Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-06-29
2004-04-20
Kielin, Erik J. (Department: 2813)
Coherent light generators
Particular active media
Semiconductor
C372S012000
Reexamination Certificate
active
06724794
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to opto-electric chip integration and, more particularly, to high yield dense integration of opto-electronic devices.
BACKGROUND
FIGS. 1 and
,
2
illustrate approaches that have been used in the prior art to attach multiple bottom emitting (or detecting) (also referred to as “backside emitting (or detecting)”) devices to form an integrated electro-optical chip.
According to the approach of
FIG. 1
, multiple lasers, are formed on a wafer substrate
102
in a conventional manner, as are multiple detectors (interchangeably referred to herein as photodetectors) on their own or on a wafer substrate in common with the lasers. Typically, the portion
104
of the substrate
102
closest to the junction between the optical devices
106
,
108
and the substrate
102
is made of a material which is optically transparent at the wavelength at which the optical devices operate. The devices
106
,
108
are then processed using conventional techniques such as wet or dry etching to form trenches
112
among the devices
106
,
108
which separate them into a series of discrete individual lasers
106
or detector
108
devices. Depending upon the particular technique used, the etched trenches
112
may stop prior to reaching the substrates
102
or extend partly into the substrates
102
. Following etching, the substrates
102
and their associated devices are inverted, aligned to the proper location over a Silicon (Si) electronic wafer
114
, and bonded to the Si electronic wafer
114
using conventional flip-chip bonding techniques. Following bonding, the entirety of the substrates
102
are thinned extremely thin, by conventional mechanical polishing methods, conventional etch techniques or some combination thereof, to on the order of about 5 microns or less to allow for close optical access to the devices and create an integrated electro-optical wafer
116
.
Optionally, the integrated electro-optical wafer
116
is then patterned, using conventional techniques, to protect the individual lasers and the individual detectors are coated with an anti-reflection (AR) coating
118
.
A related alternative approach to the technique of
FIG. 1
is shown in FIG.
2
. In this approach, lasers and detectors are formed as described above. However, when the technique of
FIG. 2
used, the trenches
112
are etched into the substrates
102
. The substrates
102
and their associated devices are then inverted, aligned to the proper location over a Silicon (Si) electronic wafer
114
, and bonded to the Si electronic wafer
114
using conventional flip-chip bonding techniques. Following bonding, the substrates
102
are then wholly removed, by conventional mechanical polishing methods, conventional etch techniques or some combination thereof, to allow for close optical access to the devices and create an integrated electro-optical wafer
116
.
Optionally, the integrated electro-optical wafer
116
is then patterned to protect the individual lasers and the individual detectors are coated with an anti-reflection (AR) coating.
The techniques of both FIG.
1
and
FIG. 2
make it possible to get optical fibers or optical lenses close enough to the devices to capture the appropriate light without allowing light coming from, or going to, adjacent devices to affect any of those adjacent devices, a problem known as “crosstalk”. Typically, this requires that the separation distance between a device and an optical fiber or optical microlens be less than 100 microns.
Additionally, both techniques ensure that there are no significant absorbing layers over the active region of the devices that will prevent light from escaping since the thinning technique of
FIG. 1
reduces the thickness of the entire substrate
102
to about 5 microns or less and the approach of
FIG. 2
removes the substrate
102
entirely, leaving multiple wholly independent optical devices.
Both of these techniques however, characteristically create opto-electronic chips that have heat dissipation problems during use and leave the individual devices more sensitive to thermal and mechanical stresses produced during the manufacturing process, thereby reducing individual device lifetimes and, accordingly, decreasing yields and overall chip life.
Moreover, for the approach of both
FIG. 1
(where the substrate is extremely thin) and
FIG. 2
(where the substrate is completely removed), stresses experienced by the devices are primarily transferred to the very thin optical device layer which is the structurally weakest part of the device.
Thus, there is a need for a way to create an integrated opto-electronic chip that is not as sensitive to the thermal and or structural stresses resulting from processing and/or use.
In addition, a manufacturer of opto-electronic devices has two avenues for obtaining the optical and electronic wafer—they can manufacture either or both themselves, or they can obtain one or both from a third party. By manufacturing both the optical devices (interchangeably referred to for simplicity as an “optical chip”) and the electronic wafer (interchangeably referred to for simplicity as an “electronic chip”), the manufacturer can take measures to ensure that the pads on each are properly placed so as to align with each other when the optical chip is positioned over the electronic chip. However, typically electrical and optical chips are not designed concurrently, even if they are designed and fabricated within the same organization. Thus, even with a single manufacturer, unless there is close coordination within the organization with regard to both the optical and electronic chip design, a lack of correspondence between contact pads on each can easily occur—particularly where one or both are also designed with sales to third parties in mind or integration with devices from other sources is contemplated. Moreover, subsequent improvements or changes in the design of either may necessitate altering the location of the contact pads, thereby introducing a pad misalignment where none previously existed.
Even worse, if the electronic chip is designed to be used with a variety of different optical chips, but the optical chips are commodity stock obtained from third parties (for example, chips containing: topside emitting vertical cavity lasers, bottom emitting vertical cavity lasers, distributed feedback (DFB) or distributed Bragg reflector (DBR) lasers (which each have better chirp and line width characteristics for long distance applications), topside receiving detectors or bottom receiving detectors) that are mass manufactured for distribution to multiple unrelated users, it is unlikely that the pads on the optical devices will all be located in the same place, even if they are otherwise compatible with the electronic chip.
For example, as shown in prior art
FIG. 3
, a single optical device
300
has contact pads
302
,
304
placed in the position specified by its manufacturer. A portion of an electronic wafer
306
also has contact pads
308
,
310
, onto which an optical device can be connected, placed in the position specified by its manufacturer. If the optical device is flipped over, for flip-chip type bonding with the electronic wafer, the contact pads
302
,
304
,
308
,
310
, of each will not be aligned as shown in prior art FIG.
4
.
This presents a problem in that it limits the ability to “mix-and match” devices. Moreover, if a chip is designed with connection to a particular other chip in mind, and subsequent events create a need to use a different device with a different contact placement, all the planning and coordination done for the original device will be irrelevant to the new device.
Thus, there is a further need for a process that facilitates the ability to mix and match devices without there being any coordination between the designers of either or the use of a standard or common contact placement scheme.
In addition, in some cases it is sometimes desirable to coat some of the devices, specifically the detectors, with an AR coating.
An AR coating prevents light from hit
Dudoff Greg
Trezza John
Kielin Erik J.
Morgan & Finnegan , LLP
Vesperman William C.
Xanoptix Inc.
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