Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Substrate dicing
Reexamination Certificate
2001-08-01
2002-04-30
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Substrate dicing
C438S462000
Reexamination Certificate
active
06379985
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
This invention is related to semiconductor structures including group III-V nitride films formed on c-face sapphire substrates.
2. Description of Related Art
High-efficiency, solid-state light-emitting devices based on group III-V nitrides (“III-V nitrides”) have sufficiently wide bandgaps for short-wavelength, visible light emission. III-V nitrides have been used in light-emitting diode (LED) devices to provide bright green-to-ultraviolet light at high efficiencies. Known LEDs cover all three primary colors of the spectrum (red, green and blue). Accordingly, these devices can be used in various combinations to produce any color.
III-V nitrides have also been used to fabricate diode lasers that operate at room temperature and emit visible light in the blue-violet range under continuous operation. Diode lasers including III-V nitrides can emit coherent radiation and focus light into small spots, enabling high-density optical information storage and printing. Blue lasers are particularly promising due to their short wavelength. In addition, blue lasers can be combined with red and green lasers to create projection displays, color film printers and other devices.
Sapphire is a commonly used substrate material for growing III-V nitride films for light-emitting devices. A-face and c-face single crystal sapphire substrates are most commonly used for growing such III-V nitride films.
SUMMARY OF INVENTION
Diode laser devices include a resonator cavity having opposed mirror surfaces. When electricity passes through the device, photons are produced, which bounce back and forth inside the resonator cavity. The photons move together in phase and at the same wavelength in the resonator cavity, which increases the light intensity. The emitted light forms a narrow column of bright light at a single wavelength, i.e., coherent light.
In order to form diode lasers, facets are formed in the semiconductor structures formed on substrates. The facets form the mirror surfaces of the resonator cavity of the laser diode. It is possible to successfully etch through III-V nitride films formed on sapphire substrates. However, sapphire is difficult to etch. Consequently, portions of the sapphire substrate adjacent to the facets formed in the III-V nitride materials by etching would not be etched through by the etching process, and would interfere with light emitted from the laser diodes. Particularly, the top surface of the sapphire substrate would reflect the emitted light back and create interference fringes in the emitted light pattern. The resulting light emission pattern would not be an acceptable far-field pattern. Accordingly, the laser diodes would be unsuitable for applications that require an acceptable far-field pattern, such as printing applications.
Methods of cleaving sapphire substrates are known. The crystalline structure of sapphire is shown in FIG.
1
. The sapphire unit cell
20
has a hexagonal crystal structure. The location and orientation of an a-plane
22
, c-planes
24
, an m-plane
26
and an r-plane
28
of the sapphire unit cell
20
are shown. The a-plane
22
has a (
11{overscore (2)}0
) orientation. The c-planes
24
form top and bottom c-faces of the sapphire unit cell
20
and have (0001) orientations. The a-plane
22
is perpendicular to the c-planes
24
. The m-planes
26
form side surfaces of the sapphire unit cell
20
and have (
1{overscore (1)}00
) orientations. The r-plane
28
is oriented at an angle &agr; of 57.6° with respect to the c-planes
24
.
The unit cell of GaN, a III-V nitride compound semiconductor, is shown in FIG.
2
. The GaN unit cell
30
has a hexagonal crystal structure and includes m-planes
32
forming side faces, and c-planes
34
forming top and bottom c-faces, of the GaN unit cell
30
.
Methods for cleaving facets for III-V semiconductor structures grown on a-face sapphire substrates are known.
FIG. 3
shows an a-face sapphire substrate
40
including a c-plane flat
42
. GaN films grown on a-face sapphire substrates have been cleaved by making a peck on the GaN surface, at an angle of 57.6 degrees with respect to the c-plane flat. A cleave is formed in a direction extending along the r-plane of the sapphire substrate and along an m-plane of GaN, as depicted by line
44
.
FIG. 4
is a side view after cleavage of a GaN film
50
formed on the a-face sapphire substrate
40
. The cleave is along the (
1{overscore (1)}02
) r-plane of the a-face sapphire substrate
40
and an m-plane of the GaN film
50
.
However, there is a need for methods for forming facets for III-V nitride films grown on c-face sapphire substrates. There is also a need for methods for forming facets for light-emitting devices comprising III-V nitride films grown on c-face sapphire substrates. This invention satisfies these and other needs and provides methods for cleaving facets for III-V nitride films formed on c-face sapphire substrates. This invention separately provides methods for cleaving facets for light-emitting devices comprising such III-V nitride films, formed on c-face sapphire substrates.
This invention also provides light-emitting devices comprising III-V nitride films formed on c-face sapphire substrates.
An exemplary embodiment of the methods for cleaving facets for III-V nitride films according to this invention comprises forming a semiconductor structure comprising at least one III-V nitride layer on the top c-face of a c-face sapphire substrate, which also includes a bottom c-face. A line of weakness is formed on the bottom c-face of the c-face sapphire substrate. The line of weakness extends in the a-plane direction of the c-face sapphire substrate. A force is applied to the bottom c-face to cleave the c-face sapphire substrate along the line of weakness in the a-plane direction, and to form a cleaved facet along an m-plane of each III-V nitride layer.
According to the invention, the semiconductor structures can include laser diodes and light-emitting diodes.
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Cervantes Tanya J.
Kneissl Michael A.
Romano Linda T.
Mulpuri Savitri
Oliff & Berridg,e PLC
Xerox Corporation
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