Look up a picture of the Great Pyramids of Giza. Observe the stones that make up the base, all the way to the top of the pyramids. Now imagine looking up from above, and the layers upon layers of stone are reduced in a 2D view, a flattened view of a humongous structure comprising thousands of stone blocks.
This is very similar to a semiconductor chip. It is a powerful, marvelous product of engineering that contributes so much to our everyday lives. Semiconductor chips are present in nearly every electronic device, from everyday products like pacemakers and cellular phones to public transport, manufacturing, pharmaceuticals, and other massive industries.
This article explores metrology in the semiconductor industry. Below, we delve into its importance and what metrology experts hope to achieve for wafer and IC manufacturing.
What Is a Semiconductor?
To better understand what is semiconductor metrology, we’ll take a closer look at what constitutes a semiconductor.
Semiconductors are substances or materials with high electrical conductivity. Silicon is the most commonly used semiconductor, followed by gallium arsenide and germanium.
Silicon, the most abundant element on the planet, second only to carbon, has been used as a semiconductor since the 1950s. It is mined from quartzite and has to undergo extraction, purification, and crystallization for silicon to be ready for semiconductor manufacturing.
Gallium arsenide is the second most used semiconductor substance. Unlike silicon, gallium arsenide is not an element but a compound created by combining gallium and arsenic. Semiconductors made from gallium arsenide are commonly used in high-frequency applications like television and telecommunication satellites.
Semiconductors are placed between conductors and non-conductors (insulators) to control and manage electric current flows throughout an electronic device. They are also referred to as integrated circuits (ICs) or simply microchips.
What Is Semiconductor Metrology?
Semiconductors play a vital role in the fabrication and manufacture of electronic devices. As such, manufacturers invest technology and time into refining their processes to produce semiconductor chips that are consistently high-quality. Metrology is crucial to achieving this goal.
Metrology is the study of measurements. In manufacturing, metrology refers to quality assurance (i.e., calibrating fabrication machines, analyzing every stage of a production line) and quality control processes (i.e., measuring the final product’s dimensions and other physical attributes) that ensure the parts or products created have the correct measurements.
- Quality assurance – calibrating fabrication machines and analyzing all stages of the production line to check for inconsistencies
- Quality control – measuring the dimensions and other physical attributes of a final product
Through metrology, manufacturers can ensure consistency of measurements in every production cycle.
Applying these principles to semiconductor manufacturing, semiconductor metrology verifies whether the physical and electrical properties of semiconductor materials are accurate, that their ideal physical specifications are met, and that variances (if any) are within tolerable limits.
Importance of Measurements: What Is Semiconductor Metrology For?
Considering the importance of semiconductors in electronics and manufacturing everyday products, ensuring quality control in their production is equally vital.
If the dimensions of a microchip exceed tolerance limits, it will no longer fit in the devices they were meant for and might be unusable for any other device. Such production waste will be costly for any company. Similarly, if components that make up a microchip don’t pass standards, they can cause malfunction or early breakdown in electronics and appliances.
For companies that manufacture semiconductors, semiconductor metrology is essential for maintaining quality standards in their microchips. For electronics manufacturers, semiconductor manufacturers with metrology experts are more appealing as partners than manufacturers without.
Types of Semiconductor Metrology Instruments
Many instruments are used to measure semiconductor chips and components. Here are some examples:
- Wafer probes – Used specifically for semiconductor wafers, which are ultra-thin slices of semiconductor material. Wafer probes are used to test the functionality of electrical circuits and can be used before or after cutting the wafers into dies.
- Ellipsometers – These measure the physical characteristics of semiconductor films like thickness, roughness, composition, and optical anisotropy.
- CD-SEM (critical-dimension scanning electron microscope) – These measure the minute details on the surface of semiconductor wafers, like fine-feature patterns of lines, holes, and bumps.
- Ion mills – These are used to etch patterns on thin semiconductor films without any chemical component. Ion mills can cut semiconductor sheets into wide, wafer-thin sheets.
- Interferometers – These are high-precision measuring instruments that can measure surface variations in microscopic objects and distances of wavelengths from different light sources.
- C-V systems – These devices measure the capacitance versus voltage (C-V) and capacitance versus time (C-t) properties of semiconductor devices.
Common Inspection Goals
Semiconductor metrologists use the tools above to inspect microchips. Below are examples of their quality control tests and goals:
- Measure the thickness of the electronic film added on top of a silicon substrate.
- Measure the diameters of holes and circuit patterns on a semiconductor wafer.
- Check the accuracy of the overlay tool that transfers patterns on a wafer.
- Check the accuracy of each overlay if patterns are imprinted on a wafer in multiple layers.
- Check for defects in the circuit patterns on the surface of semiconductor wafers (the more defects there are, the lower the quality of the chip and the higher the risk of creating defective products).
Hybrid Metrology for the Semiconductor Industry
As technology continues to evolve and become more complex, the need for ultra-precise metrology instruments and methodologies also increases. The more complex devices are, the harder it gets to obtain reliable measurements for verifying specs, establishing quality standards, identifying tolerances, etc. Moreover, using one tool for all metrology needs in a production line has become increasingly difficult.
Fortunately, many chipmakers and metrology specialists discovered a workaround: using different tool technologies and combining their data.
For example, suppose you have a stack with a copper layer at the bottom, an opaque silicon wafer on top, and another copper layer over ¼ of the surface of the wafer.
| LAYER 1 – COPPER | |||
| LAYER 2 – OPAQUE SILICON | |||
| LAYER 3 – COPPER | |||
Let’s say you want to measure the thickness of the topmost copper layer (Layer 1). If you use a topography sensor, it won’t recognize the opaque silicon layer. Instead, it will measure the distance between the top of Layer 3 and the top of Layer 1.
Hybrid metrology will be helpful in this case. Metrologists can use two sensors instead of one to get the correct measurement of Layer 1’s width (and the widths of the other two layers).
- Use a topography sensor to measure the thickness of Layers 1 and 2.
- Use a film thickness sensor to measure the thickness of Layer 2.
- Subtract the second measurement from the first.
Metrology Solutions for Semiconductor Industries
This article aims to provide an in-depth guide to semiconductor metrology. If you have more questions about metrology applications in the semiconductor industry, you can consult ATT Metrology Solutions for more helpful insights.
ATT Metrology Solutions provides complete metrology solutions for various industries. We offer onsite services, equipment rentals, and custom-integrated systems for machine calibration, measurement, and inspection needs.