Silicon carbide (SiC) superjunction (SJ) technology is an attractive proposition to reduce the specific on-state resistance (Ron,sp) of unipolar SiC power devices. Previous works have achieved 800-1700 V 4H-SiC SJ devices using the multi-epitaxial process [1,2]. However, the cost of this method is prohibitively high, the low diffusion coefficient of 4H-SiC limiting each epitaxy/implantation repeat to approximately 1 µm of growth. Trench filling epitaxy (TFE), whereby trenches are etched into n-type 4H-SiC and subsequently refilled with p-type 4H-SiC through a partially selective epitaxial process, can overcome these limitations. However, many challenges must be overcome with this technology, including the etching artifacts of 4H-SiC trenches, the morphology change of 4H-SiC trenches by unintentional H2 annealing before growth, and the formation of voids within the refill regions. Here, we report an in-depth process and characterization of 4H-SiC TFE at a reduced growth temperature of 1550 °C with TCS+C2H4+HCl “over” chlorinated chemistry and investigate the influence of various growth parameters including Si/Cl ratio, trench aspect ratio, trench sidewall angle and misalignment to the [112 ̅0] offcut direction. 4H-SiC substrates were coated in 500 nm of SiO2 before a hard mask of Ni was patterned onto the surface via photolithography, sputtering and lift-off. Trenches of width 2 and 4 µm were etched to a depth of approximately 5 µm using a reaction ion etch (RIE) process using SF6 and Ar with an Oxford Instruments PlasmaPro 100 Cobra system. Following mask removal and RCA cleaning, epitaxy was carried out within an LPE ACiS M8 RP-CVD. The Si and C precursors were trichlorosilane (TCS, SiHCl3) and ethylene (C2H4) respectively. Samples were refilled with approximately 5 µm of 4H-SiC with n-type doping markers introduced at every 1 µm step. Additional HCl was added into the process to control the Si/Cl ratio and influence the trench refill process. Refilled samples were analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (X-TEM). Reducing the growth temperature to 1550 °C is observed to significantly minimize the mesa faceting effects often observed due to H2 annealing. The addition of HCl is shown to have a profound effect on the growth process of the 4H-SiC with an optimal Cl:Si ratio of 10, showing a clear preference to grow on defined crystal planes, see Fig. 1. As a result of more uniform growth, the surface morphology of the overgrown 4H-SiC is improved with additional HCl, resulting in a smoother coalesced surface, see Fig. 1a. The inclusion of doping markers in the 4H-SiC allows the growth rate to be extracted on various surfaces, see Fig. 1b. In the full submission, we will describe the characteristics and a mechanism for the growth in these modes. Increasing HCl flow rate is shown to modify trench growth rates affecting the trench filling percentage, see Fig. 1c. Trench sidewall angle also affects growth rates on different surfaces, see Fig. 1d. To assess the impact of trench orientation, trenches were fabricated at angles θmis of -5° to +5° with respect to the [112 ̅0] crystal direction. Trench refill was observed in all cases, however, the doping markers indicated that the angle θgrowth by which the growth propagated varied with the trench angle, see Fig. 2. θgrowth was found to stay close to 0° over a range of -1.5°< θmis<+1.5° offering a wide process window and tolerance on the fabrication of such trench structures. The trench sidewall angle can be controlled by tuning the dry etch process and the effect of this on 4H-SiC refill is shown in Fig. 3. As one would expect, void formation is more prominent in trenches with steeper sidewalls and can be eliminated at these growth conditions with a sidewall angle of 8°. This work is supported by funding from EPSRC through grant number EP/W004291/1 and by funding from Horizon Europe grant number 101075709.