###### Abstract  
Laser thermal annealing (LTA) has played an important role in the fabrication of scaled semiconductor devices by reducing the heat budget of the dopant activation process. During the laser annealing of entire wafer areas, the beam scanning pattern and overlap ratio have significant effects on uniform heating during the process. In this study, a numerical simulation of the LTA process was carried out using a three-dimensional transient heat transfer model. The temperature distribution produced by different laser scan paths and beam overlap ratios was analyzed. Additionally, the behavior of the dopant (phosphorus) diffusion induced under the multipath and beam overlapping conditions was numerically investigated. According to the simulation result, a zig-zag pattern generated hot spots around the corner areas of the beam path due to the greater heat accumulation per unit area; however, a bidirectional pattern induced cold spots due to the absence of laser heating around the corner areas. It was also found that the maximum temperature reachable in the beam overlapped region was much lower than that obtained along the beam scanning path, and the most uniform heating could be obtained when the zig-zag pattern and a 50% overlap ratio were used. According to the dopant diffusion and concentration distribution predicted for the case of the zig-zag pattern and 50% overlap ratio, the difference in the dopant diffusion length was approximately thirty times within the scanned area. laser thermal annealing (LTA); numerical simulation; dopant activation; temperature distribution; multipath; beam overlap +
Footnote †: journal: Applied Sciences  
1  
(c) 2021  
(d) 2021  
(e) 2021  
been developed. An advantageous feature of MSA is that only the surface region of the wafer is heated to a high temperature while the temperature of the remaining bulk area of the wafer remains significantly lower, acting as a heat sink for thermal energy [8; 9; 10]. This mechanism rapidly dissipates the heat of the annealed region through conduction heat transfer, thus limiting dopant diffusion. [PERSON] et al. [11] reported experimental results of dopant activation and diffusion behavior for both standard RTP and FLA. It was found that the FLA method formed an ultra-shallow junction (USJ) without significant dopant diffusion. However, for FLA, radiation heat from the lamp is transferred throughout the wafer. If there is a very large temperature (usually hundreds of degrees) difference between the front and back surface of the wafer, severe wafer warpage resulting in breakage of the wafer can arise [12]. On the other hand, the heat in LTA is only confined to local and shallow surface regions of the wafer; hence, there is no warpage of the wafer when using this process. This characteristics of the laser radiation also allow reducing thermal effects in other laser-based processes [13; 14]. To date, various studies of dopant activation by LTA have been conducted. [PERSON] et al. [15] studied the activation and diffusion of As in SiGe/Si heterostructure layers during an excimer laser annealing process. It was found that SiGe layer melting was necessary to achieve low sheet resistance and high dopant activation. However, the melting induced more dopant diffusion into the bulk region. [PERSON] et al. [16] compared the effects of LTA and RTP on the dopant activation outcome in phosphorus-doped Ge. It was found that the activated carrier concentration increased by approximately 270% when LTA was used. [PERSON] et al. [17] reported laser spike annealing (LSA) using a CO\({}_{2}\) laser as a light source. According to their study, the LSA process produced better electrical performance (i.e., a larger drain current and lower sheet resistance) of a CMOS device compared to RTP owing to the higher heating temperature and shorter annealing time. It was also found that the LSA could achieve good heating uniformity without the need for additional layers.