# Defect Tailoring in HfO2/Si Films upon Post-Deposition Annealing and Ultraviolet Irradiation
## 3 Results
### Film Morphology by Atomic Force Microscopy  
Figure 4 presents the 20 \(\times\) 20 \(\upmu\)m\({}^{2}\) topographic images of the S1-S4 HfO\({}_{2}\) thin films. Initially, the image of the S1 film shows a cracked surface with some spherical particles spread on the surface. The characteristic cracked morphology of the HfO\({}_{2}\) films may be due to the type of deposition used, the dip coating, and the results of solvent evaporation on the observed morphology, opposite to the film morphology achieved by sputtering [12]. Upon thermal annealing at 350 \({}^{\circ}\)C, the size of the cracks decreased in the S2 film, indicating that the films became more compact. When UV radiation was applied to the S3 film, a decrease in the width and the length of the cracks was observed, indicating coalescence of the films, explained by the sequential bond rupture and decomposition of remnants of organic groups [7,13] by UV radiation, followed by the \"plastic\" self-healing of the film which led to the amorphization observed in the GIXRD [14]. However, in the S4 film, where both treatments (thermal and UV radiation) were combined, a further increase in the depth and size of the cracks occurred, suggesting that the bond rupture was not followed by recrystallization. [PERSON] et al. [4] and [PERSON] et al. [13] showed that increasing annealing temperature in HfO\({}_{2}\) films led to increased film compacity, which has been attributed to the decomposition of organic groups either in dip-coated or ALD films; on the other hand, [PERSON] et al. observed more compact and smooth surfaces upon UV/O\({}_{3}\) treatment [7], in correspondence with the present results. A study of increased annealing time at low temperatures coupled with UV irradiation to increase coalescence should be explored in future work.  
In Figure 5, (a) height distribution and (b) roughness root mean square values obtained from the AFM images are presented.  
Figure 4: The 20 \(\times\) 20 \(\upmu\)m\({}^{2}\) AFM topographic images of the S1–S4 HfO\({}_{2}\) thin films.  
As derived from topographic images (Figure 4), in Figure 5a, the height distribution is almost constant in S1 and S2 with 0.64 and 0.66 \(\upmu\)m, respectively, with the value of heights decreasing in S3 to 0.54 \(\upmu\)m and the value increasing in S4 to 0.61 \(\upmu\)m, obtaining a value closer to S1. In Figure 5b, the RRMS shows a similar behavior; the RRMS has a value of 118 nm of roughness in S1, increasing in S2 to 146 nm, followed by a decrease in S3 to 95 nm and an increase again in S4 to 118 nm, returning to the value obtained in S1.  
S1 and S4 present similar values in the distribution of heights and roughness, although S4 applied heat treatment and UV irradiation and, according to the literature, there should be an increase in the crystallinity of the HfO\({}_{2}\) film [12], which would contribute to an improvement in its morphological properties; however, S4 shows values and properties similar to those presented in S1, which could be due to the extended time of heat treatment and irradiation, generating a rupture of bonds in the structure of the film. The results are correspondent with those in the X-ray diffraction analysis, where it was found that S3 and S4 are amorphous.  
In future work, optimal heat treatment and UV irradiation times will be assessed to tailor the film compacity/porosity, which could benefit their use as insulators in TFTs or in electrocatalytic applications, respectively.