Method of forming article comprising an oxide layer on a...

Details Method of forming article comprising an oxide layer on a... Method of forming article comprising an oxide layer on a...

2002-01-18

2004-06-29

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

Multiple layers

C438S287000, C438S591000

Reexamination Certificate

active

06756320

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to articles that include dielectric oxide layers formed on a GaAs-based semiconductor structure.
BACKGROUND OF THE INVENTION
In the semiconductor art it is often desirable to form dielectric layers or films on various supporting structures, such as the gate insulator in field effect transistors, an insulator or passivation layer covering various areas (e.g. the extrinsic base region) of other types of transistors, such as HBTs and the like, an insulator or passivation layer surrounding the mesa or walls of a vertical cavity surface emitting laser or edge emitting lasers, etc. Regardless of the use, it is generally imperative that the dielectric layer or film be a good insulator with low defect density to enable device operation and enhance/maintain device performance. Also, the thickness of the layer must be sufficient to provide the required characteristics of the semiconductor devices, e.g. leakage current, reliability, etc.
Due to a lack of insulating layers having low interface state density and stable device operation on gallium arsenide (GaAs) based semiconductors, the performance, integration level and marketability of both digital and analog GaAs based devices and circuits is significantly limited. As is known in the art, growing oxide films by oxidizing GaAs based materials results in high interface state density and a Fermi level which is pinned at the GaAs-oxide interface.
A method of forming a thin film of Ga
2
O
3
is disclosed, for example, in M. Passlack et al., Journal of Vacuum Science &Technology, vol. 17, 49 (1999), and U.S. Pat. Nos. 6,030,453 and 6,094,295. As discussed in these references, a high quality Ga
2
O
3
/GaAs interface is fabricated using in situ deposition of gallium oxide molecules on GaAs based epitaxial layers while maintaining an ultra-high vacuum (UHV). The thus fabricated Ga
2
O
3
-GaAs interfaces have interface recombination velocities S of 5,000-30,000 cm/s and interface state densities D
it
as low as 3.5×10
10
cm
−2
eV
−1
. However, the properties of gallium oxides fabricated by this technique are inadequate for many applications because of high oxide bulk trap densities and excessive leakage current. Consequently, the performance of unipolar and bipolar devices is affected and the fabrication of stable and reliable metal-oxide-semiconductor field effect transistors (MOSFET) based on compound semiconductors has been problematic.
As discussed in U.S. Pat. No. 6,159,834, it has been determined that the aforementioned technique does not produce a high quality Ga
2
O
3
layer because of oxygen vacancies in the layer that give rise to defects that cause unacceptable oxide trap densities. The '834 patent overcomes this problem by directing a molecular beam of gallium oxide onto the surface of the wafer structure to initiate the oxide deposition, and a second beam of atomic oxygen is supplied upon completion of the first 1-2 monolayers of Ga
2
O
3
. The molecular beam of gallium oxide is provided by thermal evaporation from a crystalline Ga
2
O
3
or gallate source, and the atomic beam of oxygen is provided by any one of RF or microwave plasma discharge, thermal dissociation, or a neutral electron stimulated desorption atom source. This fabrication technique increases the quality of the Ga
2
O
3
layer by reducing the density of oxygen related oxide defects while maintaining the excellent quality of the Ga
2
O
3
-GaAs interface. However, oxide bulk trap densities are still unacceptably high and significant leakage current is observed.
As an alternative to Ga
2
O
3
, gadolinium gallium oxides (Ga
2
O
3
(Gd
2
O
3
)) have been employed as a dielectric layer on GaAs-based devices. While this oxide layer has an acceptably low leakage current density, Ga
2
O
3
(Gd
2
O
3
)-GaAs interface state densities are relatively high, resulting in unacceptable device performance.
Accordingly, it would be desirable to provide a dielectric layer structure on GaAs-based devices that has both a low defect density oxide-GaAs interface and a low oxide leakage current density.
SUMMARY OF THE INVENTION
The present invention provides, among other things, a new and improved method of manufacturing a gate quality Ga
2
O
3
-compound semiconductor structure. The present invention also provides a new and improved method of manufacturing a gate quality Ga
2
O
3
-compound semiconductor structure wherein the density of defects related to oxygen vacancies is adequate for MOSFET applications.
In accordance with one embodiment of the invention, a compound semiconductor structure is provided, which includes a GaAs-based supporting semiconductor structure. A first layer of gallium oxide is located on a surface of the supporting semiconductor structure to form an interface therewith. A second layer of a Ga—Gd oxide is disposed on the first layer.
In one particular embodiment of the invention, the Ga—Gd oxide is Gd
3
Ga
5
O
12
.
In another embodiment of the invention the GaAs-based supporting semiconductor structure is a GaAs-based heterostructure such as an at least partially completed semiconductor device. In some embodiments of the invention, the partially completed semiconductor device may be, for example, a metal-oxide field effect transistor, a heterojunction bipolar transistor, or a semiconductor laser.
In accordance with another embodiment of the invention, a method is provided of forming a dielectric layer structure on a supporting semiconductor structure. The method begins by providing a GaAs-based supporting semiconductor structure having a surface on which the dielectric layer structure is to be located. A first layer of Ga
2
O
3
is deposited on the surface of the supporting structure. A second layer of a Ga—Gd-oxide is deposited on the first layer. In this manner a dielectric layer structure is provided which has both a low defect density at the oxide-GaAs interface and a low oxide leakage current density because the dielectric structure is formed from a layer of Ga
2
O
3
followed by a layer of Ga—Gd-oxide. The Ga
2
O
3
layer is used to form a high quality interface with the GaAs-based supporting semiconductor structure while the Ga—Gd-oxide provides a low oxide leakage current density.


REFERENCES:
patent: 5597768 (1997-01-01), Passlack et al.
patent: 5665658 (1997-09-01), Passlack
patent: 5902130 (1999-05-01), Passlack et al.
patent: 5903037 (1999-05-01), Cho et al.
patent: 5962883 (1999-10-01), Hong et al.
patent: 6271069 (2001-08-01), Chen et al.
patent: 6469357 (2002-10-01), Hong et al.

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