Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Fluid growth from gaseous state combined with subsequent...
Reexamination Certificate
2000-03-06
2001-08-28
Christianson, Keith (Department: 2813)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Fluid growth from gaseous state combined with subsequent...
Reexamination Certificate
active
06281099
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for manufacturing single crystal AlN (aluminum nitride) thin films of low resistivity n-type and low resistivity p-type, which are expected to be used as next generation semiconductors.
TECHNICAL BACKGROUND
A method for forming single crystal AlN thin films by a molecular beam epitaxy method, or the like, is known (for example, Japanese Patent Unexamined Publication Nos. H8(1996)-2999 and H9(1997)-309795).
However, since an AlN has a large band gap energy such as 6.5 eV, and an acceptor or a donor itself has a low impurity level of 500 meV (4000K), carriers cannot be activated at room temperature. As a result, only AlN thin films of high resistivity can be obtained.
OBJECTS TO BE SOLVED BY THE INVENTION
If single crystal thin AlN films of low resistivity p-type and low-resistivity n-type can be synthesized, it is possible to manufacture a high power and high speed semiconductor device operable at high temperature and an ultraviolet semiconductor laser diode essential for a high density recording and a vast information transmittance by the AlN thin films. It is also possible to manufacture a transparent single crystal protective film excellent in electric conductivity and thermal conductivity by an AlN thin film of low resistant n-type, which utilizes high hardness characteristics of the AlN having high hardness next to a diamond. Furthermore, by utilizing the negative electron affinity energy of the AlN, it is possible to manufacture a display having a large surface area (such as a wall-hanging Televison Screen) made by highly efficient electron materials of single crystal AlN thin films of low resistant n-type.
MEANS FOR SOLVING THE PROBLEMS
The inventors have found the facts that, in order to solve the aforementioned problems, in forming single crystal AlN thin films on a semiconductor substrate by rapidly cooling a beam of atomic Al and atomic or molecular N obtained by exciting or decomposing N
2
with an electromagnetic wave, single crystal AlN thin films of low resistivity n-type and low resistivity p-type can be synthesized by simultaneously doping a n-type dopant and a p-type dopant in the form of atomic beam in a crystal to form pairs of a n-type dopant and a p-type dopant in the crystal.
As shown in
FIG. 1
, by forming a compound such as an O—C—O or a C—O—C by a simultaneous doping of a C acceptor and an O donor, a lower donor level or a lower acceptor level are formed, resulting in a greatly increased carrier density in an AlN crystal. As a result, AlN thin films of lower resistivity n-type and lower resistivity p-type can be formed.
In the AlN crystal, C as an acceptor and 0 as a donor take a structural position (an impurity compound) of (1) low resistivity n-type AlN or (2) low resistivity p-type AlN which forms the crystal model shown in FIG.
2
. The co-existing acceptor atom and donor atom stabilize the crystallography structural position. Accordingly, donors and acceptors can be doped in higher density.
In the method according to the present invention, an atomic O as an n-type dopant and an atomic C as a p-type dopant electrically excited by a radio wave, a laser, an x-ray, an electron beam, or the like, are simultaneously doped.
By controlling Al vapor partial pressure, N vapor partial pressure, n-type dopant vapor partial pressure and p-type dopant vapor partial pressure, the ratio (X/Y) of the n-type dopant atomic density (X) to the p-type dopant atomic density (Y) is controlled to thereby form single crystal thin films of low resistivity n-type at X/Y>1 and single crystal thin films of low resistivity p-type at X/Y<1.
Furthermore, the present invention provides a method for restoring a passivation by a hydrogen. The method includes the steps of cooling AlN thin films of low resistivity n-type and low resistivity p-type crystalized on a semiconductor substrate under low temperature and low pressure, and annealing them at high temperature for a short time in an electric field, so that the donor made of hydrogen is removed from the crystal.
Furthermore, the present invention provides a method for forming a high efficiency spin-polarized electron-beam. The method includes the steps of irradiating a circular polarized laser on a synthesized AlN thin films of low resistivity n-type and low resistivity p-type.
Furthermore, the present invention provides a method for synthesizing single crystal AlN thin films of low resistivity n-type and low resistivity p-type. In the method, in forming single crystal AlN thin films in accordance with a MOCVD method, an acceptor and a donor are simultaneously doped by introducing O(oxygen) as a n-type dopant from SiO
2
or sapphire of the substrate and C (carbon) as a p-type dopant from an organic metal compound. (Function)
According to the present invention, the impurity level of an acceptor or a donor can be lowered and the number of carriers can be greatly increased to thereby form single crystal AlN thin films of low resistivity and high quality on a semiconductor substrate. By simultaneously doping a n-type dopant and a p-type dopant, electrostatic energy or lattice energy therebetween is decreased, which enables a stable doping of a n-type dopant and a p-type dopant in high density, resulting in low resistivity . By forming pairs of an n-type dopant and a p-type dopant (impurity compound) in an AlN crystal, electron scattering of n-type and p-type carriers due to dopants can be decreased to thereby increase the carrier movement, resulting in low resistivity. In other words, according to the present invention, single crystal AlN films having a film thickness of about 0.05 to about 1.0 &mgr;m and a film resistivity of 1.0 &OHgr;cm or less can be obtained.
REFERENCES:
patent: 2-105408 (1990-04-01), None
patent: 4-346218 (1992-12-01), None
patent: 8-2999 (1996-01-01), None
patent: 9-309795 (1997-12-01), None
Sinharoy, S. et al., “Molecular beam epitaxy growth and characterization of GAN and AIGaN on 6-H SiC”, J. Vac. Sci. Tech. A 14 (3, Pt. 1), pp. 896-899 (no month given), 1996.*
Tang, X. et al. “Near band-edge transition in aluminum nitide thin films grown by metal organic chemical vapor deposition”, Appl. Phys. Lett. 72, No. 12, pp. 1501-1503, Mar. 1998.*
Niebuhr, R. et al., “Electrical and optical properties of oxygen doped GaN grown by MOCVD using N20”, J. Elect. Matls. 26, No. 10, pp. 1127-1130, Oct. 1997.*
Tucceri, R.C. et al., “SIMSand CL Characterization of manganese-doped aluminum nitride films”, Wide Bandgap Semiconductors for High-Power, High-Frequency, and High Temperature Applications, Materials Researc Society, pp. 413-418 (no month given), 1999.*
Hommerich, U. et al., “Optical characterization of erbium doped III-nitrides prepared by metalorganic molecular beam epitaxy”, Materials Reseach Society Sym Proc. p. 537 (no month given), 1999.
Armstrong Westerman Hattori McLeland & Naughton LLP
Christianson Keith
Japan Science and Technology Corporation
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