Semiconductor device manufacturing: process – Forming bipolar transistor by formation or alteration of... – Including passive device
Reexamination Certificate
2001-07-31
2002-11-12
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Forming bipolar transistor by formation or alteration of...
Including passive device
C257S539000, C438S703000
Reexamination Certificate
active
06479360
ABSTRACT:
BACKGROUND OF THE INVENTION
Semiconductor devices constructed using bipolar transistors are inclined to have their base widths formed as thinly as possible in order to achieve high speeds.
FIG. 5
shows a related method of manufacturing a semiconductor device having a bipolar transistor. An embedded n+ layer
12
an n-epitaxial growth layer
14
are formed on a p-type silicon substrate
10
taken as a semiconductor substrate. A trench element separation insulation film
16
and a filed insulation film
18
are formed on the p-type silicon substrate
10
. A silicon oxide film
11
is formed on the region forming the trench element separation insulation film
16
, the field insulation film
18
and the bipolar transistor. A surface of the p-type silicon substrate
10
is then flattened. A contact hole is then formed at the silicon oxide film
11
on the n-type epitaxial growth layer. A polysilicon film is then formed on the entire surface of the p-type silicon substrate
10
using CVD (Chemical Vapor Deposition) techniques. Predetermined patterns can then be formed from the polysilicon film by subjecting the polysilicon film to photolithographic and etching. After this, impurities are injected into the p-type silicon substrate
10
in the following manner. An n-type impurity is injected into the polysilicon pattern connected to the n-type epitaxial growth layer
14
. A p-type impurity is then injected at a polysilicon pattern constituting a base lead-out electrode. A prescribed impurity is then injected into a polysilicon pattern constituting a resistance element. The p-type silicon substrate
10
is then heated to a temperature of 900 to 1000° C. A collector n+ layer
20
diffused with n-type impurity is then formed at the n-type epitaxial growth layer
14
as a result of this heat treatment. Similarly, a base lead-out electrode
26
and a resistance element
24
having a prescribed resistance value formed at the silicon oxide film
11
as a result of this heat treatment. This situation is shown in FIG.
5
(
a
).
Next, a silicon oxide film
28
is formed as an insulation film at the surface of the p-type silicon substrate
10
. After this, an opening is formed at a prescribed region of the base lead-out electrode
26
using photolithographic and etching processes. Next, a silicon nitride film
30
is formed as an insulation film at the silicon oxide film
28
including the opening. A silicon nitride film side wall is then formed within the opening by etching. The silicon oxide film
11
is then removed from within the opening and a p-type epitaxial layer is formed at the p-type silicon substrate
10
. This p-type silicon substrate
10
is then the base p layer
32
. This situation is shown in FIG.
5
(
b
). A polysilicon film including an n-type conductive impurity that becomes an emitter lead-out electrode
36
to be described later is formed on the surface of the silicon nitride film
30
. Next, an emitter n+ layer
34
is formed at the p-type silicon substrate
10
using heat treatment. An emitter lead-out electrode
36
is then formed on the p-type silicon substrate
10
using photolithographic and etching processing, so that an npn transistor is formed as a result of the above processes. This situation is shown in FIG.
5
(
c
).
After this, a protective pattern is formed for the silicon oxide film
38
a
on the resistance element
24
. Next, polysilicon film not covered by the polysilicon oxide film
38
a
is injected with impurity ions. This ion injection is carried out in order to lower the resistance of contacts connecting interconnect formed afterwards and the resistance element. A silicon oxide film
42
is then formed on the surface of the p-type silicon substrate
10
as an insulation film. Next, a contact hole is formed at the silicon oxide film
42
using photolithographic and etching processing. This contact hole is used for electrically connecting the base lead-out electrode
26
. emitter lead-out electrode
36
, collector lead-out electrode
22
and resistance element
24
to interconnect formed afterwards. An interconnect plug
44
is then formed by burying the contact hole thus formed with a high fusion point metal such as tungsten. An aluminum alloy film constituting an interconnect film is then formed on the silicon oxide film
42
including the interconnect plug
44
. Interconnect
46
is then formed by patterning this aluminum alloy film. After this, an insulation film
48
is formed as a protective film on the silicon oxide film
42
including the interconnect
46
. This situation is shown in FIG.
5
(
d
).
The width of the base film can therefore be made thin by controlling the thickness of the base p layer
32
and the diffusion of the emitter n+ film
34
in this manner.
However, in the aforementioned semiconductor device manufacturing method there is the fear that the width of the base layer will be formed in an uneven manner due to the p-type epitaxial layer being formed in a thin manner in order to increase speed. This kind of unevenness in the base layer width dramatically influences the amplification factor of the bipolar transistor. In order to suppress this influence, the value of the resistance element
24
required in bias regulation is adjusted in line with the amplification factor of the transistor. As a method of adjustment, there is provided a method where the resistance value of the resistance element
24
is adjusted using the position of a contact for connecting with the resistance element
24
. This adjustment of the contact position is carried out by modifying the mask. However, in this method it is necessary to prepare a new mask for adjustment, and the range of adjustment of the resistance value is narrow. Further, the resistance element pattern is formed long beforehand in order to broaden the degree of freedom of setting the position of contact. Parasitic capacitance occurring between the resistance element pattern and the p-type silicon substrate
10
therefore increase and interconnect delays become more substantial.
SUMMARY OF THE INVENTION
The structure of the semiconductor device of the present invention comprises a circuit element formed on a semiconductor substrate and a resistance element, electrically connected to the circuit element and being formed on an inter-layer insulation film covering said circuit element.
Further, the resistance value of the resistance element can be set according to the characteristics of the circuit element.
In the present invention, the circuit element can be a bipolar transistor and bias regulation of the bipolar transistor can be carried out by the resistance element.
On the other hand, the method of manufacturing the semiconductor device of the present invention comprises the steps of: forming a circuit element on a semiconductor substrate; forming a first insulation film covering the circuit element; forming a contact hole for connecting. with an electrode of the circuit element in a first insulation film; forming an interconnect plug within the contact hole and a prescribed interconnect pattern on the first insulation film using a high fusion point metal film; forming a second insulation film covering the interconnect pattern; forming an opening in the second insulation film in such a manner that part of the interconnect pattern and part of the upper surface of the first insulation film are exposed; and forming a polysilicon film of a prescribed conductive impurity concentration and film thickness covering and extending over part of the interconnect pattern and part of the top surface of the first insulation film.
The polysilicon film can be formed using CVD techniques in such a manner as to control the film thickness and the impurity concentration of the polysilicon film.
In the present invention, the film thickness of the polysilicon film and the impurity concentration can be set based on the results of measurements taken of the characteristics of the circuit element prior to forming the polysilicon film.
The polysilicon film can therefore be formed using CVD techn
Lee Calvin
Oki Electric Industry Co. Ltd.
Smith Matthew
Volentine & Francos, PLLC
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