EFFECT OF HYDROGEN ADDITION ON THE PREFERRED ORIENTATION OF ALN FILMSPREPARED BY REACTIVE SPUTTERING

Aluminum nitride (AIN) films have been deposited by reactive r.f. magn etron sputtering in the mixed gas of argon, nitrogen and hydrogen. For the application of the surface acoustic wave device, it is essential to control the preferred orientation and the texture morphology of the films with deposition parameters. The changes of the preferred orient ation and microstructures with hydrogen concentration are very interes ting and have been investigated using X-ray diffraction, scanning elec tron microscopy and transmission electron microscopy (TEM). An AIN him with a (002) preferred orientation is deposited at the deposition con ditions (an r.f. power of 200 W, a sputtering pressure of 0.7 Pa (5 mT orr), and a nitrogen concentration of 25%) and the preferred orientati on changes abruptly to the mixed (100) and (110) preferred orientation as the hydrogen gas is added. As the hydrogen concentration increases , the deposition rate decreases rapidly and it is originated from the prohibition of synthesis reaction on the film surface. In addition, th e shape of the grains on the film surface changes from conical to need le-shaped with the addition of hydrogen gas. From the analysis of high -resolution TEM, it is confirmed that the short axis of the needle-sha ped grain is the c axis of the AIN film. The needle-shaped grain may b e due to the faster growth rate in the a-axis orientation than that in the c axis. It can be concluded that atomic hydrogen may prohibit the film growth to the c-axis direction rather than to the a axis. In add ition, the growth in the c-axis direction has proceeded by a ledge mec hanism. Voids and secondary grain growth have been also observed in th e needle-shaped grain.