US2008048707A1PendingUtilityA1
Characteristic evaluation apparatus for insulated gate type transistors
Est. expiryAug 25, 2018(expired)· nominal 20-yr term from priority
Inventors:Kenji Yamaguchi
H10P 74/207G01R 31/2621G01R 31/2837
57
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Claims
Abstract
The accuracy of effective channel width extraction in drain current method is improved. There are prepared a transistor with a wide channel width serving as a reference, and a transistor with a narrow channel width that becomes a candidate for extraction (step ST 1.1 ). From the characteristic curve of a plane formed by mask channel width and source-drain conductance, there is extracted a virtual point at which the change of source-drain conductance is estimated to be approximately zero even if the gate overdrive is finely changed. Then, the value of function F is calculated which is defined by the difference between the change of the conductance at the coordinate of the virtual point and the product obtained by multiplying the conductance per unit width by the change of the mask channel width (step ST 1.6 ). From a shift amount (δ) which minimizes the standard deviation of the function F to be obtained (step ST 1.7 ), the true threshold voltage of the transistor with the narrow channel width is determined (step ST 1.10 ).
Claims
exact text as granted — not AI-modified1 . A characteristic evaluation method for insulated gate type transistors, comprising:
a) preparing at least two insulated gate type transistors including first and second insulated gate type transistors that differ from each other only in mask channel width; b) extracting a threshold voltage of said first transistor that has a mask channel width larger than that of said second transistor, estimating a threshold voltage of said second transistor, and employing a value of the estimated threshold voltage as a first estimated value; c) when a difference between a gate voltage of said first transistor and said extracted threshold voltage of said first transistor is defined as a first gate overdrive, a difference between a gate voltage of said second transistors and said first estimated value is defined as a second gate overdrive, and an X-Y plane is assumed whose X-axis is said mask channel width and Y-axis is source-drain conductance, (i) extracting a virtual point at which a change of Y coordinate value is estimated to be approximately zero even if said first and second gate overdrives are finely changed, from a characteristic curve exhibiting a relationship between said mask channel widths of said first and second transistors and said source-drain conductance, (ii) defining values of an X coordinate and a Y coordinate at said virtual point as second and third estimated values, respectively, and (iii) extracting a slope of said characteristic curve at said virtual point and employing a value of the extracted slope as a fourth estimated value; d) repeating said step c) while varying said first estimated value; e) after said steps c) and d), (i) finding, from said second to fourth estimated values, optimum second to fourth estimated values with which the change of said third estimated value is equal to a product of the change of said second estimated value and said fourth estimated value, in reply to fine changes of said first and second gate overdrives, (ii) determining an optimum first estimated value that corresponds to said optimum second to fourth estimated values, and (iii) determining a true threshold voltage of said second transistor based an said optimum first estimated value; and f) determining a difference between said mask channel width and an effective channel width, based an said true threshold voltage.
2 . The method of claim 1 , wherein in said step e), said characteristic curve is approximated by using a first straight line in said X-Y plane, said first straight line passing through a first point that is given to said first transistor when said first gate overdrive has a first value and a second point that is given to said second transistor when said second gate overdrive has said first value.
3 . The method of claim 2 , wherein in said step e), said optimum second to fourth estimated values are determined from a relational expression:
F
(
δ
,
V
gtWi
)
=
dW
**
(
δ
,
V
gtWi
)
+
f
(
δ
,
V
gtWi
)
f
1
(
δ
,
V
gtWi
)
·
dW
**
1
(
δ
,
V
gtWi
)
-
DW
*
(
δ
,
V
gtWi
)
where δ is a difference between the first estimated value and the threshold voltage of said first transistor; V gtWi is said first gate overdrive; dW** is a value of an X intercept that is obtained by extrapolating said characteristic curve; f is said slope of said characteristic curve at said virtual point; DW* is an X coordinate value at said virtual point; and a prime is a first-order differentiation of V gtWi .
4 . The method of claim 2 , wherein in said step e), said optimum second to fourth estimated values are determined from a relational expression:
F
(
δ
,
V
gtWi
)
=
f
2
(
δ
,
V
gtWi
)
f
1
(
δ
,
V
gtWi
)
·
dW
**
1
(
δ
,
V
gtWi
)
-
G
m
*
(
δ
,
V
gtWi
)
where δ is a difference between the first estimated value and the threshold voltage of said first transistor; V gtWi is said first gate overdrive; dW** is a value of an X intercept that is obtained by extrapolating said characteristic curve; f is said slope of said characteristic curve at said virtual point; G m * is a Y coordinate value at said virtual point; and a prime is the first-order differentiation of V gtWi .
5 . The method of claim 2 , wherein in said step e), said optimum second to fourth estimated values are determined from a relational expression:
F
(
δ
,
V
gtWi
)
=
G
m
**
(
δ
,
V
gtWi
)
-
f
(
δ
,
V
gtWi
)
f
1
(
δ
,
V
gtWi
)
·
G
m
**
1
(
δ
,
V
gtWi
)
-
G
m
*
(
δ
,
V
gtWi
)
where δ is a difference between the first estimated value and the threshold voltage of said first transistor; V gtWi is said first gate overdrive; G m ** is a value of a Y intercept that is obtained by extrapolating said characteristic curve; f is said slope of said characteristic curve at said virtual point; G m * is a Y coordinate value at said virtual point; and a prime is the first-order differentiation of V gtWi .
6 . The method of claim 2 , wherein in said step e), said optimum second to fourth estimated values are determined from a relational expression:
F
(
δ
,
V
gtWi
)
=
G
m
**
1
(
δ
,
V
gtWi
)
f
1
(
δ
,
V
gtWi
)
+
DW
*
(
δ
,
V
gtWi
)
where δ is a difference between the first estimated value and the threshold voltage of said first transistor; V gtWi is said first gate overdrive; G m ** is a value of a Y intercept that is obtained by extrapolating said characteristic curve; f is said slope of said characteristic curve at said virtual point; DW* is an X coordinate value at said virtual point; and a prime is the first-order differentiation of V gtWi .
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