The Importance of Silicon Nitride (SiNx) in Chips

In chip manufacturing, there is a material that plays a vital role, that is silicon nitride (SiNx). Although it may not receive the same attention as other more well-known semiconductor materials such as silicon (Si), gallium arsenide (GaAs) or gallium nitride (GaN), its importance is unquestionable. It can be said that most chips will use this material.

In the semiconductor industry, silicon nitride used in various applications is often non-uniform, generally represented by SiNx. SiNx is an amorphous material whose properties depend on the ratio of nitrogen to silicon, that is, the value of x. When the value of x changes, the physical and chemical properties of silicon nitride will also change. Silicon nitride does come in many forms, including Si3N4, Si2N2, SiN, etc.

Si3N4 is a crystalline material, which means that the ratio of silicon to nitrogen is fixed. When the value of x is equal to 4/3, SiNx is equal to Si3N4. However, in practical applications, SiNx is often non-fixed, and its ratio of silicon to nitrogen can be adjusted by changing the parameters of the PVD or CVD process.

Silicon nitride has excellent insulation properties, with a resistivity of up to 10^14 Ω·cm, far exceeding some common insulating materials such as silicon oxide (SiO2). Its low dielectric constant makes it an ideal isolation layer in microwave and radio frequency applications. The silicon nitride layer also acts as a barrier to impurity diffusion in the chip. It can prevent dopants such as boron and phosphorus from changing device characteristics through diffusion. In addition, it can also prevent the diffusion of metal ions to prevent faults such as short circuits.

Silicon nitride has excellent thermal stability, which is determined by its special chemical properties and crystal structure. It can remain stable in high temperature environments without chemical decomposition or physical changes like other materials. That’s because in the crystal structure of silicon nitride, each silicon atom is combined with four nitrogen atoms in the form of a tetrahedron, and each nitrogen atom is also combined with four silicon atoms in the form of a tetrahedron. This structure makes the crystal lattice of silicon nitride extremely stable and not easy to deform. Therefore, it is used as a gate insulating layer when manufacturing high electron mobility transistors (HEMTs).

What are the advantages of SiNx over SiO2?

Better thermal stability, harder hardness, and more difficult to etch.