Active solid-state devices (e.g. – transistors – solid-state diode – Bipolar transistor structure – With means to increase current gain or operating frequency
Reexamination Certificate
2000-10-13
2003-02-18
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Bipolar transistor structure
With means to increase current gain or operating frequency
C257S592000, C257S616000, C257S197000, C257S565000
Reexamination Certificate
active
06521974
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a bipolar transistor and its manufacturing method, and particularly relates to a bipolar transistor using single crystal silicon germanium as an intrinsic base layer and its manufacturing method.
A bipolar transistor using conventional type single crystal silicon germanium as an intrinsic base layer is disclosed in Japanese published unexamined patent application No. Hei 7-106341, for example.
FIG. 15
shows the sectional structure of the conventional type bipolar transistor.
As shown in
FIG. 15
, a reference number
101
denotes a silicon substrate, and, after a high concentration n-type buried layer
102
is formed in a part of the silicon substrate
101
and a low concentration n-type silicon layer
103
which will be a collector layer is epitaxially grown on the overall surface of the silicon substrate
101
, a device isolation layer
104
is selectively formed. A high concentration n-type area
105
is formed in a part which will be a collector by implanting n-type dopant ions. After three layers of a collector-base isolation layer
106
, extrinsic base polysilicon
107
and an emitter-base isolation layer
109
are deposited, an emitter opening is formed, and a second emitter isolation layer
110
is formed on the respective side walls of the emitter-base isolation layer
109
and the extrinsic base polysilicon
107
.
Next, an overhang of the extrinsic base polysilicon
107
is formed by selectively etching the collector-base isolation layer
106
. Then, at the same time that a low concentration p-type single crystal silicon layer
111
is formed on the surface of the low concentration n-type silicon layer
103
, a low concentration p-type polysilicon layer
112
is selectively formed on the bottom of the overhang of the extrinsic base electrode. In this case, p-type dopant is diffused into the polysilicon
112
from the extrinsic base polysilicon
107
by applying heat treatment at 900° C. for five minutes, for example, to be a high concentration p-type. An intrinsic base
113
composed of a p-type single crystal silicon germanium layer is formed on the low concentration p-type single crystal silicon layer
111
by selective growth, again and a link base
114
composed of a p-type polycrystalline silicon germanium layer is simultaneously formed on the high concentration p-type polysilicon layer by selective growth again. Hereby, the intrinsic base
113
and the extrinsic base electrode
107
are connected via the link bases
112
and
114
in a self-aligned manner.
Next, an n-type single crystal silicon layer
116
is formed by implanting n-type dopant ions only into the opening using the emitter-base isolation layer
110
as a mask so that an intrinsic area of the transistor is included. After a third emitter-base isolation layer
115
is formed on the side wall of the opening, an n-type single crystal silicon layer
117
which will be an emitter is epitaxially grown, and a base electrode
118
, an emitter electrode
119
, and a collector electrode
120
are formed.
In the bipolar transistor using the conventional type single crystal silicon germanium for the intrinsic base layer, to enhance the concentration of the polysilicon layer
112
formed under the overhang of the extrinsic base electrode, it is necessary to apply annealing and diffuse dopant from the extrinsic base polysilicon
107
. Because of the annealing, n-type dopant included in the high concentration n-type buried layer
102
is diffused and the profile of impurities in the intrinsic part of the transistor varies.
Also, as contaminations such as oxygen and carbon adhere to the surface of the single crystal silicon layer
111
for annealing during epitaxial growth, a stacking fault occurs in restarted epitaxial growth.
Further, there is a problem that as the surface morphology of the single crystal silicon layer
111
is deteriorated by an oxidation-reduction reaction during annealing, a recombination center is formed on a boundary between the intrinsic base
113
and the collector layer
111
, leakage current is caused in the collector-base junction of the transistor, and the breakdown voltage is deteriorated.
Also, time for heating and cooling time between the temperature of epitaxial growth and that of annealing is required in addition to time for annealing, and the throughput of wafer processing is deteriorated.
Further, there is a problem that as an energy barrier is formed on an interface between the single crystal silicon layer
111
which will be a collector layer and the intrinsic base
113
in case the single crystal silicon germanium layer is epitaxially grown as the intrinsic base
113
, electrons injected from an emitter are inhibited by the energy barrier, base transit time is increased, and the operation of the transistor is slowed.
SUMMARY OF THE INVENTION
Therefore, the object of the invention is to provide a bipolar transistor wherein a single crystal silicon germanium layer is used for an intrinsic base layer, and little divergence of impurities from a high concentration buried layer occurs. It is also an object to provide a bipolar transistor in which breakdown voltage is high because few crystal defects occur in a base layer and little leakage current due to morphology is caused, external base resistance for enabling high-speed circuit operation is low, no energy barrier is caused between a collector and a base and in addition, it can be manufactured with a large throughput and its manufacturing method.
A bipolar transistor according to the invention is characterized in that it is provided with at least a first conductivity type of silicon layer, for example, as shown in
FIG. 1
, a low concentration n-type collector layer
3
to be a first collector area, a multilayer film composed of a first insulating film, provided on the surface of the first conductivity type of silicon layer, that is, a collector-base isolation layer
7
, a second conductivity type of polycrystal layer of a reverse conductivity type to the first conductivity type, that is, a base leading-out electrode
9
made of p-type polysilicon and a second insulating film, that is, an emitter-base isolation layer
10
, and an opening provided to the multilayer film. The bipolar transistor also includes a first single crystal silicon germanium layer of the second conductivity type provided in the opening, that is, a single crystal layer
13
made of single crystal silicon germanium, a second single crystal silicon germanium layer of the second conductivity type provided on the first single crystal silicon germanium layer of the second conductivity type, that is, a p-type intrinsic base layer
14
made of single crystal silicon germanium, a second conductivity type of polycrystalline silicon germanium layer provided so that the layer is in contact with both the second single crystal silicon germanium layer of the second conductivity type and the second conductivity type of polycrystal layer, that is, a p-type link base layer
15
made of polycrystalline silicon germanium. The bipolar transistor also includes a first single crystal area of the first conductivity type provided on the second single crystal silicon germanium layer of the second conductivity type, that is, a high concentration emitter area
20
composed of a single crystal layer and a second single crystal area of the first conductivity type formed including a part of the first single crystal silicon germanium layer of the second conductive type, that is, a selectively ion implanted collector area
18
which is the second single crystal area of the first conductivity type higher in concentration than the first single crystal silicon germanium layer of the second conductivity type and lower in the concentration than the first single crystal area of the first conductivity type.
In the bipolar transistor, the first single crystal area of the first conductivity type may be composed of a single crystal silicon layer or a single crystal silicon germanium layer.
Also, in the bipolar transistor, the second c
Kondo Masao
Oda Katsuya
Ohue Eiji
Shimamoto Hiromi
Tanabe Masamichi
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