PHOTOELECTRON SPECTROSCOPY APPLICATIONS TO SEMICONDUCTORS

Since its introduction into the modem world of chemical analysis methods 1 K. Siegbahn, et al (1), photoelectron spectroscopy has become an increasingly important method for studying semiconductor surfaces. Not only is it widely emplc ed as a surface analytic method but also it finds wide application in chemically characterizing layered structures and interfaces which are important to semiconductor device manufacture. In this tutorial paper, a brief outline of the photoemission experiment will be presented. Modern instrumentation employed in semiconductor characterization will be surveyed and examples will be discussed which demonstrate the power of photoelectron spectroscopy in characterizing semiconductors and semiconductor device structures. 

The purpose of this chapter Is to discuss the principles of photoelectron spectroscopy and Its applications In the semiconductor and microelectronics Industries. Other recent reviews (5-10) have dealt with the use of XPS, AES, SIMS and ISS for failure analysis and materials characterization for these and related Industries. 

Among the related methods, specific experimental designs for applications are emphasized. As in-system synchrotron radiation photoelectron spectroscopy (SRPES) will be applied below for chemical analysis of electrochemically conditioned surfaces, this method will be presented first, followed by high-resolution electron energy loss spectroscopy (HREELS), photoelectron emission microscopy (PEEM), and X-ray emission spectroscopy (XES). The latter three methods are rather briefly presented due to the more singular results, discussed in Sections 2.4-2.6, that have been obtained with them. Although ultraviolet photoelectron spectroscopy (UPS) is an important method to determine band bendings and surface dipoles of semiconductors, the reader is referred to a rather recent article where all basic features of the method have been elaborated for the analysis of semiconductors [150]. 

The application of photoelectron spectroscopy to semiconductors euid semiconductor device structiires has been demonstrated through its application to the silicon dioxide-silicon interface, ni-V compound semiconductor metal jimctions, and plasma etching residues. Through the use of profiling methods, chemical depth profiles are obtained and are extremely useful to device structural studies. Many methods such as in-situ film growth, film deposition, air-lock mounted pretreatment chambers, etc., have been employed to study semiconductor surfaces and device structures. 

As demonstrated by Heath et al., application of the LB technique in conjunction with semiconductor nanoparticies may lead to the generation of tunnel diodes [60]. These devices consist of a monolayer of 3.8 nm CdSe nanocrystals and an insulating bilayer of eicosanoic acid, sandwiched between an Au and an Al electrode. Advanced spectroscopic techniques such as attenuated low-energy photoelectron spectroscopy were also applied to LB-derived multilayered nanostructured assemblies of differently sized CdS particles [61]. Recent examples of applications of the LB technique... 

The results illustrated in this contribution clearly demonstrate the potential of DUV-FUV spectroscopy as a novel investigation method for the electronic states of various materials. Now, we are applying this method not only to T1O2 but also to other materials (other semiconductors such as ZnO, organic phosphates, ion liquids, and so on). It is also important to confirm the electronic changes by other methods such as X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), which is in progress. The application of this method provides critical information about the enhancement mechanism and supports the development of high-efficiency optical materials such as photocatalysts and solar cells. 

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