Sputter target, barrier film and electronic component

Details Sputter target, barrier film and electronic component Sputter target, barrier film and electronic component

2002-10-21

2004-06-15

Flynn, Nathan J. (Department: 2826)

Active solid-state devices (e.g., transistors, solid-state diode

Combined with electrical contact or lead

Of specified material other than unalloyed aluminum

C257S767000, C257S295000, C257S763000, C257S765000

Reexamination Certificate

active

06750542

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a sputter target suitable for forming a barrier material for a semiconductor substrate or the like and to a barrier film and an electronic component using the same.
BACKGROUND ART
A storage device using a ferroelectric thin film as a storage medium, namely, a so-called ferroelectric memory (FRAM), has recently been under active development. The ferroelectric memory, which is nonvolatile, has such a characteristic that storage capacity thereof is not lost even after power source is cut off. Furthermore, spontaneous polarization inversion is very rapid if the film thickness of the ferroelectric thin film is sufficiently small, so that a rapid write and read comparable to DRAM can be realized. Since a memory cell of one bit can be constituted by a single transistor and a single ferroelectric capacitor, the ferroelectric memory is also suitable for mass storage.
As a ferroelectric material, lead zirconate titanate (a solid solution of PbZrO
3
and PbTiO
3
(PZT)) having a perovskite structure is mainly used. PZT, however, has such a disadvantage that its major component Pb is likely to be diffused and vaporized at a relatively low temperature (approximately 500° C.), even though having such characteristics of a high Curie temperature (approximately 300° C.) and large spontaneous polarization, and therefore, it is said to be difficult for PZT to cope with miniaturization. Barium titanate (BaTiO
3
(BTO)) is known as a typical ferroelectric material besides PZT. BTO, however has such a disadvantage that remanent polarization thereof is greatly temperature-dependent due to small remanent polarization and a low Curie temperature (approximately 120° C.) compared with PZT.
It has been found out, however, that BTO, when epitaxially grown on a Pt/MgO(100) substrate, allows a BTO film having a film thickness of, for example, 60 nm to exhibit the Curie temperature of 200° C. or higher. Moreover, it has been confirmed that, when barium strontium titanate (Ba
a
Sr
1-a
TiO
3
(BSTO)) is epitaxially grown on a lower electrode made of Pt and strontium ruthenate (SrRuO
3
(SRO)), ferroelectricity appears in a composition region (a≦0.7) which is not expected to exhibit the ferroelectricity by nature. This is because a lattice of a BSTO crystal in a C-axis direction is extended.
Since a ferroelectric Curie temperature shifts to a higher temperature side in such a BSTO film of a Ba rich, large remanent polarization is obtainable in a room temperature zone, and sufficiently large remanent polarization can be retained even when the temperature is increased up to approximately 85° C. Consequently, a ferroelectric film suitable for the storage medium of FRAM can be realized. Meanwhile, the use of BSTO of an Sr rich can realize a thin-film capacitor whose dielectric constant reaches several times (for example, 800 or higher) as that of a capacitor made of a polycrystalline film. Such a dielectric property is suitable for DRAM.
The practical availability of semiconductor memories such as FRAM and DRAM is expected through the use of the thin-film capacitor having the epitaxially grown BTO film and BSTO film as described above. In putting these into practical use, it is necessary to combine a semiconductor substrate on which a switching transistor is formed and a memory cell using a perovskite oxide film (thin-film capacitor). At this time, a problem exists that the diffusion of elements such as Pt, Ru, Sr, and Ba, which constitute the lower electrode and the dielectric thin film of the thin-film capacitor, into the transistor has an adverse effect on a switching operation.
Under the circumstances, a barrier film which prevents mutual diffusion needs to be formed between the thin-film capacitor and the semiconductor substrate. Further, the barrier film itself needs to be epitaxially grown on the semiconductor substrate in order to obtain the above-described epitaxial effect. The use of a titaium nitride (TiN) film and a film made of Ti
1-x
Al
x
N(Ti—Al—N) which is a solid solution of TiN and aluminum nitride (AlN) has been studied as such a barrier film.
TiN, which is superior in a barrier property against Al and the like, is also utilized as a barrier metal in generally-used Si devices. It is also excellent in thermal stability since it is a chemical compound whose melting point is high (3000° C. or higher), and has a very low specific resistance, approximately 50 &mgr;&OHgr;·cm in a polycrystalline film and approximately 18 &mgr;&OHgr;·cm in an epitaxial film, which results in an advantage that contact resistance can be lowered in utilizing an electric property in the thickness-wise direction.
When TiN is used as the barrier film of the thin-film capacitor, however, oxygen is diffused onto the TiN film, for example, due to annealing at a high temperature (for example, 600° C. or higher) conducted in an element production process for controlling crystallization of the ferroelectric film so that nitrogen (N) in TiN is substituted by oxygen (O) to form an oxide film, namely, TiO
2
. The lower electrode made of Pt, SRO, and so on becomes inferior in adherence due to volume expansion thereof based on TiO
2
generated on the surface of the TiN film and due to the generation of N
2
gas. This results in a problem that peeling occurs in the lower electrode.
When Al is added to TiN to form the Ti
1-x
Al
x
N(Ti—Al—N) film, oxidation resistance can be enhanced. The Ti—Al—N film is formed by reactive sputtering in an atmosphere of argon (Ar) and nitride (N), using a Ti
1-x
Al
x
alloy (a Ti—Al alloy) target. Concerning the Ti—Al alloy target, for example, Japanese Patent Laid-open Application No. Hei 6-322530 specifies a Ti—Al alloy target constituted only of a diffusion reaction layer of high-purity Ti and high-purity Al.
Further, aiming at enhancing abrasion resistance and oxidation resistance of cutting tools, sliding components, and so on, Japanese Patent Laid-open Application No. Hei 8-134635 specifies a Ti—Al alloy target material with a relative density of 99.0 to 100% and free of any continuous defect from the surface to the bottom surface thereof. Japanese Patent Laid-open Application No. 2000-100755 specifies a Ti—Al alloy target for forming a barrier film of a semiconductor device, whose O content is in the range of 15 to 900 ppm.
Further, Japanese Patent Laid-open Application No. 2000-273623 specifies a Ti—Al alloy target, in which an Al content is 5 to 65 wt %, a radio active element such as U and Th is 0.001 ppm or lower, an alkali metal such as Na and K is 0.1 ppm or lower, Fe which is a transition metal is 10.0 ppm or lower, Ni is 5.0 ppm or lower, Co is 2.0 ppm or lower, Cr is 2.0 ppm or lower, and purity thereof including impurities is 99.995% or higher, and Japanese Patent Laid-open Application No. 2000-328242 specifies a Ti—Al alloy target containing 15 to 40 atm % or 55 to 70 atm % of Al and having a metal structure with an area ratio of a Ti
3
Al intermetallic compound being 30% or higher, and in which the number of defects with a diameter of 0.1 mm or larger is 10/100 cm
2
or less. Thus, various kinds of Ti—Al alloy targets have been developed.
The Ti—Al—N film which is formed by reactive-sputtering the conventional Ti—Al alloy target, however, is inferior in an epitaxial growth property on an Si substrate, which results in a problem of hindering the epitaxial growth of the BTO film and the BSTO film. In FRAM using such a BTO film or a BSTO film, a ferroelectric property such as remanent polarization is not sufficiently obtainable to lower the property and production yields of FRAM. When they are applied to DRAM, the property and production yields thereof are similarly lowered as well.
Further, when the Ti—Al—N film is formed by reactive-sputtering the conventional Ti—Al alloy target, sudden generation of huge dust is likely to occur while the film is formed by sputtering, which results in a problem of lowering the production yields of FRAM and DRAM. Such a problem is caused not only when the Ti—Al—N film is used as the barrier film of the t

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