The Research Of Nanometer Waveguide Fabricated On SOI And The Fabrication Process

SOI(silicon-on-insulator) is a structure of a silica layer buried between a silicon layer and the wafer. The refractive index of silicon is much higher than the refractive index of silica and air, the rib waveguide fabricated on SOI can restrict the optical field in the region with high refractive index, and the restriction at the horizontal direction is small. The high order modes can radiate easily, it will make the rib waveguide be single mode propagation with little transmission loss. Besides, the coupling loss of the rib waveguide and single mode fiber is small. The research on large cross sectional rib waveguide have been reported. In order to decrease the dimension of the device, the research of submicron rib waveguide is more and more important.The waveguide is researched in this article, and we do many experiments trying to find out fabricate process parameter, the following results are obtained:In this paper, we choose the film mode matching method to analysis the effective index, the single mode condition, polarization and transmission loss. With the wavelength of 1310 nm and 1550 nm, change the rib height, the etch depth and rib width can satisfy the single mode, at the same time, the polarization dependence is also good. In the simulation, the rib height of the waveguide is fixed, while the etch depth is kept constant. The rib width is increased by steps of 10 nm, at first, the waveguide is cut off. With the width increase, TE0 appears first, keep it increased, the following modes are TM0, TE1 and TM1. The boundary of single mode is between TM0 and TE1. Besides, the bend loss is analysed, it is in connection with the rib width, etch depth, wavelength and bend radius.The fabricate of waveguide consist of cleaning, drying, coating photoresist, prebake, exposure, development, post bake, etch and test. In the experiment, MA6 photoresist and RIE etch is used. We will show some photographs of our experiments measured by metallographic microscope, SEM and AFM. And some problems we have met during the experiments.In order to obtain smaller loss, thermal oxidation is a good choice to reduce the surface roughness of the SOI waveguide. Before the thermal oxidation, the root mean square of the surface roughness is over 11 nm. After the thermal oxidation, the SEM figure shows that the bottom of the grating is as smooth as quartz surface, while the AFM shows that the root mean square of the surface is less than 5 nm.