Talking about the Importance of Silicon Nitride (SiNx) in Chips

In chip manufacturing, there is a material that plays a crucial role, which is silicon nitride (SiNx). Although it may not have received the same attention as other more well-known semiconductor materials such as silicon (Si), gallium arsenide (GaAs), or gallium nitride (GaN), its importance is undoubtedly undeniable. It can be said that the vast majority of chips will use this material.

Why is it SiNx?

Careful friends have noticed that I used SiNx when writing the chemical formula of silicon nitride. Friends who have studied high school chemistry should know that N is the fifth main group element, and theoretically, the chemical valence should be -3, while the chemical valence of silicon is+4. The chemical formula of silicon nitride should be Si3N4. How could it be SiNx?

Firstly, let's talk about the multivalent states of nitrogen:

Nitrogen has multiple valence states, mainly because it has 5 valence electrons, and nitrogen atoms can share these electrons in different ways. Nitrogen can form different valence states, which mainly depends on the number of electrons it shares with other elements.

For nitrogen, its most stable valence state is -3, as in ammonia (NH3) and gallium nitride (GaN). However, nitrogen can also form a positive valence state by losing electrons, such as the+5 valence state in nitric acid (HNO3). In addition, nitrogen can also form valence states between -3 and+5, such as the+3 valence state in nitrite (HNO2) or the+1 and+2 valence states in some organic compounds.

Secondly, let's talk about silicon nitride as a material:

In the semiconductor industry, silicon nitride used for various applications is often non specific and is generally represented by SiNx. SiNx is an amorphous material whose properties depend on the ratio of nitrogen and silicon, i.e. the value of x. When the value of x changes, the physical and chemical properties of silicon nitride also change. There are indeed various forms of silicon nitride, including Si3N4, Si2N2, SiN, etc.

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

What is the role of SiNx in chip manufacturing?

The insulation performance of silicon nitride is very excellent, with a resistivity of up to 10 ^ 14 Ω· cm, far exceeding some common insulation materials, such as silicon oxide (SiO2). And its low dielectric constant makes it an ideal isolation layer in microwave and radio frequency applications. The silicon nitride layer also plays a role in blocking the diffusion of impurities in the chip. It can prevent dopants such as boron and phosphorus from diffusing and changing device characteristics. In addition, it can also prevent the diffusion of metal ions, etc., to prevent faults such as short circuits.

The excellent thermal stability of silicon nitride is determined by its special chemical properties and crystal structure. It can remain stable in high-temperature environments without undergoing chemical decomposition or physical shape changes like other materials. That's because in the crystal structure of silicon nitride, each silicon atom is bound to four nitrogen atoms in a tetrahedral form, and each nitrogen atom is also bound to four silicon atoms in a tetrahedral form. This structure makes the crystal lattice of silicon nitride extremely stable and less prone to deformation. Therefore, it serves as the gate insulation layer in the manufacturing of high electron mobility transistors (HEMTs).

What are the advantages of SiNx over SiO2?

Better thermal stability

Harder hardness

More difficult to etch