NDLI: Modeling and algorithm development for automated optical endpointing of an HBT emitter etch

Content Provider	Springer Nature Link
Author	Hanish, C. K. Grizzle, J. W. Chen, H. H. Kamlet, L. I. Thomas, S. Terry, F. L. Pang, S. W.
Copyright Year	1997
Abstract	This paper discusses the development of a high-accuracy endpointing algorithm for the emitter etch of a heterojunction bipolar transistor (HBT). Fabrication of high-performance HBTs using self-aligned base-emitter processes requires etching through the emitter layer and stopping with very high accuracy on the base layer. The lack of selectivity in dry etching coupled with the high etch rates possible in high density plasmas render the use of a standard timed overetch impractical, especially as device layers continue to become thinner. The etch process under study requires the complete removal of an AlInAs emitter while etching no more than 5 nm of the underlying GaInAs base layer. Etch products are monitored using optical emission spectroscopy (OES) to determine etch endpoint. The process under study relies on the intensity of the 417.2 nm Ga emission line. The detection of the Ga line indicates that the etch has reached the GaInAs layer. However, the presence of a time-varying Ga baseline signal before endpoint and significant noise in the OES signal necessitate more than a simple threshold scheme for critical endpoint detection. The algorithm presented here is based on a generalized likelihood ratio with a signature function. This algorithm is robust to variance in the optical gains of the measurement equipment and is applicable to other etch processes. Experimental results of automated endpointing using this algorithm are presented in the form of pre- and post-etch ex situ film thickness measurements.
Starting Page	1401
Ending Page	1408
Page Count	8
File Format	PDF
ISSN	03615235
Journal	Journal of Electronic Materials
Volume Number	26
Issue Number	12
e-ISSN	1543186X
Language	English
Publisher	Springer-Verlag
Publisher Date	1997-01-01
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	InP heterojunction bipolar transistor (HBT) optical emission spectroscopy selective etch Optical and Electronic Materials Characterization and Evaluation of Materials Electronics and Microelectronics, Instrumentation Solid State Physics and Spectroscopy
Content Type	Text
Resource Type	Article
Subject	Materials Chemistry Electronic, Optical and Magnetic Materials Condensed Matter Physics Electrical and Electronic Engineering

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