| 초록 |
During the past two decades, there has been a significant paradigm shift in FLASH Devices. Specifically, after 24nm device structure, there has been a big change for the planer structure to the 3D V-NAND structure. As the height of the ON stack used in 3D V-NAND increases, the W/L’s gapfill and stress control have become difficult to maintain. Accordingly, the LFW (Lower Florin Tungsten) film deposition method used in W/L changed to utilizing the ALD method instead of CVD once the height becomes over 64 stacks. As the ON Stack height increases, due to wafer warpage issue, there are potential problems in the following steps. Specifically, at the key align process of the PHOTO and ETCH step’s, there are big issues that arise. As-deposited LFW film’s warpage control needs to be controllable for stress because it’s a key main factor in 3D NAND W/L. LFW film stress with over the 2.0Gpa at CVD deposited can’t be used due to high stress, Film stress with about 1Gpa~0.5Gpa at conventional ALD is limited for N+1 device. In order to resolve the stress problems on LFW Film, the conditions of nucleation and purge method. LFW Film and main bulk LFW film deposition must be optimized, Combining such a deposition conditions and modified hardware, LFW thin film with neutral stress (100Mpa ~ -200Mpa) was created. Here, the new carrier gas is added to help control the stress. Through SIMS analysis method, the LFW bulk film’s F-concentration showed under 1/1000 (＜3.87E+17) compared to the CVD method (＞1.13E+20), as well as lower resistivity ( ＜20 μΩ-㎝) and roughness of ＜20A. This is analyzed using SEM, XRD, AFM, and TEM. Nucleation’s thickness, temperature and SIH4-W or B2H6-W gas base nucleation film is also very important. In order to prevent wafer backside deposition, edge gas control is critical, and for future devices, MO-W, FFW and new precursor, etc development seems highly necessary. |
