Semiconductor device manufacturing: process – Making passive device – Resistor
Reexamination Certificate
1998-11-06
2001-04-03
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Making passive device
Resistor
C438S931000, C438S648000, C438S656000, C438S685000
Reexamination Certificate
active
06211032
ABSTRACT:
RELATED APPLICATIONS
The present invention is related to application Ser. No. 09/188,782, U.S. Pat. No. 6,081,014, issued Jun. 27, 2000 for SILICON CARBIDE CHROME THIN-FILM RESISTOR by Mark Redford et al. which is filed on an even date herewith.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin-film resistors and, more particularly, to a method for forming a thin-film resistor.
2. Description of the Related Art
A resistor is a common circuit element that provides a specified electrical resistance under specified conditions. Electrical resistance, in turn, is defined as the ratio of the potential difference between the ends of a conductor and the current flowing through the conductor.
A thin-film resistor is a type of resistor that is used with integrated circuits and, as the name suggests, is formed from a thin layer of resistive material. Numerous resistive materials, including lightly-to-heavily doped polysilicon, silicon chrome (SiCr), nichrome (NiCr), tantalum, and cermet (Cr—SiO), have been used to form thin-film resistors.
The performance of thin-film resistors is defined by a number of parameters which include the resistor value (the resistance that is supposed to be provided by the resistor), the resistor tolerance (the extent to which the resistance may deviate from the resistor value), and the temperature coefficient of resistance (TCR) (the amount the resistance changes with changes in temperature).
It is also important that similarly formed resistors have similar resistances (known as value matching), and similar variations with changes in temperature (known as tolerance tracking). Another parameter, known as an end effect, is a measure of a change in the length of the thin-film resistor that results from metalization spiking into the thin-film resistor.
FIGS. 1A-1H
show cross-sectional views that illustrate a process for forming a conventional thin-film resistor. As shown in
FIG. 1A
, the method begins with a conventionally formed wafer
100
that includes a semiconductor material
110
, such as an epitaxial layer or a substrate, and a layer of oxide
112
approximately 5,500 Å thick which is formed on the surface of material
110
. In addition, wafer
100
also includes a surface contact region
114
.
From this point, as shown in
FIG. 1B
, a layer of aluminum
116
is cold deposited over oxide layer
112
and material
110
in contact region
114
. Following this, a first mask
120
is formed and patterned on the surface of aluminum layer
116
to define a resistor region
122
on the surface of oxide layer
112
.
Once mask
120
has been patterned, as shown in
FIG. 1C
, the unmasked regions of aluminum layer
116
are etched until aluminum layer
116
has been removed from resistor region
122
on the surface of oxide layer
112
. After this, mask
120
is removed.
Next, as shown in
FIG. 1D
, a thin-film layer of silicon chromium
124
, is deposited over aluminum layer
116
and resister region
122
on the surface of oxide layer
112
. The film composition of the silicon chromium is approximately 72% silicon and 28% chromium.
Following this, a second mask
126
is formed and patterned over thin-film resistive layer
124
to define a plurality of resistors
130
. Once mask
126
has been patterned, as shown in
FIG. 1E
, the unmasked regions of thin-film resistive layer
124
are etched until the unmasked regions of thin-film resistive layer
124
have been removed.
After this, as shown in
FIG. 1F
, aluminum layer
116
and mask
126
are removed. Next, as shown in
FIG. 1G
, a second aluminum layer
134
is cold deposited over oxide layer
112
, resistors
130
, and material
110
to form an interconnect. Next, a third mask
136
is formed and patterned on interconnect layer
134
to define metal interconnect tracks.
Once mask
136
has been patterned, as shown in
FIG. 1H
, the unmasked regions of interconnect layer
134
are etched until the unmasked regions of interconnect layer
134
have been removed. After this, mask
136
is removed.
Although the above-described process produces thin-film resistors which are adequate for the needs of current generation products, future products are expected to require thin-film resistors which have a greater precision than those currently being produced. Thus, there is a need for a thin-film resistor which has greater precision than current generation thin-film resistors.
SUMMARY OF THE INVENTION
The present invention is directed to a method for forming a thin-film resistor. The thin-film resistor of the present invention is formed on a semiconductor device which has a semiconductor material and an isolation region that is formed on the semiconductor material.
In accordance with the present invention, the method of the present invention begins by forming a layer of sacrificial material on the isolation region. Next, a selected portion of the layer of sacrificial material is removed to form an exposed portion of the isolation region.
After this, a layer of resistive material is formed over the exposed portion of the isolation region and the layer of sacrificial material. The layer of resistive material includes a percentage by weight of silicon, a percentage by weight of carbon, and a percentage by weight of chromium. Next, selected portions of the layer of resistive material are removed to form a resistor. Following this, the layer of sacrificial material is removed.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description and accompanying drawings which set forth an illustrative embodiment in which the principals of the invention are utilized.
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Aliyu Yakub
Boyle Rikki
Gregory Haydn
McGregor Chic
Redford Mark
Elms Richard
National Semiconductor Corporation
Pickering Mark C.
Pyonin Adam
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