Sensitivity Analysis of Process Parameters on Deposition Quality and Multi-Objective Prediction in Ion-Assisted Electron Beam Evaporation of Ta2O5 Films

TL;DR

This study optimizes the deposition of Ta2O5 films for high-power lasers by analyzing process parameters and predicting film quality using a Bayesian approach.

Contribution

A novel PI-BO method is proposed for small-data prediction of deposition quality in ion-assisted electron beam evaporation.

Findings

The PI-BO method achieves high prediction accuracy for refractive index and surface roughness of Ta2O5 films.

Voltage (V) and O2 flow rate (Q2) are identified as the most influential parameters for regulating deposition quality.

Optimal ranges for V and Q2 are determined as 600~700 V and 70~80 sccm, respectively.

Abstract

Tantalum pentoxide (Ta2O5) films deposited on fused silica substrates are critical components of high-power laser systems. Ion-assisted electron beam evaporation (IAD-EBE) is the mainstream technique for fabricating Ta2O5 films. However, it commonly requires extensive experimental efforts for deposition quality optimization, while each coating cycle is extremely time-consuming. To solve this issue, this work establishes a dataset targeting the surface roughness (Rq) and refractive index (n) of Ta2O5 films using atomic force microscopy, as well as ellipsometer and deposition experiments. Influence of assisting ion source beam voltage (V)/current (I) and Ar (Q1)/O2 (Q2) flow rate on the n and Rq of Ta2O5 films are analyzed. Combining energy-field mechanism analysis with a Bayesian optimization approach (PI-BO), both deposition quality prediction and feature analysis of process parameters are achieved. The determination coefficient/mean absolute error for the prediction models of n and Rq reach 0.927/0.013 nm and 0.821/0.049 nm, respectively. Based on sensitivity analysis, the weight factors of V, I, Q1, and Q2 affecting n/Rq of Ta2O5 films are determined to be 0.616/0.274, 0.199/0.144, 0.113/0.582, and 0.072/0.000. V and Q2 are identified as the core factors for regulating deposition quality. The optimal ranges for V and Q2 are 600~700 V and 70~80 sccm, respectively. This study proposes a PI-BO method for predicting Rq and n of Ta2O5 films under small-data conditions, while determining the preferred parameter ranges and their sensitivity weight factors. These findings provide effective theoretical support and technical guidance for IAD-EBE strategy design and optimization of optical films in high-power laser systems.

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