Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Powder pretreatment
Reexamination Certificate
1999-07-14
2001-10-09
Jenkins, Daniel J. (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Powder pretreatment
C419S026000, C419S045000, C419S048000, C419S049000, C419S057000, C419S060000
Reexamination Certificate
active
06299831
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the fabrication of low-oxygen copper/chromium sputter targets for use in physical vapor deposition of thin films.
BACKGROUND OF THE INVENTION
In the manufacture of sputter targets used in the semiconductor industry, and more particularly sputter targets used in physical vapor deposition (PVD) of thin films onto complex integrated circuits, it is desirable to produce a sputter target that will provide film uniformity, minimal particle generation during sputtering, desired electrical properties and minimal chip defect. Furthermore, to meet the reliability requirements for diffusion barriers or plugs of complex integrated circuits, the sputter target must have high-purity and high-density.
Cu/Cr thin films are commonly used as the adhesion/barrier layer in flip-chip bonding to form the interconnection between the semiconductor chip and the substrate, such as an aluminum bonding pad or ceramic base. The Cu/Cr film is deposited between a Cu layer and a Cr layer. The Cu layer adheres the solder, typically 90Pb/10Sn, to the chip, whereas the Cr bonds to the Al pad or ceramic base.
Current methods to achieve suitable Cu/Cr sputter targets for use in complex integrated circuits involve blending fine particle size Cu and Cr powders followed by sintering the powder by hot-pressing or hot-isostatic-pressing. Using either of these techniques to press powders with powder sizes less than 20 &mgr;m, the density of the pressed target material is about 90% of theoretical density. The fine grain size of the powder materials is believed to contribute to higher uniformity of the deposited film. However, the sputter targets fabricated by these methods have a high oxygen content, on the order of about 3000 ppm average. The inventors of the present invention have discovered that the fine powder size distribution used in Cu/Cr targets is a large contributing factor to the high oxygen content in the pressed sputter target blanks, and that oxygen in the Cu/Cr layer contributed via target sputtering is detrimental to the integrity of the film, and results in an increase in the percentage of chip defect. The sputter targets currently produced, which have an average oxygen content of about 3000 ppm, generate defects in about 3% of the semiconductor chips, on average. Thus, the Cu/Cr sputter targets fabricated by hot-pressing or hot-isostatic-pressing fine particle size powders have proved unreliable for use in complex integrated circuits.
There is thus a need to develop a method for fabricating low-oxygen, high-density Cu/Cr sputter targets that will meet the reliability requirements for complex integrated circuits, and specifically, that will decrease or eliminate chip defects due to high oxygen content.
SUMMARY OF THE INVENTION
The present invention provides a Cu/Cr sputter target having a density of at least about 90% of theoretical density and an oxygen content less than about 1000 ppm, and preferably less than 900 ppm. This high-density, low-oxygen Cu/Cr sputter target is fabricated by (a) blending a Cu powder having a controlled powder size in the range of about 20 &mgr;m to about 150 &mgr;m and an oxygen content preferably less than about 1200 ppm with a Cr powder having a controlled powder size in the range of about 20 &mgr;m to about 150 &mgr;m and an oxygen content preferably less than about 600 ppm, and a total oxygen content in the blended powder preferably less than 900 ppm and more preferably less than 800 ppm; and (b) pressing the powder for at least about 1 hour to a density of at least 90% of theoretical density. The pressed Cu/Cr target has an oxygen content less than about 1000 ppm, preferably less than 900 ppm, and the thin films deposited therefrom have about 0% defect generation.
In a first embodiment of the present invention, the blended powder is hot-isostatic-pressed at a temperature of about 950° C. to about 1050° C. and a pressure of about 10 ksi to about 40 ksi for about 1 hour to about 5 hours. In a second embodiment of the present invention, the blended powder is hot-uniaxial-pressed at a temperature of about 950° C. to about 1050° C. and a pressure of about 1 ksi to about 4 ksi for about 1 hour to about 8 hours. Prior to hot-uniaxial-pressing, the powder may be heated to about 250° C.-300° C. for about 1-4 hours in a hydrogen-purged vacuum hot-pressing chamber.
These and other objects and advantages of the present invention shall become more apparent from the accompanying drawings and description thereof.
REFERENCES:
patent: 5718778 (1998-02-01), Murata et al.
patent: 5778302 (1998-07-01), Ivanov
patent: 01309961 (1989-12-01), None
patent: WO9712074 (1997-04-01), None
ASM Handbook, vol. 7, Powder Metallurgy, pp. 308-309, 501, 1984.
Biederman Blake T.
Jenkins Daniel J.
Praxair S.T. Technology, Inc.
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