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Automatic Metal Insulator Silicon Flat Band Voltage Meter

IP.com Disclosure Number: IPCOM000079029D
Original Publication Date: 1973-Apr-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Verkuil, RL: AUTHOR

Abstract

Numerous field-effect transistor process control and development techniques throughout the semiconductor industry depend on flat band voltage measurements, performed on metal-insulator-silicon structures. A common method for flat band (V(FB)) measurements is the C-V trace method performed with an X-Y plotter.

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Automatic Metal Insulator Silicon Flat Band Voltage Meter

Numerous field-effect transistor process control and development techniques throughout the semiconductor industry depend on flat band voltage measurements, performed on metal-insulator-silicon structures. A common method for flat band (V(FB)) measurements is the C-V trace method performed with an X-Y plotter.

The automatic flat band voltage meter continuously switches between two functions at a 5 Hertz rate. In the first function, it biases the metal-insulator- semiconductor structure into accumulation to obtain the insulator capacitance (C(max)), which is then stored as an analog voltage. In the second function, an analog control circuit automatically adjusts the bias of the metal-insulator- semiconductor structure until it exhibits a flat band capacitance (C(FB)), which is a preset percentage of C(max). The resultant bias voltage is the flat band voltage V(FB) of the test structure, which may be read directly on a digital voltmeter.

In operation, the metal-insulator-semiconductor structure 10 to be tested is connected across the test terminals of capacitance meter 12. Meter 12 provides an analog DC output voltage C(out), which is directly proportional to the metal- insulator-semiconductor capacitance. The metal-insulator-semiconductor capacitance voltage characteristic is varied from accumulation to inversion by the input bias voltage to meter 12.

The circuit switches between two functions at a rate determined by the 5 Hertz oscillator 14. The first function is performed when oscillator 14 turns on transistor 16 and energizes relay 18. When relay 18 is energized, contacts 20 connect the accumulation power supply 22 to the bias input of the capacitance meter 12. By selecting the switch position for N-type substrates, or P-type substrates, the proper polarity of supply 22 will be obtained. With structure 10 now biased into accumulation, a maximum capacitance C(max) equal to the insulator capacitance will be exhibited. This maximum capacitance reading will appear as an analog output voltage C(out), which is fed into a high-input impedance unity gain buffer amplifier 24. The output of amplifier 24 then charges up capacitor 26 through the contacts 28. The resultant stored voltage on capacitor 26 is a DC analog of C(max) for the structure 10.

Capacitor 26 is connected to a second high-input impedance unity gain buffer amplifier 30. The output...