Study on defect annealing potential and bulk micro defect formation using high temperature RTA conditions for Cz‐grown silicon

Abstract

In this paper, the key parameters of a rapid thermal annealing (RTA) nitriding step are discussed with respect to vacancy‐ and oxygen precipitate (BMD)‐profile formation. These RTA key performance parameters are the maximum NH3 dissociation temperature (i), the temperature stability of the stored vacancy peak (ii), and the defect dissolution capability of self Si agglomerates at elevated temperatures (iii). This parameter study could be helpful for a future model of the vacancy in‐diffusion process into the Si near surface region. Especially the gate oxide integrity (GOI) is an important parameter to establish long life cycles in current memory devices. After NH3 RTA processing, it was surprisingly found that the GOI defect level is still influenced by small‐sized grown in particles. It is demonstrated that a complete restoration toward a high GOI signal can be achieved via a 1300 °C RTA step. The gate oxide integrity is afterwards as good as observed on a defect free polished CZ wafer.

Simulation of Nitrogen Indiffusion and Its Impact on Silicon Wafer Strength

“…The process consists of three steps to simulate the effect on nitrogen indiffusion via prenitridation (step 1), active nitridation (step 2), and vacancy outdiffusion to create a near‐surface‐defect‐free zone. [ 12 ] In step 1, the nitridation was conducted in the beginning at low temperatures and then the temperature was raised to a level >1200 °C to let nitrogen atoms, stored in the oxynitride film, effectively diffuse into the wafer. In step 2, the temperature was deceased below 1200 °C to actively nitride the surface furthermore in a mixed atmosphere of argon/NH 3 at optimized conditions.…”

Near‐Surface Defect Control by Vacancy Injecting/Out‐Diffusing Rapid Thermal Annealing

“…The described model was applied to different sizes of grown‐in octahedral BMDs and a temperature ramp which starts at 600 °C and ramps with 70 K s −1 to the soak temperature. To avoid slip at high temperatures, the ramp‐down rate from maximum temperature to 1200 °C is limited to 20 K s −1 and thereafter to 50 K s −1 down to 600 °C . An example for the results of RTA in a 100% Ar ambient is given in Figure .…”

“…The described model was applied to different sizes of grown-in octahedral BMDs and a temperature ramp which starts at 600 C and ramps with 70 K s À1 to the soak temperature. To avoid slip at high temperatures, the ramp-down rate from maximum temperature to 1200 C is limited to 20 K s À1 and thereafter to 50 K s À1 down to 600 C. [9] An example for the results of RTA in a 100% Ar ambient is given in Figure 3. The RTA process temperature was 1290 C and the soak time was 15 s. The graphs show the evolution of the depth-dependent side length of octahedral BMDs with 13, 14, and 15 nm grown in sizes.…”

“…The influence of the point‐defect formation in RTA at different applied ambient was investigated earlier and is partly used as a starting point of this simulation work . In the pioneering work of Falster et al, they reported an enhanced vacancy formation and storing in the wafer bulk by RTA at temperatures between 1100 and 1280 °C and consecutive rapid cooling.…”

“…The influence of the point-defect formation in RTA at different applied ambient was investigated earlier and is partly used as a starting point of this simulation work. [9] In the pioneering work of Falster et al, [10,11] they reported an enhanced vacancy formation and storing in the wafer bulk by RTA at temperatures between 1100 and 1280 C and consecutive rapid cooling. This excess of vacancies can be used for an improved oxygen precipitation formation and a denuded zone is built-in automatically via the near-surface out-diffusion of vacancies via cooling down.…”