Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2002-09-06
2004-05-25
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S479000
Reexamination Certificate
active
06740551
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a transistor having a structure that prevents the potential of a support substrate under a buried insulating film from greatly affecting the characteristics of a transistor formed on a SOI wafer. In particular, the present invention relates to a so-called source-body-tie transistor in which a source-body-tie region is provided in the vicinity of a source region of a transistor.
2. Description of the Related Art
FIGS. 5A
to
5
D and
FIGS. 6A
to
6
C illustrate a method of manufacturing a conventional SOI transistor, and
FIGS. 7A and 7B
are a structural plan view and a cross-sectional view of the conventional SOI transistor. Herein, a transistor is formed by using a wafer in which a P-type semiconductor film
51
is formed on a P-type support substrate via a buried insulating film. The conventional SOI transistor is formed in the semiconductor film
51
in a region surrounded by a LOCOS
58
reaching the buried insulating film as shown in
FIGS. 7A and 7B
, and each transistor is completely isolated by the LOCOS
58
. In the case of an N-type transistor, since the semiconductor film
51
is of a P-type, a transistor is formed by implanting N-type ions into source/drain regions
64
and
76
. On the other hand, in the case of a P-type transistor, a transistor is formed by implanting N-type ions into the semiconductor film
51
surrounded by the LOCOS
58
, and implanting P-type ions into source/drain regions
63
and
75
under the condition that the semiconductor film
51
is kept in an N-type. According to the manufacturing method, as shown in
FIGS. 5A
to
5
D, patterning and etching are conducted first so as to imprint an alignment mark on a wafer and a thermal oxide film
54
is formed, and a resist
56
is applied thereto. Then, alignment and exposure to light are conducted, and patterning for the purpose of implanting a well is conducted. Next, ions are implanted using the resist
6
as a mask to form a well
55
. At this time, the energy of ion implantation is controlled so that the semiconductor can have the peak of a concentration distribution. Then, a heat treatment is conducted, whereby the implanted ions are activated and diffused. Then, a nitride film
57
is formed, patterned, and thermally oxidized to form a LOCOS
58
. At this time, thermal oxidation is conducted so that the LOCOS
58
reaches the buried insulating film
52
. After forming the LOCOS
58
, a gate oxide film
59
is formed, a gate electrode
60
is formed, and ions are implanted into source/drain regions
63
,
64
,
75
and
76
of the transistor and source-body-tie regions
61
and
62
, whereby an interlayer insulating film
70
is formed. The interlayer insulating film
70
is patterned and etched to form contacts of the gate electrode
60
, the source/drain regions
63
,
64
,
75
and
76
, and the source-body-tie regions
61
and
62
.
The insulating film
52
is disposed between the support substrate
53
and the semiconductor film
51
, so that the potential of the support substrate
53
is floated. In the SOI transistor, the potential of the support substrate
53
affects the characteristics of a transistor, so that it is required to fix the potential of the support substrate
53
. The potential of the support substrate
53
is set as follows: the support substrate
53
is attached to a conductive base by a conductive adhesive when being mounted in a package, and the potential is taken from the base. Generally, the support substrate is connected to a ground terminal or a power source voltage terminal.
There is also another method of taking the potential of the support substrate side from the semiconductor film side. Specifically, a through-hole is provided so as to reach a part of the support substrate
53
through the semiconductor film
51
and the buried insulating film
52
, thereby taking a potential. In this case, in the same way as in the method of taking a substrate potential of a bulk transistor, a contact is provided on the periphery of the transistor, and the potential of the support substrate
53
is taken.
According to the conventional method of forming an SOI transistor, since there is a buried insulating film between a support substrate and a semiconductor film, a transistor on the semiconductor film is not electrically connected to the support substrate, and the potential of the support substrate is floated. However, in a complete depletion type SOI transistor and the like, a semiconductor film is entirely depleted in the thickness direction and depletion reaches a buried insulating film. Therefore, the potential of the support substrate greatly affects the characteristics of the transistor, and a change in potential of the support substrate exhibits the same characteristics as that of a back gate effect of a bulk transistor.
Therefore, it is required to fix the potential of the support substrate. Generally, according to the method of fixing the potential of the support substrate, the support substrate is attached to a conductive base by a conductive adhesive when being mounted in a package, and the potential of the base is fixed, whereby the potential of the support substrate is fixed. The potential of the support substrate is connected to a ground terminal or a power source voltage terminal.
In the case where the potential of the support substrate is fixed by the above-mentioned connection method, all the back gate voltages of transistors formed on a semiconductor film on the support substrate become the same. Therefore, either of a P-type or an N-type transistor is supplied with a back gate voltage. For example, it is assumed that an inverter circuit is formed on a wafer composed of a P-type support substrate and a P-type semiconductor film. If it is assumed that the potential of the support substrate is set at a ground potential, the state of an N-type transistor of the inverter circuit becomes equal to the state where a back gate voltage is not supplied; however, the state of a P-type transistor thereof becomes equal to the state where a back gate voltage equivalent to a power source voltage is applied. Therefore, even if a threshold voltage and a current driving ability are combined in a circuit design, the threshold voltage of a transistor changes to a power source voltage, which brings about a change in timing of a circuit and variation in a driving ability.
Particularly in a voltage regulator and a voltage detector, even if a power source voltage is changed, it is required that a constant voltage is continuously output and constant voltage detection is kept. In the case where the above-mentioned SOI transistor is used in such an IC, there occurs a problem such that an output voltage fluctuates due to the fluctuation of a power source voltage, and a detection voltage fluctuates.
Furthermore, as a method of taking a potential of a support substrate side from a semiconductor film side, there is a method of taking a potential by providing a through-hole that reaches a part of the support substrate through a semiconductor film and a buried insulating film. In this case, a through-contact is provided in the vicinity of a transistor, and a power source voltage terminal is connected to a ground terminal to fix the potential of the support substrate. However, an original SOI device has a latch-up free structure. Therefore, it is not required to provide a guard ring of a transistor, which has the effect of reducing an area. However, according to a method of providing a through-contact on the periphery of a transistor so as to fix the potential of the support substrate, the effect of reducing an area of an SOI device is decreased.
Furthermore, according to the manufacturing method of providing a through-contact on the periphery of a transistor so as to fix the potential of a support substrate, it is required to form a through-hole that reaches a part of the support substrate through a semiconductor film and a buried insulating film, resulting in increase of
Wake Miwa
Yoshida Yoshifumi
Adams & Wilks
Lattin Christopher
Niebling John F.
Seiko Instruments Inc.
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