A Beem Study of PtSi Schottky Contacts on Ion-Milled Si
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ABSTRACT Ballistic electron emission microscopy (BEEM) and deep level transient spectroscopy (DLTS) have been used to study the effects of substrate damage introduced by an ion-milling process in PtSi/n-Si Schottky contacts. Argon ions with well-defined energies of 300, 500, 700, 1000, 1500 eV were used to sputter n-type Si substrates in an ion beam sputtering system before metal deposition and silicide formation. Histograms of the PtSi/n-Si Schottky barrier height (SBH) measured by BEEM show that the mean SBH decreases with increasing ion energy, which can be explained as a result of donor-like defects that are introduced by the ion milling treatment. From DLTS measurements, we found direct evidence for the presence of such defects. INTRODUCTION Dry etching techniques are commonly used in VLSI processing, especially in deep submicron device fabrication, because of their potential for very-high-fidelity transfer of resist patterns [1]. Due to their high selectivity, reactive ion etching (RIE) and plasma etching are the most frequently used techniques to open contact holes. However, such processes may form a
residue layer on and introduce damage into a semiconductor. Although the residue layer on a Si surface can be removed by oxygen ashing followed by a HF dip, the damaged layer, which could penetrate up to hundreds of angstroms, is not easily recovered, even after high temperature anneals [2]. This un-recovered damage may strongly influence the electronic properties of the subsequently-formed metal-semiconductor (M-S) contact, e.g. I-V characteristic as well as Schottky barrier height (SBH) [3,4]. Generally, damage introduced by RIE is a combination of both physical and chemical effects [1], which makes it a difficult system to study. On the other hand, sputter etching and ion-beam milling are techniques which introduce almost purely physical effects, e.g. ion bombardment damage, since there is neither reactive gas in the processing ambient nor electrically active dopant introduced into the semiconductor [1]. In a sputter etching system, the plasma and the substrate are located in the same chamber, and ions are generated in random positions and accelerated through random distances before they bombard the substrate. Therefore, there is a broad distribution of the ion energy. In comparison, in an ion beam milling system, ions are generated in a confined space and accelerated by a fixed voltage before they bombard the substrate. The bombardment energy is well defined. In this work, we will study the effects of ion milling on the electronic properties of the M-S contact. By using the ion milling technique, we have good control over both dose and energy of the ions that cause the physical damage, and we avoid the additional complexity of chemical damage that is also present in a RIE process. 201 Mat. Res. Soc. Symp. Proc. Vol. 564 © 1999 Materials Research Society
Traditionally, the effect of substrate damage on the electronic properties of M-S interfaces is studied by I-V, C-V and deep-level transient spectroscopy
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