Semiconductor device manufacturing: process – Making passive device – Planar capacitor
Reexamination Certificate
2002-03-18
2003-08-12
Whitehead, Jr., Carl (Department: 2813)
Semiconductor device manufacturing: process
Making passive device
Planar capacitor
C438S381000, C438S396000, C438S386000, C257S516000, C257S532000, C361S311000, C361S313000, C361S321600
Reexamination Certificate
active
06605515
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a thin-film capacitor for properly performing temperature compensation of the junction capacitance of a semiconductor device, a thin-film capacitor device having the thin-film capacitor manufactured by the method, and an electronic circuit having the thin-film capacitor device for performing temperature compensation of the electronic circuit.
2. Description of the Related Art
Thin-film capacitor devices generally have a substrate and a lower electrode, a dielectric layer, and an upper layer which are deposited on the substrate in that order. The thin-film capacitor devices also have a semiconductor substrate functioning as a lower electrode and have a dielectric layer and an upper layer which are deposited on the semiconductor substrate in that order in some cases.
The thin-film capacitor devices are required to have a large relative dielectric constant and Q factor and a temperature coefficient of capacitance of near 0 at a resonant frequency.
Hitherto, the following compounds are known as dielectrics having the above characteristics: BaO—TiO
2
dielectrics containing Sm
2
O
3
, Gd
2
O
3
, Dy
2
O
3
, or Eu
2
O
3
. However, when manufacturing such dielectrics using conventional techniques, the relative dielectric constant is adjustable only in the range of 61 to 72 and the temperature coefficient of capacitance is adjustable only in the range of −24 to 31 ppm/° C.
For the above background, research and development has been conducted. A dielectric ceramic having the following structure has been proposed: a multilayer including a first dielectric ceramic sheet having a positive temperature coefficient of capacitance at a resonant frequency and a second dielectric ceramic sheet having a negative temperature coefficient of capacitance at a resonant frequency.
According to this method, the multilayered dielectric ceramic is prepared as follows: a mixture having a desired composition is formed into a disk having a diameter of 16 mm and a thickness of 9 mm, the disk is fired at 1,260° C. to 1,450° C. for several hours, a first dielectric ceramic is then obtained; and another mixture having a different composition from the above composition is formed into another disk, the disk is fired, and a second dielectric ceramic is then obtained; each of the first and second dielectric ceramics is cut into a sheet having a thickness of 1 mm; and both the sheets are layered to complete the multilayered dielectric ceramic. The relative dielectric constant and the temperature coefficient of capacitance of the multilayered dielectric ceramic can be adjusted by using materials having different relative dielectric constants or using sheets which are made of the same material and have different thicknesses.
According to the above method, since the multilayered capacitors are manufactured by layering the fired first and second dielectric ceramics, each having a thickness of 1 mm, the miniaturization and a reduction in thickness are limited. For example, thin-film capacitors having a thickness of 1 mm or less cannot be manufactured.
When the dielectric ceramic sheets are laminated, an adhesion layer or an air layer which has a different dielectric constant exists between the sheets. Such a structure has a plurality of portions, each having a different dielectric constant, in the thickness direction of the layered sheets; hence there is a problem in that it is difficult to manufacture capacitors having a desired temperature coefficient of capacitance.
Furthermore, the sheet dielectric ceramic is polycrystalline and subsequently has a plurality of grain boundaries in the thickness direction; hence, reduction in the dielectric loss at a high frequency of 1 GHz or more is difficult.
In thin-film capacitors, the desired thickness of the second dielectric thin-film is inversely proportional to a ratio of the absolute value of the temperature coefficient of capacitance to the relative dielectric constant (hereinafter referred to as a ratio &tgr;/&kgr;). That is, as the thickness of the dielectric thin-film increases, as the absolute value of the ratio &tgr;/&kgr; decreases. The relationship is more significant at a high relative dielectric constant. It is subsequently difficult to manufacture thin-film capacitors having a high relative dielectric constant and a small thickness even if the above methods are improved.
In a thin-film capacitor having a first dielectric thin-film and a second dielectric thin-film which are layered, the thickness of each of the first and second dielectric thin-films is determined according to the relative dielectric constant and the temperature coefficient of capacitance. When a capacitor device having a sheet capacitance of (C/S) pF/mm
2
includes a dielectric thin-film (controlled film: first dielectric thin-film: referred to as film C) having a relative dielectric constant &kgr;
C
and a temperature coefficient of capacitance of 0 ppm/° C., and includes another dielectric thin-film (second dielectric thin-film: referred to as film N) having a relative dielectric constant &kgr;
N
and a temperature coefficient of capacitance of &tgr;
N
ppm/° C., the following formulas (1) and (2) are obtained for the thickness t
C
of the first dielectric thin-film, the thickness t
N
of the second dielectric thin-film, and dielectric ∈
0
constant of vacuum:
t
N
=
ϵ
0
τ
(
C
/
S
)
1
(
τ
N
κ
N
)
(
1
)
and
t
C
=
ϵ
0
κ
C
(
C
/
S
)
-
t
N
κ
C
κ
N
.
(
2
)
The above formulas (1) and (2) show that the thickness &tgr;
N
of the second dielectric thin-film (film N) is determined according to the ratio &tgr;
N
/&kgr;
N
. Hitherto, in order to obtain a second dielectric thin-film having a smaller thickness, changing the ratio &tgr;
N
/&kgr;
N
, that is, increasing the ratio &tgr;
N
/&kgr;
N
by using different materials, is required. That is, developing a new dielectric material having a large value of the ratio &tgr;
N
/&kgr;
N
is necessary.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for manufacturing a thin-film capacitor for properly performing temperature compensation. In the thin-film capacitor, the miniaturization and a reduction in the thickness and the weight can be achieved. It is another object of the present invention to provide a thin-film capacitor device having the thin-film capacitor manufactured by the method. It is another object of the present invention to provide an electronic device having the thin-film capacitor manufactured by the method. It is another object of the present invention to provide an electronic circuit having the thin-film capacitor device manufactured by the method.
In order to solve the above problems, in a method for manufacturing a thin-film capacitor having a desired sheet capacitance and a desired temperature coefficient of capacitance by depositing a first dielectric thin-film having a temperature coefficient of capacitance with an absolute value of 50 ppm/° C. or less and a second dielectric thin-film having a negative temperature coefficient of capacitance, wherein the second dielectric thin-film has a structure composed of an aggregation of principal grain units each having a principal crystal grain and grain boundary layers surrounding the principal crystal grain, includes a plurality of principal grain units, and has a thickness t
N
, wherein t
N
={∈
0
&tgr;
t0t
/(C/S)}·{1/(&tgr;/&kgr;)}, wherein C/S represents the sheet capacitance, ∈
0
&tgr;
t0t
represents the desired temperature coefficient of capacitance, &tgr; represents the temperature coefficient of capacitance of the second dielectric thin-film, and &kgr; represents the relative dielectric constant of the second dielectric thin-film, the method includes determining a target value of a grain size of the second dielectric thin-film by selecting the grain size
Kitagawa Hitoshi
Sasaki Makoto
Alps Electric Co. ,Ltd.
Beyer Weaver & Thomas LLP
Hogans David L.
Jr. Carl Whitehead
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