Method of filling an opening in an insulating layer

Details Method of filling an opening in an insulating layer Method of filling an opening in an insulating layer

1999-03-24

2001-06-12

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S597000, C438S598000, C438S618000, C438S629000, C438S633000, C438S648000, C257S618000, C257S621000, C257S622000, C257S623000, C257S624000, C257S776000

Reexamination Certificate

active

06245653

ABSTRACT:

The present invention relates to the fabrication process of integrated circuits and particularly to a method of fabricating structures for interconnecting at least parts of these integrated circuits. More particularly, openings, e.g. via openings or trenches, are formed in an insulating layer and filled with Al-containing and/or Cu-containing metals.
BACKGROUND OF THE INVENTION
The ongoing focus on miniaturisation and the increasing complexity of integrated circuits demands for a continuous higher density integration. To achieve this, there is an ongoing downscaling in the dimensions of the active devices as well as of the structures interconnecting these devices. These interconnect structures can comprise multiple metal layers which are, dependent on the desired interconnect pattern, either separated one from another by means of interlayer insulating layers or connected one to the other by means of a connection through the insulating layer. To provide such a connection, first openings are formed in the insulating layer and filled thereafter with a conductive material. Examples of such openings are via holes or contact holes or trenches. To meet the high density integration requirements, the diameter of these openings is decreasing, while at the same time the aspect ratio of these openings is increasing. Furthermore also the number of openings per unit area is increasing due to the high density requirements and therefore also due to the growing number of metal layers. As a consequence the filling process of these openings and in particular the filling yield, reliability and speed are becoming more and more critical.
Classically, the filling process of these openings is a process wherein an Al-containing metal is used to fill these openings. Several methods, i.e. filling processes, have been introduced which use conventional Physical Vapour Deposition, i.e. no directional sputtering by means of e.g. a collimator. Ono et al., Proc. VMIC, 1990, p. 76, describe a method wherein the Al is deposited onto the wafer at a low deposition rate in a single-step process. The wafer is kept at a high temperature of about 500° C. during deposition to ensure contact hole/via fill (Ono et al., Proc. VMIC, 1990, p. 76). Although it is possible to fill the openings with this one step process, one of the inherent disadvantages is that this process is too slow. Another disadvantage is that openings with different aspect ratios cannot be efficiently filled simultaneously on a wafer as required in a modern metallization scheme such as dual damascene.
In another method, as in Park et al., Proc. VMIC, 1991, p. 326, the Al film is first sputter deposited cold. In order to fill the contact openings and/or via openings, the wafer is heated in situ after this deposition in order to reflow the Al into the contact openings and/or via openings. In yet another method, as described in e.g. the United States patent applications U.S. Pat. Nos. 5,371,042 and 5,270,255, a thin and continuous Al-containing seed layer is sputtered cold onto a wetting layer formed in these openings. This sputtering is performed cold in order to avoid dewetting of the Al and the TiAl
3
formation. This wetting layer typically consists of either a single Ti layer or a triple barrier layer with a Ti rich surface. After deposition of the seed layer, the remainder of the Al-containing layer is sputtered at an elevated temperature, i.e. usually in the range of 400-500 ° C., and slowly in order to give the material enough time to flow into the opening.
These methods run into problems when the diameter of the opening decreases, particularly when the diameter is in the sub 0.5 &mgr;m range and/or for aspect ratios of 2:1 or higher. Because of the increased aspect ratio the deposition of a continuous Al-containing seed layer on the inner walls of the openings by line of sight sputtering is hampered. In fact, during the seed layer formation, the formation of an additional overhang on the top of the small features is initiated. What is typically observed in case of this conventional sputtering into an high aspect ratio opening is that bridging of the top of the via occurs and that a void is created. The void will then be filled by way of Al-containing bulk diffusion, i.e. from top to bottom, which is inherently slower than Al-containing surface diffusion, i.e. from bottom to top, in the temperature range used in the filling process. Consequently yield and reliability of this filling process for openings with high aspect ratios and sub 0.5 &mgr;m diameters is questionable, whereas the productivity is far too low.
AIM OF THE INVENTION
It is an aim of the present invention to introduce the principle of reaction enhanced wetting and simultaneous seed layer formation as a basis for a reliable Al-containing metal fill process. The idea is, in contrast to avoiding the TiAl formation, to use this reaction to its advantage for the creation of an ultra-thin continuous Al-containing seed layer. The latter will allow a bottom to top fill during the subsequent Al-containing metal deposition, independent of the dimension and geometry of the opening. As a consequence, the filling process proceeds much faster and is production worthy.
SUMMARY OF THE INVENTION
In an aspect of the invention a method for filling an opening in an insulating layer is disclosed comprising the steps of:
a) forming at least one opening in an insulating film;
b) forming a continuous wetting layer at least on an inner side wall of said opening;
c) depositing a first metal layer at least on said wetting layer at an elevated first temperature to thereby form a metal seed layer; and
d) depositing a second metal layer at an elevated second temperature to fill said opening from the bottom to the top.
The composition of the first metal layer, the deposition rate of the first metal layer and the composition of the wetting layer are correlated and are selected to meet the following criteria. At first the wetting layer has to be chosen such that during the deposition of the first metal layer dewetting is avoided, particularly a reaction between the wetting layer and this first metal layer is initiated. This reaction induces the wetting. Examples of such wetting layers are Ti-containing layers or Co-containing layers or Ni-containing layers. Examples of metal layers are Al-containing layers, e.g. Al, AlCu, AlSiCu, AlGeCu, AlSi, AlGe, or Cu-containing layers. At second, the deposition rate of the first metal layer is such that there is sufficient metal available to induce a reaction between the wetting layer and the first metal and simultaneously to form a metal seed layer. Particularly, in an embodiment of the invention, the first metal layer is an Al-containing layer, the wetting layer is a Ti rich layer, the reaction involved is between Al and Ti, i.e. 3Al+Ti→Al
3
Ti and a Al seed layer is formed. Alternatively, the first metal layer can be a Cu-containing layer, the wetting layer can be a Co rich or a Ti rich layer, the reaction involved can be between Cu and Ti or between Cu and Co, and a Cu seed layer can be formed.
According to the method of the present invention, during the deposition of the first and the second metal layer the temperature has to be sufficiently high in order to facilitate the flow of the metal. Particularly, the elevated first and second temperature have to be chosen close to the melting point of the metal under pressurized conditions, i.e. in vacuum. Therefore, these temperatures are typically in the range from 100° C. below the melting point of said metal layer in vacuum to about the melting point of said metal layer in vacuum. Particularly when said metal layer is an Al-containing layer, like e.g. Al or AlCu, these temperatures are typically in the range from 400° C. to 500° C. Even more particularly, the deposition of the first metal layer and the deposition of the second metal layer can be performed subsequently in a chamber of a deposition tool without breaking vacuum, i.e. without switching between low pressure and atmospheric pressure. Furthermore also th

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