Oxidation and diffusion
When etched in the same dilute hydrofluoric acid, how do the etch rates of thermal oxide and CVD oxide generally compare?
- AThermal oxide etches more slowly (it is denser)
- BThermal oxide etches faster
- CThey always etch at the same rate
Show answer and explanation
Answer: A. Thermal oxide etches more slowly (it is denser)
Thermal oxide is dense with few defects, so it etches slowly in hydrofluoric acid. CVD oxide may have lower density or contain hydrogen depending on deposition conditions, so it generally etches faster. The etch-rate ratio relative to thermal oxide is used as an indicator of film quality.