Patent Description:
With data rate increases over time, electrical interconnects cannot keep up with the energy efficiency requirements for sustained bandwidth. Optical interconnect architectures demonstrate unparalleled long distance signaling capability. As such the transition from electrical to optical interconnects has already begun, especially for long distance communications.

Integrated waveguides in the package substrate are a promising approach for low cost methods to enable fast and long range transmission of signals within the package. However, methods for efficiently routing signals within the in-package waveguide are lacking. In particular, significant optical losses are observed due to alignment offset created as a result of multiple patterning operations required to route the waveguide signal within the package. <CIT> discloses a photoelectric conversion module in which an optical device and an optical waveguide are arrayed in a horizontal direction. <CIT> discloses an optoelectronic hybrid printed circuit board provided with an inter-chip optical interconnection direct-coupling structure. <CIT> discloses a method and device for enhancing laser beam transmitting efficiency by accurately controlling an interval between a light emitting element and an optical waveguide substrate without causing any fluctuation in the interval in a mounting structure of the light transmitting element in which the light emitting element is mounted on the optical waveguide substrate. <CIT> discloses an embedded optical fiber module adapted to fit in a recess of a package substrate. <CIT> discloses a photoelectric hybrid substrate and a manufacturing method thereof to minimize an error generated by shrinkage in aligning an optical axis.

Described herein are optical waveguide architectures to provide chip-to-chip communications, in accordance with various embodiments. In the following description, various aspects of the illustrative implementations will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that the present invention may be practiced with only some of the described aspects. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the illustrative implementations. However, it will be apparent to one skilled in the art that the present invention may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative implementations.

Various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present invention, however, the order of description should not be construed to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.

As noted above, embedded optical waveguides within a package substrate currently have significant optical losses due to alignment offsets created as a result of multiple patterning operations. Accordingly, embodiments disclosed herein include self-aligned reflective surfaces on opposite ends of the optical waveguide. In an embodiment, the optical waveguide provides a lateral path for routing signals, and the reflective surfaces allow for coupling with dies positioned above the package substrate. Due to the self-aligned nature of the reflective surfaces, optical losses are minimized.

In some embodiments, the optical waveguide is over the package substrate. That is, the optical waveguide may be between the dies and the package substrate. In other embodiments, the optical waveguide is at least partially embedded in the package substrate. At least partially embedded may refer to a waveguide that has a bottom surface and sidewall surfaces covered by the package substrate, while a top surface of the waveguide is exposed to the atmosphere. In yet another embodiment, the optical waveguide is fully embedded in the package substrate, so that all surfaces along a length of the waveguide are covered by the package substrate.

In an embodiment, the waveguides may comprise a high index of refraction material. For example, the index of refraction may be greater than <NUM>. In other embodiments, the waveguides may comprise air. For example, a reflective cladding may surround a void in the package substrate, and the optical signal propagates through the void without any solid material along the optical path.

In an embodiment, the reflective surfaces may be part of the optical waveguide. For example, differences in index of refraction may allow for a complete reflection of the signal at the ends of the waveguide. In other embodiments, reflective structures are provided at the ends of the waveguide. The reflective structures may have unique structures due to the self-aligned process. For example, the reflective structures comprise trapezoidal shaped cross-sections with a triangular notch along a bottom surface. In other embodiments not according to the claimed invention, the reflective structures may comprise parallelogram shaped cross-sections.

Referring now to <FIG>, a cross-sectional illustration of an electronic system <NUM> is shown, not in accordance with an embodiment. In this embodiment, the electronic system <NUM> may comprise a board <NUM> (such as a printed circuit board (PCB). A package substrate <NUM> is coupled to the board by interconnects <NUM>. While shown as solder balls, it is to be appreciated that the interconnects <NUM> may comprise any interconnect architecture, such as sockets or the like. In an embodiment, a pair of dies <NUM>A and <NUM>B are provided over the package substrate <NUM>. First level interconnects (FLIs) <NUM> may couple the package substrate <NUM> to the dies <NUM>A and <NUM>B.

In an embodiment, an optical waveguide <NUM> (sometimes referred to as simply "waveguide <NUM>") is at least partially embedded in the package substrate <NUM>. The waveguide <NUM> comprises a first end <NUM> and a second end <NUM>. The first end <NUM> is provided below the first die <NUM>A and the second end <NUM> is provided below the second die <NUM>B. In an embodiment, photonics regions <NUM> on the first die <NUM>A and the second die <NUM>B are directly over the first end <NUM> and the second end <NUM> of the waveguide <NUM>. As such, an optical signal (represented by the dashed line) can be sent between the first die <NUM>A and the second die <NUM>B.

In an embodiment, the first end <NUM> and the second end <NUM> have sloped surfaces. As such, the direction of the optical signal can be changed from vertical to horizontal. In an embodiment, the sloped surfaces are approximately <NUM>°, though it is to be appreciated that other angles may also be used. The reflection of the first end <NUM> and the second end <NUM> may be the result of mismatches in the index of refraction between the waveguide <NUM> and the package substrate <NUM>. For example, a material with an index of refraction greater than that of the package substrate may be used in order to provide total internal reflection at the first end <NUM> and the second end <NUM>. In other embodiments (as will be described in greater detail below) the reflection at the first end <NUM> and the second end <NUM> may be made by reflective structures that are self-aligned to the waveguide <NUM>.

Referring now to <FIG>, a cross-sectional illustration of an electronic system <NUM> is shown, not in accordance with an additional embodiment. The electronic system <NUM> may be substantially similar to the electronic system <NUM> described in <FIG>, with the exception of the placement of the waveguide <NUM>. Instead of being embedded in the package substrate <NUM>, the waveguide <NUM> is provided between the dies <NUM>A and <NUM>B and the package substrate <NUM>. In such an embodiment, the waveguide <NUM> comprises an index of refraction material that is higher than air in order to provide the total internal reflection needed to rout optical signals from the first die <NUM>A to the second die <NUM>B.

Referring now to <FIG>, a cross-sectional illustration of an optical waveguide <NUM> partially embedded in a package substrate <NUM> is shown, not in accordance with an embodiment. The waveguide <NUM> may have a bottom surface and sidewall surfaces that are contacted by the package substrate <NUM>. A top surface of the waveguide <NUM> may be exposed to the atmosphere. In an embodiment, the optical waveguide <NUM> comprises a high index of refraction material, such as high index polymers or dielectrics. Particularly, the index of refraction of the waveguide <NUM> is higher than the index of refraction of the surrounding package substrate <NUM> and atmosphere.

Due to the differences in the index of refraction, total internal reflection is provided when an optical signal <NUM> reaches the first end <NUM> and the second end <NUM> of the waveguide <NUM>. The waveguide <NUM> may be patterned with an angled patterning process. As such, the first end <NUM> and the second end <NUM> may be sloped in order to redirect the optical signal <NUM> vertically to allow communication between overlying dies (not shown). Since the first end <NUM> and the second end <NUM> are patterned during the patterning to form the waveguide <NUM>, the first end <NUM> and the second end <NUM> may be referred to as being self-aligned. A more detailed description of the angled patterning process is provided below.

Referring now to <FIG>, a cross-sectional illustration of an optical waveguide <NUM> in a package substrate <NUM> is shown, not in accordance with an additional embodiment. The optical waveguide <NUM> may comprise a first end <NUM> that is sloped and a second end <NUM> that is vertical. The second end <NUM> may be substantially coplanar with an edge <NUM> of the package substrate <NUM>. In such an embodiment, the optical signal <NUM> may be routed off the package substrate <NUM> to another device. In an embodiment, the materials for the optical waveguide <NUM> and package substrate <NUM> in <FIG> may be substantially similar to those described above with respect to <FIG>.

Referring now to <FIG>, a series of cross-sectional illustrations depicting a process for forming an embedded waveguide similar to the one shown in <FIG> is shown, not in accordance with an embodiment.

Referring now to <FIG>, a cross-sectional illustration of a package substrate <NUM> is shown, not in accordance with an embodiment. The package substrate <NUM> may comprise a plurality of laminated dielectric layers with conductive routing <NUM>. The package substrate <NUM> may be cored or coreless. While a single layer of conductive routing <NUM> is shown, it is to be appreciated that a plurality of conductive routing, vias, pads, etc. may be provided in the package substrate <NUM>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a photo-imageable dielectric (PID) <NUM> is disposed over the package substrate <NUM> is shown, in accordance with an embodiment. The PID <NUM> may be disposed with any suitable process, such as lamination.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a first exposure is shown, not in accordance with an embodiment. In an embodiment, a mask <NUM> may be used to cover a portion of the PID <NUM>. A first exposure <NUM> is used to expose portions of the PID <NUM> to form exposed PID <NUM>. The first exposure <NUM> may be an angled exposure. As such, the unexposed portion of the PID <NUM> may have a parallelogram shape.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a second exposure is shown, not in accordance with an embodiment. In an embodiment, the second exposure <NUM> may be done at an angle that mirrors the angle of the first exposure <NUM>. As a result, the unexposed portions of the PID <NUM> may have a trapezoidal shape. It is to be appreciated that while two different exposures are made of the PID <NUM>, the mask <NUM> may not move between the different exposures.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after the unexposed portions of the PID <NUM> are removed is shown, not in accordance with an embodiment. In this embodiment, the unexposed portions may be removed with a developing process to form a trench <NUM>. Removal of the unexposed portions of the PID <NUM> results in the exposure of a first sloped surface <NUM> and a second sloped surface <NUM> at opposite ends of the trench <NUM>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after an optical waveguide <NUM> is disposed into the trench <NUM> is shown, not in accordance with an embodiment. In an embodiment, the optical waveguide <NUM> comprises a high index of refraction material. Particularly, the index of refraction of the optical waveguide <NUM> is higher than the index of refraction of the PID <NUM> and the package substrate <NUM>. The optical waveguide <NUM> comprises a first end <NUM> over the surface <NUM> and a second end <NUM> over the surface <NUM>.

Referring now to <FIG>, a cross-sectional illustration of an optical waveguide <NUM> that is disposed over a package substrate is shown, not in accordance with an embodiment. In an embodiment, a layer <NUM> with a low index of refraction material is provided under the waveguide <NUM>. The layer <NUM> may be disposed over the package substrate (not shown). For example, the layer <NUM> may comprise SiO<NUM> or SiN in some embodiments.

In an embodiment, the waveguide <NUM> comprises a high index of refraction material. As such, an optical signal <NUM> can be retained within the waveguide <NUM> using total internal reflection. In a particular embodiment, the waveguide <NUM> is a developed PID material. That is, the waveguide <NUM> may be the result of a patterning process. The optical signal <NUM> may reflect off of a first end <NUM> and a second end <NUM> in order to rout the optical signal <NUM> vertically to overlying dies (not shown).

Referring now to <FIG>, a cross-sectional illustration of an optical waveguide <NUM> is shown, not in accordance with an additional embodiment. In an embodiment, the optical waveguide <NUM> includes a first end <NUM> that is sloped and a second end <NUM> that is vertical. The second end <NUM> may be substantially coplanar with an edge <NUM> of the layer <NUM> (and the package substrate (not shown)). Similar to the embodiment in <FIG>, the optical waveguide <NUM> is provided above the package substrate instead of being embedded in the package substrate. The materials of the optical waveguide <NUM> and the layer <NUM> in <FIG> may be substantially similar to the materials described above with respect to <FIG>.

Referring now to <FIG>, a series of cross-sectional illustrations depicting a process for forming an optical waveguide on a package substrate <NUM> is shown, not in accordance with an embodiment.

Referring now to <FIG>, a cross-sectional illustration of a package substrate <NUM> is shown, not in accordance with an embodiment. In this embodiment, the package substrate <NUM> may be substantially similar to the package substrate <NUM> described above. For example, the package substrate <NUM> may comprise dielectric layers with conductive routing <NUM>. In an embodiment, a layer <NUM> with a low refractive index is provided over the package substrate <NUM>. For example, the layer <NUM> may comprise SiO<NUM> or SiN. The layer <NUM> may be deposited with a sputtering process, or any other suitable material deposition process. In an embodiment, a PID <NUM> is provided over the layer <NUM>. The PID <NUM> may be a positive resist material. That is, exposed regions of the PID <NUM> will be developed away.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after the exposed portions of the PID <NUM> are developed and removed is shown, not in accordance with an embodiment. As shown, the residual portions of the unexposed PID <NUM> have a trapezoidal shape that can be used as an optical waveguide <NUM>. The waveguide <NUM> comprises a first end <NUM> with a sloped surface and a second end <NUM> with a sloped surface.

Referring now to <FIG>, a cross-sectional illustration of an optical waveguide <NUM> in a package substrate <NUM> is shown, not in accordance with an additional embodiment. In an embodiment, the waveguide <NUM> may include a reflective cladding <NUM>. The reflective cladding <NUM> may be provided between a low loss material of the waveguide <NUM> and the package substrate <NUM>. The use of a reflective cladding <NUM> allows for lower index of refraction materials to be used for the waveguide <NUM>. Instead of providing an index of refraction that is higher than that of the package substrate <NUM>, all that is required is that the index of refraction be higher than that of the atmosphere (e.g., greater than approximately <NUM>). As such, the material for the waveguide may be selected based on loss characteristics. For example, the material of the waveguide <NUM> may be a dielectric without any fillers.

In this embodiment, the reflective cladding <NUM> may be provided over a bottom surface of the waveguide <NUM> and over the first end <NUM> and the second end <NUM>. As such, an incoming optical signal <NUM> may be propagated through the waveguide <NUM> by reflecting off of the reflective cladding <NUM> on the first end <NUM> and the second end <NUM>. In an embodiment, the reflective cladding <NUM> may comprise a thin, smooth layer, such as a material deposited with an electroless plating process or a liquid metal ink (LMI) process. For example, the reflective cladding <NUM> may comprise copper, gold, silver, palladium, or the like.

Referring now to <FIG>, a cross-sectional illustration of an optical waveguide <NUM> on a package substrate <NUM> is shown, not in accordance with an additional embodiment. In this embodiment, the optical waveguide <NUM> comprises a reflective cladding <NUM> between the optical waveguide <NUM> and the package substrate <NUM>. In an embodiment, a first end <NUM> has a sloped surface and a second end <NUM> has a vertical surface. The second end <NUM> may be substantially coplanar with an edge <NUM> of the package substrate <NUM>. In an embodiment, the materials of the optical waveguide <NUM> and the reflective cladding <NUM> may be substantially similar to those described above with respect to <FIG>.

Referring now to <FIG>, a series of cross-sectional illustrations depicting a process for forming an optical waveguide in a package substrate is shown, not in accordance with an embodiment.

Referring now to <FIG>, a cross-sectional illustration of a package substrate <NUM> is shown, not in accordance with an embodiment. In an embodiment, the processing to get to the structure shown in <FIG> may be substantially similar to the processing operations described above in <FIG>, and will not be repeated here. Particularly, an angled patterning process is used to form a PID <NUM> with a trench <NUM>. The trench <NUM> may comprise a first sloped sidewall <NUM> and a second sloped sidewall <NUM>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a reflective cladding <NUM> is deposited is shown, not in accordance with an embodiment. In this embodiment, the reflective cladding <NUM> may be deposited with an electroless plating process or any other conformal deposition process that can provide a smooth surface. In an embodiment, the reflective cladding <NUM> may comprise copper, gold, silver, palladium, or the like.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a waveguide <NUM> is disposed in the trench <NUM> is shown, not in accordance with an embodiment. In an embodiment, the waveguide <NUM> has a first end <NUM> and a second end <NUM>. The first end <NUM> and the second end <NUM> are sloped surfaces in order to allow for the optical signal to be routed vertically to overlying dies (not shown).

Referring now to <FIG>, a cross-sectional illustration of an optical waveguide <NUM> in a package substrate <NUM> is shown, in accordance with an embodiment of the claimed invention. In this embodiment, the optical waveguide <NUM> comprises a first end <NUM> and a second end <NUM>. The first end <NUM> and the second end <NUM> may be adjacent to reflective structures <NUM>. The optical signal <NUM> reflects off of the reflective structures <NUM> to be routed to overlying dies (not shown). In an embodiment, the optical waveguide <NUM> may comprise a material with a high index of refraction, such as materials described above.

In an embodiment, the waveguide <NUM> is fully embedded in the package substrate <NUM>. Particularly, a dielectric layer <NUM> is disposed over a top surface of the waveguide <NUM>. That is, dielectric material from the package substrate <NUM> and the dielectric layer <NUM> may be provided over the bottom surface and a portion of the top surface of the waveguide <NUM>. Accordingly, embodiments may include burying the waveguide <NUM> in any layer of the package substrate <NUM>.

In this embodiment, the reflective structures <NUM> have trapezoidal shaped cross-sections with a triangular notch <NUM> on a bottom surface. The notch <NUM> may be filled by dielectric material, or may remain as a void in the package. The novel shape of the reflective structures <NUM> are a result of patterning processes, which will be described in greater detail below. The reflective structures <NUM> may be copper or other reflective material.

Referring now to <FIG>, a cross-sectional illustration of an optical waveguide <NUM> on a package substrate <NUM> is shown, in accordance with an embodiment. In this embodiment, the waveguide <NUM> comprises a first end <NUM> and a second end <NUM>. The first end <NUM> is adjacent to a reflective structure <NUM> and the second end <NUM> is substantially coplanar with an edge <NUM> of the package substrate <NUM>. In an embodiment, the reflective structure <NUM> may be substantially similar to the reflective structures described above in <FIG>. The waveguide <NUM> may comprise a material with a high index of refraction.

Referring now to <FIG> a series of cross-sectional illustrations depicting a process for forming an optical waveguide in a package substrate <NUM> is shown, in accordance with an embodiment.

Referring now to <FIG>, a cross-sectional illustration of a package substrate <NUM> with a positive resist layer <NUM> is shown, in accordance with an embodiment. In this embodiment, the resist layer <NUM> may be deposited with any suitable deposition process.

Referring now to <FIG>, a cross-sectional illustration of the package substrate after a first exposure of the resist layer <NUM> is made. In an embodiment, the exposure may be an angled patterning using a greyscale mask (not shown). As shown arrows <NUM> may be a high dose and arrow <NUM> may be a low dose. The high dose areas <NUM> are shown in a first shading, and the low dose area is shown with a second shading <NUM>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate after a second exposure of the resist layer <NUM> is made. The exposure may be an angled patterning (in a direction opposite from the first patterning) using a greyscale mask. As shown, the second patterning overlays the first pattern to form a low dose region that is a trapezoidal shape. The high dose regions <NUM> have trapezoidal shapes with triangular notches of low dose regions <NUM> along a bottom surface. It is to be appreciated that the low dose region <NUM> may get a double exposure. However, so long as there is a sufficient delta between the high dose regions <NUM> and the low dose regions <NUM> then the subsequent developing processes will be able to be executed properly.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a first developing process is shown, in accordance with an embodiment. In an embodiment, the first developing process is a fast develop that only removes the high dose regions <NUM>. As shown, openings <NUM> are provided between the unexposed regions of the resist layer <NUM> and the low dose regions <NUM>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a plating process is shown, in accordance with an embodiment. The plating may result in reflective structures <NUM> being formed in the openings <NUM>. The reflective structures have a trapezoidal shaped cross-sections with a triangular notch in the bottom surfaces. In an embodiment, the reflective structures <NUM> may comprise copper or the like.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a second developing process is shown, in accordance with an embodiment. The second development process may be a longer develop in order to remove the low dose regions <NUM>. Removal of the low dose regions <NUM> may result in the formation of a trench <NUM> between the reflective structures <NUM>. In an embodiment, the notches <NUM> in the reflective structures <NUM> may be voids in some embodiments.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a high index of refraction material <NUM> is disposed is shown, in accordance with an embodiment. The high index of refraction material <NUM> may be deposited with a conformal deposition process, such as a spray coating or a sputtering process. In some embodiments, a hydrophobic treatment of the resist <NUM> may be made prior to deposition of the material <NUM> to prevent the material <NUM> from sticking to the resist <NUM>. In an embodiment, the material <NUM> may be a high index polymer or dielectric.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a dielectric layer <NUM> is laminated and a planarization process is done is shown, in accordance with an embodiment. The dielectric layer <NUM> may be laminated over the material <NUM> and the planarization process recesses the dielectric layer <NUM> and the material <NUM> to expose the top surfaces of the reflective structures <NUM>. The recessing results in the formation of the optical waveguide <NUM>. The waveguide <NUM> comprises a first end <NUM> and a second end <NUM>. The first end <NUM> and the second end <NUM> are adjacent and contacting the reflective structures <NUM>. After the planarization process, the resist <NUM> may be stripped, as shown in <FIG>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after an additional dielectric layer <NUM> is laminated is shown, in accordance with an embodiment. As shown, the dielectric layer <NUM> covers the edge surfaces of the reflective structures <NUM> opposite from the waveguide <NUM>. In an embodiment, a planarization process may be used to expose the top surfaces of the reflective structures <NUM> after the dielectric layer <NUM> is laminated. In the illustrated embodiments, the notches <NUM> may be filled with dielectric material or the notches <NUM> may define a void in the package.

Referring now to <FIG>, a cross-sectional illustration of an electronic package with a waveguide <NUM> embedded in a package substrate <NUM> is shown, in accordance with an embodiment. In this embodiment, the waveguide <NUM> comprises a reflective cladding <NUM>. The reflective cladding <NUM> may be copper or the like. In an embodiment, the waveguide <NUM> may be air within the reflective cladding <NUM>. A first end <NUM> of the waveguide <NUM> may be adjacent to a reflective structure <NUM>, and the second end <NUM> of the waveguide <NUM> may be adjacent to a reflective structure <NUM>. The reflective structures <NUM> have trapezoidal shaped cross-sections with a triangular notch <NUM> formed in a bottom surface. In an embodiment, the reflective structures <NUM> route an optical signal <NUM> from within the waveguide <NUM> up to overlying dies (not shown). In an embodiment, a dielectric layer <NUM> may surround surfaces of the reflective structures <NUM> opposite from the waveguide <NUM>.

Referring now to <FIG>, a cross-sectional illustration of a waveguide <NUM> is shown, in accordance with an additional embodiment. Instead of a pair of reflective structures <NUM>, only a single reflective structure <NUM> is provided adjacent to the first end <NUM>. The second end <NUM> of the waveguide <NUM> is substantially coplanar with an edge <NUM> of the package substrate <NUM>. While referred to as the second end <NUM>, it is to be appreciated that the waveguide <NUM> may be air filled between the reflective cladding <NUM>, and that there may not be a solid surface at the second end <NUM>.

Referring now to <FIG>, a series of cross-sectional illustrations depicting a process for forming a waveguide in a package substrate is shown, in accordance with an embodiment. In this embodiment, the structure in <FIG> may be formed using processing operations similar to those described above in <FIG>, and will not be repeated here.

Referring now to <FIG>, a cross-sectional illustration of a structure for forming an embedded waveguide is shown, in accordance with an embodiment. The structure comprises a package substrate <NUM> with a patterned resist layer <NUM>. At this point in the process flow, the high dose regions of the positive resist layer <NUM> have been removed and reflective structures <NUM> have been formed. The low dose regions <NUM> of the positive resist layer <NUM> remain at this point in the process flow.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after the low dose regions <NUM> are removed to form a trench <NUM> and a portion of a reflective cladding <NUM> is formed is shown, in accordance with an embodiment. Removal of the low dose regions <NUM> may also form notches <NUM> that are air voids in a bottom surface of the reflective structures <NUM>. The reflective cladding <NUM> may form a bottom surface of the waveguide. The reflective cladding <NUM> may comprise copper. Additionally, the reflective cladding <NUM> may directly couple the two reflective structures <NUM> together.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a thermally decomposable layer <NUM> is disposed over the exposed surfaces is shown, in accordance with an embodiment. In an embodiment, the thermally decomposable layer <NUM> comprises a material that can be removed at elevated temperatures. In an embodiment, the thermally decomposable layer <NUM> is deposited with a conformal process, such as a spray coating process.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a dielectric lamination and planarization process is shown, in accordance with an embodiment. In an embodiment, the dielectric layer <NUM> is disposed over the thermally decomposable layer <NUM>. A planarization process may then be implemented to expose the top surfaces of the reflective structures <NUM>. After the planarization process, the resist layer <NUM> may be stripped.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after an additional dielectric layer <NUM> is laminated to cover the outside surfaces of the reflective structures <NUM> and the thermally decomposable layer <NUM> is removed is shown, in accordance with an embodiment. An additional planarization process may be done between the dielectric layer <NUM> lamination and the removal of the thermally decomposable layer <NUM>. The removal of the thermally decomposable layer <NUM> results in the formation of a void that is used as the waveguide <NUM>. As shown, a portion of the dielectric layer <NUM> appears floating over the waveguide <NUM>. However, it is to be appreciated that the floating portion is supported out of the plane of <FIG>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a top portion of the cladding <NUM> is formed is shown, in accordance with an embodiment. In an embodiment, the top portion of the cladding <NUM> over the floating portion of the dielectric <NUM> may be done with an electroless plating process or the like. In some embodiments, the top portion of the cladding <NUM> may be omitted. Additionally, a high index of refraction liquid material may be dispensed into the waveguide <NUM> in some embodiments.

Referring now to <FIG>, a cross-sectional illustration of an optical waveguide <NUM> in a package substrate <NUM> is shown, not in accordance with an embodiment. In this embodiment, the optical waveguide <NUM> comprises a high index of refraction material, such as a high index polymer or dielectric. In this embodiment, the waveguide <NUM> comprises a first end <NUM> and a second end <NUM>. The first end <NUM> and the second end <NUM> are adjacent to reflective structures <NUM> and <NUM>, respectively. The first structure <NUM> is a mirror image of the second structure <NUM>. The reflective structures <NUM> and <NUM> reflect an optical signal <NUM> that passes through the waveguide <NUM> to overlying dies (not shown). In this embodiment, a dielectric layer <NUM> embeds the waveguide <NUM>. The dielectric layer <NUM> may be considered as part of the package substrate <NUM> in some embodiment. not according to the claimed invention.

Referring now to <FIG>, a cross-sectional illustration of a package substrate <NUM> with a waveguide <NUM> is shown, not in accordance with an additional embodiment. The waveguide <NUM> is similar to the waveguide <NUM> in <FIG>, with the exception of the second end <NUM> ending at an edge <NUM> of the package substrate <NUM>. There is also no reflective structure <NUM> at the second end <NUM> of the waveguide <NUM>.

Referring now to <FIG>, a series of cross-sectional illustrations depicting a process for forming an embedded waveguide is shown, not in accordance with an embodiment.

Referring now to <FIG>, a cross-sectional illustration of a package substrate <NUM> is shown, not in accordance with an embodiment. A resist layer <NUM> may be disposed over a top surface of the package substrate <NUM>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after the resist layer <NUM> is exposed is shown, not in accordance with an embodiment. In an embodiment, the resist layer may be exposed using a two-photon-polymerization (2PP) variable exposure. This results in a low dose exposure <NUM> and high dose exposures <NUM>. The low dose region <NUM> may have a trapezoidal shape, and the high dose regions <NUM> may have parallelogram shapes. The two high dose regions <NUM> may be mirror images of each other. For a positive tone resist, such as diazoalkylquinone doped with a 2PP marker with a high 2P cross-section may be used to provide the 2PP variable exposure.

Referring now to <FIG>, a cross-sectional illustration after the high dose regions <NUM> are removed with a first developing process is shown, not in accordance with an embodiment. In this embodiment, the duration of the first developing process is short in order to ensure that none of the low dose region <NUM> is removed. Removal of the high dose regions <NUM> results in the formation of trenches <NUM>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after reflective structures <NUM> and <NUM> are disposed in the trenches <NUM> is shown, not in accordance with an embodiment. In this embodiment, the reflective structures <NUM> and <NUM> may comprise copper formed with any suitable plating process. The reflective structures <NUM> and <NUM> may be mirror images of each other, and have parallelogram shaped cross-sections.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after the low dose region <NUM> is removed is shown, not in accordance with an embodiment. Removal of the low dose region <NUM> results in the formation of a trench <NUM> between the reflective structures <NUM> and <NUM>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a layer <NUM> with a high index of refraction is disposed over the exposed surfaces is shown, not in accordance with an embodiment. In an embodiment, the layer <NUM> may be conformally deposited (e.g., with a spray coating or sputtering process). In some embodiments, a hydrophobic treatment is applied to the resist layer <NUM> to prevent deposition on the resist layer <NUM>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a dielectric layer <NUM> is deposited and planarized is shown, not in accordance with an embodiment. In this embodiment, the planarization process exposes the top surfaces of the reflective structures <NUM> and <NUM>. The planarization process also reduces the layer <NUM> to form the waveguide <NUM> between the reflective structures <NUM> and <NUM>. The waveguide <NUM> comprises a first end <NUM> next to the reflective structure <NUM> and a second end <NUM> next to the reflective structure <NUM>. After the planarization process, the resist layer <NUM> may be removed.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after an additional dielectric layer <NUM> is laminated and planarized is shown, not in accordance with an embodiment. In an embodiment, the additional dielectric layer <NUM> covers the sidewall surfaces of the reflective structures <NUM> and <NUM> opposite from the waveguide <NUM>.

Referring now to <FIG>, a cross-sectional illustration of an embedded waveguide <NUM> is shown, not in accordance with an embodiment. In an embodiment, the structure comprises a package substrate <NUM>. A pair of reflective structures <NUM> and <NUM> are provided over the package substrate <NUM>. The reflective structures <NUM> and <NUM> may be mirror images of each other and be connected together by a reflective cladding <NUM>. In this embodiment, a dielectric layer <NUM> covers sidewall surfaces of the reflective structures <NUM> and <NUM>.

In this embodiment, a portion of the dielectric layer <NUM> may be above the waveguide <NUM>. The waveguide <NUM> may comprise cladding layers <NUM> and be air filled. The waveguide <NUM> has a first end <NUM> and a second end <NUM>. Optical signals <NUM> propagate along the waveguide <NUM> and reflect off of the reflective structures <NUM> and <NUM> to overlying dies (not shown).

Referring now to <FIG>, a cross-sectional illustration of an embedded waveguide <NUM> is shown, not in accordance with an additional embodiment. The waveguide <NUM> in <FIG> is similar to the waveguide in <FIG>, with the exception of the second end <NUM> ending at an edge <NUM> of the package substrate <NUM>. That is, there is no second reflective structure <NUM> in the embodiment shown in <FIG>.

Referring now to <FIG> a series of cross-sectional illustrations depicting a process for forming an embedded waveguide is shown, not in accordance with an embodiment. The structure shown in <FIG> may be fabricated using processing operations substantially similar to those described above with respect to <FIG>, and will not be repeated here.

Referring now to <FIG>, a cross-sectional illustration of a package substrate <NUM> with a patterned resist layer <NUM> is shown, not in accordance with an embodiment. A trench <NUM> may be formed in the patterned resist layer <NUM>. In this embodiment, a first reflective structure <NUM> and a second reflective structure <NUM> are formed at edges of the trench <NUM>. The reflective structures <NUM> and <NUM> may be mirror images of each other. For example, the reflective structures <NUM> and <NUM> may have parallelogram shaped cross-sections.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a bottom cladding <NUM> is disposed over the package substrate <NUM> is shown, not in accordance with an embodiment. The bottom cladding <NUM> may be copper or the like. The bottom cladding <NUM> connects the first reflective structure <NUM> to the second reflective structure <NUM>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate after a thermally decomposable layer <NUM> is disposed over exposed surfaces is shown, not in accordance with an embodiment. The thermally decomposable layer <NUM> may be a material that decomposes at elevated temperatures. In this embodiment, the thermally decomposable layer <NUM> may be deposited with a spray coating process or the like.

Referring now to <FIG>, a cross-sectional illustration after a dielectric layer is laminated and a planarization process is implemented is shown, not in accordance with an embodiment. In an embodiment, the dielectric layer <NUM> is disposed over the thermally decomposable layer <NUM>. The planarization process may be used to expose the top surfaces of the reflective structures <NUM> and <NUM>. After the planarization process, the resist layer <NUM> may be stripped.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after an additional dielectric layer <NUM> is laminated to cover the outside surfaces of the reflective structures <NUM> and <NUM> and the thermally decomposable layer <NUM> is removed is shown, in accordance with an embodiment. An additional planarization process may be done between the dielectric layer <NUM> lamination and the removal of the thermally decomposable layer <NUM>. The removal of the thermally decomposable layer <NUM> results in the formation of a void that is used as the waveguide <NUM>. As shown, a portion of the dielectric layer <NUM> appears floating over the waveguide <NUM>. However, it is to be appreciated that the floating portion is supported out of the plane of <FIG>.

Referring now to <FIG>, a cross-sectional illustration of the package substrate <NUM> after a top portion of the cladding <NUM> is formed is shown, not in accordance with an embodiment. In this embodiment, the top portion of the cladding <NUM> over the floating portion of the dielectric <NUM> may be done with an electroless plating process or the like. In some embodiments, the top portion of the cladding <NUM> may be omitted. Additionally, a high index of refraction liquid material may be dispensed into the waveguide <NUM> in some embodiments. In this embodiment, the waveguide <NUM> comprises a first end <NUM> adjacent to the first reflective structure <NUM> and a second end <NUM> adjacent to the second reflective structure <NUM>.

Referring now to <FIG>, a plan view illustration of an electronic package <NUM> is shown, not in accordance with an embodiment. As shown, an array of optical paths <NUM><NUM>-<NUM> are provided across the surface of the package substrate <NUM>. While three optical paths <NUM> are shown, it is to be appreciated that any number of optical paths <NUM> may be used. In an embodiment, each of the optical paths <NUM> comprises a pair of reflective structures <NUM> and an optical waveguide <NUM>. The horizontal portion of the optical waveguide <NUM> is below the surface of the package substrate <NUM>.

Referring now to <FIG>, a plan view illustration of an electronic package <NUM> is shown, not in accordance with an additional embodiment. In an embodiment, a waveguide plane <NUM> is provided. The waveguide plane <NUM> includes wider reflective structure <NUM> and waveguide <NUM>. The extended width allows for multiple signals to be passed along the single waveguide plane <NUM>. Such an embodiment may be useful when light scattering within the waveguide <NUM> is negligible.

<FIG> illustrates a computing device <NUM> not in accordance with one implementation of the invention. The computing device <NUM> houses a board <NUM>. The board <NUM> may include a number of components, including but not limited to a processor <NUM> and at least one communication chip <NUM>. The processor <NUM> is physically and electrically coupled to the board <NUM>. In some implementations the at least one communication chip <NUM> is also physically and electrically coupled to the board <NUM>. In further implementations, the communication chip <NUM> is part of the processor <NUM>.

These other components include, but are not limited to, volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flash memory, a graphics processor, a digital signal processor, a crypto processor, a chipset, an antenna, a display, a touchscreen display, a touchscreen controller, a battery, an audio codec, a video codec, a power amplifier, a global positioning system (GPS) device, a compass, an accelerometer, a gyroscope, a speaker, a camera, and a mass storage device (such as hard disk drive, compact disk (CD), digital versatile disk (DVD), and so forth).

The processor <NUM> of the computing device <NUM> includes an integrated circuit die packaged within the processor <NUM>. In some implementations of the invention, the integrated circuit die of the processor may be communicatively coupled to an additional die through a self-aligned optical waveguide. The term "processor" may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory.

The communication chip <NUM> also includes an integrated circuit die packaged within the communication chip <NUM>. In accordance with another implementation of the invention, the integrated circuit die of the communication chip may be communicatively coupled to an additional die through a self-aligned optical waveguide, in accordance with embodiments described herein.

Claim 1:
An electronic package (<NUM>), comprising:
a package substrate (<NUM>);
a first die (110A) over the package substrate;
a second die (110B) over the package substrate; and
an optical waveguide (<NUM>) on the package substrate, wherein a first end (<NUM>) of the optical waveguide is below the first die and a second end (<NUM>) of the optical waveguide is below the second die, and wherein the optical waveguide communicatively couples the first die to the second die;
characterized in that
the electronic package further comprises a first reflective structure (<NUM>) at the first end (<NUM>) of the optical waveguide and a second reflective structure (<NUM>) at the second end (<NUM>) of the optical waveguide;
and in that the first reflective structure and the second reflective structure have trapezoidal cross-sections with a triangular notch (<NUM>) in a bottom surface.