In this article, we propose the development
of a recurrent neural
network (RNN)-based model predictive controller (MPC) for a plasma
etch process on a three-dimensional substrate using inductive coupled
plasma (ICP) analysis. Specifically, the plasma etch process is simulated
by a multiscale model: (1) A macroscopic fluid model is applied to
simulate the gas flows and chemical reactions of plasma. (2) A kinetic
Monte Carlo (kMC) model is applied to simulate the etching process
on the substrate. Subsequently, proper orthogonal decomposition (POD)
is used to derive the empirical eigenfunctions of the plasma model.
Then the empirical eigenfunctions are utilized as basis functions
within a Galerkin’s model reduction framework to compute a
low-order system capturing dominant dynamics of the plasma model.
Additionally, RNN is introduced to approximate dynamics of both the
reduced-order plasma system and the microscopic etch process. The
training data for the RNN models are generated from discrete sampling
of open-loop simulations. A probability distribution function is also
involved to present the stochastic characteristic of the kMC model.
The trained RNN models are then implemented as the prediction model
in the development of MPC to achieve desired control objectives. Closed-loop
simulation results are presented to compare the performance of the
model predictive controller and a proportional-integral (PI) controller,
which show that the proposed MPC framework is effective and exhibits
better performance than does a PI controller.