Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2001-07-31
2003-09-09
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192120, C204S298150, C204S298160, C204S298230, C204S298280, C427S128000, C427S255500, C427S571000, C118S730000
Reexamination Certificate
active
06616816
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims the priority of Japanese Patent Application No. 2000-233593, filed in Japan on Aug. 1, 2000, the entire contents of which is hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of Industry to Which the Invention Belongs
The present invention pertains to a substrate processing device and processing method and, in particular, it relates to a substrate-processing device in which a film is grown on a substrate while a magnetic field is imparted in a prescribed direction of the substrate.
2. Discussion of Related Art
In recent years, in the field of semiconductors and magnetic films, magnetic heads and recording elements have been proposed which employ a GMR (Giant Magnetoresistive structure) or a TMR (Tunnel Magnetoresistive structure) which generate an MR (Magnetoresistive effect) in which the electric resistance value is significantly altered by an external magnetic field (R&D Research and Development, July 1999, Vol. 41 No. 8 p 14-16).
A brief description of the MR effect will be given with reference to FIG.
3
. By way of example, a film comprising the principal GMR structure function has an Fe pin layer
301
, Cu spacer layer
302
, and IrMn free layer
303
. The direction of magnetization of the pin layer
301
, which is magnetized in advance in a constant direction
304
, is unaltered by the external magnetic field
305
. On the other hand, the direction of magnetization
306
of the free layer
303
can be reversed by the external magnetic field
305
. In multiple-layer films, the electrical resistance value when the pin layer
301
and the direction of magnetization of the free layer
303
are opposed, as in FIG.
3
(
b
), is different than when they are the same, as in FIG.
3
(
a
). Accordingly, when a voltage is imparted into the multiple-layer film MR, such as shown in
FIG. 4
, the magnetic data can be detected by the measurement of the resistance values.
Utilizing the anisotropy of the electric resistance, the leakage magnetic field of a magnetic disk is detected and can be used in heads of magnetic disks. In addition, electrical resistance changes are maintained even if there is no electric current flow, so their application as a non-volatile memory (MRAM: Magnetic Random Access Memory) is anticipated.
In reality, these GMR structures are laminated multiple-layer structures of 5 to 9 layers of magnetic and non-magnetic materials and, in the production thereof, by virtue of the fact that the film is grown while a magnetic field is imparted, the pin layer, which is supported in the direction of magnetization, must be magnetized in the one direction.
As is shown in
FIG. 5
, for the final formation of elements, patterning must be performed with pellets
503
of the MR multi-layer structure aligned with a prescribed direction
502
of the substrate
501
. In order to afford the uniformity of the characteristics of these elements within the substrate surface, a magnetic field
504
, applied to the elements during growth, must conform with the prescribed direction of the substrate and be imparted uniformly within the substrate surface.
Hitherto, a substrate of diameter 100 mm or 125 mm has been employed for the production of magnetic heads and, as shown in
FIG. 6
, a magnet has been deployed in the outer circumference of the substrate in such a way that a magnetic field of a prescribed direction parallel with the substrate surface is generated and the film is grown. That is to say, a magnet
603
, in which a permanent magnet is assembled, is arranged in the outer circumference of a substrate holder
601
and a substrate
602
, and a magnetic field vector
604
is imparted in a constant direction on the substrate surface. The numbers in FIG.
6
(
b
) represent magnetic field strength.
In the case of a magnetic film for MRAM or magnetic heads, a magnetic field of uniform direction must be maintained at all times during growth at ±1.5 degree or less from the prescribed orientation and, if a displacement greater than this occurs, large deviations in the pin layer holding power arise, and a nonuniformity in product performance occurs which markedly lowers the productivity.
On the other hand, because the characteristics of a magnetic device are altered significantly depending on the film thickness, uniformity of film thickness within the substrate surface is extremely important. This is explained with reference to FIG.
7
. FIG.
7
(
a
) is a specific example of an MR structure, in which the pin layer is a 2-layer configuration of CoFe
701
and NiFe
702
. FIG.
7
(
b
) shows, taking the film thickness of the CoFe layer
701
as 8 nm, the changes in holding power when the film thickness of the NiFe layer
702
was altered from 0.2 to 20 nm. As is shown in the diagram, it can be seen that the holding power was significantly altered even when the film thickness of the NiFe layer was different by just 1 nm. For this reason, when the uniformity of film thickness within the surface is poor, large deviations are generated in the holding power of devices taken from the substrate and the yield is markedly lowered. In this way, the uniformity of film thickness is extremely important in terms of consideration of productivity, and the film thickness distribution within the substrate surface [=(Maximum value−Minimum value)/(Maximum value+Minimum value)] must be ±1.5% or less and, in estimates of the performance of devices of the prior art, it must be suppressed to ±1% or less.
To improve the uniformity of film thickness within the substrate surface, a method exists in which the center axis of an evaporating source is arranged to be offset from the substrate central axis, and the film is grown while the substrate is rotated. This is a method hitherto employed in sputtering methods, vacuum-deposition methods, and MBE (Molecular Beam Epitaxy) (J. Sakai, S. Murakami, et al., J. Vacuum Science and Technology B 1989 p 1657). An example of a configuration of a sputtering device of the prior art employed for the growth of a MR film is shown in FIG.
8
.
FIG.
8
(
a
) is a diagram that shows the geometrical position relationship between a substrate
801
and a sputtering target
804
. The sputtering target
804
, is offset
805
in the outer circumferential direction from a substrate center axis
802
, and is fixed at a diagonal angle
806
. During film manufacture, the substrate
801
has self-rotation
803
about the substrate center axis
802
. FIG.
8
(
b
) shows the film thickness distribution when a film is formed on a substrate of diameter 200 mm using a target of diameter 87.5 mm. The film thickness distribution using a substrate of diameter 200 mm [=(Maximum value−Minimum value)/(Maximum value+Minimum value)] is ±0.45% and, by the employment of an offset-growth method—which involves substrate rotation—an extremely good film thickness uniformity can be obtained even if a comparatively small evaporating source is employed.
It will be noted that, to obtain a good film thickness distribution within the surface without the use of substrate rotation, by way of example, for a substrate of 200 mm a large sputtering target of diameter 450 mm or more is required, and the device costs and material cost are very high. In addition, in the case in which a different type of material is continuously grown while maintaining in vacuum without contaminated gas, a large chamber in which a plurality of large targets are arranged is required and extremely unfavorable conditions, from the point of view of economics, have to be accepted.
Accordingly, using a device in which a large substrate of diameter 125 mm is to be processed, a configuration is adopted in which the substrate is arranged in the approximate center of the chamber, the target center axis is displaced outward from the substrate center axis, and the substrate caused to rotate and, by virtue of this, it is possible for a film thickness distribution within the substrat
Anelva Corporation
Burns Doane , Swecker, Mathis LLP
McDonald Rodney G.
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