Measurement of Oxide Thickness for Mos Device

Topics: MOSFET, Capacitor, Nitrogen Pages: 7 (1834 words) Published: February 23, 2011
A procedure to characterize oxide thickness and conductor layers that are grown or deposited on semiconductor is by studying the characteristics of a MOS capacitor that is formed of the conductor - insulator - semiconductor layers. For a capacitor formed with oxide thickness of 510 Å (measured optically), here in this research author measures the oxide thickness by the SUPREM

Simulator. Its accuracy depends on the quality of models,
parameters and numerical techniques it employ. Authors also
verify the result by measurment of capacitance at different
voltages using LCR meter and the curve drawn through Visual
Engineering Environment Programming (VEE Pro) software.
Based on the oxide thickness measurement of a MOS capacitor, one can measure the device parameters, mainly the substrate
dopant concentration and other parameter. This research was
completed in BEL Laboratory.
VEE Programming, Oxide thickness measurement, MOS
devices, LCR meter, VLSI.
The real importance of capacitance-voltage curve (C-V)
measurement techniques in microelectronics field is that, a large number of device parameters can be extracted from two
seemingly simple curves: high frequency C-V curve and
quasistatic C-V curve. These parameters can provide critical device and process information.
We can divide the parameters into three groups.
A). Includes typical MOS device parameters such as oxide
thickness, flatband voltage, threshold voltage etc.
B). Oxide charge parameters, includes interface trap charge
density, mobile ion charge density etc.
C). Consists of doping-related parameters.
Also using C-t data, carrier generation lifetime and
recombination lifetime can be extracted.
This research addresses the oxide thickness that can be extracted from a high-frequency C-V (HF-CV) curve. In this research
authors first measures the oxide thickness using SUPREM
programming and then proved that the thickness by using other method with the LCR meter and VEE Pro Software are same.
Parameters of MOS device can be automatically calculated from data excel sheet at the end of the C-V test and then be
automatically entered into the Data worksheet for the further test. 2. MEASUREMENT TECHNOLOGY
For the oxide thickness measurement, author fabricates MOS
capacitors on a 4 inch diameter & 800 micron thick N-type silicon wafer and the grown layers were characterized by Capacitance - Voltage curve measurements.
2.1. Fabrication of MOS Device
To fabricate metal-oxide-semiconductor, the silicon wafers were cleaned by following the standard cleaning procedure to remove insoluble organics and metallic contaminants. After that, a layer of oxide, approximately 500 Å thick, was grown on the silicon

wafers using a dry oxidation process at 650oC for 60 minutes, with a pre-ramp of 5 oC per minute so that we reached at 950 oC and then a flat temp of 950 oC for the 110 minutes and at last postramp of 5 oC per minuts for 60 minutes with N2 (12) & O2 (32).

All these process are shown in below programming of SUPREM.
For top layer we will use Aluminum due to its ease of processing, ability to reduse native SiO2, which is always present in silicon wafers, exposed to atmosphere and its low resistivity. About 2000 Å of aluminium was then deposited over the oxide layer using a sputtering [2, 3].

Various techniques are used to increase the sputtering rates, use of magnetic field near the target to increase the generation of ions. Introduction of electrons by the use of an electron gun as a third electrode was also tried [4].

2.2. Introduction of SUPREM
SUPREM-III (Stanford University PRocess Engineering Model
Version 0-83) is a computer program that allows the user to
simulate the various processing steps used in the manufacturing of silicon integrated circuits or discrete devices. The types of processing steps, simulated by the current version of the program are inert ambient drive-in, oxidation of silicon and silicon...
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