Photon emission microscopy (PEM),

Photon Emission Microscopy (PEM),
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Photon emission microscope (PEM) uses the principle of electron-hole recombination from defects and/or structures. Figure 4913a shows the typical optical system of a PEM in the reflection imaging mode. During photon emission imaging, the filter and the beam splitter are moved out of the optical axis for optimum sensitivity.

Typical optical system of a PEM in the reflection imaging mode

Figure 4913a. Typical optical system of a PEM in the reflection imaging mode. [2]

For PEM measurements, the most important performance parameter is sensitivity, which depends on:
         i) the wavelength,
         ii) the camera detectivity,
         iii) the optics,
         iv) other sources of noise in the system.
Although PEM systems have been commercially available and are widely used in microelectronic failure analysis, there is no known practical and reliable method to quantify their sensitivity. Operators often use their own failed IC chips, usually not reproducible from lab to lab, to estimate the comparative sensitivity performance of such systems. [2]

Range of wavelength sensitivity

Figure 4913b. Detected wavelengths of OBIRCH, PEM, and LIT measurements. [1]

Table 4913. Comparisons of accuracies of fault localization with PEM technique and other techniques.

Fail device	LIT			PEM			Fault verification technique	Example
Fail device	Accuracy	Misidentified device	Reason of misidentification	Accuracy	Misidentified device	Reason of misidentification	Fault verification technique	Example
Short between nets	100%	N/A	N/A	0%	NMOS transistor	NMOS is turned on by shorting	Optical microscopy and FIB	page4912
Poly capacitor inside a regulator	33%	Unknown	Unknown	0%	Unknown	Unknown	Optical microscopy	page4911
Short through gate oxide in a trransistor: Identified common hotspots between LIT and PEM	33%	Transistors	Direct connection to the gate of the failing PMOS transistor	33%	Transistors	Secondary effect of the gate signal of the failed PMOS transistor	FIB	page4916

Accuracy = (total hotspots-over-counted locations)/total hotspots (%)

The photon emission is normally blocked by the thick front metallization, even though it penetrates the thin barrier metal to reach the PEM detector. [3] Therefore, in some cases, frontside photon emission is used, while in other cases, backside photon emission is needed.

The inaccuracy of the defect localization can occur due to some reasons. For instance, the open defects exhibit characteristic phenomena of inducing photoemissions from overdriven transistors due to undesired voltage applied to the controlled gate from the high resistance connecting path. [4] Although, these saturated transistors should exhibit certain level of leakages through the VDD and ground, the combine leakages from several saturated transistors may not be detectable from curve tracing if the failures are not gross.


(a)	(b)

[1] Paul Hubert P. Llamera and Camille Joyce G. Garcia-Awitan, Thermal Failure Analysis of Functional Failures by IR Lock-in Thermal Emission, ISTFA™ 2019: Conference Proceedings from the 45th, (2019).
[2] JCH Phang, DSH Chan, SL Tan, WB Len, KH Yim, LS Koh, CM Chua, and LJ Balk, A Review of Near Infrared Photon Emission Microscopy and Spectroscopy, Proceedings of 12th IPFA 2005, Singapore.
[3] Abul Khair Yahya, Nik Tajuddin Yusof, Yusnani Mohamad Yusof, Noble Failure Analysis Procedure for Trench MOSFET Technology Devices Through Detail Electrical Parameter Characterization and Unique Fault Isolation Technique, 2012 19th IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits, DOI: 10.1109/IPFA.2012.6306269, (2012).
[4] A. C. T. Quah, G. B. Ang, D. Nagalingam, C. Q. Chen, H. P. Ng, S.P. Neo, J. Lam, Z.H. Mai, Failure Analysis Methodology on Resistive Open Defects, ISTFA 2014: Conference Proceedings from the 40th International Symposium for Testing and Failure Analysis, November 9–13, 2014, Houston, Texas, USA.

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