Phenomenological Single-Particle
Modeling of Reactive Transport
in Semiconductor Processing
4.5 Atomic Layer Processing for Novel 3D
Memory Technologies
One key technology which can be unlocked by the continuing development of thermal ALP is the 3D integration of novel memories [143]. The ongoing success of 3D NAND flash memory demonstrates that it is possible to create a charge storage structure — whether a charge trap or a floating gate — in a vertical 3D stack without relying on planar technology [105]. This stacking has enormously increased the density of memory technology, therefore, similar ideas can be applied to novel memory technologies such as resistive random-access memory (ReRAM) [166]. To enable the patterning of these sophisticated material stacks at the sidewalls of a high AR structure, conformality in thermal ALP will have to be taken to its limits. Topography modeling can be an invaluable tool in this development by providing insight into the reactive transport issues limiting conformality, as well as enabling the investigation and simulation of devices with realistic shapes.
To aid the development of new 3D memory technologies, Fischer et al. from Lam Research have developed a 3D NAND-like test structure and used it to investigate thermal ALD and ALE [149]. These structures are
oxide-nitride (ON) stacks with either 76 or 98 ON pairs, to a maximum height of
The material chosen to be investigated on the test structure is hafnium oxide (HfO2) which is a promising material for novel memory technologies [166]. It was deposited using thermal ALD from
H2O and an undisclosed hafnium-based reactant [149], achieving a
Having demonstrated ALD of the investigated HfO2, the next step in the development of thermal ALP is the establishment of an etching method. Fischer et al. propose thermal ALE of HfO2 from dimethylaluminum chloride (DMAC) and HF [149], following a similar ligand-exchange reaction to that from Eqs. (4.3) and (4.4). They thoroughly investigate the necessary DMAC dosing by exploring two different reactors: Low-pressure and high-pressure. Several reactor conditions were investigated, extracting an EPC profile from TEM measurements for each experiment.
The low-pressure reactor experiments were performed at
The high-pressure experiments performed etching at
Nonetheless, reactive transport modeling can be used to further characterize and fine-tune this process. This is achieved by applying the model described in Section 4.2
assuming the DMAC is the limiting reactant. It has been reported that the HF dose has only a very slight impact in the EPC profile [149], therefore, it is reasonable to assume that the process is DMAC-limited. The effects of
HF are captured by a global reduction in the maximum EPC which is extracted from each experiment. The simulated EPC profiles are obtained by dividing the etch depth at each
Given the complex fluorination and ligand-exchange chemical process,
Due to the comparatively higher noise of TEM data in comparison to the optical profilometry reported in Section 4.4, the calibrated simulations in Fig. 4.12 demonstrate only qualitative agreement. Nonetheless, the parameters reported in Tab. 4.4 already enable a preliminary
analysis. They enable a first estimation of
Even though the obtained results are qualitative in nature, they already show a path for the investigation of device performance. The entire 3D NAND-like stack from [149] has been simulated using Silvaco’s Victory
Process [55], shown in Fig. 4.13. Both the ON deposition and the RIE are assumed to be ideal and are thus geometrically modeled. The thermal ALP of HfO2 is
modeled with the presented reactive transport model implemented in the Open Model Library. For the ALD step, the parameters from Tab. 4.3 are used. From the multiple
reported thermal ALE conditions, the low-pressure, high HF dose, and the