Abstract:
One embodiment of the present invention provides a system to facilitate using selective etching to form optical components on a circuit device. The system operates by receiving a substrate composed of a first material including a buffer layer composed of a second material. The system forms a sacrificial layer composed of a third material on the buffer layer. Next, the system forms an optical fiber core composed of a fourth material on the sacrificial layer. After the optical fiber core has been formed, the system performs an etching operation using a selective etchant to remove the sacrificial layer. The system also applies a cladding layer to the optical fiber core.

Description:
RELATED APPLICATION 
     The subject matter of this application is related to the subject matter in co-pending non-provisional applications by the same inventors as the instant application entitled, “Method and Apparatus for Fabricating Structures Using Chemically-Selective Endpoint Detection,” having Ser. No. 09/900,300, and filing date Jul. 5, 2001, “Fabricating Structures Using Chemo-Mechanical Polishing and Chemically-Selective Endpoint Detection,” having Ser. No. 09/900,299, and filing date Jul. 5, 2001, and “Method of Fabricating Three-Dimensional Components Using Endpoint Detection,” having Ser. No. 10/061,501, and filing date Jan. 31, 2002. 
    
    
     GOVERNMENT LICENSE RIGHTS 
     This invention was made with United States Government support under Grant Numbers N00014-93-C-0114 and N00014-96-C-0219, awarded by the Office of Naval Research. The United States Government has certain rights in the invention. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a process for manufacturing structures on a substrate. More specifically, the present invention relates to creating optical components within an integrated circuit through a process that uses chemically-selective endpoint detection. 
     2. Related Art 
     The dramatic advances in computer system performance during the past 20 years can largely be attributed to improvements in the processes that are used to fabricate integrated circuits. By making use of the latest fabrication processes, integrated circuit designers can presently integrate computing systems comprised of hundreds of millions of transistors onto a single semiconductor die which is a fraction of the size of a human fingernail. 
     Integrated circuit fabrication technology is also being used to fabricate optical devices such as lasers within integrated circuit devices, and which have dimensions measured in fractions of microns. 
     A typical fabrication process builds structures through successive cycles of layer deposition and subtractive processing, such as etching. As the dimensions of individual circuit elements continue to decrease, it is becoming necessary to more tightly control the etching operation. For example, in a typical etching process, etching is performed for an amount of time that is estimated by taking into account the time to etch through a layer to reach an underlying layer, and the time to overetch into the underlying layer. However, this process can only be controlled to +/−100 Angstroms, which can be a problem when fine control of dimensions is required. 
     Furthermore, conventional etching processes that indiscriminately etch all exposed surfaces are not well suited to manufacture some structures that require tighter control over subtractive processing operations. As circuit structures become smaller, there is less tolerance available to account for uncertainties in the manufacturing process. 
     Additionally, connecting optical devices within an integrated circuit typically requires aligning optical fibers with an optical device such as a laser, or converting the optical signals to electrical signals at the source and converting the electrical signals back to optical signals at the destination. Aligning optical fibers with an optical device is difficult and time consuming because of the small dimensions involved, while converting the form of the signals can lead to signal degradation. 
     What is needed is a method of fabricating and connecting optical components that does not have the difficulties listed above. 
     SUMMARY 
     One embodiment of the present invention provides a system to facilitate using selective etching to form optical components on a circuit device. The system operates by receiving a substrate composed of a first material including a buffer layer composed of a second material. The system forms a sacrificial layer composed of a third material on the buffer layer. Next, the system forms an optical fiber core composed of a fourth material on the sacrificial layer. After the optical fiber core has been formed, the system performs an etching operation using a selective etchant to remove the sacrificial layer. The system also applies a cladding layer to the optical fiber core. 
     In one embodiment of the present invention, the system adds a filler to fill the cavity left by removing the sacrificial layer and planarizes the circuit device using chemo-mechanical polishing to create a planarized surface. 
     In one embodiment of the present invention, the substrate is Si and the buffer layer is SiGe or SiGeC. Using SiGeC for the buffer layer allows growth of a thicker buffer layer than when using SiGe. In this embodiment, the sacrificial layer is Si, the optical fiber core is SiO 2 :GeO 2 , the selective etchant used to remove the sacrificial layer is KOH or tetramethylammonium hydroxide (TMAH), and the cladding layer on the optical fiber core is SiO 2 . It is appreciated that other materials and etchants may be used. 
     In one embodiment of the present invention, the buffer layer is SiGeC, wherein carbon is greater than or equal to one atomic percent. 
     In one embodiment of the present invention, the buffer layer is SiGeC, wherein carbon is less than or equal to one atomic percent. 
     In one embodiment of the present invention, the filler is SiO 2 . 
     In one embodiment of the present invention, the buffer layer is an epitaxial layer. 
     In one embodiment of the present invention, the sacrificial layer is an epitaxial layer. 
     In one embodiment of the present invention, the optical fiber core is an epitaxial layer. 
     In one embodiment of the present invention, the system splits the optical fiber core into multiple optical fiber cores to form an optical multiplexer. 
     In one embodiment of the present invention, the system combines multiple optical fiber cores into a single optical fiber core to form an optical demultiplexer. 
     One embodiment of the present invention provides a system to facilitate integrating active or passive components on a circuit device that includes an optical fiber core that was epitaxially grown. During operation, the system receives this circuit device, and etches a cavity into the circuit device, wherein the cavity passes through the optical fiber core. The system also creates an active device within the cavity that is aligned with the optical fiber core. 
     In one embodiment of the present invention, etching the cavity includes etching into a buffer layer below the optical fiber core. 
     In one embodiment of the present invention, etching the cavity includes etching into a substrate layer below the optical fiber core. 
     In one embodiment of the present invention, the substrate layer includes a doped semiconductor region that can form part of the active device. 
     In one embodiment of the present invention, the system applies a metallization layer to the active device to form conduction paths for the active device. 
     In one embodiment of the present invention, the metallization layer forms a mirror metallization. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1A illustrates preparing a circuit device with a sacrificial layer in accordance with an embodiment of the present invention. 
     FIG. 1B illustrates forming optical fiber cores on the sacrificial layer in accordance with an embodiment of the present invention. 
     FIG. 1C illustrates removing the sacrificial layer and cladding the optical fiber core in accordance with an embodiment of the present invention. 
     FIG. 1D illustrates including a filler in accordance with an embodiment of the present invention. 
     FIG. 2A illustrates an optical multiplexer in accordance with an embodiment of the present invention. 
     FIG. 2B illustrates an optical demultiplexer in accordance with an embodiment of the present invention. 
     FIG. 3 is a flowchart illustrating the process of forming optical fiber cores on a circuit device in accordance with an embodiment of the present invention. 
     FIG. 4A illustrates a longitudinal cross-section view of a circuit device in accordance with an embodiment of the present invention. 
     FIG. 4B illustrates cavities etched into the circuit device in accordance with an embodiment of the present invention. 
     FIG. 4C illustrates active devices formed in the cavities in the circuit device in accordance with an embodiment of the present invention. 
     FIG. 4D illustrates metallization applied to the circuit device in accordance with an embodiment of the present invention. 
     FIG. 5 is a flowchart illustrating the process of forming active devices in the circuit device in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
     Creating a Circuit Device with an Optical Fiber Core 
     FIG. 1A illustrates preparing a circuit device with a sacrificial layer in accordance with an embodiment of the present invention. The circuit device includes substrate  102 , which can include the material Si. Note that the materials described herein include only one possible combination. A practitioner with ordinary skill in the art will be able to readily substitute other suitable materials for the ones described. 
     Buffer layer  104  is epitaxially grown on substrate  102 . Buffer layer  104  can include SiGe or SiGeC. Using SiGeC allows the growth of thicker layers than does using SiGe. Note that using different materials for the various layers allows use of different chemical etchants to selectively etch the various layers. 
     Sacrificial layer  106  is epitaxially grown on buffer layer  104 . Sacrificial layer  106  can include Si and is used to transfer the crystalline structure of buffer layer  104  to layers that are grown on sacrificial layer  106 . Sacrificial layer  106  will be selectively etched away after forming these additional layers. Epitaxial blocking layer  1   08  has been added to the circuit device to control where additional layers will be grown on sacrificial layer  106 . Epitaxial blocking layer  108  can include SiO 2  or SiN. 
     FIG. 1B illustrates forming optical fiber cores on the sacrificial layer in accordance with an embodiment of the present invention. Optical fiber cores  110  are epitaxially grown on sacrificial layer  106  and can include SiGe or SiO 2 :GeO 2 . Optical fiber cores  110  can include beams through the circuit device and can be routed through the circuit device as needed. Note that the material composition may be controlled during growth of optical fiber cores  110  to create a graded index optical fiber core. 
     FIG. 1C illustrates removing the sacrificial layer and the addition of cladding to the optical fiber core in accordance with an embodiment of the present invention. After growth of optical fiber cores  110 , epitaxial blocking layer  108  is removed and sacrificial layer  106  is selectively etched using an etchant such as KOH or TMAH. Cladding layer  112  can then be added to optical fiber cores  110 . A typical material for cladding layer  112  is SiO 2 . Note that applying cladding layer  112  by thermal oxidation will tend to round optical fiber cores  110 , thereby enhancing the graded index effect. Note also that SiGe and SiGeC can be selectively etched using hydrofluoriclnitric/acetic (HNA) acids. 
     FIG. 1D illustrates including filler  114  in accordance with an embodiment of the present invention. Filler  114  can include any suitable material, gas, or liquid such as the same material, SiO 2 , used for cladding layer  112 . Note that filler  114  is optional and may be wholly or partially omitted. 
     Optical Multiplexers and Demultiplexers 
     FIG. 2A illustrates an optical multiplexer in accordance with an embodiment of the present invention. Optical fiber core  202  is branched into optical fiber cores  204 ,  206 , and  208 . Note that optical fiber core  202  may branch into more or less optical fiber cores than shown. The optical multiplexer can be created by controlling the apertures in epitaxial blocking layer  108 . 
     FIG. 2B illustrates an optical demultiplexer in accordance with an embodiment of the present invention. Optical fiber cores  210 ,  212 , and  214  are combined into optical fiber core  216 . Note that optical fiber core  202  may combine more or less optical fiber cores than shown. The optical demultiplexer can be created by controlling the apertures in epitaxial blocking layer  108 . 
     Forming Optical Fiber Cores 
     FIG. 3 is a flowchart illustrating the process of forming optical fiber cores on a circuit device in accordance with an embodiment of the present invention. The system starts by receiving substrate  102  including buffer layer  104  (step  302 ). Next, the system forms epitaxial sacrificial layer  106  on buffer layer  104  (step  304 ). Note that sacrificial layer  106  is used to transfer the crystalline template from buffer layer  104  to layers grown on sacrificial layer  106  such as optical fiber cores  110 . 
     Epitaxial blocking layer  108  is then applied to sacrificial layer  106  (step  306 ). Next, photoresist is applied to epitaxial blocking layer  108  (step  308 ). After photoresist has been applied, the system exposes and develops the photoresist to create a pattern on the photoresist (step  310 ). Next, epitaxial blocking layer  108  is etched to transfer the pattern layer  108  (step  312 ). 
     Optical fiber cores  110  are then epitaxially grown on the exposed portions of sacrificial layer  106  (step  314 ). Next, epitaxial blocking layer  108  is removed (step  316 ). After epitaxial blocking layer  108  has been removed, sacrificial layer  106  is removed by selective etching (step  318 ). 
     Cladding layer  112  is then added to optical fiber cores  110  (step  320 ). Finally, filler  114  can be added to the cavity if desired (step  322 ). 
     Creating Active Devices 
     FIG. 4A illustrates a longitudinal cross-section view of a circuit device in accordance with an embodiment of the present invention. The circuit device includes substrate  402 , buffer layer  406 , cladding layer  408 , filler  410 , and optical fiber core  412 . The process described above in conjunction with FIGS. 1 through 3 can create these layers. 
     Substrate  402  can include regions  404 . Regions  404  can be doped semiconductor regions such as N-type or P-type Si, or can be intrinsic Si. As previously noted, the materials described herein are exemplary and are not to be construed as the only possible materials for creating the various layers and structures. Photoresist  414  is applied, exposed, and developed to create windows for etching the structures. 
     FIG. 4B illustrates cavities etched into the circuit device in accordance with an embodiment of the present invention. Cavities have been etched into the circuit device using a combination of dry etching and wet etching, wherein wet etching has been used to selectively remove buffer layer  406  while not etching into regions  404  in substrate  402 . Note that etching may be used to over-etch into regions  404  if desired. Note also, that etching may be stopped at buffer layer  406  or within buffer layer  406  if desired. 
     FIG. 4C illustrates active devices formed in the cavities in the circuit device in accordance with an embodiment of the present invention. Various active layers may be grown within the cavities to form active regions  418  and  419 . Note that circuit layers  420  and  422  are aligned with optical fiber core  412 . This allows coupling optical signals through optical fiber core  412  between circuit layers  420  and  422  without the need to couple the signals into an external optical fiber or converting the optical signal to an electrical signal and back to an optical signal. Photoresist  416  has been added for subsequent exposure and developing to create a pattern for metallization. 
     FIG. 4D illustrates metallization applied to the circuit device in accordance with an embodiment of the present invention. Metallization  424  has been added to active regions  418  and  419  to allow electrical coupling of signals into and out of active regions  418  and  419 . Mirror metallization  426  has been added to the circuit elements of active region  419 . Other configurations are equally likely. 
     Forming Active Devices 
     FIG. 5 is a flowchart illustrating the process of forming active devices in the circuit device in accordance with an embodiment of the present invention. The system starts by receiving the circuit device including optical fiber core  412  (step  502 ). This circuit device with optical fiber core  412  can be constructed as described above in conjunction with FIGS. 1 through 3. 
     Next, photoresist  414  is applied to the surface of the circuit device (step  504 ). Photoresist  414  is then exposed through a mask and developed to form a pattern on the circuit device (step  506 ). 
     Next, the various layers are etched to form cavities within the circuit device (step  508 ). Note that this etching can include a combination of dry etching and wet etching. The etching can be stopped within buffer layer  406 , at regions  404 , or can be over-etched into regions  404 . Selective chemical etching can be used to automatically terminate etching at regions  404 . 
     Active devices are then created within the cavities etched into the circuit device (step  510 ). These active devices can include active devices such as lasers, optical switches, etc., or passive devices such as lenses, mirrors, etc. Note that circuit layers  420  and  422  of the active devices are self-aligned with optical fiber core  412  eliminating the necessity of connecting an external optical fiber or converting the optical signal to an electrical signal to couple signals between circuit layers  420  and  422 . 
     After forming the active devices in active regions  418  and  419 , photoresist  416  is applied to the surface (step  512 ). Next a pattern is exposed and developed in photoresist  416  (step  514 ). Finally, metallization  424  and  426  is applied to the circuit device (step  516 ). 
     The foregoing descriptions of embodiments of the present invention have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. It is appreciated that other active (e.g. moveable mirrors, etc.) and passive devices (e.g. lenses, micro-lenses, gratings, etc.) may be fabricated using the present invention. The scope of the present invention is defined by the appended claims.