Semiconductor device and process of fabrication thereof

Details Semiconductor device and process of fabrication thereof Semiconductor device and process of fabrication thereof

2000-05-08

2002-05-21

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Making field effect device having pair of active regions...

Having insulated gate

C438S263000

Reexamination Certificate

active

06391701

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and the process of fabricating such a device, and more particularly to a semiconductor device having its gate oxide films differ from each other in film thickness and formed on a same semiconductor substrate, and a process of fabrication thereof.
2. Description of the Related Art
It is required to increase a degree of integration of system LSIs and like circuits in the art, wherein these circuits have a plurality of functions and are formed on a same semiconductor substrate. In a semiconductor device thus formed, a plurality of voltage levels are often used. In such a case, a plurality of gate insulation films varying in film thickness are formed on the same semiconductor substrate, wherein a thickness of each of the gate insulation films is dependent on each of the voltage levels used therein. One of conventional semiconductor devices of this type is disclosed in Japanese Laid-open Patent No. Hei 10-223774.
Now, with reference to sectional views shown in
FIGS. 6A
to
6
E, a conventional process of fabricating such conventional semiconductor device will be described, wherein the conventional semiconductor device is provided with a plurality of gate insulation films which are different from each other in film thickness.
In this conventional process of fabricating the conventional semiconductor device, first, as shown in
FIG. 6A
, a field insulation film
2
is formed on a device isolation region (hereinafter may also be referred to as an ISO region) of an upper surface of a semiconductor substrate
1
by using a LOCOS (Local Oxidation of Silicon) process which is well known in the art. As a result, a plurality of device forming regions (ACTA and ACTB regions) are separated from each other and defined as individual device forming regions by such formation of the field insulation film
2
.
Then, as shown in
FIG. 6B
, a plurality of gate insulation films
3
are formed on the surface of the semiconductor substrate
1
having been exposed in these device forming regions. Subsequent to the above, a resist film
4
is formed to cover all the field insulation film
2
and the gate insulation films
3
.
After that, as shown in
FIG. 6C
, the resist film
4
is patterned by photolithography and etching: to form an opening portion
5
of the resist film
4
in a position corresponding to that of the device forming region (ACTB region) in which a second gate insulation film
6
thin in film thickness should be formed; and, to cover the other device forming region (ACTA region) in which a first gate insulation film
3
a
thick in film thickness is formed. Then, the gate insulation film
3
thus exposed through the opening portion
5
of the resist film
4
is removed by wet-etching with the use of the thus patterned resist film
4
as a mask.
Subsequent to the above, as shown in
FIG. 6D
, all the resist film
4
is removed. After that, the surface of the semiconductor substrate
1
is subjected to a thermal oxidation process in positions corresponding to those of the device forming regions ACTA and ACTB, and thereby: additionally forming the second gate insulation film
6
in the surface of the semiconductor substrate
1
in the positions corresponding to those of the ACTB regions; and, increasing the gate insulation film
3
in film thickness due to addition of a newly oxidized portion of the surface of the semiconductor substrate
1
thereto to form the first gate insulation film
3
a
thick in film thickness in the positions corresponding to those of the ACTA regions.
Now, as shown in
FIG. 6E
, a polysilicon film is formed and patterned over an entire surface of the semiconductor substrate
1
, so that a plurality of the gate electrodes
7
is formed. Then, the first gate insulation film
3
a
and the second gate insulation film
6
are selectively removed by etching with the use of the gate electrodes
7
as masks, so that only those of the first gate insulation film
3
a
and the second gate insulation film
6
having been covered by the gate electrodes
7
remain unremoved to form a first gate insulation film
3
b
and a second gate insulation film
6
a
, respectively.
Subsequent to the above, drain/source region, S/D regions
8
a
,
8
b
, are formed in the exposed surface of the semiconductor substrate
1
in positions adjacent to opposite sides of each of the gate electrodes
7
by ion implantation of a conductive impurity into the surface of the semiconductor substrate
1
with the use of the gate electrode
7
as a mask.
The above ion implantation process is followed by well-known conventional process steps, so that the conventional semiconductor device having its first and its second gate insulation film
3
b
,
6
a
differ from each other in film thickness is completed in fabrication.
Now, a problem to be solved by the present invention will be described.
In the above-mentioned conventional process of fabricating the semiconductor device, however, there is a danger that a so-called “teardrop (“Mizutama” in Japanese language)” defect appears in each of the surface of the gate insulation film
3
and the surface of the semiconductor substrate
1
, in which defect the additional first gate insulation film
3
a
and the second gate insulation film
6
additionally formed are not formed in the gate insulation film
3
and the surface of the semiconductor substrate
1
, respectively, during the process step shown in FIG.
6
D.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a semiconductor device and a process of fabricating such a device, wherein: the semiconductor device has its gate insulation films differ from each other in film thickness; and, the process of fabrication of the device is capable of preventing each of a surface of a semiconductor substrate of the device and a surface of each of the gate insulation films of the device from being contaminated, and therefore capable of normally forming a new gate insulation film on each of the surface of the previous gate insulation film and the surface of the semiconductor substrate.
According to a first aspect of the present invention, there is provided a process of fabricating a semiconductor device provided with a plurality of gate insulation films varying in film thickness, wherein the gate insulation films are formed on the same semiconductor substrate, the process of fabricating a semiconductor device including the steps of:
selectively forming a device isolation region on a surface of the semiconductor substrate to form a plurality of device forming regions which are separated from each other through the device isolation region;
forming the first gate insulation film in each of the device forming regions on a surface of a semiconductor substrate;
forming a protection film made of an inorganic material on the first gate insulation film, wherein the inorganic material is resistant to an etching action exerted on the first gate insulation film;
forming a first photosensitive etching-resistance film on the protection film, wherein the first photosensitive etching-resistance film is resistant to an etching action exerted on the protection film;
patterning the first photosensitive etching-resistance film to form an opening portion of the first photosensitive etching-resistance film in a predetermined one of the device forming regions;
etching the protection film through the opening portion of the first photosensitive etching-resistance film to have the first gate insulation film exposed in the predetermined one of the device forming regions;
removing the thus exposed first gate insulation film by using the protection film as a mask so that the surface of the semiconductor substrate is exposed; and
forming the second gate insulation film on the thus exposed surface of the semiconductor substrate.
In the foregoing, a preferable mode is one wherein the second gate insulation film is formed in a condition in which a protection film is not removed.
Also, a preferable mode

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