The unit in semiconductor: Angstrom

What is Angstrom?

Angstrom (symbol: Å) is a very small unit of length, primarily used to describe the scale of microscopic phenomena, such as the distances between atoms and molecules or the thickness of thin films in wafer manufacturing. One angstrom is equal to \(10^{-10}\) meters, which is equivalent to 0.1 nanometers (nm).

To illustrate this concept more intuitively, consider the following analogy: The diameter of a human hair is approximately 70,000 nanometers, which translates to 700,000 Å. If we imagine 1 meter as the diameter of the Earth, then 1 Å compares to the diameter of a small grain of sand on the Earth's surface.

In integrated circuit manufacturing, the angstrom is particularly useful because it provides an accurate and convenient way to describe the thickness of extremely thin film layers, such as silicon oxide, silicon nitride, and doped layers. With the advancement of semiconductor process technology, the ability to control thickness has reached the level of individual atomic layers, making the angstrom an indispensable unit in the field.

In integrated circuit manufacturing, the use of angstroms is extensive and crucial. This measurement plays a significant role in key processes such as thin film deposition, etching, and ion implantation. Below are several typical scenarios:

1. Thin Film Thickness Control

Thin film materials, such as silicon oxide (SiO₂) and silicon nitride (Si₃N₄), are commonly used as insulating layers, mask layers, or dielectric layers in semiconductor manufacturing. The thickness of these films has a vital impact on device performance.  

For example, the gate oxide layer of a MOSFET (metal oxide semiconductor field-effect transistor) is typically a few nanometers or even a few angstroms thick. If the layer is too thick, it can degrade device performance; if it's too thin, it may lead to breakdown. Chemical vapor deposition (CVD) and atomic layer deposition (ALD) technologies allow for the deposition of thin films with angstrom-level accuracy, ensuring the thickness meets design requirements.

2. Doping Control  

In ion implantation technology, the penetration depth and dose of the implanted ions significantly affect semiconductor device performance. Angstroms are frequently used to describe the distribution of implantation depth. For instance, in shallow junction processes, the implantation depth can be as small as tens of angstroms.

3. Etching Accuracy

In dry etching, precise control over the etching rate and stop time down to the angstrom level is essential to avoid damaging the underlying material. For example, during gate etching of a transistor, excessive etching can result in degraded performance.

4. Atomic Layer Deposition (ALD) Technology

ALD is a technique that enables the deposition of materials one atomic layer at a time, with each cycle typically forming a film thickness of only 0.5 to 1 Å. This technology is particularly beneficial for constructing ultra-thin films, such as gate dielectrics used with high-dielectric constant (High-K) materials.

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