Pores in SiO2 layer
Here is an interesting discovery of nanopores in the SiO2 layer after the laser annealing. Basically I was doing laser annealing on free-standing OS membrane the other day. It’s an excimer laser with 248nm wavelength, 25ns FWHM and spot size of 2.6 mm diameter. Same setup we used before in ORNL. The sample we test was OS free-standing membrane with 20 nm thick SiO2 and 15nm a-Si. The energy density we used was around 120mJ/cm2. The following are the TEM images of annealed samples.
It seems that the amorphous Si has crystallized by absorbing the laser annealing. More interestingly, agglomerated Si nanoparticles as well as nanopores in the underneath SiO2 layer also formed after the annealing. A lot of these pores in the SiO2 film were adjacent to the crystallized Si nanoparticles. In order to confirm these pores are from the SiO2 layer, I did diffraction on the featherless area and crystals area. The follows are the diffraction images.
The diffraction image clear proves the amorphous nature of the SiO2 film, which confirms that these pores are in the SiO2 layer. The reason for these pores formation is still unclear but this is definitely something quite interesting since this is the first time we see the pores formed in the SiO2 layer after the annealing. Any discussion or comments?