Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2002-03-06
2003-11-04
Le, D (Department: 2818)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S706000, C156S345310
Reexamination Certificate
active
06642151
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processes, materials and devices for plasma etching of Si—Ge layers for fabricating optically smooth Si—Ge surfaces, and particularly to fabricating waveguides in opto-electronic integrated circuits employing Si—Ge.
BACKGROUND OF THE INVENTION
A waveguide is a conductor or directional transmitter for electromagnetic waves. Waveguides are, for example employed in opto-electronic integrated circuits. An opto-electronic integrated circuit (OEIC) device combines optics with electronics in an integrated form. OEIC technology is commonly used for example in optical fiber communication devices and methods. A typical OEIC includes conventional IC (integrated circuit) components as well as optical components. Conventional IC components include for example, transistors, diodes, resistors and electrically conductive interconnects. Examples of optical components include light receiving devices such as photodiodes, light emitting devices such as light emitting diodes (LED), optical reflectors such as metallic mirrors, optical filters and waveguides.
Typical OEIC waveguides are optical interconnects that provide an optical path between optical and/or opto-electronic components. Conventional waveguide materials that are employed in OEIC devices include monocrystalline silicon. Typically, an OEIC waveguide is embedded within sidewalls and top and bottom claddings. It is recognized that roughness of waveguide sidewall surfaces, and roughness of the surfaces of top and/or bottom claddings, results in light scattering that causes a significant light propagation loss when light is transmitted through the waveguide. It is therefore highly desirable to provide sidewall and cladding surfaces adjacent the waveguide that exhibit very low surface roughness.
Also, it is desirable to employ a waveguide sidewall material that is similar to the waveguide material in chemical and physical properties, particularly including mechanical and thermal properties, in order to maximize the reliability and durability of the waveguide structure in the OEIC device.
Desirably, techniques for fabricating OEIC waveguides should employ relatively low fabricating temperatures in order to limit, or avoid if possible, heat caused damage or degradation of other components of the OEIC structure such as a semiconductor wafer.
Si—Ge (silicon-germanium, also known as germanium doped silicon) is a suitable material for waveguides. Particularly when an Si—Ge waveguide is enclosed within Si—Ge sidewalls such that the Si—Ge waveguide material has a higher refractive index than the refractive index of the Si—Ge sidewall material. However, conventional Si—Ge etch techniques using etch chemistries such as HBr/Cl
2
, result in Si—Ge sidewall roughness that causes a high level of light scattering. Also, these conventional etch chemistries exhibit a relatively low etch selectivity to organic photoresist; this low selectivity typically ranges from about 2-3:1. It has been found that this low selectivity is unsuitable for successfully etching the typical requirements of 1.5-7 &mgr;m Si—Ge with 1-2 &mgr;m resist.
Accordingly, the need exists for improved techniques for fabricating optically smooth Si—Ge surfaces and for fabricating Si—Ge waveguides exhibiting a very low light propagation loss.
SUMMARY OF THE INVENTION
The present invention provides novel methods and techniques for etching Si—Ge, which are particularly useful for fabricating optically smooth Si—Ge surfaces.
In one embodiment of the present invention a novel etch technique is employed for etching Si—Ge, wherein SF
6
/hydrofluorocarbon etch chemistries are used at low bias power and wherein the etch technique is highly selective to organic photoresist. This etching technique results in optically smooth Si—Ge surfaces.
In another embodiment of the present invention an Si—Ge waveguide is fabricated by etching a cavity having optically smooth sidewall surfaces and an optically smooth bottom surface in a layer of a first Si—Ge composition, using SF
6
/hydrofluorocarbon plasma etch chemistry at low bias power, and then filling the cavity with a second Si—Ge composition that has a higher refractive index than the first Si—Ge composition. A cladding layer is subsequently deposited on the second Si—Ge composition that is formed in the cavity, thus fabricating the waveguide.
In a further embodiment of the present invention an Si—Ge waveguide is fabricated by etching a cavity having optically smooth sidewall surfaces and an optically smooth bottom surface in a first layer of a first Si—Ge composition, using SF
6
/fluorocarbon etch chemistries of the present invention, and then filling the cavity with a second Si—Ge composition that has a higher refractive index than the first Si—Ge composition. The top surface of the second Si—Ge composition is then etched, using SF
6
/hydrofluorocarbon etch chemistries of the present invention to provide an optically smooth top surface of the second Si—Ge composition that is deposited in the cavity. Subsequently, a second layer of the first Si—Ge composition is then deposited on the etched top surface of the second Si—Ge composition. A cladding layer is then formed on the second layer of the first Si—Ge composition. This technique results in a waveguide core having optically smooth top, side and bottom surfaces.
In another embodiment of the present invention a waveguide core is fabricated by subtractively etching a layer of a first Si—Ge composition that is deposited on an optically smooth first layer of a second Si—Ge composition wherein the first Si—Ge composition has a higher refractive index than the second Si—Ge composition. The subtractive etching technique of the present invention includes SF
6
/bydrofluorocarbon etch techniques of the present invention. A second layer of the second Si—Ge is deposited as a conformal layer on the core. Excess second layer material is removed from the core, and a top cladding layer is deposited on the core thereby forming the waveguide, wherein the core has optically smooth bottom and side surfaces.
In a further embodiment of the present invention a cluster tool is employed for executing processing steps of the novel techniques for fabricating Si—Ge waveguides of present invention. These processing steps include photoresist removal, Si—Ge etching, Si—Ge deposition and top cladding layer deposition, wherein the processing steps are carried out within the vacuum environment of the cluster tool.
In another embodiment of the present invention a manufacturing system is provided for fabricating Si—Ge waveguides of the present invention. This system includes a controller, such as a computer, that is adapted for interacting with a plurality of fabrication stations. Each of these fabrication stations performs a processing step that is utilized to fabricate the waveguides. Operative links provide connections between the controller and the fabrication stations. A data structure, such as a computer program, causes the controller to control the processing steps which are performed at the fabrication stations.
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Khan Anisul
Kumar Ajay
Nallan Padmapani
Applied Materials Inc
Bach Joseph
Dalhuisen Albert J
Le D
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