Advanced Statistical Process Control of Critical PECVD SiNx Thin Films

D. Wolfe, F. Li, M. Chen, Y. Yang, D. Wang, D. Hou and F. Monzon
Global Communication Semiconductors, Inc.
23155 Kashiwa Court, Torrance, CA 90505

Keywords: SPC, PECVD, SiNx, MIM_CAP, Breakdown Voltage, HBT.


From a process & equipment engineering perspective, maintaining ultra-tight control over Metal-Insulator-Metal Device Capacitor (MIM_CAP) variability, and hence tight wafer-to-wafer and lot-to-lot insulator film property control, is a key challenge. To understand MIM_CAP pF trending, advanced Statistical Process Control (SPC) techniques were applied to critical Plasma-Enhanced Chemical Vapor Deposited (PECVD) Silicon Nitride (SiNx) MIM_CAP thin-films within the GCS high-performance Heterojunction Bipolar Transistor (HBT) product flow.
Thickness & refractive index trend data over large time periods were filtered & analyzed based on Central Limit Theorem considerations, and correlations were made to MIM_CAP. Based on these findings, the SiNx thickness process control limits were fine-tuned and MIM_CAP variation, as calculated using Cpk, showed a marked improvement from 0.47 to 1.02.
Additional sources of variability, e.g. non-linearity in C vs. thickness analysis shown in Fig 2, will be discussed theoretically and directly correlated to low-frequency (LF) oscillations within the refractive index vs. time SPC trend charts.
Breakdown Voltage data correlations (not shown) will also be discussed.

Paper 6a.2.pdf