Semiconductor device manufacturing: process – Having magnetic or ferroelectric component
Reexamination Certificate
2001-10-10
2002-10-01
Chaudhuri, Olik (Department: 2813)
Semiconductor device manufacturing: process
Having magnetic or ferroelectric component
C438S048000, C438S104000
Reexamination Certificate
active
06458603
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for fabricating a micro-technical structure, in particular a ferromagnetic structure for use in a MRAM (Magneto-resistive Random Access Memory), wherein a mask is structured, the mask is arranged on a substrate and the micro-technical structure is generated on a surface region of the substrate which is not covered by the mask. The invention also relates to a micro-technical component having a substrate and a micro-technical structure arranged on the substrate.
Particularly in the case of microelectronic components, i.e. electronic components whose structure dimensions reach the micron range and even the sub-micron range, special, highly developed structuring processes are employed. Structures with particularly small dimensions are desired in particular for the development of data memories. However, structuring processes of this type are also employed for microstructures for other applications, such as for example write and/or read heads for hard disks.
It is known to use lithography processes and etching processes to structure thin layers and layer systems. In particular, in this case the lithography processes generate structures in photo resist layers, and etching processes transfer these structures into the thin layers or layer systems which lie below the photo resist layers. Anisotropic plasma etching processes, such as for example RIE (Reactive Ion Etching), RSE (Reactive Sputter Etching), ECR etching (Electron Cyclotron Resonance etching), ICP etching (Inductively Coupled Plasma etching) and CAIBE (Chemically Assisted Ion Beam Etching) are known for layer structuring in the micron (&mgr;m) and sub-micron (sub-&mgr;) range. With etching processes of this type, it is necessary for the reaction products formed from the material which is to be etched away to pass into the gas phase so that they can be removed from the reaction chamber. Numerous materials which are suitable for microstructures in terms of their physical properties cannot be satisfactorily structured using some or all of the known etching processes, since the reaction products which are formed during the etching form a passivating layer on the surface of the material which is to be etched, thus preventing further etching and removal of the material. Furthermore, etching processes in general may lead to redeposition of the material which has been etched off, for example on etching masks, the edges of the regions which are to be etched and on parts of the etching chamber. This leads, for example, to undesirable inclined etching flanks and changes to the dimensions of etching masks. However, electrical short circuits caused by electrically conductive redeposition on the flanks of multilayer systems may also occur.
Particularly for use in future MRAMs (Magneto resistive Random Access Memories), structures with ferromagnetic materials, such as Ni, Fe and Co, as well as alloys comprising these materials, are produced and tested for suitability. When structuring these materials using etching processes, the nonvolatile passivating layers described above are formed. S. J. Pearton, et al., in the publication “High Rate Etching of Metals for Magneto Electronic Applications,” Electrochemical Society Proceedings Vol. 97-21, pages 270-85 (hereinafter “Pearton”) propose using a plasma etching process with a high ion density, in order to avoid the formation of a disruptive passivating layer. According to Pearton, the high ion density leads to a high ion flux, so that normally nonvolatile reaction products are sputtered away. Pearton proposes etching ferromagnetic metal alloys, such as NiFe and NiFeCo, in the presence of Cl in the etching gas. Although this leads to higher etching rates than with pure Ar etching gas, chlorine-containing compounds that are thereby formed lead to corrosion of the metal alloys after the etching. The chlorine-containing compounds have to be removed in a further process step.
It is reported in the publication “Assessment of Dry Etching Damage in Permalloy Thin Films” by S. D. Kim et al., Journal of Applied Physics, Vol. 85, No. 8, pages 5992-5994, dated Apr. 15, 1999, that plasma dry etching processes, such as IBE (Ion Beam Etching) and RIE (Reactive Ion Etching), in the case of NiFe (Permalloy), lead to the magnetic properties being impaired, on account of the bombardment with ions.
A further drawback of plasma etching techniques is the low selectivity of the etching action both with respect to the etching mask and with respect to the substrate on which the material to be etched is arranged. This leads to etching masks being worn away and to undesirable structuring of the substrate.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method of fabricating a micro-technical structure and a micro-technical component with a micro-technical structure formed on a substrate, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and wherein the generation of the final lateral dimensions of the structure (structuring) effects and/or causes and/or has caused as far as possible no damage to the structure and the substrate. Particularly in the case of structures comprising ferromagnetic materials, the magnetic properties of these materials are not to be adversely affected by the structuring and subsequent process steps caused by the structuring.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of fabricating a micro-technical structure, in particular a ferromagnetic structure for an MRAM. The method comprises the following steps:
providing a substrate;
forming a structured shadow mask on the surface of the substrate, and defining on the surface an uncovered surface region not covered by the mask and a shadow region shadowed but not covered by the mask; and
depositing material through the mask in a directed deposition process and forming the micro-technical structure on the uncovered surface region of the substrate not covered by the mask.
With the above and other objects in view there is also provided a micro-technical component, comprising:
a substrate; and
a micro-technical structure formed on the substrate and extending along a common interface with the substrate, the micro-technical structure having been fabricated with the above-outlined method, and a shaping of a surface or at least one layer of the structure at an edge of the structure resulting only from a deposition of the structure material in the directed deposition process.
An important idea of the present invention is to arrange the material of the structure on the substrate in the same process step as at least part of the structuring of the structure which is to be fabricated. The structure is laterally delimited in at least one location of the substrate purely by the fact that the structure material is arranged on the substrate. This eliminates the need for a following etching process, which could cause damage to the structure and/or the substrate.
In one embodiment, a mask is structured and arranged on the substrate in such a manner that the mask shadows but does not cover a surface region of the substrate. In the direction of a surface normal, the mask is situated at a distance from the surface in this surface region. Then, material of the structure which is to be fabricated is deposited on the substrate in a directed deposition process. The term “directed deposition process” is understood as meaning a deposition process wherein the material which is to be deposited generally moves in a directed manner, namely in a straight line, toward the deposition location. This does not rule out the possibility of the direction of movement of the material which is to be deposited being changed, for example by the interaction of a plurality of particles of the material being deposited and/or deflection from structure edges and/or by scattering on fixed structures. However, most of the material which is to be deposited will
Kersch Alfred
Miethaner Stefan
Schwarzl Siegfried
Wendt Hermann
Chaudhuri Olik
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Schillinger Laura
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