Method for growing low-defect single crystal heteroepitaxial...

Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor

Reexamination Certificate

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C117S084000, C117S095000, C438S478000

Reexamination Certificate

active

06488771

ABSTRACT:

ORIGIN OF THE INVENTION
The invention described herein was made by employees of the United States Government and may be used by or for the Government for governmental purposes without payment of any royalties thereon or therefor.
FIELD OF THE INVENTION
The invention relates to the growth of semiconductor device crystal films, and more particularly, to a method for producing high quality films of silicon carbide (SiC), aluminum nitride (AlN), gallium nitride (GaN), and other materials or compounds on atomically flat crystalline surfaces. Specifically, the invention enables the growth of low defect heteroepitaxial single crystal films on atomically flat crystal surfaces. The semiconductor devices find application in high power, high frequency, high temperature and high radiation environments, as well as use in optoelectronic devices such as lasers and light-emitting diodes.
BACKGROUND OF THE INVENTION
This invention relates to the controlled growth of crystal films for application to the fabrication of semiconductor devices. The invention is particularly applicable to the production of crystals (herein used to include crystal films) of silicon carbide, aluminum nitride, gallium nitride, diamond, and other materials. A primary aspect of the invention is related to silicon carbide (SiC) and the nitrides (e.g., AlN and GaN) of the Group III elements; however, the invention has much broader applications and can be used for other elemental crystals and compounds. For example, films of ternary and quaternary compounds (and higher order compounds) of the III-V elements (e.g., GaAlN) could be grown. Also, elemental single crystal films, such as silicon and diamond could also be grown.
The term “atomically-flat” is known in the art and is generally referred to herein as meaning a surface that is totally without any atomic-scale or macro-scale steps over an area defined by selected boundaries that may be created by grooves in a manner to be further described herein with reference to FIG.
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. Many of the methodologies of the present invention are shared with that of U.S. Pat. No. 5,915,194, as well as U.S. Pat. No. 6,165,874, both of which are herein incorporated by reference.
Semiconductor devices, including MISFETs and other device structures all related to the present invention, are used in a wide variety of electronic applications. Semiconductor devices include diodes, transistors, integrated circuits, sensors, and opto-electronic devices, such as light-emitting diodes and diode lasers. Various semiconductor devices using silicon or compound semiconductors, such as gallium arsenide (GaAs) and gallium phosphide (GaP) are commonly used. In order to fabricate semiconductor devices, it is necessary to be able to grow high-quality, low-defect-density single-crystal films with controlled impurity incorporation while possessing good surface morphology. The substrate upon which the film is grown should also be a high-quality, low-defect-density single crystal. In recent years, there has been an increasing interest in research on wide-bandgap semiconductors for use in high temperature, high power, high frequency, and/or high radiation operating conditions under which silicon and conventional III-V semiconductors cannot adequately function. Particular research emphasis has been placed on SiC, and III-nitride alloys, including AlN, GaN, InGaN, AlGaN, and others.
Conventional semiconductors are unable to meet some of the increasing demands of the automobile and aerospace industries as they move to smarter and more electronic systems. New wide bandgap materials are being developed to meet the diverse demands for more power at higher operating temperatures. Two of the most promising emerging wide bandgap semiconductors are silicon carbide (SiC) and gallium nitride (GaN). At over three electron volts, the bandgap of these materials is nearly three times as large as that of silicon. This advantage theoretically translates into very large improvements in power handling capabilities and higher operating temperatures that will enable revolutionary product improvements. Once material-related technology obstacles are overcome, SiC's properties are expected to dominate high power switching and harsh-environment electronics for manufacturing and engine control applications, while GaN will enable high power high frequency microwave systems at frequencies beyond 10 GHz. To date the best SiC devices to our knowledge are homojunction (i.e., wafer and device layers are all hexagonal SiC), while GaN devices are heterojunction (i.e., SiC or sapphire wafers with device layers of GaN, AlGaN, AlN, etc.) because production of bulk GaN wafers is not practical at the present time.
Silicon carbide crystals exist in hexagonal, rhombohedral and cubic crystal structures. Generally, the cubic structure, in particular, the zincblende structure is referred to as &bgr;-SiC or 3C-SiC, whereas numerous polytypes of the hexagonal and rhombohedral structures are collectively referred to as &agr;-SiC. To our knowledge, only bulk (i.e., large) crystals of the a polytypes have been grown to date with reasonable quality and size acceptable for device applications. The &bgr; (or 3C) polytype can only be obtained as small (less than 1 cm
2
) blocky crystals or thick epitaxial films on small 3C substrates or crystal films of poor quality grown heteropitaxially on some other substrate. The most commonly available &agr;-SiC polytypes are 4H-SiC and 6H-SiC; these are commercially available as polished wafers, presently up to 75 mm in diameter. Each of the SiC polytypes has its own specific advantages over the others. For example, (1) 4H-SiC has a significantly higher electron mobility compared to 6H-SiC; (2) 6H-SiC is used as a substrate for the commercial fabrication of GaN blue light-emitting diodes (LED's); and (3) 3C-SiC has a high electron mobility similar to that of 4H-SiC and may function over wider temperature ranges, compared to the &agr; polytypes, but crystals of sufficient quality and size have not been readily obtainable.
Silicon carbide polytypes are formed by the stacking of double layers, also referred to as bilayers, of covalently bonded Si and C atoms. As will be more fully described later, each double layer may be situated in one of three atomic stacking positions known as A, B, and C. The sequence of stacking determines the particular polytype; for example, the repeat sequence for 3C-SiC is ABCABC . . . (or ACBACB . . . ) the repeat sequence for 4H-SiC is ABACABAC . . . and the repeat sequence for 6H is ABCACBABCACB . . . From this it can be seen that the number in the polytype designation gives the number of double layers in the repeat sequence and the letter denotes the structure type (cubic, hexagonal, or rhombohedral). The stacking direction is designated as the crystal c-axis and is in the crystal <0001> direction; it is perpendicular to the basal plane which is the crystal (0001) plane. The SiC polytypes are polar in the <0001> directions; in one direction, the crystal face is terminated with silicon (Si) atoms; in the other direction, the crystal face is terminated with carbon (C) atoms. These two faces of the (0001) plane are known as the silicon face (Si-face) and carbon face (C-face), respectively. As will be more fully described later with respect to FIG.
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(A), the 3C-SiC (i.e., cubic) polytype has four equivalent stacking directions, and thus there are four equivalent planes, the (111) planes, that are basal planes. As used herein, “basal plane” shall refer to either the (0001) plane for a &agr;-SiC, or the (111) plane of 3C-SiC. The term “vicinal (0001) wafer” shall be used herein for wafers whose polished surface (the growth surface) is misoriented less than 10° from the basal plane. The angle of misorientation shall be referred to herein as the tilt angle. The term “homoepitaxial” shall be referred to herein as epitaxial growth, whereby the film and the substrate (wafer) are of the same polytype and material, and the term “heteroepitaxial” shall be referred to herein as epitaxial g

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