Electrical resistors – With base extending along resistance element – Resistance element coated on base
Reexamination Certificate
2001-03-08
2002-12-03
Easthom, Karl D. (Department: 2832)
Electrical resistors
With base extending along resistance element
Resistance element coated on base
C338S307000, C338S308000
Reexamination Certificate
active
06489882
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resistor device, and more particularly, to a thin-film resistor fabricated on a semiconductor wafer displaying superior performance and higher stability.
2. Description of the Prior Art
In semiconductor integrated circuit designs, a simple resistor is often made from a gate conductive layer or an impurity-doped layer in a predetermined area of the semiconductor wafer. However, the resistance typically obtained from the gate conductive layer and the impurity-doped layer is often insufficient. One approach to increase the resistance is to design a larger surface area of the resistor. However, it is undesirable to make this resistor device having a large surface area in a highly-integrated ULSI product. Furthermore, the resistance of the silicon-containing gate conductive layer and impurity doped layer varies with temperature changes, which results in instability of the resistance values. Therefore, there is a need for fabricating a stable thin-film resistor with lower conductivity on a semiconductor wafer.
Please refer to FIG.
1
and FIG.
2
. FIG.
1
and
FIG. 2
are cross-sectional diagrams schematically showing a method of forming a resistor
20
on a dielectric layer
12
according to the prior art. As shown in
FIG. 1
, a resistor
20
is produced by first sequentially forming a resistance layer
14
and a protective layer
16
on the surface of the dielectric layer
12
. The resistance layer
14
and the protective layer
16
are defined by conventional photolithographic and etching processes. A conductive layer
18
, made of an aluminum alloy, is then formed on the protective layer
16
. As shown in
FIG. 2
, a large portion of the conductive layer
18
and the protective layer
16
positioned on the resistance layer
14
is removed by a wet-etching process. The remaining portion at the two ends of the resistance layer
14
functions as two electrical terminals for the two ends of the resistance layer
14
.
The wet-etching process is an isotropic etching process with equal horizontal and vertical etching depths. To define the conductive layer
18
properly through wet etching, the surface area of the resistance layer
14
and the protective layer
16
must be large. Only if the resistance layer
14
and protective layer
16
is large can a large portion of the conductive layer
18
and protective layer
16
be removed while still preserving the two portions at the ends of the resistance layer
14
. Although this method can be utilized in processing gate widths greater than 3 micrometers, it is ineffective in processing narrower gate widths.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to provide an improved thin-film resistor with much more stable resistance and a smaller required surface area.
In accordance with the objective of the present invention, the present invention provides a thin-film resistor on a dielectric layer of a semiconductor wafer. The thin-film resistor has a dielectric layer deposited on the semiconductor wafer. A patterned resistance layer is formed on the dielectric layer. A buffering layer is formed on the resistance layer, the buffering layer comprising two openings above two opposite ends of the resistance layer. A protective layer is positioned on the buffering layer and comprises two openings above the two openings of the buffering layer. An insulating layer covers the upper and side surfaces of the protective layer, the side surface of the buffering layer and the resistance layer, and the dielectric layer. The insulating layer has two openings above the two openings of the protective layer. Two conductive layers are positioned in the two openings of the buffering layer, the protective layer and the insulating layer, and are in contact with the two ends of resistance layer. The conductive layers are used as two electric terminals for electrically connecting to the two ends of the resistance layer.
It is an advantage of the present invention that the thin-film resistor thus formed comprises a resistance layer below a buffering layer and a protective layer. The buffering layer buffers the thermal stress exerted on the resistance layer, and the protective layer protects the resistance layer from plasma damage. The resulting thin-film resistor has a much more stable resistance.
This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.
REFERENCES:
patent: 3717514 (1973-02-01), Burgess
patent: 3997551 (1976-12-01), Minagawa et al.
patent: 4862197 (1989-08-01), Stoffel
patent: 4975386 (1990-12-01), Rao
patent: 5083183 (1992-01-01), Kobayahsi
patent: 5254497 (1993-10-01), Liu
patent: 5285099 (1994-02-01), Carruthers et al.
patent: 5525831 (1996-06-01), Ohkawa et al.
patent: 5852311 (1998-12-01), Kwon et al.
patent: 6194775 (2001-02-01), Usami
Easthom Karl D.
Hsu Winston
United Microelectronics Corp.
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