Patent ID: 6020753
Filing Date: 2000-02-01
Classification: G01R

Abstract:
In a TFT having a channel layer of a silicon thin film and a gate insulating film of a silicon oxide film, a method of evaluating the reliability of the TFT in a -BT stress state in which a gate is supplied with arbitrary constant voltage V.sub.G and held at an arbitrary constant temperature T based on the following expressions:.DELTA.V.sub.th .varies.t.sup..alpha. ( 3a) ##EQU21## where .DELTA.V.sub.th represents the threshold voltage shift amount of the TFT, t time, .alpha. time coefficient, q elementary electric charge, d voltage coefficient, k Boltzmann constant, t.sub.0X the thickness of the gate oxide film, .phi..sub.0 temperature coefficient, and .DELTA.V.sub.th.tau. the tolerant threshold voltage shift amount of the TFT, and .beta.=1/.alpha. said method comprising the steps of:determining the time coefficient .alpha. in expression (3a) based on the relation between a threshold voltage shift amount .DELTA.V.sub.th obtained from at least one -BT stress test and time t;determining voltage coefficient d in expression (4a) based on the relation between a threshold voltage shift amount .DELTA.V.sub.th obtained from at least two -BT stress tests and different gate voltages V.sub.G applied in the tests;determining the temperature coefficient .phi..sub.0 in expression (5a) based on the relation between a threshold voltage shift amount .DELTA.V.sub.th obtained from at least two -BT stress tests and different temperatures T used in the tests; andin expression (6) obtained from the relation between expressions (3a), (4a), determining the following constant of proportion using said determined time coefficient .alpha., voltage coefficient d and temperature coefficient .phi..sub.0, ##EQU22## thereby obtaining the life of the TFT from expression (8) obtained by transforming expression (6) using said determined constant of proportion c.sub.2 and the tolerant threshold voltage shift amount .DELTA.V.sub.th.tau. of the TFT.