Low Resistivity Nickel Germanosilicide Contacts to Ultra-shallow Junctions Formed by the Selective Si 1-x Ge x Technolog
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Low Resistivity Nickel Germanosilicide Contacts to Ultra-shallow Junctions Formed by the Selective Si1-xGex Technology for Nanoscale CMOS Jing Liu, Hongxiang Mo, Mehmet C. Öztürk Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7920, USA. ABSTRACT In this paper, we present our recent results on nickel germanosilicide contacts formed on p+-n and n+-p junctions formed by selective deposition of in-situ doped Si1-xGex alloys. Our results show that ultra-thin, low resistivity NiSi1-xGex contacts can be formed at temperatures as low as 300 °C on both boron and phosphorus doped Si1-xGex layers. Ultra-shallow junctions with excellent reverse leakage behavior and a contact resistivity ~ of 10-8 ohm-cm2 were successfully demonstrated. The thermal stability of NiSi1-xGex was found to be limited to 500 °C on p+-Si1+ xGex and 600 °C on n -Si1-xGex. It was found that by inserting a thin Pt interlayer between Ni and Si1-xGex, the quality of the NiSi1-xGex contacts could be significantly improved. The Pt interlayer was found to improve the interface morphology, which was found to have a direct impact on the electrical properties of the contacts. INTRODUCTION One of the key challenges for future CMOS technology nodes is to form source/drain junctions with very small parasitic series resistance. This requires fundamentally new junction and contact formation technologies to produce ultra-shallow junctions with super-abrupt doping profiles, above solid solubility dopant activation and contact resistivity values near 10-8 ohm-cm2. Recently, this laboratory reported a new technology based on selective deposition of heavily doped Si1-xGex alloys in source/drain regions isotropically etched to the desired depth [1]. Of particular interest to this paper is the smaller bandgap of Si1-xGex resulting in a smaller metalsemiconductor barrier height, which is a key advantage in reducing the contact resistivity of future junctions. Previous work in this laboratory showed that nickel germanosilicide (NiSi1-xGex) appears to be the promising candidate to form low resistivity contacts to heavily doped p-type and n-type Si1-xGex alloys [2-3]. This paper presents recent experimental results on self-aligned NiSi1-xGex contacts with emphasis on electrical properties the junctions. EXPERIMENTS Boron doped Si1-xGex alloys with a doping level of ~1×1021 cm-3 and Ge content of ~ 45% were deposited by ultrahigh vacuum rapid thermal chemical vapor deposition (UHVRTCVD) at 500 ºC. Phosphorus doped Si1-xGex alloys were deposited at 750ºC with a Ge content of ~ 20% and a phosphorous doping level of 2×1020 cm-3. Ni and Pt layers were deposited in a UHV sputtering system. The native oxide on the wafers was removed in 1% HF. Solid phase reactions between metal and Si1-xGex were obtained by rapid thermal annealing (RTA) in a nitrogen ambient for 30 seconds. The sheet resistance was determined by four-point-probe
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