A study on chemical delayering method to expose tunnel window and oxide in wafer fabrication

In this study, we have developed a rapid chemical delayering method to expose tunnel window and its oxide in the EEPROM device in wafer fabrication. HB91 (9 parts of nitric acid, HNO₃ and 1 part of buffer oxide etchant, BOE) has been used to remove polysilicon layers instead of Sodium Hydroxide (NaOH) currently used. After characterization, the procedures of the new delayering method using HB91 to expose the ONO layer and tunnel window & its oxide layer are: Sample preparation → Dilute HF (1 part of HF, 49% with 5 parts of DI water) deprocessing for 10 mins → HB91 at room temperature for 8 secs → RIE (relative ion etching) for 30 secs → HB91 at room temperature for 6 secs → Optical and SEM inspection. Application results showed that this new method is rapid and repeatable of the results.