This disclosure is related to the field of integrated circuits and more specifically to photonic integrated circuits with transparent substrates.
As increased demands are placed on data communication rates, the use of photons instead of electrons as a medium for communication has increased. Photonic communication holds the promise of higher speed, lower power, and decreased cross-talk. At each location in a photonic communication system that requires signal processing, the photonic signal content must be converted to electronic signals. This interface between the photonic and electronic worlds requires physical alignment of optical fibers to photodiodes to convert from photonic to electronic signals. It also requires alignment of optical fibers to light generation sources such as vertical cavity surface-emitting lasers (VCSEL's). This interface also opens up possible degradations of the signal and opportunities for noise injection and cross-talk.
Accordingly, methods and systems to address some of the difficulties inherent in photo-to-electro and electro-to-photo connections are an ongoing need in the discipline. Details of improvements as elaborated in the description provided herein are presented below.
The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview, and is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
A photonic device is described that contains discrete patterns on the back side of a transparent substrate that perform several functions. The patterns include anti-reflection coating (ARC) in certain areas but not in other areas, as well as light blocking in certain areas and not in others. The patterned layers provide improved product performance and improved radiation tolerance.
In one aspect of the disclosure, a method for selectively applying a reflective coating on an optical circuit supporting transparent substrate having a front side and a back side is provided, comprising: patterning a first layer having at least one of a front side light reception area and a front side light transmission area on a front side of the substrate, wherein a portion of a non-light reception and non-light transmission areas is designated as a non-photonic circuitry area on the front side of the substrate; patterning a second layer having at least one of a back side light reception area and a back side light transmission area on a back side of the substrate, substantially replicating the corresponding front side light reception area and front side light transmission on the front side of the substrate; and disposing an optical blocking area on the back of the substrate, corresponding to a portion of the non-light reception and non-light transmission areas.
In another aspect of the disclosure, an optical circuit supporting structure is provided, comprising: a transparent substrate having a front side and a back side; a patterned first layer having at least one of a light reception area and a light transmission area disposed on a front side of the substrate, wherein a portion of the non-light reception and non-light transmission areas is designated as a non-photonic circuitry area on the front of the substrate; a patterned second layer having at least one of a light reception area and a light transmission area disposed on a back side of the substrate, substantially replicating the corresponding light reception area and light transmission on the front of the substrate; and an optical blocking area disposed on the back of the substrate, corresponding to a portion of the non-light reception and non-light transmission areas.
In yet another aspect of the disclosure, an optical circuit supporting structure is provided, comprising: means for patterning a first layer having at least one of a front side light reception area and a front side light transmission area on a front side of the substrate, wherein a portion of the non-light reception and non-light transmission areas is designated as a non-photonic circuitry area on the front of the substrate; means for patterning a second layer having at least one of a back side light reception area and a back side light transmission area on a back side of the substrate, substantially replicating the corresponding front side light reception area and front side light transmission on the front of the substrate; and means for disposing an optical blocking area on the back of the substrate, corresponding to a portion of the non-light reception and non-light transmission areas.
These aspects are indicative, however, of but a few of the various ways in which the principles of the claimed subject matter may be employed and the claimed subject matter is intended to include all such aspects and their equivalents. Other advantages and novel features may become apparent from the following detailed description when considered in conjunction with the drawings. As such, other aspects of the disclosure are found throughout the specification.
The alignment of optical fibers to electronic circuits is conceptually simple, but in practice is difficult. Such a system is described in U.S. Pat. No. 6,421,474 to Jewell et al, titled “Electro-optical mechanical assembly for coupling a light source or receiver to an optical waveguide.” The use of an integrated circuit with a transparent substrate allows the possibility of bringing in light from the back side of the die, thereby avoiding metallization and structures that are present on the front side of the die that would block light. An example of such a system is described in “A quad 2.7 Gb/s parallel optical transceiver,” by Ahadian, J.; Englekirk, M.; Wong, M.; Li, T.; Hagan, R.; Pommer, R.; Kuznia, C., Radio Frequency Integrated Circuits (RFIC) Symposium, 2004. Digest of Papers. 2004 IEEE, pp. 13-16, 6-8 Jun. 2004. Some areas of the die where outgoing light leaves the transparent die are preferred to have a slightly reflective surface in order to use the reflected light which impinges on an integrated photo-detector to measure average outgoing light intensity. This integrated photo-detector is described in U.S. Pat. No. 6,421,474. Other areas of the die which have transmission of incoming light are preferred to have an anti-reflective coating to maximize the transmission of weak incoming light signals into the high-speed photo-detectors.
As can be seen in the related art of
In the system 200 illustrated in
In view of the above difficulties in the related art, in order to minimize reflection, an anti-reflective coating(s) (ARC) can be placed on the surface of the layer from which reflections are desired to be minimized. However, in such a configuration, the application of an ARC on the transparent substrate's back side 102 in the location where the outgoing light exits the transparent substrate 103 would result in a reduction of minimization of reflected light 204 for detection by the reflected light sensor 203, thereby making it difficult or impossible to monitor optical conditions with this technique.
In addition to signal-containing light, stray light 108 can also impinge on receptors in the transparent substrate systems of 100 and 200. Stray light 108 may come from ambient light such as room light or microscope light during circuit testing or after assembly into a larger system, for example. Stray light 108 may also be reflected and/or refracted light from other signal-containing light paths. Stray light 108 may also be scattered in materials that the light is passing through. Stray light 108 can interact with circuitry, causing degradation of circuit functions such as increased noise, change from desired circuit voltage levels, or cross-talk between signal paths. In view of the difficulties and challenges described above, various exemplary embodiments for methods and systems are described herein that overcome the difficulties of the existing solutions by providing selective ARC patterning.
In one of various exemplary embodiments, a method and system of selectively patterning ARC on the back side of a transparent substrate is described. Understanding that a transparent wafer photonics assembly can have several different optical requirements for the back side of the wafer, this ARC can be selectively patterned to judiciously eliminate it from locations where it is not desired. In addition, a blocking layer can also deposited and patterned to remove it only where light is desired to pass through the transparent substrate and, if desired, to provide an electrical potential for improved radiation tolerance. 100211
ARC materials can be configured with a different index of refraction from the materials in contact with either side, and often (but not necessarily) have a thickness that is equal to one quarter of the wavelength of the light frequency of interest, resulting in a canceling of the reflected wave and increased transmission of the wave. Typical materials used for optical ARCs are inorganic materials such as MgF2 (index of refraction n=1.38), CaF2 (n=1.3 to 1.48), Al2O3 (n=1.6), and various other metal oxides, as non-limiting examples. Organic compounds can also be used, and can be commercially purchased from manufacturers such as Brewer Science, for example. As can be appreciated by one skilled in the art, many different materials can serve this purpose well. Accordingly, the materials listed above are provided to show some of many possible applicable materials and are not intended to form an exhaustive list. Therefore, other materials may be used without departing from the spirit and scope of this disclosure.
As shown in
In one exemplary embodiment, a transparent wafer of sapphire (Al2O3) has an ARC material of MgF2 deposited thereupon. MgF2 can be sputtered onto a transparent wafer using the technique of physical vapor deposition. Other, alternative deposition techniques, such as chemical vapor deposition, sol-gel spin-on, or other suitable techniques can also be used to deposit ARC material. Once the material has been deposited, the technique of photolithography can be used to create a pattern of desired shapes in photo-resist on the back side of the wafer. Because of the optical transparency of a sapphire wafer, alignment of the back side pattern to existing structures on the front of the wafer can be facilitated using photolithography alignment techniques that are known in the semiconductor industry. For example, photo-resist remains in places where it is desired for the MgF2 to remain. In places where MgF2 is desired to be removed, photo-resist is removed. A suitable material removal technique can now be used to remove the MgF2 layer in the exposed areas of the wafer. Several different techniques can be used to remove MgF2, such as physical sputtering (for example, argon ion sputtering), wet etching (for example nitric acid), plasma etching, or laser-assisted etching (for example, LESAL), and so forth. Because sapphire is resistant to most etchants, removal of the MgF2 with little damage to the sapphire is possible.
In another exemplary embodiment, the ARC can be deposited over a patterned layer of material which is soluble in a solution that does not etch MgF2 or the transparent substrate. This so-called “lift-off” technique, then removes the ARC by physically removing the underlying material where the ARC is not desired via lifting off the ARC material from those areas, leaving the ARC where the patterned material was not left. Patterned materials can include photosensitive materials such as photo-resist or polyimide, and so forth. Alternatively, liftoff materials such as SiO2 can be deposited, photo-resist spun on and patterned, SiO2 removed where the ARC material is desired to remain, then the photo-resist removed, leaving a pattern of the hard mask. The ARC is applied over the liftoff material, then the lift-off process proceeds as previously described. This process flow is useful when, for example, high-temperature processing is desired after lift-off material patterning that would deform or destroy organic materials like photo-resist or polyimide.
In another exemplary embodiment, the transparent substrate may be glass or quartz, or any suitable transparent material to the “light” being transmitted/received. Either MgF2 or Al2O3 can be used to form an ARC layer on glass or quartz because their index of refraction differs sufficiently from that of glass. Other ARC materials could similarly be used that have an index of refraction different from that of the substrate. Similar techniques of deposition and etch to those described above for the sapphire substrate can be used to pattern the ARC layer with a glass or quartz substrate. It should be appreciated that non-visible light may be utilized with concomitant “transparent” substrates and ARC materials, understanding that these modifications are within the spirit and scope of this disclosure.
In yet another exemplary embodiment, the ARC can be an organic material. The organic ARC can be, in one exemplary embodiment, applied as a liquid to the wafer surface and then dried to form a thin film of material. Organic ARC can be patterned with wet etch, dry etch, or the liftoff technique described elsewhere in this application.
The ARC may be left everywhere except where the IPD is located. In some other cases it may be desirable to leave ARC only where the incoming light passes through the transparent substrate.
Light impinging on circuitry can affect the electrical performance of the circuitry through the generation of current due to the photoelectric effect. Referring back to
In one exemplary embodiment, the light-blocking material may be poly-crystalline silicon (polysilicon) deposited using chemical vapor deposition. If the photo-detectors are sensitive to visible light, then a polysilicon film of about 1 μm thickness or more would be sufficient to block substantially all the visible light that impinges on the transparent wafer back side 102 surface. As can be appreciated by one skilled in the art, other materials can be used as light-blocking layers. For example, metal layers commonly used in semiconductor processing, such as aluminum, titanium, titanium nitride, copper, tungsten, or titanium-tungsten alloy would block light transmission very effectively. As another example, of innumerous examples, organic materials with dyes or additives that absorb light of the wavelengths of interest could be used. Standard photolithographic techniques of patterning and etching to those described above can be used to pattern the light-blocking material.
In view of the above explanation, there are several possible alternative sequences of deposition and patterning of the ARC and light blocking layer. In one exemplary sequence, the ARC is deposited and patterned, and then the light-blocking layer is deposited and patterned. In another exemplary sequence, the light-blocking layer is deposited and patterned, and then the ARC is deposited and patterned. In yet another possible exemplary sequence, first the ARC layer is deposited, and then the light-blocking layer is deposited. Then the light-blocking layer is patterned and removed where it is not desired. Next, the ARC layer is removed where it is not desired. In this exemplary sequence, ARC can only be removed in locations where the light-blocking layer has already been removed. In a further possible exemplary sequence, first the light-blocking layer is deposited, then the ARC layer is deposited. Next, the ARC layer is patterned and removed where it is not desired, then the light-blocking layer is patterned and removed where it is not desired. In this exemplary sequence, the light-blocking layer can only be removed in locations where ARC has already been removed. As can be appreciated by one skilled in the art, other variations of the exemplary processing sequences listed above may be defined without departing from the spirit and scope herein.
In addition to the function of blocking stray light, a conductive layer on the wafer back side 102 can improve radiation response or provide potential radiation effect improvement. This is thought to happen by providing a sink for holes generated during ionizing radiation, improving the radiation response of a product. This is accomplished by inducing an electric field across the dielectric substrate during irradiation. Referring now to
It should be expressly understood that the terms front and back are relative terms and may be interchanged depending on design preference. Therefore, the description of various elements of the exemplary embodiments, having “front” and “back” may be reversed, based on the intents and objectives of the designer. Also, while the embodiments are described in the context of coherent light, non-coherent light or non-visible light (x-ray, infrared, etc.) may be utilized, if applicable. Therefore, the light sources are not constrained to solely being lasers.
In
The ARC material and light blocking material can be deposited and patterned at the wafer level before the die are singulated from the wafer. This allows parallel batch processing of all die on the wafer simultaneously, possibly reducing production costs. It is also possible to apply and pattern the ARC and light blocking materials at the die level after the die have been singulated from the wafer.
By coordinating the sequencing and/or arrangement of the respective elements shown, for example, in FIGS. 3 and 4A-B, an increase in efficiency light capture and noise reduction can be achieved for optical systems, specifically for optically transparent substrate-based systems. In combination with the exemplary embodiment described in
As one of several different modifications that can be implemented, the exemplary ARC may be placed in areas that previously would be designed for non-reflection, to now allow reflection, for reasons that may be apparent. Conversely, in some areas where ARC is considered a necessity, it may be expedient or desirable to remove the ARC to allow reflected light to “interfere” on a controlled level, or for other reasons that may be apparent. Thus, numerous modifications may be made by one of ordinary skill in the art, that are within the purview of this disclosure.
This application claims the benefit of U.S. Provisional Patent Application No. 61/227,368, filed Jul. 21, 2009, the contents of which are hereby incorporated by reference in its entirety.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US10/42466 | 7/19/2010 | WO | 00 | 3/27/2012 |
Number | Date | Country | |
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61227368 | Jul 2009 | US |