exchanging the tip, the 4-point wafer tilt chuck is adjusted and secured in place to allow for further testing. It comes in two sizes: small (100 mm + 150 mm) and large (150 mm + 200 mm).

AccuFilm Ultra Method Pack

Film delamination and cracking are caused by poor mechanical strength and/or poor flexibility. KLA Instruments AccuFilm technology is widely used to optimize thin-film processes, and AccuFilm Ultra provides the highest sensitivity for evaluating film elasticity and strength by measuring the Elastic Modulus E and Hardness H.

The H/E ratio assesses the primary material deformation mechanisms before fracture. The AccuFilm Ultra Method Pack also reduces substrate interference, ensuring measurement results accurately reflect film qualities.

AccuFilm Ultra’s sensitivity minimizes result scatter by more than 55%, allowing the identification of even extremely minute process modifications.

AccuFilm Ultra elastic modulus results (green) for a low-k film are not influenced by the material properties of the substrate (shown in red, for comparison). Very low measurement scatter delivers sensitivity to very small process changes

Figure 2. AccuFilm Ultra elastic modulus results (green) for a low-k film are not influenced by the material properties of the substrate (shown in red, for comparison). Very low measurement scatter delivers sensitivity to very small process changes. Image Credit: KLA Instruments

Adhesion Method Pack

Adhesion can be measured directly or indirectly. Some material systems fail in a way that enables the direct measurement of adhesion energy (J/m2).

The G200X accomplishes this by inserting a conical or wedge-shaped diamond tip into the top surface layer, causing enough stress at the film interface to trigger a debonding event under controlled test settings. The debonded blister area is measured, and the energy needed to propagate the adhesion failure is computed.

Material factors like elastic modulus and hardness, as well as system properties like bonding energy, film thickness, residual stress, and fault distribution, all influence whether this form of blister failure occurs under indentation load.

Delamination “flower” caused by indentation with a conical-spherical tip geometry

Figure 3. Delamination “flower” caused by indentation with a conical-spherical tip geometry. Image Credit: KLA Instruments

Fracture Toughness Method Pack

Once cracking failure has occurred, fracture toughness measures the energy required to propagate one of these cracks. Fracture toughness numbers reported in the literature are frequently based on bulk, polycrystalline material data.1

Moving to single crystal or epitaxial layers eliminates the usual science of toughening materials (e.g., grain boundaries, interface engineering), resulting in more brittle materials that require further testing.

KLA Instrument's nanoindenters enable the exact application of mechanical forces capable of initiating and propagating cracks in substrates and epitaxial layers. Multiple metrics, including quantitative fracture toughness, crack initiation load, and film spallation load, can be used to describe crack growth resistance.

Numerous indenter geometries are offered for researching cracking in specialized applications. Using Semi Pack hardware SPM with nano-positioning stages delivers improved accuracy and sensitivity of crack length measurements versus visual approaches for quantifying fracture toughness.

Thin Film Scratch Method Pack

Indirect adhesion evaluation can be performed utilizing specialized Thin Film Scratch analysis, in which the scratch critical load records the start of cracking failures under dynamic loading.

During the Thin Film Scratch test, a pointed or wedge-shaped diamond tip is utilized to dynamically scratch the film stack as it passes through the layers. As the scratch moves through the layers, it creates immense compressive tension in front of the tip.

This tremendous compressive stress causes interface failures and can scoop the film, separating it from the underlying layers.

The loads at which each layer is scooped off are again determined by material parameters like elastic modulus and hardness and system properties like bonding energy, film thickness, residual stress, and fault distribution.

Indentation fracture in a low-k thin film on a silicon substrate

Figure 4. Indentation fracture in a low-k thin film on a silicon substrate. Image Credit: KLA Instruments

Scratch test analysis on 617 nm low-k thin film showing cohesive brittle failure and film spallation

 Figure 5. Scratch test analysis on 617 nm low-k thin film showing cohesive brittle failure and film spallation. Image Credit: KLA Instruments

Survey Scanning: Analytical SPM

Survey Scanning uses the Nano Indenter G200X’s precise, repeatable X/Y motion mechanism and 10 nm linear encoders to perform SPM evaluations of residual surface damage. Survey scanning is particularly useful for assessing blister area, crack lengths, and residual scratch damage.

Survey Scan of residual surface damage caused by Thin Film Scratch Test analysis

Figure 6. Survey Scan of residual surface damage caused by Thin Film Scratch Test analysis. Image Credit: KLA Instruments

Automated Measurement Routines

The G200X Semi Pack automates routines, allowing users to easily acquire the information required for analyzing material systems.

Automatic transitions from indentation and scratch testing to automatic capturing of microscope images and scanned surfaces of residual damage are easily commanded during batch setup so that they are performed in series without additional user interaction.

Application Use Cases

The G200X Semi Pack measurement capabilities can be used for measurement and characterization throughout the semiconductor and/or compound semiconductor production process, such as:

  • Compound semiconductor material systems
  • Display films
  • Epitaxial layers
  • Formulation
  • GaN cracking
  • Lamellar layer brittleness
  • Low-k thin films
  • Metallization layers
  • Process optimization
  • Semiconductor material systems
  • Silicon carbide brittleness

Summary

The Nano Indenter G200X Semi Pack consists of analytical solutions specifically designed for the characterization of semiconductor and compound semiconductor materials.

As external influences and uncertain material qualities are likely to induce latent flaws later in the device manufacturing process or manifest as field failures, this solution package gives new important data to assist reduce these failures and increase lifetime yields.

References

  1. Matweb Material Property Data. Available at: www.matweb.com

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This information has been sourced, reviewed and adapted from materials provided by KLA Instruments.

For more information on this source, please visit KLA Instruments.

Article Revisions

  • Nov 5 2024 - Meta Description updated and a product link added

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