Atomic‐Layer‐Deposited Al<sub>2</sub>O<sub>3</sub> as Effective Barrier against the Diffusion of Hydrogen from SiN<sub><i>x</i></sub>:H Layers into Crystalline Silicon during Rapid Thermal Annealing
Lailah Helmich, Dominic Walter, Dennis Bredemeier, Jan Schmidt
Abstract
Stacks of hydrogen‐lean aluminum oxide, deposited via plasma‐assisted atomic‐layer‐deposition, and hydrogen‐rich plasma‐enhanced chemical vapor‐deposited silicon nitride (SiN x ) are applied to boron‐doped float‐zone silicon wafers. A rapid thermal annealing (RTA) step is performed in an infrared conveyor‐belt furnace at different set‐peak temperatures. The hydrogen content diffused into the crystalline silicon during the RTA step is quantified by measurements of the silicon resistivity increase due to hydrogen passivation of boron dopant atoms. These experiments indicate that there exists a temperature‐dependent maximum in the introduced hydrogen content. The exact position of this maximum depends on the composition of the SiN x layer. The highest total hydrogen content, exceeding 10 15 cm −3 , is introduced into the silicon bulk from silicon‐rich SiN x layers with a refractive index of 2.3 (at λ = 633 nm) at an RTA peak temperature of 800 °C, omitting the Al 2 O 3 interlayer. Adding an Al 2 O 3 interlayer with a thickness of 20 nm reduces the hydrogen content by a factor of four, demonstrating that Al 2 O 3 acts as a highly effective hydrogen diffusion barrier. Measuring the hydrogen content in the silicon bulk as a function of Al 2 O 3 thickness at different RTA peak temperatures provides the hydrogen diffusion length in Al 2 O 3 as a function of measured temperature.