In the semiconductor manufacturing process, the deposition of thin films is one of the core steps. Friends who have been in contact with CVD should have heard of TEOS more or less. As an important deposition source, TEOS is especially important in the formation of low-temperature silicon oxide. In the process, he played an irreplaceable role. Today we are going to talk about this substance.
What is TEOS?
TEOS (tetraethoxysilane, Tetraethoxysilane), is a silicon organic compound, its chemical formula is Si(OC2H5)4. This means that one silicon atom is linked to four ethoxy (OC2H5) groups. Silicon atoms are at the center of these four groups, forming a geometry called a regular tetrahedron.
Physical properties: It is a colorless and transparent liquid at room temperature, with an alcohol-like smell. It starts to boil at 169 °C, but starts to evaporate at 45 °C and has high volatility. It is soluble in water and has good solubility with alcohols and ketones. Density is less than water. Vapor is heavier than air.
Chemical properties: It can be slowly oxidized in the air, so it needs to be sealed when stored.
Application of TEOS in CVD
TEOS is a common silicon source in the chemical vapor deposition process, and is generally used to generate SiO2 thin films, which can be used as dielectric layers, isolation layers, protective layers, etc.
Mechanism of TEOS generating silica by LPCVD or PECVD process:
In the LPCVD process, TEOS and oxygen react on the substrate surface under certain temperature and pressure to generate silicon dioxide and ethanol. The chemical reaction equation is:
Si(OC2H5)4 + 2O2 → SiO2 + 4C2H5OH
During this process, the silicon atoms in the TEOS molecule react with oxygen to form silica and release ethanol. Silicon dioxide accumulates on the substrate surface as a deposit, forming a silicon dioxide film.
In the plasma-enhanced CVD process, TEOS and oxygen are simultaneously stimulated by a high-frequency electric field on the substrate surface to generate plasma. The ions and free radicals in the plasma can promote the reaction of TEOS and oxygen. The advantage of the PECVD process is that it can be performed at a lower temperature and is suitable for temperature-sensitive substrates.
Whether by LPCVD or PECVD, TEOS can produce silicon dioxide films with good coverage and uniformity.
Dangers of TEOS?
Health risks: TEOS can enter the human body through inhalation and skin contact. It is an irritant to the respiratory system, skin and eyes and can cause allergic reactions, dermatitis or serious eye damage. Prolonged or repeated exposure may cause difficulty breathing, coughing, headache, nausea and vomiting.
Fire Risk: TEOS is a flammable liquid that can form flammable vapor/air mixtures in air. Therefore, it is necessary to keep away from fire sources and ensure good ventilation. TEOS reacts violently when it comes in contact with water, this reaction can generate a lot of heat and has the potential to cause a fire.
Therefore, when handling or using TEOS, appropriate safety precautions must be taken, including wearing protective clothing and glasses, using appropriate respiratory protection, etc. At the same time, appropriate safe storage and disposal measures should be in place to prevent leakage or accidental exposure of TEOS.