Active solid-state devices (e.g. – transistors – solid-state diode – Bipolar transistor structure – With specified electrode means
Reexamination Certificate
2001-07-23
2004-05-04
Pham, Long (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Bipolar transistor structure
With specified electrode means
Reexamination Certificate
active
06730986
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to integrated circuit devices and methods of forming integrated circuit devices, and more particularly to bipolar junction transistors and methods of forming bipolar junction transistors.
BACKGROUND OF THE INVENTION
Attempts to develop bipolar junction transistors (BJTs) having higher operating speeds than conventional silicon-based bipolar junction transistors have led to the development of GaAs-based BJTs and heterojunction bipolar junction transistors (HBTs). However, the use of materials such as GaAs and the formation of HBT devices typically increases the complexity and cost of fabricating BJTs.
To address these limitations associated with GaAs-based BJTs and HBTs, continuing attempts have been made to develop silicon-based BJTs having improved electrical characteristics (e.g., higher operating speeds). For example, as described in U.S. Pat. No. 5,286,996 to Neudeck et al., entitled “Triple Self-Aligned Bipolar Junction Transistor”, self-alignment techniques have been developed to reduce fabrication complexity and reduce reliance on critical photolithographically defined masking and patterning steps. Recent attempts to develop self-aligned BJTs have also included the design of vertical and lateral scaling and base resistance reduction techniques. For example, a vertical scaling technique is disclosed in an article by Takashi Uchino et al., entitled “15-ps ECL/74-GHz f
T
Si Bipolar Technology”, IEDM Technical Digest, pp. 67-70 (1993). A lateral scaling technique is also disclosed in an article by A. Pruijmboom et al., entitled “18ps ECL-Gate Delay in Laterally Scaled 30 Ghz Bipolar Transistor”, IEDM Technical Digest, pp. 825-828 (1994). A base resistance reduction technique is disclosed in an article by C. Yoshino et al., entitled “A 62.8 GHz f
max
LP-CVD Epitaxially Grown Silicon Base Bipolar Transistor with Extremely High Early Voltage of 85.7V”, 1995 Symposium on VLSI Technology, Technical Digest, pp. 131-132 (1995). Unfortunately, the techniques disclosed in these articles may not be useful in developing BJTs having both high cutoff frequency f
T
and high maximum oscillating frequency f
max
.
In order to simultaneously improve the cutoff frequency and the maximum oscillating frequency of a BJT, it may be necessary to optimize the diffusion profile of extrinsic base region dopants diffused from a polysilicon base electrode. For example, if the extrinsic base region dopants are diffused to define a large extrinsic base region, the base-collector junction capacitance may increase and limit the cutoff frequency. However, if the extrinsic base region dopants are diffused to define a small extrinsic base region, the base resistance may increase to a level that is too high.
Other techniques for forming BJTs are disclosed in an article by Mamoru Ugajin et al., entitled “Very-High f
T
and f
max
Silicon Bipolar Transistors Using Ultra-High-Performance Super Self-Aligned Process Technology for Low-Energy and Ultra-High-Speed LSI's”, IEDM Technical Digest, pp. 735-738, (1995). In this article, emphasis is placed on reducing lateral dimensions in order to reduce base-collector junction capacitance and base resistance and increase f
T
. The f
max
of the BJT disclosed in this article was also reported as being twice as large as the f
max
disclosed in an article by Chikara Yamaguchi et al., entitled “0.5-um Bipolar Technology Using a New Base Formation Method: SST1C”, IEEE Proceedings of the Bipolar Circuits and Technology Meeting, pp. 63-66, (1993).
FIGS. 1-2
illustrate a conventional bipolar junction transistor, as described in the aforementioned Ugajin et al. article. In particular,
FIGS. 1-2
illustrate a bipolar junction transistor having an N+ epitaxial intrinsic collector region
13
that is formed on a buried extrinsic collector layer
11
within a P-type substrate
10
. Field oxide isolation regions
15
are also formed in the substrate
10
, as illustrated. Electrical isolation is also provided by a plurality of trench-based isolation regions that include an oxide layer
19
lining the trenches
17
and highly-doped channel-stop regions
18
at the bottoms of the trenches. The trench-based isolation regions also include polysilicon regions
21
that act as floating field rings. An N+ polysilicon collector contact
33
is also provided on the buried layer
11
and P+ polysilicon base electrodes
23
are provided on the field oxide isolation regions
15
. The illustrated bipolar junction transistor also includes first and second interlayer insulating layers
25
and
37
, an emitter electrode
31
, intermediate emitter, base and collector contacts
51
,
53
and
55
(which may comprise tungsten) and emitter, base and collector wiring layers
52
,
54
and
56
.
Referring now to
FIG. 2
, region A within
FIG. 1
is illustrated in greater detail. As illustrated by
FIG. 2
, the bipolar junction transistor also includes an emitter region
41
, an intrinsic base region
43
and an extrinsic base region
42
. The extrinsic base region
42
may be formed as a self-aligned region by diffusing dopants from the polysilicon base electrode
23
into the intrinsic collector region
13
. As illustrated, the width of the extrinsic base region
42
may be dependent on the width W
2
of the contact formed between the polysilicon base electrode
23
and the intrinsic collector region
13
. The first interlayer insulating layer
25
may comprise silicon nitride and sidewall spacers
29
may be formed on sidewalls of the polysilicon base electrode
23
, as illustrated. The polysilicon emitter electrode
31
may also be formed in the opening
27
(having a width W
1
) between the sidewall spacers
29
. Emitter region dopants can also be diffused from the emitter electrode
31
into the intrinsic base region
43
, to define a self-aligned emitter region
41
. Unfortunately, because the patterning of the polysilicon base electrodes
23
typically requires a critical photolithographically defined masking and patterning step, the width of the opening W
1
and therefore the width of the intrinsic base region
43
and emitter region
41
may be relatively large. Such large dimensions may result in relatively large parasitic capacitance and may limit integration and the maximum oscillating frequency f
max
.
Thus, notwithstanding the above-described bipolar junction transistors and methods of forming bipolar junction transistors, there continues to be a need for more highly integrated bipolar junction transistors having improved electrical characteristics.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide bipolar junction transistors having improved electrical characteristics and improved methods of forming bipolar junction transistors.
It is another object of the present invention to provide highly integrated bipolar junction transistors and methods of forming highly integrated bipolar junction transistors.
It is still another object of the present invention to provide methods of forming bipolar junction transistors that utilize self-alignment techniques to more accurately control the dimensions of critical regions within the transistor.
These and other objects, advantages and features of the present invention are provided by bipolar junction transistors that utilize trench-based base electrodes and lateral base electrode extensions to facilitate the use of preferred self-alignment processing techniques. According to one embodiment of the present invention, a bipolar junction transistor is provided that includes an intrinsic collector region of first conductivity type (e.g., N-type) in a semiconductor substrate. A trench (e.g., ring-shaped trench) is also provided in the substrate. This trench extends adjacent the intrinsic collector region. According to a preferred aspect of the present invention, a base electrode of second conductivity type (e.g., P-type) is provided in the trench and a base region of second conductivity type is provided in the intrinsic collector region. This base
Farahani Dana
Myers Bigel Sibley & Sajvoec
Samsung Electronics Co,. Ltd.
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