High Selective Etching of SiO2/Si by ArF Excimer Laser

Dry etching of SiO2 insulation layer has been required in the Si semiconductor manufacturing process. The etching of SiO2/Si is chemically carried out by using HF solution. We successfully demonstrated a new method for exclusive etching of SiO2 using the nitrosyle fluoride (NFO) gas which was produced from the mixed gas of NF3 and O2 with an ArF excimer laser irradiation.SiO2 and Si substrates were placed side by side in a reaction cell which was filled with 3% O2 gas in NF3 at the gas pressure of 380 Torr. ArF excimer laser beam was irradiated parallel to the substrates. The laser fluence was kept at lOOmJ/cm2. As soon as the mixed gas of NF3 and O2 was irradiated with the ArF laser beam, an intermediate product of NFO was produced. The chemical behavior of NFO was confirmed from the UV absorption spectrum with absorption in the 310 to 330nm wavelength region. In the presence of SiO2, the absorption of NFO diminished. The absorption of NO2, instead of NFO, appeared at 350nm. This indicates that the oxygen atoms of SiO2 were pulled out by NFO.The etching reactions continued for 3 minutes after irradiation when the SiO2 and Si substrates were kept in an atmosphere of the reactant gases. As a result, not the Si but SiO2 substrate was etched with the depth of 2000Å.