Separation of stress-free AlN/SiC thin films from Si substrate

Abstract

Abstract. We separated AlN/SiC film from Si substrate by chemical etching of the AlN/SiC/Si heterostructure. The film fully repeats the size and geometry of the original sample and separated without destroying. It is demonstrated that a buffer layer of silicon carbide grown by a method of substitution of atoms may have an extensive hollow subsurface structure, which makes it easier to overcome the differences in the coefficients of thermal expansion during the growth of thin films. It is shown that after the separation of the film from the silicon substrate, mechanical stresses therein are almost absent. IntroductionNowadays scientists are actively searching for new ways to obtain high quality semiconductor thin films and heterostructures, in particular, gallium nitride that is used in LEDs and other electronics [1,2] and aluminum nitride. For the growth of such films sapphire and SiC substrates are used mainly [3][4][5], less often silicon or other substrates, but all of these substrates has some disadvantages. Sapphire has very low thermal conductivity and is dielectric, so the additional conducting contacts should be added. SiC is more suitable, because its thermal conductivity is high and close to the conductivity of the copper. In addition, the lattice parameters of SiC and AlN/GaN are much closer to each other [6]. Since SiC substrates are already widely used in practice, it allows one to suggest, that the use of SiC as a substrate for the growth of AlN/GaN heterostructures looks very promising. Nevertheless, a significant drawback of using single-crystal SiC in the manufacturing of devices is the high price of SiC substrates of good quality and desired polytype. One of the promising types of substrates which solves these problems are substrates of nano-SiC/Si, grown by substitution of silicon atoms to carbon atoms [7] directly in the silicon substrate. In fact, the authors of that work for the first time in world practice implemented method of successive substitution of carbon atoms instead of native silicon atoms right inside the substrate without destroying its crystalline structure. The method resembles the "genetic synthesis" of protein structures in biology. The quality of SiC thin film obtained by this method are far superior than quality of films grown on silicon substrates by conventional methods. The method is simple and cheap, and the presence of pores beneath the surface of SiC allows to overcome the mechanical stresses resulting from the lattice mismatch. Thus the study of the method [7] is prospective for the development of thin film technology.