Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Amorphous semiconductor
Reexamination Certificate
2000-07-31
2001-08-14
Christianson, Keith (Department: 2813)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Amorphous semiconductor
Reexamination Certificate
active
06274463
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to seeding a media layer using its most favorable growth substrate. More specifically, the present invention relates to seeding the crystallization of a media layer using a substrate that encourages a favorable growth morphology, while fabricating the media layer on one or more layers that lead to an unfavorable growth morphology.
Articles and publications set forth herein are presented for the information contained therein: none of the information is admitted to be statutory “prior art” and we reserve the right to establish prior inventorship with respect to any such information.
BACKGROUND ART
There are many cases in thin film device processing where a given material grows with a favorable morphology on one substrate type but not on another. One method for improving growth morphology on an unfavorable growth substrate is to deposit an underlayer (i.e. a buffer layer) on the substrate having an unfavorable growth morphology, followed by depositing an active layer on the buffer layer. The buffer layer must promote a favorable growth morphology for the active layer. In particular, for photoconductive or cathoconductive devices such as those potentially used in high-density data storage devices, an ideal buffer layer would include: a favorable growth morphology for a data layer that is deposited on the buffer layer; a smooth surface upon which to deposit the data layer; the buffer layer must be electrically insulating and thermally conductive; and the buffer layer must be non-reactive with both the data layer and the substrate the buffer layer is deposited on. Unfortunately, a buffer layer which meets all those requirements may not exist.
Another method for improving growth morphology on an unfavorable growth substrate is to use a wafer-bonding approach. In this method, an active layer is deposited on a first substrate that includes a layer having a favorable growth morphology, then the first substrate may be mechanically bonded to a second substrate having an unfavorable growth morphology. However, bonding the first and second wafers with the degree of flatness and robustness needed for many applications would be very difficult. The first and second substrates can be made from similar or dissimilar materials. For example, the first substrate can be a semiconductor substrate and the second substrate can be glass. Additionally, wafer bonding often requires several processing steps to planarize the active layer and to reduce the thickness of the first and/or the second substrate. The planarization steps can include chemical mechanical polishing (CMP) and the substrates can be reduced in thickness by planarization and/or by wet/dry etching steps. Those steps can often result in damage to the active layer and the number of steps involved complicate the fabrication process and can result in reduced yield. Moreover, applications that require a high degree of flatness and separation control between substrates will not tolerate wafer bonding. For instance, in ultra-high density storage devices, information can be written onto the active layer and read from the active layer using an electron beam current. Any damage to the active layer or variations in the thickness of the active layer can result in the data being corrupted or the inability to accurately write data to or read data from the active layer. A more detailed discussion of ultra-high density storage devices and the storage of data in a storage medium can be found in U.S. Pat. No. 5,557,596 to Gibson et al.
Accordingly, there is a need to seed the growth of an active layer using its most favorable growth substrate without resorting to the use of a buffer layer or wafer bonding. Furthermore, there is a need to seed the growth of the active layer without having to deposit the active layer directly on a substrate having a favorable growth morphology.
SUMMARY OF THE INVENTION
The method of the present invention discloses a solution wherein growth of a media layer is seeded on its most favorable substrate without using a buffer layer or wafer bonding. Uses for the media layer of the present invention include but are not limited to a medium for an ultra-high density data storage device that stores data in the media layer using a coherent beam of light or an electron beam, for example.
One advantage of the present invention is that standard microelectronic processing steps and commonly available processing equipment can be used to crystallize an amorphous media layer. For instance, lateral solid epitaxial overgrowth is a commonly used technique for silicon on insulator (SOI) and gallium nitride (GaN) device fabrication and that technique can be used to deposit the media layer of the present invention. See for example, Moniwa et al., Applied Physics Letters, Vol. 52, No. 21, pg. 1788, May 23, 1988. Moreover, the overgrowth of the media layer is applied not with the goal of making a silicon (Si) device on a Si wafer, but to make a compound semiconductor device on an insulating layer like silicon oxide (SiO
2
), for example.
Another advantage of the present invention is that it permits the seeding of the growth of a compound semiconductor material such as a III-VI material, a I-III-VI material, or a IV-V-VI material on silicon, a favorable substrate for growth, while fabricating the actual device on an insulating layer such as SiO
2
, an unfavorable substrate for growth but a useful substrate for photoconductive and cathoconductive devices. SiO
2
and its analogs like SiN
x
are also useful dielectric layers for heterojunction diodes which also may be used in high-density data storage devices. The media layer of the present invention has the appropriate electrical properties for use in a photoconductive or photovoltaic detector scheme as part of an ultra-high density storage device.
Broadly, the present invention is embodied in a method for crystallizing an amorphous film formed on an underlaying layer having an unfavorable crystalline growth morphology. A favorable growth substrate has a first unfavorable growth layer formed a seeding surface thereof. An aperture is formed in the first unfavorable growth layer. The aperture extends through the first unfavorable growth layer down to the favorable growth substrate and exposes the seeding surface. An amorphous media layer is formed on the first unfavorable growth layer. The amorphous media layer covers the first unfavorable growth layer so that a portion of the amorphous media layer fills the aperture and is in contact with the seeding surface. A crystallized media layer is formed by annealing the amorphous media layer. Resulting is a nucleation of a crystalline phase of the amorphous media layer that begins at the seeding surface and propagates into the remainder of the amorphous media layer so that the entirety of the amorphous media layer is crystallized. The crystallized media layer is then treated to destroy electrical communication between the crystallized media layer and the favorable growth substrate. Essentially, the crystallized media layer is electrically insulated from the favorable growth substrate to prevent a short circuit between the favorable growth substrate and the crystallized media layer.
In one embodiment of the present invention, the first unfavorable growth layer is a dielectric material that electrically insulates the favorable growth substrate from the crystallized media layer.
In another embodiment of the present invention, a second unfavorable growth layer is formed on the first unfavorable growth layer.
In one embodiment of the present invention, the second unfavorable growth layer is a dielectric material.
In another embodiment of the present invention, the second unfavorable growth layer is an electrically conductive material.
In yet another embodiment of the present invention, the favorable growth substrate is a semiconductor material.
In one embodiment of the present invention, the amorphous media layer is annealed to crystallize the amorphous media layer by heating the amorphous media laye
Christianson Keith
Denny III Trueman H.
Hewlett--Packard Company
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