Focused ion beam micromachining of silicon and gallium arsenide using gallium and gold liquid metal ion sources

Application of focused ion beam(FIB) technology is increasing rapidly. A particularly important application is focused ion beam micromachining(FIBM). This technique is used in areas such as mask repair, IC modification, and opto-electronic device fabrication, where knowledge of the sputtering yield is critically important. Because of the importance of sputtering yields, the following series of experiments was undertaken.; The sputtering yield of single crystal (100) oriented Si and GaAs were measured as functions of ion energy and angle of incidence for Ga{dollar}sp+{dollar} ion bombardment. These materials were chosen because of their importance in FIBM, particularly integrated circuit repair and opto-electronic device fabrication. In addition, the effects of ion dose, beam scan velocity and ion channeling were investigated. For comparison, the sputtering yield for {dollar}Ausp{lcub}+,++{rcub}{dollar} bombardment of GaAs was also measured, and single crystal (111) oriented Si was bombarded by Ga{dollar}sp+{dollar} to test the effects of crystal orientation.; The results of the above experiments were analyzed in terms of Sigmund's linear cascade theory of sputtering. A brief overview of the theory is presented to show how the angular and energy dependence of the sputtering yield enter into the theory. The dependence of the sputtering yield on incident angle and ion energy is then compared to theoretical predictions.; The above yield measurements were made by machining a rectangular crater of a consistent size and shape, chosen to minimize the effects of redeposition and facilitate the measurement of the sputter crater volume. Real applications of FIBM involve the machining of more complicated structures, where the net sputtering yield can be significantly different. To check the applicability to FIBM of the above measurements, they were compared to measurements made for more complex structures typical of FIBM.; In the course of machining these structures, an equation was derived which relates the shape of the surface to be machined, to the scan velocity of the beam and the sputtering yield of the target. The time dependence of the beam position required to create the desired surface was obtained by solving a nonlinear partial differential equation. Several different surface contours were machined using this technique. The sputtering yield was measured for one particularly simple example, and was then compared to the yield measurements described above. Two other examples illustrate the application of the equation to the production of more complicated surfaces.