Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1998-02-17
2003-01-07
Whitehead, Jr., Carl (Department: 2822)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S637000, C438S782000
Reexamination Certificate
active
06503825
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming multi-layer wiring structure on a semiconductor wafer or on a glass substrate.
2. Description of Related Art
In general, a device being formed on a semiconductor wafer or on a glass substrate has a multi-layer wiring structure, in with which wiring of lower and upper layers are electrically connected through a so-called via hole.
And, under such a multi-layer wiring structure in which only an insulating film or layer lies between the upper wiring layer and the lower wiring layer, an unevenness of the lower wiring layer still remains on the surface of the insulating film or layer, and it causes a cut down of the upper wiring layer which is formed on the uneven surface by a CVD method. Therefore, technologies for flattening are normally applied, by which recesses are filled up with SOG (Spin-On-Glass: silicon oxide film which is formed by coating and baking solution of silicon compound). Among those technologies regarding an inorganic SOG including Si—H chemical bond, it is disclosed in, for example, Japanese Patent Laying-Open No. Hei 8-316,228 (1996).
The SOG, which is disclosed in Japanese Patent Laying-Open No. Hei 8-316,228 (1996), however, is the inorganic SOG including the Si—H chemical bond, therefore, it shows high dielectric constant in comparison with that of an organic SOG, and is easy as to cause cracking due to heat.
The organic SOG does not have the problems that the inorganic SOG has. On the other hand, it is easy to cause a defect which is called “poisoned via” when a resist film is treated by a so-called ashing process by using oxygen gas. Especially in the organic SOG, an organic group (for example, a methyl group (CH
3
)) is bonded to Si, and the methyl group is larger than hydrogen atom of the inorganic SOG in atomic radius thereof, therefore, it causes serious problems.
Explaining this by referring to
FIG. 5
showing a method for forming a multi-layer wiring structure of conventional art, first of all, as shown in FIG.
5
(
a
), after being formed with a lower wiring layer
101
thereon, the substrate W is further formed with a hillock protection film
102
by CVD. Further, as shown in FIG.
5
(
b
), the SOG film
103
is formed on it and thereafter, as shown in FIG.
5
(
c
), an upper wiring layer
104
is formed on the SOG film
103
. Further, a patterned resist layer
105
is provided as shown in FIG.
5
(
d
), and as shown is FIG.
5
(
e
), the via hole (or through hole)
106
is formed by using the patterned resist layer
105
as a mask through an etching process on the hillock protection film
102
, the SOG film
103
and the upper wiring layer
104
. Next, as shown in FIG.
5
(
f
), the patterned resist layer
105
is removed by the ashing process. Furthermore, as shown in FIG.
5
(
g
), conductive material
107
such as aluminum is filled within the via hole
106
, thereby electrically connecting between them and constructing the multi-layer wiring structure.
And, in the case that the organic SOG is applied to, as shown in FIG.
5
(
f
), the organic components thereof are decomposed or resolved when the resist layer is treated by the ashing process, and the productions such as water, etc., are stored within the films, thereby causing the defect
108
being called the “poisoned via”.
Therefore, a method as shown in
FIG. 6
, in which the organic SOG is used and an etching back process is necessarily included therein, is applied. Namely, as shown in FIG.
6
(
a
), after being formed with the lower wiring layer
101
, the substrate W is further formed with the hillock protection film
102
by the CVD, and further on it is formed the SOG film
103
. Next, as shown in FIG.
6
(
b
), the etching back process is treated for removing the organic SOG film
103
by a predetermined thickness with an oxygen plasma, etc., thereby removing the organic SOG film
103
just above the lower layer wiring
101
. Thereafter, as shown in FIG.
6
(
c
), the upper wiring layer
109
is formed, and as shown in FIG.
6
(
d
), the patterned resist layer
105
is formed to cover on the upper wiring layer
104
. As shown in FIG.
6
(
e
), by treating with the etching process and the ashing process continuously, the via hole
106
is formed on the hillock protection layer
102
and the upper wiring layer
104
as well as removing the resist layer, and further, as shown in FIG.
6
(
f
), the conductive material
107
such as aluminum is filled within the via hole
106
, thereby electrically connecting between them and constructing the multi-layer wiring structure.
By treating with the etching back process as shown in
FIG. 6
, the via hole is not formed in a position where the organic SOG film
103
is located, therefore, the “poisoned via” will not occur.
However, in recent years, a further promoted microscopic processing (for instance, less than 0.3 &mgr;m) is required, and if the wiring pattern is miniaturized, the thickness of the organic SOG becomes thick where the wiring patterns are concentrated or close to each other, while it is thin where the wiring patterns are coarse or rough.
Under such condition, if the organic SOG film is etching backed, there is a disadvantage that even the wiring layer is also removed by the etching process where the wiring patterns are coarse or rough.
SUMMARY OF THE INVENTION
For dissolving the disadvantages mentioned in the above, in accordance with the present invention, there is provided a method for forming multi-layer wiring structure, wherein a lower wiring layer and a upper wiring layer are electrically connected through a via hole, comprising the following steps: forming an organic SOG layer directly or through a predetermined film including a hillock protection layer on said lower wiring layer; forming said upper wiring layer on said organic SOG layer without processing of etching back; forming a via hole through an etching process by using a patterned resist layer provided on said upper wiring layer as a mask; performing an ashing process with a plasma by making ion or radical which is induced from oxygen gas as a main reactant, under an atmosphere of pressure ranging from 0.01 Torr to 30.0 Torr; and burying said via hole with conductive material so as to electrically connect between said lower wiring layer and said upper wiring layer.
By performing the process of making the ion or radical which is induced from the oxygen gas as the main reactant under pressure ranging from 0.01 to 30.0 Torr, preferably, by performing the ashing process under low pressure ranging from 0.01 to 1.2 Torr, it is possible to suppress the decomposition or resolution of the organic group(for example, the CH
3
group, etc.) which is bonded to the Si atom of the organic SOG film, and as a result of this, the “poisoned via” and so on will not occur during the ashing process. Accordingly, it can be accomplished without such the etching back.
A carbon content of said organic SOG layer lies between 5 through 25 in atomic weight %, more preferably, between 8 through 20 in atomic weight %. Here, the carbon content can be theoretically calculated from a reaction amount of the alkoxysilane compound for preparing a coating liquid of forming the organic SOG, and it is the ratio of carbon atom weight with respect to the total atomic weight of all elements.
If the carbon content is less than the range mentioned above, since the organic component is too small to thicken the film or layer, it is easy to cause the cracks therein in addition to losing an inherent advantage thereof, i.e., low dielectric constant. On the other hand, if it is too much, it is not preferable since shortage occurs in adhesion between an insulating layer which is provided on an upper layer.
For obtaining the film having the carbon content mentioned in the above, it is preferable to use, for example, a coating liquid containing a compound, which is obtained through hydrolysis and condensation of at least one being selected from alkoxysilane compounds in an organic solvent under existence of a
Hagiwara Yoshio
Iida Hiroyuki
Matsushita Atsushi
Ohbuchi Kazuto
Brophy Jamie L.
Jr. Carl Whitehead
Mercahnt & Gould P.C.
Tokyo Ohka Kogyo Ltd.
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