Semiconductor Metrology

university wafer substrates

What substrates are used for semiconductor metrology?

There are several substrates that are commonly used for semiconductor metrology, including:

  1. Silicon: Silicon is the most commonly used substrate for semiconductor manufacturing and metrology due to its excellent material properties, including its high purity, stability, and reproducibility.

  2. Quartz: Quartz substrates are used for optical measurements in semiconductor metrology due to their high transparency to visible and ultraviolet light.

  3. Sapphire: Sapphire substrates are used for certain types of metrology, such as measuring the thickness of thin films, due to their high mechanical and thermal stability.

  4. Gallium arsenide (GaAs): GaAs substrates are used for certain types of semiconductor devices, such as high-speed electronics and optoelectronics.

  5. Silicon carbide (SiC): SiC substrates are used for power electronics and high-temperature applications due to their high thermal conductivity and wide bandgap.

The choice of substrate depends on the specific application and the properties of the semiconductor material being measured.

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Metrology for the Next Generation of Semiconductor Devices

As semiconductor devices continue to advance and become more complex, metrology techniques must also evolve to meet the demands of the industry. Some of the key metrology challenges that need to be addressed for the next generation of semiconductor devices include:

  1. Three-dimensional (3D) structures: With the development of 3D integrated circuits, metrology techniques need to be adapted to measure the thickness, shape, and alignment of layers in these complex structures.

  2. Nanoscale features: As semiconductor devices continue to shrink, metrology techniques must be able to measure features at the nanoscale level, such as the width of nanowires, the height of ultra-thin films, and the spacing between transistors.

  3. Non-destructive testing: As semiconductor devices become more expensive and complex, non-destructive metrology techniques are needed to avoid damaging the device during the testing process.

  4. Material characterization: As new materials are introduced in the manufacturing process, metrology techniques need to be able to measure and characterize their physical, electrical, and chemical properties.

To address these challenges, new metrology techniques are being developed, including advanced optical and X-ray-based techniques, as well as machine learning and artificial intelligence-based approaches. By continually advancing and improving metrology techniques, the semiconductor industry can ensure the quality and reliability of the next generation of semiconductor devices.

What are Semiconductor Metrology Tools?

Semiconductor metrology tools are a wide range of instruments and equipment that are used to measure and characterize the physical, electrical, and chemical properties of semiconductor materials and devices. Some of the key semiconductor metrology tools include:

  1. Scanning Electron Microscopes (SEM): SEMs are used to generate high-resolution images of the surface of a sample and to measure the dimensions of features down to the nanoscale level.

  2. Atomic Force Microscopes (AFM): AFMs use a small probe to scan the surface of a sample and create a 3D image of its topography at the atomic scale.

  3. Optical Metrology Tools: Optical metrology tools include ellipsometers, spectrophotometers, and interferometers, which are used to measure the optical properties of semiconductor materials, such as refractive index, absorption coefficient, and thickness.

  4. X-ray Diffraction (XRD): XRD is used to determine the crystal structure and orientation of semiconductor materials.

  5. Electrical Characterization Tools: These tools include probes and testers that are used to measure the electrical properties of semiconductor devices, such as resistivity, conductivity, and capacitance.

  6. Film Thickness Measurement Tools: These tools include profilometers, ellipsometers, and other types of instruments that are used to measure the thickness of the various layers of materials deposited on a semiconductor wafer.

Semiconductor metrology tools are critical for ensuring the quality and reliability of semiconductor devices, which are used in a wide range of electronic products. By using these tools to measure and characterize the properties of semiconductor materials and devices, manufacturers can ensure that their products meet the desired specifications and performance standards.



What Is Semiconductor Metrology?

Metrology is an important part of semiconductor manufacturing, from material discovery and technology development to integration and process control. It also has a role in test and inspection6,47.

As devices shrink in size and become more three-dimensional (3D) in shape, metrology becomes an increasingly important part of their production. This makes understanding the measurement requirements5,7 even more critical.

What is metrology?

Metrology is the science of measurement, encompassing both experimental and theoretical determinations at any level of uncertainty in any field of science or technology. It is a vital component of any quality system that ensures that products are made to the correct engineering, regulatory and customer specifications.

For manufacturers, metrology is used in two primary ways: before production begins and post-production. In the former, metrological instruments are used to determine if manufacturing equipment and tools are up to par. If they aren't, they may need to be repaired or replaced.

In the latter, metrology is used to verify that parts are made to the right dimensions, per engineering drawings. If they aren't, the parts might not fit together correctly or function properly, causing quality issues and regulatory compliance problems.

Depending on the nature of the industry, semiconductor metrology can be extremely important to the success of any product team. For example, automotive, medical device and aerospace manufacturers require high levels of accuracy in their dimensional measurements. This is because these industries rely on extreme precision for their products to be reliable and functional.

This requires sophisticated characterization tools that can measure critical dimensional parameters on the nanoscale, and at several orders of magnitude in sensitivity. These tools allow semiconductor manufacturers to analyze and test their devices in a cost-effective manner, shortening the development cycle while decreasing manufacturing costs.

One important element of semiconductor metrology is the traceability of measurements. It's essential that measurement systems are well-established and under strict quality control. This is done through the establishment of an unbroken chain of calibrations to specified measurement standards, such as those maintained by the International Bureau of Weights and Measures (BIPM).

In addition, metrology is also essential for ensuring that products are manufactured or utilized in accordance with engineering requirements, regulatory standards, customers' requirements and legal obligations. These requirements are the foundation for a quality-oriented business and should be taken seriously by all.

Metrology can be broken down into three subfields: scientific metrology, applied metrology and legal metrology. In scientific metrology, new methods of measurement are developed and standardized. The results of this work are then used to establish rules of traceability, which allow for the consistent implementation of measurement standards.

Measurement Techniques

Metrology is an essential tool for the manufacturing process of semiconductors. It helps in identifying defects early on in the manufacturing process to prevent waste and increase yield. It also helps in ensuring that the quality of the final product is of the required level.

There are many different measurement techniques that can be used in semiconductor metrology, including surface topography measurements and characterization. These can be applied to thin film deposition, lithography and other manufacturing steps.

X-ray fluorescence (XRF) and X-ray diffractometers are important metrology instruments that are used to unambiguously determine crystal structure, crystal orientation, film thickness and residual stress in silicon wafers or epitaxial films or substrates. These systems have lateral resolution of about 10 nm to 20 nm and can be applied in 3D, including in nanoscale structures.

AFM is another important metrology technique for nanoscale devices. It can be applied to the lateral profile of a thin film layer or to probe the topography of a device, with a lateral resolution of about 1 nm to 10 nm and high dopant gradient resolution (about 3 nm/dec).

CD-SAXS69 is an X-ray scatterometry method that uses a variable angle, transmission X-ray beam to non-destructively determine the average shape of periodic nanostructured elements. This method is not typically used in the fab due to its long characterisation time, but it is an area of intense research.

Specialized critical dimension scanning electron microscopes (CD-SEMs) are a key instrument for IC production. They are characterized by low electron landing energy, through-lens secondary electron detectors and fast and accurate sample-stages. The ability to quickly and accurately measure the position, size, and depth of features on wafers has made CD-SEMs one of the most popular and widely used metrology instruments in IC production.

The ability to trace measurements to a reference is important for many of these dimensional and compositional parameters, as sub-nm deviations could have serious implications for device performance140. Instrument traceability is a robust process that involves a rigorous analysis of the error sources, the physics of the measurement, and the measurand definition to reduce the impact of method divergence142.

Measurement Requirements

Semiconductor metrology is used to determine the dimensions, linewidths, and potential defect levels of semiconductor devices at various stages of production. This allows manufacturers to optimize their processes and ensure the quality of their final products.

The demand for advanced technologies has resulted in the creation of new measurement requirements for the semiconductor industry. These measurements are used to control the wafer and thin film manufacturing process, optimize product design, and reduce production costs.

Today’s manufacturing standards require the use of specialized inspection equipment to meet strict dimensional constraints. These equipment includes laser, optical, and electron beam technologies.

These tools can help improve a wide range of processes, including surface roughness testing, lithography, and chemical treatment. Additionally, they can assist in the detection of defects in the semiconductor device, which can have a negative impact on performance.

As a result, there are many different types of semiconductor metrology systems on the market. These systems typically incorporate laser, optical, and electron beam technology to inspect the properties of a semiconductor.

In order to meet the stringent dimensional constraints of semiconductor manufacturing, semiconductor metrology instruments must be designed for wafer and thin film in-line inspection after a semiconductor is processed. These tools enable semiconductor manufacturers to reduce their manufacturing costs and shorten their product development cycles.

Some of the most common semiconductor metrology applications include detecting defects in silicon, measuring the thickness of a semiconductor film, and testing for thin film adhesion and scratch resistance. These measuring instruments operate in the nano- and sub-nanometer range to help ensure the performance of semiconductor devices.

The International Roadmap for Devices and Systems (IRDS) lists a number of dimensional parameters that will be important for semiconductor metrology over the next 15 years. These include lateral gate-all-around (VGAA) nanowire diameter, nanowire roughness and uniformity, half pitch, and gate length, among others.

These dimensional measurements will have to be performed for all levels of semiconductor device architecture, from FinFET to 3DVLSI. The evolution of these device architectures, as forecasted by the IRDS, will introduce new metrology challenges for semiconductor engineers.

Measurement Solutions

Semiconductor production is highly time-sensitive and requires accurate measurements and inspections at every step of the process. This is why metrology is a vital tool for semiconductor manufacturing, as it provides manufacturers with the tools they need to ensure that their production lines run smoothly and produce high-quality products.

For example, optical metrology can be used to detect and measure defect levels on wafers as well as identify defects that could impact their performance. These systems use laser, optical, and electron beam technologies to provide the accuracy and resolution that manufacturers need to control the quality of their products and improve the output of their production lines.

Optical metrology solutions for chip manufacturing can include a variety of options, such as CD-SEM, AFM, and X-ray scattering equipment. These can be combined to form a hybrid metrology system that offers several advantages.

Quartz Imaging's PCI AM module adds advanced semiconductor metrology functionality to the company’s standard Quartz PCI image measurement software. It allows engineers to automatically measure layers, trenches, pillars, lines, spaces, complex features and 2D shapes, including contact holes and vias, in cross-section or top-view images from SEMs (X-SEMs) and TEMs.

With the AM module, engineers can make rapid and efficient automatic feature measurements with a few clicks on an image. They can also combine a group of features within one image for faster, more accurate results.

The AM module can also be set up to capture all the measurements from a group of images into a single spreadsheet grid for aggregation into standard Quartz PCI reports. This can significantly reduce the amount of data collection required to get accurate results.

Wavefront phase imaging is a new semiconductor metrology technique that can capture millions of data points in a few milliseconds with sub-nanometer height accuracy and higher spatial resolution than other techniques. This type of measurement is ideal for measuring the surface roughness and thickness of grinded wafers, as well as Total Thickness Variation (TTV) of dielectric substrates.

The technology combines chromatic confocal scanning electron microscopy (SEM) with high-resolution diffraction optics. The system can be configured for a wide range of applications, such as measuring warpage/bow, thickness of films and substrates, total thickness variation, and other geometric properties.

Video: Learn about Semiconductor Metrology

What is Semiconductor Metrology Key Measurements?

Semiconductor metrology is the process of measuring and characterizing the physical, electrical, and chemical properties of semiconductor materials and devices used in the manufacturing of electronic components. This involves a wide range of techniques and tools that are used to ensure that the semiconductors produced meet the desired specifications.

Some of the key measurements that are made in semiconductor metrology include:

  1. Film thickness: measuring the thickness of the various layers of materials deposited on a semiconductor wafer.

  2. Electrical properties: measuring the electrical properties of the semiconductor material, such as resistivity, conductivity, and capacitance.

  3. Optical properties: measuring the optical properties of the semiconductor material, such as refractive index, absorption coefficient, and bandgap energy.

  4. Structural properties: measuring the structure and morphology of the semiconductor material, such as crystal orientation, defects, and surface roughness.

Semiconductor metrology is critical for ensuring the quality and reliability of semiconductor devices, which are used in a wide range of electronic products, including computers, smartphones, and other consumer electronics.