Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1998-11-23
2001-03-27
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S289000, C257S321000, C257S411000
Reexamination Certificate
active
06208001
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to insulator layers for gallium arsenide semiconductor devices and, more particularly, to insulator layers derived from Group IIa metal fluorides which are formed on single crystal gallium arsenide substrates.
Materials used in semiconductor devices must have good semiconducting properties, good electron mobility, and the ability to host an insulating material. Several materials are available which have good semiconducting properties and good electron mobilities but which are unsuitable because a good insulator cannot be formed on them. Silicon, however, is widely used in semiconductor devices because silicon dioxide forms naturally on silicon and silicon dioxide is a good insulator. The disadvantage of silicon is that its mobility is not as high as other semiconductors and silicon dioxide is not the strongest insulator available. This means that compromises in speed and performance are made when silicon is used in electronic devices.
Gallium arsenide (GaAs) is also a semiconductor and is used in some electronic applications. A device made out of GaAs would be faster than the same device made out of silicon because GaAs has an electron mobility that is considerably higher than that of silicon. Unfortunately, there is no native insulating oxide suitable for GaAs electronic devices. Also, many opto-electronic devices using GaAs substrates rely on epitaxial insulator/semiconductor heterostructures with abrupt interfaces which further increases the challenge of finding a suitable insulator for GaAs substrates for these applications.
Several materials have been used to provide insulating films on III-V compound semiconductor devices. Some of these films were previously used on silicon semiconductor devices. Examples of these film materials include SiO
2
, Si
3
N
4
, Al
2
O
3
, and P
2
O
3
films. New films have also been developed specifically for the III-V compound semiconductors. For instance, A. J. Shuskus (U.S. Pat. No. 4,546,372) developed an essentially oxygen-free, amorphous, phosphorous-nitrogen glass passivating film for III-V compound semiconductors. Similarly, J. Nishizawa et al. (U.S. Pat. No. 4,436,770) disclose new gallium oxynitride and aluminum oxynitride insulating films for III-V compound semiconductors. However, these materials have found only limited application.
Although the high dielectric strength of barium fluoride (BaF
2
) (100) makes it a potentially interesting candidate as an insulating material, unfortunately BaF
2
and GaAs are severely lattice mismatched (~10% mismatched), which is a condition previously considered to be detrimental to epitaxial growth. The lattice mismatch problem has not been the only condition hindering the growth of epitaxial BaF
2
(100) on GaAs. It is known that the (100) face of the cubic fluorite structure of barium fluoride has a surface free energy far in excess of the (111) face. See, L. J. Schowalter et al., CRC Critical reviews in Solid State and Materials Sciences, pp. 367 (1989). For this reason, it has been thought that (111) growth is favored over (100) growth. Even when (100) growth is achieved, surface free energy considerations predict faceting of the (100) growth front into (111) asperites. This behavior has been observed for CaF
2
, as described in the above-cited Schowalter et al. publication, and BaF
2
, as described by M. F. Stumborg et al.,
J. Appl. Phys
. 77(6), 2739 (1995).
Clemens el al.,
J. Appl. Phys
. 66(4), 1680 (1989), reported being able to grow (100)-oriented BaF
2
on GaAs, but the orientation switched to (111) after only ~20 Å of film thickness. Furthermore, streaky RHEED patterns were not observed until the (111) orientations began to dominate. Films grown with a 400° C. substrate temperature exhibited signs of misoriented mosaic structures (i.e., rings in the RHEED patterns). Depositions at higher temperatures (580° C.) did not yield streaky RHEED patterns, leading Clemens el al. to state a conclusion that no two-dimensional growth of (100)-oriented barium fluoride seemed possible.
Truscott et al.,
J of Crystal Growth
, 81, 552 (1987), also investigated the growth of BaF
2
on GaAs as well as the reverse heterostructure. They also found temperature dependent RHEED patterns indicative of (100) and (111) growth modes. However, they reported no achievement of two-dimensional BaF
2
(100) layers. In fact, they reported their BaF
2
films to be conducting, presumably due to Ga diffusion into the BaF
2
layer.
In view of the above, it would be desirable to provide an improved thin film insulator for gallium arsenide electronic devices which yields high quality device characteristics such as high-break down voltage.
SUMMARY OF THE INVENTION
In accordance with this invention, a unique insulator layer for single crystal gallium arsenide substrates is provided in which the insulator layer is compliantly matched with the substrate and the insulator layer is free of defects causing surface roughness problems which could impair device performance.
To accomplish this, the insulator layer is formed on a gallium arsenide substrate as an integral composite or variegated structure including (1) a uniform homogenous film of Group IIa metal atoms attached directly onto a gallium arsenide substrate surface in the form of a monolayer, and (2) a single crystal epitaxial film of a Group IIa metal fluoride deposited on the monolayer.
To fabricate the uniform, defect-free homogenous film portion of the insulator layer, the homogenous film is formed as the reaction product of a reaction between a Group IIa metal fluoride vapor and a gallium arsenide substrate surface in the presence of an arsenic gas overpressure. The arsenic gas overpressure effectively causes a monolayer of group IIa metal atoms to attach and form directly upon the gallium arsenide substrate surface without unreacted metal atoms (i.e., metal atoms not directly attached to the substrate surface) remaining in the homogenous film when the reaction is completed (i.e., the monolayer formation is completed) and a deposition of the epitaxial film of Group IIa metal fluoride onto the monolayer has commenced. The monolayer serves as a compliant interfacial layer that prevents lattice-mismatching problems from arising as between the gallium arsenide substrate and the epitaxial metal fluoride layer. Since the insulator layer can be fabricated in this manner in extremely thin submicron thicknesses while still being defect-free (i.e., without surface roughness problems and other crystalline defects such as dislocations and stacking faults), gallium arsenide electronic components which incorporate the insulator layer are endowed with superior break-down voltage characteristics, among other things.
The single crystal gallium arsenide substrate, upon which the insulator layer can be formed and utilized, may be a wafer or epitaxial layer of gallium arsenide, or a gallium arsenide based semiconductor alloy or a heterostructure of super-lattice made of a combination of gallium arsenic based alloys, or any of these forms of gallium arsenide as provided on another suitable substrate. Preferably, the single crystal gallium arsenide substrate surface and the single crystal epitaxial Group IIa metal fluoride film both are (100) oriented. In another preferred embodiment, the Group IIa metal fluoride used in fabricating the insulator film is barium fluoride.
A wide variety of gallium arsenide semiconductor devices can benefit from incorporating the insulator film of the present invention, including gallium arsenide metal insulator semiconductor field effect transistors (MISFETs), charge couple devices (CCDs), integrated circuit capacitors, nonvolatile memory, optical waveguides, and so forth. e
REFERENCES:
patent: 4291327 (1981-09-01), Tsang
patent: 4550331 (1985-10-01), Milano
patent: 4692993 (1987-09-01), Clark et al.
patent: 4847666 (1989-07-01), Heremans et al.
patent: 5124762 (1992-06-01), Childs et al.
patent: 5352917 (1994-10-01), Ohmi
patent: 5435264 (1995-07-01), Santiago et al.
patent: 2-266569 (1
Boulais Kevin A.
Chu Tak Kin
Santiago Francisco
Stumborg Michael F.
Bechtel, Esq. James B.
Hoch, Esq. Ramon R.
Jackson, Jr. Jerome
The United States of America as represented by the Secretary of
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