Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2001-04-25
2004-03-23
Pert, Evan (Department: 2829)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S057000, C438S069000
Reexamination Certificate
active
06709886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to methods of fabricating micromachine devices, and more specifically, to fabricating silicon micromachined optical attenuators and switches for a plurality of light beams propagating along a respective plurality of beam paths.
2. Description of the Related Art
Micro-electro-mechanical systems (MEMS) are physically small systems with both electrical and mechanical components, and with dimensions on the order of microns. To achieve the small dimensions of the various components, MEMS are typically fabricated using techniques which were developed in part for integrated circuit fabrication. MEMS-based devices are found in an increasing number of applications, such as inkjet-printer cartridges, accelerometers that deploy car airbags, and other sensors and actuators. MEMS has developed into a growth industry with an estimated yearly market of tens of billions of dollars. In addition, MEMS-based optical systems, such as optical attenuators and switches, are becoming increasingly important in the field of telecommunications and computer networks.
A variable optical attenuator (VOA) is a device which can adjust the optical signal power passing through an optical fiber transmission circuit, such as dense wavelength-division multiplexing (DWDM) systems. Because the amount of light passing through an optical fiber depends on the wavelength of the light, VOAs are often needed to ensure power equalization of the individual wavelengths by adjusting the intensity for each wavelength. VOAs used in fiber optic communications system may use absorptive or reflective techniques to controllably adjust the transmitted power.
An optical switch is a device which can selectively switch optical signals from one optical circuit to another, and are typically used in optical systems such as optical add/drop multiplexers (OADMs). Various technologies can be used in optical switches, including, but not limited to, physically shifting an optical fiber to drive one or more alternative fibers, physically moving a reflective element, electro-optic effects, or magneto-optic effects.
MEMS technology has been identified as being able to satisfy the requirements of optical systems in the telecommunications and computer networking fields. These requirements include multi-channel operation in a dense package, high reliability, sufficiently fast operation, and inexpensive fabrication techniques.
Typically, multiple MEMS devices are fabricated on the same wafer substrate to take advantage of economies of scale. To separate the MEMS devices from one another, the wafer substrate is diced and separated into chips, each of which comprises at least one of the MEMS devices. However, MEMS devices also typically contain various fragile components, such as the flaps, cantilevers. These MEMS components are often damaged by the standard processes of dicing and separating the wafer substrate into chips, thereby reducing the yield of MEMS devices obtained from a given wafer substrate.
Previous attempts to improve the yield of MEMS devices from diced and separated wafer substrates have included the addition of a photoresist layer to the wafer substrate, thereby covering the MEMS devices and providing structural support during the dicing and separating processes. However, the application of a photoresist layer includes a spin coating method, which induces forces and stresses which can also damage fragile MEMS devices. Spin coating also is inefficient for large area substrates and the use of photoresist materials leads to environmental, health, and safety issues. In addition, photoresist layers typically are not conformal and have poor step coverage, especially when applied to high aspect ratio structures.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a method of fabricating a module for at least partially intercepting a light beam propagating along a beam path comprises providing a single crystal silicon substrate with a first substrate surface and a second substrate surface. The method further comprises forming a reflector support layer on the first substrate surface. The method further comprises forming a support frame and at least one reflector by etching the substrate from the second substrate surface. The method further comprises forming at least one electrical conduit on the reflector support layer. The method further comprises forming a reflector support by etching the reflector support layer from the first substrate surface. The reflector support is mechanically coupled to the support frame and the reflector. The reflector support is movable such that the reflector is movable substantially perpendicularly to the first substrate surface.
According to another aspect of the present invention, a method of fabricating a module for at least partially intercepting a light beam propagating along a beam path comprises providing a substrate comprising single crystal silicon, a first substrate surface, a second substrate surface, and an etch stop layer below the first substrate surface. The method further comprises providing a reflector support layer comprising the etch stop layer. The method further comprises forming a support frame and at least one reflector by etching the substrate from the second substrate surface to the etch stop layer. The method further comprises forming at least one electrical conduit on the reflector support layer. The method further comprises forming a reflector support by etching the reflector support layer from the first substrate surface. The reflector support is mechanically coupled to the support frame and the reflector. The reflector support is movable such that the reflector is movable substantially perpendicularly to the first substrate surface.
According to another aspect of the present invention, a method of fabricating a device on a substrate, where the device comprises at least one fragile component, comprises providing the substrate and forming the device on the substrate. The method further comprises forming a conformal layer on the device by depositing a polymeric material in a vapor phase onto the substrate. The method further comprises dicing and separating the substrate into a plurality of chips. At least one chip contains the device, and the conformal layer provides structural support for the fragile component of the device. The method further comprises removing the conformal layer from the device subsequently to dicing the substrate into the plurality of chips.
According to another aspect of the present invention, a method of fabricating a module for at least partially intercepting a light beam propagating along a beam path comprises providing a single crystal silicon substrate with a first substrate surface and a second substrate surface. The method further comprises forming a reflector support layer on the first substrate surface. The method further comprises forming a support frame and at least one reflector by etching the substrate from the second substrate surface. The method further comprises forming at least one electrical conduit on the reflector support layer. The method further comprises forming a conformal layer by depositing a polymeric material in a vapor phase onto the substrate from the second substrate surface. The method further comprises forming a reflector support by etching the reflector support layer. The reflector support is mechanically coupled to the support frame and the reflector. The reflector support is movable such that the reflector is movable substantially perpendicularly to the first substrate surface.
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Chiu Chen-Wei
Jiang Fukang
Tsao Tom
Geyer Scott B.
Knobbe Martens Olson & Bear LLP
Pert Evan
Umachines, Inc.
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