| Integrated optics is a subject about the study of optical phenomena in thin films and the integration of optical components. It is based on optoelectronics, microelectronics and modern optical theory using the technology of thin film and microelectronics. Its goal is to integrate optical components with different properties and structures on thin film. So the fabrication of high-quality optical crystal films is very important. The thickness of membrane can be precisely controlled through ion implantation combined with wafer bonding or ion implantation combined with chemical etching method. The properties of obtained films reach the level which is approximate to the bulk materials. Using this method we can realize the batch production of thin films. This technology shows a good application prospect. Related research has been carried out in abroad. The most successful example is the fabrication of lithium niobate thin film heterostructures by He ion implantation. The research on integration of the related devices on this structure is also carried out. Research about crystal ion slicing of other optical material is still in the exploratory stage. To achieve the fabrication of other crystal films as well as final production, there are still many challenges. There are also many difficulties to overcome, including the understanding of ion implantation process, the nature of the defect and the mechanism of defect evolution. So we chose different materials implanted by ion to study the inner changes of crystal and the defect structures caused by ion implantation. We will reveal the defects and lattice change in film fabrication. Through continuous exploration on ion implantation and subsequent processing conditions we successfully prepared film with crystal properties close to bulk materials. In the end, the method of using ion implantation to achieve the preparation of lithium tantalate and potassium titanium oxide phosphate single crystal is established, which provides a theoretical and experimental reference for the preparation of optical materials by ion implantation.This research can be divided into two parts, which are the mechanism of ion implantation for the fabrication of lithium tantalate single crystal film and the preparation of potassium titanium oxide phosphate film, respectively. In the study of mechanism of lithium tantalate film fabrication, we analyzed lattice damage induced by ion implantation and the lattice strain and stress. Defect structure and its evolution versus annealing process are characterized. Through a foaming model and the minimum dose of blistering obtained in experiment, we calculated the value of the bubble radius and internal gas pressure. More fully understanding and the physical principles of blistering are established in this paper. In the process of etching KTP, we found that He ion implanted single crystal had a strong selective etching. The etching rate in the heavy damage area was 1000 times higher than that of other regions. KTP single crystal thin films were successfully prepared by ion implantation and wet etching. The properties of the films will be further improved by annealing. By means of H and He co-implantation into KTP, we analyzed the changes of the KTP lattice structure and the establishment and release of the stress induced by the implantation. Results showed that the lattice strain of KTP was from a plastic deformation. In summary, ion implantation effect and mechanism of film exfoliation are the main content of this paper.In this paper, the main contents and results are as follow:(1) The implantation of 120 keV H ions into lithium tantalate results in an ion range of 800nm deep from the surface. We found that when the dose is less than 6×1016 ions/cm2, no blistering is observed on the surface of the sample. Rutherford backscattering channel spectra show that the lattice damage for 5-8 ×1016 ions/cm2 samples are almost the same. At the same time the higher dose required lower annealing temperature and shorter accumulation time. The actual H content after the implantation is lower than the theoretical value, and even lower than the 30% of theoretical value. By high resolution transmission electron microscope, a heavy crystal lattice damage layer is formed at the end of the ion range, and the depth of the layer is consistent with the result from SRIM simulation. And in the surface region which is above the damage, the lattice is almost as good as bulk material. This layer is corresponding to the film that we want to exfoliate. The high resolution transmission electron microscope picture shows that the damage layer is composed of a number of clusters. The physical model of blistering is established. And using the measured minimum dose of blistering, surface energy density of lithium tantalate is calculated, which is the first report of lithium tantalate surface energy density. According to the structure of Griffith crack model and FvK theory, we calculate the pressure difference of inner bubble. The tangential stress value is also given. Finally the numerical relationship between the bubble radius and stress are given.(2) In the process of achieving the exfoliation of the LiTaO3 by He ion implantation, we found that only the dose of 5×1016 ions/cm2 was feasible. When the dose is less than the minimum, there is no surface blistering. But the surface will crack when the dose is larger than that. In the annealing process, strip of thin film on sample surface is obtained. The exfoliated thin film is with the width about 10-1000μm. We observed the existence of nanobubbles in He implanted samples by high resolution TEM image. These bubbles can cause the strain of the surrounding lattice and the stress distribution is reconstructed by the high resolution X-ray diffraction experiment. At the same time, by adjusting the current density of the ion beam, we study the effect of temperature on the sample. When the current density is 9μA/cm2, the surface of the sample is blistered directly. The results of RBS experiments are also given. The cumulative process of lattice displacement damage is also analyzed. High current density means high temperature, so the vacancy and interstitial can easily combine to result in annihilation. Hence RBS yield will be small. When implantation in the low current density, interstitial and vacancy diffusion are not obvious and therefore damage will be accumulated. In this case, high-yield RBS/ channeling spectrum is obtained.(3) Using different compositions and different ion implantation sequences, we study film splitting by H and He co-implantation. In the experiments, we found that the effect of implantation sequence on the film splitting was very obvious. The samples implanted by He first were more easily to be exfoliated. We proposed the model of synergistic effect from H and He to realize thin film delamination. Through the RBS test, we found that the total ion dose needed from the H first sample was significantly higher than that of the sample first implanted by He. At the same time, the TEM results also showed that the two kinds of implant were different. The X-ray diffraction results showed that the stress of the sample implanted by H was significantly lower than that of the sample implanted first by He. These can be explained by the H and He synergistic effect. Finally using x-ray diffraction to observe the annealing effect on the recovery of the lattice strain, we found the stress release was achieved through the surface blistering or fracture.(4) We use 2MeV He ion implantation into single crystal KTP. After implantation a heavy damage layer formed at the depth of 5 microns below the surface. The sample was placed in a diluted HF solution to study the etching process. In the etching process, we found an obvious selectivity etching. Etching edge is clear, which can be observed by the scanning electron microscopy. Compared with SRIM simulation result, the etching area is found to correspond to a certain damage threshold. In heavily damaged area, etching rate can reach 1000 times higher than that of the bulk. Through the study of different etching conditions, mainly etching temperature, etching solution concentrations, we found that the etching rate increase with the HF concentration and temperature, but etching selectivity decreases. We use the optimized etching conditions to obtain 5 microns thick KTP films. The properties of single crystal thin film were characterized by synchrotron radiation and Raman scattering. The film is still very good and the annealing will further improve the properties of the films.(5) With high current and low current beam,110 keV H ions and 190keV He ions were implanted sequentially whose doses are both 4×1016 ions/cm2. An obvious damage zone was formed in 850nm under the sample surface. Through the using of different current density, we found an amorphous layer induced by low current, indicating accumulated damage in this sample. High current means high temperature. The resumption of the lattice damage occurs due to temperature induced diffusion of defects to annihilate. After a series of annealing treatments and tests, the damage of the sample can be recovered in part, and the related stress will be reduced. But we found plastic deformation in Z-cut KTP crystal will prevent blistering, namely in Z-cut KTP crystal will shrink, which makes subsequent film splitting difficult. This study will help a lot in the smart cut of KTP. |
PDF Full Text Request