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Removal of Charge in the Gate Region of a FET

IP.com Disclosure Number: IPCOM000081960D
Original Publication Date: 1974-Sep-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Hornung, A: AUTHOR [+2]

Abstract

During the manufacture of field-effect transistors (FET's) positive charges may accumulate in the dielectric layer 1. The positive charges are generated by radiation (such as x-rays or electrons) knocking electrons out of the dielectric material. The radiation is commonly produced in the deposition of the dielectric by sputtering and in electron-beam photolithography. Positive charges in the dielectric 3 under the FET gate 2 and between the source 4 and drain 5 interfere with the operation of the FET by causing large threshold voltage shifts, and it is desired to rid the dielectric 1 of these charges.

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Removal of Charge in the Gate Region of a FET

During the manufacture of field-effect transistors (FET's) positive charges may accumulate in the dielectric layer 1. The positive charges are generated by radiation (such as x-rays or electrons) knocking electrons out of the dielectric material. The radiation is commonly produced in the deposition of the dielectric by sputtering and in electron-beam photolithography. Positive charges in the dielectric 3 under the FET gate 2 and between the source 4 and drain 5 interfere with the operation of the FET by causing large threshold voltage shifts, and it is desired to rid the dielectric 1 of these charges.

The positive charges in the dielectric 1 are removed by exposure to ultraviolet (UV) radiation. The UV radiation penetrates the dielectric material and excites electrons from the silicon substrate into the dielectric's conduction band. Also, electrons in the FET gate 2 may be excited into the dielectric conduction band by the UV radiation. The excited electrons then move to the positive charges and neutralize them. The UV radiation itself produces fast surface states or positive charges at the silicon/dielectric interface 4. These fast surface states may be removed by annealing at 30 degrees C. To remove the positive charges without UV radiation requires annealing at 450 degrees C.

The technique of removing the positive charge in the dielectric may be used with any dielectric that is transparent to UV radiation. Suitable...