Method for manufacturing semiconductor device

Details Method for manufacturing semiconductor device Method for manufacturing semiconductor device

2002-09-05

2003-11-11

Dang, Phuc T. (Department: 2818)

Semiconductor device manufacturing: process

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

Having insulated gate

C438S250000

Reexamination Certificate

active

06645807

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device provided with electrodes or wiring that are formed sandwiching an adhesion layer on a dielectric film.
In semiconductor memories, the reduction in size of memory cells due to the miniaturization of the design is progressing. For example, DRAM (Dynamic Random Access Memory) memory cells, which are one type of semiconductor memories, are made of a memory cell transistor and a capacitor for charging electron. In DRAMs, even though the memory cells have been reduced in size and the area of the capacitor projected onto the substrate (referred to as “capacitor area” in the following) has become small, it is not possible to reduce the capacitance of the capacitor, in order to reduce the power consumption and in order to prevent soft errors. The capacitance of the capacitor is generally proportional to the relative dielectric constant of the dielectric material used for the dielectric film (capacitance dielectric film) constituting the capacitor as well as to the capacitor area, and inversely proportional to the film thickness of the capacitance dielectric film. However, if the film thickness of the capacitance dielectric film is made small in order to increase the capacitance of the capacitor, then the leak current in the capacitor increases. As a result, it becomes necessary to shorten the refresh cycle of the memory cells, so that the power consumption increases. This means that there is a limit to how thin the capacitance dielectric film can be made.
In order to address this problem, in recent years, the use of dielectric materials with high relative dielectric constant (high-k material) for the capacitance dielectric film has been researched as a way of increasing the capacitance of the capacitor. High-k materials that have been researched in detail include for example metal oxides such as aluminum oxide or tantalum pentoxide (composition formula: Ta
2
O
5
), barium strontium titanium oxide (composition formula: (Ba
(1-x)
Sr
x
)TiO
3
; referred to as “BST” in the following), lead zirconium titanium oxide (referred to as “PZT” in the following), and strontium bismuth tantalum oxide (referred to as “SBT” in the following), which have a perovskite crystal structure.
When the dielectric film is formed using such a high-k material, then, in general, chemical reactions are utilized often, and the formation of the dielectric film is performed in an oxidizing atmosphere, so that if silicon, which has been used conventionally, is used as the electrode material, the silicon tends to be oxidize. That is to say, a silicon oxide film with a low relative dielectric constant is formed, so that it becomes difficult to increase the capacitance of the capacitor. Consequently, a precious metal or a refractory metal or the like is used for the electrodes of capacitors using such a high-k material for the capacitance dielectric film. Furthermore, a precious metal or a refractory metal or the like is used also for the electrodes of capacitors using a ferroelectric material instead of a high-k material for the capacitance dielectric film.
More specifically, when the high-k material tantalum pentoxide is used for the capacitance dielectric film, then ruthenium (symbol of element: Ru), tungsten (symbol of element: W), molybdenum (symbol of element: Mo) or the like is used for the electrodes. Furthermore, when BST is used for the capacitance dielectric film, then Ru, ruthenium dioxide (composition formula: RuO
2
), platinum (symbol of element: Pt), iridium (symbol of element: Ir) or the like is used for the electrodes. Moreover, when a ferroelectric material such as SBT or PZT is used for the capacitance dielectric film, then Pt, Ir, iridium dioxide (composition formula: IrO
2
) or the like is used for the electrodes.
FIG. 3
shows the cross-sectional structure of a conventional capacitor using BST for the capacitance dielectric film.
As shown in
FIG. 3
, an interlayer dielectric film
52
is formed on a semiconductor substrate
51
, on which a memory cell transistor (not shown in the figure) is formed. In the interlayer dielectric film
52
, a plug
53
for connection with this memory cell transistor is formed. On the interlayer dielectric film
52
including the top of the plug
53
, an adhesion layer
54
is formed, and a lower electrode
55
is formed on that adhesion layer
54
. The adhesion layer
54
is made of titanium (symbol of element: Ti) or tantalum (symbol of element: Ta) or of an oxide or a nitride of these metals. On the lower electrode
55
, a capacitance dielectric film
56
is formed so as to cover the top surface and the lateral surfaces of the lower electrode
55
. On the capacitance dielectric film
56
, an upper electrode
57
is formed. The three-layered structure of the lower electrode
55
, the capacitance dielectric film
56
and the upper electrode
57
constitutes the capacitor. The lower electrode
55
and the upper electrode
57
are made of Pt. The capacitance dielectric film
56
is made of a BST film with a thickness of about 25 nm.
Here, the adhesion of the lower electrode
55
to the dielectric film is weak, so that if the lower electrode
55
is formed directly on the interlayer dielectric film
52
, then there is the possibility that the lower electrode
55
separates from the interlayer dielectric film
52
. To prevent this, the adhesion layer
54
made of a metal such as Ti or Ta or an oxide (e.g. TiO
x
, TaO
x
) or a nitride (e.g. TiN
x
, TaN
x
) of these metals is arranged between the lower electrode
55
and the interlayer dielectric film
52
, thus improving the adhesion of the lower electrode
55
to the underlying dielectric film. It should be noted that recently, oxides and nitrides of, for example, titanium aluminum, tantalum silicon or tantalum aluminum have been used as the material for the adhesion layer
54
.
However, such an adhesion layer oxidizes much easier than the electrodes made of a refractory metal or precious metal. Furthermore, depending on the thickness and the formation method of the adhesion layer, the metal atoms constituting the adhesion layer (referred to as “adhesion layer metal” in the following) may be diffused throughout the lower electrode and be deposited on the surface of the lower electrode. When in this situation a high-k film such as a BST film is formed as the capacitance dielectric film, then it is ordinarily formed in an oxidizing atmosphere of about 300 to 700° C., so that the adhesion layer metal that has been deposited on the surface of the lower electrode is oxidized. As a result, a volume expansion occurs due to the oxidized layer formed on the surface of the lower electrode, so that an excess force is exerted on the capacitor portion or film separation occurs.
On the other hand, a method of suppressing the diffusion of the adhesion layer metal throughout the electrode and the deposition on the electrode surface is conceivable in which a sufficiently oxidized adhesion layer is formed first. However, the following problems occur if in the course of forming, for example, a titanium oxide (TiO
x
) film as the adhesion layer a Ti film is annealed in an oxidizing atmosphere to form the TiO
x
film, or the TiO
x
film is deposited while letting Ti react with oxygen in a vapor phase, or the TiO
x
film is deposited using a reactive sputtering process, by admixing oxygen when sputtering Ti.
In the case of annealing a Ti film in an oxidizing atmosphere, a temperature of at least 500° C. is necessary, so that impurities included in the source and drain regions of the transistor already formed on the substrate are diffused again, so that the desired transistor properties cannot be obtained.
In the case of depositing the TiO
x
film while letting Ti react with oxygen, or in the case of depositing the TiO
x
film using a reactive sputtering process, the Ti may not be sufficiently oxidized, so that as mentioned above, Ti atoms are diffused throughout the Pt film (i.e. the Pt electrode) serving as the lower electrode, and d

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