Patent Publication Number: US-2011068423-A1

Title: Photodetector with wavelength discrimination, and method for forming the same and design structure

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure relates generally to photodetectors and methods of forming the same, and more particularly to optical photodetectors. The disclosure also relates to a design structure of the aforementioned. 
     2. Background Art 
     Image sensors have been used in digital cameras and a wide variety of other imaging devices. The image sensor is typically a complementary metal-oxide semiconductor (CMOS) sensor or a charged coupled device (CCD). CMOS image sensors are increasingly being used in imaging devices instead of CCDs because of lower power consumption, lower system cost, and the ability to randomly access image data. To detect particular colors/wavelengths or frequencies, known CMOS imaging technology requires semiconductors with different band gaps, a semiconductor with various color input filters formed from dye impregnated resists, polymer-based color filters, and/or Fabry-Perot interference layers. Also, additional components such as microlenses are often needed. 
     SUMMARY 
     An aspect of the present invention relates to a photodetector comprising: a semiconductor substrate; a photoconversion device within the semiconductor substrate; a first layer over the photoconversion device; a second layer over the first layer; and a waveguide having a radius r positioned over the first layer and the photoconversion device, wherein r is in a range from approximately 1,000 angstroms (Å) to approximately 4,000 Å. 
     A second aspect of the present invention relates to an image sensor comprising: an array of photodetectors, each photodetector comprising: a semiconductor substrate; a photoconversion device within the semiconductor substrate; a first layer over the photoconversion device; a second layer over the first layer; and 
     a waveguide having a radius r positioned over the first layer and the photoconversion device, wherein r is in a range from approximately 1,000 angstroms (Å) to approximately 4,000 Å. 
     A third aspect of the present invention relates to a method of forming a photodetector comprising: forming a photoconversion device within a semiconductor substrate; forming a first layer over the photoconversion device; forming a second layer over the first layer; and forming a waveguide having a radius r positioned over the first layer and the photoconversion device, wherein r is in a range from approximately 1,000 angstroms (Å) to approximately 4,000 Å. 
     A fourth aspect of the present invention relates to a design structure embodied in a machine readable medium for designing, manufacturing, or testing a photodetector, the design structure comprising: a semiconductor substrate; a photoconversion device within the semiconductor substrate; a first layer over the photoconversion device; a second layer over the first layer; and a waveguide having a radius r positioned over the first layer and the photoconversion device, wherein r is in a range from approximately 1,000 angstroms (Å) to approximately 4,000 Å. 
     The illustrative aspects of the present invention are designed to solve the problems herein described and/or other problems not discussed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
         FIG. 1  depicts an embodiment of a photodetector, in accordance with the present invention; 
         FIG. 2  depicts an embodiment of an image sensor, in accordance with the present invention; and 
         FIG. 3  depicts a flow diagram of a design process used in photodetector design, manufacture, and/or test, in accordance with the present invention. 
     
    
    
     It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings. 
     DETAILED DESCRIPTION 
     It has been discovered that using semiconductors with different band gaps, a semiconductor with various color input filters formed from dye impregnated resists, polymer-based color filters, and/or Fabry-Perot interference layers as well as components such as microlenses in semiconductor imager applications present several undesirable constraints for high volume manufacturing. Examples of the constraints are the difficulty in achieving uniform chemical properties in the in the polymer color filters, uniform filter thickness, stability of the color filters in the semiconductor imager and uniform positioning of color filters in a semiconductor imager. Conventional polymer color filters, Fabry-Perot interference layers, and microlenses also complicate the manufacturing process because they are separate components that must be integrated into the semiconductor imaging product. 
     An embodiment of a photodetector is presented in accordance with the present invention. Referring to  FIG. 1 , a photodetector  10  is provided having a semiconductor substrate  15 , a photoconversion device  20 , a first layer  25 , a second layer  30 , and a waveguide  35 . 
     Semiconductor substrate  15  may be comprised of but not limited to silicon, germanium, silicon germanium, silicon carbide, and those consisting essentially of one or more Group III-V compound semiconductors having a composition defined by the formula Al x1 Ga X2 In X3 As Y1 P Y2 N Y3 Sb Y4 , where X1, X2, X3, Y1, Y2, Y3, and Y4 represent relative proportions, each greater than or equal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 being the total relative mole quantity). Semiconductor substrate  15  may also be comprised of Group II-VI compound semiconductors having a composition Zn A1  Cd A2 Se B1 Te B2 , where A1, A2, B1, and B2 are relative proportions each greater than or equal to zero and A1+A2+B1+B2=1 (1 being a total mole quantity). The processes to provide semiconductor substrate  15 , as illustrated and described, are well known in the art and thus, no further description is necessary. In an embodiment of the present invention, semiconductor substrate  15  may comprise a p-type doped substrate. Examples of p-type dopants include but are not limited to boron (B), indium (In), and gallium (Ga). 
     Semiconductor substrate  15  has within it photoconversion device  20 . In an embodiment of the present invention, photoconversion device  20  may comprise a photogate, photoconductor, or a photodiode. The aforementioned, as illustrated and described, are well known in the art and thus, no further description is necessary. In an embodiment of the present invention photoconversion device  20  is a photodiode. In another embodiment, the photodiode may be a p+/n diode. In another embodiment, the photodiode may be a n+/p diode. The processes to provide photoconversion device  20  within semiconductor substrate  15 , as illustrated and described, are well known in the art and thus, further description also is not necessary. 
     First layer  25  is a dielectric material that is deposited over photoconversion device  20 . In an embodiment of the present invention, first layer  25  may comprise a material selected from the group consisting of silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), hafnium oxide (HfO 2 ), hafnium silicon oxide (HfSiO), hafnium silicon oxynitride (HfSiON), zirconium oxide (ZrO 2 ), zirconium silicon oxide (ZrSiO), zirconium silicon oxynitride (ZrSiON), aluminum oxide (Al 2 O 3 ), titanium oxide (Ti 2 O 5 ) and tantalum oxide (Ta 2 O 5 ). In another embodiment, first layer  25  may comprise an n-type doped material. Examples of n-type dopants include but are not limited to phosphorous (P), arsenic (As), and antimony (Sb). In an embodiment of the present invention, first layer  25  may have a dielectric constant (k) in a range from approximately 1,000 angstroms (Å) to approximately 10,000 Å. 
     First layer  25  is deposited over photoconversion device  20  and/or semiconductor substrate  15  using any now known or later developed techniques appropriate for the material to be deposited including but are not limited to, for example: chemical vapor deposition (CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD), semi-atmosphere CVD (SACVD) and high density plasma CVD (HDPCVD), rapid thermal CVD (RTCVD), ultra-high vacuum CVD (UHVCVD), limited reaction processing CVD (LRPCVD), metalorganic CVD (MOCVD), sputtering deposition, ion beam deposition, electron beam deposition, laser assisted deposition, thermal oxidation, thermal nitridation, spin-on methods, physical vapor deposition (PVD), atomic layer deposition (ALD), chemical oxidation, molecular beam epitaxy (MBE), plating, and evaporation. First layer  25  has thicknesses that may vary, but in one embodiment, the thickness is in a range from approximately 1,000 angstroms Å) to 10,000 Å. 
     In an embodiment of the present invention, semiconductor substrate  15  is an n-type doped substrate and first layer  25  is a p-typed doped dielectric material. Various embodiments of the aforementioned are described supra. 
     Second layer  30  is comprised of a dielectric material or metal that is deposited over first layer  25 . In an embodiment of the present invention, second layer  25  may be comprised of the same dielectric materials described supra for first layer  25 . In another embodiment, second layer  30  may be an opaque dielectric material. In another embodiment, second layer  30  is translucent. In another embodiment, second layer  30  is comprised of a metal selected from the group consisting of tungsten (W), tantalum (Ta), aluminum (Al), ruthenium (Ru), platinum (Pt), etc. or any electrically conductive compound including but not limited to titanium nitride (TiN), titanium carbide (TiC), tantalum carbide (TaC), tantalum nitride (TaN), tantalum carbon nitride (TaCN), tantalum carbide oxynitride (TaCNO), ruthenium oxide (RuO 2 ), nickel silicide (NiSi), nickel-platinum silicide (NiPtSi), etc. and combinations and multi-layers thereof. 
     When second layer  30  comprises a dielectric material, it is deposited on first layer  25  using any of the techniques described supra for the deposition of first layer  25  or later developed techniques appropriate for the material to be deposited. When second layer  30  comprises a metal or an electrically conductive compound, it is deposited using any now known or later developed techniques appropriate for the metal or the electrically conductive compound to be deposited including but are not limited to, for example: chemical vapor deposition (CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD), semi-atmosphere CVD (SACVD) and high density plasma CVD (HDPCVD), rapid thermal CVD (RTCVD), ultra-high vacuum CVD (UHVCVD), limited reaction processing CVD (LRPCVD), metalorganic CVD (MOCVD), sputtering deposition, ion beam deposition, electron beam deposition, laser assisted deposition, thermal oxidation, thermal nitridation, spin-on methods, physical vapor deposition (PVD), atomic layer deposition (ALD), chemical oxidation, molecular beam epitaxy (MBE), plating, and evaporation. 
     Waveguide  35  is positioned over first layer  25  and photoconversion device  20 . Waveguide  35  propagates electromagnetic radiation with a frequency (f)&gt;f co  and wavelengths (L)&lt;L co , where co denotes a cutoff, to photoconversion device  20 . L co  is dependent on waveguide radius (r) and is given by the equation L co =2.6r. Only radiation with wavelengths shorter than L co  will propagate through waveguide  35  to photoconversion device  20 . Waveguide  35  may be comprised of a dielectric material as described supra or air. When waveguide  35  comprises a dielectric material, the refractive index of the dielectric material must be less than the refractive index of second layer  30  to allow propagation of electromagnetic radiation. 
     Waveguide  35  may have a radius in a range from approximately 1,000 Å to approximately 4,000 Å. When the waveguide radius is approximately 4,000 Å, electromagnetic radiation shorter than 10,000 Å (red, green, and blue light) is propagated through waveguide  35  to photoconversion device  20 . When the waveguide radius is approximately 2,000 Å, radiation shorter than 5,000 Å (green and blue light) is propagated through waveguide  35 . When waveguide radius is approximately 1,000 Å, radiation shorter than 2,500 Å (blue light) is propagated through waveguide  35  to photoconversion device  20 . Selecting the radius of waveguide  35  allows one to control the specific wavelength or specific range of wavelengths being detected by photoconversion device  20 . 
     In an embodiment of the present invention, waveguide  35  and second layer  30  may be comprised of a dielectric material wherein the refractive index of second layer  30  is greater than the dielectric material of waveguide  35 . In another embodiment, waveguide  35  may be comprised of a dielectric material and second layer  30  may be comprised of a metal or electrically conducting compound. In another embodiment, waveguide  35  may be comprised of air and second layer  30  may be comprised of a metal or electrically conducting compound. 
     In an embodiment of the present invention, photodetector  10  may be incorporated in a digital camera. In another embodiment, photodetector  10  may be incorporated in a light spectrum analyzer. In another embodiment, photodetector  10  may be an optical photodetector. 
     Photodetector  10  is devoid of an element or combination of elements selected from the group consisting of a polymer color filter, a dye impregnated resist, and a Fabry-Perot interference layer. 
     An embodiment of an image sensor is presented in accordance with the present invention. Referring to  FIG. 2 , an image sensor  50  is provided having an array of photodetectors  10 , see  FIG. 1 . The array comprises a two-dimensional organization of photodetectors  10  in rows and columns. Photodetectors  10  each comprise a semiconductor substrate  15 , a photoconversion device  20 , a first layer  25 , a second layer  30 , and a waveguide  35 . The description of photodetectors  10  and their elements  15 ,  20 ,  25 , and  35 , and various embodiments of each are provided supra. In an embodiment of the present invention, each photodetector  10  may be operatively connected to an active amplifier and the array of photodetectors  10  may be operatively connected to an integrated circuit. The processes to operatively connect photodetector  10  to an active amplifier and the array of photodetectors  10  to the integrated circuit, as described, are well known in the art and thus, no further description is necessary. 
     In another embodiment, the image sensor  50  may comprise photodetectors  10  wherein each photodetector  10  shares the same characteristics or each photodetector  10  independently has different characteristics such as radius of waveguide  35 , the composition of first layer  25 , the composition of second layer  30 , the composition of waveguide  35 , photoconversion device  20 , etc. 
     In an embodiment of the present invention, image sensor  50  may be a CMOS image sensor. In another embodiment, image sensor  50  may be a CCD image sensor. In an embodiment of the present invention, image sensor  50  may be incorporated in a digital camera. In another embodiment, image sensor  50  may be incorporated in a light spectrum analyzer. In another embodiment, image sensor  50  may be devoid of an element or combination of elements selected from the group consisting of a polymer color filter, a dye impregnated resist, and a Fabry-Perot interference layer. 
     An embodiment of a method of forming a photodetector is presented in accordance with the present invention. Referring to  FIG. 1 , a method of forming a photodetector  10  is provided having the steps of forming a photoconversion device  20  within a semiconductor substrate  15 , forming a first layer  25  over photoconversion device  20 , forming a second layer  30  over first layer  25 , and forming a waveguide  35  having a radius r positioned over first layer  25  and photoconversion device  20 , wherein r is in a range from approximately 1,000 Å to approximately 4,000 Å. 
     A semiconductor substrate  15  is provided. The description of semiconductor substrate  15  and various embodiments are provided supra. A photoconversion device  20  is formed within semiconductor substrate  15 . The processes to form photodetector  10  within semiconductor substrate  15 , as described, are well known in the art and thus, no further description is necessary. In an embodiment of the present invention, photoconversion device  20  may be selected from the group consisting of a photogate, a photoconductor, and a photodiode. In another embodiment, photoconversion device  20  formed within semiconductor substrate  15  is the photodiode. 
     First layer  25  is formed over photoconversion device  20  and/or semiconductor substrate  15  by deposition using any now known or later developed techniques appropriate for the material to be deposited as described supra. The description of first layer  25  and various embodiments also are provided supra. 
     Second layer  30  is formed over first layer  25  by deposition using any now known or later developed techniques appropriate for the material to be deposited as described supra. The description of second layer  25  and various embodiments also are provided supra. 
     A waveguide  35  having a radius r positioned over first layer  25  and photoconversion device  20  is formed, wherein r is in a range from approximately 1,000 angstroms Å to approximately 4,000 Å. Waveguide  35  is formed by using any now known or later developed techniques appropriate for waveguide  35  formation. Examples include but are not limited to forming waveguide  35  into second layer  25  via photolithography, routing, punching, laser ablation, etching, etc. 
     The radius of waveguide  35  may be formed in a range approximately 1,000 Å to approximately 4,000 Å. In an embodiment of the present invention, the radius may be approximately 4,000 Å. In another embodiment, the radius may be approximately 2,000 Å. In another embodiment, the radius may be approximately 1,000 Å. One having ordinary skill in the art will recognize now known or later developed techniques that are used to selectively choose the radius of waveguide  35  during waveguide  35  forming step. As described supra, selecting the radius of waveguide  35  allows one to control the specific wavelength or specific range of wavelengths being detected by photoconversion device  20 . One having ordinary skill in the art also will recognize that selecting a particular waveguide  35  radius to control the specific wavelength or range of wavelengths being detected is not limited to the radii or ranges of radii described supra but selecting is optimized with routine experimentation to determine the appropriate radius/radii length that corresponds to the detection of a specific wavelength or specific range of wavelengths. 
     A design structure embodied in a machine readable medium for designing, manufacturing, or testing photodetector(s) is presented in accordance with the present invention. The design structure comprises a semiconductor substrate; a photoconversion device within the semiconductor substrate; a first layer over the photoconversion device; a second layer over the first layer; and a waveguide having a radius r positioned over the first layer and the photoconversion device, wherein r is in a range from approximately 1,000 Å to approximately 4,000 Å. 
     Referring to  FIG. 3 , a block diagram of an exemplary design flow  100  used for example, in photodetector design, manufacturing, and/or test is shown. Design flow  100  may vary depending on the type of IC being designed. For example, a design flow  100  for building an application specific IC (ASIC) may differ from a design flow  100  for designing a standard component. Design structure  120  is preferably an input to a design process  110  and may come from an IP provider, a core developer, or other design company or may be generated by the operator of the design flow, or from other sources. Design structure  120  comprises an embodiment of the invention as shown in  FIG. 1  and  FIG. 2  in the form of schematics or HDL, a hardware-description language (e.g., Verilog, VHDL, C, etc.). Design structure  120  may be contained on one or more machine readable medium. For example, design structure  120  may be a text file or a graphical representation of an embodiment of the invention as shown in  FIG. 1  and  FIG. 2 . Design process  110  preferably synthesizes (or translates) an embodiment of the invention as shown in  FIG. 1  and  FIG. 2  into a netlist  180 , where netlist  180  is, for example, a list of wires, transistors, logic gates, control circuits, I/O, models, etc. that describes the connections to other elements and circuits in an integrated circuit design and recorded on at least one of machine readable medium. For example, the medium may be a CD, a compact flash, other flash memory, a packet of data to be sent via the Internet, or other networking suitable means. The synthesis may be an iterative process in which netlist  180  is resynthesized one or more times depending on design specifications and parameters for the circuit. 
     Design process  110  may include using a variety of inputs; for example, inputs from library elements  130  which may house a set of commonly used elements, circuits, and devices, including models, layouts, and symbolic representations, for a given manufacturing technology (e.g., different technology nodes, 32 nm, 45 nm, 90 nm, etc.), design specifications  140 , characterization data  150 , verification data  160 , design rules  170 , and test data files  185  (which may include test patterns and other testing information). Design process  110  may further include, for example, standard circuit design processes such as timing analysis, verification, design rule checking, place and route operations, etc. One of ordinary skill in the art of integrated circuit design can appreciate the extent of possible electronic design automation tools and applications used in design process  110  without deviating from the scope and spirit of the invention. The design structure of the invention is not limited to any specific design flow. 
     Design process  110  preferably translates an embodiment of the invention as shown in  FIG. 1  and  FIG. 2 , along with any additional integrated circuit design or data (if applicable), into a second design structure  190 . Design structure  190  resides on a storage medium in a data format used for the exchange of layout data of integrated circuits and/or symbolic data format (e.g. information stored in a GDSII (GDS2), GL1, OASIS, map files, or any other suitable format for storing such design structures). Design structure  190  may comprise information such as, for example, symbolic data, map files, test data files, design content files, manufacturing data, layout parameters, wires, levels of metal, vias, shapes, data for routing through the manufacturing line, and any other data required by a semiconductor manufacturer to produce an embodiment of the invention as shown in  FIG. 1  and  FIG. 2 . Design structure  190  may then proceed to a stage  195  where, for example, design structure  990 : proceeds to tape-out, is released to manufacturing, is released to a mask house, is sent to another design house, is sent back to the customer, etc. 
     The foregoing description of various aspects of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of the disclosure as defined by the accompanying claims.