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Title: Characterisation of molecular nitrogen implanted silicon for multiple thicknesses of gate oxide in a 0.5μm CMOS process
Author: Rennie, Michael
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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The continuing scaling of CMOS devices for performance advantages has resulted in an accompanying thinning of the gate oxide insulator and an increase in the level of hot carrier effects for a fixed power supply voltage. Nitrogen incorporated into the gate oxide through the nitridation of silicon oxide from a gas source has been extensively studied to improve the robustness of devices to hot carrier effects. Although reduced growth rates have been observed with nitrided oxides, there has not been a comprehensive study of MOS device performance utilising this mechanism to selectively grow gate oxides with different thicknesses. One of the advantages is their potentially improved hot carrier robustness through the incorporation of nitrogen. The dry oxidation kinetics of silicon implanted with low dose (1014-1015 cm-2) molecular nitrogen has been extensively studied in this work to establish the possibility of using the implanted nitrogen for adjusting the oxidation rate of silicon. This work established that the oxidation rate is determined by the pile-up of nitrogen at the silicon oxide-silicon interface in a surface reaction rate limited process. The nitrogen implanted silicon technique has been incorporated into a 0.5μm CMOS process to determine the feasibility of growing multiple thicknesses of gate oxide during a single oxidation step. In this work, the gate oxide is grown after direct implantation of molecular nitrogen into both NMOS and PMOS device areas. This allows for easy integration into an existing process as the implantation is carried out during the same step as threshold adjustment implants. The hot carrier reliability and boron penetration properties of gate oxides grown under high nitrogen dose conditions are improved in a similar way to nitridation from a gas source. Increased nitrogen dose in the silicon however, shows a deterioration of the MOS device mobility and gate oxide integrity. The localised thinning of the gate oxide is shown to be responsible and the inhomogeneous redistribution of nitrogen is attributed to the deterioration of the device characteristics. Sufficient device performance and reliability however can be achieved using low dose molecular nitrogen such that the simultaneous growth of 150Å and 90Å gate oxides can be realised on a CMOS technology microprocessor chip for 3.3V and 5V power supply interface applications.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available