Heavily boron-doped effect on the etch rates of <111> single-crystal silicon in TMAH solutions

The purpose of this paper is to study the heavily boron-doped effect on the etch rates of boron-doped <;111> single-crystal silicon in different TMAH solutions. The boron atoms were heavily doped in <;111> single-crystal silicon by using diffusion process. We change the pre-deposition time and annealing time of diffusion process to form different concentration distributions. The samples were pre-deposited at 1100°C and driven in at 1100°C to create relatively flat doping profiles with about 2 μm depth. In this study, we have investigated the etch-stop properties of heavily boron-doped silicon in 5% TMAH solution and 5% dual-doped TMAH solution at different process temperatures. In our work, the etch selectivity of undoped <;111> silicon to boron-doped <;111> silicon is 15:1 as the diffusion process is under the pre-deposition time of 90 minutes and the drive-in time of 60 minutes. The undoped <;100>/ boron-doped <;111> silicon etch selectivity can be achieved to about 260. In this work, the suspended structures of <;111> silicon layers were successfully manufactured by using <;111> silicon substrate in a dual-doped TMAH solution. The suspended structures have high filled factor, large area and long legs. The large area of a device could increase the radiated power of a micro heater to enhance thermal radiation and raise infrared absorption of an infrared sensor to improve the output signal of the sensor. The long legs can reduce the thermal conductance of a thermal sensor to promote the sensitivity of the sensor. The applications of the suspended structures include gas sensors, flow meters, pressure sensors, micro heaters, infrared sensor, etc.