Why is oxide not used in the CVD process in the manufacture of gate oxide in the NMOS device?

I know that chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, high-performance solid materials. The process is often used in the manufacture of semiconductors to produce thin films, there are several CVD methods, such as LPCVD, PECVD etc.
Depending on the material used, the temperature and the correct material can penetrate the substrate, creating a thin layer on the substrate used in the process.

My question

Why is oxide not used in the CVD process in the manufacture of gate oxide in the NMOS device?

I can't find the reasons and the main causes.