TWO DIMENSIONAL (2D) DOPING PROFILE IN PATTERNED InP/InGaAs LAYERS USING PLASMA FOCUSED ION BEAM (PFIB)
2Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa, Israel, Israel
Doping is an important process in semiconductor technology since the performance of the semiconductor devices depend on their doping concentration and distribution. The common methods for dopant profiling like Secondary Ion Mass Spectrometry (SIMS) and Electrochemical Capacitance Voltage (ECV) can provide only the depth profile. With scaling down the semiconductor devices, the lateral doping profile is becoming as critical as the depth. Therefore, for process development, control and failure analysis there is a need for an analytical method that enables site-specific 2D doping profiles with high resolution, throughput and reliability. Hence, it would be advantageous to utilize scanning electron microscopy, which is widely used in the semiconductor industry.
In the Secondary Electron (SE) image, the p-n junction is visible with the p-type brighter than the n-type [1]. The SE top view image presents only the lateral diffusion. In order to measure the depth it is necessary to cleave the sample. As the pattern becomes smaller, site-specific cleavage is difficult and cleaving is destructive to the wafer production. Focused Ion Beam (FIB), has the ability to create site-specific cross-sections. However, Ga+ milling, even at low energies, reduces the attainable contrast to levels insufficient for reliable and sensitive analysis because of the surface amorphisation damaged layer and Ga implantation, which in turn modifies the electrical properties and crystallinity [2, 3]. Ion implantation can be eliminated by using Xe+ milling. Hence, Plasma FIB can be a promising technique for site-specific 2D dopant profiling in semiconductor devices. An additional benefit of this analysis is that it can be performed on patterned wafers and real devices for both process control and failure analysis.
Most of the reported work on 2D dopant profiling has been carried on blank Si wafers by using Ga+ FIB. Very few studies were performed on compound semiconductors like InP [4]. There are no reported works on the use of plasma FIB.
This work presents the use of Xe+ plasma dual beam FIB, for 2D dopant profiling in patterned InP/InGaAs wafers. The milling steps enabling the p and n-type contrast values similar to cleaved samples will be presented and discussed.
Acknowledgment: The authors would like to acknowledge, advice and technical support from Thermofisher Scientific, Eindhoven NanoPort
References:
1. C.P. Sealy, M. R. Castell and P. R. Wilshaw, "Mechanism for secondary electron dopant contrast in the SEM", Journal of Electron Microscopy, 49(2), 311-321 (2000).
2. P. Kazemian, A. C. Twitchett, C. J. Humphreys, et al. "Site-specific dopant profiling in a scanning electron microscope using focused ion beam prepared specimens", Appl. Phys. Lett. 88, 212110 (2006).
3. Augustus K.W. Chee, "Unravelling new principles of site-selective doping contrast in the dual-beam focused ion beam/scanning electron microscope", Ultramicroscopy 213, 112947 (2020).
4. Daisuke Tsurumi, Kotaro Hamada, and Yuji Kawasak, "Observation of two-dimensional p-type dopant diffusion across a p+ InP/n– InGaAs interface using scanning electron microscopy", Journal of Applied Physics 113, 144901 (2013).