The effects of nuclear and electronic stopping powers on ion irradiated novolac-diazoquinone films

The structure and surface modifications induced in ion irradiated AZ-1350 J photoresist films as function of energy, fluence and the amount of electronic and nuclear deposited energy density are investigated in detail. The films have been irradiated with 380 keV He+, 4 MeV I2+ and 800 keV Xe2+ ions, in a fluence range from 1013 to 1016 cm-2. At these energies, the ranges of the ions are larger than the thickness of the films and the transferred energy to the films extends from nearly pure electronic (for He+) to predominantly nuclear stopping power (for Xe2+). The structural, chemical and mechanical properties of the samples were investigated through the techniques of nuclear reaction analysis, elastic recoil detection analysis, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and nanoindentation. When the electronic stopping prevails, as for 380 keV He+ irradiation at low and intermediate fluences, the deposited electronic energy density is the main cause for the observed increase of hardness (H), Young modulus (E) and gel fraction through the cross-linking process, preserving most of the chemical characteristics of the original material. When nuclear stopping is large (Xe and I irradiations) the cross-linking process is only present at very low fluences. At intermediate and higher fluences the transference of nuclear energy density induces a large loss of oxygen and hydrogen and the photoresist is progressively transformed into an amorphous carbon layer. At the highest fluences, the hardness, Young modulus, density and Raman spectra are characteristics of a hydrogenated amorphous carbon system. We also show that the loss of hydrogen as function of fluence is well explained by the bulk molecular recombination model, which assumes that the hydrogen leaves the irradiated materials in molecular form