In the manufacturing process of semiconductor wafer foundries with relatively advanced production processes, nearly 50 different types of gases are needed. Gases are generally divided into bulk gases and special gases.

Application of gases in microelectronics and semiconductor industries The use of gases has always played an important role in semiconductor processes, especially semiconductor processes are widely used in various industries. From ULSI, TFT-LCD to the current micro-electromechanical (MEMS) industry, semiconductor processes are used as product manufacturing processes, including dry etching, oxidation, ion implantation, thin film deposition, etc.

For example, many people know that chips are made of sand, but looking at the entire process of chip manufacturing, more materials are needed, such as photoresist, polishing liquid, target material, special gas, etc. are indispensable. Back-end packaging also requires substrates, interposers, lead frames, bonding materials, etc. of various materials. Electronic special gases are the second largest material in semiconductor manufacturing costs after silicon wafers, followed by masks and photoresists.

The purity of gas has a decisive influence on component performance and product yield, and the safety of gas supply is related to the health of personnel and the safety of factory operation. Why does the purity of gas have such a great impact on the process line and personnel? This is not an exaggeration, but is determined by the dangerous characteristics of the gas itself.

Classification of common gases in the semiconductor industry

Ordinary Gas

Ordinary gas is also called bulk gas: it refers to industrial gas with a purity requirement lower than 5N and a large production and sales volume. It can be divided into air separation gas and synthetic gas according to different preparation methods. Hydrogen (H2), nitrogen (N2), oxygen (O2), argon (A2), etc.;

Specialty Gas

Specialty gas refers to industrial gas that is used in specific fields and has special requirements for purity, variety, and properties. Mainly SiH4, PH3, B2H6, A8H3, HCL, CF4, NH3, POCL3, SIH2CL2, SIHCL3, NH3, BCL3, SIF4, CLF3, CO, C2F6, N2O, F2, HF, HBR, SF6… and so on.

Types of Spicial gases

Types of special gases: corrosive, toxic, flammable, combustion-supporting, inert, etc.
Commonly used semiconductor gases are classified as follows:
(i) Corrosive/toxic: HCl 、BF3、 WF6、HBr、SiH2Cl2、NH3、 PH3、Cl2、 BCl3…
(ii) Flammable: H2、 CH4、 SiH4、PH3、AsH3、SiH2Cl2、B2H6、CH2F2、CH3F、CO…
(iii) Combustible: O2、Cl2、N2O、NF3…
(iv) Inert: N2、CF4、C2F6、C4F8、SF6、CO2、Ne、Kr、He…

In the process of semiconductor chip manufacturing, about 50 different types of special gases (referred to as special gases) are used in oxidation, diffusion, deposition, etching, injection, photolithography and other processes, and the total process steps exceed hundreds. For example, PH3 and AsH3 are used as phosphorus and arsenic sources in the ion implantation process, F-based gases CF4, CHF3, SF6 and halogen gases CI2, BCI3, HBr are commonly used in the etching process, SiH4, NH3, N2O in the deposition film process, F2/Kr/Ne, Kr/Ne in the photolithography process.

From the above aspects, we can understand that many semiconductor gases are harmful to the human body. In particular, some of the gases, such as SiH4, are self-igniting. As long as they leak, they will react violently with oxygen in the air and start to burn; and AsH3 is highly toxic. Any slight leakage may cause harm to people’s lives, so the requirements for the safety of the control system design for the use of special gases are particularly high.

Semiconductors require high-purity gases to have “three degrees”

Gas purity

The content of impurity atmosphere in the gas is usually expressed as a percentage of gas purity, such as 99.9999%. Generally speaking, the purity requirement for electronic special gases reaches 5N-6N, and is also expressed by the volume ratio of impurity atmosphere content ppm (part per million), ppb (part per billion), and ppt (part per trillion). The electronic semiconductor field has the highest requirements for the purity and quality stability of special gases, and the purity of electronic special gases is generally greater than 6N.

Dryness

The content of trace water in the gas, or wetness, is usually expressed in dew point, such as atmospheric dew point -70℃.

Cleanliness

The number of pollutant particles in the gas, particles with a particle size of µm, is expressed in how many particles/M3. For compressed air, it is usually expressed in mg/m3 of unavoidable solid residues, which includes oil content.