Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1996-04-25
2001-10-23
Jones, Dwayne C. (Department: 1614)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S618000, C438S622000, C438S627000, C438S628000, C438S629000, C438S632000, C438S635000, C438S643000, C438S644000, C438S648000, C438S650000, C438S653000, C438S654000, C438S656000, C438S658000, C438S660000, C438S722000, C438S906000, C438S619000
Reexamination Certificate
active
06306761
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of improving a burying characteristic in burying a recessed portion formed in an insulating film with a conductive film by high pressure reflow.
Recent VLSIs are required to integrate millions of elements on a chip of several mm square. Such a VLSI is essential to adopt a multilayer interconnection structure for suppressing an increase in area ratio of an interconnecting portion on the basis of the total chip area. The thickness of an interlayer insulating film for insulating upper and lower interconnections from each other, however, cannot be thinned more than a specified value for ensuring the insulating performance. This makes it difficult to reduce the design rule of a substrate in the vertical direction as compared with that in the horizontal direction. Moreover, from now on, such an interlayer insulating film tends to be planarized by chemical/mechanical polishing (CMP) or the like for ensuring the resolution of lithography and the reliability of an upper interconnection, and thereby a local difference in thickness is increased for the interlayer insulating film on a substrate. This tends to increase the aspect ratio of a connection hole opened in the interlayer insulating film. For example, there appears a connection hole having an aspect ratio increased up to a value of from 4 to 5.
To cope with the increased aspect ratio of a connection hole, it has come to be important to bury the connection hole with a conductive (metal) film, and various metal burying techniques such as a brancket W (tungsten)-CVD method, high temperature Al sputtering method, and Al reflow method have been examined, and partially put in practice.
The blanket W-CVD method for forming a W film over the entire surface of a substrate has been most extensively used at present from the viewpoints of an excellent burying characteristic and a high process stability. Such a technique, however, is practically used only for a plug portion (buried in a connection hole) because a Ti based adhesive layer must be formed for enhancing adhesiveness of the W film to an insulating film and the resistivity of W is higher than Al. Accordingly, this technique has various problems that an etch-back process of the W film is required; the terminal determination of the etch-back is difficult; an interconnection extracting portion to be connected to the plug portion must be formed on the interlayer insulating film by patterning of an Al film; and WF
6
as a source gas for the W film is expensive. These factors increase the number of processes and complicate the processes, to thereby reduce the throughput and increase the cost.
On the contrary, the high temperature Al sputtering method and the Al reflow method are advantageous in that the number of processes is smaller than the bracket W-CVD method because the plug portion and the interconnection extracting portion can be simultaneously formed by a single kind of metal. The high temperature Al sputtering method is intended to promote the surface migration of Al atoms deposited on a substrate by keeping the substrate at a high temperature during sputtering, thereby improving the burring characteristic in-situ. On the other hand, the Al reflow method is intended to form an Al film on a substrate by a usual method such as sputtering and to heat the substrate at a temperature in a range of from a recrystallization temperature of Al to a melting point (about 660° C.) of Al, thereby allowing the Al film to reflow on the substrate for burying. Each of these techniques, however, is required to heat a substrate at a temperature more than about 500-550° C. for burying, which tends to exert adverse effect on the already formed Al interconnection, to generate an Al spike on the Si substrate, or to degrade the surface planarization of the Al film itself. The burying abilities of these techniques are also low. For example, these techniques are limited to be applied to a hole having an aspect ratio less than about 2 to 3, and consequently, they are impossible to cope with the future high aspect ratio.
In view of the foregoing, a high pressure reflow method modified from the above-described Al reflow method has been proposed. This method is intended to perform-the reflow in an inert gas atmosphere at a pressure in a range of about from several tens to one hundred and several tens atm as described in “Abstracts of IEDM, pp. 105-108, 1994”. This method will be described below with reference to FIG.
15
.
Referring to
FIG. 15
, a viahole
33
is opened in a SiO
x
interlayer insulating film
32
covering a lower interconnection
31
in such a manner as to reach the lower interconnection
31
. A Ti underlying film
34
is formed in such a manner as to cover on the inner surface of the viahole
33
, and an Al—Cu conductive film
35
containing Cu in an amount of from 0.5 to 2% is formed in such a manner as to block the opening end of the viahole
33
. Here, the Ti film
34
, which is provided for enhancing adhesiveness between the SiO
x
interlayer insulating film
32
and the Al—Cu film
35
, is typically formed by sputtering (hereinafter, referred to as “sputtering film”).
The Al—Cu film
35
is also typically formed by sputtering. The sputtering, however, is originally poor in step coverage. In particular, when the opening diameter of the viahole
33
is fine at the sub-half micron level and the aspect ratio of the viahole is large, sputter particles are difficult to reach the bottom of the hole; and the deposited film becomes thick while forming an overhung near the opening end of the hole and then the leading ends of the overhung portions are joined to each other to block the opening end. A void
36
shown in
FIG. 15
is formed by such a mechanism. The deposition profile on the wafer, however, is extremely advantageous for the high pressure reflow method intended to press the conductive film in the connection hole while applying a high pressure to the conductive film in an inert atmosphere such as Ar. With such a high pressure reflow method, the viahole
33
can be perfectly buried with the Al—Cu film
35
in the suitable condition, and the surface of the Al—Cu film
35
is planarized. At this time, an inert gas remaining in the void
36
seems to be absorbed by the Al—Cu film
35
.
In addition, the high pressure reflow is performed at a substrate temperature of from 400 to 450° C., which is lower than that (about 500 to 550° C.) of the high temperature Al sputtering or a usual Al reflow. This is advantageous in preventing connection breakage of a contact portion with the Si substrate, preventing adverse effect exerted on an already formed Al interconnection, and preventing surface roughness of the Al—Cu film itself. The high pressure reflow-method can also cope with a connection hole having an aspect ratio in a range of about from 4 to 5.
Incidentally, the detail mechanism of burying a connection hole by the high pressure reflow method is not perfectly apparent; however, it is known by experience that the growth of a hard metal oxide having a high melting point on the surface of a conductive film obstructs the thermal flow of the conductive film to suppress the smooth burying. Such a metal oxide may be formed on the upper surface of a conductive film or at the boundary with an underlying film depending on the kinds of the multilayer structure, forming method and forming system of the conductive film. In each case, the metal oxide film degrades the burying characteristic. The formation of such a metal oxide film will be described with reference to
FIGS. 16 and 17
.
FIG. 16
shows a state that an Al oxide film
37
is grown on the surface of the Al—Cu film
35
in FIG.
15
. The sputtering system used for forming the Al—Cu film
35
is usually independent from the high pressure reflow system for allowing the Al—Cu film to reflow at a high pressure, and thereby the wafer completed in sputtering is carried from the sputtering system once to atmospheric
Delacroix-Muirheid C.
Jones Dwayne C.
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
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