Figure 7. LIST OF ILLUSTRATIONS — (Cont'd) Three-dimensional surface potential map of capacitors Figure 8. ASLEEP micrograph showing dislocation pipes in silicon wafer as denoted by arrows Figure 9. X-ray topograph showing Lomer-Cattrell dislocation networks Figure 11. Energy band diagram for silicon showing the position of the Fermi level, (A) Expected work function values from Fermi level shifts Figure 13. Optical photomicrograph of integrated circuit utilized in the Page 12 13 15 15 16 18 Figure 14. Micrographs of integrated circuit showing specific area analyzed (A) Optical photomicrograph of test circuit (B) ASLEEP image of test circuit 222 21 21 Figure 15. ASLEEP image and Auger spectra of indium phosphide surface after an ASLEEP image and Auger electron spectra of indium phosphide 25 Figure 18. ASLEEP image of indium phosphide prior to oxidation treatment ...... 26 Figure 19. ASLEEP image of indium phosphide after oxidation 27 Figure 20. A comparison of ASLEEP image, SEM image, and scanning Auger 29 Figure 21. ASLEEP image of gallium arsenide wafer showing the effect of two 30 PREFACE This study was carried out at the Naval Research Laboratory as a part of the Semiconductor Technology Program in the Electronic Technology Division at the National Bureau of Standards. The Semiconductor Technology Program serves to focus NBS efforts to enhance the performance, interchangeability, and reliability of discrete semiconductor devices and integrated circuits through improvements in measurement technology for use in specifying materials and devices in national and international commerce and for use by industry in controlling device fabrication processes. The work was supported by the Defense Advanced Research Projects Agency* through the National Bureau of Standards' Semiconductor Technology Program, NBS Order Nos. 501718 and 711782. The contract was monitored by R. L. Raybold as the Contracting Officer's Technical Representative (COTR). Drs. W. M. Bullis and K. F. Galloway provided technical review of this report for the National Bureau of Standards. Certain commercial equipment, instruments, or materials are identified in this report in order to adequately specify the experimental procedure. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the material or equipment identified is necessarily the best available for the purpose. Larger scale drawings of the mechanical parts and detailed listings of the computer programs and subroutines are available on request from the COTR, TECH-A-361, National Bureau of Standards, Washington, DC 20234. *Through ARPA Order 2397. AUTOMATED SCANNING LOW-ENERGY ELECTRON PROBE A. Christou Naval Research Laboratory This report summarizes the results of a three-year effort in the develop- Key words: Automated scanning low-energy electron probe; lateral The scanning low-energy electron probe (SLEEP) is an electron beam probing technique whereby an electron beam is first accelerated (to provide beam definition) and then decelerated by a grid placed in front of the sample to be probed [1]. The sample under investigation is scanned by the electron beam in the retarding field region. Only those electrons whose energies are sufficient to overcome the local sample potential barriers are collected. This collected current is measured in the sample-cathode circuit. Similarly, electrons with insufficient energy to overcome sample surface potential are reflected from the sample and may be collected to form the mirror mode operation. Thus, either the directly collected current or reflected current provides a surface potential map of the sample. In the work reported here, only the collected current mode was utilized. The SLEEP technique is inherently simple. The basic apparatus consists of a low-energy gun structure (800 to 900 V) and a standard vidicon electromagnetic beam focusing and deflection system. Depending on the type of data, precision, accuracy and detail required, control and collection can be carried out by manual techniques or by minicomputer. Similarly, depending on the sophistication of the measurement required, vacuum equipment may range from the rudimentary (10-6 torr) to the more advanced oil-free ultra-high vacuum (10-11 torr). In the present investigation a Data General Nova 800 computer has been interfaced to the scanning low-energy electron probe to control data collection and signal processing, thus forming an Automated Scanning Low-Energy Electron Probe (ASLEEP) system. An ultrahigh vacuum system was also utilized in order to provide for a contamination free system. Figure 1 shows the vacuum system for the ASLEEP experiments while figure 2 shows the computer and interface electronics. The ASLEEP experiments have been designed to explore |