Semiconductor device manufacturing: process – Forming bipolar transistor by formation or alteration of... – Complementary bipolar transistors
Reexamination Certificate
1998-10-30
2003-07-22
Coleman, William David (Department: 2823)
Semiconductor device manufacturing: process
Forming bipolar transistor by formation or alteration of...
Complementary bipolar transistors
C438S325000
Reexamination Certificate
active
06596600
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device having an integrated injection logic (IIL) cell structure, and a method of fabricating the same.
The integrated injection logic, which is often referred to as “I
2
L”, cell comprises a common semiconductor substrate, a constant current source transistor, and a switch transistor, both of the constant current source transistor and the switch transistor being formed on the above common semiconductor substrate. The most specific feature of the I
2
L cell lies in that a logic circuit can be easily incorporated therein with high density by the same processing as that of bipolar transistors. The I
2
L cells have been widely used before CMOS (complementary MOS insulating gate field-effect transistor integrated circuit) became widespread.
At present, as the circuit element is made large-scale, high-speed, low in power consumption, and inexpensive much more by microminiaturization based on CMOS, it is frequently observed that CMOS plays a leading part in forming logic circuits.
On the other hand, the I
2
L cell structure makes it possible to make a linear circuit in the form of semiconductor chip. In a small or middle scale manufacturing process, the I
2
L cell structure is inexpensive, and hence used in commercial sector.
Logic circuits based on the I
2
L cell structure also can be made large-scale, high-speed, low in power consumption, and inexpensive by microminiaturization of circuit element similarly to the CMOS.
In the I
2
L cell structure, as a means for realizing the microminiaturization of circuit element, it is considered that structure and manufacturing method of emitter/base self-align structure bipolar transistor based on upper and lower two layers of polycrystalline silicon are applied to the I
2
L cell structure (see T. H. Ning, Symp. of VLSITECH, Invited Paper, Page 34 (1981)).
The logic circuit based on the I
2
L cell structure includes a multi-collector structure composed of a plurality of collector regions and collector electrodes formed within the unit cell. However, in this I
2
L cell, switching speeds are different at every collectors composing the multi-collector structure. As a consequence, a designing of circuit becomes difficult, and such logic circuit has not yet been made large-scale.
Switching speeds can be different at every collector in the above multi-collector structure. That is, a base series resistance R
B
is increased as the position of the collector becomes distant from the base, and a current amplification factor and a cutoff frequency at a switching transistor (bipolar transistor in the reverse direction) provided within the I
2
L cell structure are lowered when a potential drop occurs at that portion, resulting in the switching speed being lowered.
FIG. 1A
is a plan view of a unit cell of conventional I
2
L cell structure, and
FIG. 1B
is a cross-sectional view thereof.
In this example, as illustrated in
FIGS. 1A and 1B
, on an n-type emitter region
60
surrounded by an emitter electrode deriving region
60
a heavily doped with n-type impurity, there is formed a base region
61
composed of a p-type intrinsic base region
61
s
and an external base region
61
g
heavily doped with p-type impurity, and an injector region
62
heavily doped with p-type impurity. A plurality of collector regions
63
heavily doped with n-type impurity are formed on the intrinsic base region
61
s.
An emitter electrode E, a base electrode B, an injector electrode I, and collector electrodes C (collector electrodes C
1
through C
5
) are respectively formed on respective regions of the emitter electrode deriving region
60
a
, the external base region
61
g
, the injector region
62
, and the collector region
63
to make an ohmic contact.
Of the above-mentioned regions, the intrinsic base region
61
a
, and the external base region
61
g
are formed by implanting ions of low impurity concentration and high impurity concentration through masks.
FIG. 2
is a graph showing a relationship between an injection current of an I
2
L ring type oscillator and a delay time in the I
2
L cell structure shown in
FIGS. 1A and 1B
while an ion injection dose of the external base region
61
g
is taken as a parameter. In the I
2
L ring type oscillator, unit cells of odd number are selected. In each unit cell, a base electrode and a collector electrode are connected in series to a base electrode or a collector electrode of adjacent unit cell, and an output of a final gate (base electrode or collector electrode) is oscillated as an input of the first gate, thereby measuring an oscillation frequency and a switching delay time.
A base electrode of adjacent cell and one collector electrode in a plurality of collector electrodes are sequentially connected by Al wire or the like.
Specifically, assuming that B
1
, B
2
, B
3
, . . . B
n
are base electrodes of 1, 2, 3, . . . , nth (n is an odd number) unit cells, and that C
1
, C
2
, C
3
, . . . , C
n
are collector electrodes, then electrodes of the same kinds are connected in such a way as in B
1
-B
2
, C
2
-C
3
, B
3
-B
4
, . . . , C
n−1
-C
n
or electrodes of different kinds are connected in such a way as in B
1
-C
2
, B
2
-C
3
, B
3
-C
4
, B
4
-C
3
, . . . , B
n−1
-C
n
and finally the electrodes B
n
-C
1
are connected in a loop-fashion, thereby forming the ring type oscillator.
In
FIG. 2
, the vertical axis represents a delay time (n/s), and the horizontal axis represents an injection current (&mgr;A), each of which is represented by a logarithmic scale.
In
FIG. 2
, crosses show measured results obtained when a dose of ions implanted on the external base region
61
g
is 1×10
14
cm
−2
and a layer resistance is 500 &OHgr;/□, and open circles show measured results obtained when a dose of ions implanted on the external base region
61
g
is 2×10
14
cm
−2
and the layer resistance is 315 &OHgr;/□. Open triangles show measured results obtained when the dose of ions implanted on the external base region
61
g
is 3×10
14
cm
−2
, and the layer resistance is 230 &OHgr;/□, and open squares show measured results obtained when the dose of ions implanted on the external base region
61
g
is 5×10
14
cm
−2
and the layer resistance is 150 &OHgr;/□.
When the ring type oscillator comprises a base and a collector which are disposed most closely to each other, or when a base electrode and a collector electrode disposed adjacent to this base electrode in the unit cell are used in the ring type oscillator and these electrodes are disposed at the end of the opposite side of the injector (curve group A in FIG.
2
), study of
FIG. 2
reveals that a delay time has no dose dependence.
On the other hand, when the ring type oscillator comprises a base electrode and a collector electrode which are disposed most distant from each other, or when the base electrode adjoins the injector and the collector disposed at the end of opposite side of the injector and the base electrode in the unit cell is used in the ring type oscillator (curve group B in FIG.
2
), study of
FIG. 2
reveals that a delay time is reduced as the dose is increased, i.e., operation speed is increased in the large current side where the injector current is 10 &mgr;A or higher.
In general, the I
2
L cell is formed at the same time the bipolar transistor is formed on the same semiconductor substrate as other device.
Specifically, I
2
L cells based on an emitter/base self-align bipolar transistor and a collector/base self-align switch transistor are simultaneously formed by first and second semiconductor layers of polycrystalline silicon.
FIG. 3A
is a plan view of such I
2
L cell structure, and
FIG. 3B
is a cross-sectional view thereof.
In the unit cell of the I
2
L cell structure shown in the plan view of
FIG. 3A
, an injector I, a base B, collectors C (collectors C
1
to C
3
) and an emitter E are formed from right in
FIG. 3A
, in that order.
In the cross-sectional view of
FIG. 3B
, an emitter buried regi
Coleman William David
Kananen Ronald P.
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