Wafer and thin film instrumentation consists of devices such as critical defect scanning electron microscopes (CD-SEMs), ion mills, quartz crystal microbalance (QCM) monitors, RHEED systems, ellipsometers, imaging systems, and C-V systems. The equipment is employed in metrology or monitoring of in-situ thin film parameters while thin film or semiconductor wafer processing is taking place.

Types of Wafer and Thin Film Instrumentation

Wafer and thin film instrumentation supports a broad range of options, including:

Quartz crystal microbalance (QCM) units measure mass and viscosity instead of geometric thickness in procedures taking place on or near surfaces as well as within thin films. Mass density to thickness conversion requires physical density input. The electromechanical QCM (EQCM) features the ability to quantify current efficiency.

Scanning electron microscopes (SEM) generate images of surfaces and composition of materials at the scale comparable to that of electrons. One application is the classification of defects and identifying their source.

Reflection high-energy electron diffraction (RHEED) works on a similar principal to the SEM. They study surfaces of crystalline materials and gather data solely from a sample's surface layer. Electron interference at the atomic level causes the diffraction patterns that identify the structure of the sample.

Ewald's spheres are deployed in electron transmission, x-ray, or neutron interferometry for identifying crystalline arrangements. The Ewald sphere operates based on the principle of diffraction, wave vectors, and constructive interference for reconstructing the design using the reciprocal lattice

Electron gun performance sets limits on a system's resolution and testing functions. Tungsten features low work function, and tungsten cathodes serve as a source of electrons.

Operation

Integrated circuit manufacturing requires cleanrooms, with exceptionally fine filters eliminate airborne impurities that cause defects. Workers in semiconductor facilities must wear cleanroom suits protecting the wafers from contamination. Wafers comprise of pure silicon built into cylindrical ingots or boules using the Czochralski procedure. The ingot slices are polished flat and quality checked before use with the final product.

Fabrication of semiconductors involves four activities:

• Removal: Wet or dry etching and chemical-mechanical planarization (CMP) removes excess elements from the wafer.
• Patterning: UV lithography followed by plasma ashing prepare the surface for the next stage of production.
• Deposition: Physical or chemical vapor deposition (PVD or CVD), molecular beam epitaxy (MBE), or atomic layer deposition (ALD) coat the patterns with new substances.
• Electrical property modification: Changes in the electrical properties of transistor units rely on diffusion furnaces or ion implantation. Rapid thermal annealing (RTA) or ultraviolet processing (UVP) activate the dopant.

The steps engaging the components include:

Front-end-of-line (FEOL) processing serves transistor manufacturing activities engaging highly pure or strained silicon wafers.

Back-end-of-line (BEOL) processing is involved in the interconnections needed in semiconductor devices. Silicon glass or silicon oxycarbide is incorporated as the dielectric between the contact surfaces.

Subtractive or additive tasks are essential in connecting different parts of the electronics using aluminum, copper, or gold depending on the objective. The most common form is subtractive lithography, in which multiple layers of elements and wiring are constructed through planarization techniques. The complexity, connectivity, electrical properties, and working environment of the item dictate the material combinations and number of layers necessary. CMP is a standard method deployed with up to three interconnected levels. Dry etch back is recommended for more than four layers of connectivity.

Wafer Testing

Ellipsometry or reflectometry controls gate oxide thickness, refractive index, extinction coefficients of photoresist, and other coatings with enhanced precision. Metrology verifies the quality of silicon wafers prior to testing. If several dies fail on an individual wafer, the whole unit is subject to scrapping to eliminate the cost of further treatment. Virtual metrology also provides predictions of wafer properties based on statistical models rather than conducting actual physical measurements.

Testing Devices

Semiconductor components run through a battery of electrical tests. The yield is determined by calculating the proportion of devices on a wafer exhibiting proper functioning. An electronic tester is deployed for assessment. Bad chips are marked with a drop of dye. The dye markers are tracked through the procedure ensuring the defected chips are excluded from further stages of production.

Applications

Wafer and thin film instrumentation serves a diverse scope of applications, including:

• Photovoltaics
• Optoelectronics
• Optical and functional coatings
• Surface chemistry
• Biotechnology

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Cognex Corp. | Micro-Epsilon