Photoelectron Emission Microscopy (PEEM)

The PhotoElectron Emission Microscope (PEEM) is a novel microscope that has several features that may be useful for failure analysis, dopant profiling, as well as being a diagnostic tool for Si. PEEM is a non-scanning technique that has a nominal spatial resolution of 80 nm, in addition to a large field of view (200 mm) that allows video rate analysis.  Thus, this technique offers high spatial resolution and good temporal resolution necessary for practical inspection of large areas of devices.  Perhaps more importantly, PEEM has unique contrast mechanisms that are relevant to device characterization.

The PEEM technique floods the sample under study with ultraviolet light from a conventional mercury arc lamp. The illumination stimulates electron emission from the sample and the applied electric field draws the electrons into a focusing column.  The final image is then formed on a phosphorus screen where the data is recorded with a CCD camera (click to see System Hardware).

 To understand how contrast mechanisms, individually and in combination, produce a PEEM image, we have performed both theoretical and experimental studies on simple device models.  Theoretical studies, which include models based on standard surface science ideas along with numerical simulations of the microscope, are being used to establish a quantitative basis for PEEM image interpretation.  Models of samples with regions of different photothreshold, vertical structure and lateral fields have been constructed.  Experimentally, a number of devices have also been designed and fabricated in-house to investigate the contrast mechanisms individually.  The results from each approach have been used together to investigate how information may be extracted from PEEM images of device samples.

We have applied the technique to several integrated circuit analysis tasks.

Quantifying Si dopant levels

We have quantified how varying levels of dopant in silicon correspond to degrees of image contrast, based on the principle that less photon energy is needed to stimulate electron emission from silicon with higher dopant concentrations.

  Voltage contrast

In addition, we can generate edge contrast in isolated structures by applying voltages, and view metal structures buried by oxide.

Relevant Publications

K. Siegrist, V. W. Ballarotto, M. Breban, R. Yongsunthon, E. D. Williams, Imaging Buried Structures Using Photoelectron Emission Microscopy, Appl. Phys. Lett. 84, 1419 (2004). 

K. Siegrist, E.D. Williams and V.W. Ballarotto, Characterizing Topography-Induced Contrast in Photoelectron Emission Microscopy, J. Vac. Sci. Technol. A 21(4), 1098 (2003). 

V.W. Ballarotto, M. Breban, K. Siegrist, R.J. Phaneuf and E.D. Williams, Photoelectron Emission Microscopy of Ultra-Thin Oxide Covered Devices, J. Vac. Sci. Technol. B 20, 2514 (2002). 

V.W. Ballarotto, K. Siegrist, R.J. Phaneuf and E.D. Williams, Model for Doping-Induced Contrast in PEEM, J. Appl. Phys. 91(1), 469 (2002). 

V.W. Ballarotto, K. Siegrist, E.D. Williams and W. Vanderlinde, A Study of Photoelectron Emission Microscopy Contrast Mechanisms Relevant to Microelectronics,  2002 ISTFA Conference Proceedings. 

V.W. Ballarotto, K. Siegrist, R.J. Phaneuf, E.D. Williams, W.-C. Yang and R.J. Nemanich, Photon Energy Dependence of Contrast in Photoelectron Emission Microscopy of Si Devices, Appl. Phys. Lett. 78(22), 3547 (2001). 

S. Aggarwal, S.B. Ogale, C.S. Ganpule, S.R. Shinde, V.A. Novikov, A.P. Monga, M.R. Burr, R. Ramesh, V. Ballarotto and E.D. Williams, Oxide Nanostructures through Self-Assembly, Appl. Phys. Lett. 78(10), 1442 (2001). 

V.W. Ballarotto, K. Siegrist, R.J. Phaneuf, E.D. Williams, and S. Mogren, PEEM Imaging of Dopant Contrast in Si(001), Surface Science 461, L570-L574 (2000). 

S. Aggarwal, A.P. Monga, S.R. Perusse, R. Ramesh, V. Ballarotto, E.D. Williams, B. R. Chalamala, Y. Wei, R.H. Reuss, Spontaneous Ordering of Oxide Nanostructures, Science 287, 2235 March (2000).